IE43137B1 - Production of 1,1-dihalo-4-methylpenta-1,3-or 1,4-dienes - Google Patents

Abstract

MD/Q/PP.28025/28647 Improved process for making 1, 1-dihalo-4-,methyl pentadienes (especially 1, 1-dichloro-4-methyl-1,3-pentadiene) by reaction between isobutene and a trihaloethylene in the vapour phase at temperatures up to about 600.degree.C. The 1:4pentadiene isomer formed can be isomerised to the 1:3-pentadiene isomer. The process is simpler and more efficient than known processes, and the products are intermediates for making insecticides.

Description

This invention relates to the manufacture of 1,1 dihalo - 4 - methylpenta - 1,3 - or 1,4 - dienes.

According to the present invention there is provided a process for the manufacture of a 1,1 - dihalo - 4 methylpenta - 1,3 - cr 1,4 - diene which comprises interacting isobutene with a 1,1,2 - trihalo - ethylene in the vapour phase at elevated temperature.

The process of the invention is applicable, for example, in the manufacture of 1,1 - dihalo - 4 methylpenta -1,3 or 1,4 - dienes in which dihalo represents dichloro, dibromo or chlorobromo. The substituents in the 1 - position of the 1,1,2 trihalo - ethylene starting material will correspond to the desired substituents in tbe 1-position of the 1,l-dihalo-4-methyl-penta1,3 or J.14-diene; thus the 1,1,2-trihaloethylene may be, for example a 1,l-dichloro-2-haloethylene, a 1,l-dibromo-2haloethylene or a l-chloro-l-bromo-2-haloethylene. Ξ The substituent in the 2-position of the 1,1,2-trihaloethylene starting material is preferably chlorine or bromine; thus, for example, when the desired 1,l-dihalo-4-methylpentadiene is a l,l-dichloro-4-methylpentadiene, the 1,1,2trihaloethylene used as starting material may be 1,1,210 trichloroethylene or l,l-dichloro-2-bromoethylene.

The l,l-dihalo-4-methylpentadierte directly produced is usually the l,l-dihalo-4-methyl-l,4-diene, though the isomeric 1,3-diene may be formed in various proportions. The 1,4-diene may readily be converted into the isomeric 1,3-diene by the additional step of heating with a suitable conversion catalyst, for example by heating with p-toluene sulphonic acid, preferably at a temperature in the range from 100°C to 170°C.

The isomerisation step may be carried out on 1,4-diene which has been separated from the reaction product but may, if desired, be carried out without prior separation of the 1,1dihalo-4-methyl-l,4-pentadiene from the reaction mixture.

The process of the invention is ^specially applicable to the manufacture of l,l-dichloro-4-m'ethyl-l,3-pentadiene, which is an intermediate in the preparation of 2-(2,2-dichlorovinyl)~ 3,3-dimethyl cyclopropane-l-carboxylic acid. The said carboxylic acid is itself an intermediate in the preparation of insecticides, for example the 3-phenoxybenzyl ester thereof.

The preparation of -the said carboxylic acid from 1,1dichloro-4-methyl-l,3-pentadiene is described by Farkas et al (Collection Czechoslovak. Qhem. Commun. (1959), 24 pp. 22302236). In this publication, however, the intermediate 1,1dichloro-4-methyl-l,3-pentadiene was prepared from isobutene by a relatively complex multi-stage process and in poorer yield than by the process of our present invention.

In the process of the present invention the reaction may be carried out for example at a temperature in the range from 250°C to 600°C. It is preferred, however, that the temperature should not exceed 550°C since at higher temperatures the diene produced is unstable and lowering of yield occurs.

The preferred temperature range is from 450°C to 550°C, especially the range from 475°C to 525°C.

It is preferred to use a reaction mixture containing at least 1 mole of the trihaloethylene per mole of isobutene.

For the greatest efficiency of reaction it is especially preferred to use at least 3 moles of the trihaloethylene per mole of isobutene. There is no strict upper limit to the trihaloethylene/isobutene ratio, provided that sufficient isobutene is present to cause the reaction to proceed at a reasonable rate; in general, however, it is preferred to use from 3 to 10 moles (for example from 3 to 6 moles) Of trihaloethylene per mole of isobutene, i.e. the trihaloethylene/ isobutene ratio is preferably from 3/1 to 10/1, especially 3/1 to 6/1.

The process may conveniently be performed by passing the gaseous mixture through a reactor which may be, for example, a heated glass or metal tube, and cooling the exit gases to separate out the higher boiling point fraction which contains the product. Such a process may readily be adapted to run continuously, with the unreacted isobutene and trihaloethylene being recycled to the reactor, whilst the product fraction is continuously removed.

The residence time in the reaction zone is preferably not more than 20 seconds. Residence times of not more than 15 seconds (for example from 5 to 15 seconds) are especially preferred.

The reaction is preferably carried out at substantially atmospheric pressure but higher or lower pressures may be used if desired.

It may be advantageous to add a free-radical initiator (e.g. jt-butylhydroperoxide or hydrogen peroxide) to the reaction mixture to further enhance the efficiency of the process. The concentration of such initiators may be varied over a wide range, but it is preferably kept to a minimum, the optimum concentration for particular reaction conditions and/or for a particular reactor being readily established by easy trial. In general, concentrations of initiator of up to 2 mole % are sufficient; in many cases much lower concentrations, e.g. about 0.25 mole %, are sufficient.

The invention is illustrated by the following Examples. ι ST EXAMPLE 1 ’A'flow of isobutene at a rate of Ϊ2 ml/min, was passed down through a vertical glass tube (length 20 cm., capacity 30 ml) maintained at 480°C, and liquid trichloroethylene (2 ml 23 m.mol) was introduced gradually during 17 min. from a syringe through a rubber serum cap arranged so that the liquid dropped onto the warm glass above the heated zone and evaporated before entering the reactor. The reaction mixture contained 2.5 moles of trichloroethylene per mole of isobutene and the residence time in the reaction zone was seconds.

The exit gases were passed through a trap cooled in icewater and a liquid product (2 ml) collected. This was examined and. shown to consist largely of unreacted trichloroethylene, but also contained 1,1-dichloro-4-methyl-1,4pentadiene (0.4 m.mol). Treatment of the whole of this reaction mixture with ^-toluenesulphonic acid (0.1 g) within a sealed tube at 150°C for one hour yielded a mixture containing l,l-dichloro-4-methyl-l,3-pentadiene (0.4 a, mol), No trace of the 1,4-diene could be found.

EXAMPLE 2 The procedure of Example 1 was repeated, except that the reactor was maintained at 540°C whilst a flow of isobutene was passed through at a rate of 100 ml/min and trichloroethylene (14.4 g) was passed into the reactor over 2 hours.

The reaction mixture contained 0.2 mole of trichloroethylene per mole of isobutene and the residence time in the reaction zone was 5 seconds. The collected liquid product was fractionally distilled to give trichloroethylene (10.3 g), and l,l-dichloro-4-methyl-l,4-pentadiene (1.95 g), EXAMPLE 3 Using the procedure and quantities of Example 2 but maintaining the temperature at 508°C, and adding t-butyl hydroperoxide (0.03 g) to the trichloroethylene yielded a liquid product which on fractionation was shown to comprise trichloroethylene (12.7 g) and l,l-dichloro-4-methyl-l,4pentadiene (1.35 g).

EXAMPLE 4 A flow of isobutene at a rate of 150 ml/minute was mixed with a flow of trichloroethylene (derived by vaporisation of liquid trichloroethylene introduced at a rate of 3 ml/minute) and passed through an empty tube (effective internal volume 250 ml) maintained at a temperature of 475°C + 25°C.

The molar ratio of trichloroethylene to isobutene was 5:1 and the residence time in the reactor was 6 seconds.

The exit gases were cooled by passing them through a trap at -78°C. The liquid product thus obtained after flow of reactants for 1 hour contained 15.4 grams of 1,1-dichloro4-methyl-l,4-pentadiene. Thus, for every 100 moles of isobutene fed, 27.2 moles of l,l-dichloro-4-methyl-l,4-pentadiene were obtained. 3137 EXAMPLE 5 Isobutene*and·trichloroethylene vapour were passed into a tubular glass reactor 80 cm in. length, having an effective internal volume of 3 litres. The flow rates of trichloroethylene and isobutene were 13.3 and 2.7 millimoles per minute, respectively, giving a trichloroethylene to isobutene molar ratio of 5 to 1 in the reactor. The gaseous feed, to which was also added 0.25 mole % of t^-butylhydroperoxide, was passed into the reactor for 4 hours, during which time the reactor was maintained at 510°C _+ 25°C. The residence time in the reactor was 10 seconds.

The exit gases were again cooled by passing them through a trap at -78°C, the liquid product so obtained being analysed by gas-liquid chromatography. The product was shown to contain 1,l-dichloro-4-methyl penta-l,4-diene and 2.5dimethylhexa-l,5-diene. Conversion to the first-mentioned product, based on trichloroethylene fed, was 6.5%,the yield being 81% calculated on trichloroethylene consumed.. EXAMPLE 6 The general procedure of Example 5 was repeated but using trichloroethylene recovered from the effluent of Example 5 as the source of trihaloethylene. This gave similar results, demonstrating that it is possible to recycle the trichloroethylene, 92% of which was recovered from the effluent of Example 5.

Claims (25)

CLAIMS:

1. A process for ,the manufacture of a 1,1-dihalo4-methylpenta-l,3 or 1,4-diene which comprises interacting isobutene with a 1,1,2-trihaloethylene in the vapour phase at elevated temperature.

2. ’. A process according to Claim 1 wherein the trihaloethylene starting material is-a 1,1dichloro-2-halOethylene, a l,l-dibromo-2haloethylene or a l-chloro-l-bromo-2-haloethylene.

3. A process according to Claim 1 or Claim 2 wherein the substituent in the 2-position of the trihaloethylene is chlorine or bromine.

4. A process according to any of the preceding claims wherein the trihaloethylene is 1,1,2trichloroethylene.

5. A process according to any of the preceding ( claims wherein the reaction is carried out at a temperature in the range from 250°C to 600°C.

6. A process according to Claim 5 wherein the reaction is carried out at a temperature in the range from 250°C to 550 °C.

7. A process according to Claim 6 wherein the reaction is carried out at a temperature in the range from 450°C to 550°C. - 9 3137

8. A process according to Claim 7 wherein the reaction is carried out at a temperature in the range from 475 °C to 525 °C.

9. A process according to any of the preceding claims wherein the reaction mixture initially contains at least 1 mole of the trihaloethylene per mole of isobutene.

10. A process according to Claim 9 wherein the reaction mixture initially contains at least 3 moles of the trihaloethylene per mole of isobutene.

11. A process according to Claim 10 wherein the reaction mixture initially contains from 3 to 10 moles of the trihaloethylene per mole of isobutene.

12. A process according to any of the preceding claims wherein the residence time in the reaction zone is not more than 20 seconds.

13. A process according to Claim 12 wherein the residence time is from 5 to 15 seconds.

14. A process according to any of the preceding claims wherein, a fr.ee-radical initiator is added to the reaction mixture,

15. A process according to any of the preceding claims wherein a l,l-dihalo-4-methyl-l,4~pentadiene is produced and subsequently isomerised to the corresponding 1,l-dihalo-4-methyl-l,3-pentadiene. 10 43137

16. A process according to Claim 15 wherein 1.1- dichloro-4-methyl~l,4-pentadiene is produced and subsequently isomerised to 1.1- dichloro-4-methyl-l,3-pentadiene.

17. A process according to Claim 15 or Claim 16 wherein the isomerisation is carried out by heating with p-toluene sulphonic acid.

18. A process according to Claim 17 wherein the isomerisation is carried out at a temperature in the range from 100°C to 170°C.

19. A process according to any of Claims 15 to 18 wherein the isomerisation is carried out without prior separation of the l,l-dihalo-4-methyl1,4-pentadiene from the reaction mixture.

20. A process for the manufacture of a 1,1-dihalo4-methylpentadiene according to Claim 1 and substantially as described, with reference to and as shown in ahy one of Examples 1 to 4.

21. A process for the manufacture of a 1,1-dihalo4-methylpentadiene according to Claim 1 and substantially as described, with reference to and as shown in Example 5 or Examnle 6.

22. A l,l-dihalo-4-methyl-l,4-pentadiene whenever prepared by a method claimed in any of Claims 1 to 14, Claim 20 or Claim 21, 11 a i at

23. A l,l-dihalo-4-methyl-l,3-pentadiene whenever prepared by a method claimed in any of Claims 1 to 21.

24. A l,l-dichloro-4-methyl-l,4-pentadiene whenever prepared by a method claimed in any of Claims 1 to 14, Claim 20 or Claim 21.

25. A I,l-dichloro-4-methyl-l,3-pentadiene whenever prepared by a method claimed in any of Claims 1 to 21.