Hydrates of Organic Compounds. XIII. The Confirmation of the Formation of Clathrate-Like Hydrates of Tetrabutylammonium and of Tetraisopentylammonium Polyacrylates

A thermal analytic method using a differential scanning calorimeter has been applied to aqueous solutions of a series of tetraalkylammonium polyacrylates ((R4NOOCCHCH2)n; R=CH3, C2H5, n-C3H7, n-C4H9, n-C5H11, and i-C5H11). It was found that only tetrabutylammonium polyacrylate and tetraisopentylammonium polyacrylate could form stable hydrates having a large number of moles of water per single R4NOOCCHCH2 unit of the polyacrylates (hydration numbers). The melting points and hydration numbers of these two hydrates were 11.2 °C, 30±1 for the tetrabutylammonium polyacrylate hydrate and 19.5 °C, 42±2 for the tetraisopentylammonium polyacrylate hydrate, respectively. Judging from the melting points, hydration numbers, and the concentration dependence of the dissolution temperatures, these hydrates were regarded as clathrate-like. The tetrabutylammonium polyacrylate hydrate seems to be iso-structural with (n-C4H9)4NF hydrate and the tetraisopentylammonium polyacrylate hydrate with (i-C5H11)4NF hydrate.