Title of Invention

AN IMPROVED PROCESS FOR THE PREPARATION OF BENZALDEHYDE

Abstract

This invention relates to an improved process for the preparation of benzaldehyde. In the process, benzaldehyde is prepared by oxidizing toluene using electrochemically generated cerium (IV) methanesulphonate in methanesulphonic acid as oxidizing agent at a temperature of 75-80°Cfor a period of 10 to 25 minutes with vigorous stirring to obtained a solution and recovering the benzaldehyde by extraction with an organic solvent 1,2-dichloromethane.

Full Text

of benzalchloride with concentrated sulphuric acid has the disadvantage of forming large amount of dilute sulphuric acid as a waste product (Nippon Kayaka Company JP.KOKAI. 7589337, 1973 (T.Ishikura)). Partial oxidation of toluene can be carried out either in gas phase or in liquid phase with oxygen. In this process, benzaldehyde is easily further oxidised to different products in addition to benzoic acid and carbon monoxide. Conditions must therefore be carefully chosen to favor only partial oxidation. In the gas phase oxidation of toluene, a catalyst bed in a tube bundle or fluidised bed reactor with oxygen in a gaseous mixture such as air is used at a temperature of 250 - 260 °C. The reaction is exothermic, hence effective cooling is necessary. Only 40-60 % of the theoretical yield was obtained based on the toluene used. The oxidation of toluene in the gas phase produces maleicanhydride in addition to substantial quantities of benzoic acid, carbon monoxide and carbon dioxide. In liquid phase oxidation, the reaction was conducted at a range of 80 -250 °C using cobalt, manganese, iron or chromium compounds (alone or combination) as catalyst. A pressure at which reaction medium remains liquid is chosen along with oxidation promoters. When a cobalt catalyst is used conversion rates of upto 25% are obtained with 40 - 50 % aldehyde selectivity. There are some electrochemical processes for the production of benzaldehyde from toluene by anodic oxidation [(M.Kagami and K.Kushibe Japan.Pat.73 28, 442 (1973), M.A.Halter and T.P.Malloy, US-Pat.4,212, 711 (1980), J.P.Milingion and I.M.Dalrymple, Brit.Pat.2,140,034 (1986) ]. The selectivity of the product in the earlier electrochemical process does not exceed 75 % in dry methonal or ethonal containing expensive NaBF4, NaClO4 or Et4NBF4 as a supporting electrolyte. The electrochemical process using eerie sulphate in H2SO4 has also been carried out. But eerie sulphate has the drawback of marginal solubility in H2SO4. The invented mediated process is an improved process giving an yield of 85-90% benzaldehyde using Cerium (IV) methanesulphonate. The main objective of this invention is to develop a method for the preparation of benzaldehyde in good yield using electrochemically generated cerium (IV) methanesulphonate in an undivided electrochemical cell. Another object is to provide a process for preparation of benzaldihyde with 90% yield with 99% purity. In the present invention, this system was extended to prepare benzaldehyde in a batch reactor at a temperature of 75 - 80 °C with vigorous stirring. The main advantage of this process is that the oxidant Cerium (IV) methanesulphonate can be regenerated in good current efficiency and hence the process is very economical. Also, the organic oxidations are fast under conditions where the cerium salts are soluble and the organic products are immiscibile with the aqueous solutions making for facile product separation. Accordingly/^improved process for the prepration of benzaldehyde which £ oxidising toluene using electrochemically generated cerium (IV) methanesulphonate as an oxidising agent at a temperature ranging between 75 - 90 °C for a period in an undivided electrochemical cell at an anode current density ranging between 10 to 30 A / dm2 using DSA / C>2 type anode and stainless steel cathode ranging between 10 to 25 minutes with vigorous stirring to obtain a solution and recovering the benzaldehyde by extraction method. The present invention provides an improved process for the prepration of benzaldehyde oxidising toluene using electrochemically generated cerium (IV) methanesulphonate as an oxidising agent at a temperature of 75 - 80 °C for a period of 10 to 25 minutes with vigorous stirring to obtain a solution and recovering the benzaldehyde by extraction with an organic solvent 1,2 -dichloromethane. The following examples are given by way of illustration of the present invention and should not be construed to limit the scope of the invention. Example 1: Electrochemical oxidation step Cell type Anode Cathode Electrolyte Concentration of free methanesulfonic acid Current passed Current density Temperature Cell voltage Duration Current efficiency Conversion undivided DSA-O2(0.48dm2) Stainless Steel (0.06 dm2) Cerium (III) methanesulphonate 0.6 molar (2 lit) 6 molar lOA/hr 20 A/dm2 50° C 3.4V 7.65 hrs 35% 83% Chemical oxidation step (under Nitrogen atmosphere) Concentration of Ce(IV) methanesulphonate Concentration of free methanesulphonic acid Toluene taken Temperature Duration Yield of benzaldehyde Purity of the product 0.5 molar (2 lit) 6 molar 0.178 moles (16.4 g) 80° C lOmin. 90%(17g) 98.6 % (by HPLC) Example 2: Electrochemical oxidation step Cell type Anode Cathode Anolyte 0.6 molar (2.0 lit) Catholyte Cell voltage Current passed Current density Temperature Duration Current efficiency Conversion Divided DSA-O2(ldm2) Stainless Steel (1 dm2) Cerium (III) methanesulphonate methanesulphonic acid 6.0 molar(2.0 lit) 3.8V lOA/hr 10 A/dm2 50° C 7.05 hrs 38% 83% 6 Chemical oxidation step (without nitrogen atmosphere) Concentration of Ce(IV) methanesulphonate Concentration of free methanesulfonic acid Toluene taken Temperature Duration Yield of benzaldehyde Purity of the product 0.5 molar (2 lit) 6.0 molar 0.178 moles (16.4 g) 80° C 10 min 69%(13g) 98% (by HPLC) Example 3 Electrochemical oxidation step Cell type Anode Cathode Electrolyte Concentration of free methanesulfonic acid Undivided DSA-O2(0.48dm2) Stainless Steel (0.06 dm2) Cerium (III) methanesulphonate 0.6 molar (2.0 lit) 6.0 molar Cell voltage Current passed 3.8V lOA/hr Current density : 20 A/dm2 Temperature : 50° C Duration : 7.65 hrs Current efficiency : 35 % Conversion : 83 % Chemical oxidation step (under nitrogen atmosphere) Concentration of Ce(IV) methanesulphonate : 0.5 molar (2 lit) Concentration of free 6.0 molar 0.25 moles (23 g) 80° C 25 min. 49%(13g) 98% (by HPLC) methanesulfonic acid Toluene taken Temperature Duration Yield of benzaldehyde Purity of the product The main advantages of the present invention are 1. The conversion of the toluene is high. The formation of benzaldehyde is in higher yield in comparison with chemical methods. 2. There is no bye-product formation in comparison with chemical methods. 3. No spent reagent disposal. Hence this process is eco-friendly. 4. As this electrochemical oxidation of cerium (III) to cerium (IV) can be carried out in an undivided cell with high current efficiency, the improved process leads to simplification of cell design and hence economical. 5. This process is competitive with all known commercial routes. We Claim: 1. An improved process for the preparation of benzladehyde which comprises oxidizing toluene using electrochemically generated cerium (IV) methanesulphonate as an oxidizing agent at a temperature ranging between 75-90°C for a period in of 10 to 25 minutes in an undivided electrochemical cell at an anode current density ranging between 10 to 30 A / dm2 using DSA / 02 type anode and stainless steel cathode with vigorous stirring to obtain a solution and recovering the bezaldehyde by extraction method. 2. An improved process as claimed in claims 1 wherein the mole ratio of toluene to cerium (IV) methanesulphonate is 1:3 to 1:6 for the chemical oxidation step. 3. An improved process as claimed in claims 1 to 2 wherein the solvent used for extraction of benzaldehyde is selected from chloroform, 1,2-dichloromethane. 4. An improved process as claimed in claims 1 to 3 wherein the maximum yield of benzaldehyde was obtained using the oxidizing agent having a concentration of 6.0 molar free methanesulphonic acid. 5. An improved process as claimed in claims 1 to 4 where the chemical oxidation is carried out at 80°C. 6. An improved process as claimed in claims 1 to 5 wherein the duration of oxidation is 10 minutes gives 90% yield of benzaldehyde. 7. An improved process as claimed in claims 1-7 wherein the purity of benzaldehyde is 99%. 8. An improved process for preparation of benzaldehyde substantially as herein described with reference to the examples.

Documents:

296-DEL-2002-Abstract-(05-03-2008).pdf

296-del-2002-abstract.pdf

296-DEL-2002-Claims-(05-03-2008).pdf

296-del-2002-claims.pdf

296-DEL-2002-Correspondence-Others-(05-03-2008).pdf

296-del-2002-correspondence-others.pdf

296-del-2002-description (complete)-05-03-2008.pdf

296-del-2002-description (complete).pdf

296-DEL-2002-Form-1-(05-03-2008).pdf

296-del-2002-form-1.pdf

296-del-2002-form-18.pdf

296-del-2002-form-2.pdf

296-DEL-2002-Form-3-(05-03-2008).pdf

296-del-2002-form-3.pdf