Hydrates of Organic Compounds. VIII. The Effect of Carboxylate Anions on the Formation of Clathrate Hydrates of Tetrabutylammonium Carboxylates

The solid-liquid phase diagrams of binary mixtures of tetrabutylammonium carboxylates, (n-C4H9)4 NOOCR (R=H-n-C10H21 including various alkyl groups replaced by either methyl or ethyl group), with water were examined in order to confirm the formation of clathrate-like hydrates. The results can be summarized as follows: (1) for 14 carboxylates the formation of a clathrate-like hydrate is newly confirmed; (2) judging from melting points and hydration numbers, the hydrates can be classified into three groups: I, II, and III; (3) the group I hydrates, formed by the carboxylates with R=H, CH3, C2H5, n-C3H7, i-C3H7, and t-C4H9, have hydration numbers around 30 and are the most stable hydrates among those examined in this experiment, with the exceptions of 2-methylpropionate and 2,2-dimethylpropionate hydrates; (4) the group II hydrates, with hydration numbers around 39, are formed by the salts with R=n-C4H9, s-C4H9, i-C4H9, and all the C5H11, and are relatively unstable (mp=5–11 °C); (5) the group III hydrates, ...