Title of Invention	"AN IMPROVED PROCESS FOR THE PRODUCTION OF ESTERS FROM CARBOXYLIC ACIDS USING MODIFIED CLAY CATALYSTS"
Abstract	An improved process for the production of esters from carboxylic acid using modified clay catalyst by reacting carboxylic acid with alcohol in a molar ratio of about 1:5 in presence of solvent medium and metal exchanged montmorrilonite as catalyst in a ratio of about 40:1 at a temperature ranging from 80°C to 130°C for a period in the range of 2.5 to 15 hours and recovering esters by separating catalyst through Alteration and removing the solvent by known methods.

Title of Invention

"AN IMPROVED PROCESS FOR THE PRODUCTION OF ESTERS FROM CARBOXYLIC ACIDS USING MODIFIED CLAY CATALYSTS"

Abstract

An improved process for the production of esters from carboxylic acid using modified clay catalyst by reacting carboxylic acid with alcohol in a molar ratio of about 1:5 in presence of solvent medium and metal exchanged montmorrilonite as catalyst in a ratio of about 40:1 at a temperature ranging from 80°C to 130°C for a period in the range of 2.5 to 15 hours and recovering esters by separating catalyst through Alteration and removing the solvent by known methods.

Full Text	This invention relates to an improved process for the production of esters from carboxylic acids using modified clay catalysts. The present invention particularly relates to an ecofriendly process for the production of esters from aromatic, aliphatic, α,ß-unsarurated, mono- and di-carboxylic acids using modified clay catalysts, dispensing the use of corrosive and toxic H2S04 and expensive resins. Thus, this process totally eliminates the disposal of salts formed consequent to the neutralisation of H2SO4. Development of solid acids to replace commonly employed mineral acid and anhydrous aluminium chloride in the classical Friedel-Crafts reactions, etherification and esterification practiced in conventional industry is of topical interest. The esters are widely used in the industry as intermediates in fine chemicals, drugs, plastisizers, perfumes, food preservatives, cosmetics, Pharmaceuticals, solvents and as chiral auxiliaries. The esterification reaction is used for the production of many large volume chemicals such as dimethyl tartrate, methyl cinnamate, dimethyl phthalate, methyl salicylate and other esters. Several effective methods are executed presently in the esterification process in indusrty using liquid/soluble acids. A British patent, Brit. 642-718, 13 Sept., 1950 describes the esterification of fatty acids with excess of monohydric alcohols in presence of H2S04. Another British patent by Celanese Corpn. of America, Brit. 710-803, June 16, 1954, describes a method for the esterification of acetic acid with ethanol to get ethyl acetate in presence of H2SO4. An US patent US 2686180, Aug. 10, 1954, described the preparation of methyl salicylate in 72% yields using carbodimides at 110°C with a tedious work-up procedure. Dow patented a method, US, 3154574, 27 Oct.64, for resorcinol esterification at 100°C using potassium carbonate, CO2, Conc. HC1, POC13, PhOH and PhMe. Condensing agents such as tosyl chloride, trifluoro acetic anhydride, polyphosphate ester and dicyclohexyl carbodimide are used to optimise the reaction of equimolar amounts of alcohol and carboxylic acids, but the workup procedure is tedious. In industry, the esterification is generally carried by H2SO4 which poses several problems such as corrosion of reaction vessels, catalyst recovery and waste disposal. Thus, it is desirable to use heterogeneous catalysts with advantages of ease of separation of the products, decreased corrosion of the reactor and possible regeneration of catalyst. The use of cationic exchangers as solid acid catalysts offer distinct advantages over conventional methods. In general, the strongly acidic sulfonated resins comprised of copolymers of styrene, ethylvinylbenzene, and divinylbenzene are used most widely in the industry. The inherent disadvantage in the application of these resins lies in the higher cost of the resins. Present trends in the area is set to develop solid acids from cheaply available sources, especially clays. A Japanese patent by Mitsui Petrochemical Inds. Ltd., Jpn Kokai Tokkyo Koho; Jp 5920413, 19 Nov, 1984 described the esterification of ethylene glycol with ethyl acetate in toluene under reflux conditions using Na~-montmorillonite as catalyst to produce 81% of monoester. British Petroleum Co., PLC, patent, U.K. Pat. Appl. GB-2175300, 26 Nov., 1986 described alkyl halides reacted with carboxylic acids at 200-300°C in presence of H~-montmorillonite to give esters in 95% yields. A Japanese patent, Jpn. Kokai Tokkyo Koho Jp, 0341042, 21Feb., 1991 describes the etherification of Me2CHOH by Al3+-montmorillonite at 130-190°C under high pressures to give (Me2CH)2O. Japanese patent, Jpn Kokai Tokkyo Koho Jp, 03294243, 25 Dec., 1991 describes carboxylic acids and alcohols or olefins reacts in presence of Zr2+-montmorillonite to give esters. Esterification process patented by Texaco Chemicals Co., US, 5183947, 2 Feb. 1993, describes tertiary butanol reacts with methanol in presence of phosphoric acid treated montmorillonite to give methyl-t-butyl ether. The use of high The pressures and temperatures make the processes unattractive. Although many useful and reliable methods for the esterification of carboxylic acids have been reported in the literature using other solid acids and solid super acids such as heteropolyacids supported on carbon, SiO2-Al2O3, zeolites, sulphated zirconia, and niobic acid in liquid and vapour phase reactions, the selectivities and the yields are not attractive prepositions. The main object of the present invention is to provide an improved process for the production of esters from carboxylic acids using modified clay catalyst which obviates the drawbacks of known methods. Another objective of the present invention is the development of environmentally friendly active solid acid catalysts for the esterification of carboxylic acids using cheaply available montmorillonite as a support. Metal-exchanged montmorillonite catalysts were prepared as described in example 1 and employed in the esterification reactions of carboxylic acids, example 2 to 24. Accordingly the present invention provides a process for the preparation of esters from carboxylic acids using modified clay catalysts which comprises reacting carboxylic acids with alcohol in solvent medium in the presence of metal exchanged clay as catalyst for atleast at 80°C-130°C for a period in the range of 2.5 to 15hrs, and recovering corresponding esters by conventional methods. The clay catalyst used may be metal - ion exchanged clay, such as Cu2+, A13+, Zn2+, Ce3+, Fe3+ and H+. The alcohol used may be such as methyl and ethyl alcohols as the esterification agents and the amount used may range from 2.5 to 5 mmols/mmol of substrate. Carboxylic acids used may be such as malonic acid, glutaric acid, adipic acid, maleic acid, phthalic acid, cinnamic acid, stearic acid, azelic acid, p-isobutyl 2-methyl, phenyl acetic acid and chloroacetic acid. Solvent used for the reaction may be aromatic hydrocarbons such as Benzene and Toluene, Recovery of esters may be carried out by separating the catalyst through filtration and removing the solvent by rotavapor. The process of the present invention is illustrated with the following examples. However, it should not limit the scope of the invention. Example 1 A series of catalysts were prepared. a) K10 montmorillonite - Montmorillonite employed in the synthesis was obtained from Fluka Grade (K10) with exchange capacity of 0.8 equi.. b) Kunipia clay - Japanese clay (e.c., 1.15 equi.) was taken as it is without any modification. c) Ambica clay - Indian clay was taken as such without any modification. d) Fe3+-exchanged montmorillonite catalyst: To a 1 It. stirred aqueous solution of anhydrous FeCl3 (1.0 M), 80 g of K10-montmorillonite was added. Stirring was maintained for 16-30 hrs in order to saturate the exchange capacity of K10 montmorillonite. The clay suspension was centrifuged and the supernatant solution was discarded. Washing cycles were repeated until disappearance of Cl- ions from the discarded water. The clay was dried overnight in an oven at 120°C and finely ground in a mortar. e) Al3+ - exchanged catalyst: To a 1 It. stirred aqueous solution of anhydrous AlCl3 (1.0 M), 80 g of K10-montmorillonite was added. Stirring was maintained for 16-30 hrs in order to saturate the exchange capacity of K10 montmorillonite. The clay suspension was centrifuged and the supernatant solution was discarded. Washing cycles with distilled water were repeated until disappearance of Cl" ions from the discarded water. The clay was dried overnight in an oven at 120°C and finely ground in a mortar. f) Zn2+ -exchanged catalyst. To a 1 It. stirred aqueous solution of anhydrous ZnCl2 (1.0 M), 80 g of KlO-montmorillonite was added. Stirring was maintained for 16-30 hrs in order to saturate the exchange capacity of K10 montmorillonite. The clay suspension was centrifuged and the supernatant solution was discarded. Washing cycles were repeated until disappearance of Cl" ions from the discarded water. The clay was dried overnight in an oven at 120°C and finely ground in a mortar. f) CM" " - exchanged catalyst: To a 1 It. stirred aqueous solution of CuCl2 (1.0 M), 80 g of KlO-montmorillonite was added. Stirring was maintained for 16-30 hrs in order to saturate the exchange capacity of K10 montmorillonite. The clay suspension was centrifuged and the supernatant solution was discarded. Washing cycles were repeated until disappearance of Cl" ions from the discarded water. The clay was dried overnight in an oven at 120°C and finely ground in a mortar. h) Ce3 + - exchanged catalyst: To a 1 It. stirred aqueous solution of CeCl3 (1.0 M), 80 g of K10-montmorillonite was added. Stirring was maintained for 16-30 hrs in order to saturate the exchange capacity of K10 montmorillonite. The clay suspension was centrifuged and the supernatant solution was discarded. Washing cycles were repeated until disappearance of Cl" ions from the discarded water. The clay was dried overnight in an oven at 120°C and finely ground in a mortar. i) H+ - exchanged catalyst: To a 1 It. stirred aqueous solution of HC1 (1.0 M), 80 g of Na+ -montmorillonite was added. Stirring was maintained for 16-30 hrs in order to saturate the exchange capacity of Na+ - montmorillonite. The clay suspension was centrifuged and the supernatant solution was discarded . Washing cycles were repeated until disappearance of Cl- ions from the discarded water. The clay was dried overnight in an oven at 120°C and finely ground in a mortar. Example 2 A two-necked round bottom flask equipped with a Dean-Stark trap was charged with a mixture of L-tartaric acid (1.5g) and methanol (2ml) [1: 5 molar ratio], toluene (10ml) as solvent and Fe3+- Montmorillonite (0.25g). The solution was heated under reflux with stirring until no further water separation was observed, and also followed the reaction by thin layered chromatography (TLC). On completion of the reaction, ethyl acetate (10ml) was added to the reaction mixture. The catalyst was filtered through a sintered ware funnel (G-4), and the reaction mixture was concentrated on rotavapor to obtain the crude product. Sodium bicarbonate solution supersaturated with brine was added to the above obtained crude product to remove any unconverted starting material. The product was extracted with ethyl acetate, dried (over anhydrous Na2SO4), and concentrated on a rotavapor to get pure product (1.513 g). Thus obtained (+)-Di-methyl L-tartrate was crystallised in benzene (bottle grade), crystals were separated by filtration and dried in Abderhalden, ground to powder and checked the optical purity. [α]D was +22.2 ( C=2 in water), (Lit., [α]D +21 ± 1° (C=l in water). Example 3 A two-necked round bottom flask equipped with a Dean-Stark trap was charged with a mixture of L-tartaric acid (1.5g) and methanol (2ml) [1: 5 molar ratio], toluene (10ml) as solvent and Cu2+- Montmorillonite (0.25g). The solution was heated under reflux with stirring until no further water separation was observed, and also followed the reaction by thin layered chromatography (TLC). On completion of the reaction, ethyl acetate (10ml) was added to the reaction mixture. The catalyst was filtered through a sintered ware funnel (G-4), and the reaction mixture was concentrated on rotavapor to obtain the crude product. Sodium bicarbonate solution supersaturated with brine was added to the above obtained crude product to remove any unconverted starting material. The product was extracted with ethyl acetate, dried (over anhydrous Na2SO4 ), and concentrated on a rotavapor to get pure product (1.502 g). Thus obtained (+)-Di-methyl L-tartrate was crystallised in benzene (bottle grade), crystals were separated by filtration and dried in Abderhalden, ground to powder and checked the optical purity. [α]D was +22.2 ( C=2 in water), (Lit., [α]D +21 ± 1° (C=l in water). Example 4 A two-necked round bottom flask equipped with a Dean-Stark trap was charged with a mixture of L-tartaric acid (1.5g) and methanol (2ml) [1: 5 molar ratio], toluene (10ml) as solvent and Zn2+- Montmorillonite (0.25g). The solution was heated under reflux with stirring until no further water separation was observed, and also followed the reaction by thin layered chromatography (TLC). On completion of the reaction, ethyl acetate (10ml) was added to the reaction mixture. The catalyst was filtered through a sintered ware funnel (G-4), and the reaction mixture was concentrated on rotavapor to obtain the crude product. Sodium bicarbonate solution supersaturated with brine was added to the above obtained crude product to remove any unconverted starting material. The product was extracted with ethyl acetate, dried (over anhydrous Na2SO4), and concentrated on a rotavapor to get pure product (1.498 g). Thus obtained (+)-Di-methyl L-tartrate was crystallised in benzene (bottle grade), crystals were separated by filtration and dried in Abderhalden, ground to powder and checked the optical purity. [α]D was +22.2 ( C=2 in water), (Lit., [α]D +21 ± 1° (C=l in water). Example 5 A two-necked round bottom flask equipped with a Dean-Stark trap was charged with a mixture of L-tartaric acid (1.5g) and methanol (2ml) [1: 5 molar ratio], toluene (10ml) as solvent and Al3+- Montmorillonite (0.25g). The solution was heated under reflux with stirring until no further water separation was observed, and also followed the reaction by thin layered chromatography (TLC). On completion of the reaction, ethyl acetate (10ml) was added to the reaction mixture. The catalyst was filtered through a sintered ware funnel (G-4), and the reaction mixture was concentrated on rotavapor to obtain the crude product. Sodium bicarbonate solution supersaturated with brine was added to the above obtained crude product to remove any unconverted starting material. The product was extracted with ethyl acetate, dried (over anhydrous Na2SO4), and concentrated on a rotavapor to get pure product (1.520 g). Thus obtained (+)-Di-methyl L-tartrate was crystallised in benzene (bottle grade), crystals were separated by filtration and dried in Abderhalden , ground to powder and checked the optical purity. [α]D was +22.2 ( C=2 in water), (Lit., [α]D +21 i 1° (C=l in water). Example 6 A two-necked round bottom flask equipped with a Dean-Stark trap was charged with a mixture of L-tartaric acid (1.5g) and methanol (2ml) [1: 5 molar ratio], toluene (10ml) as solvent and Ce3+ Montmorillonite (0.25g). The solution was heated under reflux with stirring until no further water separation was observed, and also followed the reaction by thin layered chromatography (TLC). On completion of the reaction, ethyl acetate (10ml) was added to the reaction mixture. The catalyst was filtered through a sintered ware funnel (G-4), and the reaction mixture was concentrated on rotavapor to obtain the crude product. Sodium bicarbonate solution supersaturated with brine was added to the above obtained crude product to remove any unconverted starting material. The product was extracted with ethyl acetate, dried (over anhydrous Na2SO4), and concentrated on a rotavapor to get pure product (1.510 g). Thus obtained (+)-Di-methyl L-tartrate was crystallised in benzene (bottle grade), crystals were separated by filtration and dried in Abderhalden , ground to powder and checked the optical purity. [α]D was +22.2 ( C=2 in water), (Lit., [α]D +21 ± 1° (C=l in water). Example 7 A two-necked round bottom flask equipped with a Dean-Stark trap was charged with a mixture of L-tartaric acid (1.5g) and methanol (2ml) [1: 5 molar ratio], toluene (10ml) as solvent and H+- Montmorillonite (0.25g). The solution was heated under reflux with stirring until no further water separation was observed, and also followed the reaction by thin layered chromatography (TLC). On completion of the reaction, ethyl acetate (10ml) was added to the reaction mixture. The catalyst was filtered through a sintered ware funnel (G-4), and the reaction mixture was concentrated on rotavapor to obtain the crude product. Sodium bicarbonate solution supersaturated with brine was added to the above obtained crude product to remove any unconverted starting material. The product was extracted with ethyl acetate, dried (over anhydrous Na2SO4), and concentrated on a rotavapor to get pure product (1.499 g). Thus obtained (+)-Di-methyl L-tartrate was crystallised in benzene (bottle grade), crystals were separated by filtration and dried in Abderhalden, ground to powder and checked the optical purity. [α]D was +22.2 ( C=2 in water), (Lit., [α]D +21 ± 1° (C=l in water). Example 8 A two-necked round bottom flask equipped with a Dean-Stark trap was charged with a mixture of L-tartaric acid (1.5g) and methanol (2ml) [1: 5 molar ratio], toluene (10ml) as solvent and K10- Montmorillonite (0.25g). The solution was heated under reflux with stirring until no further water separation was observed, and also followed the reaction by thin layered chromatography (TLC). On completion of the reaction, ethyl acetate (10ml) was added to the reaction mixture. The catalyst was filtered through a sintered ware funnel (G-4), and the reaction mixture was concentrated on rotavapor to obtain the crude product. Sodium bicarbonate solution supersaturated with brine was added to the above obtained crude product to remove any unconverted starting material. The product was extracted with ethyl acetate, dried (over anhydrous Na2SO4), and concentrated on a rotavapor to get pure product (1.068 g). Thus obtained (+)-Di-methyl L-tartrate was crystallised in benzene (bottle grade), crystals were separated by filtration and dried in Abderhalden , ground to powder and checked the optical purity. [α]D was +22.2 ( C=2 in water), (Lit., [α]D +21 ± 1° (C=l in water). Example 9 A two-necked round bottom flask equipped with a Dean-Stark trap was charged with a mixture of L-tartaric acid (1.5g) and methanol (2ml) [1: 5 molar ratio], toluene (10ml) as solvent and Ambica clay (Indian clay) (0.25g). The solution was heated under reflux with stirring until no further water separation was observed, and also followed the reaction by thin layered chromatography (TLC). On completion of the reaction, ethyl acetate (10ml) was added to the reaction mixture. The catalyst was filtered through a sintered ware funnel (G-4), and the reaction mixture was concentrated on rotavapor to obtain the crude product. Sodium bicarbonate solution supersaturated with brine was added to the above obtained crude product to remove any unconverted starting material. The product was extracted with ethyl acetate, dried (over anhydrous Na2SO4), and concentrated on a rotavapor to get pure product (1.192 g). Thus obtained (+)-Di-methyl L-tartrate was crystallised in benzene (bottle grade), crystals were separated by filtration and dried in Abderhalden, ground to powder and checked the optical purity. [α]D was +22.2 ( C=2 in water), (Lit.,[α]D +21 ± 1° (C=l in water). Example 10 A two-necked round bottom flask equipped with a Dean-Stark trap was charged with a mixture of L-tartaric acid (1.5g) and methanol (2ml) [1:5 molar ratio], toluene (10ml) as solvent and Kunipia clay (Japanese clay) (0.25g). The solution was heated under reflux with stirring until no further water separation was observed, and also followed the reaction by thin layered chromatography (TLC). On completion of the reaction, ethyl acetate (10ml) was added to the reaction mixture. The catalyst was filtered through a sintered ware funnel (G-4), and the reaction mixture was concentrated on rotavapor to obtain the crude product. Sodium bicarbonate solution supersaturated with brine was added to the above obtained crude product to remove any unconverted starting material. The product was extracted with ethyl acetate, dried (over anhydrous Na2SO4), and concentrated on a rotavapor to get pure product (1.459 g). Thus obtained (+)-Di-methyl L-tartrate was crystallised in benzene (bottle grade), crystals were separated by filtration and dried in Abderhalden , ground to powder and checked the optical purity. [α]D was +22.2 ( C=2 in water), (Lit., [α]D +21 ± 1° (C=l in water). Example 11 A two-necked round bottom flask equipped with a Dean-Stark trap was charged with a mixture of L-tartaric acid (1.5g) and methanol (2ml) [1:5 ratio], toluene (10ml) as solvent. This reaction was carried out in the absence of the catalyst. The solution was heated under reflux with stirring and the reaction was monitored by thin layered chromatography (TLC). No water separation was observed. Therefore, it implies that no reaction took place. TABLE 1 Esterification of L-tartaric acid with MeOH [1:5 molar ratio], using various metal exchanged clay catalysts; (Table Removed) It was found that Fe3+ -montmorillonite displayed higher activity, and for the first time it was used (Table 1, the reaction time is less with Fe3--montmorillonite than with the other exchanged montmorillonites, Cu2+, Al3+, Zn2+, Ce3- and FT.) in the esterification reactions. Example 12 A two-necked 100ml round bottom flask, equipped with a Dean-Stark trap, was charged with a mixture of malonic acid (1.5g), methanol (3ml), [1:5 molar ratio], toluene (10ml) as solvent and Fe3+- Montmorillonite (0.25g). The solution was heated under reflux with stirring until no further water separation was observed, and also followed the reaction by thin layered chromatography (TLC). On completion of the reaction the catalyst was filtered through a sintered ware funnel (G-4), and the reaction mixture concentrated on rotavapor to obtain the crude product. A saturated solution of sodium bicarbonate was added to the above product to remove unconverted starting material. The product was extracted with ether, dried (over anhydrous Na2SO4), and concentrated on rotavapor to get pure product (1.333g). Example 13 A two-necked 100ml round bottom flask, equipped with a Dean-Stark trap, was charged with a mixture of succinic acid (1.5g), methanol (2.54 ml), [1:5 molar ratio], toluene (10ml) as solvent and Fe3+- Montmorillonite (0.25g). The solution was heated under reflux with stirring until no further water separation was observed, and also followed the reaction by thin layered chromatography (TLC). On completion of the reaction the catalyst was filtered through a sintered ware funnel (G-4), and the reaction mixture concentrated on rotavapor to obtain the crude product. A saturated solution of sodium bicarbonate was added to the above product to remove unconverted starting material. The product was extracted with ether, dried (over anhydrous Na2SO4), and concentrated on rotavapor to get pure product (1.299g). Example 14 A two-necked 100ml round bottom flask, equipped with a Dean-Stark trap, was charged with a mixture of glutaric acid (1.5g), methanol (2.27ml), [1:5 molar ratio], toluene (10ml) as solvent and Fe3+- Montmorillonite (0.25g). The solution was heated under reflux with stirring until no further water separation was observed, and also followed the reaction by thin layered chromatography (TLC). On completion of the reaction the catalyst was filtered through a sintered ware funnel (G-4), and the reaction mixture concentrated on rotavapor to obtain the crude product. A saturated solution of sodium bicarbonate was added to the above product to remove unconverted starting material. The product was extracted with ether, dried (over anhydrous Na2SO4), and concentrated on rotavapor to get pure product (1.236g). Example 15 A two-necked 100ml round bottom flask, equipped with a Dean-Stark trap, was charged with a mixture of adipic acid (1.5g), methanol (2.04 ml), [1:5 molar ratio], toluene (10ml) as solvent and Fe3+- Montmorillonite (0.25g). The solution was heated under reflux with stirring until no further water separation was observed , and also followed the reaction by thin layered chromatography (TLC). On completion of the reaction the catalyst was filtered through a sintered ware funnel (G-4), and the reaction mixture concentrated on rotavapor to obtain the crude product. A saturated solution of sodium bicarbonate was added to the above product to remove unconverted starting material. The product was extracted with ether, dried (over anhydrous Na2SO4), and concentrated on rotavapor to get pure product (1.608g). Example 16 A two-necked 100ml round bottom flask, equipped with a Dean-Stark trap, was charged with a mixture of maleic acid (1.5g), methanol (5.2ml), [1:10 molar ratio], toluene (10ml) as solvent and Fe3+- Montmorillonite (0.25g). The solution was heated under reflux with stirring until no further water separation was observed , and also followed the reaction by thin layered chromatography (TLC). On completion of the reaction the catalyst was filtered through a sintered ware funnel (G-4), and the reaction mixture concentrated on rotavapor to obtain the crude product. A saturated solution of sodium bicarbonate was added to the above product to remove unconverted starting material. The product was extracted with ether, dried (over anhydrous Na2SO4), and concentrated on rotavapor to get pure product (1.321g). Example 17 A two-necked 100ml round bottom flask, equipped with a Dean-Stark trap, was charged with a mixture of phthalic acid (1.5g), methanol (1.8ml), [1:5 molar ratio], toluene (10ml) as solvent and Fe3+- Montmorillonite (0.25g). The solution was heated under reflux with stirring until no further water separation was observed , and also followed the reaction by thin layered chromatography (TLC). On completion of the reaction the catalyst was filtered through a sintered ware funnel (G-4), and the reaction mixture concentrated on rotavapor to obtain the crude product. A saturated solution of sodium bicarbonate was added to the above product to remove unconverted starting material. The product was extracted with ether, dried (over anhydrous Na2SO4), and concentrated on rotavapor to get pure product (1.051 g). Example 18 A two-necked 100ml round bottom flask, equipped with a Dean-Stark trap, was charged with a mixture of cinnamic acid (1.5g), methanol (2.0ml), [1:5 molar ratio], toluene (10ml) as solvent and Fe3+- Montmorillonite (0.25g). The solution was heated under reflux with stirring until no further water separation was observed, and also followed the reaction by thin layered chromatography (TLC). On completion of the reaction the catalyst was filtered through a sintered ware funnel (G-4), and the reaction mixture concentrated on rotavapor to obtain the crude product. A saturated solution of sodium bicarbonate was added to the above product to remove unconverted starting material. The product was extracted with ether, dried (over anhydrous Na2SO4), and concentrated on rotavapor to get pure product (1.157 g). Example 19 A two-necked 100ml round bottom flask, equipped with a Dean-Stark trap, was charged with a mixture of stearic acid (1.5g), methanol (1.0ml), [1:5 molar ratio], toluene (10ml) as solvent and Fe3+- Montmorillonite (0.25g). The solution was heated under reflux with stirring until no further water separation was observed , and also followed the reaction by thin layered chromatography (TLC). On completion of the reaction the catalyst was filtered through a sintered ware funnel (G-4), and the reaction mixture concentrated on rotavapor to obtain the crude product. A saturated solution of sodium bicarbonate was added to the above product to remove unconverted starting material. The product was extracted with ether, dried (over anhydrous Na2SO4), and concentrated on rotavapor to get pure product (1.208 g). Example 20 A two-necked 100ml round bottom flask, equipped with a Dean-Stark trap, was charged with a mixture of azeleic acid (1.5g), methanol (1.6ml), [1:5 molar ratio], toluene (10ml) as solvent and Fe3+- Montmorillonite (0.25g). The solution was heated under reflux with stirring until no further water separation was observed , and also followed the reaction by thin layered chromatography (TLC). On completion of the reaction the catalyst was filtered through a sintered ware funnel (G-4), and the reaction mixture concentrated on rotavapor to obtain the crude product. A saturated solution of sodium bicarbonate was added to the above product to remove unconverted starting material. The product was extracted with ether, dried (over anhydrous Na2S04), and concentrated on rotavapor to get pure product (0.827 g). Example 21 A two-necked 100ml round bottom flask, equipped with a Dean-Stark trap, was charged with a mixture of p-Isobutyl 2-methyl,phenyl acetic acid (ibuprofen) (1.5g), methanol (1.46ml), [1:5 molar ratio], toluene (10ml) as solvent and Fe3+- Montmorillonite (0.25g). The solution was heated under reflux with stirring until no further water separation was observed , and also followed the reaction by thin layered chromatography (TLC). On completion of the reaction the catalyst was filtered through a sintered ware funnel (G-4), and the reaction mixture concentrated on rotavapor to obtain the crude product. A saturated solution of sodium bicarbonate was added to the above product to remove unconverted starting material. The product was extracted with ether, dried (over anhydrous Na2SO4), and concentrated on rotavapor to get pure product( 1.056 g). TABLE 2 Esterification of various carboxvlic acids with MeOH [1:5 molar ratio] Using Fe3+ - (Table Removed) a: 1:10 molar ratio (acid : alcohol) b: Reaction performed in presence of Fe3+ - montmorillonite as catalyst. c: Reaction performed in presence of H+- montmorillonite as catalyst. 1. Fe3+ - montmorillonite is an eflBcient catalyst for the esterification of various carboxylic acids such as aliphatic, aromatic, α,ß - unsaturated, mono and di-carboxylic acids. 2. Fe3+- montmorillonite was found to be more active than H+ - montmorillonite in the esterificsation of maleic acid ( S.No. 5, example 16). Example 22 A two-necked 100ml round bottom flask, equipped with a Dean-Stark trap, was charged with a mixture of chloroacetic acid (Immol), methanol (5mmol), [1:5 molar ratio], toluene (5ml) as solvent and Fe3+- Montmorillonite (0.10g). The solution was heated under reflux with stirring, and also followed the reaction by thin layered chromatography(TLC). On completion of the reaction the catalyst was filtered through a sintered ware runnel (G-4), and the reaction mixture concentrated on rotavapor to obtain the crude product. Example 23 A two-necked 100ml round bottom flask, equipped with a Dean-Stark trap, was charged with a mixture of chloroacetic acid (Immol), ethanol (5mmol), [1:5 molar ratio], toluene (5ml) as solvent and Fe3+- Montmorillonite (0.10g). The solution was heated under reflux with stirring, and also followed the reaction by thin layered chromatography (TLC). On completion of the reaction the catalyst was filtered through a sintered ware runnel (G-4), and the reaction mixture concentrated on rotavapor to obtain the crude product. Example 24 A two-necked 100ml round bottom flask, equipped with a Dean-Stark trap, was charged with a mixture of chloroacetic acid (Immol), ethanol (5mmol), [1:5 molar ratio], benzene (5ml) as solvent and Fe3+- Montmorillonite (0.10g). The solution was heated under reflux with stirring, and also followed the reaction by thin layered chromatography (TLC). On completion of the reaction the catalyst was filtered through a sintered ware funnel (G-4), and the reaction mixture concentrated on rotavapor to obtain the crude product. The results are mentioned in Table 3. TABLE 3 Esterification of Chloroacetic acid with Alcoholfs) (1:5 molar ratio) Using Fe3+ Montmorillonite as catalyst; (Table Removed) Toluene was found to be an effective solvent than benzene in esterification of chloroacetic acid by Fe3+- montmorillonite based on the yields. The present process has the following advantages: 1. An ecofriendly process for the production of esters with better activity than the conventional process. 2. It was found that Fe3+ -montmorillonite displayed higher activity, and for the first time it was used in the esterification reactions. ( In Table 1, the reaction time is less with Fe3+- montmorillonite than with the other exchanged montmorillonites, Cu2+, A13+, Zn2+, Ce3+ and H+ In Table 2, the esterification of maleic acid with ET- montmorillonite gave 66% of dimethyl maleate where as Fe3+- montmorillonite gave 100% conversion with 78% dimethyl maleate and 22% monomethyl maleate). 3. The selectivity and yields are very good, 4. The reactions are simple with easy workup procedure. 5. The support of the catalyst is cheap and abundantly available in nature. 6. The use of H2SO4, hazardous and corrosive chemical is dispensed with. 7. The present process envisage no disposal problem as the catalyst can be used for several cycles. The catalyst was subjected to four cycles which displayed almost consistent activity. 8. The present process is environmentally safe since there is no effluent disposable problem. We Claim: 1. An improved process for the production of esters from carboxylic acid using metal exchanged montomorrilonite clay catalysts which comprises reacting carboxylic acid with alcohol in a molar ratio of about 1:5 in presence of solvent medium and catalyst in a ratio of about 40:1 at temperature ranging from 80°C to 130°C period in the range of 2.5 to 15 hours and recovering esters by separating catalyst through filtration and removing the solvent by known methods. 2. An improved process for claim 1 wherein various metal ioa used in catalyst is selected from Cu 2+, A13T, Zn2+, Ce3+, Fe3+ and H+. 3. An improved process as claimed in claim 1 wherein the alcohols used is selected from methyl alcohol, ethyl alcohol as esterification agent and the amount used ranges from 2.5 to 5 mmols/mole of substrate. 4. An improved process as claimed in claim 1 wherein carboxylic acids used is such as aromatic, aliphatic, a, p-unsaturated mono- and dicarboxylic acids such as malonic acid, succinic acid, glutaric acid, adipic acid, maleic acid, phthalic acid, cinnamic acid, stearic acid, azelic acid, p-isobutyl 2-methyl, phenyl acetic acid (lbuprofen) and chloroacetic acid. 5. An improved process as claimed in claim 1 wherein solvent used is aromatic hydrocarbon such as benzene, toluene, xylene. 6. An improved process for the production of esters from carboxylic acid using metal- exchanged montmorrilonite clay catalysts substantially as herein described with reference to example accompanying the specification.

Full Text

This invention relates to an improved process for the production of esters from carboxylic acids using modified clay catalysts. The present invention particularly relates to an ecofriendly process for the production of esters from aromatic, aliphatic, α,ß-unsarurated, mono- and di-carboxylic acids using modified clay catalysts, dispensing the use of corrosive and toxic H2S04 and expensive resins. Thus, this process totally eliminates the disposal of salts formed consequent to the neutralisation of H2SO4.
Development of solid acids to replace commonly employed mineral acid and anhydrous aluminium chloride in the classical Friedel-Crafts reactions, etherification and esterification practiced in conventional industry is of topical interest. The esters are widely used in the industry as intermediates in fine chemicals, drugs, plastisizers, perfumes, food preservatives, cosmetics, Pharmaceuticals, solvents and as chiral auxiliaries. The esterification reaction is used for the production of many large volume chemicals such as dimethyl tartrate, methyl cinnamate, dimethyl phthalate, methyl salicylate and other esters.
Several effective methods are executed presently in the esterification process in indusrty using liquid/soluble acids. A British patent, Brit. 642-718, 13 Sept., 1950 describes the esterification of fatty acids with excess of monohydric alcohols in presence of H2S04. Another British patent by Celanese Corpn. of America, Brit. 710-803, June 16, 1954, describes a method for the esterification of acetic acid with ethanol to get ethyl acetate in presence of H2SO4. An US patent US 2686180, Aug. 10, 1954, described the preparation of methyl salicylate in 72% yields using carbodimides at 110°C with a tedious work-up procedure. Dow patented a method, US, 3154574, 27 Oct.64, for resorcinol esterification at 100°C using potassium carbonate, CO2, Conc. HC1, POC13, PhOH and PhMe.
Condensing agents such as tosyl chloride, trifluoro acetic anhydride, polyphosphate ester and dicyclohexyl carbodimide are used to optimise the reaction of equimolar amounts of alcohol and carboxylic acids, but the workup procedure is tedious.
In industry, the esterification is generally carried by H2SO4 which poses several problems such as corrosion of reaction vessels, catalyst recovery and waste disposal. Thus, it is desirable to use heterogeneous catalysts with advantages of ease of separation of the products, decreased corrosion of the reactor and possible regeneration of catalyst.
The use of cationic exchangers as solid acid catalysts offer distinct advantages over conventional methods. In general, the strongly acidic sulfonated resins comprised of copolymers of styrene, ethylvinylbenzene, and divinylbenzene are used most widely in the industry. The inherent disadvantage in the application of these resins lies in the higher cost of the resins.
Present trends in the area is set to develop solid acids from cheaply available sources, especially clays. A Japanese patent by Mitsui Petrochemical Inds. Ltd., Jpn Kokai Tokkyo Koho; Jp 5920413, 19 Nov, 1984 described the esterification of ethylene glycol with ethyl acetate in toluene under reflux conditions using Na~-montmorillonite as catalyst to produce 81% of monoester. British Petroleum Co., PLC, patent, U.K. Pat. Appl. GB-2175300, 26 Nov., 1986 described alkyl halides reacted with carboxylic acids at 200-300°C in presence of H~-montmorillonite to give esters in 95% yields. A Japanese patent, Jpn. Kokai Tokkyo Koho Jp, 0341042, 21Feb., 1991 describes the etherification of Me2CHOH by Al3+-montmorillonite at 130-190°C under high pressures to give (Me2CH)2O. Japanese patent, Jpn Kokai Tokkyo Koho Jp, 03294243, 25 Dec., 1991
describes carboxylic acids and alcohols or olefins reacts in presence of Zr2+-montmorillonite to give esters. Esterification process patented by Texaco Chemicals Co., US, 5183947, 2 Feb. 1993, describes tertiary butanol reacts with methanol in presence of phosphoric acid treated montmorillonite to give methyl-t-butyl ether. The use of high The pressures and temperatures make the processes unattractive.
Although many useful and reliable methods for the esterification of carboxylic acids have been reported in the literature using other solid acids and solid super acids such as heteropolyacids supported on carbon, SiO2-Al2O3, zeolites, sulphated zirconia, and niobic acid in liquid and vapour phase reactions, the selectivities and the yields are not attractive prepositions.
The main object of the present invention is to provide an improved process for the production of esters from carboxylic acids using modified clay catalyst which obviates the drawbacks of known methods. Another objective of the present invention is the development of environmentally friendly active solid acid catalysts for the esterification of carboxylic acids using cheaply available montmorillonite as a support.
Metal-exchanged montmorillonite catalysts were prepared as described in example 1 and employed in the esterification reactions of carboxylic acids, example 2 to 24.
Accordingly the present invention provides a process for the preparation of esters from carboxylic acids using modified clay catalysts which comprises reacting carboxylic acids with alcohol in solvent medium in the presence of metal exchanged clay as catalyst for atleast at 80°C-130°C for a period in the range of 2.5 to 15hrs, and recovering corresponding esters by conventional methods.
The clay catalyst used may be metal - ion exchanged clay, such as Cu2+, A13+, Zn2+, Ce3+, Fe3+ and H+.
The alcohol used may be such as methyl and ethyl alcohols as the esterification agents and the amount used may range from 2.5 to 5 mmols/mmol of substrate.
Carboxylic acids used may be such as malonic acid, glutaric acid, adipic acid, maleic acid, phthalic acid, cinnamic acid, stearic acid, azelic acid, p-isobutyl 2-methyl, phenyl acetic acid and chloroacetic acid.
Solvent used for the reaction may be aromatic hydrocarbons such as Benzene and Toluene,
Recovery of esters may be carried out by separating the catalyst through filtration and removing the solvent by rotavapor.
The process of the present invention is illustrated with the following examples. However, it should not limit the scope of the invention.
Example 1 A series of catalysts were prepared.
a) K10 montmorillonite - Montmorillonite employed in the synthesis was obtained from
Fluka Grade (K10) with exchange capacity of 0.8 equi..
b) Kunipia clay - Japanese clay (e.c., 1.15 equi.) was taken as it is without any
modification.
c) Ambica clay - Indian clay was taken as such without any modification.
d) Fe3+-exchanged montmorillonite catalyst: To a 1 It. stirred aqueous solution of
anhydrous FeCl3 (1.0 M), 80 g of K10-montmorillonite was added. Stirring was
maintained for 16-30 hrs in order to saturate the exchange capacity of K10 montmorillonite. The clay suspension was centrifuged and the supernatant solution was discarded. Washing cycles were repeated until disappearance of Cl- ions from the discarded water. The clay was dried overnight in an oven at 120°C and finely ground in a mortar.
e) Al3+ - exchanged catalyst: To a 1 It. stirred aqueous solution of anhydrous AlCl3 (1.0
M), 80 g of K10-montmorillonite was added. Stirring was maintained for 16-30 hrs in
order to saturate the exchange capacity of K10 montmorillonite. The clay suspension
was centrifuged and the supernatant solution was discarded. Washing cycles with
distilled water were repeated until disappearance of Cl" ions from the discarded water.
The clay was dried overnight in an oven at 120°C and finely ground in a mortar.
f) Zn2+ -exchanged catalyst. To a 1 It. stirred aqueous solution of anhydrous ZnCl2 (1.0
M), 80 g of KlO-montmorillonite was added. Stirring was maintained for 16-30 hrs in
order to saturate the exchange capacity of K10 montmorillonite. The clay suspension
was centrifuged and the supernatant solution was discarded. Washing cycles were
repeated until disappearance of Cl" ions from the discarded water. The clay was dried
overnight in an oven at 120°C and finely ground in a mortar.
f) CM" " - exchanged catalyst: To a 1 It. stirred aqueous solution of CuCl2 (1.0 M), 80 g
of KlO-montmorillonite was added. Stirring was maintained for 16-30 hrs in order to
saturate the exchange capacity of K10 montmorillonite. The clay suspension was
centrifuged and the supernatant solution was discarded. Washing cycles were repeated
until disappearance of Cl" ions from the discarded water. The clay was dried overnight in an oven at 120°C and finely ground in a mortar.
h) Ce3 + - exchanged catalyst: To a 1 It. stirred aqueous solution of CeCl3 (1.0 M), 80 g of K10-montmorillonite was added. Stirring was maintained for 16-30 hrs in order to saturate the exchange capacity of K10 montmorillonite. The clay suspension was centrifuged and the supernatant solution was discarded. Washing cycles were repeated until disappearance of Cl" ions from the discarded water. The clay was dried overnight in an oven at 120°C and finely ground in a mortar.
i) H+ - exchanged catalyst: To a 1 It. stirred aqueous solution of HC1 (1.0 M), 80 g of Na+ -montmorillonite was added. Stirring was maintained for 16-30 hrs in order to saturate the exchange capacity of Na+ - montmorillonite. The clay suspension was centrifuged and the supernatant solution was discarded . Washing cycles were repeated until disappearance of Cl- ions from the discarded water. The clay was dried overnight in an oven at 120°C and finely ground in a mortar.
Example 2
A two-necked round bottom flask equipped with a Dean-Stark trap was charged with a mixture of L-tartaric acid (1.5g) and methanol (2ml) [1: 5 molar ratio], toluene (10ml) as solvent and Fe3+- Montmorillonite (0.25g). The solution was heated under reflux with stirring until no further water separation was observed, and also followed the reaction by thin layered chromatography (TLC). On completion of the reaction, ethyl acetate (10ml) was added to the reaction mixture. The catalyst was filtered through a sintered
ware funnel (G-4), and the reaction mixture was concentrated on rotavapor to obtain the crude product.
Sodium bicarbonate solution supersaturated with brine was added to the above obtained crude product to remove any unconverted starting material. The product was extracted with ethyl acetate, dried (over anhydrous Na2SO4), and concentrated on a rotavapor to get pure product (1.513 g).
Thus obtained (+)-Di-methyl L-tartrate was crystallised in benzene (bottle grade), crystals were separated by filtration and dried in Abderhalden, ground to powder and checked the optical purity. [α]D was +22.2 ( C=2 in water), (Lit., [α]D +21 ± 1° (C=l in water).
Example 3
A two-necked round bottom flask equipped with a Dean-Stark trap was charged with a mixture of L-tartaric acid (1.5g) and methanol (2ml) [1: 5 molar ratio], toluene (10ml) as solvent and Cu2+- Montmorillonite (0.25g). The solution was heated under reflux with stirring until no further water separation was observed, and also followed the reaction by thin layered chromatography (TLC). On completion of the reaction, ethyl acetate (10ml) was added to the reaction mixture. The catalyst was filtered through a sintered ware funnel (G-4), and the reaction mixture was concentrated on rotavapor to obtain the crude product.
Sodium bicarbonate solution supersaturated with brine was added to the above obtained crude product to remove any unconverted starting material. The product was
extracted with ethyl acetate, dried (over anhydrous Na2SO4 ), and concentrated on a rotavapor to get pure product (1.502 g).
Thus obtained (+)-Di-methyl L-tartrate was crystallised in benzene (bottle grade), crystals were separated by filtration and dried in Abderhalden, ground to powder and checked the optical purity. [α]D was +22.2 ( C=2 in water), (Lit., [α]D +21 ± 1° (C=l in water).
Example 4
A two-necked round bottom flask equipped with a Dean-Stark trap was charged with a mixture of L-tartaric acid (1.5g) and methanol (2ml) [1: 5 molar ratio], toluene (10ml) as solvent and Zn2+- Montmorillonite (0.25g). The solution was heated under reflux with stirring until no further water separation was observed, and also followed the reaction by thin layered chromatography (TLC). On completion of the reaction, ethyl acetate (10ml) was added to the reaction mixture. The catalyst was filtered through a sintered ware funnel (G-4), and the reaction mixture was concentrated on rotavapor to obtain the crude product.
Sodium bicarbonate solution supersaturated with brine was added to the above obtained crude product to remove any unconverted starting material. The product was extracted with ethyl acetate, dried (over anhydrous Na2SO4), and concentrated on a rotavapor to get pure product (1.498 g).
Thus obtained (+)-Di-methyl L-tartrate was crystallised in benzene (bottle grade), crystals were separated by filtration and dried in Abderhalden, ground to powder and
checked the optical purity. [α]D was +22.2 ( C=2 in water), (Lit., [α]D +21 ± 1° (C=l in water).
Example 5
A two-necked round bottom flask equipped with a Dean-Stark trap was charged with a mixture of L-tartaric acid (1.5g) and methanol (2ml) [1: 5 molar ratio], toluene (10ml) as solvent and Al3+- Montmorillonite (0.25g). The solution was heated under reflux with stirring until no further water separation was observed, and also followed the reaction by thin layered chromatography (TLC). On completion of the reaction, ethyl acetate (10ml) was added to the reaction mixture. The catalyst was filtered through a sintered ware funnel (G-4), and the reaction mixture was concentrated on rotavapor to obtain the crude product.
Sodium bicarbonate solution supersaturated with brine was added to the above obtained crude product to remove any unconverted starting material. The product was extracted with ethyl acetate, dried (over anhydrous Na2SO4), and concentrated on a rotavapor to get pure product (1.520 g).
Thus obtained (+)-Di-methyl L-tartrate was crystallised in benzene (bottle grade), crystals were separated by filtration and dried in Abderhalden , ground to powder and checked the optical purity. [α]D was +22.2 ( C=2 in water), (Lit., [α]D +21 i 1° (C=l in water).
Example 6
A two-necked round bottom flask equipped with a Dean-Stark trap was charged with a mixture of L-tartaric acid (1.5g) and methanol (2ml) [1: 5 molar ratio], toluene
(10ml) as solvent and Ce3+ Montmorillonite (0.25g). The solution was heated under reflux with stirring until no further water separation was observed, and also followed the reaction by thin layered chromatography (TLC). On completion of the reaction, ethyl acetate (10ml) was added to the reaction mixture. The catalyst was filtered through a sintered ware funnel (G-4), and the reaction mixture was concentrated on rotavapor to obtain the crude product.
Sodium bicarbonate solution supersaturated with brine was added to the above obtained crude product to remove any unconverted starting material. The product was extracted with ethyl acetate, dried (over anhydrous Na2SO4), and concentrated on a rotavapor to get pure product (1.510 g).
Thus obtained (+)-Di-methyl L-tartrate was crystallised in benzene (bottle grade), crystals were separated by filtration and dried in Abderhalden , ground to powder and checked the optical purity. [α]D was +22.2 ( C=2 in water), (Lit., [α]D +21 ± 1° (C=l in water).
Example 7
A two-necked round bottom flask equipped with a Dean-Stark trap was charged with a mixture of L-tartaric acid (1.5g) and methanol (2ml) [1: 5 molar ratio], toluene (10ml) as solvent and H+- Montmorillonite (0.25g). The solution was heated under reflux with stirring until no further water separation was observed, and also followed the reaction by thin layered chromatography (TLC). On completion of the reaction, ethyl acetate (10ml) was added to the reaction mixture. The catalyst was filtered through a sintered
ware funnel (G-4), and the reaction mixture was concentrated on rotavapor to obtain the crude product.
Sodium bicarbonate solution supersaturated with brine was added to the above obtained crude product to remove any unconverted starting material. The product was extracted with ethyl acetate, dried (over anhydrous Na2SO4), and concentrated on a rotavapor to get pure product (1.499 g).
Thus obtained (+)-Di-methyl L-tartrate was crystallised in benzene (bottle grade), crystals were separated by filtration and dried in Abderhalden, ground to powder and checked the optical purity. [α]D was +22.2 ( C=2 in water), (Lit., [α]D +21 ± 1° (C=l in water).
Example 8
A two-necked round bottom flask equipped with a Dean-Stark trap was charged with a mixture of L-tartaric acid (1.5g) and methanol (2ml) [1: 5 molar ratio], toluene (10ml) as solvent and K10- Montmorillonite (0.25g). The solution was heated under reflux with stirring until no further water separation was observed, and also followed the reaction by thin layered chromatography (TLC). On completion of the reaction, ethyl acetate (10ml) was added to the reaction mixture. The catalyst was filtered through a sintered ware funnel (G-4), and the reaction mixture was concentrated on rotavapor to obtain the crude product.
Sodium bicarbonate solution supersaturated with brine was added to the above obtained crude product to remove any unconverted starting material. The product was
extracted with ethyl acetate, dried (over anhydrous Na2SO4), and concentrated on a rotavapor to get pure product (1.068 g).
Thus obtained (+)-Di-methyl L-tartrate was crystallised in benzene (bottle grade), crystals were separated by filtration and dried in Abderhalden , ground to powder and checked the optical purity. [α]D was +22.2 ( C=2 in water), (Lit., [α]D +21 ± 1° (C=l in water).
Example 9
A two-necked round bottom flask equipped with a Dean-Stark trap was charged with a mixture of L-tartaric acid (1.5g) and methanol (2ml) [1: 5 molar ratio], toluene (10ml) as solvent and Ambica clay (Indian clay) (0.25g). The solution was heated under reflux with stirring until no further water separation was observed, and also followed the reaction by thin layered chromatography (TLC). On completion of the reaction, ethyl acetate (10ml) was added to the reaction mixture. The catalyst was filtered through a sintered ware funnel (G-4), and the reaction mixture was concentrated on rotavapor to obtain the crude product.
Sodium bicarbonate solution supersaturated with brine was added to the above obtained crude product to remove any unconverted starting material. The product was extracted with ethyl acetate, dried (over anhydrous Na2SO4), and concentrated on a rotavapor to get pure product (1.192 g).
Thus obtained (+)-Di-methyl L-tartrate was crystallised in benzene (bottle grade), crystals were separated by filtration and dried in Abderhalden, ground to powder and
checked the optical purity. [α]D was +22.2 ( C=2 in water), (Lit.,[α]D +21 ± 1° (C=l in water).
Example 10
A two-necked round bottom flask equipped with a Dean-Stark trap was charged with a mixture of L-tartaric acid (1.5g) and methanol (2ml) [1:5 molar ratio], toluene (10ml) as solvent and Kunipia clay (Japanese clay) (0.25g). The solution was heated under reflux with stirring until no further water separation was observed, and also followed the reaction by thin layered chromatography (TLC). On completion of the reaction, ethyl acetate (10ml) was added to the reaction mixture. The catalyst was filtered through a sintered ware funnel (G-4), and the reaction mixture was concentrated on rotavapor to obtain the crude product.
Sodium bicarbonate solution supersaturated with brine was added to the above obtained crude product to remove any unconverted starting material. The product was extracted with ethyl acetate, dried (over anhydrous Na2SO4), and concentrated on a rotavapor to get pure product (1.459 g).
Thus obtained (+)-Di-methyl L-tartrate was crystallised in benzene (bottle grade), crystals were separated by filtration and dried in Abderhalden , ground to powder and checked the optical purity. [α]D was +22.2 ( C=2 in water), (Lit., [α]D +21 ± 1° (C=l in water).
Example 11
A two-necked round bottom flask equipped with a Dean-Stark trap was charged with a mixture of L-tartaric acid (1.5g) and methanol (2ml) [1:5 ratio], toluene (10ml) as
solvent. This reaction was carried out in the absence of the catalyst. The solution was heated under reflux with stirring and the reaction was monitored by thin layered chromatography (TLC). No water separation was observed. Therefore, it implies that no reaction took place.
TABLE 1
Esterification of L-tartaric acid with MeOH [1:5 molar ratio], using various metal
exchanged clay catalysts;

(Table Removed)
It was found that Fe3+ -montmorillonite displayed higher activity, and for the first time it was used (Table 1, the reaction time is less with Fe3--montmorillonite than with the other exchanged montmorillonites, Cu2+, Al3+, Zn2+, Ce3- and FT.) in the esterification reactions.
Example 12
A two-necked 100ml round bottom flask, equipped with a Dean-Stark trap, was charged with a mixture of malonic acid (1.5g), methanol (3ml), [1:5 molar ratio], toluene (10ml) as solvent and Fe3+- Montmorillonite (0.25g). The solution was heated under reflux with stirring until no further water separation was observed, and also followed the reaction by thin layered chromatography (TLC). On completion of the reaction the catalyst was filtered through a sintered ware funnel (G-4), and the reaction mixture concentrated on rotavapor to obtain the crude product.
A saturated solution of sodium bicarbonate was added to the above product to remove unconverted starting material. The product was extracted with ether, dried (over anhydrous Na2SO4), and concentrated on rotavapor to get pure product (1.333g).
Example 13
A two-necked 100ml round bottom flask, equipped with a Dean-Stark trap, was charged with a mixture of succinic acid (1.5g), methanol (2.54 ml), [1:5 molar ratio], toluene (10ml) as solvent and Fe3+- Montmorillonite (0.25g). The solution was heated under reflux with stirring until no further water separation was observed, and also followed the reaction by thin layered chromatography (TLC). On completion of the reaction the catalyst was filtered through a sintered ware funnel (G-4), and the reaction mixture concentrated on rotavapor to obtain the crude product.
A saturated solution of sodium bicarbonate was added to the above product to remove unconverted starting material. The product was extracted with ether, dried (over anhydrous Na2SO4), and concentrated on rotavapor to get pure product (1.299g).
Example 14
A two-necked 100ml round bottom flask, equipped with a Dean-Stark trap, was charged with a mixture of glutaric acid (1.5g), methanol (2.27ml), [1:5 molar ratio], toluene (10ml) as solvent and Fe3+- Montmorillonite (0.25g). The solution was heated under reflux with stirring until no further water separation was observed, and also followed the reaction by thin layered chromatography (TLC). On completion of the reaction the catalyst was filtered through a sintered ware funnel (G-4), and the reaction mixture concentrated on rotavapor to obtain the crude product.
A saturated solution of sodium bicarbonate was added to the above product to remove unconverted starting material. The product was extracted with ether, dried (over anhydrous Na2SO4), and concentrated on rotavapor to get pure product (1.236g).
Example 15
A two-necked 100ml round bottom flask, equipped with a Dean-Stark trap, was charged with a mixture of adipic acid (1.5g), methanol (2.04 ml), [1:5 molar ratio], toluene (10ml) as solvent and Fe3+- Montmorillonite (0.25g). The solution was heated under reflux with stirring until no further water separation was observed , and also followed the reaction by thin layered chromatography (TLC). On completion of the reaction the catalyst was filtered through a sintered ware funnel (G-4), and the reaction mixture concentrated on rotavapor to obtain the crude product.
A saturated solution of sodium bicarbonate was added to the above product to remove unconverted starting material. The product was extracted with ether, dried (over anhydrous Na2SO4), and concentrated on rotavapor to get pure product (1.608g).
Example 16
A two-necked 100ml round bottom flask, equipped with a Dean-Stark trap, was charged with a mixture of maleic acid (1.5g), methanol (5.2ml), [1:10 molar ratio], toluene (10ml) as solvent and Fe3+- Montmorillonite (0.25g). The solution was heated under reflux with stirring until no further water separation was observed , and also followed the reaction by thin layered chromatography (TLC). On completion of the reaction the catalyst was filtered through a sintered ware funnel (G-4), and the reaction mixture concentrated on rotavapor to obtain the crude product.
A saturated solution of sodium bicarbonate was added to the above product to remove unconverted starting material. The product was extracted with ether, dried (over anhydrous Na2SO4), and concentrated on rotavapor to get pure product (1.321g).
Example 17
A two-necked 100ml round bottom flask, equipped with a Dean-Stark trap, was charged with a mixture of phthalic acid (1.5g), methanol (1.8ml), [1:5 molar ratio], toluene (10ml) as solvent and Fe3+- Montmorillonite (0.25g). The solution was heated under reflux with stirring until no further water separation was observed , and also followed the reaction by thin layered chromatography (TLC). On completion of the reaction the catalyst was filtered through a sintered ware funnel (G-4), and the reaction mixture concentrated on rotavapor to obtain the crude product.
A saturated solution of sodium bicarbonate was added to the above product to remove unconverted starting material. The product was extracted with ether, dried (over anhydrous Na2SO4), and concentrated on rotavapor to get pure product (1.051 g).
Example 18
A two-necked 100ml round bottom flask, equipped with a Dean-Stark trap, was charged with a mixture of cinnamic acid (1.5g), methanol (2.0ml), [1:5 molar ratio], toluene (10ml) as solvent and Fe3+- Montmorillonite (0.25g). The solution was heated under reflux with stirring until no further water separation was observed, and also followed the reaction by thin layered chromatography (TLC). On completion of the reaction the catalyst was filtered through a sintered ware funnel (G-4), and the reaction mixture concentrated on rotavapor to obtain the crude product.
A saturated solution of sodium bicarbonate was added to the above product to remove unconverted starting material. The product was extracted with ether, dried (over anhydrous Na2SO4), and concentrated on rotavapor to get pure product (1.157 g).
Example 19
A two-necked 100ml round bottom flask, equipped with a Dean-Stark trap, was charged with a mixture of stearic acid (1.5g), methanol (1.0ml), [1:5 molar ratio], toluene (10ml) as solvent and Fe3+- Montmorillonite (0.25g). The solution was heated under reflux with stirring until no further water separation was observed , and also followed the reaction by thin layered chromatography (TLC). On completion of the reaction the catalyst was filtered through a sintered ware funnel (G-4), and the reaction mixture concentrated on rotavapor to obtain the crude product.
A saturated solution of sodium bicarbonate was added to the above product to remove unconverted starting material. The product was extracted with ether, dried (over anhydrous Na2SO4), and concentrated on rotavapor to get pure product (1.208 g).
Example 20
A two-necked 100ml round bottom flask, equipped with a Dean-Stark trap, was charged with a mixture of azeleic acid (1.5g), methanol (1.6ml), [1:5 molar ratio], toluene (10ml) as solvent and Fe3+- Montmorillonite (0.25g). The solution was heated under reflux with stirring until no further water separation was observed , and also followed the reaction by thin layered chromatography (TLC). On completion of the reaction the catalyst was filtered through a sintered ware funnel (G-4), and the reaction mixture concentrated on rotavapor to obtain the crude product.
A saturated solution of sodium bicarbonate was added to the above product to remove unconverted starting material. The product was extracted with ether, dried (over anhydrous Na2S04), and concentrated on rotavapor to get pure product (0.827 g).
Example 21
A two-necked 100ml round bottom flask, equipped with a Dean-Stark trap, was charged with a mixture of p-Isobutyl 2-methyl,phenyl acetic acid (ibuprofen) (1.5g), methanol (1.46ml), [1:5 molar ratio], toluene (10ml) as solvent and Fe3+- Montmorillonite (0.25g). The solution was heated under reflux with stirring until no further water separation was observed , and also followed the reaction by thin layered chromatography (TLC). On completion of the reaction the catalyst was filtered through a sintered ware funnel (G-4), and the reaction mixture concentrated on rotavapor to obtain the crude product.
A saturated solution of sodium bicarbonate was added to the above product to remove unconverted starting material. The product was extracted with ether, dried (over anhydrous Na2SO4), and concentrated on rotavapor to get pure product( 1.056 g).
TABLE 2 Esterification of various carboxvlic acids with MeOH [1:5 molar ratio] Using Fe3+ -
(Table Removed)
a: 1:10 molar ratio (acid : alcohol)
b: Reaction performed in presence of Fe3+ - montmorillonite as catalyst.
c: Reaction performed in presence of H+- montmorillonite as catalyst.
1. Fe3+ - montmorillonite is an eflBcient catalyst for the esterification of various carboxylic
acids such as aliphatic, aromatic, α,ß - unsaturated, mono and di-carboxylic acids.
2. Fe3+- montmorillonite was found to be more active than H+ - montmorillonite in the
esterificsation of maleic acid ( S.No. 5, example 16).
Example 22
A two-necked 100ml round bottom flask, equipped with a Dean-Stark trap, was charged with a mixture of chloroacetic acid (Immol), methanol (5mmol), [1:5 molar ratio], toluene (5ml) as solvent and Fe3+- Montmorillonite (0.10g). The solution was heated under reflux with stirring, and also followed the reaction by thin layered chromatography(TLC). On completion of the reaction the catalyst was filtered through a sintered ware runnel (G-4), and the reaction mixture concentrated on rotavapor to obtain the crude product.
Example 23
A two-necked 100ml round bottom flask, equipped with a Dean-Stark trap, was charged with a mixture of chloroacetic acid (Immol), ethanol (5mmol), [1:5 molar ratio], toluene (5ml) as solvent and Fe3+- Montmorillonite (0.10g). The solution was heated under reflux with stirring, and also followed the reaction by thin layered chromatography (TLC). On completion of the reaction the catalyst was filtered through a sintered ware runnel (G-4), and the reaction mixture concentrated on rotavapor to obtain the crude product.
Example 24
A two-necked 100ml round bottom flask, equipped with a Dean-Stark trap, was charged with a mixture of chloroacetic acid (Immol), ethanol (5mmol), [1:5 molar ratio], benzene (5ml) as solvent and Fe3+- Montmorillonite (0.10g). The solution was heated under reflux with stirring, and also followed the reaction by thin layered chromatography (TLC). On completion of the reaction the catalyst was filtered through a sintered ware
funnel (G-4), and the reaction mixture concentrated on rotavapor to obtain the crude
product.
The results are mentioned in Table 3.
TABLE 3
Esterification of Chloroacetic acid with Alcoholfs) (1:5 molar ratio) Using Fe3+ Montmorillonite as catalyst;
(Table Removed)
Toluene was found to be an effective solvent than benzene in esterification of chloroacetic acid by Fe3+- montmorillonite based on the yields.
The present process has the following advantages:
1. An ecofriendly process for the production of esters with better activity than the
conventional process.
2. It was found that Fe3+ -montmorillonite displayed higher activity, and for the first time it
was used in the esterification reactions. ( In Table 1, the reaction time is less with Fe3+-
montmorillonite than with the other exchanged montmorillonites, Cu2+, A13+, Zn2+, Ce3+
and H+ In Table 2, the esterification of maleic acid with ET- montmorillonite gave
66% of dimethyl maleate where as Fe3+- montmorillonite gave 100% conversion with
78% dimethyl maleate and 22% monomethyl maleate).
3. The selectivity and yields are very good,
4. The reactions are simple with easy workup procedure.
5. The support of the catalyst is cheap and abundantly available in nature.
6. The use of H2SO4, hazardous and corrosive chemical is dispensed with.
7. The present process envisage no disposal problem as the catalyst can be used for several
cycles. The catalyst was subjected to four cycles which displayed almost consistent
activity.
8. The present process is environmentally safe since there is no effluent disposable
problem.

We Claim:
1. An improved process for the production of esters from carboxylic acid using metal
exchanged montomorrilonite clay catalysts which comprises reacting carboxylic acid
with alcohol in a molar ratio of about 1:5 in presence of solvent medium and catalyst in a
ratio of about 40:1 at temperature ranging from 80°C to 130°C period in the range
of 2.5 to 15 hours and recovering esters by separating catalyst through filtration and removing the solvent by known methods.
2. An improved process for claim 1 wherein various metal ioa used in catalyst is selected
from Cu 2+, A13T, Zn2+, Ce3+, Fe3+ and H+.
3. An improved process as claimed in claim 1 wherein the alcohols used is selected from
methyl alcohol, ethyl alcohol as esterification agent and the amount used ranges from 2.5
to 5 mmols/mole of substrate.
4. An improved process as claimed in claim 1 wherein carboxylic acids used is such as
aromatic, aliphatic, a, p-unsaturated mono- and dicarboxylic acids such as malonic acid,
succinic acid, glutaric acid, adipic acid, maleic acid, phthalic acid, cinnamic acid, stearic
acid, azelic acid, p-isobutyl 2-methyl, phenyl acetic acid (lbuprofen) and chloroacetic
acid.
5. An improved process as claimed in claim 1 wherein solvent used is aromatic
hydrocarbon such as benzene, toluene, xylene.
6. An improved process for the production of esters from carboxylic acid using metal-
exchanged montmorrilonite clay catalysts substantially as herein described with
reference to example accompanying the specification.

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Patent Number

215342

Indian Patent Application Number

1685/DEL/1998

PG Journal Number

11/2008

Publication Date

14-Mar-2008

Grant Date

25-Feb-2008

Date of Filing

18-Jun-1998

Name of Patentee

COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH

Applicant Address

RAFI MARG, NEW DELHI-110001, INDIA.

Inventors:

#	Inventor's Name	Inventor's Address
1	BOYAPATI MANORANJAN CHOUDARY	INDIAN INSTITUTE OF CHEMICAL TECHNOLOGY, HYDERABAD, ANDHRA PRADESH.
2	VELDURTHY BHASKER	INDIAN INSTITUTE OF CHEMICAL TECHNOLOGY, HYDERABAD, ANDHRA PRADESH.
3	MANNEPALLI LAKSHMI KANTAM	INDIAN INSTITUTE OF CHEMICAL TECHNOLOGY, HYDERABAD, ANDHRA PRADESH.
4	KOTTAPALLI KOTESWARA RAO	INDIAN INSTITUTE OF CHEMICAL TECHNOLOGY, HYDERABAD, ANDHRA PRADESH.
5	KONDAPURAM VIJAYA RAGHAVAN	INDIAN INSTITUTE OF CHEMICAL TECHNOLOGY, HYDERABAD, ANDHRA PRADESH.

PCT International Classification Number

C07C 69/74

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA