Title of Invention	AN IMPROVED PROCESS FOR THE ELECTROCHEMICAL PREPARATION OF BENZALDEHYDE FROM BENZYL ALCOHOL
Abstract	The present invention provides an improved process for the electrochemical preparation of benzaldehyde from benzyl alcohol by electrochemical oxidation of benzyl alcohol in an bi-phase solvent containing sodium bromide as the electrolyte in an undivided electrochemical cell at a current density of 50 mA/cm2 and at 30°C temperature with high yield (98%) and high conversion (100%). The top layer containing the acidic aqueous sodium bromide solution as electrolyte and the bottom layer containing benzyl alcohol dissolved in chloroform. The electrolysis was carried out at 30°C temperature with stirring speed of 50 rpm at atmospheric pressure.

Title of Invention

AN IMPROVED PROCESS FOR THE ELECTROCHEMICAL PREPARATION OF BENZALDEHYDE FROM BENZYL ALCOHOL

Abstract

The present invention provides an improved process for the electrochemical preparation of benzaldehyde from benzyl alcohol by electrochemical oxidation of benzyl alcohol in an bi-phase solvent containing sodium bromide as the electrolyte in an undivided electrochemical cell at a current density of 50 mA/cm2 and at 30°C temperature with high yield (98%) and high conversion (100%). The top layer containing the acidic aqueous sodium bromide solution as electrolyte and the bottom layer containing benzyl alcohol dissolved in chloroform. The electrolysis was carried out at 30°C temperature with stirring speed of 50 rpm at atmospheric pressure.

Full Text	Field of the invention The present invention relates to an improved process for the electrochemical preparation of benzaldehyde from benzyl alcohol. More particularly, the presemt invention relates to an improved process for the electrochemical preparation of benzaldehyde from benzyl alcohol in aqueous medium containing sodium bromide as an electrolyte with platinum both as anode and cathode in an undivided electrochemical cell. Background of the invention The Product benzaldehyde is widely used as an intermediate in the manufacture of dyestuff, flavoring chemicals (e.g. cinnamldehyde, amyl cinnamldehyde and benzyl benzoate), and perfumery chemicals, in acridine dyes, pharmaceuticals and fine chemicals. It can be also used as a corrosion inhibitor and a solvent for polyester resins. Hitherto preparation of benzaldehyde by the hydrolysis of the corresponding side chain halogenated toluene compounds such as benzyl chloride at a temperature range of 100-200°C. at normal or higher pressures in the presence of an excess hydrochloric acid (U.S. Pat. No. 4,229,379). In U.S. Pat. No. 4,450,298 a process is described for the vapor phase catalytic hydrolysis of benzyl chloride to benzaldehyde using a catalyst comprising activated carbon treated with sulphuric acid or impregnated with a metal chloride such as iron (III) chloride or a metal sulphate such as cupric sulphate. A major disadvantage of these processes is the generation of large amount of effluent. The benzaldehyde produced by these routes does not meet food grade specifications. Vapor phase or liquid phase oxidation of toluene by air is environmentally benign and provided the desired selectivities to the market driven products. World patent WO 95/20560 discloses a liquid phase process for the manufacture of benzaldehyde by the oxidation of toluene in presence of oxygen in a temperature and pressure range of 120 -200.°C. and 2-50 atm, respectively in the presence of a catalyst comprising cobalt or manganese as a metal ion and bromide as a promoter. 10% conversion of toluene and 45% selectivity to benzaldehyde is obtained. Borgaonkaret al, [ I & EC Prod. Res. Dev, 23(3), 459 (1984)] have reported lower (10%) conversion of toluene and 90% yield of benzaldehyde by the use of cobalt acetate and either sodium bromide or paraldehyde as a promoter in presence of air. A process for the vapor phase oxidation of toluene to benzaldehyde and benzoic acid using a catalyst containing a mixture of silver vanadate and lead vanadate or silver arsenate in presence of oxygen or ozone is described in U.S. Pat. No. 3,485,876. This catalyst system suppresses the formation of benzoic acid and degradation to carbon dioxide. According to U.S. Pat. No. 3,946,067, aromatic aldehydes such as benzaldehyde or substituted benzaldehydes were manufactured by the vapour-phase oxidation of aralkyl compounds, like toluene or substituted toluenes, in the presence of catalyst containing palladium metal and phosphoric acid at a temperature of less than 250 °C. The aromatic aldehydes are produced in a single reaction step. The drawbacks of the process are that the conversion of toluene has to be kept very low (70%). Also, the process is not suitable as large amounts of carbon dioxide are formed due to high temperature used in the reaction. U.S. Pat. No. 4,390,728 describes a process in which the oxides of various metals (viz. Cu, Fe, Pb, Mo, U, and P) with promoter were used for the production of benzaldehyde by the oxidation of toluene. At a temperature of 475-550 °C, a conversion of 35-50% and selectivity of 40-70% to benzaldehyde was obtained. Another process for the production of benzaldehyde was reported by Ray et al. [Ind. J. Technol., 21(4), 137 (1983)] at a conversion of about 15% and selectivity of 70% with significant amount of C02 formation. Hence, the major disadvantages of the above processes are the use of high temperatures and lower conversion of toluene. The formation of large amount of carbon dioxide ultimately will affect the overall yield and is also not environmentally clean. An electrochemical process using redox mediated system is described in Indian patent No.62426 for the oxidation of toluene to benzaldehyde. In this redox system the space time yield is low and the process is two stage processes for oxidation of toluene. These are the drawbacks in this electrochemical process and there is no electrochemical process on oxidation of benzyl alcohol to benzaldehyde with aqueous NaBr medium. Wherein, because of the above drawbacks these processes are not promising for the production of benzaldehyde by toluene oxidation. The drawbacks are low yield and low selectivity and the reactions are conducted at very high pressure and temperature with hazardous raw materials in all the above-referred chemical method. Radical bromination on a benzylic position has been achieved using bromine, and N-bromo succinimide. In addition, bromine complex of styrene vinyl pyridine copolymer and bromotrichloro ethane and copper(ll) bromide have been reported to be effective for benzylic bromination. Majority of brominating agents require the presence of peroxide or other radical initiator. Side chain bromination using sodium bromate and bromotrimethyl silane pair is also reported. But these methods are not suitable for commercialization due to poor yield. Moreover they had become the biggest obstacle to environmental safety. On the basis of the electrochemical technology, it is possible to carry out a desired electrochemical oxidation by a two-phase electrolysis resulting in high yield and high selectivity for benzaldehyde and substituted benzyl benzaldehydes. Hence the invented process includes an improved process for the electrochemical preparation of benzaldehyde from benzyl alcohol in aqueous medium containing sodium bromide as an electrolyte with platinum as anode and cathode in an undivided electrochemical cell at a current density of 50 mA/cm2 and in room temperature with high yield (98%) and high conversion (100%). The depleted concentration of sodium bromide can be made up by adding required amount of additional salt in the aqueous phase and can be reused. There are also no wastewater problems. The wastewater consists solely of aqueous sodium bromide solution. Objectives of the invention The main objective of the present invention is to provide an improved process for the electrochemical preparation of benzaldehyde from benzyl alcohol in aqueous medium containing sodium bromide as a electrolyte with platinum as anode and cathode in an undivided electrochemical cell. Yet another object of the present invention is to develop a process, which will be eco-friendly and avoids the effluent disposal problem. Another object of this investigation is to explore a new electrolyte system consisting of metal bromides such as sodium, potassium, calcium or a combination of any of the above two metal salts preferably sodium bromide. Yet another object of this invention is to use a very low concentration of NaBr solution (25%) to achieve high yield to benzaldehyde. Yet another object of this invention is to reduce the formation of side products such as benzyl bromide and benzoic acid. Yet another object of the invention is to eliminate the formation of carbon dioxide. Yet another object of this invention is this process can be operated at room temperature and avoids high temperature. Yet another object of this invention is the solvent used for the system is chloroform or acetonitrile or other solvents Summary of the invention Accordingly the present invention provides an improved process for the electrochemical preparation of benzaldehyde from benzyl alcohol which comprises subjecting the benzyl alcohol to electrochemical oxidation in a two phase solvent system of aqueous and organic solvent containing alkali or alkaline earth metal bromide as electrolyte and catalytic amount mineral acid in an undivided electrochemical cell having an anode and a cathode, at a current density of 40-60 mA/cm2, at a temperature of 25-40°C, for a period of 1-3 hrs, followed by the separation of the desired product by known method. In an embodiment of the present invention the anode used is platinum or DSA. In yet another embodiment the cathode used is selected from platinum and stainless steel. In yet another embodiment the organic solvent used in two-phase solvent system is is selected from chloroform and acetonitrile. In yet another embodiment the alkali metal bromide used is selected from the group consisting of sodium bromide, potassium and calcium bromide. In yet another embodiment the mineral acid used is HBr. In yet another embodiment the oxidation is carried out at 30°C temperature. In yet another embodiment the yield of benzaldehyde obtained is in the range of 95-99%. In yet another embodiment the conversion of benzyl alcohol in oxidation is 100%. In yet another embodiment, the concentration of NaBr is in the range of 10-50%, preferably 20- 30%. In yet another embodiment the amount of benzyl alcohol taken with respect to chloroform is in the range of 10-100 g/l preferably 25-50 g/l. In another embodiment of the invention, the yield of benzaldehyde obtained in the range of 95-99% without formation of benzoic acid and benzyl bromide as side products. In still another embodiment of the invention, the conversion of benzyl alcohol in the oxidation is in the range of 98-100%. The present invention provides an improved process for the for the electrochemical preparation of benzaldehyde from benzyl alcohol in aqueous medium containing sodium bromide as a electrolyte with platinum as anode and cathode in an undivided electrochemical cell at a current density of 50 mA/cm2 and in room temperature with high yield (98%) and high conversion (100%). Detail description of the invention The process of the present invention comprises subjecting benzyl alcohol oxidation in two-phase system in an organic solvent and in the presence of aqueous NaBr system and a bromide source as a promoter. The reaction is carried out in the presence of aqueous and an organic solvent system (two-phase system) and at a temperature in the range of 25-50 °C. and at atmospheric pressure for a period of 4-6 F/mol. After the reaction is complete, the reaction mixture is separated by any conventional method such as distillation. The aqueous electrolyte system consists of metal selected from sodium, calcium and potassium or a combination of any of the above two metals, with bromide as a promoter. The percentage of aqueous NaBr used is in the range of 10-50% and preferably in the range of 20-30%. The ratio of benzyl alcohol to chloroform is used in the range of 10-100 g/l and preferably in the range of 25-50 g/l. After the reaction is complete, the reaction mixture phase was separated. The reactants and products were analyzed by GC and HPLC. The present invention produces benzaldehyde with high yield (preferably 95-99%) without other byproducts such as benzyl bromide and benzoic acid. The two-phase electrolysis system is necessary for obtaining high yield of benzaldehyde from benzyl alcohol. The single phase electrolysis allows very low selectivity to benzaldehyde. The novelty of the process is the preparation of benzaldehyde from benzyl alcohol in aqueous medium at 30°C temperature by biphasic electrolysis and also used to syntheses of regioselective substituted benzaldehydes without formation of the benzyl bromide or benzoic acids. Moreover yields of benzaldehyde and substituted benzaldehydes are obtained about 90 to 99%. The reactive species formed by the electrolytic oxidation of the halide ion in an aqueous phase can be continuously taken into the organic layer and then reacts with the substrate giving regioselective products. The electrolysis can be performed in mild condition without any hazardous reagents at atmospheric pressure. Good mass transfer, high conversion and yield could be achieved in this electrochemical cell. The cell design is simple and cost effective. The following examples are given by way of illustration of the working of the invention in actual practice and therefore should not be construed to limit the scope of the present invention. EXAMPLE. 1. Anode. : Platinum (10 cm2) Cathode : Platinum (10 cm2) Current Density : 50 mA/cm2 Electrolyte : NaBr(12.5g);H2O(50ml);CHCI3(25ml);HBr(5ml) Temperature : 30°C Amount of benzyl alcohol : 1 ml (1.05 g ) Charge passed : 5.5 F/mole Total current : 1.43 Ahr Current rate : 0.5 A Cell Voltage : 1.3 V Time of electrolysis : 2 hrs 52 mins Amount of Benzaldehyde : 1.01 g Yield : 98% Current efficiency : 36 % Conversion : 100 % EXAMPLE. 2. Anode. : Platinum (10 cm2) Cathode : Platinum (10 cm2) Current Density : 50 mA/cm2 Electrolyte :NaBr(12.5g);H2O(50ml);CHCI3(25ml);HBr(5 ml) Temperature : 40°C Amount of benzyl alcohol : 1ml (1.05 g) Charge passed : 5.5 F/mole Total current : 1.43 Ahr Current rate : 0.5 A Cell Voltage : 1.8 V Time of electrolysis : 2hrs 52 mins Amount of Benzaldehyde 0.76 g Yield : 74% Current efficiency : 36% Conversion : 80% EXAMPLE. 3. Anode. .Platinum (10cm2) Cathode : Platinum (10 cm2) Current Density : 50 mA/cm2 Electrolyte : NaBr(12.5 g); H2O(50 ml);CHCI3(25ml) ;HBr(5ml) Temperature : 30°C Amount of benzyl alcohol : 5 ml ( 5.25g) Charge passed : 5.5 F/mol Total current : 7.15Ahr Current rate : 0.5 A Cell Voltage : 1.4 V Time of electrolysis : 14 hrs 20mins Amount of Benzaldehyde formed : 3.45 g Yield : 67% Current efficiency : 36 % Conversion : 78 % EXAMPLE. 4. Anode. : Platinum (10 cm2) Cathode : Platinum (10 cm2) Current Density : 50 mA/cm2 Electrolyte :NaBr(12.5g);H2O(50ml);CH3CN(25ml);HBr(5 ml) Temperature : 30°C Amount of Toluene taken : 1ml(1.05g) Charge passed : 5.5 F/mol Total current : 1.43 Ahr Current rate : 0.5 A Cell Voltage : 1.4 V Time of electrolysis : 2 hrs 52 mins Amount of Benzaldehyde formed : 0.94 g Yield : 91 % Current efficiency : 36 % Conversion : 100% EXAMPLE. 5. Anode. : Platinum (10 cm2) Cathode : Platinum (10 cm2) Current Density : 50 mA/cm2 Electrolyte :NaBr(12.5g); H2O(50 ml);CHCI3 (25 ml);HBr(5 ml) Temperature : 30°C Amount of Toluene taken : 1 ml (1.05 g) Charge passed : 2 F/mol Total current : 0.52 Ahr Current rate : 0.52A Cell Voltage : 1.4V Time of electrolysis : 1 hr Amount of benzaldehyde : 0.54 g Yield : 52% Current efficiency : 52 % Conversion : 60 % EXAMPLE. 6. Anode. : DSA(10cm2) Cathode : Stainless steel (10 cm2) Current Density : 50 mA/cm2 Electrolyte : NaBr(12.5g);H2O(50ml);CHCI3(25ml);HBr(5ml) Temperature : 30°C Amount of benzyl alcohol : 1 ml (1.05 g ) Charge passed : 5.5 F/mole Total current : 1.43 Ahr Current rate : 0.5 A Cell Voltage : 1.3 V Time of electrolysis : 2 hrs 52 mins Amount of Benzaldehyde : 1.01 g Yield : 98% Current efficiency : 36 % Conversion : 100% The Advantages of the present invention are 1. The present invention produces benzaldehyde as a major product with high yield (preferably 95-99%) at higher conversion of benzyl alcohol. 2. The present invention eliminates the effluent problem, which is the major drawback of the conventional processes due to the use of hydrochloric acid. Moreover, in this present invention there is no formation of benzoic acid compared to conventional processes. 3. The two phase system reported in the present invention works at a lower temperature and hence the formation of carbon dioxide is negligible which ultimately affect the yield and loss of solvent, thus the process is environmentally benign. 4. The present invention eliminates the usage of catalyst or promoter which is the major drawback in the conventional processes We Claim 1. An improved process for the electrochemical preparation of benzaldehyde from benzyl alcohol which comprises subjecting the benzyl alcohol to electrochemical oxidation in a two phase solvent system of aqueous and organic solvent containing alkali or alkaline earth metal bromide as electrolyte and catalytic amount mineral acid in an undivided electrochemical cell having an anode and a cathode, at a current density of 40-60 mA/cm2, at a temperature of 25-40°C, for a period of 1-3 hrs, followed by the separation of the desired product by known method. 2. An improved process as claimed in claim 1, wherein the anode used is platinum or DSA. 3. An improved process as claimed in claims 1&2, wherein the cathode used is selected from platinum and stainless steel. 4. An improved process as claimed in claims 1-3, wherein the organic solvent used in two-phase solvent system is selected from chloroform and acetonitrile. 5. An improved process as claimed in claims 1-4, wherein the alkali metal bromide used is selected from the group consisting of sodium bromide, potassium and calcium bromide. 6. An improved process as claimed in claims 1-5, wherein the mineral acid used is HBr. 7. An improved process as claimed in claims 1-6, wherein the oxidation is carried out at 30°C temperature. 8. An improved process as claimed in claims 1-7, wherein the yield of benzaldehyde obtained is in the range of 95-99%. 9. An improved process as claimed in claims 1-8, wherein the conversion of benzyl alcohol in oxidation is 100%. 10. An improved process for the electrochemical preparation of benzaldehyde from benzyl alcohol, substantially as herein described with reference to the examples.

Full Text

Field of the invention
The present invention relates to an improved process for the electrochemical preparation of benzaldehyde from benzyl alcohol. More particularly, the presemt invention relates to an improved process for the electrochemical preparation of benzaldehyde from benzyl alcohol in aqueous medium containing sodium bromide as an electrolyte with platinum both as anode and cathode in an undivided electrochemical cell.
Background of the invention
The Product benzaldehyde is widely used as an intermediate in the manufacture of dyestuff, flavoring chemicals (e.g. cinnamldehyde, amyl cinnamldehyde and benzyl benzoate), and perfumery chemicals, in acridine dyes, pharmaceuticals and fine chemicals. It can be also used as a corrosion inhibitor and a solvent for polyester resins.
Hitherto preparation of benzaldehyde by the hydrolysis of the corresponding side chain halogenated toluene compounds such as benzyl chloride at a temperature range of 100-200°C. at normal or higher pressures in the presence of an excess hydrochloric acid (U.S. Pat. No. 4,229,379). In U.S. Pat. No. 4,450,298 a process is described for the vapor phase catalytic hydrolysis of benzyl chloride to benzaldehyde using a catalyst comprising activated carbon treated with sulphuric acid or impregnated with a metal chloride such as iron (III) chloride or a metal sulphate such as cupric sulphate. A major disadvantage of these processes is the generation of large amount of effluent. The benzaldehyde produced by these routes does not meet food grade specifications.
Vapor phase or liquid phase oxidation of toluene by air is environmentally benign and provided the desired selectivities to the market driven products. World patent WO 95/20560 discloses a liquid phase process for the manufacture of benzaldehyde by the oxidation of toluene in presence of oxygen in a temperature and pressure range of 120 -200.°C. and 2-50 atm, respectively in the presence of a catalyst comprising cobalt or manganese as a metal ion and bromide as a promoter. 10% conversion of toluene and 45% selectivity to benzaldehyde is obtained. Borgaonkaret al, [ I & EC Prod. Res. Dev, 23(3), 459 (1984)] have reported lower (10%) conversion of toluene and 90% yield of

benzaldehyde by the use of cobalt acetate and either sodium bromide or paraldehyde as a promoter in presence of air.
A process for the vapor phase oxidation of toluene to benzaldehyde and benzoic acid using a catalyst containing a mixture of silver vanadate and lead vanadate or silver arsenate in presence of oxygen or ozone is described in U.S. Pat. No. 3,485,876. This catalyst system suppresses the formation of benzoic acid and degradation to carbon dioxide. According to U.S. Pat. No. 3,946,067, aromatic aldehydes such as benzaldehyde or substituted benzaldehydes were manufactured by the vapour-phase oxidation of aralkyl compounds, like toluene or substituted toluenes, in the presence of catalyst containing palladium metal and phosphoric acid at a temperature of less than 250 °C. The aromatic aldehydes are produced in a single reaction step. The drawbacks of the process are that the conversion of toluene has to be kept very low (70%). Also, the process is not suitable as large amounts of carbon dioxide are formed due to high temperature used in the reaction. U.S. Pat. No. 4,390,728 describes a process in which the oxides of various metals (viz. Cu, Fe, Pb, Mo, U, and P) with promoter were used for the production of benzaldehyde by the oxidation of toluene. At a temperature of 475-550 °C, a conversion of 35-50% and selectivity of 40-70% to benzaldehyde was obtained.
Another process for the production of benzaldehyde was reported by Ray et al. [Ind. J. Technol., 21(4), 137 (1983)] at a conversion of about 15% and selectivity of 70% with significant amount of C02 formation. Hence, the major disadvantages of the above processes are the use of high temperatures and lower conversion of toluene. The formation of large amount of carbon dioxide ultimately will affect the overall yield and is also not environmentally clean.
An electrochemical process using redox mediated system is described in Indian patent No.62426 for the oxidation of toluene to benzaldehyde. In this redox system the space time yield is low and the process is two stage processes for oxidation of toluene. These are the drawbacks in this electrochemical process and there is no electrochemical process on oxidation of benzyl alcohol to benzaldehyde with aqueous NaBr medium.

Wherein, because of the above drawbacks these processes are not promising for the production of benzaldehyde by toluene oxidation. The drawbacks are low yield and low selectivity and the reactions are conducted at very high pressure and temperature with hazardous raw materials in all the above-referred chemical method.
Radical bromination on a benzylic position has been achieved using bromine, and N-bromo succinimide. In addition, bromine complex of styrene vinyl pyridine copolymer and bromotrichloro ethane and copper(ll) bromide have been reported to be effective for benzylic bromination. Majority of brominating agents require the presence of peroxide or other radical initiator. Side chain bromination using sodium bromate and bromotrimethyl silane pair is also reported. But these methods are not suitable for commercialization due to poor yield. Moreover they had become the biggest obstacle to environmental safety. On the basis of the electrochemical technology, it is possible to carry out a desired electrochemical oxidation by a two-phase electrolysis resulting in high yield and high selectivity for benzaldehyde and substituted benzyl benzaldehydes.
Hence the invented process includes an improved process for the electrochemical preparation of benzaldehyde from benzyl alcohol in aqueous medium containing sodium bromide as an electrolyte with platinum as anode and cathode in an undivided electrochemical cell at a current density of 50 mA/cm2 and in room temperature with high yield (98%) and high conversion (100%). The depleted concentration of sodium bromide can be made up by adding required amount of additional salt in the aqueous phase and can be reused. There are also no wastewater problems. The wastewater consists solely of aqueous sodium bromide solution.
Objectives of the invention
The main objective of the present invention is to provide an improved process for the electrochemical preparation of benzaldehyde from benzyl alcohol in aqueous medium containing sodium bromide as a electrolyte with platinum as anode and cathode in an undivided electrochemical cell.
Yet another object of the present invention is to develop a process, which will be eco-friendly and avoids the effluent disposal problem.

Another object of this investigation is to explore a new electrolyte system consisting of metal bromides such as sodium, potassium, calcium or a combination of any of the above two metal salts preferably sodium bromide.
Yet another object of this invention is to use a very low concentration of NaBr solution (25%) to achieve high yield to benzaldehyde.
Yet another object of this invention is to reduce the formation of side products such as benzyl bromide and benzoic acid.
Yet another object of the invention is to eliminate the formation of carbon dioxide.
Yet another object of this invention is this process can be operated at room temperature and avoids high temperature.
Yet another object of this invention is the solvent used for the system is chloroform or acetonitrile or other solvents
Summary of the invention
Accordingly the present invention provides an improved process for the electrochemical preparation of benzaldehyde from benzyl alcohol which comprises subjecting the benzyl alcohol to electrochemical oxidation in a two phase solvent system of aqueous and organic solvent containing alkali or alkaline earth metal bromide as electrolyte and catalytic amount mineral acid in an undivided electrochemical cell having an anode and a cathode, at a current density of 40-60 mA/cm2, at a temperature of 25-40°C, for a period of 1-3 hrs, followed by the separation of the desired product by known method.
In an embodiment of the present invention the anode used is platinum or DSA.
In yet another embodiment the cathode used is selected from platinum and stainless steel.
In yet another embodiment the organic solvent used in two-phase solvent system is is selected from chloroform and acetonitrile.
In yet another embodiment the alkali metal bromide used is selected from the group consisting of sodium bromide, potassium and calcium bromide.
In yet another embodiment the mineral acid used is HBr.

In yet another embodiment the oxidation is carried out at 30°C temperature.
In yet another embodiment the yield of benzaldehyde obtained is in the range of 95-99%.
In yet another embodiment the conversion of benzyl alcohol in oxidation is 100%.
In yet another embodiment, the concentration of NaBr is in the range of 10-50%, preferably 20- 30%.
In yet another embodiment the amount of benzyl alcohol taken with respect to chloroform is in the range of 10-100 g/l preferably 25-50 g/l.
In another embodiment of the invention, the yield of benzaldehyde obtained in
the range of 95-99% without formation of benzoic acid and benzyl bromide as side
products.
In still another embodiment of the invention, the conversion of benzyl alcohol in the oxidation is in the range of 98-100%.
The present invention provides an improved process for the for the electrochemical preparation of benzaldehyde from benzyl alcohol in aqueous medium containing sodium bromide as a electrolyte with platinum as anode and cathode in an undivided electrochemical cell at a current density of 50 mA/cm2 and in room temperature with high yield (98%) and high conversion (100%).
Detail description of the invention
The process of the present invention comprises subjecting benzyl alcohol oxidation in two-phase system in an organic solvent and in the presence of aqueous NaBr system and a bromide source as a promoter. The reaction is carried out in the presence of aqueous and an organic solvent system (two-phase system) and at a temperature in the range of 25-50 °C. and at atmospheric pressure for a period of 4-6 F/mol. After the reaction is complete, the reaction mixture is separated by any conventional method such as distillation. The aqueous electrolyte system consists of metal selected from sodium, calcium and potassium or a combination of any of the above two metals, with bromide as a promoter. The percentage of aqueous NaBr used is in the range of 10-50% and preferably in the range of 20-30%. The ratio of benzyl

alcohol to chloroform is used in the range of 10-100 g/l and preferably in the range of 25-50 g/l.
After the reaction is complete, the reaction mixture phase was separated. The reactants and products were analyzed by GC and HPLC. The present invention produces benzaldehyde with high yield (preferably 95-99%) without other byproducts such as benzyl bromide and benzoic acid. The two-phase electrolysis system is necessary for obtaining high yield of benzaldehyde from benzyl alcohol. The single phase electrolysis allows very low selectivity to benzaldehyde.
The novelty of the process is the preparation of benzaldehyde from benzyl alcohol in aqueous medium at 30°C temperature by biphasic electrolysis and also used to syntheses of regioselective substituted benzaldehydes without formation of the benzyl bromide or benzoic acids. Moreover yields of benzaldehyde and substituted benzaldehydes are obtained about 90 to 99%. The reactive species formed by the electrolytic oxidation of the halide ion in an aqueous phase can be continuously taken into the organic layer and then reacts with the substrate giving regioselective products. The electrolysis can be performed in mild condition without any hazardous reagents at atmospheric pressure. Good mass transfer, high conversion and yield could be achieved in this electrochemical cell. The cell design is simple and cost effective.
The following examples are given by way of illustration of the working of the invention in actual practice and therefore should not be construed to limit the scope of the present invention.
EXAMPLE. 1.
Anode. : Platinum (10 cm2)
Cathode : Platinum (10 cm2)
Current Density : 50 mA/cm2
Electrolyte : NaBr(12.5g);H2O(50ml);CHCI3(25ml);HBr(5ml)
Temperature : 30°C

Amount of benzyl alcohol : 1 ml (1.05 g )
Charge passed : 5.5 F/mole
Total current : 1.43 Ahr
Current rate : 0.5 A
Cell Voltage : 1.3 V
Time of electrolysis : 2 hrs 52 mins
Amount of Benzaldehyde : 1.01 g
Yield : 98%
Current efficiency : 36 %
Conversion : 100 %
EXAMPLE. 2.
Anode. : Platinum (10 cm2)
Cathode : Platinum (10 cm2)
Current Density : 50 mA/cm2
Electrolyte :NaBr(12.5g);H2O(50ml);CHCI3(25ml);HBr(5 ml)
Temperature : 40°C
Amount of benzyl alcohol : 1ml (1.05 g)
Charge passed : 5.5 F/mole
Total current : 1.43 Ahr
Current rate : 0.5 A
Cell Voltage : 1.8 V
Time of electrolysis : 2hrs 52 mins
Amount of Benzaldehyde 0.76 g
Yield : 74%
Current efficiency : 36%
Conversion : 80%

EXAMPLE. 3.
Anode. .Platinum (10cm2)
Cathode : Platinum (10 cm2)
Current Density : 50 mA/cm2
Electrolyte : NaBr(12.5 g); H2O(50 ml);CHCI3(25ml) ;HBr(5ml)
Temperature : 30°C
Amount of benzyl alcohol : 5 ml ( 5.25g)
Charge passed : 5.5 F/mol
Total current : 7.15Ahr
Current rate : 0.5 A
Cell Voltage : 1.4 V
Time of electrolysis : 14 hrs 20mins
Amount of Benzaldehyde formed : 3.45 g
Yield : 67%
Current efficiency : 36 %
Conversion : 78 %
EXAMPLE. 4.
Anode. : Platinum (10 cm2)
Cathode : Platinum (10 cm2)
Current Density : 50 mA/cm2
Electrolyte :NaBr(12.5g);H2O(50ml);CH3CN(25ml);HBr(5 ml)
Temperature : 30°C
Amount of Toluene taken : 1ml(1.05g)
Charge passed : 5.5 F/mol
Total current : 1.43 Ahr
Current rate : 0.5 A
Cell Voltage : 1.4 V
Time of electrolysis : 2 hrs 52 mins
Amount of Benzaldehyde formed : 0.94 g

Yield : 91 %
Current efficiency : 36 %
Conversion : 100%
EXAMPLE. 5.
Anode. : Platinum (10 cm2)
Cathode : Platinum (10 cm2)
Current Density : 50 mA/cm2
Electrolyte :NaBr(12.5g); H2O(50 ml);CHCI3 (25 ml);HBr(5 ml)
Temperature : 30°C
Amount of Toluene taken : 1 ml (1.05 g)
Charge passed : 2 F/mol
Total current : 0.52 Ahr
Current rate : 0.52A
Cell Voltage : 1.4V
Time of electrolysis : 1 hr
Amount of benzaldehyde : 0.54 g
Yield : 52%
Current efficiency : 52 %
Conversion : 60 %
EXAMPLE. 6.
Anode. : DSA(10cm2)
Cathode : Stainless steel (10 cm2)
Current Density : 50 mA/cm2
Electrolyte : NaBr(12.5g);H2O(50ml);CHCI3(25ml);HBr(5ml)
Temperature : 30°C
Amount of benzyl alcohol : 1 ml (1.05 g )
Charge passed : 5.5 F/mole
Total current : 1.43 Ahr

Current rate : 0.5 A
Cell Voltage : 1.3 V
Time of electrolysis : 2 hrs 52 mins
Amount of Benzaldehyde : 1.01 g
Yield : 98%
Current efficiency : 36 %
Conversion : 100%
The Advantages of the present invention are
1. The present invention produces benzaldehyde as a major product with high yield (preferably 95-99%) at higher conversion of benzyl alcohol.
2. The present invention eliminates the effluent problem, which is the major drawback of the conventional processes due to the use of hydrochloric acid. Moreover, in this present invention there is no formation of benzoic acid compared to conventional processes.
3. The two phase system reported in the present invention works at a lower temperature and hence the formation of carbon dioxide is negligible which ultimately affect the yield and loss of solvent, thus the process is environmentally benign.
4. The present invention eliminates the usage of catalyst or promoter which is the major drawback in the conventional processes

We Claim
1. An improved process for the electrochemical preparation of benzaldehyde from benzyl alcohol which comprises subjecting the benzyl alcohol to electrochemical oxidation in a two phase solvent system of aqueous and organic solvent containing alkali or alkaline earth metal bromide as electrolyte and catalytic amount mineral acid in an undivided electrochemical cell having an anode and a cathode, at a current density of 40-60 mA/cm2, at a temperature of 25-40°C, for a period of 1-3 hrs, followed by the separation of the desired product by known method.
2. An improved process as claimed in claim 1, wherein the anode used is platinum or DSA.
3. An improved process as claimed in claims 1&2, wherein the cathode used is selected from platinum and stainless steel.
4. An improved process as claimed in claims 1-3, wherein the organic solvent used in
two-phase solvent system is selected from chloroform and acetonitrile.
5. An improved process as claimed in claims 1-4, wherein the alkali metal bromide
used is selected from the group consisting of sodium bromide, potassium and
calcium bromide.
6. An improved process as claimed in claims 1-5, wherein the mineral acid used is
HBr.
7. An improved process as claimed in claims 1-6, wherein the oxidation is carried out at 30°C temperature.
8. An improved process as claimed in claims 1-7, wherein the yield of benzaldehyde obtained is in the range of 95-99%.
9. An improved process as claimed in claims 1-8, wherein the conversion of benzyl alcohol in oxidation is 100%.
10. An improved process for the electrochemical preparation of benzaldehyde from benzyl alcohol, substantially as herein described with reference to the examples.

Documents:

http://ipindiaonline.gov.in/patentsearch/GrantedSearch/viewdoc.aspx?id=OlKt7CdNdIeu9ROPXpgOcQ==&loc=+mN2fYxnTC4l0fUd8W4CAA==

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Patent Number

271022

Indian Patent Application Number

601/DEL/2008

PG Journal Number

06/2016

Publication Date

05-Feb-2016

Grant Date

29-Jan-2016

Date of Filing

11-Mar-2008

Name of Patentee

COUNCIL OF SCIENTIFIC & INDUSTRIAL RESEARCH

Applicant Address

ANUSANDHAN BHAWAN, RAFI MARG, NEW DELHI-110 001,INDIA

Inventors:

#	Inventor's Name	Inventor's Address
1	MANICKAM ANBU KULANDAI NATHAN	CENTRAL ELECTROCHEMICAL RESEARCH INSTITUTE, KARAIKUDI-6, INDIA
2	THASAN RAJU	CENTRAL ELECTROCHEMICAL RESEARCH INSTITUTE, KARAIKUDI-6, INDIA
3	KUMARASAMY KULANGIAPPAR	CENTRAL ELECTROCHEMICAL RESEARCH INSTITUTE, KARAIKUDI-6, INDIA
4	ARUNACHALAM MUTHUKUMARAN	CENTRAL ELECTROCHEMICAL RESEARCH INSTITUTE, KARAIKUDI-6, INDIA

PCT International Classification Number

C25B 3/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA