Fused organic salts. 8. Properties of molten straight-chain isomers of tetra-n-pentylammonium salts

Abstract

A representative selection of the 64 straight-chain isomers of tetra-n-pentylammonium cation (Q+) has been prepared. Twenty-seven halides, perchlorates, and tetraphenylborates of these cations make up a suite of salts in which the cation's shape and the asymmetry of placement of its charge vary widely. Temperatures, heats, and entropies of solid-solid transition and fusion were measured by hot-stage microscopy and differential scanning calorimetry. Phase diagrams for a number of salt-salt and salt-nonelectrolyte systems were studied by hot-stage microscopy, and the permissible limits of structure variation in Q+ for observation of complete miscibility of two solid salts are reported. The effect of Q+ structure on the critical solution temperatures of salt-nonelectrolyte systems are reported for two nonelectrolytes. The molar volume ( V,) and surface tension (a) of 1 1 liquid salts were determined over a 30-40 O C temperature range near the freezing point. As the charge placement in Q+ becomes progressively more asymmetric, the quantity u / V,'I3, taken as a measure of the cohesive energy density, rises to a maximum and then falls abruptly. The rising portion of this curve is predicted by a simple electrostatic model. Possible origins of the descending portion are discussed. A prefreezing anomaly for liquid dimethyldioctylammonium perchlorate is characterized by sharp breaks in the temperature dependence of surface tension and viscosity some 30 and 40 OC above the freezing point. RJ values for chromatography of Q+C104-and Q+Ph4B-on thin silicic acid layers in three solvent systems are reported. The dominant retardation mechanism appears to be nonelectrostatic.The simple R4N+A-salts have been productive tools in electrolyte-solution chemistry,'-1° fused-salt chemistry,' and organic reactivity m a n i p u l a t i~n . l~-~~ Some important aspects of their chemistry remain to be developed, however. Detailed modeling of charge distribution, shielding, and interaction with solvent and counterion largely remain to be worked out.16-20 More simply, the radii of these ions are not accurately fixed. The most commonly used values are equivalent-sphere radii determined from molecular models.21 Both in the crystal22 and in ion pairs in solution23 Br-is known to approach n-Pr4N+ more closely than the equivalent-sphere radius would imply; it penetrates between the alkyl chains of Pr4N+. There is evidence that organic ions bearing the charge on a peripheral atom display effective radii in their electrostatic interactions that are much closer to the van der Waals radii of the charge-bearing atom than to the mean radii of the organic ions as a whole.24 Since the charge in R4N+ is neither peripheral nor perfectly buried, the effective electrostatic radius must depend upon what charged site or sites the ion is interacting with. Can useful effective electrostatic radii for R4N+ be determined? Most of the work done with R4N+ has used the simple symmetrical ions tetramethyl through tetrabutyl. Radii of any description are presently lacki...

Is Universal, Simple Melting Point Prediction Possible?

“…Nevertheless, each polymorph might have its own distinct melting temperature. [27][28][29]167] [25] ) in the lattice and also assume the solid-state entropy to be unchanged. Then, the melting point of a crystal of a hypothetical, energetically more favored conformer would be 19.0 8C according to Equation (3):…”

Ionic liquids based on guanidinium cations and TFSI anion as potential electrolytes

“…And cg11TFSI, cg12TFSI and cg13TFSI had the same rule, too. Trialkylsulfonium-based ILs [19], quaternary ammonium based ILs [31] and quaternary phosphonium based ILs [32] have been reported to have the same relationship of the melting point to the structure of cations. And it have been considered as the reason, that reduction in the symmetry of cations causes blocking ideal close-packing of the ions in the solid state lattice and depression of melting points.…”

Surface tension of binary mixtures of imidazolium and ammonium based ionic liquids with alcohols, or water: Cation, anion effect

“…The surface tension of ILs are lower than that for water (71.98 mN m −1 at 293.15 K, 0.1 MPa) [19], but higher than the values for alkane (24.47 mN m −1 for decane at 293.15 K, 0.1 MPa) [20]. The lowest values were observed for the tetraalkylammonium salts with perchlorate anion, [ClO 4 ] − ; from 9.6 to 9.7 mN m −1 for different alkyl substituents [21]. The surface tension of ammonium and imidazolium salts decreases as the number of methylene moieties substituted to the cation increases.…”