Cyclodimerization of crotonaldehyde to form cyclohexadienecarbaldehydes and tolaldehydes over solid base catalysts

• Published in: Reaction kinetics, mechanisms and catalysis Vol. 105; no. 2; pp. 401 - 412
• Main Authors: Kurokawa, Hideki, Yanai, Masashi, Ohshima, Masa-aki, Miura, Hiroshi
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 01.04.2012
• Subjects: Catalysis; Chemistry; Chemistry and Materials Science; Industrial Chemistry/Chemical Engineering; Physical Chemistry; Magnesium oxide; α, β-Unsaturated aldehydes; Calcium oxide
• ISSN: 1878-5190; 1878-5204
• DOI: 10.1007/s11144-011-0381-5

The cyclodimerization of crotonaldehyde was performed over acid or base catalysts in the gas phase. We first attempted the reaction over various acid and base catalysts using a pulse reactor. The typical bases, CaO and MgO, effectively promoted the reaction to form methylcyclohexadienecarbaldehydes (MCHC) and tolaldehydes. In contrast, no significant formation of the dimers was observed over the acid catalysts, such as SiO 2 –Al 2 O 3 and H-mordenite. Aluminum oxide also promoted the dimerization, indicating that the dimerization proceeds on the weaker base sites. The main products in the formed dimers were 6-methylcyclohexa-1,3-dienecarbaldehyde and o -tolualdehyde. In addition, small amounts of 4-methylcyclohexa-1,5-dienecarbaldehyde and p -tolaldehyde were produced as dimers. When the dimerization was performed over CaO, MgO, and Al 2 O 3 using a fixed-bed flow reactor, the catalytic activities of all the catalysts significantly decreased during the initial stage of the reaction. The TG–DTA analysis of the used catalysts clearly indicated that a large amount of the condensation products had adsorbed on the catalyst surface. The maximum selectivity to the dimers (MCHC and tolaldehydes) was 38% for an approximate 30% conversion, which was obtained during the initial stage of the reaction over the Al 2 O 3 and CaO catalysts.