Entropy of Fusion of Molecular Complexes

Rastogi, R. P.; Nigam, R. K.; Sharma, Ramprakash; Girdhar, H. L.

doi:10.1063/1.1734140

Cited by 16 publications

(7 citation statements)

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“…13 In the work presented here we have studied one particular cocrystal forming system-benzophenone (BZP) and diphenylamine (DPA) in which we found that a co-crystal can form under solidstate grinding (mortar and pestle) at ambient temperatures. The binary phase diagram for this system was first reported in 1933 by Warner and Lee, 14 later revisited by Rastogi et al 15 and is reproduced in Fig. 1.…”

mentioning

confidence: 59%

How does grinding produce co-crystals? Insights from the case of benzophenone and diphenylamine

2007

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A benzophenone-diphenylamine co-crystal nucleates from a submerged eutectic-is this a possible mechanism of grinding induced synthesis of such materials?The early discovery of co-crystals, or molecular complexes as they are also referred to in the literature, resulted from the measurement of two component phase diagrams 1 and associated crystallisation from melt phases. 2 Subsequently crystallisation from solution has also been used as a method for preparing co-crystals, particularly when suitable samples are required for X-ray analysis and structure determination. 3,4 These methods have been complemented, in recent years, by the use of co-grinding of potential co-crystal formers either as dry solids or in the presence of a solvent drop. 5 This grinding technique has been popularised on two counts-first that it requires little or no solvent and hence is seen as environmentally friendly 6,7 and second because it is possible to use this as a screening aid to generate novel co-crystalline phases not apparently found in conventional crystallisation from solution. 5 Despite its evident utility little work has been devoted to understanding the mechanism of this grinding process, an issue bound to limit its ultimate commercial efficacy. For example, Kuroda et al. 8 produced co-crystals of racemic-bis-b-naphthol and benzoquinone by solid state grinding and postulated that the shearing and molecular diffusion processes occurring during grinding generated a different adduct structure to that recovered from solution. In the work of Rastogi et al. with picric acid complexes, 9,10 on the other hand, vapour diffusion was suggested as a mass transfer mechanism during solid state grinding. Shan et al. 11 explained solvent drop grinding on the basis of additional degrees of freedom, enhancement of molecular collisions and formation of tiny co-crystal seeds. In the wider context of grinding induced solid state covalent synthesis, Rothenberg et al. 12 have presented evidence suggesting the formation of a liquid phase in the binary phase diagram as essential to facilitate intermolecular contacts, mass transfer and chemical reaction. Recently Kaupp proposed a three step solid-state mechanism, derived from atomic force microscopy studies, which involves long-range anisotropic molecular migration. 13 In the work presented here we have studied one particular cocrystal forming system-benzophenone (BZP) and diphenylamine (DPA) in which we found that a co-crystal can form under solidstate grinding (mortar and pestle) at ambient temperatures. The binary phase diagram for this system was first reported in 1933 by Warner and Lee, 14 later revisited by Rastogi et al. 15 and is reproduced in Fig. 1. We found that co-grinding of the two components in solid form created the stable polymorphic structure first identified by Warner and Lee 14 as having a melting point of 40.2 uC and a crystal structure identical to that first determined in 1972 16 based on an H-bonded carbonyl-amine dimer. In order to explore in more detail how this reaction procee...

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confidence: 59%

How does grinding produce co-crystals? Insights from the case of benzophenone and diphenylamine

2007

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“…This has been accounted for by the unfavorable interactions between ephedrine and water, which counteract the lower melting point. 17 The solubility of the 1:1 salt is considerably higher, as expected due to ionization. In the melt, the eutectic between ephedrine and the 1:1 salt occurs at x ≈ 0.2, which is similar to the corresponding position for the solution eutectic.…”

Section: Salt: Ephedrine and Pimelic Acidmentioning

confidence: 84%

“…The melting entropies of both A and B were each set equal to Walden's constant (54 J/mol•K), giving enthalpies of melting for both A and B of 20.2 kJ/mol. The variations of melting points with mole fraction were each plotted using the equation of Schroder-van Laar 17 and are shown as continuous lines in Figure 1. This assumes ideal (adiabatic) mixing of A and B in all melt compositions.…”

Section: Methodsmentioning

confidence: 99%

“…Scheme shows the molecular structures of benzophenone (BZP) and diphenylamine (DPA). These two molecules form a 1:1 cocrystal which has been studied extensively. ,, The cocrystal is expected to contain a hydrogen bond from the amine to the carbonyl. If this is broken on melting, then the cocrystal is expected to have a correspondingly large enthalpy of melting compared to its components.…”

Section: Cocrystal: Benzophenone and Diphenylaminementioning

confidence: 99%

“…The melting point data for the cocrystal and its components are given in Table . ,, The two components have similar melting properties. The melting entropies of the two components give values close to Walden’s rule.…”

Section: Cocrystal: Benzophenone and Diphenylaminementioning

confidence: 99%

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On the Melting of Binary Organic Compounds

Black

Woon

Davey

2018

Crystal Growth & Design

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The melting behaviors of three binary organic compounds, a racemate, a cocrystal, and a salt, are compared with their individual components and with each other. The three compounds are the racemic compound of mandelic acid, the benzophenone–diphenylamine cocrystal, and ephedrine pimelate. Similarities and differences are accounted for by changes in entropy, hydrogen bonding, molecular conformation, and charged state on melting. An unusual combination of thermodynamic, structural, and spectroscopic data gives insight into the nature and extent of association in these melts. The three binary compounds show surprisingly similar melting thermodynamics. The main differences are in the salt system, driven by ionization and access to a 2:1 salt. The implications for melt and solution eutectics are discussed.

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