Organic Eutectics Research Articles

Small molecule organic eutectics as candidates to replace plastics.

Legislative change and shifting consumer sentiment drive a need to replace polymers in certain products. Herein, we highlight that eutectic molecular glasses and liquids are promising but underutilized candidate materials....

Crystal Engineering of Binary Organic Eutectics: Significant Improvement in the Physicochemical Properties of Polycyclic Aromatic Hydrocarbons via the Computational and Mechanochemical Discovery of Composite Materials

Derivatives of polycyclic aromatic hydrocarbons (PAHs) are widely used in optoelectronic materials. However, the poor solubility of unfunctionalized PAHs represents a challenge for the continued application of these compounds in emerging technologies. For organic compounds bearing one or more functional groups capable of engaging in directional hydrogen or halogen-bonding interactions, the crystal engineering toolkit currently offers many routes for optimizing the solid-state properties of these compounds. Such efforts typically lead to the discovery of periodic crystal forms that display strong adhesive intermolecular forces between the molecular fragments. By contrast, the crystal engineering of organic eutectic composites is relatively unexplored and poorly understood. Here, we report the mechanosynthesis and experimental characterization of the properties of three eutectic composites of pyrene (PYR) and anthracene (ANTH) that were discovered using the coformer bisphenol A (BPA) or phenothiazine (PTZ). The resulting eutectic composites (PYR-BPA, PYR-PTZ, and ANTH-PTZ) display significant melting point depressions ranging from 19 to 51 °C relative to the melting point of the PAH. The equilibrium solubilities of the composite materials were also observed to be 2–5 times greater than that of the PAH. The crystal engineering of eutectic solid forms is currently hampered by the lack of reliable empirical or theoretical tools for predicting their formation. A weighted Monte Carlo simulation was used to estimate the mixing energies and binding modes of a limited set of molecular pairs, leading to temperature-dependent interaction parameters that show promise in the selection of coformers with a high likelihood of forming eutectic composites. Complementary dispersion-corrected density functional theory (DFT-D) calculations on a set of PYR and ANTH composite models reveal that organic eutectic composites are not driven to form on the basis of favorable thermodynamics as evidenced by an average interaction energy of 2.60 kJ mol–1 across the series. Synthon incompatibility and molecular shape mismatch appear to be important factors to consider in targeting eutectic solid forms. This work paves the way for the systematic crystal engineering of organic eutectic solid forms with tunable physicochemical properties using a synergistic computational modeling and mechanosynthesis approach.

Some physicochemical studies on organic eutectics and inter-molecular compounds

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.

Comprehending the Formation of Eutectics and Cocrystals in Terms of Design and Their Structural Interrelationships

The phenomenon of cocrystallization, which encompasses the art of making multicomponent organic solids such as cocrystals, solid solutions, eutectics, etc. for novel applications, has been less studied in terms of reliably and specifically obtaining a desired cocrystallization product and the issues that govern their formation. Further, the design, structural, and functional aspects of organic eutectics have been relatively unexplored as compared to solid solutions and cocrystals well-established by crystal engineering principles. Recently, eutectics were proposed to be designable materials on par with cocrystals, and herein we have devised a systematic approach, based on the same crystal engineering principles, to specifically and desirably make both eutectics and cocrystals for a given system. The propensity for strong homomolecular synthons over weak heteromolecular synthons and vice versa during supramolecular growth was successfully utilized to selectively obtain eutectics and cocrystals, respectively, in two model systems and in two drug systems. A molecular level understanding of the formation of eutectics and cocrystals and their structural interrelationships which is significant from both fundamental and application viewpoints is discussed. On the other hand, the obscurity in establishing a low melting combination as a eutectic or a cocrystal is resolved through phase diagrams.

Some physicochemical studies on organic eutectics

The phase diagrams of phenothiazine with each of m-nitrobenzoic acid ( m-NBA) and m-dinitrobenzene ( m-DNB) have been studied by thaw-melt method. These materials have been characterized by X-ray diffraction. Growth behavior of the parent components, eutectic and charge transfer complex (CTC) studied by measuring the rate of movement of the growth front in a capillary suggests the applicability of Hillig–Turnbull equation for the system. Microstructure and electrical conductivities of congruent melting complexes and eutectics have been determined. The low electrical conductivities of these materials have been due to weak interaction and mixed stacking of donor and acceptor. Excess thermodynamics functions of the charge-transfer (CT) materials and eutectics have been determined.

Thermochemical and microstructural studies on binary organic eutectics and complexes

The phase diagram, solidification kinetics and differential scanning calorimetry of a few charge-transfer (CT) complexes of pyrene with p-benzoquinone, m-dinitrobenzene and m-nitrobenzoic acid have been studied. These materials have been characterized by X-ray diffraction. Microstructure and electrical conductivities of congruent melting complexes and eutectics have been determined. The data indicate that side-by-side nucleation of donor and acceptor results both in eutectic as well as CT complex formation under the present experimental conditions. This explains low electrical conductivities of these materials due to weak interaction and mixed stacking of donor and acceptor. Excess thermodynamics functions of the CT materials and eutectics have been determined and results have been discussed in the light of electron donor–acceptor interactions between the components.

Solidification behaviour of binary organic eutectics and monotectics; 1,2,4,5-tetrachlorobenzene– m-aminophenol system

The phase-diagram of the 1,2,4,5-tetrachlorobenzene– m-aminophenol system studied by the thaw–melt method shows the formation of a eutectic at 120.0°C (0.946 mole fraction of m-aminophenol) and a monotectic at 136.0°C (0.094 mole fraction of m-aminophenol) with a consolute temperature at 177.0°C. The growth kinetic studies at different undercoolings (Δ T) by the capillary method give straight lines for the plots between log v and log Δ T where v is the rate of movement of solid–liquid interface. From the enthalpy of fusion of the pure components, the eutectic and the monotectic determined by the DSC method, different thermodynamic parameters such as enthalpy of mixing, excess thermodynamic functions and entropy of fusion were calculated. While the microstructure of the pure components give their faceted growth, the eutectic and the monotectic show their characteristic features.

Chemistry and characterization of binary organic eutectics and molecular complexes. The urea-m-nitrobenzoic acid system

Abstract Solid-liquid equilibrium data on a binary organic system involving urea and m -nitrobenzoic acid show the formation of a 1:1 molecular complex surrounded by two eutectics. Growth data studied by measuring the growth velocity ( v ) at different undercoolings ( ΔT ) by following the rate of movement of the interface suggest that they obey the Hillig-Turnbull equation, v = u ( ΔT ) n , where u and n are constants depending on the nature of the materials involved. From the heat of the fusion values, determined by the D.S.C. method, the heat of mixing, entropy of fusion, roughness parameter, interracial energy, radius of the critical nucleus and the excess thermodynamic functions were calculated. While the X-ray diffraction data show that the eutectics are not a mechanical mixture of the components under investigation, the microstructural investigations give their characteristic features. The spectral studies suggest intermolecular hydrogen bonding between the components forming the molecular complex.

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.

Some physicochemical studies on binary organic eutectics and 1:1 addition compound; benzidine-p-nitrophenol system

The phase diagram of benzidine with p-nitrophenol shows a 1:1 molecular complex with congruent melting point and two eutectics. The linear growth data on the pure components, the eutectics and the molecular complex, as determined by measuring the rate of movement of the growth front in a capillary, justify the square relationship between growth velocity and undercooling. Thermochemical, X-ray diffraction and microscopic studies have been carried out to investigate the characteristics of the solid eutectics. The microstructural investigations reveal faceted growth of the addition compound, and a typical characteristic growth of this class of eutectics. X-ray diffraction studies suggest that there is orientation of some atomic planes during their formation. Infrared (IR) and nuclear magnetic resonance (NMR) spectral investigations suggest that there is intermolecular hydrogen bonding between the two components forming the molecular complex.

A physicochemical study on organic eutectics and addition compound; benzidine–pyrogallol system

The phase diagrams of the binary organic system of benzidine–pyrogallol was determined by the thaw–melt method. The solidification behaviour of the pure components, their eutectics, and the addition compound were studied by measuring the movement of growth front in a capillary. From the data on X-ray diffraction, thermal and microscopic investigations it can be inferred that the eutectics are not simple mechanical mixtures of the components involved. The IR and NMR spectral investigations were carried out to throw light on the nature of bonding between the two components forming the addition compound.

Chemistry of Binary Organic Eutectics and Molecular Complexes: Phenanthrenem. Nitrobenzoic Acid System

Abstract Phase diagram, linear velocity of crystallization, thermochemistry, microstructure, electrical conductivity, X-ray diffraction and spectral behaviour of phenanthrenem nitrobenzoic acid system have been studied. The results obtained in the present investigation have been discussed in the light of recent advancement in the area of organic eutectics and molecular complexes.

Physicochemical studies on organic eutectics and the 1:1 addition compound: benzidine-α-naphthol system

The phase-diagram of the benzidine-α-naphthol system, determined by the thaw-melt method, shows the formation of a 1∶1 addition compound surrounded by two eutectics. From the linear velocity of crystallization data on pure components, eutectics and the addition compound, determined by the capillary method at different undercoolings, it can be inferred that they obey the Hillig-Turnbull equation. The X-ray diffraction studies suggest that the eutectics are not simply mechanical mixtures of two components. Heats of fusion data on the pure components, eutectics and addition compound, determined by differential scanning calorimetry, show that there is an associative interaction between the two components forming the eutectic melt. While the microstructural studies reveal that the microstructures of eutectics and the addition compound differ widely from those of the parent components, the spectral investigations suggest intermolecular hydrogen bonding between the two components.

Some physicochemical studies on organic eutectics and 1:2 addition compound; benzidine-β-naphthol system

With a view to elucidating the chemistry of the benzidine-β-naphthol system, its phase diagram was determined by the thaw-melt method. The solidification behaviour of the pure components, the eutectics and the addition compound was studied at different degrees of supercooling by the capillary method. From the data obtained by X-ray diffraction, thermal and microscopic studies, it can be inferred that the eutectics are not simple mechanical mixtures of the components involved. Infrared and NMR spectral investigations were carried out to clarify the nature of bonding between the two components forming the addition compound.

Some physicochemical studies on binary organic eutectics

Solid-liquid equilibrium data on binary systems of phenanthrene with p-chloronitrobenzene, p-dibromobenzene and diphenyl show the formation of simple eutectics in each case. The linear growth velocity ( v) of pure components and eutectics at different undercoolings (Δ T) obey the Hillig-Turnbull equation v = u(Δ T n where u and n are constants. The observed solidification behaviour of the eutectics is explained by the mechanism proposed by W.C. Winegard, S. Mojka, B.M. Thall and B. Chalmers, Can. J. Chem., 29 (1951) 320. The experimental values for the heat of fusion of eutectics, compared with the theoretical values calculated from the law of mixtures, suggest a cluster formation in the eutectic melt. Using heats of fusion data, excess thermodynamic function, surface energy and critical radius were calculated in order to throw light on the mechanism of solidification and the nature of the interaction between the components forming the eutectic. The microstructural examinations of pure components and eutectics suggest thinly branched eutectic structures resulting from coupled growth of the component phases.

Solidification Behaviour of Organic Eutectics and Addition Compounds

Solidification Behaviour of Organic Eutectics and Addition Compounds

Chemistry of organic eutectics: Phenanthrene — benzoic acid and phenanthrene — cinnamic acid systems

Solid-liquid equilibrium data for binary systems of phenanthrene with benzoic acid and cinnamic acid, expressed in the form of temperature-composition curves, show the formation of a simple eutectic in each case. Linear velocity of crystallisation (v), studied by capillary method at different undercoolings (ΔT), suggests the applicability of Hillig-Turnbull equation, v = u(ΔT) n, where u and n are constants depending on the nature of solidification. Data on heats of fusion of pure components and eutectics, determined by the DTA method, infer appreciable interaction among the components in the eutectic melts. To highlight the nature of interactions among the components forming the eutectic melt, the excess thermodynamic functions such as hE, sE, and gE were computed. Microscopic studies reveal that the structure of eutectic is different from those of the parent components. Infrared spectra, recorded in the region, 4000 —625 cm−1, indicate weak interactions among the components in the eutectic.

Some Physicochemical Studies on Organic Eutectics and 1:2 Addition Compounds

With a view to elucidate the physical chemistry of organic eutectics and 1:2 addition compounds, phase diagram, linear velocity of crystallization, thermochemistry, microstructure, X-ray diffraction and spectrak behaviour of p. phenylenediamine-α.naphthol and p. phenylenediamine-β.naphthol systems have been studied. The phase diagrams show the formation of two eutectics and a 1:2 addition compound in each case and growth kinetics suggest the applicability of Hillig-Turnbull equation. While x-ray diffraction, microstructure and thermochemical studies infer that the eutectics are not simple mechanical mixtures of the two components, the spectral investigations suggest the hydrogen bonding between two components forming the addition compounds

Thermochemical studies on organic eutectics and molecular complexes

The phase diagrams of the binary systems of picric acid with naphthalene, anthracene and phenanthrene, and of α-naphthol withp-toluidine, determined by the thaw-melt method, show the formation of a molecular complex and two eutectics in each system. The heats of the pure components, eutectics and molecular complexes were determined by differential scanning calorimetry. Comparison of the experimental heats of fusion with the theoretical values calculated via the mixture law suggests cluster formation in the melts. The entropy of fusion, enthalpy of mixing and excess thermodynamic functions were also calculated from the heat of fusion data.

Some physicochemical studies on organic eutectics and 1:1 addition compound; p-phenylenediamine – benzoic acid system

The phase diagram of p-phenylenediamine – benzoic acid system, determined by the thaw–melt method, shows the formation of two eutectics and a 1:1 addition compound. The linear velocity of crystallization of pure components, eutectics and addition compound, determined by measuring the movement of growth front in a capillary, suggests that crystallization data obey the Hillig–Turnbull equation. Using experimental values of heats of fusion, entropy of fusion and excess thermodynamic functions were calculated and the results are explained on the basis of cluster formation in the melts. X-ray diffraction data infer that these eutectics are not simply the mechanical mixture of the two components and there is preferential ordering of atomic planes during their formation. The infrared spectral studies suggest the formation of intermolecular hydrogen bonding between the components forming the molecular complex. Keywords: organic eutectics, growth kinetics, phase diagram, thermochemistry, X-ray diffraction studies.