Hydrolytic process

Biological fermentation Glucose, furfural Shredding, air separation Used in conjunction with the hydrolytic process... 

Although the previous two sections of this chapter emphasized hydrolytic processes, two mechanisms that led to O- or N-acylation were considered. In the discussion of acid-catalyzed ester hydrolysis, it was pointed out that this reaction is reversible (p. 475). Thus, it is possible to acylate alcohols by reaction with a carboxyhc acid. To drive the reaction forward, the alcohol is usually used in large excess, and it may also be necessary to remove water as it is formed. This can be done by azeotropic distillation in some cases. 

Physicochemical Impact of Fluorine Substitution on Hydrolytic Processes... 

In the crystallization of these hydrated salts from aqueous solutions it is essential that a low pH (high level of acidity) is maintained, otherwise hydrolysis occurs and yellow impurities contaminate the products. Similarly, if the salts are redissolved in water, the solutions turn yellow/brown. The hydrolytic processes are complicated, and, in the presence of anions with appreciable coordinating tendencies, are further confused by displacement of water from the coordination sphere of the iron. However, in aqueous solutions of salts such as the perchlorate the following equilibria are important ... 

One of the syntheses of f1 udalanine begins with base promoted condensation of ethyl fluoroacetate and ethyl oxalate to give This is then converted by hydrolytic processes to the insoluble hydrated lithium salt of fluoropyruvate (58). This last is reductively aminated by reduction with sodium boro-deuteride and the resulting racemate is resolved to give D-flu-dalanine (59). 

For the most common series of corrosive agents, water, steam, acids, alkalis and salts, the hydrolytic processes peculiar to each determine the mechanism of attack. Thus, under the right circumstances, hydrolytic attack on the bridging oxygens can occur in the following way ... 

It is obvious that vacuum drying will not prevent the hydrolysis. On the contrary, evacuation of the air might stimulate and accelerate the hydrolytic process because HF saturation pressure is higher than that of water. 

It is, therefore, required that all initial compounds be dried properly prior to performing the reduction. This procedure is not at all trivial and refers, first of all, to the diluent salts, and especially to potassium fluoride, KF, which is characterized by a strong hygroscopic property and a tendency to form stable crystal hydrates. The problem of contamination due to hydrolytic processes can usually be resolved in two manners. The first is to apply another tantalum-containing complex fluoride compound that does not undergo hydrolysis. The second involves the adjustment of the reduction process parameters and use of some additives that will "collect" the oxygen present, in the form of water, hydroxyl groups or other compounds. 

Another reason is that xylo-oligosaccharides of defined structure are very important substrates that serve as model compounds for the optimization of hydrolytic processes and in enzymic assays. The enormous development... 

More definitive evidence of enzymatic attack was obtained with 1 1 copolymers of e-caprolactone and 6-valerolactone crosslinked with varying amounts of a dilactone (98,99). The use of a 1 1 mixture of comonomers suppressed crystallization and, together with the crosslinks, resulted in a low-modulus elastomer. Under in vitro conditions, random hydrolytic chain cleavage, measured by the change in tensile properties, occurred throughout the bulk of the samples at a rate comparable to that experienced by the other polyesters no weight loss was observed. However, when these elastomers were implanted in rabbits, the bulk hydrolytic process was accompanied by very rapid surface erosion. Weight loss was continuous, confined to the... 

Details of the hydrolytic process are somewhat more complicated because the acid-catalyzed hydrolysis proceeds via the initial protonation of an alkoxy oxygen followed by bond cleavage. Because the protonation can involve the exocyclic or endocyclic alkoxy group, two different sets of initial products are possible. However, in both cases the ultimate degradation products remain the same. These two possible reaction paths are shown on page 130. 

During food processing, interactions of antioxidants with proteins and other food constituents take place, and the activity of some antioxidants may change as a result of hydrolytical processes because glycosides and esters are converted... 

However, when subtilisin E was replaced by subtilisin Carlsberg, the hydrolysis of the S-N bond in some A(-acyl arenesulfinamides 34 unexpectedly became the main hydrolytic process giving under the kinetic resolution conditions, in addition to the unreacted substrates, the corresponding sulfinic acids and... 

The absorption efficiency of the different carotenoids is variable. For example, (3-cryptoxanthin has been reported to have higher absorption efficiency than a-cryptoxanthin in rats (Breithaupt and others 2007). Carotenoids must be liberated from the food before they can be absorbed by intestinal cells (Faulks and Southon 2005). Mechanical disruption of the food by mastication, ingestion, and mixing leads to carotenoid liberation (Guyton and Hall 2001). The enzymatic and acid-mediated hydrolysis of carbohydrates, lipids, and proteins (chemical breaking of the food) also contributes to carotenoids liberation from the food matrix (Faulks and Southon 2005). Once released, carotenoids must be dissolved in oil droplets, which are emulsified with the aqueous components of the chyme. When these oil droplets are mixed with bile in the small intestine, their size is reduced, facilitating the hydrolytic processing of lipids by the pancreatic enzymes (Pasquier and others 1996 Furr and Clark 1997 ... 

Using the same approach again, both hydrolytic processes seen above will be expected to occur and the pH of the solution will depend on the relative values of pKa and pAb, but be independent of the... 

Metal ion-catalyzed hydrolytic processes have been studied for a long time, and many interesting systems have been explored which give valuable information about catalysis. However, with very few exceptions the catalysis afforded by these systems in water is disappointing when compared with enzymatic systems where a metal ion cofactor activates a substrate and a nucleophilic or basic group in an acyl or phos-phoryl transfer process. It has been noted that bulk water may not be a good medium to approximate the medium inside the active site of an enzyme where it is now known that the effective dielectric constants resemble those of organic solvents rather than water. 

Hydrolytic enzymes, 10 303 Hydrolytic polymerization, 19 748 Hydrolytic process, influences on, 10 281 Hydrolytic reactions, selective, 16 400 Hydrolytic stability, of ethylene-tetrafluoroethylene copolymers, 18 322-325... 

The sol-gel methodology can also be applied to non-hydrolytic processes. The preparation of methylsilsesqui-oxane-titanium oxide hybrid by the etherolysis-condensation of a mixture of methyltrichlorosilane and metal chloride,353 354 and by the condensation of preformed poly(methylsilsesquioxane) carrying Si-OH and Si-OCHj groups with titanium(iv) -butoxide,355 has been reported. 

The attractive (80) features of MOFs and similar materials noted above for catalytic applications have led to a few reports of catalysis by these systems (81-89), but to date the great majority of MOF applications have addressed selective sorption and separation of gases (54-57,59,80,90-94). Most of the MOF catalytic applications have involved hydrolytic processes and several have involved enantioselec-tive processes. Prior to our work, there were only two or three reports of selective oxidation processes catalyzed by MOFs. Nguyen and Hupp reported an MOF with chiral covalently incorporated (salen)Mn units that catalyzes asymmetric epoxidation by iodosylarenes (95), and in a very recent study, Corma and co-workers reported aerobic alcohol oxidation, but no mechanistic studies or discussion was provided (89). 

The first comparison of the kinetics of E-site GTP hydrolysis and microtubule elongation was carried out by MacNeal and Purich (1978a). Their results indicated that the hydrolysis and elongation reactions were coupled because there was only a very slight lag in the hydrolytic process at the concentrations of microtubule protein employed. These data do not distinguish between two mechanistic alternatives ... 

In a sediment system, the hydrolysis rate constant of an organic contaminant is affected by its retention and release with the sohd phase. Wolfe (1989) proposed the hydrolysis mechanism shown in Fig. 13.4, where P is the organic compound, S is the sediment, P S is the compound in the sorbed phase, k and k" are the sorption and desorption rate constants, respectively, and k and k are the hydrolysis rate constants. In this proposed model, sorption of the compound to the sediment organic carbon is by a hydrophobic mechanism, described by a partition coefficient. The organic matrix can be a reactive or nonreactive sink, as a function of the hydrolytic process. Laboratory studies of kinetics (e.g., Macalady and Wolfe 1983, 1985 Burkhard and Guth 1981), using different organic compounds, show that hydrolysis is retarded in the sohd-associated phase, while alkaline and neutral hydrolysis is unaffected and acid hydrolysis is accelerated. 

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