CS270369B1 - Process for the production of benzyl acetate by the benzylation of alkaline ethanes - Google Patents

Abstract

Benzyl acetate is used in perfumery. It is prepared either by esterification or alkylation of alkali acetates. The process consists in the reaction of sodium or potassium acetate and benzyl chloride in a medium of acetic acid, from which water has been removed by the action of acetic hydride. A solution of 1.0 to 1.2 mol of sodium or potassium acetate in acetic acid is freed from all the water present by heating and the corresponding amount of acetic hydride. The reaction with 1 mol of benzyl chloride takes place under boiling conditions. The advantages of the process are high yields, 85 to 96% of theory; practically no by-products and the possibility of industrial use.

Description

The invention relates to a method for producing benzyl acetate from sodium or potassium acetate by reacting them with benzyl chloride in an anhydrous acetic acid environment.

To obtain benzyl acetate, the alkylation of sodium or potassium acetate with benzyl halides is an alternative method of its preparation by etherification, which starts from benzyl alcohol and suitable derivatives of acetic acid. According to literature data, the alkylation preparation can be carried out in a two-phase system under catalysis by two-phase catalysts, quaternary ammonium salts, or their precursors - tertiary amines. Methods for the preparation of benzyl acetate in an anhydrous environment without these catalysts and in a single phase have also been described. For example, in the reaction of potassium acetate with benzyl chloride in polyethylene glycol 400 at a temperature of 110 °C, benzyl acetate is allegedly obtained in a yield of 80% of theory (F. Theil et al., 3rd edition, Chem. 327, 350-362 (1985)). The literature also describes a method for preparing benzyl acetate in protonic solvents such as acetone, methanol or formic acid in the presence of zinc acetate (K.N. Gurundut et al. Tetrahedron 38, 1843-1846 (1982)).

An industrially suitable method has now been found for the preparation of benzyl acetate from sodium or potassium acetate and benzyl chloride in an acetic acid environment, from which water has been removed by the action of acetic anhydride.

The method of producing benzyl acetate from benzyl chloride and alkali acetate in acetic acid according to the present invention consists in that a solution of 1.0 to 1.2 mol of sodium or potassium acetate in acetic acid is freed from all present water by treating with an appropriate amount of acetic anhydride and reacting with 1 mol of benzyl chloride by boiling the anhydrous reaction mixture.

Dissolving technical anhydrous sodium and potassium acetates in glacial acetic acid is also slightly exothermic. Preparation of sodium or potassium acetate by partial neutralization of the acetic acid with solid sodium or potassium hydroxide is also technically feasible. In order to avoid possible inconveniences with strongly exothermic hydrolytic decomposition of acetic anhydride by water present in the reaction mixture, it is preferable to add it at a reaction temperature of 115 to 120 °C, which is maintained at a suitable rate of acetic anhydride addition. Benzyl chloride can be added to the reaction mixture all at once; preferably at a temperature of 90 to 110 °C, so that it does not precipitate the dissolved alkali metal acetate by cooling it deeply.

Alkylation of alkali metal acetate is manifested by the formation of soluble alkali metal chloride. The course of the benzylation reaction can be followed exactly by liquid chromatography. The fact that at the same heat input and during the reaction mixture, the achievable temperature value in the reaction mixture decreases according to the degree of reaction of alkali metal acetate to a steady value; which is 8 to 10 °C lower; than the temperature of the boiling reaction mixture at the beginning of the reaction with benzyl chloride. The reaction time is 4 to 8 hours.

The isolation of the product can be advantageously carried out by vacuum deethylation of the solvent, which is acetic acid, which passes into the precursor along with any unreacted benzyl chloride and can be used directly for the subsequent batch.

Sodium or potassium chloride, suspended in the crude product after the distillation of acetic acid, is taken up in the required amount of water and the resulting aqueous solution forms the lower layer. The product is then washed with water or vacuum-distilled. The large front fraction is added to the next batch.

If it should prove necessary to remove the benzyl chloride atoms radically, it is possible to add a small amount of a tertiary amine, for example triethylamine, after concentrating the reaction mixture in vacuo; briefly heat the product to 80 to 100°C and then wash with water. The benzyl chloride bound in the quaternary amine compound is dissolved together with the alkali chloride.

CS 270 369 Bl

If the starting benzyl chloride contains higher chlorinated impurities, for example benzene chloride, it is advisable to briefly heat the crude product with a catalytic amount of Roney nickel before distillation and directly deethylate it without filtration.

By the process according to the invention, benzyl acetate with a content of over 99% of the substance itself is obtained from high-quality raw materials in a yield of 85 to 95% of theory and is usable for perfumery purposes.

Example 1

To the 200 g of glacial acetic acid ee, 112.9 g of technically anhydrous potassium acetate (moisture content 4.5%), which corresponds to 1.1 mol of potassium acetate, are added with stirring from a sealed container. The reaction mixture is heated to boiling for 30 min. and without achieving complete dissolution; 28.7 g of acetic anhydride, i.e. an amount corresponding to the moisture in the potassium acetate, are added dropwise at a temperature of 115 to 125 °C. After 30 min. of heating to boiling, 126.5 g (1 mol) of benzyl chloride are added all at once at a temperature of 90 to 110 °C. The reaction mixture is kept at boiling for 6 hours and then the solvent is distilled off in vacuo. 200 to 220 g of acetic acid are collected. To the remaining suspension, at a temperature below 60 °C, about 400 ml of water is added; the solid phase ee dissolves while stirring, ^the free solution is drained from the bottom and the product is washed again with 200 ml of water. Distillation in vacuum yields 134.6 g of a substance with a melting point of 116 to 118 °C/1.56 kPa and a content of 99.7% benzyl acetate; which corresponds to a yield of 89% of theory.

Example 2'

To the 200 g of glacial acetic acid, 92.1 g of technical anhydrous sodium acetate containing 2% moisture (1.1 mol of sodium acetate) are added with stirring. The moisture is removed similarly to example 1 by adding acetic anhydride, in this case in an amount of 10.4 g. The reaction with benzyl chloride and further processing are identical to the procedure according to example 1. When the reaction mixture is concentrated, 190 to 200 g of anhydrous acetic acid are obtained. Distillation of the crude product yields 138 g of a substance containing 99.6% benzyl acetate (92% of theory).

Example 3

To the 137 g of glacial acetic acid presented, a total of 48 g (1.2 mol) of solid flaky sodium hydroxide is added from a sealable container in two or more portions, which dissolves with the evolution of heat. At a temperature of 115 to 125 °C, 122.4 g (1.2 mol) of acetic anhydride is then added dropwise at such a rate; that the prescribed temperature is maintained spontaneously. After 30 minutes of heating to 120 °C, 126.6 g (1 mol) of benzyl chloride is added to the reaction mixture at a temperature of 90 to 110 °C. The reaction is completed by boiling for 6 hours. The product is obtained according to the procedure of Example 1, with a yield of 131.6 g of 88% benzyl acetate with a purity of 99.7%. The acetic acid distillate is approximately 200 g.

Claims (1)

A method for producing benzyl acetate by benzylation of alkali acetates, characterized in that 1.0 to 1.2 mol of sodium or potassium acetate are dissolved in acetic acid with the addition of acetic anhydride in an amount corresponding to the moisture content of the reactants and are reacted with 1 mol of benzyl chloride while boiling the reaction mixture.