A study of the cyclodehydrohalogenation of 12-(2-chloro-5- methylphenyl)benz[a]anthracene

TR Number
Journal Title
Journal ISSN
Volume Title
Virginia Polytechnic Institute

In the study of the cyclodehydrogenation of 12-(3-methylphenyl)benz[a]anthracene, Zajac pointed out that the hydrocarbon might undergo ring closure at either of the ortho positions of the phenyl ring. These positions are not equivalent with respect to the methyl group and ring closure might yield either 2-methyl dibenzo[a,l]pyrene or 4-methyldibenzo[a,l]- pyrene or a mixture of both isomers.

When the compound, 12-(J-methylphenyl)benz[a]-anthracene, was dehydrogenated only one isomer was isolated. The isomer which was isolated could be either of the two possibilities. Therefore, it was decided to synthesize 2-methyldibenzo[a,l]pyrene unequivocally. By comparing the physical properties of the compound synthesized unequivocally with those of the compound from the cyclodehydrogenation of 12-(3-methylphenyl)benz[a]anthracene it can be determined which isomer was isolated by Zajac. Therefore, 12-{ 2-chloro-5-methylphenyl)benz[a]-anthracene was synthesized; this compound could then be cyclodehydrohalogenated to the corresponding 2-methyldibenzo[a,l]]pyrene. Using potassium hydroxide-quinoline and alkoxides led only to the recovery of starting material or to the destruction of it, depending on whether the reaction conditions were mild or drastic. Aluminum chloride destroyed the starting material in reaction time as short as five minutes. Stannic chloride destroyed only part of the starting material. An aluminum chloride-stannic chloride mixture also destroyed the starting material. In none of the experiments mentioned could the presence of 2-methyldibenzo[a,l]pyrene be detected. Although the right conditions for the cyclodehydrohalogenation were not found, the data obtained during the gas chromatographic studies are very valuable because it can be used for the other phases of the work being done in This Laboratory.