R.N. Rai

Physical Chemistry of Organic Eutectics

Phase diagrams of urea-α-naphthol and urea-benzoic acid systems, determined by the thaw-melt method, show the formation of simple eutectic in each case. The growth velocity data, determined at different undercooling (ΔT) by observing the rate of movement of interface in a capillary, obey the Hillig-Turnbull equation, v=u(ΔT)n, where u and n are constants depending on the nature of the materials. Using enthalpy of fusion, undercooling (ΔT) and melting point data, entropy of fusion, interfacial energy, enthalpy of mixing, critical radius size and excess thermodynamic functions were calculated. The microstructural investigations give characteristic features of the eutectics.

Solid-liquid equilibrium and thermochemical properties of organic eutectic in a monotectic system

The phase-diagram of an organic analogue of a metal-non-metal system, involving p-dichlorobenzene-succinonitrile (DCB-SCN), shows the formation of a eutectic and a monotectic with large miscibility gap in the system. The monotectic and the eutectic contain 0.0272 and 0.9429 mole fractions of SCN, respectively, and the critical temperature is 126 degreesC above the monotectic horizontal. The heat of mixing. entropy of fusion, roughness parameter, interfacial energy and excess thermodynamic functions wen calculated based on enthalpy of fusion data determined via differential scanning calorimeter method. The interfacial energy shows the applicability of wetting condition, while the microstructures of the pure components, namely, DCB and SCN show faceted and non-faceted morphology, those of the eutectic and the monotectic show peculiar characteristic features.

Synthesis, physicochemical and optical characterization of novel fluorescing complex: o-phenylenediamine-benzoin.

The complex of o-phenylenediamine (o-PDA) and benzoin (BN) was synthesized adopting solid state reaction by mixing of their melt together followed by chilling. The phase diagram study shows the formation of a complex in 1:1 molar ratio with congruent melting point and two eutectics lying on either side of complex. The formation of complex was confirmed using the FTIR, NMR, mass spectroscopy, powder XRD and DSC studies. The optical properties of the parent component, their complex and few other compositions nearby the complex were studied using absorption and laser luminescence techniques. The significantly higher green/yellow emission was noted with newly synthesized complex as compared to that of their parents as well as other compositions of o- PDA and BN.

Solid–liquid equilibrium, thermal and physicochemical studies of organic eutectics

The solid–liquid phase equilibrium data of two binary organic systems, namely, urea (U)–3-aminophenol (AP) and 3-hydroxybenzaldehyde (HB)–β-napthaol (BN) show formation of a eutectic in each case. The enthalpies of fusion of the pure components and binary eutectics have been determined using differential scanning calorimeter (Mettler DSC-4000) system. The thermal properties of the materials such as heat of mixing, entropy of fusion, roughness parameter, interfacial energy and excess thermodynamic functions were computed using the enthalpy of fusion values. The microstructures of eutectics were developed using unidirectional thermal gradient and interested region were photographed.

Solid-liquid equilibrium, thermal, and physicochemical studies on salicylamide-4-nitrophenol and 2-cyanoacetamide-4- aminoacetophenone organic eutectic systems

The solid–liquid phase equilibrium data of two binary organic systems, namely, salicylamide–4-nitrophenol and 2-cyanoacetamide–4-aminoacetophenone show the formation of a eutectic in each case. The values of enthalpy of fusion of pure components and binary eutectics have been determined using differential scanning calorimeter (Mettler DSC-4000 system). The thermal properties of the materials, such as, heat of mixing, entropy of fusion, roughness parameter, interfacial energy, and excess thermodynamic functions were computed using the enthalpy of fusion values. The microstructures of eutectics were developed using unidirectional thermal gradient, and regions of interest for microstructures were photographed.

Solidification behaviour of binary organic monotectic alloys

The solid-liquid equilibrium data on a faceted-nonfaceted system involving diphenyl and succinonitrile show the formation of a eutectic (0.9679 mole fraction of succinonitrile) and a monotectic (0.0742 mole fraction of succinonitrile) with a liquid miscibility gap in the system. From the linear velocity of crystallization data on the pure components, the eutectic and the monotectic, determined by the capillary method at different undercoolings, it can be inferred that they obey the Hillig-Turnbull equation. The microstructural investigations show peculiar characteristic features in the eutectic and the monotectic.

Remarkable dielectric properties of 1 : 2 inter-molecular compound of 2-(4-(dimethylamino) benzylideneamino) benzoic acid and urea due to excited-state intramolecular proton transfer

The phase diagram of 2-(4-(dimethylamino) benzylideneamino) benzoic acid (DMABAB)–urea (U) gives two eutectics E1 (mp 107.0 °C) and E2 (mp 138.0 °C) with 0.01 and 0.86 mole fractions of urea, respectively, and a 1 : 2 inter-molecular compound (IMC) with a congruent melting point of 219.0 °C, which has a high dielectric constant (e = 0.9 × 103) and reasonable electrical conductivity in the order ∼5 × 10−6 S m−1. This is due to the remarkable packing of U molecules in the IMC, where it shows coupling of two different types of cyclic hydrogen-bonded motifs alternating to form a corrugated sheet or chain of rings extending along the b axis via N–H⋯O hydrogen bonding interactions. In the presence of an electric field, an inter-molecular proton transfer process occurs in the NH⋯O bonds of the chain of the U molecules, which leads to disproportionate defects and the formation of polar domains on the macroscopic scale. An appropriate quantity of the IMC is synthesized via a green synthetic method, which has a monoclinic crystal system with the P21/c centrosymmetric space group. Additionally, its crystal data and hydrogen bonding parameters are determined. According to powder X-ray diffraction, spectral and thermal characterization, the eutectics are a mechanical mixture of the IMC and pure components, although the IMC behaves as a pure compound. The IMC shows a broad emission band in the range of 350 to 580 nm with a quantum yield of almost 1 (0.99) upon excitation at the λmax absorption (300 nm) in MeOH solution at a concentration of 1 × 10−5 M.

Thermal, physicochemical and spectroscopic studies on some novel organic complexes obtained by green synthesis

The solid–liquid equilibrium phase diagram and thermochemical studies on two binary organic systems involving N-methylurea (MU) with 4-nitrophenol (NP) and 3-nitrobenzoic acid NBA were studied. Both systems show the formation of an equimolar intermolecular compound (IMC) and two eutectics (E1 and E2) one on either side of the IMC. Thermodynamic parameters such as heat of mixing, entropy of fusion, roughness parameter, interfacial energy and excess thermodynamic functions of intermolecular compounds and eutectics were calculated using the experimentally determined enthalpy of fusion by the DSC method. The spectroscopic studies, FTIR and NMR, of both the IMCs along with their parent compounds revealed the hydrogen bonding association between the parent moieties forming the complex. The findings were also confirmed by the appearance of new peaks in the powder XRD of the complexes in addition to their parent compounds.

Phase diagram and thermochemical properties of organic eutectic in a monotectic system

The phase diagram of a binary organic system involving diphenyl and succinonitrile shows the formation of a eutectic (0·968 mole fraction of succinonitrile) and a monotectic (0·074 mole fraction of succinonitrile) with a large miscibility gap in the system, the upper consolute temperature being 53·5°C above the monotectic horizontal. From the enthalpy of fusion of the pure components, the eutectic and the monotectic, determined by the DSC method, the enthalpy of mixing, Jackson’s roughness parameter, interfacial energy, size of the critical nucleus and excess thermodynamic functions were calculated.