CA1147349A - Process for 1,1-dihalo-4-methyl-1, 3-pentadienes - Google Patents

Abstract

PROCESS FOR 1,1-DIHALO-4-METHYL-1,3-PENTADIENES
Abstract of the Disclosure 1,1-Dihalo-4-methyl-1,3-pentadienes are prepared by the catalytic dehydrohalogenation of 1,1,1,3-tetrahalo-4-methylpentanes, in a novel process which involves heating the latter to a temperature of from about 150°C to about 200°C in the presence of a catalytic amount of a nitrogen base halide salt selected from the group consisting of tertiary amine hydrohalides in which the substituents on the nitrogen atom are alkyl or cycloalkyl containing a minimum of 3 carbon atoms each, N-alkyl alkyleneimine hydrohalides in which the alkyl group contains from 1 to 6 carbon atoms and the alkylene group contains from 3 to 7 carbon atoms, quinoline hydrohalides, and tetraalkylammonium halides in which at least three of the alkyl groups contain a minimum of 3 carbon atoms each.

Description

~73~

PROCESS FOR 1,1-DIHAL0-4-METHYL-1,3-PENTADIENES
.
Background of the Invention This invention relates to the preparation of 1,1-dihalo-4-methyl-1,3-pentadienes, which are key intermediates in a known method for the production of certain pyrethroid insecticides.
The term "pyrethroid" is commonly used to encompass both naturally occurring and synthetic derivatives of cyclo-propane carboxylic acid. Such compounds have been well known for many years as broad spectrum insecticides. They have generated particular interest in the insecticide art since in spite of their high potency in controlling insects, they have a low -toxicity toward mammals, and they degrade readily after application, avoiding the accumulation of harmful residues in the soil or plant tissues.
One of the most successful pyrethroids is 3'-phenoxybenzyl 2~ dichlorovinyl)-3,3-dimethylcyclopro-pane carboxylate, first reported by Elliott et al., Nature, 244, 456-457 (1973); ibid., 246, 169-170 (1973). This com-pound and others similar in structure have an outstanding combination of insecticide properites, notably an unusually high potency. Since the discovery of this class of compounds-, much effort has been expended in developing economical pro-cesses for their manufacture.
The precursor ethyl 2-(~ dichlorovinyl)-3,3-dimethylcyclopropane carboxylate was first prepared by amethod known prior to the Elliott et al~discovery. This r~ethod is attributed to Farkas et al., Coll. Czech. Chem.
Comm., _, ~230 (1959), and involves the condensation of - chloral with either isobutenyl magnesium bromide or iso-butylene, using a free radical catalyst with the latter, to produce a mixture of pentenols. The pentenols are then reacted as follows:

~2 OH .

C ~ (CH3CO)20 OH ~ acetates Cl~ ~

Zn, CH3CO2H CC
acetates ~_ .- ,~ p toluene C ~ ~ sulfonic acid . _ ' CC~
.

CC ~ . ~Cu~020 ~ Cl /==\ C02C2H5 ` ` ` Cl ~

/\

This compound is then converted to the Elliott et al.
pyrethroid by ester interchange.
`
The overall conversion of isobutylene to ~
dichloro-4-methyl-1,3-pentadiene~ the key intermediate in 5 the above reaction scheme, is reportedly less than 40%.
Furthermore, for every kilogram of 1,1-dichloro-4 methyl-1,3-pentadiene produced, more than a kilogram of zinc dust ~s consumed It is clearly desirable to find more practical and economical methods of producing the diene.

... .

.

_3_ A number of processes have been developed to prt~duce the diene by direct synthesis. One such process, which is based on the addition of trichloroethylene to iso-butylene, is described in Hewertson et al., Ger. Offen.

2,629,868 (1977); Chemical Abstracts, 86, 15188s (1977).
This process involves two steps: first, a hot-tube reaction between the starting materials with a free radical initiator to form the l,4-diene, followed by an acid-catalyzed rearrangement to the l,3-diene. Another process, described in Holland et al., U.S. Patent No. 4,056,574 (1977), involves the oxidative coupling of isobutylene with vinyli-dene chloride in the presence of palladi~un acetate. The product achieved' by this process is a mixture o~ the 1,3-and 1,4-diene isomers together with non-chlorinated dienes.

Other processes involve the formation of either the'' unsaturated diene precursor, or a precursor containing a single double bond, folLowed by dehydrohalogenation, dehydra-tion, or both to form the diene. CLeare, U.S. Patent No.
4,018,838 (1977), describes a simplified version of the Farkas et al. process described above, wherein the trichloro-pentenol is reacted directly with powdered zinc in glacial acetic acid to form the diene. Kay et al.~ Ger. Offen.
2,~57,148'(1977), Ch~m~c-l Abser=c~s, 87, 92654p (1977), describes the electrochemical reduction of the trichloro-pentenol in sulfuric acid dissolved in methanol. A similar process is disclosed in Alvarez et al., U.S. Pa~ent No.
4~022~672 (1977~o Scharpf, U.S. Patent No. 4,081,088 (1978), describes the formation of the l,l-dihalo-4~methyl-1-penten-

3-one by the condensation of a vinylidene halide and an isobutyryl halide in the presence of a Lewis acid9 followed by reduc~ion of the ketone to the alco~ol with aluminurn isopropoxide and isopropanol, and dehydration o~ thé alcohol to the dienè using an activated clay. A
similar process is reported by ~yseia et al., British Patent No. 1,493,228 (1977), in which the reduction is performed by an alkali metal borohydride. Lupichuk, U.S. Patent No.

4,070,4Q4 ~1978), describes the condensation of ~. ~

3-methyl-1-butene with a carbon tetrahalide, followed by the base-induced dehydrohalogenation of the resulting 1,1,1,3- -tetrahalo-4-methylpentane to form the diene. Alkali metal hydroxides are designated as preferred bases for the dehydro-~alogenation, and one equlvalent is used for each mole ofhydrohalide eliminated. The product is characterized by low yields and substantial by-prodact formation.

Dehy~rohalogenation has also been disclosed in Belgian Patent No. 842,180 (1976) to Shell International Research, wherein an equivalent of tertiary amine is used for each mole of hydrohalide eliminated. Dehydrohalogenation combined with dehydration has been disclosed in Lantzsch et al.~ British Patent No. 1,494,817 (1977).

Summary of the Invention It has now been discovered that 1,1-dihalo-4-methyl-1,3-pentadienes can be prepared to a high degree of selectivity by the catalytic dehydroh~logenation of 1,1,1,3-tetrahalo-4-me~hylpentane.

.
Specifically, the process of the present invention comprises heating a 1,1,1,3-tetrahalo-4-methylpentane to a temperature of from about 150C to about 200C in the presence of a catalytic amount of a nitrogen base halide salt selected rom the group consisting of tertiary amine hydrohalides in which the substituents on the ni~rogen atom are alkyl or cycloalkyl containing a minimum of 3 carbon atoms each, N-alkyl alkyleneimine hydrohalides in which the alkyl group contains from 1 to 6 carbon atoms and the alkylene gxoup contains from 3 to 7 carbon al:oms, . quinoline hydrohalides, and tetraalkylammonium halides in which at least three of the alkyl groups contain a minimum of 3 carbon a~oms each.

, . ... .
.~ , .

~473 The term "alkyl" is used herein to in lude both straight- and branched-chain saturated monovalent hydro-carbon radicals. Examples are methyl, ethyl, n-propyl, n-butyl, lsobutyl, n-hexyl, 2-ethylhexyl, s-heptyl, n-nonyl, n-dodecyl, etc. The alkyl radicals attached to a given n~trogen atom may be the same or different and are subject only to the limitations of steric hindrance which are apparent to one skilled in the art. The preferred trialkyl-amine hydrohalides are those in which the three alkyl groups are identical, and range from 3 to 18 carbon a~oms each.
The most preferred are those with three identical alkyl groups ranging from 4 to 15 carbon atoms each. The pre-ferred N-alkyl pyrrolidine hydrohalides are those in which the alkyl group ranges from 1 to 3 carbon atoms. The pre-ferred tetraalkylammonium halides are those in which thealkyl groups are all straight-chain alkyls and the toLal number of carbon atoms in all four alkyl groups ranges from 10 to 40, more preferably from 12 to 36~ and most preferably from 16 to 32.

The preferred cycloalkyl groups are those ranging from 5 to 8 carbon atoms, most preferably from 6 to 8 carbon atoms. The carbon atoms in the cycle are optionally sub-stituted by alkyl groups. Examples include cyclopentyl, cyclohexyl, 3-methyLcyclohexyl, cyc lohep tyl, e tc~ -The term N-alkyl alkyleneimine is used herein to denote a compound of the formula ' (C ~ N-R
where n is an integer and R is an alkyl group. As stated above, R ranges from 1 to 6 car~on atoms and n ranges from 3 ~o 7. Preferably, R is rom 1 to 3 carbon atoms and n is from 4 to 6. Examples are N-ethyl azetidine, N-methyl pyrrolidine, N-propyl piperidine, etc.

All carbon atom ranges are in~ended to be inclu-sive of their upper and lower limits.

,.. ...

~7~9 The terms "halogen," "halo," and "halide" are used herein to include ~luorine, chlorine, bromine, and iodine. PreEerred halogens are chlorine and bromine, with chlorine particularly preferred.

The term "catalytie amount" is used herein to denote any amount of the catalyst which will cause the liberation of anhydrous hydrohalic acid from the tetra-halogenated starting material.

Detailed Description of the Invention According to the process o~ the present invention, the 1,1,1,3-tetrahalo-4-methylpentane and the nitrogen base ~al~ are combined in the liquid phase and heated, and hydro-halic acid is evolved as a gas The product, 1,1-dihalo-4-methyl-1,3-pentadiene, is then recovered from the reaction mixtare.

The process can be operated over a wide temperature range, limited only by the desirability or minimizing char-ring and by-product formation which may occur at high tempera-ture, and by a low reaction rate at low ~emperatures. In practical opera'ion, a temperature ranging from about 150C
to`about 200C, and preerably from aDou~ 170C``to about 190C, is employed. A condenser or heat exchanger can be positioned above the reaction vessel to facilitate tempera-t~re control and to condense any volatilized hydrocarbon fr~m the hydrohalide gas which is driven off, and ~o return the condensate to the reaction mixture. With a condenser, the reaction is generally run under a partial re1ux~ since full reflux at atmospheric pressure generally requires a temperature higher than desired.

Aithough^t~e systém pressùre is not critical and ~- 30 can vary over a broad range, a pressure which is approximately atmospheric is the most practical ~or the dehydrohalo~enation reaction. Higher pressures offer little advantage since they .~, .

~ 7 of~en necessitate a higher reaction temperature which is undesirable for the reasons stated above. A high pressure may also aggravate corrosion problems since the gas phase above the reaction mixture is largely hydrohalic acid. Sub-atmospheric pressures may offer an advantage under certainconditions, however, since they may promote the evolution of the hydrchalide gas and permit efficient operation at a lower reaction temperature. A purge of inert gas such as nitrogen can also be used to promo~e the removal of hydrogen halide gas~

There is no critical amount of catalyst for this reaction. Any amount which will promote the reaction rate, i.e., cause the evolution o~ hydrohalide gas, will suffice.
The actual amount which should be used is largely a function of economic considerations, since the reaction rate increases with increasing catalyst concen~ration. Generally, the amount of catalyst is such that the initial mole ratio o~
catalyst to alkane starting material is from about 0.05 to about 5.0, preferably from about 0.2 to about 2Ø

The catalyst can be pre-formed external to the reaction system prior to being placed in the reaction vessel, or it can be prepared in the reaction vessel itself. For in situ catalyst prepara~ion, a propexly selected amine is reacted with either anhydrous hydrogen halide gas or an appro-priate organic halide, depending on whether ~he desired catalyst is an amine hydrohalide or a quaternary ammonium salt~ It is occasionally convenient to heat the catalys~
thus fonmed, in order to plaee it in the molten form, prior to addition of ~he alkane if the catalyst is a solid at ambient temperature.

Any method of combining the catalyst with the alkane wlll suffice; either one may be added to the vessel first.
When the rea tion is run as a batch wide process, it is gen-erally most convenient to combine the two components a~ ambi-ent ~emperature and then to heat the mixture up to thetemperature level desired. The reaction is gPnerally com-plete within a few hours.
.,.,~,~

73~

Rather than a mixture o~ diene isomers, the pro-ducta when the process is run to completion, c~ sists essentially of the l,l-dihalo-4-methyl-1,3-pentadiene.
Once the reaction is complete, the product can be separated from the catalyst by distillation. It is advantageous to place the vessel under a partial vacuum during the dis-tillation, so that the'distillation can occur at a tempera-ture at or below the reaction temperature.

The process can also be operated on a continuous basis, whereby the alkane is continually fed to the system and both the 'diene and the hydr~halide gas are continuously removed. In this type of operation, the alkane is added to the cata'lyst while the latter is already at reaction tem-' perature. Continuous processes require either a recycle system or a fractionating column OL considerably greater complexity than a simple condenser, since a substantial residence time is needed to complete the removal of two moles of hydrohalide. A higher concentration of catalyst is also needed. Improvements i~ efficiency can be achieved, '' 20 however, by using a multi-stage system, such as a cascading reactor arrangement. The various stages permit the use of a combination of dif~erent temperatures and catalyst concen-trations, which can be adjusted ~o maximize yield and mini-mize the quantity of trichlorina~ed olefin in the product.
Product controL can also be achieved by the use oE a semi-continuous process whereby feed and product streams are intermittently shut down while the reaction remains running.

- ID general, the diene product can be recovered from the reaction mixture by any conventional techni~ue, although simple dis~illation under vacuum is the most practical ~' method. The catalyst remaining in the still pot can then be re-used indefinitely for the treatment o~ a new batch of starting ~aterial; no catalyst regeneration is necessary unless the starting material itself contains high-boiling , , 73~
~ g impurities which accumulate in th~ reaction vessel. The product itself can be fu~her purified by any conventional means. Olefin intermediates present in the product can be either removed or converted to the diene by an additional dehydrohalogena~ion. In general, the amount of olefin formed can be minimized by increasing the reaction temperature, or lncreasing the amount of catalyst used or the reaction time, or by careful selection of the catalyst. The hydrohalide gas can be pressurized, scrubbed, or fed to some other pro~
cess for use as a halogenation or neutralization ~ ent.

It should be clear from the above description that numerous variations on the basic process are possible, and all are intended to be incLuded within the scope of the pre-sent invention. The following examples are offered for purposes of illustration only, and are intended neither to define nor limit the invention in any manner.

A 0.3-lit~r reaction vessel equipped with stirrer, thermometer? and condenser and mounted in a heating mantle was charged wi~h 14.2 grams (g) ~0.167 mole) of N-methyl- -2Q pyrrolidine and 112 g (0.5 mole) o 1,1,1,3-tetrachloro-4-methylpentane, hereinafter referred to as "TCMP," at ro~m temperature. Heat was then applied while anhydrous hydrogen chloride was added below the liquid surface; A total of 6.5 g ~0.178 mole) of HCl was added. When the system tem-perature reached 185C, gas bubbles began to evolve from the reaction mixture. The system was then kept under reflux for 7 1/4 hours, while the temperature gradually dropped from 185~C down to 170C due to the changing composition of the reaction mixture. The reaction was monitored by gas chromatographic analyses of liquid samples taken at periodic intervals from the vessel. Prior to injection, each sample was dissolved in carbon disulfide~ then washed first with dilute HCl, and then water. The chromatogram data, exclu-.. . . . . . . .. . ..
sive of the CS2 content of each sample, was as follows:

~' .
~. j .

TABLE I. Product Analyses Reaction Produc~ in Area Percents Time (h) DC~IP Tri TCMP
1~0 41.5 1~.1 44.4 2.0 62~4 11.8 25.8 3.0 77.7 8.1 14.1

5.0 94.7 ~.4 2.8

6.0 96.~ 1.8 1.6 -

7.25 98.6 1.0 0.4 DCMP ~ Dichloro-4~methyl-1,3-pentadiene Tri : Trichlorinated olefins~
TCMP : 1,1,1,3-Tetrachloro-4-methylpentane In each caseS a single diene peak appeared. When the final reaction mixture was distilled and analyzed by nuclear mag-netie resonance (NMR) spec~roscopy, it was confirmed that the only diene present was 1,1-dichloro-4-methyl-1,3-pentadiene, hereinafter referred to as "DCMP.t' No otherisomers were detected. The trichlorinated olefin inter-mediates appeared as several isomers in separate peaks on the chroma~ogram. The area percents for these were com ~ined to provide the ~igures shown aboveO Area percents are ~aken from direct measurements of the area undex eac~
peak on the chromatogram trace. They are essentially equivalent to mole percents, particularly where the;figures are very close to zero or 100. ~ -After the last sample was ~aken the system was partially evacuated, lowering the pressure ~o 16 milli-meters Cmm) of mercury. The produc~ was distilled of fr~m the reaction mixture at this pressure at a ~emperature of 61-65C. ~The product was ~hen ~ried, weighed, and analyzed. The yield o diene was 64.0 g, at 95.6 weigh~
percenk puri~y, corresponding to 81.0% yield.

~ ~.

~ ~L14~

-The procedure of Example 1 was followed using 67.2 g (0.3 mole) of TCMP and 16.6 g ~0.06 mole) of te~ra-bu~ylammonium chloride. The lat~er was preformed, so that nn in situ cataly~t generation was required. The reaction was initiated at 166C and proceeded for 3.5 hours, while the reflux temperature fell to 157C. Gas chromatographic analy~is of the final product showed 72% DCMP, 10% tri-chlorinated olefins, and 3% TCMP (area percents). No diene isomer~ o~ DCMP were detected.
.

E:_ The procedure o~ Example 1 was followed using 196 g (0.5 mole) of Alamine 336R, 112 g (0.5 le) of TCMP, and sufficient anhydrous HCl to saturate the reac~ion vessel.
Alamine 336 is a commercial pro~uct obtainable from Henkel Corporation, Kankakee, Illinoi~9 and is identîfied as tri-caprylylamine, wherein the tenm "caprylyl" represent~ a mixture of s~raight-chain, sa~urated alkyl radical~ of 8 to 10 carbon atoms each, with the 8-~arbon chain predominating.
Alamine 336 has a molecular weight of 392.

The reaction was run for 2 ho~rs, reflu2in~ a~
180-188C. The f~nal product analysis revealed 98% (area~

DCMP, and no TCMP, trichlorinated 012~in~ or diene isomer~
of DoMP were detected. The distllled product wei~hed 72.0 g and ~ad a purity of 94% (weight)~ corre~ponding to a ~5%
yield.

Th~ procedure o~ Example 1 was followedg u8ing 106 g t0-3 mole) of ~ri-n-octyl~mdne and 67.2 g ~0.3 mol~
of ToMP, saturated with anhydrous HCl. After 3 hours of reac~ion ~ime at 180~190C, the reaction mixture analy~is ~howed 88% (area~ DCMP, 6% trichlorinated olefins, and no TCMP or diene isomers of DCMP. The dist~lled product weighed 42.3 g ~ith an assay of 91.4% (weight), for a yiald of 90.7%.

~4~3~ -2~

The procedure o~ Example 1 was ollowed, using 64.6 g (0.5 mole) o quinoline and 112 g ~0.5 mole) of TCMP, saturated with anhydrous HCi, After 3.5 hour~ of reaction time at 170-180C, the reaction mixture analysis showed 92% (area) DCMP and no TCMP, trichlorina~ed olefins, or DCMP isomers. The distilled product weighed 69.2 g with an assay of 92.4% (weight) corresponding to 90.0% yield.

The procedure of Example 1 was followed, using 130~5 g (0.25 mole) of tri-n-dodecylamine and 56 g ~0.25 . 10 mole) of TCMP, saturated with anhydrous HCl. After 5 hours of reaction time at 181-190C, the reaction mixture analysis showed 98% (area) DCMP and no TCMP, trichl~ inated olefins, : or DCMP isomers. A distilled product weighed 34.5 g with an assay of 96% (weight), corresponding to a g3% yield.

The procedure of Example 1 was followed, using 72.0 g (0.5 mole~ of ~rl-n~propylamine and 112 g (0.5 mole) o TCMP, saturated wi~h ~nhydrous HCl. After 2 hours of reaction time at 173-175C, the reaction mixture analysis showed 98% (area3 DCMP with no TCMP, trichlorinated olefins, or DCMP isomers. The distilled product weighed 69.6 g with -; an assay of 96.3%, corresponding to a 92% yield.

, The procedure of Example 1 was followed, using 78 g (0.5 mole) of diethylcyclohexylamine and 112 g (0.5 mole) of TCMP, saturated with anhydrous HCl. After 2 hours of reaction ~ime at 169-174C, the reaction mixture was analyzed to show 98% (area) DCMP, and no other dienes~ TCMP, or trichlorinated olefins. The distilled product weighed 70.0 g with an assay o 96.4%, corresponding to a 93% yiPld.
.

~q~' 34~
~ .

This example demonstrates the use of the catalyst tri-n-butylamine hydr~chloride at reduced pressure.

A reaction flask equipped with stirrer, thermo-meter, condenser, and oil heating bath, and connected through a dry ice/isopropyl alcohol-coo~ed trap to a water aspiratora was charged with 95 ml (74 g, ~.40 mole) of tri-n-butylamine and purged with nitrogen. Anhydrous hydrogen chloride gas was then added to the flask below the liquid surface until 30 g (0.80 mole, or 100% excess) had been 10 added. The excess HCl (that quanti~y above the amount required to form the amine hydrochloride) remained in the flask, dissolved in the liquid.

During the HCl addition, the temperature had risen to 94C. Following the HCl addition, 48 g (0.21 mole) of T~MP (97% pure3 was added rapidly to the system and the heating was begun by raising the ~emperature of the oil heating bath to 183C. As the temperature rose, the dis-solYed HCl escaped rom the reaction mixture. When the temperature o~ the reaction mixture rose to ~67C, ~he system was~placed under partial v~acuum of 354 Torx ~absolute pressurs). The reaction temperature stabilized at 162-163C
as the system refluxed and;HCl gas evolved ~rom the liquid.
The reaction procéeded for 3~1/2 hours,~ring which time several samples were taken rom the reaction mixture for analysisO; Each sample was added to a hexane/water mixture, and a sample of ~he hexane phase was injected~into a chroma-tographic column. Th~ procedure eliminated the catalyst from the analysis since the~water phase ex~racted the catalyst from the mixture~ The results are shown in Table II.

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

~,~

~ 7 3 TABLE II
Product Analyse~
Reaction Product in Area Percents Time (h~ DCMP Tri TC~æ
0.05 0.5 3.5 96.0 0.6 39.5 23.5 37.0 2.0 97.0 1.5 1~5 2.5 9~.5 1.0 0.5 3.0 ~00.0 0 0 DCMP ~ Dichloro-4-methyl-1,3-pen~adiene : Tri : Trichlorinated oleflns TCMP : 1,1,1,3-Tetrachloro-4-me~hylpentane .
After khe last sample was taken, the oil heatiL~g bath wa~ lowered and the system was purged with nitrogen.
The reaction mixture was then distilled under a pressure o~ 0.7 torr as the temperature was gradually increa~ed to S 140Q'C. A dry ice/i~opropyl alcohol-cooled trap followed :: by a liquid nitrogen-cool~d trap connected in series were used to collect the dis~illate. The catalyst rexained in ~he reaction flask and a cloudy oil ~eighing 31.1 g formed in the dry ice trap. ~o~hing a~ all deposited ln the li~uid nitrogen trap. The oil in the dry ice trap was dried with ~odium sulfate crystals and fil~ered to give 30.0 g t)f a pale yellow oil which was~purged with nitrogen for one h~
: hour. A~alysis by ga~chromatography/lass spectrometry con~inmed:the produ~t a~ dichloro-4 methyl 1,3~penta-}.5 diene a'c 91.8% by weigh~, corresporlding to 89~0% yield of .theore'cical~ No other diene was d~tected.

~hi8 example d~monstra~es the use of a subsurface nitrogen purge to promote ~he rem~val o~ HCl, u~ing tri-n-bu~ylamine hydroch~oride catalyst.

~ .

7 3 ~9 ~15-The reaction ~lask of Example 9 was charged with 238 ml (185 g, l.00 mole) of tri-n-butylamine under nitrogen, followed by 42 g ~1.15 moles) of anhydrous HCl to form the hydrochloride of the amine. Then 115 g (0.50 mole) of TCMP
was added and the system was heated as before. Although an aspirator was connected to the condenser at the outlet of the reaction ~lask; it was run gently such that the system pressure was within 1 or 2 torr of atmospheric at all times.

When the temperature of the reaction mixture reached 165~C, a flow of nitrogen was ~egun below the liquid surface at a rate of 123 ml/min as measured by a calibrated rotameter. The 'temperature was maintained at this lev~l without re~l~ for three hours, during which time s~veral samples were taken and analyæed as in Example 9. The results are shown in Table III.

BLE III
Product Analyses Reaction Product in Area Percents Time (h) _ 0 6.3 12.5 81.2 0.5 43~5 20.0 3602 0.3 ' 1.0 64.0 1705 17.5 1.0 1.5 80.0 11.5 6.5 ~
2.0 88~0 ~.5 1.5 ~ 4.0 3O0 94.0 1.0 -- 5.0 DCMP : 1,1-Dichloro-4-methyl-1,3-pentadiene Tri : Trichlorinated olefins TCMP : 1~1,1,3-Tetrachloro-4-methylpentane After the las~ sample was taken, the product was recovered as in Example g7 to give 73.2 g of a product which a^nalyz-e-~ as 90~.~ wei^ght'pe~cent'D'CMP, or a yl~ld of 87.5%
of theoretical.

Claims (10)

WHAT IS CLAIMED IS:

1. A process for the preparation of a 1,1-dihalo-4-methyl-1,3-pentadiene which comprises heating a 1,1,1,3-tetrahalo-4-methylpentane to a temperature of from about 150°C to about 200°C in the presence of a catalytic amount of a nitrogen base halide salt selected from the group consisting of tertiary amine hydrohalides in which the substituents on the nitrogen atom are alkyl or cycloalkyl containing a minimum of 3 carbon atoms each, N-alkyl alkyleneimine hydrohalides in which the alkyl group contains from 1 to 6 carbon atoms and the alkylene group contains from 3 to 7 carbon atoms, quinoline hydrohalides, and tetraalkylammonium halides in which at least three of the alkyl groups contain a minimum of 3 carbon atoms each.

2. A process according to Claim 1 in which the nitrogen base halide salt is selected from the group con-sisting of tertiary amine hydrohalides in which the substi-uents on the nitrogen atom are C3-C8 alkyl or C5-C8 cycloalkyl, N-alkyl alkyleneimine hydrohalides in which the alkyl group contains from 1 to 3 carbon atoms and the alkylene group contains from 4 to 6 carbon atoms, quinoline hydrohalides, and tetraalkylammonium halides with a total of 10 to 40 carbon atoms.

-17- .

3. A process according to Claim 1 in which the nitrogen base halide salt is selected from the group con-sisting of tertiary amine hydrohalides in which the substi-tuents on the nitrogen atom are C4-C15 alkyl, or C6-C8 cycloalkyl, N-alkyl alkyleneimine hydrohalides in which the alkyl group contains from 1 to 3 carbon atoms and the alkylene group contains from 4 to 6 carbon atoms, quinoline hydrohalides, and tetraalkylammonium halides with a total of 16 to 32 carbon atoms.

4. A process according to Claims 1, 2, or 3, in which the nitrogen base halide salts are chlorides or.
bromides.

5. A process according to Claims 1, 2, or 3 in which the nitrogen base halide salts are chlorides.

6. A process according to Claims 1, 2, or 3 in which the 1,1-dihalo-4-methyl-1,3-pentadiene is 1,1-dichloro-4-methyl-1,3-pentadiene.

7. A process according to Claims 1, 2, or 3 in which the initial mole ratio of nitrogen base halide salt to 1,1,1,3-tetrahalo-4- methylpentane is from about 0.05 to about 5Ø

8. A process according to Claims 1, 2, or 3 in which the initial mole ratio of nitrogen base halide salt to 1,1,1,3-tetrahalo-4-methylpentane is from about 0.2 to about 2Ø

9. A process according to Claims 1, 2, or 3 in which the 1,1,1,3-tetrahalo-4-methylpentane is heated to a temperature of from about 170°C to about 190°C.

10. A process for the preparation of 1,1-dichloro-4-methyl-1,3-pentadiene which comprises heating 1,1,1,3-tetrachloro-4-methylpentane to a temperature of from about 170°C to about 190°C in the presence of from about 0.2 to 2.0 moles of a nitrogen base halide salt per mole of 1,1,1,3-tetrachloro-4-methylpentane, said nitrogen base halide salt being selected from the group consisting of tertiary amine hydrochlorides in which the substituents on the nitrogen atom are C4-C15 alkyl or C6-C8 cycloalkyl, N-alkyl alkyleneimine hydrochlorides in which the -alkyl group contains from 1 to 3 carbon atoms and the alkylene group contains from 4 to 6 carbon atoms, quinoline hydrochlorides, and tetraalkylammonium chlorides with a total of 16 to 32 carbon atoms.