IMPROVED PROCESS FOR PREPARING UNSYMMETRICAL DIALKYL SULFIDES

Abstract

The invention relates to an improved process for preparing unsymmetrical dialkyl sulfides by reacting a monoalkyl sulfide with at least one alkyl halide in the presence of base.

Claims

1. A process for preparing unsymmetrical dialkyl sulfides of the formula (I),
R.sup.1—S—R.sup.2   (I), comprising the reaction of an alkyl sulfide of the formula (II),
H—S—R.sup.2   (II), with an alkyl halide of the formula (III),
R.sup.1—X   (III), wherein in the formulae (I), (II) and/or (III) R.sup.1 is a C.sub.1—C.sub.3-alkyl radical, R.sup.2 is a C.sub.4—O.sub.12 alkyl radical, X is halogen, at least in the presence of a base, wherein a reaction mixture is formed, and the temperature of the reaction mixture during the reaction is in a range from 15 to 100° C..

2. The process as claimed in claim 1, wherein the reaction is carried out in the presence of water and a phase transfer catalyst comprising a quaternary ammonium salt of the formula (IV),
R.sup.3R.sup.4.sub.3N.sup.+Y.sup.−  (IV), in which R.sup.3 is hydrogen or methyl, R.sup.4 is a C.sub.4—C.sub.12 alkyl radical, X is halogen.

3. The process as claimed in claim 1, wherein R.sup.2 in formula (I) and formula (II) is n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n-undecyl or n-dodecyl.

4. The process as claimed in claim 1, wherein the alkyl halide of the formula (III) is used in an amount from 0.9 to 3 molar equivalents, based on the alkyl sulfide of the formula (II).

5. The process as claimed in claim 2, to wherein the phase transfer catalyst is used in an amount from 0.001 to 0.05 mol.

6. The process as claimed in claim 1, wherein the base is used in an amount from 0.9 to 2 molar equivalents, based on the alkyl sulfide of the formula (II).

7. The process as claimed in claim 1, wherein the base is sodium hydroxide or potassium hydroxide.

8. The process as claimed in claim 2, wherein to a mixture of the alkyl sulfide of the formula (II) and the phase transfer catalyst, and optionally water, is simultaneously added base, and alkyl halide of the formula (III).

9. The process as claimed in claim 2, wherein the reaction of the alkyl halide of the formula (III) and the alkyl sulfide of the formula (II) in the presence of base takes place in such a way that at the beginning of the reaction, from 0.01 to 0.05 mol of base, based on 1.0 mol of alkyl sulfide of the formula (II), is added to the mixture at least comprising alkyl sulfide of the formula (II), optionally phase transfer catalyst and optionally water, before alkyl halide of the formula (III) is added to the reaction mixture.

10. The process as claimed in claim 1, wherein the reaction takes place in a closed reactor.

11. The process as claimed in claim 10, wherein the partial pressure of alkyl halide of the formula (III) in the gaseous space above the liquid reaction mixture within the closed reactor is from 100 to 1500 hPa.

12. The process as claimed in claim 1, wherein the reaction of the alkyl halide of the formula (III) and the alkyl sulfide of the formula (II) takes place in the absence of organic solvents.

Description

EXAMPLES

Example 1: Butyl methyl sulfide (inventive)

[0031] 5500 g (59.76 mol) of butanethiol were initially charged in a reactor at 25° C. 7625 g of water and 60.1 g (0.13 mol) of Aliquat® 336 (mixture of N-methyl-N,N,N-trioctylammonium chloride and N-methyl-N,N,N-tridecylammonium chloride) were added thereto, whereby a biphasic mixture was generated. 250 g of aqueous sodium hydroxide solution (50% by weight, 3.14 mol) were then first added to the mixture with mixing, the temperature being kept between 25 and 40° C. 3320 g (65.76 mol) of chloromethane were then metered into the closed reactor at an initial pressure of 500 hPa below the surface of the liquid in such a way that the pressure in the reactor did not rise above 1200 hPa. Parallel to the addition of the chloromethane, 4767 g of aqueous sodium hydroxide solution (50% by weight, 59.58 mol) were metered in over the course of 3 hours, so that the temperature of the reaction mixture was in the range of 25 to 40° C. After the addition of chloromethane and sodium hydroxide solution had ended, the reaction mixture was mixed at 25 to 40° C. for a further 30 minutes. After the reaction had ended, a biphasic mixture was present in the reactor. The lower aqueous phase was first drained from the reactor and then the upper phase comprising the product was removed from the reactor. The crude product was thus obtained in an amount of 5995 g with a purity of 99% by weight (56.95 mol), which corresponds to a yield of 95% of theory.