CS245334B1 - A method of inhibiting the polymerization of the reaction mixture in the manufacture of methyl methacrylate - Google Patents

Abstract

The solution relates to a method of inhibiting the polymerization of the reaction mixture in the production of methyl methacrylate from acetone cyanohydrin and sulfuric acid and subsequent esterification with methanol. As an inhibitor, either to the amidation or to the esterification or to both stages, 0.005 to 0.5, preferably 0.05% by weight of a substance selected from the group comprising N-isopropyl-N'-diphenyl-p-phenylenediamine, 4-aminodiphenylamine and distillation residues obtained by distilling off 4-aminodiphenylamine from the reaction mixture obtained by the reaction of 4-aminodiphenylamine with acetone and hydrogen is added to the input acetone cyanohydrin. This method of inhibition reduces the content of organic impurities in the crude product by 40%. At the same time, the quality of the waste sulfate liquors is improved. and waste from the production of the antioxidant CD is utilized.

Description

The present invention relates to a method for inhibiting the polymerization of a reaction mixture in the production of methyl methacrylate from acetone cyanohydrin and sulfuric acid and subsequent esterification with methanol. As an inhibitor, 0.005 to 0.5, preferably 0.05% by weight, of acetone cyanohydrin is added to the starting acetone cyanohydrin, either in the amidation or in the esterification or in both steps. a compound selected from the group consisting of N-isopropyl-N‘-diphenyl-p-phenylenediamine, 4-aminodiphenylamine and distillation residues obtained by distilling off 4-aminodiphenylamine from the reaction mixture obtained by reacting 4-aminodiphenylamine with acetone and hydrogen. This method of inhibition reduces the content of organic impurities in the crude product by 40%. At the same time, the quality of the waste sulfate liquors is improved. and utilize wastes from the production of CD antioxidant.

SUMMARY OF THE INVENTION The present invention provides a process for inhibiting the polymerization of a reaction mixture in the production of methyl methacrylate by reacting acetone cyanohydrin with sulfuric acid and methanol.

In the synthesis of methyl methacrylate from acetone cyanohydrin and sulfuric acid, the sulfuric acid amide is formed in the first step by dehydration with sulfuric acid according to equation (1) (H * CN f Η 0Π ² 135 ° C)

C n.

(D from which, in the next step, an intermediate methacrylic acid is formed by hydrolysis in aqueous medium and subsequent esterification with methanol to give methyl methacrylate according to equation (2)

CH2-C ~ CH 3 COOH + CH ₃

CH2 = C—

CH3 low concentration about 2 times higher efficiency. This is increased by the synergistic action of the by-products present in the distillation residues from the synthesis of the industrially produced antioxidant CD, i.e., N-isopropyl-N‘-diphenyl-p-phenylenediamine —COOCH3 + H2O.

Substances produced in both stages are susceptible to polymerization and therefore need to be inhibited. In practice, a variety of inorganic and organic inhibitors or combinations thereof are used as inhibitors to inhibit. These include, for example, inorganic ones that are predominantly used to inhibit the amidation of the Cu ⁺⁺ salt, the CnCl 2 salt, or the MnCl 2 '.

Organic inhibitors include pyrocatechin, hydroquinone, phenothiazine, tannin, phenol distillation residues, fulven, methylene blue, thiourea, N, N,-dinaphthyl-p-phenylenediamine, β-naphthol, phenylhydrazine, O-aminophenol and the like. They are used largely in an amount that adversely affects either by contaminating the resulting product by distillation (e.g. phenothiazine), either remaining in the waste sulphate liquors. The ammonium sulphate crystal obtained from these liquors is contaminated with these inhibitors and, in addition, the crystallization apparatuses, in particular the evaporator tubes, are clogged.

According to the process of the invention, inhibition of the polymerization of the reaction mixture in the production of methyl methacrylate by reaction of acetone cyanohydrin with sulfuric acid and methanol is carried out by adding 0.005 to 0.5, preferably 0.05%, to the acetone cyanohydrin amidation and / or esterification of the amidation mixture. wt. a compound selected from the group consisting of N-isopropyl-N‘-diphenyl-p-phenylenediamine, 4-aminodiphenylamine and distillation residues obtained by distilling 4-aminodiphenylamine from the reaction mixture obtained by reacting 4-aminodiphenylamine with acetone and hydrogen.

The advantage of this inhibition process compared to the prior art is in addition to the above-mentioned <O> ^-N v

Hfl- CH

Cl-H / 3

CD,

These residues are otherwise undesirable waste and are disposed of by incineration.

The crude ester produced with the inhibitor according to the invention has, for example, a 40% lower content of chromatographically determined by-products than conventional phenothiazine.

The content of organic impurities in the solution of acidic sulphate liquors resulting from esterification decreases by an average of 15% when used with the inhibitors according to the invention, compared to that with phenothiazine, and a solids content of polymers of 50%. Also, the quality of the ammonium sulfate crystal obtained from these lyes by neutralization with ammonia is improved by a nitrogen content of from 20.7% to 21.2%.

Example 1

To the amidation mixture continuously prepared from 95 wt. parts by weight of acetone cyanohydrin and 165 wt. 0.05 parts by weight of sulfuric acid are added at 80 ° C. Works of distillation residues from the production of 4-aminodiphenylamine as an intermediate in the production of CD antioxidant. The mixture was heated to 135 ° C for 30 min. After subsequent esterification of 60 wt. parts of methanol and 66 wt. 100 g of crude methyl methacrylate with 3.62 wt. % of organic impurities. In the same experiment with phenothiazine, the impurity content in the crude ester is even 5.92 wt. %. Example 2

The amidation mixture was prepared with 490 wt.

parts of acetone cyanohydrin and 442 wt. parts of sulfuric acid and after reaction at 135 ° C, esterification with 300 wt. parts of methanol and 310 wt. parts of water to which the distillation residues from the production of 4-aminodiphenylamine as a solution in the crude ester in an amount of 0.05 wt. percent on acetone cyanohydrin feed. 500 wt. parts of the crude ester containing 3.2 wt. % organic impurities. Example 3

The amidation mixture was prepared according to Example 1 and 0.1 wt. parts of N-isopropyl-N‘-diphenyl-p-phenylenediamine. This gives a crude ester containing 3.15 wt. % organic impurities. The content of organic impurities in acidic sulphate liquors after esterification decreased by 15% compared to the phenothiazine inhibited assay, i.e. to 3.05 wt. %. The polymer content decreases by 50% to 0.52 wt. %.

Example 4

The amidation mixture was prepared according to Example 1 as well as the esterification to which 0.2 wt. parts of 4-aminodiphenylamine. This gives a crude ester containing 3.7 wt. percent organic impurities.

Claims (1)

A process for inhibiting the polymerization of a reaction mixture in the production of methyl methacrylate by reacting acetone cyanohydrin with sulfuric acid and methanol by means of p-phenylenediamine-based compounds, characterized in that 0.005 to 0.006 to 0.005 to 0.005 to 0.005 to 0.005 to 0.005 to 0.005 to 0.005 to 0.005 to 60% acetone cyanhyrin are added. %, Preferably 0.05 wt. a compound selected from the group consisting of N-isopropyl-N‘-diphenyl-p-phenylenediamine, 4-aminodiphenylamine and distillation residues obtained by distilling 4-aminodiphenylamine from the reaction mixture obtained by reacting 4-aminodiphenylamine with acetone and hydrogen.