Quantitative assessment of the effect of anhydrous zinc chloride catalysis on the synthesis of some imine derivatives in toluene

Abstract

Imines are formed when any primary amines react with an aldehyde or a ketone under specific conditions. The classical synthesis reported by Schiff involves the condensation of a carbonyl compound with an amine under azeotropic distillation. In the 1990s an in-situ method for water elimination was developed using dehydrating solvents such as tetramethyl orthosilicate or trimethyl orthoformate another way to remove the water by-product is to use substances that function as Bronsted-Lowry or Lewis acids like ZnCl₂, TiCl₄, MgSO₄, H₃COOH, Mg(ClO₄)₂ to activate the carbonyl group of benzaldehyde, catalyse the nucleophilic attack by amines, and dehydrate the system, and eliminate water as the final steps. Anhydrous zinc chloride has been extensively used in literature for its affordability and reliability, however there is limited information if any, of its quantitative effects in synthesis, this has prompted this present study. The reaction involved the condensation between 4-Methoxybenzaldehyde and para- substituted aniline derivatives (4-chloroaniline, 4-nitroaniline and 4-methylaniline) in toluene. The reaction process was evaluated to determine the effect of temperature, concentration of anhydrous zinc chloride and effect of microwave assisted synthesis on the yield of the products. Results show that increasing the concentration anhydrous zinc chloride at elevated temperature increases the yield of the imine derivatives studied.

Keywords: Imines, anhydrous zinc chloride, toluene, microwave assisted synthesis