Nonhydrolytic hydroxylation reaction

Scheme 2.1 shows three examples of nonhydrolytic hydroxylation reactions. 

Scheme 2.1 Schematic of nonhydrolytic hydroxylation reactions, (a) Reaction of metal halides with alcohols coordination of the alcohol to the metal center, followed by elimination of an alkyl halide RX. (b) Guerbet-type reaction of a metal isopropoxide with benzyl...

Nonhydrolytic sol-gel routes are not necessarily completely water-free. Although the initial reaction mixture might be anhydrous, specific organic reactions are able to produce water in situ (e.g., aldol condensation and esterification reactions), rendering the system in principle hydrolytic. Therefore, nonhydrolytic sol-gel processes are often also called nonaqueous. But even in the absence of water, it is possible to have hydroxylation reactions. 

IMP does not accumulate in the cell but is converted to AMP, GMP, and the corresponding diphosphates and triphosphates. The two steps of the pathway from IMP to AMP (fig. 23.11) are typical reactions by which the amino group from aspartate is introduced into a product. The 6-hydroxyl group of IMP (tautomeric with the 6-keto group) is first displaced by the amino of aspartate to give adenylosuccinate, and the latter is then cleaved nonhydrolytically by adenylosuccinate lyase to yield fumarate and AMP. In the condensation of aspartate with IMP, cleavage of GTP to GDP and phosphate provides energy to drive the reaction. 

Both stages are controlled by condensation chemistry that can include, as a first step, hydrolysis of hydrated metal ions or metal alkoxide molecules [6, 7] (hydrolytic sol-gel processing). The condensation chemistry in this case is based on olation/oxolation reactions between hydroxylated species. The hydroxylated species for further condensation can be formed also by a non-hydrolytic route, that is, by reactions between metal chlorides and alcohols with electron-donor substituents [8]. The nonhydrolytic sol-gel processing may... 

Alkoxide sol-gel precursors can be converted to the same hydroxylated activated substances by nonhydrolytic routes. The thermal intermolecular hydroxylation was used as a first step for gelation of Zr02 at 200-300°C in a conventional reactor [23] or inside the channels of mesostmctured SBA-15 siKca [24]. Partially hydroxylated alkoxides can be synthesized by reactions between metal chlorides and alcohols with electron-donor substituents or reactions between basic alkoxides and carbonyl compounds like ketones [9]. 

Other functional silanes also can be hydrolyzed or reacted by nonhydro-lytic techniques to give polyorganosiloxanes. For example, the reactions of chlorosilanes or alkoxy silanes with alcohols, esters, or hydroxyl groups are examples of the nonhydrolytic process [Eq. (17)] [42,43]. 

Diols are a group of reducing agents that have attracted regular use in nonhydrolytic systems to prepare Pt nanostructures two such examples are HDD [11, 40, 43, 137] and DDD [40, 137]. These compounds have two neighboring hydroxyl groups, and function as mild reductants at elevated temperatures in the reactions this in turn leads to relatively slow reaction kinetics that can be controlled. 

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