Some physicochemical studies on organic eutectics and inter-molecular compounds

Abstract

Phase diagrams of o-phenylenediamine (OPDA)–N,N-dimethylaminobenzaldehyde (DMAB) and salicylamide (SAM)–m-nitro benzoic acid (NBA) systems, determined by the thaw-melt method, show the formation of two eutectics and one inter-molecular compound (IMC) in each case. These inter-molecular compounds were synthesized by the solvent-free method involving thermally initiated molten state reactions. Their characterization by the IR and the 1H NMR techniques suggest the formation of a new compound. Absorption spectrum of IMC of OPDA–DMAB system shows band at 245 nm due to the π → π* transition and another broad band observed from 280 to 440 nm is attributed to the n → π* transition. Their IMC shows fluorescence at 388 nm with a Stokes shift (93 nm) and quantum efficiency (0.0032) upon excitation at 350 nm in ethyl alcohol. Emission and absorption were observed in case of SAM–NBA system too. While the values of enthalpy and entropy of fusion of inter-molecular compound in case of OPDA–DMAB are 23.58 kJ mol−1 and 57.20 J mol−1, respectively, in the case of SAM–NBA system the corresponding values are 69.50 kJ mol−1 and 170.00 J mol−1. The values of interfacial energy in case of OPDA–DMAB and SAM–NBA inter-molecular compounds are 37.84 × 10−3 and 40.39 × 10−3 J m−2, respectively.