Title of Invention | AN IMPROVED PROCESS FOR PRODUCTION OF HYDROXYACETOPHENONES |
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Abstract | The present invention relates to an improved process for the production of hydroxyacetophenones. The process is for production of ortho- and para-hydroxyacetophenones. In the process hydroxyacetophenones is produced at high selectivity to the para - isomer by vapour phase acetylation of phenol in the presence of a catalyst containing a heteropoly compound. The invention discloses the ability of the supported catalyst system to carry out condensation reactions in the vapor phase and isomerisation reactions in the liquid phase, simultaneously at the same reaction temperature, making use of the higher boiling point of the products formed in the first step. This type of catalytic activity of the supported heteropoly catalyst is unique and this property is employed successfully in the present invention.. |
Full Text | The present invention relates to an improved process for the production of hydroxyacetophenones. This invention particularly relates to a process for production of ortho- and para-hydroxyacetophenones. More particularly, the present invention relates to a process for producing hydroxyacetophenones at high selectivity to the para- isomer by the vapour phase acetylation of phenol in the presence of a catalyst containing a heteropoly compound. Hydroxyacetophenones (ortho- and para- ), especially para -hydroxyacetophenone, are starting materials for the preparation of many plastic intermediates. Hence many processes have been developed for their production. Catalytic Fries rearrangement of phenyl acetate is the basis of all well known industrial processes for the production of para and ortho hydroxyacetophenones. Early methods for the industrial production of hydroxyacetophenones by the rearrangement of phenyl acetate used aluminium chloride or anhydrous HF gas; both of them showed more selectivity for the para isomer (Text book of Practical Organic Chemistry 3rd edition, Vogel A I (ELBS, Longmans Group Ltd London) 1971, 676). These catalysts cause heavy environmental pollution and hence not suitable for present day industrial production of hydroxyacetophenones. Recently H-ZSM-5 and H-beta zeolites (Vogt A, Kouwenlioven H W, Prins R, Applied catal A Gen 123 (1995) 37), Nafion acidic resin and Nafion on silica composite catalysts (Heidekum M A, Mark H A & Hoelderich W F ./ catalysis 176 (1998)260; Sharghi H, Kaboudin B & Hashem S ./ chem Res Synops (1998) 628; J chem Res (M) (1998) 2678) at 150°C have been claimed to give a para to ortho selectivity ratio of 4.3 : 1 and 4.7 : 1 respectively. A German patent (Hoelderich W F & Heidekum M A, Ger pat, 19,637,976 (1998)) describes the Fries rearrangement of phenyl acetate with 50% conversion into para- and ortho- hydroxyacetophenones with Nafion NR 50 catalyst in the presence of phenol or cumene at 150-200°C. Methane sulphonic acid loaded on alumina has been claimed to produce more ortho isomer in the rearrangement of phenyl acetate (Sharghi H, Kaboudin B & Hashem S, ,/ chem Res Synops, 1998, 260). Subbarao et al have reported the isomerization of phenyl acetate with high ortho selectivity using modified ZSM-5 zeolites (Subbarao Y A, Kulkarni S J, Subhramanyam M & Rama Rao, Tet. left., 34 1993 7799; Appl. Cat. A Gen., 133 1995 LI). A need, therefore, exists for developing a new and improved eco-friendly process for the production of hydroxyacetophenones. Some industrial applications of silica supported heteropoly acid (HPA) catalysts have been reported from CSIR in the past The HPA catalysed reactions carried out by us include selective formation of guaiacol from catechol and methanol (Gopinathan C, Gopinathan S, Hundekar A M, Pandit S K, Deshmukh K K & Ratnasamy P, Ind Pat, 373/DEL/93); 7-hydroxybenzofuran from catechol and methallyl alcohol ( Gopinathan C, Gopinathan S, Mitra R B & Ratnasamy P, US Pat, 5,382,702 (1995); Ind. Pat. 368/DEL/93); N-acetylaminophenol from hydroquinone and ammonium acetate (Gopinathan C, Gopinathan S, Joseph K, Pardhy S A & Ratnasamy P, US Pat, 5,856,575 (1999); Ind.Pat, 956/DEL/94); acetonitrile from ammonia and acetic acid (Gopinathan C, Gopinathan S, Hundekar A M, Pandit S K & Joseph K, Ind. Pat. 279/DEL/92) and methyl chloride / methyl bromide from methanol and HC1 / HBr (Alekar N A, Sajanikumari C S, Trissa Joseph, Unny I R, Sarada Gopinathan and Gopinathan C, Ind, J of Techno/. 7 (2000) 79. In these applications, the catalytic behaviour of Keggin HPA is due to its Bronsted acidity coupled with the large surface area (about 380 m2/g) of the silica gel support. The silica gel supported HPA catalyst is thermally stable and has a long catalytic activity under the reaction conditions The catalyst is non-polluting and can be used without loss of activity for a long period. The inventors of the present invention extended this invention for the one step synthesis of hydroxyacetophenones in the vapour phase reaction of phenol and acetic anhydride. The reactions known so far, including those reported in the above references, are condensation/dehydration reactions catalysed by the supported heteropoly acid catalyst either in the liquid phase or in the vapour phase . The present invention discloses the ability of the supported catalyst system to carry out condensation reactions in the vapor phase and isomerisation reactions in the liquid phase, simultaneously at the same reaction temperature, making use of the higher boiling point of the products formed in the first step. This type of catalytic activity of the supported heteropoly catalyst is unique and this property is employed successfully in the present invention for the first time. The parameters of the reaction could be adjusted accurately in downward flow reactor system to get the required product namely a mixture of ortho- and para- hydroxyacetopheones. The object of the present invention is to provide an improved process for the production of hydroxyacetophenones by contacting phenol and acetic anhydride over a solid catalyst consisting of a heteropoly acid supported on a catalyst support such as silica, thoria or titania. Accordingly the present invention provides an improved process for the production of hydroxyacetophenones which comprises; contacting feed consisting either a mixture of phenol and acetic anhydride in the molar proportion of 0.5 : 1 to 1:2 or phenyl acetate over a supported solid heteropoly acid catalyst such as herein described at a temperature in the range of ! 00 to 250°C, pressure in the range of 1 to 5 atmospheres and liquid hourly space velocity (LHSV) between 0.5 to 5 for a period ranging from 1 to 12 hrs, recovering the product from reaction mixture by conventional methods. In one of the embodiments of the present invention the heteropoly acid catalyst used may be phosphotungstic acid or silicotungstic acid. In another embodiment the support may be silica, thoria or titania, preferably silica. In another embodiment, the concentration of the heteropoly acid in the supported catalyst composite may be from 2-40 wt%, preferably around 15%. In yet another embodiment, the molar proportion of the reactants, namely phenol and acetic anhydride, may be varied form 0.5:1 to 1:2. In yet another embodiment, the liquid hourly space velocity (LHSV) may be from 0.5 to 5. In another embodiment, pure phenyl acetate may be used as the feed for preparation of hydroxyacetophenones over the same composite catalyst. In yet another embodiment, the reaction temperature used in the process may be varied from 100 to 250°C, preferably around 200 °C. In another rembodiment, the reaction may be conducted at a pressure between 1-5 atmospheres, preferably one atmosphere. The process of the present invention is described herein below with examples that are illustrative only and should not be construed to limit the scope of the present invention in any manner. Example 1 Phosphotungstic acid (15 g in 150 ml water) was allowed to mix with coarse silica gel (85 g; mesh size -5+12, activated at 110°C for 6 h before use) for 12 h at room temperature (30°C). The contents were then evaporated to dryness on a water bath and later activated for 12 h at 400°C in air in a muffle furnace. The catalyst thus prepared was preserved in glass bottle. This catalyst showed a surface area of about 300 m2/g. Example 2 Silicotungstic acid (15 g in 150 ml water) was allowed to mix with coarse silica gel (85 g; mesh size -5+12, activated at 110°C for 6 h before use) for 12 h at room temperature (30°C). The contents were then evaporated to dryness on a water bath and later activated for 12 h at 400°C in air in a muffle furnace. The catalyst thus prepared was preserved in glass bottle. This catalyst showed a surface area of about 300 m2/g. Example 3 The experiments were carried out in a downward flow reactor of diameter 2 cm, made of quartz tube, which was kept in a shell furnace of length 32 cm. The catalyst, prepared in Example 1, (11 g) was filled in the quartz reactor tube and placed in the furnace in such a way that it was in the middle of the heating zone and was heated to 100°C in a current of nitrogen. The feed consisted of a 1:1 molar mixture of phenol and acetic anhydride. An horizontal feed pump (Sage make) was provided with a 100 mL glass syringe to deliver the feed over the catalyst at a LHSV of 1.5 (17 g/h). The products coming out from the bottom outlet of the reactor were rejected for the first one h. and then collected at two-hour intervals and weighed (about 33 g each time). This was analysed by GC (HP 5890 with megabore capillary column) and GC-MS (Shimadzu GC17A coupled with QP 5000 MS) for identification and quantification of phenol, acetic anhydride, acetic acid, ortho- and para-hydroxyacetophenones (HAPs) and other minor products. The temperature of the reaction was raised by 10°C after every 2 h till 220°C was reached. Every time the product was collected separately, weighed and analysed. Results are tabulated in table 1. Example 4 The experiments were carried out in a downward flow reactor of diameter 2 cm, made of quartz tube, which was kept in a shell furnace of length 32 cm. The catalyst, prepared in Example 2, (11 g) was filled in the quartz reactor tube and placed in the furnace in such a way that it was in the middle of the heating zone and was heated to 210°C in a current of nitrogen. The feed consisted of a 1:1 molar mixture of phenol and acetic anhydride. An horizontal feed pump (Sage make) was provided with a 100 mL glass syringe to deliver the feed over the catalyst at a LHSV of 1.5 (17 g/h). The products coming out from the bottom outlet of the reactor were rejected for the first one h. and then collected at two-hour intervals and weighed (about 33 g each time). This was analysed by GC (HP 5890 with megabore capillary column) and GC-MS (Shimadzu GC17A coupled with QP 5000 MS) for identification and quantification of phenol, acetic anhydride, acetic acid, ortho- and para-hydroxyacetophenones (HAPs) and other minor products (Table 1). Table 1 - One step synthesis of hydroxyacetophenones from phenol and acetic anhydride over heteropoly acid (c) on silica catalyst (Table Removed) Example 5 The experiments were carried out in a downward flow reactor of diameter 2 cm, made of quartz tube, which was kept in a shell furnace of length 32 cm. The catalyst, prepared in Example 1, (11 g) was filled in the quartz reactor tube and placed in the furnace in such a way that it was in the middle of the heating zone and was heated to 210°C in a current of nitrogen. The feed consisted of pure phenyl acetate. An horizontal feed pump (Sage make) was provided with a 100 mL glass syringe to deliver the feed over the catalyst at a LHSV of 1.5 (17 g/h). The products coming out from the bottom outlet of the reactor were rejected for the first one h. and then collected at two-hour intervals and weighed (about 33 g each time). This was analysed by GC (HP 5890 with megabore capillary column) and GC-MS (Shimadzu GC17A coupled with QP 5000 MS) for identification and quantification of unreacted phenyl acetate, ortho- and para- hydroxyacetophenones and any other minor products. Example 6 The experiments were carried out in a downward flow reactor of diameter 2 cm, made of quartz tube, which was kept in a shell furnace of length 32 cm. The catalyst, prepared in Example 2, (11 g) was filled in the quartz reactor tube and placed in the furnace in such a way that it was in the middle of the heating zone and was heated to 210°C in a current of nitrogen. The feed consisted of pure phenyl acetate. An horizontal feed pump (Sage make) was provided with a 100 mL glass syringe to deliver the feed over the catalyst at a LHSV of 1.5 (17 g/h). The products coming out from the bottom outlet of the reactor were rejected for the first one h. and then collected at two-hour intervals and weighed (about 33 g each time). This was analysed by GC (HP 5890 with megabore capillary column) and GC-MS (Shimadzu GC17A coupled with QP 5000 MS) for identification and quantification of unreacted phenyl acetate, ortho- and para- hydroxyacetophenones and any other minor reaction products. Example 7 The experiments were carried out in a downward flow reactor of diameter 2 cm, made of quartz tube, which was kept in a shell furnace of length 32 cm. The catalyst, prepared in Example 1, (11 g) was filled in the quartz reactor tube and placed in the furnace in such a way that it was in the middle of the heating zone and was heated to 170°C in a current of nitrogen. The feed consisted of pure phenyl acetate. An horizontal feed pump (Sage make) was provided with a 100 mL glass syringe to deliver the feed over the catalyst at a LHSV of 1.5. (17 g/h) The products coming out from the bottom outlet of the reactor were rejected for the first one h. and then collected at two-hour intervals and weighed (about 33 g each time). This was analysed by GC (HP 5890 with megabore capillary column) and GC- MS (Shimadzu GC17A coupled with QP 5000 MS) for identification and quantification of unreacted phenyl acetatel, ortho- and para- hydroxyacetophenones and any other minor products. The temperature of the reaction was raised by 10°C after every two h till 250°C was reached. Every time the product was collected separately, weighed and analysed. Combined results of Examples 5-7 are tabulated in table 2. Table 2 - Effect of temp, on the isomerisation of phenyl acetate (Table Removed) (a) Based on weight % (b) Expressed as a percentage of the total products formed. Advantages of the invention : 1. Direct one-step vapour phase catalytic acetylation of phenol with acetic anhydride gives hydroxyacetophenones via phenyl acetate. 2. Phenyl acetate formation in the presence of the catalyst from phenol and acetic anhydride in 1 : 1 molar proportion is >95% at 140°C. 3. At 200-230°C and in presence of the catalyst, phenyl acetate undergoes Fries rearrangement to form hydroxyacetophenones in >11% yield. 4. The silica supported heteropoly acid catalyst gives a high para selectivity. The ratio of para- to ortho- hydroxyacetophenone is >90%, which is one of the highest reported so far. 5. The high boiling fractions left after the separation of phenyl acetate and hydroxyacetophenones, contain the useful chemical namely l,l,l-tris(4- hydroxyphenyl) ethane. 6. The silica supported heteropoly acid catalyst is eco-friendly, stable and has long catalytic life. 7. The unchanged phenyl acetate may be separated and recycled to get more rearranged products. We Claim: 1. An improved process for the production of hydroxyacetophenones which comprises; contacting feed consisting either a mixture of phenol and acetic anhydride in the molar proportion of 0.5 : 1 to 1:2 or phenyl acetate over a supported solid heteropoly acid catalyst such as herein described at a temperature in the range of 100 to 250°C, pressure in the range of 1 to 5 atmospheres and liquid hourly space velocity (LHSV) between 0.5 to 5 for a period ranging from 1 to 12 hrs, recovering the product from reaction mixture by conventional methods. 2. An improved process as claimed in claim 1 wherein, the solid catalyst used is a heteropoly compound supported on silica, thoria, titania, more preferably on silica. 3. An improved process as claimed in claims 1 to 2 wherein the heteropoly compound is such as phosphotungstic acid, silicotungstic acid. 4. An improved process as claimed in Claims 1 to 3 wherein, the heteropoly compound concentration on the support material is between 2 to 40% by weight. 5. An improved process as claimed in claims 1 to 4 wherein, the temperature of the process is preferably 200°C. 6. An improved process as claimed in claims 1 to 5 wherein, the pressure is preferably 1 atmosphere. 7. An improved process for the production of hydroxyacetophenones as substantially described hereinbefore with reference to examples contained therein. |
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Patent Number | 242172 | ||||||||||||||||||||||||
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Indian Patent Application Number | 965/DEL/2000 | ||||||||||||||||||||||||
PG Journal Number | 34/2010 | ||||||||||||||||||||||||
Publication Date | 20-Aug-2010 | ||||||||||||||||||||||||
Grant Date | 17-Aug-2010 | ||||||||||||||||||||||||
Date of Filing | 01-Nov-2000 | ||||||||||||||||||||||||
Name of Patentee | COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH | ||||||||||||||||||||||||
Applicant Address | RAFI MARG, NEW DELHI-110001 | ||||||||||||||||||||||||
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PCT International Classification Number | C07C 45/64 | ||||||||||||||||||||||||
PCT International Application Number | N/A | ||||||||||||||||||||||||
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