CA1072126A

CA1072126A - Diene production

Info

Publication number: CA1072126A
Application number: CA256,214A
Authority: CA
Inventors: Warren Hewertson; David Holland; David J. Milner
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 1975-07-02
Filing date: 1976-07-02
Publication date: 1980-02-19
Also published as: IE43137L; LU75277A1; IT1064095B; IE43137B1; JPS527907A; DK297576A; NL7607264A; AU1523576A; DE2629868A1; FR2362102A1

Abstract

MD/Q/PP.28025/28647 ABSTRACT OF THE DISCLOSURE

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°C. The 1:4-pentadiene 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

MD/Q/PP.28025i28647 This invention relates to the manufacture of l,l-dihalo-4-methylpentadienes.
According to the present invention there is provided a process for the manufacture of a l,l-dihalo-4~methylpentadiene 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 l,l-dihalo-4-methylpentadienes in which "dihalo~' represents dichloro, dibromo or chlorobromo.
The substituents in the l-position of the 1,1,2-trihalo-ethylene starting material will correspond to the desired :' ~

-.. . - : -. . . : : . . - -. :
.
- . ~ .. . ~ . . ~ :
, ~ . . ,, : . -- ~ : .
- -, -.: : - - - - :
- : : : . , -- : .
- :

1072~2~

substituents in the l-position of the l,l-dihalo-4-methyl-pentadiene; thus the 1,1,2-trihaloethylene may be, for example a l,l-dichloro-2-haloethylene, a 1,1-dibromo-2-haloethylene or a l-chloro-l-bromo-2-haloethylene.
The substituent in the 2-position of the 1,1,2-trihalo--ethylene starting material is preferably chlorine or bromine;
thus, for example, when the desired l,l-dihalo-4-methyl-pentadiene is a l,l-dichloro-4-methylpentadiene, the 1,1,2-trihaloethylene used as starting material may be 1,1,2-trichloroethylene or ljl-dichloro-2-bromoethylene. --The 1,1-dihalo-4-methylpentadiene directly produced is usually the 1,1-dihalo-4-methyl-1,4-diene, though the isomeric 1,3-diene may be formed in various proportions. The 1,4-diene may readily be converted into the isomeric l,3-diene by the additional step of heating with a suitable conversion catalyst, for exampie by heating with p-toluene sulphonic acid, preferably at a temperature in the range from 100C to 170C.
The isomerisation step may be carried out on 1,4-diene which has been separated from the reaction product but may, if

2~ desired, be carried out without prior separation of the 1,1-dihalo-4-methyl-1,4-pentadiene from the reaction mixture.
The process of the invention is especially applicable to the manufacture of l,l-dichloro-4-methyl-1,3-pentadiene, which is an intermediate in the preparation of 2-(2,2-dichlorovinyl)-

3,3-dimethyl cyclopropane-l-carboxylic acid. ~he said carboxylic acid is itself an intermediate in the preparation of insecticides, for example ~he 3-phenoxybenzyl ester thereof.

' . ' ' ':

~072~Z6

4.

The preparation of the said carboxylic acid from 1,1-dichloro-4-methyl-1,3-pentadiene is described by Farkas et al (Collection Czechoslovak Chem. Commun. (1959), 24 pp. 2230-2236). In this publication, however, the intermediate 1,1-dichloro-4-methyl-1,3-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 10 250C to 600C. It is preferred, however, that the tempera-ture should not exceed 550C since at higher temperatures the diene produced is unstable and lowering of yield occurs.
The preferred temperature range is from 450C to 550C, especially the range from 475C to 525C.
It is preferred to use a reaction mixture containing at least 1 mole of the trihaloethylene per mole of isobutene.
~or 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 20 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) trihalo-ethylene per mole of isobutene, i.e. the trihaloethylene/
25 isobutene ratio is preferably from 3/1 to 10/1, especially 3/1 to 6/1.

~ . -: - - .. . : . . . .

, - : . -, . . . . .

' ~ ' ~ . , - ' -The process may conveniently be performed by passingthe 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 Iesidence 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. t-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 ~ept 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 concen-trations, e.g. about 0.25 mole %, are sufficient.
The invention is illustrated by the following Examples.

.

-' ' :
~ '. , - - . .

~o7ZlZ6 6.

~XAMPLE 1 A flow of isobutene at a rate of 12 ml/min was passed down through a vertical glass tube (length 20 cm., capacity 30 ml) maintained at 480C, and liquid trichloroethylene (2 ml 23 m.mol) was lntroduced 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 16 seconds.
The exit gases were passed through a trap cooled in ice-water and a liquid product (2 ml) collected. This was examined and shown to consist largely of unreacted trichloro-ethylene, but also contained 1,1-dichloro-4-methyl-1,4-pentadiene (0.4 m.mol). Treatment of the whole of this reaction mixture with p-toluenesulphonic acid (0.1 g) within a sealed tube at 150C for one hour yielded a mixture containing 1,1-dichloro-4-methyl-1,3-pentadiene (0.4 m. mol).
No trace of the 1,4-diene could be found.

The procedure of Example 1 was repeated, excep*-that the reactor was maintained at 540C whilst a flow of isobutene was passed through at a rate of 100 ml/min and trichloro-ethylene (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 1,1-dichloro-4-methyl-1,4-pentadiene (1.95 g).

Using the procedure and quantities of Example 2 but maintaining the temperature at 508C, 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 1,1-dichloro-4-methyl-1,4-pentadiene (1.35 9).
EXAMPL~ 4 A 1OW 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 + 25C.
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 -78C. The liquid product thus obtained after flow of reactants for 1 hour contained 15.4 grams of l,l-dichloro-4-methyl-1,4-pentadiene. Thus, for every 100 moles of iso-butene fed, 27.2 moles of 1,1-dichloro-4-methyl-1,4-pentadiene were obtained.
-' .

107ZlZ6 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-butylhydro-peroxide, was passed into the reactor for 4 hours, during which time the reactor was maintained at 510C + 25C. The residence time in the reactor was 10 seconds.
The exit gases were again cooled by passing them through a trap at -78C, the liquid product so obtained being analysed by gas-liquid chromatography. The product was shown to contain 1,1-dichloro-4-methyl penta-1,4-diene and 2.5-dimethylhexa-1,5-diene. Conversion to the first-mentioned product, based on trichloroethylene in the fed, was 6.5%, the yield being 81% calculated on trichloroethylene consumed.

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 trichloro-ethylene, 92% of which was recovered from the effluent of Example 5.

-- , ' -- , .. . .. : :
'- ' ' ' ' - :

- . .

Claims

The embodiments of the invention in which an exclusive privilege and property is claimed are defined as follows;

1. A process for the manufacture of a 1,1-dihalo-4-methylpenta-1,3-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 1,1-dichloro-2-haloethylene, a 1,1-dibromo-2-haloethylene or a 1-chloro-1-bromo-2-halo-ethylene.

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

4. A process according to Claim 1 wherein the tri-haloethylene is 1,1,2-trichloroethylene.

5. A process according to Claim 1 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.

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 Claim 1 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 Claim 1 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 Claim 1 wherein a free-radical initiator is added to the reaction mixture.

15. A process according to Claim 1 wherein a 1,1-dihalo-4-methyl-1,4-pentadiene is produced and subsequently isomerised to the corresponding 1,1-dihalo-4-methyl-1,3-pentadiene.

16. A process according to Claim 15 wherein 1,1-dichloro-4-methyl-1,4-pentadiene is produced and subsequently isomerised to 1,1-dichloro-4-methyl-1,3-pentadiene.

17. A process according to 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 Claim 15,16 or 17 wherein the isomerisation is carried out without prior separation of the 1,1-dihalo-4-methyl-1,4-pentadiene from the reaction mixture.