Side-chain alkylation of heterocyclic compounds over modified zeolites

Abstract

The reaction of 2-methylpyrazine with formaldehyde to 2-vinylpyrazine and also the reaction of 4-picoline with benzaldehyde were carried out over modified basic zeolite catalysts. The side-chain alkylation of 2-methylpyrazine with formaldehyde was carried out at 300°C and 0.5 h 1 weight hourly space velocity over alkali or alkaline earth metal ion modified basic zeolites. The molar ratio of 2-methylpyrazine: formaldehyde: water was 1:2:1. The catalyst used was 4 g with 18-30 mesh size and feed rate was 2 ml.h 1 . The selectivities of 2-vinylpyrazine were >98 at 23.5, 22.0, 16.0, 18.9 and 21.8 percent conversions of 2-methylpyrazine over K-ZSM-5 (SiO 2 /Al 2 O 3 = 30, 3 wt% K), Rb-ZSM-5 (30), Sr-ZSM-5 (30), Ba-ZSM-5 (30) and K-Cs-ZSM-5 (30, 1 wt% Cs & 3 wt% K), zeolites at time on stream= 6 h, respectively. In case of Cs + , Mg 2+ and Ca 2+ , the catalyst was deactivated due to the coking and the conversions were decreased <10 percent. We have studied the effects of reaction temperature, variation of the amount of water, mole ratio, weight hourly space velocity (W.H.S.V.), the calcination temperature, potassium (K) precursor, the amount of cation (K) promoter. The reaction of 4-picoline with benzaldehyde was carried out at 300°C and 0.5 h 1 W.H.S.V. The molar ratio of 4-picoline: benzaldehyde was 1:2. The liquid product selectivities of 4-pyridylstyrene were 93.1, 76.4, 89.2, 84.4, 90.8 and 78.9 percent at 26.2, 19.4, 45.3, 13.1, 19.4 and 20.1 wt percent conversion of 4-picoline over NaY, NaX, CsY (3 wt% Cs), KY (3wt% K), K-MCM-41 (4 wt%) and CeY (3 wt% Ce) catalysts respectively, we have studied the effects of various catalysts, reaction temperature, molar ratio and weight hourly space velocity. The alkali and alkaline earth metal ion modified basic zeolites are active in the side-chain alkylation of the substituted heterocyclic compounds.