A process for preparing ring-halogenated .alpha.-methylstyrenes from the corresponding .alpha.-halocumenes is disclosed. The dehydrohalogenation is accomplished using only water and optionally an organic solvent. The process eliminates the need for added base and a phase-transfer catalyst.

FIELD OF THE INVENTION 
The present invention relates to a process for preparing ring-substituted 
.alpha.-methylstyrenes. More particularly the present invention relates to 
the preparation of ring halogenated .alpha.-methylstyrenes by the 
dehydrohalogenation of the corresponding ring-halogenated 
.alpha.-halocumenes. 
BACKGROUND OF THE INVENTION 
Ring-halogenated .alpha.-methylstyrenes are intermediates for the 
preparation of plant-protection agents (see, for example, U.S. Pat. No. 
4,211,548). U.S. Pat. No. 4,594,467 describes a process in which 
3,5-dichloro-.alpha.-methylstyrene is prepared by the dehydrobromination 
of .alpha.-bromo-3,5-dichlorocumene with an alkali metal hydroxide 
solution in the presence of a phase-transfer catalyst above 70degrees 
Centigrade (.degree.C.). While this process enjoys excellent yields, it 
has the disadvantage of requiring the use of expensive and often toxic 
phase-transfer catalysts that must be removed after completion of the 
reaction. The separation of catalyst from the reaction mixture often 
requires multiple unit operations. After separation, the phase-transfer 
catalyst requires recycle or disposal. It would be clearly beneficial to 
have an efficient process that eliminates the need of the phase-transfer 
catalyst. 
Furthermore, the process described hereinabove utilizes a caustic or basic 
medium such as, for example, sodium hydroxide. Such caustic solutions are 
incompatible with glass-lined vessels. Again, it is highly desirable to 
have a process that does not require the addition of a base to accomplish 
the desired elimination. 
SUMMARY OF THE INVENTION 
The present invention is directed to a process for preparing a 
ring-halogenated c-methylstyrene compound of the Formula (I) 
##STR1## 
wherein 
R represents halogen and n represents 1 or 2 which comprises contacting a 
ring-halogenated .alpha.-halocumene compound of the Formula (II) 
##STR2## 
wherein 
X is chloro or bromo and R and n are as previously defined with water at 
ambient pressure and at a temperature from about 70.degree. to about 
130.degree. C. in the absence of an added base and in the absence of a 
phase-transfer catalyst. 
As used herein, the term halogen refers to fluorine, chlorine, bromine and 
iodine. 
With respect to the ring-halogenated .alpha.-methylstyrene of Formula (I), 
R is preferably chloro, and n is preferably 2. It is also preferred that R 
is substituted in the 3- and/or 5-positions of the phenyl ring. Most 
preferably, R is chloro, n is 2, and R is substituted at the 3- and 
5-positions on the ring, i.e., the compound known as 
3,5-dichloro-.alpha.-methylstyrene. 
With respect to the ring-halogenated .alpha.-halocumene of Formula (II), X 
is preferably bromo. It is also preferred that R is chloro, and n is 2. It 
is further preferred that R is substituted in the 3-and/or 5-positions of 
the phenyl ring. Most preferably, X is bromo, R is chloro, n is 2, and R 
is substituted at the 3- and 5-positions on the ring, i.e., the compound 
known as .alpha.-bromo-3,5-dichlorocumene. 
The present invention has the advantage of preparing ring-halogenated 
.alpha.-methylstyrenes without the need for a phase-transfer catalyst and 
without the need for an added base.

DETAILED DESCRIPTION OF THE INVENTION 
The heating of the .alpha.-halocumene starting material of Formula (II) 
with water is carried out at temperatures ranging from about 70.degree. to 
about 130.degree. C., preferably from about 95.degree. to about 
115.degree. C. 
Optionally, the reaction mixture may also contain a liquid inert organic 
solvent in an amount effective to at least dissolve the .alpha.-halocumene 
compound of Formula (II) so as to improve the handling of this starting 
material and the recovery of the product. Representative inert organic 
solvents suitable for dissolving the .alpha.-halocumene compound include 
but are not limited to halogenated aromatics and aliphatic hydrocarbons 
such as chlorobenzene, chloroform, carbon tetrachloride; or non-halogen 
containing aromatic or aliphatic hydrocarbons such as benzenes, xylenes, 
hexane, cyclohexane, pentanes, etc. Generally, the inert organic solvent 
can be present in an amount ranging from 0 to about 2 parts by weight 
inert organic solvent to about 1 part by weight .alpha.-halocumene, 
preferably from about 0 to about 1 part by weight inert organic solvent. 
Water, at least equivalent in quality to that used for industrial purposes, 
can be used in the process of the present invention. The amount of water 
in association with the .alpha.-halocumene of Formula (III) should be an 
amount effective to promote dehydrohalogenation of said 
.alpha.-halocumene. Generally, water is present in an amount ranging from 
about 1 to about 4 parts by weight .alpha.-halocumene to about one part by 
weight water, preferably from about one part water to about 1.1 to about 1 
part by weight .alpha.-halocumene. 
The heating of the .alpha.-halocumene and water, and optionally, organic 
solvent should be maintained for a period effective to convert the 
.alpha.-halocumene to .alpha.-methylstyrene, preferably from about 1 to 
about 24 hours (hr), more preferably from about 2 to about 6 hr. The 
reaction mixture should be stirred during the course of the heating. 
Separation to recover the desired .alpha.-methylstyrene compound of Formula 
(I) from the reaction mixture can be accomplished by phase separation of 
the aqueous and organic layers. The organic layer containing the desired 
.alpha.-methylstyrene compound can be treated by conventional procedures, 
such as stripping, distillation, or crystallization. 
The following examples illustrate the present invention in a manner by 
which it can be practiced but, as such, should not be construed as 
limitations upon the overall scope of the same. 
EXAMPLE 1 
A sample of 273.2 g of crude .alpha.-bromo-3,5-dichlorocumene (BrDCC-62.4 
percent purity) with the balance monochlorobenzene (MCB) is treated with 
100 milliliters (ml) water, and the mixture is stirred and heated at 
100.degree.-105.degree. C. for 3.5 hr. Phase inversion of the water and 
the organic layer occurs after about 1 hr. After 3.5 hr an additional 50 
ml water is added, and the mixture is heated an additional 2 hr. The 
mixture is allowed to cool, the phases are separated by decantation, the 
product phase is washed with an additional 25 ml water, and the aqueous 
phase is extracted with an additional 10 ml MCB. The crude product weighs 
225.4 g and contains 50.8 percent 3,5-dichloro- .alpha.-methylstyrene 
(DCAMS-96 percent yield). Distillation is done through a short Vigreaux 
column. MCB is removed at 15-20 millimeters (Mm) mercury (Hg) at an 
overhead temperature of 35.degree. C. The fraction containing 
3,5-dichloro- .alpha.-methylstyrene is taken at an overhead temperature of 
108.degree.-110.degree. C. The product cut contains a 94 percent yield of 
3,5-dichloro- .alpha.-methylstyrene. 
EXAMPLE 2 
A sample of 124.3 g of crude solvent-free .alpha.-bromo-3,5-dichlorocumene 
(BrDCC-91 percent purity) and 93 ml of water are stirred and heated at 
100.degree.-110.degree. C. for 3 hr. The mixture is allowed to cool, the 
phases are separated by decantation, and the product phase washed with 10 
ml water. The product is distilled through a short Vigreaux column under 
vacuum with an overhead temperature of 157.degree.-160.degree. C. and the 
pot temperature is maintained at 155.degree.-200.degree. C. The overheads 
contain a 95 percent yield of 3,5-dichloro-.alpha.-methylstyrene.