Note: Descriptions are shown in the official language in which they were submitted.
10721Z6
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
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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.
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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.
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10721Z6
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.
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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.
EXAMPLE 2
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.
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10721Z6
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).
EXAMPLE 3
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.
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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-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.
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 trichloro-
ethylene, 92% of which was recovered from the effluent of
Example 5.
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