Synthesis nonaqueous solvents

Metal organic decomposition (MOD) is a synthesis technique in which metal-containing organic chemicals react with water in a nonaqueous solvent to produce a metal hydroxide or hydrous oxide, or in special cases, an anhydrous metal oxide (7). MOD techniques can also be used to prepare nonoxide powders (8,9). Powders may require calcination to obtain the desired phase. A major advantage of the MOD method is the control over purity and stoichiometry that can be achieved. Two limitations are atmosphere control (if required) and expense of the chemicals. However, the cost of metal organic chemicals is decreasing with greater use of MOD techniques. 

An example of a synthesis utilizing a nonaqueous solvent is a common procedure that is used to prepare [Cr(NH3)s]Cl3. The reaction is... 

Carbodiimides are, in general, useful compounds for effecting certain dehydrative condensations, e.g., in the formation of amides, esters, and anhydrides. These two crystalline water-soluble carbodiimides are especially useful in the synthesis of peptides and in the modification of proteins. The excess of reagent and the co-product (the corresponding urea) are easily separated from products with limited solubility in water. The hydrochloride is best employed in nonaqueous solvents (methylene chloride, acetonitrile, dimethylformamide). The methiodide is relatively stable in neutral aqueous systems, and thus is recommended for those media. 

The position of the equilibrium in the overall reaction. An example is provided by the hydrolases that catalyze cleavage of amide, ester, and phosphodiester linkages using water as the entering nucleophile. Because enzymes usually act in an environment of high water content, the equilibrium almost always favors hydrolysis rather than the reverse reactions of synthesis. However, in a nonaqueous solvent the same enzyme will catalyze synthetic reactions. 

PLATINUM COMPLEXES SUITABLE AS PRECURSORS FOR SYNTHESIS IN NONAQUEOUS SOLVENTS... 

In many cases, only the first point is important, and thus a great deal of work in this field has been carried out with protic nonaqueous solvents such as alcohols (MeOH, EtOH, IPrOH) and acids (e.g., acetic acid) [99-105], However, there are many reactions for which the second and third points are also relevant. Hence, there are many reports on the use of solvents such as acetonitrile, methylene chloride, THF, DMSO, DMF, and electrolytes from the R +X- family (R = alkyl, X = CE, BF4E etc.) in unique organic synthesis. Several typical examples are summarized in Table 11 [106-115],... 

The most common and important nitrogen-hydrogen compound is ammonia. Because liquid ammonia is a commonly used nonaqueous solvent, it was discussed in Section 5.2.3 and its properties are listed in Table 5.5. Approximately 22 billion pounds of NH3 are used annually, mostly as fertilizer or as the starting material for preparing nitric acid. The Haber process is used for the synthesis of NH3 from the elements ... 

A preponderance of the transition-metal pseudohalogen complexes reported in the literature are prepared in aqueous media. Several oxidation states of many transition metals are either unstable in the presence of water or form only oxygen-coordinated species. Thus, these metal ions will not form pseudohalogen complexes in the normal manner. The following method, using polar, nonaqueous solvents is suitable for the preparation of isothiocyanate complexes of several of these ions. As an example of the preparation of such complexes, the synthesis of potassium hexakis(isothiocyanato)niobate(V) is described. 

The ammines of cobalt(II) are much less stable than those of cobalt(III) thermal decomposition of [Co(NH3)6]Cl2 is characterized by reversible loss of ammonia, whereas that of [Co(NH3)6]Cl3 is not. In his classic dichotomy of complexes, Biltz regarded [Co (NH 3)3] Cl 2 as the prototype of the normal complex and [Co(NH3)6]Cl3 as that of the Werner or penetration complex. Hexaamminecobalt-(II) chloride has been prepared by the action of gaseous ammonia on anhydrous cobalt (II) chloride or by displacing water from cobalt(II) chloride 6-hydrate with gaseous ammonia. It may also be synthesized in nonaqueous solvents by passing dry ammonia through solutions of cobalt(II) chloride in ethanol, acetone, or methyl acetate. Syntheses in the presence of water include heating cobalt(II) chloride 6-hydrate in a sealed tube with aqueous ammonia and alcohol and the treatment of aqueous cobalt(II) chloride with aqueous ammonia followed by precipitation of the product with ethanol. The latter method is used in this synthesis. Inasmuch as the compound is readily oxidized by air, especially when wet, the synthesis should be performed in an inert atmosphere. 

Enzymatic reactions in nonaqueous solvents have generated a great deal of interest, fueled in part by the commercial application of enzymes as catalysts in specialty synthesis. The increasing demand for enantiopure pharmaceuticals has accelerated the study of enzymatic reactions in organic solvents containing... 

Hexaamminecobalt(III) salts are generally prepared " by the oxidation of am-moniacal cobalt(II) solutions by either H2O2 or O2 in the presence of a catalyst. The preparation procedure most often employed involves the aerial oxidation of an ammoniacal cobalt(II) solution in the presence of a carbon catalyst. The new procedure employs the same reaction conditions but utilizes a nonaqueous solvent to simplify the synthesis and to prepare the acetate salt, which is very soluble in water. 

Nonaqueous solvent synthesis systems were used for silica or other composition (e.g., transition metal oxides,[26] sulfide mesophase[26]). 

Sarney, D.B. Vulfson, E.N. Enzymatic synthesis of sugar fatty acid esters in solvent-free media. In Enzymes in Nonaqueous Solvents Methods and Protocols (Methods in Biotechnology Vol. 15) Vulfson, E.N., Hailing, P.J., Holland, H.L., Eds. Humana Press Totawa, 2001 531-543. 

---