Title of Invention

A PROCESS FOR THE PREPARATION OF 2-(4- ACETYL) AMINO-BENZYLIDENE CYCLOALKANONES

Abstract

A process for the preparation of 2-(4-acetyl) aminobenzylidene cycloalkanones of general formula 1 of the drawing accompanying this specification, which comprises reacting in an inert atmosphere a substituted cycloalkanone with acetic anhydride in an aqueous medium, in the presence of acid, stirring the reaction mixture at a temperature in the range of 35 to 45°C, for a period ranging from 4 to 10 hours, cooling the reaction mixture to room temperature, neutralizing the reaction mixture using alkali metal hydroxide, extracting the mixture with a dipolar aprotic solvent, washing the organic layer using alkali metal bicrbonate, drying the organic part over suitable drying agent at room temperature for 12 to 16 hours, removing the dipolar aprotic solvent under reduced pressure, and separating the product by column chromatography using a suitable eluent mixture to give the 2-(4-acetyl) aminobenzylidene cycloalkanones of general formula 1, wherein R=nil, -CHz-, -CH

Full Text

This invention relates to a process for the preparation of monosubstituted cycloalkanones. More particularly it relates to the preparation of 2-(4-acetyl amino benzylidene) cycloalkanones having general formula 1 given in the drawing accompanying this specification wherein R = nil, -CH2-, -CHlCH^)-; Rl=carboalkyl group. These precursors of liquid crystalline polymers are useful for non- linear optical application potentials. The precursors prepared by the process of this invention are based on mono substituted cyclohexanones/ cyclopentanones. The precursors are prepared from 2-(4-amino benzylidene) cycloalkanones having general formula 2 given in the drawing accompanying this specification wherein R = nil, -CH^-/ CH(CH3)~. In our copending application number NF-327/96, we have described and claimed a process for the preparation of 2-(4-amino benzylidene) cycloalkanones. The precursors prepared by the process of this invention can be further reacted under suitable reaction conditions to prepare new mesogens useful for the synthesis of side chain liquid crystalline polymers. The side chain liquid crystalline polymer so prepared is useful for non-linear optical applications. The need for newer materials for use in non-linear optical application is strongly felt by researchers. The need is desired by those involved in the developmental efforts for optical signaling manipulation, parallel optical image processing systems in the wake of developments in the area of fibre optics. The material development is directed towards materials with non- linear properties. Properties that are critical for materials to qualify for nonlinear optical applications include transparency, thermal, photochemical and chemical stability, dielectric constant etc. Both inorganic and organic salts exhibit non-linear optical properties. Materials that have been extensively used in the area of non-linear optical applications are inorganic salts such as potassium dideuterium phosphate, lithium nibbate, potassium titanyl phosphate etc. Organic materials offer the advantage of high density packing and specific arrangement of molecules in the crystalline state. While the organic materials offer superior properties in comparison with inorganic materials, practical utilization poses several problems. In addition, the development of organic materials which offer superior non-linear optical properties have been hindered because of the low threshold limits of these materials on exposure to strong radiations such as laser beam. Amongst the various approaches towards development of materials for non-linear optical applications such as crystal growth, growth in confined structures, monolayer assemblies such as the Langmuir-Bludget films and poled polymer systems. The precursors prepared by the process of this invention can be used in the preparation of side chain liquid crystalline polymers for poled polymer systems. The advantages offered by the poled polymer systems are greater flexibility in the selection of mesogenic arid polymericstructures and ease of fabrication of devices. The side chain liquid crystalline polymer synthesised using the mesogen as per the process of this invention could be used in poled polymer systems. Poling of polymers is done by subjecting the polymer usually in the form of a film to an external electric field at an elevated temperature followed by cooling to ambient temperature before the applied external field is removed. During this process the dipolar species in the polymer film would reorient and a net alignment is retained in the film. For a polymer to be useful for non-linear optical applications, it must satisfy primary optical property requirements. The primary optical property is characterised by the material having substantial transparency to light of desired frequency. The precursors prepared by the process of this invention can be further reacted under suitable reaction conditions to prepare new mesogens useful for the synthesis of side chain liquid crystalline polymers. The side chain liquid crystalline polymer prepared is useful for non-linear optical applications. The main object of the present invention is therefore to provide a process for the preparation of monosubstituted cycloalkanones. The monosubstituted cycloalkanones namely, 2-(4-acetyl amino benzylidene) cycloalkanones are reportedly synthesised for the first time by the inventors of the present invention and hence there are no earlier methods known for the preparation of these compounds. Accordingly, the present invention provides a process for the preparation of 2-(4-acetyl aminobenzylidene) cycloalkanones of general formula 1 of the drawing accompanying this specification, which comprises reacting in an inert atmosphere a substituted cycloalkanone with acetic anhydride in an aqueous medium, in the presence of acid, stirring the reaction mixture at a temperature in the range of 35 to 45°C, for a period ranging from 4 to 10 hours, cooling the reaction mixture to room temperature, neutralizing the reaction mixture using alkali metal hydroxide, extracting the mixture with a dipolar aprotic solvent, washing the organic layer using alkali metal bicrbonate, drying the organic part over suitable drying agent at room temperature for 12 to 16 hours, removing the dipolar aprotic solvent under reduced pressure, and separating the product by column chromatography using a suitable eluent mixture to give 2-(4-acetyl) aminobenzylidene cycloalkanones of general formula 1, wherein R=nil, -CH2-, -CH2 (CH3). In an embodiment of the present invention, the gas used for inert atmosphere may be such as nitrogen or argon. In yet another embodiment of this invention, the substituted cycloalkanone used may be such as 2- (4-amino benzylidene) cyclohexanone, 2-(4-amino benzylidene) q^clopentanone, 2-(4-amino benzylidene) - 4- methyl cyclohexanone. In another embodiment of the invention, the acid used may be such as hydrochloric acid, sulphuric acid, nitric acid. In yet another embodiment of the invention, the alkali metal hydroxide used may be such as sodium hydroxide, potassium hydroxide. In yet another embodiment of the invention, the alkali metal bicarbonate used may be such as sodium bicarbonate, potassium bicarbonate. In yet another embodiment of the invention, the. dipolar aprotic solvent used may be such as carbon tetrachloride, dichloromethane, dichloroethane. In yet another embodiment of the invention, the drying agent used may be such as sodium sulphate, magnesium sulphate. In yet another embodiment of the invention, the product separation may be effected by column chromatography using a silica-gel column. In yet another embodiment of the invention, the eluent mixture used for the separation of the product is a mixture of acetone and petroleum ether at ratio ranging from 5 : 95 to 11 : 89. The invention is described with reference to the examples given below which are illustrative in nature and should not be construed to limit the scope of this invention. Example 1 0.402 gram of 2-(4-amino benzylidene) cyclohexanone was dissolved in 35 ml of distilled water and 0.204 gram of acetic anhydridewas added to the above solution under stirring. 0.20 gram of sulphuric acid was added arid stirring was continued from 4 to 10 hours at a temperature of 35°C. The resulting reaction mixture was cooled to ambient temperature and neutralised with dilute sodium hydroxide solution, extracted with dichloromethane and washed with sodium bicarbonate. The dichloromethane extract was dried over sodium sulphate and concentrated under reduced pressure. The crude product was purified by silica-gel column chromatography using 8% (V/V) acetone in petroleum ether as eluent to get pure 0.442 gram 2-(4-acetylamino benzylidene) cyclohexanone. Example 2 0.30 gram of 2-(4-amino benzylidene) cyclohexanone was dissolved in 25 ml of distilled water and 0.14 gram of acetic anhydride was added to the above solution under stirring. 0.15 gram of sulphuric acid was added and stirring was continued for 6 hours at a temperature of 40°C. The resulting reaction mixture was cooled to ambient temperature and neutralised with dilute potassium hydroxide solution, extracted with dichloroethane and washed with sodium bicarbonate. The dichloroethane extract was dried over magnesium sulphate and concentrated under reduced pressure. The crude product was purified by silica-gel column chromatography using 8% (V/V) acetone in petroleum ether as eluent to get pure 0.29 gram of 2- (4-acetylamino benzylidene) cyclohexanone. Example 3 0.45 gram of 2-(4-amino benzylidene) cyclohexanone was dissolved in 40 ml of distilled water and 0.22 gram of acetic anhydride was added to the above solution under stirring. 0.22 gram of sulphuric acid was added and stirring was continued for 10 hours at a temperature of 45°C. The resulting reaction mixture was cooled to ambient temperature and neutralised with dilute potassium hydroxide solution, extracted with chloroform and washed with potassium bicarbonate. The chloroform extract was dried over magnesium sulphate and concentrated under reduced pressure. The crude product was purified by. silica-gel column chrotnatography using 8% (V/V) acetone in petroleum ether as eluent to get pure 0.44 gram of 2-(4-acetylamino benzylidene) cyclohexanone. Example 4 0.370 gram of 2-(4-amino benzylidene) cyclopentanone was dissolved in 35 ml of distilled water and 0.202 gram of acetic anhydride was added to the above solution under stirring. A drop of sulphuric acid was added and stirring was continued fOr 4 hours at a temperature of 35°C. The resulting reaction mixture was cooled to ambient temperature and neutralised with dilute sodium hydroxide solution, extracted with dichloromethane and washed with sodium bicarbonate. The dichloromethane extract was dried over sodium sulphate and concentrated under reduced pressure. The crude product was purified by silica-gel column chromatography using 8% (V/V) acetone in petroleum ether as eluent to get pure 0.420 gram 2-(4-acetylamino benzylidene) cyclopentanone. Example 5 0.370 gram of 2-(4-amino benzylidene) cyclopentanone was dissolved in 35 ml of distilled water and 0.202 gram of acetic anhydride was added to the above solution under stirring. A drop of sulphuric acid was added and stirring was continued for 4 hours at a temperature of 35°C. The resulting reaction mixture was cooled to ambient temperature and neutralised with dilute sodium hydroxide solution, extracted with dichloromethane and washed with sodium bicarbonate. The dichloromethane extract was dried over sodium sulphate and concentrated under reduced pressure. The crude product was purified by silica-gel column chromatography using 8% (V/V) acetone in petroleum ether as eluent to get pure 0.420 gram 2-(4-acetylamino benzylidene) cyclopentanone. Example 6 0.55 gram of 2-(4-amino benzylidene) cyclopentanone was dissolved in 50 ml of distilled water and 0.30 gram of acetic anhydride was added to the above solution under stirring. 0.25 gram of sulphuric acid was added and stirring was continued for 6 hours at a temperature of 40°C. The resulting reaction mixture was cooled to ambient temperature and neutralised with dilute potassium hydroxide solution, extracted with dichloroethane and washed with sodium bicarbonate. The dichloroethane extract was dried over magnesium sulphate and concentrated under reduced pressure. The crude product was purified by silica-gel column chromatography using 8% (V/V) acetone in petroleum ether as eluent to get pure 0.63 gram of 2 - (4-acetylamino benzylidene)cyclopentanone. Example 7 0.74 gram of 2-(4-amino benzylidene) cyclopentanone was dissolved in 70 ml of distilled water and 0.42 gram of acetic anhydride was added to the above solution under stirring. 0.32 gram of sulphuric acid was added and stirring was • continued for 10 hours at a temperature of 45°C. The resulting reaction mixture was cooled to ambient temperature and neutralised with dilute potassium hydroxide solution, extracted with chloroform and washed with potassium bicarbonate. The chloroform extract was dried over magnesium sulphate and concentrated under reduced pressure. The crude product was purified by silica-gel column chromatogr£iphy using 8% (V/V) acetone in petroleum ether as eluent to get pure 0.85 gram of 2- (4-acetylamino benzylidene) cyclopentanone. Example 8 0.435 gram of 2-(4-amino benzylidene)-4-methyl cyclohexanone was dissolved in 35 ml of distilled water and 0.202 gram of acetic anhydride was added to the above solution under stirring. A drop of sulphuric acid was added and stirring was continued for 4 hours at a temperature of 45°C. The resulting reaction mixture was cooled and neutralised with dilute sodium hydroxide solution, extracted with dichloromethane and washed with sodium bicarbonate. The dichloromethane extract was dried over sodium sulphate and concentrated under reduced pressure. The crude product was purified by silica-gel column chromatography using 8% (V/V) acetone in petroleum ether as eluerit to get pure 0.450 grain 2- (4 -acetylamino benzyl idene) -4 -methyl cyclohexanone. Example 9 0.62 gram of 2-(4-amino benzylidene)-4-methyl cyclohexanone was dissolved in 50 ml of distilled water and 0.30 gram of acetic anhydride was added to the above solution under stirring. 0.25 gram of sulphuric acid was added and stirring was continued for 6 hours at a temperature of 40°C. The resulting reaction mixture was cooled to ambient temperature and neutralised .with dilute potassium hydroxide solution, extracted with dichloroethane and washed with sodium bicarbonate. The dichloroethane extract was dried over magnesium sulphate and concentrated under reduced pressure. The crude product was purified by silica-gel column chromatography using 8% (V/V) acetone in petroleum ether as eluent to get pure 0.68 gram of 2-(4-acetylamino benzylidene)-4-methyl cyclohexanone. Example 10 0.88 gram of 2-(4-amino benzylidene) cyclohexanone was dissolved in 70 ml of distilled water and 0.40 gram of acetic anhydride was added to the above solution under stirring. 0.22 gram of hydrochloric acid was added and stirring was continued for 10 hours at a temperature of 45°C. The resulting reaction mixture was cooled to ambient temperature and neutralised with dilute potassium hydroxide solution, extracted with chloroform and washed with potassium bicarbonate. The chloroform extract was dried over magnesium sulphate and concentrated under reduced pressure. The crude product was purified by silica-gel column chromatography using 8% (V/V) acetone in petroleum ether as eluent to get pure 0.44 gram of 2-(4-acetylamino benzylidene)-4-methyl cyclohexanone. The advantages of the invention are : 1. The product obtained as per the process -of this invention meets the stringent purity requirements as a mesogen for the preparation of new side chain liquid crystalline polymers for non-linear optical applications. 2. The process is amenable to scale up to meet the requirements which are usually small. We claim : 1. A process for the preparation of mono substituted cycloalkanones, which comprises reacting in an inert atmosphere a substituted cycloalkanone with acid anhydride in an aqueous medium, in the presence of acid, stirring the reaction mixture at a temperature in the. range of 35 to 45°C, for a period ranging from 4 to 10 hours, cooling the reaction mixture to ambient temperature, neutralising the reaction mixture using alkali metal hydroxide, extracting the mixture with a dipolar aprotic solvent, washing the organic layer using alkali metal bicarbonate, drying the organic part over suitable drying agent at ambient temperature for 12 to 16 hours, removing the dipolar aprotic solvent under reduced pressure, and separating the product by column chromatography using a suitable eluent mixture to give the monosubstituted cycloalkanones of general formula 1, wherein R=nil, -CH2-/ -CH(CH3)- and Rl = carboalkyl group. 2. A process as claimed in claim 1, wherein, the gas used for inert atmosphere is such as nitrogen or argon. 4. A process as claimed in claims 1 to 3, wherein, the substituted cycloalkanone used is such as 2-(4-amino benzylidene) cyclohexanone, 2-(4-amino benzylidene) cyclopentanone, 2-(4-amino benzylidene)-4-methyl cyclohexanone. 5. A process as claimed in claims 1 to 4, wherein, the acid used is such as hydrochloric acid, sulphuric acid, nitric acid. 6. A process as claimed in claims 1 to 5, wherein, the alkali metal hydroxide used is such as sodium hydroxide, potassium hydroxide. 7. A process as claimed in claims 1 to 6, wherein, the alkali metal bicarbonate used is such as sodium bicarbonate, potassium bicarbonate. 8. A process as claimed in claims 1 to 7, wherein, the dipolar aprotic solvent used is such as carbon tetrachloride, dichloromethane, dichloroethane. 9. A process as claimed in claims 1 to 8, wherein, the drying agent used is such as sodium sulphate, magnesium sulphate. 10. A process as described in claims 1 to 9, wherein, the eluent mixture used to separate the product is a mixture of acetone and petroleum ether at a ratio ranging from 5 : 95 to 11 : 89. 11. A process for the preparation of monosubstituted cycloalkanones of formula 1 of the drawing accompanying this specification wherein R=nil, -CH2-, -CH3- and Rl = carboalkyl group substantially as hereinbefore described with reference to the examples .

Documents:

3346-del-1997-abstract.pdf

3346-del-1997-claims.pdf

3346-del-1997-complete specification (granted).pdf

3346-del-1997-correspondence-others.pdf

3346-del-1997-correspondence-po.pdf

3346-del-1997-description (complete).pdf

3346-del-1997-drawings.pdf

3346-del-1997-form-1.pdf

3346-del-1997-form-19.pdf

3346-del-1997-form-2.pdf