DEHYDROBROMINATION OF SUBSTITUTED alpha -HALOCUMENE

Abstract: A process for preparing substituted alpha-methylstyrene by heating the corresponding alpha-halocumene to a temperature up to 130 DEG C. Water and optionally an organic compound are used as solvent.

Description: DEHYDROBROMINATION OF SUBSTITUTED -HALOCUMENE The present invention relates to processes for preparing su-bstituted α-methylstyrenes. Substituted α-methylstyrenes are compounds useful as intermediates for preparing pesticides, such as herbicides and insecticides, and elastomer compositions. U.S. Patent 3 J 067 > 182 describes a process for 0 preparing isopropenylbenzyl chloride in which isopropylbenzyl chloride (89 percent para-, 11 percent ortho) is chlorinated, and the chlorinated material is distilled at a boiling point of 73°C to 7*°C at 0.01 to 5 0.05 millimeters of mercury pressure absolute (1.33 to 6.67 Pa) to yield isopropenylbenzyl chloride. Inherently, this process operates at very low, sub- atmospheric pressures. In order to provide such low pressures, fairly sophisticated and expensive pressure 0 reduction vessels are used. U.S. Patent 1,687.903 describes a process wherein styrols are prepared from chlorethylbenzols by £ - heating the chlorethylbenzols to decomposition tεmperatures ranging from 500-725°C. Clearly, such a process has the disadvantage of large energy requirements to maintain such high temperatures. U.S. Patent 4,59*4,467 describes a process wherein 3 . 5-dichloro-α-methylstyrene is prepared by dehydrobromination of α-bromo-3.5-dichlorocumene, in an alkaline medium at a temperature above 70°C, using a quaternary ammonium phase-transfer catalyst. Processes utilizing a caustic or basic medium, such as sodium hydroxide (NaOH) are incompatible with reaction vessels which are glass lined. While some of these processes may generally 5 achieve good yields, they have the disadvantage of requiring the use of expensive and often toxic catalysts which must be removed at the completion of the reaction. This separation of the.catalyst from the reaction mixture and its disposal often requires the 0 use of multiple handlings. After separation, the phase transfer catalyst requires waste disposal and/or recycling procedures using elaborate and expensive recycling apparatus. It would clearly be desirable to c provide a process which makes unnecessary the need to utilize catalysts. The present invention is directed to a process for preparing a substituted α-methylstyrene "compound of 0 the formula: 5 wherein R represents halogen, an alkyl group having from 1 to 6 carbon atoms, an alkoxy group having from 1 to 6 carbon atoms or trifluoromethyl and n represents 0, 1, 2, 3. 4 or 5; characterized by (a) heating, under ambient pressures, a mixture of water and α-halocumene compound of the formula: wherein X is chloro, bromo or iodo; to a temperature effective to convert the α-halocumene compound to α-methylstyrene compound; and (b) separating the α-methylstyrene compound formed therein from said mixture. In the desired α-methylstyrene of Formula (I), preferably R is chloro and n is 2. Also, preferred is that R is substituted in the 3- and 5-positions on the phenyl ring. Most preferably, R is chloro, n is 2 and R is substituted at the 3- and 5-positions on the ring, a compound known as 3.5-diehloro-α-methylstyrene (DCAMS). -_ Regarding the α-halocumene starting material of Formula (II), preferably X is bromo. Also preferred, is that R is chloro and n is 2. Also preferred is that R is substituted in the 3- and 5-position on the ring. Most preferably, X is bromo, R is chloro, n is 2 and R 10 is substituted at the 3- and 5-position on the ring, a compound known as α-bromo-3,5-dichlorocumene (BrDCC) . The present invention has the advantage of preparing substituted α-methylstyrenes without the need 15 for catalysts, while providing substituted α-methyl¬ styrenes in yields and purity as good or better than that described by other known methods. The heating of the α-halocumene starting 20 material of Formula II with water, and optionally with an organic solvent, is carried out at temperatures ranging from ambient to 130 degrees Centigrade (°C), preferably from 95° to 115°C. 25 Optionally, the reaction mixture may also contain a liquid inert organic solvent in an amount effective to at least dissolve the α-halocumene compound of Formula II so as to improve handling of this starting material. Representative inert organic 30 solvents suitable for dissolving the α-halocumene compound include but are not limited to halogenated aromatic and aliphatic hydrocarbons such as monochlorobenzene, chloroform, carbon tetrachloride; or , c 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 2 parts by weight inert organic solvent to 1 part by weight α-halocumene, preferably from 0 to 1 5 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 10 in association with the α-halocumene of Formula II should be an amount effective to promote dehydrohalo- genation of said α-halocumene. Generally, water is present in an amount ranging from 1 to 4 parts by weight α-haiocumene to one part by weight water, 15 preferably from one part water to 1.1 to 1 part by weight α-halocumene. The reaction mixture of water ,and α-halocumene may contain minor amounts of impurities such as metal 20 or base contaminants. Such impurities may be present in amounts which allow- the process to operate substantially the same way to give substantially the same results as if the process were run using a mixture c - which does not possess added or inherent impurities. The heating of the α-halocumene and water, and optionally, organic solvent should be maintained for a period effective to convert the α-halocumene to 30 α-methylstyrene, preferably from 1 to 24 hours, more preferably from 2 to 6 hours. The reaction mixture should be stirred during the course of the heating. Separation to recover the desired α-methyl- -,,- styrene compound of Formula I from the reaction mixture can be accomplished by phase separation of the aqueous and organic layers, i.e., decanting the aqueous layers. The decanted organic layer containing the desired α-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. Example 1 A sample of 273•2 g of crude α-bromo-3,5- -dichlorocumene (BrDCC-62.4 percent purity) with the balance monochlorobenzene (MCB) was treated with 100 milliliters (ml) water, and the mixture was stirred and heated at 100-105 degrees Centigrade (°C) for 3.5 hours. Phase inversion of the water and the organic layer occurred after 1 hour. After 3.5 hours an additional 50 ml water was added, and the mixture was heated an additional 2 hours. The mixture was allowed to cool, the phases were separated by decantation, the product phase was washed with an additional 25 ml water, and the aqueous phase was extracted with an additional 10 ml monochlorobenzene (MCB). The crude product weighs 225.4 g and contains 50.8 percent 3,5-dichloro-α- meth 1styrene (DCAMS-96 percent yield) . Distillation was done through a short vigreaux column. Monochlorobenzene was removed at 15-20 millimeters (mm) mercury (Hg) (2000 " to 2666 Pa) at an overhead temperature of 35°C. The fraction containing 3,5-dichloro-α-methylstyrene was taken at an overhead temperature of 108-110°C. The product cut contains a 94 percent yield of 3,5-dichloro-α-methylstyrene. Example 2 A sample of 124.3 g of crude solvent-free α-bromo-3 > 5-dichlorocumene (BrDCC-91 percent purity) and 93 ml of water were stirred and heated at 100-110°C for 3 hours. The mixture was allowed to cool, the phases were separated by decantation, and the product phase washed with 10 ml water. The product was distilled through a short vigreaux column under vacuum with an overhead temperature of 157-160°C and the pot temperature was maintained at 155-200°C. The overheads contain a 95 percent yield of 3.5-dichloro-α-methyl- styrene.

Claims: CLAIMS 1. A process for preparing a substituted α-methylstyrene compound of the formula: wherein R represents halogen, an alkyl group having from 1 to 6 carbon atoms, an alkoxy group having from 1 to 6 carbon atoms or trifluoromethyl and n represents 0, 1, 2, 3 ? 4 or 5; characterized by (a) heating, under ambient pressures, a mixture of water and α-halocumene compound of the formula: wherein X is chloro, bromo or iodo; to a temperature effective to convert the α-halocumene compound to α-methylstyrene compound; and (b) separating the α-methylstyrene compound formed therein from said mixture. 2. The process of Claim 1 wherein the reaction mixture is heated to a temperature ranging between ambient to 130 degrees Centigrade. 3. The process of Claim 1 wherein the reaction mixture is heated to a temperature ranging between 95 to 115 degrees Centigrade. .4. The process of Claim 1 wherein water is present in an amount ranging from 1 to 4 parts by weight to 1 part by weight α-halocumene compound. 5. The process of Claim 1 wherein the water is present in an amount ranging from 1.1 to 1 part by weight to 1 part by weight α-halocumene compound. 6. The process of Claim 1 wherein the reaction mixture of water and the α-halocumene compound also contains an inert organic solvent in an amount effective to dissolve said α-halocumene compound. 7. The process of Claim 6 wherein the inert organic solvent is a halogenated aromatic or aliphatic hydrocarbon. 8. The process of Claim 7 wherein the inert solvent is monochlorobenzene, chloroform or carbon tetrachloride. 9. The process of any one of Claims 1 to 8 wherein the α-halocumene compound of Formula II, R is chloro, X is bromo and n is 0, 1 or 2. 10. The process of any one of Claims 1 to 8 wherein the α-halocumene compound is α-bromo-3 > 5- dichlorocu ene.

Inventors: JOHNSON MARK R, JOHNSON, MARK, R.
Applicants: DOW CHEMICAL CO, THE DOW CHEMICAL COMPANY
Application year: 1988
Main classification: C07C17
IPC codes: C07C17