A Study Involving the Synthesis of Unsymmetrical Dibenzylcarbinols

The synthesis of some unsymmetrical dibenzylcarbinols was attempted through a Grignard reaction involving para-substituted benzyl halides and phenylacetaldehyde. It was found that the Grignard reaction does not produce the desired carbinols. Evidence is presented to show that the Grignard reagent initiates an aldol condensation of the phenylacetaldehyde which is further catalyzed by the alkoxide ions formed in the reaction. The resulting aldol undergoes a Grignard reaction to form a substituted pentanediol which partially dehydrates upon distillation at reduced pressure. A reaction mechanism is proposed to account for the formation of the reaction products. An alternate synthetic route was proposed for the preparation of unsymmetrical dibenzylcarbinols, and 1-phenyl-3-(p-chlorophenyl)-2-propanol was successfully prepared in this manner. The 3, 5-dinitrobenzoate and the phenylurethan derivatives of this carbinol were also prepared. This is the first reported synthesis for 1-phenyl-3-(p- chlorophenyl)-2-propanol.