Homogeneous solution, rapid hydrolysis

For the total hydrolysis of polysaccharides, trifluoroacetic acid (TFA) has important advantages over sulfuric acid. The reaction time is short and there is no need for conventional neutralization, as TFA is volatile and can be removed by evaporation. Several methods have been developed, depending on the substance to be hydrolyzed. Soluble saccharides (e.g., polyoses) can be hydrolyzed with diluted TFA, while cellulose, pulp, and wood need treatments with concentrated TFA in homogeneous solution. The presence of lignin impedes the hydrolysis of polysaccharides thus, especially for wood samples, an intensive treatment with TFA is necessary, and correction values have to be considered. Several application examples show that the hydrolysis with TFA enables a rapid quantitative determination of the composition of polysaccharides, pulps, and woods. 

Alkenes, Arenes, and Alkanes. Aqueous solutions of Oxone can epoxidize alkenes which are soluble under the reaction conditions for example, sorbic acid (eq 4). (the high selectivity for epoxidation of the 4,5-double bond here is noteworthy). Alternatively, the use of a cosolvent to provide homogeneous solutions promotes epoxidation (eq 5). Control of the pH to near neutrality is usually necessary to prevent hydrolysis of the epoxide. Rapidly stirred heterogeneous mixtures of liquid alkenes and aqueous Oxone solutions buffered with NuHCOb also produce epoxides, as shown in eq 6. ... 

The concept that a catalyst provides an alternate mechanism for accomplishing a reaction, and that this alternate path is a more rapid one, has been developed in many individual cases. The basis of this idea is that the catalyst and one or more of the reactants form an intermediate complex, a loosely bound compound which is unstable, and that this complex then takes part in subsequent reactions which result in the final products and. the regenerated catalyst. Homogeneous catalysis can frequently be explained in terms of this concept. For example, consider catalysis by acids and bases.. In aqueous solutions acids and bases can increase the rate of hydrolysis of sugars, starches, and esters. The kinetics of the hydrolysis of ethyl acetate catalyzed by hydrochloric acid can be explained by the following mechanism ... 

Water and alkoxides are not miscible so that a co-solvent, usually the parent alcohol, is currently added in order to mix both reagents and get a clear solution. However alcohol denatures proteins so that such a solvent should be avoided when mixing water and alkoxides. Actually alcohol has been shown to be an unnecessary additive in the silicon sol-gel chemistry (Avnir, 1987). Hydrolysis occurs at the water/silane interface giving alcohol as a reaction product. The mixture then becomes rapidly homogeneous even if unstirred. Better mixing and faster hydrolysis are obtained when the preparation is sonicated before adding proteins (Ellerby, 1992). Hydrolysis is usually performed under acid conditions... 

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