Cation hydrated form

Iodine is only slightly soluble in water and no hydrates form upon dissolution. The solubiHty increases with temperature, as shown in Table 2 (36). Iodine is soluble in aqueous iodide solutions owing to the formation of polyiodide ions. For example, an equiHbrium solution of soHd iodine and KI H2O at 25°C is highly concentrated and contains 67.8% iodine, 25.6% potassium iodide, and 6.6% water. However, if large cations such as cesium, substituted ammonium, and iodonium are present, the increased solubiHty may be limited, owing to precipitation of sparingly soluble polyiodides. Iodine is also more... 

Miscellaneous Compounds. Among simple ionic salts cerium(III) acetate [17829-82-2] as commercially prepared, has lV2 H2O, has a moderate (- 100 g/L) aqueous solubiUty that decreases with increased temperature, and is an attractive precursor to the oxide. Cerous sulfate [13454-94-9] can be made in a wide range of hydrated forms and has solubiUty behavior comparable to that of the acetate. Many double sulfates having alkaU metal and/or ammonium cations, and varying degrees of aqueous solubiUty are known. Cerium(III) phosphate [13454-71 -2] being equivalent to mona2ite, is very stable. 

As with resoles, we can use a three-phase model to discuss formation of a novolac. Whereas the resole is activated through the phenol, activation in novolacs occurs with protonation of the aldehyde as depicted in Scheme 12. The reader will note that the starting material for the methylolation has been depicted in hydrated form. The equilibrium level of dissolved formaldehyde gas in a 50% aqueous solution is on the order of one part in 10,000. Thus, the hydrated form is prevalent. Whereas protonation of the hydrate would be expected to promote dehydration, we do not mean to imply that the dehydrated cation is the primary reacting species, though it seems possible. 

In all the examples studied, the difference in the free energy between the anhydrous and hydrated species is 4 kcal/mole or less. ° Both electron deficiency and resonance stabilization are necessary for covalent hydration to be measurable. The necessity for electron deficiency is clearly shown in the following examples. The cation of 1,4,5-triazanaphthalene is anhydrous, but the cation of 1,4,5,8-tetraazanaphthalene is predominantly hydrated. 1,6-Naphthyridine cation is anhydrous, whereas the cations of the 3- and 8-nitro derivatives are predominantly hydrated. Also, the percentages of the hydrated form in the neutral species of 2-hydroxy-1,3-diaza-, 1,3,8-... 

There are other soUd states which sometimes confuse the measurement and definition of solubiUty. The dmg may crystaUize as a hydrate, i.e. under inclusion of water molecules. If the hydrate form is more stable than the pure form it may be difficult to measure the intrinsic solubility of the drug at all. Often drugs tend to precipitate in an amorphous form, often under the inclusion of impurities. As with metastable polymorphs, such amorphous precipitates may lead to erroneously high solubility measurements. CommerciaUy, drugs are often crystallized in salt form, e.g. as the hydrochloride salt, a cation with a chloride anion. In these co-crystallized salts, a much lower solubility than the intrinsic solubility will typi-... 

Acyl complexes can also result from the reaction of terminal alkynes with cationic, hydrated complexes of iron (Entry 4, Table 2.7) [47]. An electrophilic vinylidene complex is probably formed as intermediate this then reacts with water and tautomerizes to the acyl complex. 

Both type I and type II water forms were detected, and the I/II mole ratio was rather constant at 1 2.2 for the Na+ form having the low H2O/SO3 mole ratios of 0.06, 0.5, and 1.2. These numbers were derived from the areas under the two deconvoluted peaks. The ratio of type I to II water molecules decreases in the order for the series Na+ > K+ > Rb+ > Cs+, which is reasonable considering that the cation hydration number decreases in this order and shows the structure-breaking action of cations with... 

The first dinitrogen complex, characterized in 1965, resulted From the reduction of commercial ruthenium trichloride [containing some Ru(lV)] by hydrazine hydrate. The pentuammine(dinitrogen)ruthenium(Il) cation that formed could be isolated in a variety of salts.50 Soon other methods were found to synthesize the complex, such as the decomposition of the pentaammineazido complex, [Ru NH3)3N,Jj+, and even direct reaction with nitrogen gas ... 

This investigation began with a study of lumazines in which the ionizable hydrogen atom on N-3 was replaced by a methyl group. It was found that 3,8-dimethyllumazine (11) (with or without further methyl groups in the 6- and 7-positions) showed no anomalies of pAa or UV spectra, neither as the neutral species nor the cation. Alkali produced a monoanion of pKa 6.4, which must necessarily have come from a hydrated form. This anion had a UV maximum at shorter wavelengths, corresponding to loss of a double bond (see Scheme 1). Such an anion is clearly related to that of pteridine (3), which has pKa 11.2. 

Hydroxotitanate anion, however, has never been detected in the course of hydrolysis of titanium alkoxides. On the basis of electron microscopy data, Diaz-Guemes et al. [477] suggested the two-step adsorption mechanism for the above reaction. According to his assumption hydrolysis of titanium alkox-ide results in a gel of hydrated titanium oxide, which is further diffused by M2+ cations to form crystalline MDTi03 ... 

---