Intermolecular hydrogen bonds and proton transfer equilibrium in some nitro cresols-aliphatic amines-acetonitrile or methanol systems

Abstract

Intermolecular hydrogen bonds between two nitro cresols, 2-nitro-4-methylphenol (NMP) and 3-methyl-4-nitrophenol (MNP) with three aliphatic amines morpholine (MO), Benzylamine (BA) and triethylamine (TEA) have been investigated in acetonitrile and methanol applying UV-Vis spectroscopy. It has been found that the proton transfer complex formation is retarded in acetonitrile leading to a sharp decrease in the proton transfer equilibrium constants (K PT). On the other hand, the proton transfer complex formation is strongly favored in methanol leading to a sharp increase in K PT. The presence of a single ortho substituent and strong intramolecular hydrogen bond does not inhibit the proton transfer process. It has been recorded from this work that the intramolecular hydrogen bond is not broken in acetonitrile but broken in methanol. It has been found alsa that TEA is sterically hindered in forming hydrogen bonds when compared to primary and secondary amines. Moreover, the present contribution proved that acetonitrile binds the phenol OH as hydrogen bonding proton acceptor while methanol binds as a proton donor with the phenol OH.