Solid state stability salts

If one excludes zwitterionic structures which appear to have less stability than the other forms, there are four possible structures for the imidazolin-2-ones (52-55 X = O) (Scheme 18). IR evidence points to a carbonyl form (53 X = 0) in the solid state, while the characteristic absorption in the UV region supports their designation in solution as the carbonyl forms. If their melting points are compared with imidazoles (e.g. imidazole, 90 C imidazolin-2-one, 250 °C), the high values may point to the presence in the solid state of salt-like structures. Benzimidazolinones, and other fused-ring imidazolin-2-ones, appear to exist and react as the ketone forms (66RCRI22). 

Results for the sodium salt were interpreted as indicating a sequential two step degradation. The trihydrate showed first order kinetics at 37 and 50 C but at the higher temperatures its degradation rate was consistent with formation of a solid plus a gas. Rate constants were derived which were extrapolated to 20°C and used to calculate the time for 10% degradation as 1.25 and 3.2 years for the sodium salt and trihydrate respectively. However, these authors made no mention of the possible effect of water content which is well known to be important for the solid state stability of all penicillins. 

Insoluble salts may be prepared using high molecular weight counterions to reduce the solubility of the drug for formulation of a suspension, to improve chemical stability, provide improvements in solid-state stability, reduce acid lability and permit formulation of tasteless or controlled release products. Erythromycin stearate, which is poorly soluble in acidic media (an enteric salt), is less prone to decomposition in gastric fluids than the more acid-soluble free base. 

Table 10.2 Direct and indirect methods for evaluating the solid state stability of salt and co-crystal forms. 

An ordered structure stabilized by non-covalent interactions between the 7i-electronic moieties and their substituents in a gel was observed using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The addition of a solid-state TBA salt of CF (10 equivalents) to the octane gel resulted in a gradual transition to the solution state, beginning from the areas close to where the solid salts were added (Figure 4.4a(ii)). After the receptor molecules in the gel formed... 

Thermodynamic data show that the stabilities of the caesium chloride-metal chloride complexes are greater than the conesponding sodium and potassium compounds, and tire fluorides form complexes more readily tlrair the chlorides, in the solid state. It would seem that tire stabilities of these compounds would transfer into tire liquid state. In fact, it has been possible to account for the heats of formation of molten salt mixtures by the assumption that molten complex salts contain complex as well as simple anions, so tlrat tire heat of formation of the liquid mixtures is tire mole fraction weighted product of the pure components and the complex. For example, in the CsCl-ZrCU system the heat of formation is given on each side of tire complex compound composition, the mole fraction of the compound... 

The calculated barrier to dissociation of the [S3N2] dication into [SN]" and [S2N] in the gas phase is 10.9 kcal mof . However, lattice-stabilization effects allow the isolation of [MEg] salts (M = As, Sb) of this six r-electron system in the solid state from the cycloaddition of [SN] and [S2N] cations in SO2 (Eq. 5.11)."° The S-S and S-N bond distances in the planar, monomeric dication are shorter than those in the... 

Salts of diazonium ions with certain arenesulfonate ions also have a relatively high stability in the solid state. They are also used for inhibiting the decomposition of diazonium ions in solution. The most recent experimental data (Roller and Zollinger, 1970 Kampar et al., 1977) point to the formation of molecular complexes of the diazonium ions with the arenesulfonates rather than to diazosulfonates (ArN2 —0S02Ar ) as previously thought. For a diazonium ion in acetic acid/water (4 1) solutions of naphthalene derivatives, the complex equilibrium constants are found to increase in the order naphthalene < 1-methylnaphthalene < naphthalene-1-sulfonic acid < 1-naphthylmethanesulfonic acid. The sequence reflects the combined effects of the electron donor properties of these compounds and the Coulomb attraction between the diazonium cation and the sulfonate anions (where present). Arenediazonium salt solutions are also stabilized by crown ethers (see Sec. 11.2). 

Water is involved in most of the photodecomposition reactions. Hence, nonaqueous electrolytes such as methanol, ethanol, N,N-d i methyl forma mide, acetonitrile, propylene carbonate, ethylene glycol, tetrahydrofuran, nitromethane, benzonitrile, and molten salts such as A1C13-butyl pyridium chloride are chosen. The efficiency of early cells prepared with nonaqueous solvents such as methanol and acetonitrile were low because of the high resistivity of the electrolyte, limited solubility of the redox species, and poor bulk and surface properties of the semiconductor. Recently, reasonably efficient and fairly stable cells have been prepared with nonaqueous electrolytes with a proper design of the electrolyte redox couple and by careful control of the material and surface properties [7], Results with single-crystal semiconductor electrodes can be obtained from table 2 in Ref. 15. Unfortunately, the efficiencies and stabilities achieved cannot justify the use of singlecrystal materials. Table 2 in Ref. 15 summarizes the results of liquid junction solar cells prepared with polycrystalline and thin-film semiconductors [15]. As can be seen the efficiencies are fair. Thin films provide several advantages over bulk materials. Despite these possibilities, the actual efficiencies of solid-state polycrystalline thin-film PV solar cells exceed those obtained with electrochemical PV cells [22,23]. 

A solution-state and solid-state nuclear magnetic resonance study of the complex and its separate components in both their neutral and ionized (TMP hydrochloride and SMZ sodium salt) forms was undertaken in order to elucidate the TMP-SMZ interactions. Inspection of the data for the complex in the solid state shows that the 13C chemical shifts are consistent with the ionic structure proposed by Nakai and coworkers105 (14). Stabilization of the complex is achieved by the resulting ionic interaction and by the formation of two intermolecular hydrogen bonds. 

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