DE1042588B - Process for the production of ª ‡, ª ‡ -dichloro-ªŠ-caprolactam - Google Patents

Description

Process for the preparation of aa-dichloro-e-caprolactam The invention relates to a process for the preparation of a, o, -dichloro-e-caprolactam of the formula It is known from the reports of the German Chemical Society, Vol. 63 B (1930), pp. 502 to 507, and from Chemical Abstracts, Vol. 24 (1930), Spafte 2999 , E-Caprolaetam with a chlorinating agent such as phosphorus pentachloride , to react in the presence of xylene and hydrolysileren the resulting chlorinated reaction product to a, a-dichloro-e-caprolaetatn. The yield is 30 to 40% of theory. It has now been found that much higher yields of a, a-dichloro-e-caprolactam are obtained if the process for the preparation of a, a-dichloro-e-caprolactam is carried out Treating e-caprolactam with phosphorus pentachloride and hydrolyzing the chlorinated reaction product, which carries out the chlorination in the presence of added phosphorus oxychloride.

The chlorination of e-caprolactam is known to take place with formation of phosphorus trichloride and phosphorus oxychloride as by-products. The phosphorus oxychloride formed According to the process, can be used as an additional reaction medium. used while treated the phosphorus trichloride with chlorine to convert it into phosphorus pentachloride can be used to chlorinate other e-CaprcKlactam # s.

Chlorination of e-Caprolaetam with phosphorus pentachloride in the presence of phosphorus oxychloride is carried out at a reaction temperature above 50 'C and preferably at 80 to 85'C. The rate of reaction varies with temperature; 1 to 5 hours is usually sufficient to bring the reaction to practical completion. On 1 mol of e-Caprolactain in manner known per se, preferably 3 moles of phosphorus pentachloride are used. However, an excess of the latter can also be used.

In order to prevent or suppress side reactions, it is advantageous to first mix e-caprolactam and phosphorus pentachloride and to add phosphorus oxychloride to these two reactants at a temperature below 35 ° C. and above this freezing point of the mixture and then the chlorination at above 50 'C to execute.

.After completion of the chlorination stage, the reaction mixture is in distilled in a manner known per se, preferably under reduced pressure, until all volatile products, including phosphorus oxychloride, phosphorus trichloride and hydrogen chloride, are away. The residue is then poured over ice or in dilute, aqueous alkali, z. B. sodium carbonate, hydrolyzed. a, a-Dichlo # r-e-caprolactam falls out of the aqueous Mixture of and is in the usual way by filtering from "-, separated and optionally, lls, z. B. by recrystallization from ligroin, purified.

The by-products of the chlorination stage, phosphorus trichloride and phosphorus oxychloride, can be obtained as a mixture during the distillation. This mixture can then be treated with chlorine gas to convert phosphorus trichloride to phosphorus pentachloride. The resulting mixture of phosphorus pentachloride and phosphorus oxychloride can be recycled for the chlorination of further e-caprolactams, but these two are preferably first separated by customary methods. In this way, an otherwise undesirable excess of phosphorus trichloride in the reaction vessel is avoided.

The following examples explain the process according to the invention.

Example 1 17 g (0.15 mol) of e-caprolactam, dissolved in 50 cc of phosphorus oxychloride, are added dropwise at such a rate to a solution of 94 g (0.45 mol) of phosphorus pentachloride in 150 cc of phosphoc> ro -, ychlo, given rid with stirring that a reaction temperature of 78 to 82'C is maintained. When the addition is complete, the mixture is refluxed (104 ° C.) for 15 minutes. The solvent and volatile by-products are removed by vacuum distillation and the liquid residue is added in portions to crushed ice. cr 0 'After the solution has warmed to room temperature, 18.3 g (67 % of theory) of a, c, -dichloro-a-eaprolaetam with a melting point of 123 to 126 ° C. are obtained by filtration. EXAMPLE 2 To 94 g of phosphorus pentachlaride (0.45 mol) 17 g (0.15 mol) of e-caprolaetam are slowly added in such a way that the temperature of the mixture is kept at 27 to 32 ° C. Then 60 cem phospharoxychloride are added and the temperature is kept at 70 ° C. for 1 hour. The reaction mixture is cooled and concentrated by vacuum distillation. The residue is hydrolyzed with crushed ice, the crystalline product is separated off by filtration, washed with water and dried. Yield 24 - (87.90 / G of theory) a, a-dichloro-e-caprolactam, F. 123 to 125 ' C.

Example 3 188 g (0.91 mol) of phosphorus pentachloride and 34 g (0.30 mol) of e-caprolactam are mixed at 10 to 15 ° C. 50 ceni of phosphorus oxychloride are added to the mixture at 15 to 70 ° C., and the reaction temperature is then held at 70 ° C. for 2 hours, with 49.7 g (91.1% of theory) of a, a-dichloro-e-caprolactam having a melting point 121 to 12311 C can be obtained.

Example 4 The distillate obtained according to Example 1 , which consists of a mixture of phosphorus trichloride and phosphorus, yr-chloride, is treated in a manner known per se with an equivalent amount of chlorine gas in order to convert the phosphorus trichloride into phosphorus pentachloride. An amount of e-caprolactam is added such that the molar ratio of lactam to phosphorus pentachloride in the mixture is 1: 3 and the mixture is refluxed for about 15 minutes. The reaction product is then placed under reduced pressure. concentrated, the oily residue hydrolyzed in ice water and then neutralized with sodium carbonate. Yield 670 / G of crude a, a-dichloro-e-caprolactam; F.119 to 122'C.

Claims (1)

PATIENT CLAIM: Process for the production of α, α-dichloro-e-caprolactam by treating e-caprolactam with phosphorus pentachloride and hydrolyzing the chlorinated reaction product, characterized in that the chlorination is carried out in the presence of added phosphorus oxychloride. Publications considered: Reports of the German Chemical Society, Vol. 63 (1930), pp. 502 to 507.