Crystalline salts chemical stability

The physical form of the salt must be taken into account and several issues must be considered (Serajuddin and Pudipeddi, 2002). Forexample, amorphous material might result. Even if crystalline, the salt form might prove to be polymorphic. On crystallization or recrystallization, formation of a hydrate or a solvate might occur, and the effect of temperature and humidity on this form should be investigated. Both the physical and chemical stability of the different candidate salt forms in the solid state will ultimately deLne the optimal form of the drug. 

C. Search for crystalline salts I. Chemical stability VII. CONCLUSION ... 

Solid-state characterization is one of the most important functions of the preformulation group, which is assigned the responsibility of making recommendations for further formulation work on a lead compound. Physical properties have a direct bearing on both physical and chemical stabilities of the lead compound. Much of the later work on formulation will depend on how well the solid state is characterized from the decisions to compress the drug into tablets to the selection of appropriate salt forms. The studies reported in this section, of course, apply to those drugs that are available in solid form, crystalline or amorphous, pure or amalgamated. 

Barium is a member of the alkaline-earth group of elements in Group 2 (IIA) of the period table. Calcium [7440-70-2], Ca, strontium [7440-24-6], Sr, and barium form a closely allied series in which the chemical and physical properties of the elements and their compounds vary systematically with increasing size, the ionic and electropositive nature being greatest for barium (see Calcium and calcium alloys Calcium compounds Strontium and STRONTIUM COMPOUNDS). As size increases, hydration tendencies of the crystalline salts increase solubilities of sulfates, nitrates, chlorides, etc, decrease (except fluorides) solubilities of halides in ethanol decrease thermal stabilities of carbonates, nitrates, and peroxides increase and the rates of reaction of the metals with hydrogen increase. 

The designations a, /3, or y after some formulas refer to particular crystalline forms (which are customarily identified by Greek letters). Data for salts except oxalates are taken mainly from A. E. Martel and R. M. Smith, Critical Stability Constants. Vol. 4 (New York Plenum Press, 1976). Data for oxalates are from L. G. Sitlen and A. E. Martell, Stability Constants of Metal-Ion Complexes, Supplement No. 1 (London The Chemical Society, Special Publication No. 25,1971). Another source R. M. H. Verbeeck et al., Inorg. Chem. 1984, 23, 1922. 

The atructural stability of a Variety of commercially available hydrothernally dealuminated Y type zeolitee in high pH ammonium salt eclutions vas studied It was found that such zeolites can lose large amounts of crystallinity, the susceptibility to structure loss increasing with salt concentration and pH, and with increases in both the chemical and framework eilica/alumina ratio of the zeolite ... 

A less frequent but nonetheless interesting problem arises in the chemical modification of liquid, or low-melting, active principles in solid prodrugs, suitable for tablet or capsule preparation. Indeed solid dosage forms are still the most widely used for the administration of medicines, as well for patient acceptability and convenience for product stability and ease of manufacture. Their preparation implies that the active principle can itself be handled as a stable solid, an objective that is usually attained by one of the following strategies formation of a salt or a molecular complex, formation of a crystalline covalent derivative, introduction of symmetry. 

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