Self- and Cross-Aldol Condensation of Propanal Catalyzed by Anion-Exchange Resins in Aqueous Media

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title = "Self- and Cross-Aldol Condensation of Propanal Catalyzed by Anion-Exchange Resins in Aqueous Media",
abstract = "Carbon-carbon bond formation using strong and weak anion-exchange resins as green catalysts for self- and cross-aldol condensation of propanal in aqueous media was investigated. The reaction pathway followed the route of aldol condensation to a beta-hydroxy aldehyde and dehydration to an alpha,beta-unsaturated aldehyde. The resulting products were further converted to hemiacetal, and/or acetal moieties, which were confirmed by FT-IR and NMR. In self-condensation using strong anion-exchange resin, 97{\%} conversion of propanal was achieved with 95{\%} selectivity to 2-methyl-2-pentenal within 1 h using 0.4 g/mL resin at 35 degrees C. The conversion and selectivity using weak anion exchanger was lower. During cross-aldol condensation of propanal with formaldehyde, 3-hydroxy-2-methyl-2-hydroxymethylpropanal was obtained as the main product through first and second cross-condensation followed by hydration reaction in acidic aqueous conditions. The strong anion-exchange resin provided maximal propanal conversion of 80.4{\%} to the product with 72.4{\%} selectivity after 7 h reaction at 35 degrees C and resin concentration of 1.2 g/mL. Using weak anion-exchange resin, the optimal conversion of propanal was 89.9{\%} after 24 h at 0.8 g/mL resin and 35 degrees C, and the main product was 3-hydroxy-2-methylpropanal by first cross-aldol condensation along with relatively minor amounts of methacrolein and 3-hydroxy-2-methyl-2-hydroxymethylpropanal.",
author = "Sang-Hyun Pyo and Martin Hedstr{\"o}m and Stefan Lundmark and Nicola Rehnberg and Rajni Hatti-Kaul",
year = "2011",
doi = "10.1021/op200004p",
language = "English",
volume = "15",
pages = "631--637",
journal = "Organic Process Research and Development",
issn = "1083-6160",
publisher = "The American Chemical Society (ACS)",
number = "3",