Method for making o- and p- haloalkyl styrenes

#The invention relates generally to certain substituted styrenes and more particularly to the preparation of 3,4-dialkoxy styrenes and haloalkyl styrenes by dehydrohalogenation.

#It has been proposed that 3,4-dialkoxy styrenes (substituted styrenes) be prepared by dehydrohalogenating chloro-1-(3,4-dialkoxyphenyl)ethanes using pyridine as the dehydrohalogenating reagent. In the prior art, 3,4-(dimethoxy)styrenes have also been prepared by the thermal dehydration of 1-(3,4-dimethoxyphenyl)ethanol and by methylation of 4-hydroxy-3-methoxy styrene with methyl iodide or dimethyl sulfate. These methods have not been entirely satisfactory because the yields are rather low. Very low yields are obtained in the dehydrohalogenation process because of the formation of the quaternary salt of pyridine with the chloro compound. The thermal dehydration process is also relatively expensive because of the high temperature required for the reaction.

#It has also been proposed that haloalkyl styrenes be prepared by at least partially dehydrohalogenating halogenated haloalkylphenyl ethanes using pyridine as the dehydrohalogenating reagent. These styrenes have also been prepared by haloalkylating styrene. The same disadvantages that the use of pyridine presents in its use in preparing dialkoxy styrenes occur in such methods.

#The substituted styrenes prepared according to the process of this invention correspond to the following formulae I and II: ##STR3## wherein each R.sub.1 is an alkyl radical of 1 to 4 carbon atoms and preferably methyl; ##STR4## wherein R.sub.2 is an alkylene radical of 1 to 4 carbon atoms and preferably methylene, and X is a halogen atom selected from the group consisting of chlorine, bromine, and iodine, and preferably is chlorine.

#In a stepwise method of preparation of the substituted styrenes, a 1-(3,4-dialkoxyphenyl)ethanol wherein each alkoxy moiety has 1 to 4 carbon atoms may be used as a starting material to prepare a compound of formula I. In the preferred embodiment, 1-(3,4-dimethoxyphenyl)ethanol is used. The starting material is converted in step (1) to its intermediate halogen derivative by reacting it with a suitable halogenating agent. Suitable halogenating agents are, for example, in chlorination, thionyl chloride; in bromination, hydrogen bromide, thionyl bromide, or phosphorus tribromide; in iodination, the standard iodinating agents, e.g. I.sub.2. For example, 1-(3,4-dimethoxyphenyl)ethanol is converted to 1-chloro-1-(3,4-dimethoxyphenyl)ethane by reaction with thionyl chloride.

#The halogen derivative is then in step (2) dehydrohalogenated by reaction with an amine acceptor of the generic formula: ##STR5## wherein R is an alkyl group of 1 to 6 carbon atoms, n is an integer having a value of from 1 to 5, and at least one alkyl group is attached to a carbon atom closest to the nitrogen atom and when n is more than 1, the alkyl groups may be the same or different groups, as the dehydrohalogenating reagent to prepare the formula I compound.