Cyclization of alkanediols in high-temperature liquid water with high-pressure carbon dioxide

Dehydration of 1,4-butanediol (1,4-BDO) to tetrahydrofuran (THF), 2R,5R-hexanediol (2R,5R-HDO) to 2,5-dimethyltetrahydrofuran (2,5-DMTHF), and 2,5-dimethyl-2,5-hexanediol (2,5-DM-2,5-HDO) to 2,2,5,5-tetramethyltetrahydrofuran (2,2,5,5-TMTHF) proceeded in high-temperature liquid water at 523 K. The formation rates of cyclic ethers were enhanced by high-pressure carbon dioxide (16.2 MPa). The order of dehydration rates in high-temperature water with carbon dioxide was 2,5-DM-2,5-HDO > 2R,5R-HDO > 1,4-BDO (tertiary > secondary > primary alcohols), which was the same order as the stability of corresponding carbocation species.

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► An environmentally benign technique with water and carbon dioxide is applied for catalytic dehydration of primary, secondary, and tertiary alcohols.
► Intramolecular cyclization of alcohols proceeds in high-temperature water and the rates are enhanced by the addition of high-pressure carbon dioxide.
► The order of intramolecular dehydration rates is tertiary > secondary > primary alcohol.