TECHNICAL FIELD

The present disclosure relates to a process of preparation of benzyl benzoate. The disclosure relates to conversion of benzaldehyde to benzyl benzoate with catalytic amount of sodium methoxide in tetrahydrofuran in good yield, which is apparently unprecedented for this product of high commercial value.

BACKGROUND

Benzyl benzoate, is of importance in the dye and perfumery industries. There are several previous reports of the Tishchenko approach to benzyl benzoate. However, these invariably involve expensive and/or toxic catalysts or stoichiometric reagents. For instance, a recent report employs as catalyst a lanlhanide formamidinate in a solvent-free process. Benzyl benzoate has been traditionally prepared by: (i) transesterification between methyl benzoate and benzyl alcohol; (ii) reaction between sodium benzoate and benzyl chloride; (iii) Tishchenko reaction between benzaldehyde and benzyl alcoholate.

The direct conversion of benzaldehyde to benzyl benzoate continues to receive much attention. The present disclosure provides a process for the preparation of benzyl benzoate in a cost effective manner.

SUMMARY OF THE DISCLOSURE

Accordingly the present disclosure provides a process for the preparation of benzyl benzoate; said process comprising acts of mixing benzaldehyde and a solution of alkali metal salt of an alcohol to form slurry, and treating the slurry with water to obtain the benzyl benzoate.

DETAILED DESCRIPTION

The present disclosure is in relation to a process for preparation of esters, said process comprising steps of

a) mixing benzaldehyde and a solution of alkali metal salt of an alcohol to form slurry, and

b) treating the slurry with water to obtain the benzyl benzoate.

In another embodiment of the disclosure, the alkali metal is selected from a group comprising sodium and potassium, preferably sodium.

In still another embodiment of the present disclosure, the alcohol is selected from a group comprising methanol and benzyl alcohol, preferably methanol.

In yet another embodiment of the present disclosure, concentration of the benzaldehyde is in range of about 1% to about 10% w/v, preferably 3.5% w/v and of the alkali metal salt of alcohol is in the range of about 1mol % to about 20mol%, preferably 10mol% of
benzaldehyde.

In yet another embodiment of the present disclosure, the solution of alkali metal salt of alcohol is in a solvent selected from a group comprising tetrahydrofuran, dimethyl sulphoxide, carbon tetrachloride, dichloromethane and toluene, preferably
tetrahydrofuran.

In yet another embodiment of the present disclosure, the slurry is obtained by stirring the benzaldehyde and the alkali metal salt of alcohol.

In yet another embodiment of the present disclosure, the stirring is carried out at a temperature ranging from about 20oC to about 30oC, preferably at about 25oC.

In yet another embodiment of the present disclosure, wherein the stirring is carried out for a period ranging from about 12h to about 20h, preferably for about 16h.

In yet another embodiment of the present disclosure, the benzyl benzoate is extracted from step (b) comprising acts of

a) dissolving the benzyl benzoate in a solvent to form a solution of benzyl benzoate,

b) drying the solution of benzyl benzoate, and

c) removing the solvent from solution of benzyl benzoate to extract the benzyl benzoate.

In yet another embodiment of the present disclosure, the solvent is selected from a group comprising ethyl acetate, trichloromethane and diethyl ether, preferably ethyl acetate.

In yet another embodiment of the present disclosure, the drying is carried out using a drying agent selected from a group comprising sodium sulphate, magnesium sulphate, calcium sulphate and calcium chloride, preferably sodium sulphate.

In yet another embodiment of the present disclosure, the drying agent is in its anhydrous form.

In yet another embodiment of the present disclosure, the removal of the solvent is carried out by method selected from a group comprising distillation and evaporation, preferably distillation.

Benzyl benzoate has been prepared by treating benzaldehyde with a catalytic quantity of sodium methoxide in THF at room temperature. The yields are excellent (~ 70%) and the overall procedure simple and straightforward. The reaction apparently proceeds via the intermediacy of methyl benzoate and benzyl alcoholate, the direct products of the Tishchenko reaction. These then react to produce benzyl benzoate and sodium methoxide, the latter thus acting as a catalyst.

The present method is an outgrowth of a mechanism-based approach to the Cannizzaro and Tishchenko reactions. Essentially, as these are termolecular processes involving two molecules of aldehyde and one of base in the rate determining step, concentration effects on the rate would be critical. Thus, for instance, a doubling of the concentrations would have an eight-fold effect on the rate. This means that a reaction occurring over a period of (say) 16 hours under the present conditions, would need over 5 days under the previous conditions. The process is also characterized by environmental compatibility, as the reagents/solvents employed are of relatively low toxicity.

Scheme 1. Mechanism of the reaction of benzaldehyde with catalytic sodium methoxide in THF at 25° C.

The mechanism of the process is depicted in Scheme 1 above. Thus, benzaldehyde (1) reacts with methoxide ion (step a) to form the tetrahedral intermediate 2, which reacts with another molecule of I in a hydride-transfer process (step b) depicted in I. The immediate products of this redox process are methyl benzoate (3) and benzyl alcoholate anion (4) which react further (step c) to produce benzyl benzoate (5) and methoxide ion. The regenerated methoxide ion is then recycled catalytically to step a.

The yield of benzyl benzoate is much lower if benzyl alcoholate anion is employed (Table 1), possibly a steric effect of the bulkier benzyl alcoholate anion. The reaction also essentially failed with substituted benzaldehydes (Table 1, items 3-5).
Table 1: Products formed in the reaction with different aromatic aldehydes (1) in THF at 25 ºC under various conditions.

An example of the preparation of benzyl benzoate is given below for understanding; however, it should not be construed as limiting the scope of the disclosure to the said example.

Example 1: Benzaldehyde (1.0 mmol) is added to a solution of NaOMe (0.1 mmol) in dry THF (3.0 mi) and the mixture stirred at 25 ºC for 16 h. The thick slurry is treated with water (1 ml) and the resulting mixture extracted with ethyl acetate (5 ml); the extracts are dried (Na2S04) and the solvent distilled off in vacuo to obtain the crude benzyl benzoate product. This is purified by column chromatography (Si02), and identified spectrally. Yield: 60-80%.

Spectroscopic characterization of benzyl benzoate- IR: Vmax 1718 cm"' (C=0); 'H NMR (300 MHz in CDCI3): H (relative to internal tetramethylsilane) 8.09-8.06 (m, 2H, ArH), 7.58-7.53 (m, 2H, ArH), 7.46-7.31 (m, 6H, ArH). 5.36 (s, 2H, OCH2).

While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.

WE CLAIM

1. A process for preparation of benzyl benzoate comprising acts of

a) mixing benzaldehyde and a solution of alkali metal salt of an alcohol to form a slurry, and

b) treating the slurry with water to obtain the benzyl benzoate.

2. The process as claimed in claim 1, wherein the alkali metal is selected from a group comprising sodium and potassium, preferably sodium,

3. The process as claimed in claim 1, wherein the alcohol is selected from a group comprising methanol and benzyl alcohol, preferably methanol.

4. The process as claimed in claim 2, wherein concentration of the benzaldehyde is in range of about 1% to about 10% w/v, preferably 3.5% w/v and of the alkali metal salt of alcohol is in the range of about 1mol % to about 20mol%, preferably I0mol% of benzaldehyde.

5. The process as claimed in claim 1, wherein the solution of alkali metal salt of alcohol is in a solvent selected from a group comprising tetrahydrofuran, dimethyl sulphoxide, carbon tetrachloride, dichloromethane and toluene, preferably tetrahydrofuran.

6. The process as claimed in claim 1, wherein the slurry is obtained by stirring the benzaldehyde and the alkali metal salt of alcohol.

7. The process as claimed in claim 6, wherein the stirring is carried out at a temperature ranging from about 20oC to about 30°C, preferably at about 25oC

8. The process as claimed in claim 6, wherein the stirring is carried out for a period ranging from about 12h to about 20h, preferably for about 16h.

9. The process as claimed in claim 1, wherein the benzyl benzoate is extracted from step (b) comprising acts of

a) dissolving the benzyl benzoate in a solvent to form a solution of benzyl benzoate,

b) drying the solution of benzyl benzoate, and

c) removing the solvent from solution of benzyl benzoate to extract the benzyl benzoate.

10. The process as claimed in claim 9, wherein the solvent is selected from a group comprising ethyl acetate, trichloromethane and diethyl ether, preferably ethyl acetate.

11. The process as claimed in claim 9, wherein the drying is carried out using a drying agent selected from a group comprising sodium sulphate, magnesium
sulphate, calcium sulphate and calcium chloride, preferably sodium sulphate.

12. The process as claimed in claim 11, wherein the drying agent is in its anhydrous form.

13. The process as claimed in claim 9, wherein the removal of the solvent is carried out by method selected from a group comprising distillation and evaporation, preferably distillation.