Reactions of cyclopropylcarbinol in dilute hydrochloric acid

Abstract

The treatment of cyclopropylcarbinol (1-OH) with dilute HCl bas been used as a method for the preparation of cyclobutanol (2-OH). While 2-OH is the major product in this reaction, a careful investigation showed the presence of a total of 13 products, namely, the alcohols 1-OH, 2-OH, and allylcarbinol (3-OH), cyclopropylcarbinyl, cyclobutyl and allylcarbinyl chlorides (1-Cl, 2-Cl and 3-Cl, respectively), dicyclopropylcarbinyl, cyclobutyl cyclopropylcarbinyl, allylcarbinyl cyclopropylcarbinyl, dicyclobutyl and allylcarbinyl cyclobutyl ethers (1-O-1, 2-O-1, 3-O-1, 2-O-2, and 3-O-2, respectively), as well as butyraldehyde and isobutyraldehyde. The alcohols, chlorides, and ethers likely arose from reactions of the bicyclobutonium ion with available nucleophiles in the reaction mixture. The minor amounts of the two aldehydes may be due to a ring opening isomerization of 2-methylcyclopropanol, the latter in turn resulted from a net 1,3-hydride shift in the cyclopropylcarbinyl cation, probably via an edge-protonated cyclopropane-type of species. Treatment of [α-14C]cyclopropylcarbinol (1-OH-α-14C) with dilute HCl gave samples of 1-OH-x-14C, 2-OH-x-14C, and 3-OH-x-14C the degradation of which showed that ail three methylene groups in these alcohols have become equivalent, indicating a complete equilibration between isotope-position labeled bicyclobutonium ions.