Direct hydrolysis

Formic acid is currently produced iadustriaHy by three main processes (/) acidolysis of formate salts, which are ia turn by-products of other processes (2) as a coproduct with acetic acid ia the Hquid-phase oxidation of hydrocarbons or (3) carbonylation of methanol to methyl formate, followed either by direct hydrolysis of the ester or by the iatermediacy of formamide. 

Coproductioa of ammonium sulfate is a disadvantage of the formamide route, and it has largely been supplanted by processes based on the direct hydrolysis of methyl formate. If the methanol is recycled to the carbonylation step the stoichiometry corresponds to the production of formic acid by hydration of carbon monoxide, a reaction which is too thermodynamicaHy unfavorable to be carried out directly on an iadustrial scale. 

Iron oxide yellows can also be produced by the direct hydrolysis of various ferric solutions with alkahes such as NaOH, Ca(OH)2, and NH. To make this process economical, ferric solutions are prepared by the oxidation of ferrous salts, eg, ferrous chloride and sulfate, that are available as waste from metallurgical operations. The produced precipitate is washed, separated by sedimentation, and dried at about 120°C. Pigments prepared by this method have lower coverage, and because of their high surface area have a high oil absorption. 

Besides direct hydrolysis, heterometaHic oxoalkoxides may be produced by ester elimination from a mixture of a metal alkoxide and the acetate of another metal. In addition to their use in the preparation of ceramic materials, bimetallic oxoalkoxides having the general formula (RO) MOM OM(OR) where M is Ti or Al, is a bivalent metal (such as Mn, Co, Ni, and Zn), is 3 or 4, and R is Pr or Bu, are being evaluated as catalysts for polymerization of heterocychc monomers, such as lactones, oxiranes, and epoxides. An excellent review of metal oxoalkoxides has been pubUshed (571). 

Again, the recommended names (phosphonic acid and phosphonates) have found more general acceptance for organic derivatives such as RP03 , and purely inorganic salts are still usually called phosphites. The free acid is readily made by direct hydrolysis of PC l3 in cold CCI4 solution ... 

In 1967, Heidelberger, Stacey et al. reported the purification, some structural features, and the chemical modification of the capsular polysaccharide from Pneumococcus Type I. Difficulties of direct hydrolysis of the polysaccharide were overcome and it was possible to identify some of the fragments in the hy-drolyzate. At least six products resulted from nitrous acid deamination. Two were disaccharides, which were identified, and sequences of linked sugar units were proposed. As modification of the polysaccharide decreased the amounts of antibody precipitated by anti-pneumococcal Type I sera, the importance of the unmodified structural features in contributing to the specificity of the polysaccharide was indicated. 

Direct hydrolysis of (monohalogenoalkyl)quinoxalines can be difficult but indirect routes are available. Alcoholysis and phenolysis are usually straightforward processes. The following examples illustrate both direct and indirect procedures. 

Other inverting glucosidases which conform to the pattern of direct hydrolysis of glycosyl fluorides having the correct anomeric configuration, and transglycosylation with inversion if the anomeric configuration is opposite to that of the natural substrates are trehalase from rabbit renal cortex and from the yeast Candida tropicalis, and ) -D-xylosidase from Bacillus pu-milis. ... 

Castro CE, RS Wade, DM Riebeth, EW Bartnicki, NO Belser (1992b) Biodehalogenation rapid metabolism of vinyl chloride by a soil Pseudmonas sp. Direct hydrolysis of a vinyl C-Cl bond. Environ Toxicol Chem 11 757-764. 

Transfer of the acyl group from the acylzirconocene chloride to aluminum (transmetala-tion) by treatment with aluminum chloride has been reported to give an acylaluminum species in situ, and the possibility of the acylaluminum acting as an acyl anion donor has been suggested (Scheme 5.5) [7]. However, the acyl anion chemistry through this trans-metalation procedure appears to be limited since only protonolysis to the aldehyde proceeds in good yield, which could be achieved by direct hydrolysis of the acylzirconocene chloride. 

In humans, ca. 10% of the urinary metabolites of epicainide (4.29, Fig. 4.3), an antiarrhythmic agent, is accounted for by the carboxylic acid derivative 4.32. Three distinct pathways are possible for the formation of this metabolite, namely direct hydrolysis of the secondary amide function of epicainide (Fig. 4.3, Pathway a), hydrolysis of the primary amide (4.30) resulting... 

N - Benzyl- N -p icolinoylpiperazine (EGYT-475, 4.88), a compound with potential antidepressant activity, underwent similar hydrolysis. After intravenous administration, picolinic acid (4.89) was one of its major urinary metabolites in rats the other product, A-benzylpiperazine (4.90) was also detected, but at much lower levels, since it was further transformed by A-de-benzylation [55], Since the products of direct hydrolysis of these cyclic tertiary amides (i.e., the corresponding secondary amines) were found at substantial levels, it appears that oxidative A-monodealkylation is not an essential step for hydrolysis in these compounds, in contrast to the findings for A,A-diethylbenzamide. This contradicts the hypothesis [52] (see above) that the steric bulk of the tertiary amide group impedes direct hydrolysis. Here, although the degree of steric bulk is at least comparable, direct hydrolysis clearly takes place. 

Fig. 4.5. Major routes of metabolism for lidocaine (4.128). Direct hydrolysis yields 2,6-dimethylaniline (2,6-xylidine, 4.129) and 2-(diethylamino)acetic acid (diethylglycine, 4.130). Hydrolysis of the metabolites monoethylglycinexylidine (4.131) and glycinexylidine (4.132) also yields 4.129. The metabolites 4.131 and 4.132 also undergo hydroxylation at the aromatic ring to form 4.133 and 4.134, respectively, which, in turn, are hydrolyzed to 4-hydroxy-2,6-dimethylaniline (4.135). This compound can also be formed by oxidation of 4.129. 

The antihypertensive agent tripamide (4.267), when incubated with rat liver microsomes or partially purified microsomal arylamidase, was extensively hydrolyzed to 4-chloro-3-sulfamoylbenzoic acid (4.268) [171]. This metabolite seems to be produced by direct hydrolysis, since the other metabolites formed by oxidation of the cycloalkyl moiety remained unchanged when incubated with rat liver microsomes. The mechanism of hydrolysis of tripamide has not yet been fully elucidated. The inhibition of the reaction by O-ethyl 0-(4-nitro-phenyl) phenyl phosphothionate indicates that amidases may be involved. 

The metabolic fate of the benzylpenicillin-human serum albumin conjugate was studied in rats [149]. The conjugate was taken up by the liver, where it underwent enzymatic cleavage to form benzylpenicilloic acid. Thus, the benzylpenicilloic acid excreted in urine may be formed either by direct hydrolysis of the /3-lactam ring, or by catabolism of protein conjugates formed in vivo. 

Fig. 8.14. Stepwise activation of dihydrotrigonelline-based chemical delivery systems, first by oxidation to a pyridinium cation (Reaction a), and then by hydrolysis to trigonelline and the drug ROH (Reaction b). Direct hydrolysis (Reaction c) is slow in comparison to the Reactions...

A further condition for good brain delivery, one that is particularly relevant in the present context, is that e) direct hydrolysis of the dihydropyridine pro-prodrug (Fig. 8.14, Reaction c) does not compete with oxidation, especially in the periphery, since this would decrease the amount of CDS available for brain delivery. In fact, the pyridinium metabolite is more susceptible than the dihydropyridine pro-prodrug to alkaline and enzymatic hydrolysis, since the carbonyl C-atom of the pyridinium compound (B, Fig. 8.15) is much more electrophilic than that of the dihydropyridine (A, Fig. 8.15). 

The classic caustic fusion of sulfonic acid salts has been used for preparing 2,6-dinaphthol and its derivatives. Other more recent procedures have employed the direct hydrolysis of aryl bromides and the oxidation of aryl Grignard reagents. ... 

Plant. In plants, mevinphos is hydrolyzed to phosphoric acid dimethyl ester, phosphoric acid, and other less toxic compounds (Hartley and Kidd, 1987). In one day, the compound is almost completely degraded in plants (Cremlyn, 1991). Casida et al. (1956) proposed two degradative pathways of mevinphos in bean plants and cabbage. In the first degradative pathway, cleavage of the vinyl phosphate bond affords methylacetoacetate and acetoacetic acid, which may be precursors to the formation of the end products dimethyl phosphoric acid, methanol, acetone, and carbon dioxide. In the other degradative pathway, direct hydrolysis of the carboxylic ester would yield vinyl phosphates as intermediates. The half-life of mevinphos in bean plants was 0.5 d (Casida et ah, 1956). In alfalfa, the half-life was 17 h (Huddelston and Gyrisco, 1961). 

Polymer-melamine crosslinks are also broken during exposure to UV light. Although some crosslink scission occurs in the dark by direct hydrolysis, the rate of scission (as measured by the rate of disappearance of residual methoxy functionality) Increases dramatically with Increasing UV light Intensity (11). Scission occurs with UV light in the absence of humidity but at a much reduced rate. 

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