One-pot synthesis of cyclic aldol tetramer and a, β-unsaturated aldol from linear aldehydes using quaternary ammonium combined with sodium hydroxide as catalysts

XU Hai-feng(许海峰)^{1, 2}, ZHONG Hong(钟宏)^{1, 2}, WANG Shuai(王帅)^{1, 2}, LI Fang-xu(李方旭)^{1, 2}

(1. School of Chemistry and Chemical Engineering, Central South University, Changsha 410083, China;
2. Key Laboratory of Resources Chemistry of Nonferrous Metals of Ministry of Education (Central South University),
Changsha 410083, China)

Abstract:One-pot synthesis of cyclic aldol tetramer and a, β-unsaturated aldol from C₃-C₈ linear aldehydes using phase-transfer catalyst (PTC), quaternary ammonium, combined with sodium hydroxide as catalysts was investigated. Butanal was subjected for detail investigations to study the effect of parameters. It was found that the selectivity of cyclic aldol tetramer depends greatly on the operating conditions of the reaction, especially the PTC/butanal molar ratio. The average selectivity of 2-hydroxy-6-propyl-l, 3, 5-triethyl-3-cyclohexene-1-carboxaldehyde (HPTECHCA) was 54.41% using tetrabutylammonium chloride combined with 14% (mass fraction) NaOH as catalysts at 60 °C for 2 h with a PTC-to-butanal molar ratio of 0.09:1. Pentanal was more likely to generate cyclic aldol tetramer compared with other aldehydes under the optimum experimental conditions. Recovery of the PTC through water washing followed by adding enough sodium hydroxide from the washings was also demonstrated.

Key words:aldol condensation; one-pot synthesis; phase-transfer catalyst; aldehyde