Abstract
The solubilization of barbiturates by chloral hydrate was investigated by solubility measurement and a molecular interaction was found to be due to the hydrogen bonding from infrared and 1H-and 13C-nuclear magnetic resonance (NMR) spectra. In water the stability constants of 1 : 2 complex, K1 : 2' were larger than those of 1 : 1 complex, K1 : 1. The stability constants in benzene were larger compared to those in water. For the N-methyl series K1 : 2 values could not be obtained. The stability constants decreased with increasing of the polarity of solvent and pKa of proton donors. It was found that chloral hydrate had the extraordinary reactivity in molecular interaction. The intensities of the OH strechting bands of chloral hydrate decreased by the addition of phenobarbital and a new band due to the hydrogen bonded OH appeared. The OH protons of chloral hydrate shifted to downfield by the addition of metharbital. Meanwhile, the 13C signals of carbonyl groups at 2-and 4-or 6-C of hexethal shifted to lower field in the presence of chloral hydrate. The former shift occurs to the farthest at the lower concentration of ligand and the latter proceeds with the increase of ligand. This may indicate that 2-carbonyl group forms the hydrogen bond with chloral hydrate preceedingly and 4-or 6-carbonyl group participates subsequently.
