Hydrates of Organic Compounds. V. The Clathrate Hydration of Alcohols

A new method for examining the ability of a given substance to form a hydrate with the same structure as that of a reference substance has been established. By using this method, for a series of alcohols ranging from methyl alcohol to pentyl alcohol, including their isomers, the ability to form a clathrate hydrate of either Structure I or Structure II has been investigated. It has been found that: (1) methyl alcohol has the ability to form both Structure I and II hydrates; (2) ethyl alcohol has the ability to form a Structure II hydrate; (3) all C3-alcohols (propyl, isopropyl, allyl, and propargyl alcohol) can actually form Structure II hydrates with relatively high (around −10 °C) incongruent melting points, and (4) among the C4- and C5-alcohols, only t-butyl alcohol has the ability to form a Structure II hydrate. However, it is uncertain for methyl and ethyl alcohols whether they actually can form such hydrates even in the absence of a reference substance. These results strongly suggest that the size and/or shape limitation plays an important role in the formation of alcohol hydrates with a gas-hydrate structure, just as has been found for the formation of ether and ketone hydrates.