STUDIES ON THE ALKYLATION OF QUINIZARIN

Abstract

Quinizarin a precursor to anthracyclines was subsequently alkylated with α, β-unsaturated aldehydes - crotonaldehyde, acrolein and ethyl acrylate using piperidinium acetate as a catalyst and ethanol as solvent. Quinizarin was synthesized using phthalic anhydride and parachlorophenol with concentrated sulphuric acid as solvent and catalyst in synergism with boric acid at 2600C to give a yield of 36.3%, then reduced to leucoquinizarin using Sn in concentrated hydrochloric acid with glacial acetic acid as solvent and refluxed for five hours to give a yield of 35.6%. The alkylating reagent crotonaldehyde was synthesized by aldol condensation of acetaldehyde with concentrated sulphuric acid as catalyst at a yield of 27.1% while acrolein was synthesized by the dehydration of glycerol using potassium bicarbonate as catalyst at a yield of 94.8%. Leucoquinizarin was alkylated with crotonaldehyde, acrolein and ethyl acrylate using piperidinium acetate as a catalyst in ethanol. The alkylation with crotonaldehyde and ethyl acetate was done by reflux for three and five hours respectively and resulted in a 1, 4 addition and a subsequent aldol annelation reaction accompanied by a 1,3 sigmatropic shift to give a pentacyclic ring at a yield of 42.1% and 61% respectively. Acrolein gave a polymeric product.