Inorganic esters, hydrolysis

The term acid catalysis is often taken to mean proton catalysis ( specific acid catalysis ) in contrast to general acid catalysis. In this sense, acid-catalyzed hydrolysis begins with protonation of the carbonyl O-atom, which renders the carbonyl C-atom more susceptible to nucleophilic attack. The reaction continues as depicted in Fig. 7. l.a (Pathway a) with hydration of the car-bonium ion to form a tetrahedral intermediate. This is followed by acyl cleavage (heterolytic cleavage of the acyl-0 bond). Pathway b presents an mechanism that can be observed in the presence of concentrated inorganic acids, but which appears irrelevant to hydrolysis under physiological conditions. The same is true for another mechanism of alkyl cleavage not shown in Fig. 7.Fa. All mechanisms of proton-catalyzed ester hydrolysis are reversible. 

Fig. 7.1. a) Specific acid catalysis (proton catalysis) with acyl cleavage in ester hydrolysis. Pathway a is the common mechanism involving a tetrahedral intermediate. Pathway b is SN1 mechanism observed in the presence of concentrated inorganic acids. Not shown here is a mechanism of alkyl cleavage, which can also be observed in the presence of concentrated inorganic acids, b) Schematic mechanism of general acid catalysis in ester hydrolysis. 

In this chapter, the words cleavage and de-esterification are often used to make it clear that reactions other than hydrolysis may be involved in the breakdown of some inorganic esters. This is particularly true for nitrates, and various phosphates and phosphonates, as discussed in the relevant sections. 

Linear Secondary Alcohol Ethoxylates (LSAE). The hydrophobes of LSAE are made via borate-modified oxidation of n-parafiins to form inorganic esters followed by hydrolysis. The resulting alcohols contain secondary hydroxyl groups randomly located along the linear alkyl chain. LSAE biodegrade slightly slower than LPAE (13.14). 

In a number of classes of systems, the catalytic and other chemical effects of metal ions on reactions of organic and inorganic molecules are generally recognized the catalysis of nucleophilic reactions such as ester hydrolysis the reactions of alkenes and alkynes in the presence of metal carbonyls (8, 9, 69) stereospecific polymerization in the presence of Ziegler catalysts (20, 55, 56) the activation of such small molecules as H2 (37), 02 (13), H202 (13), and possibly N2 (58) and aromatic substitution reactions of metal-cyclopentadienyl compounds (59, 63). 

Hydrolysis of alkyl halides 0-4 Hydrolysis of inorganic esters 0-6 Hydrolysis of enol ethers, acetals, or ortho esters... 

The transfer of the adenylyl group from ATP to a tyrosine residue is used to regulate some enzymes. The other product of the adenylylation reaction (top) is inorganic pyrophosphate. Hydrolysis of the adenylyl-tyrosine ester bond releases AMP (bottom). 

The base One equivalent, at least, of a base relative to the aryl halide must be present to achieve the alkene substitution catalytically. Most often a tertiary amine is employed. Secondary amines also appear to be suitable but primary amines usually are not. The base strength of the amine is important since only quite basic amines such as triethylamine work well. Acetate salts, carbonates and bicarbonates also are suitable bases but solubility may cause difficulties in some instances. The addition of a phase transfer agent such as a quaternary ammonium salt has often solved this problem. The inorganic bases, of course, may cause other problems such as ester hydrolysis, aldol condensations and other undesired side reactions. 

Acyclic hydroxy compounds by hydrolysis of alkyl esters of polybasic inorganic acids—e.g., alcohols via olefins + inorganic acid + hydrolysis... 

A particular versatile method to prepare stable templates and casts is the sol-gel process. In this process an inorganic ester is hydrolyzed to form the free acid. Afterwards the acid condenses to form a three-dimensional network or gel (Scheme 1). Usually it is desirable to have a fast hydrolysis which has a large reaction constant ki followed by a slower polycondensation with a smaller constant A 2- This allows one to homogenize the solution and cast it into the desired form before it solidifies. The values of ki and /C2 can in many cases be adjusted by changing pH and temperature of the solution. 

Figure 20 Possible mechanisms for sulfate ester hydrolysis catalyzed by members of the AS family. Formation of the sulfoenzyme (a) nucleophilic attack of the hydrated FGly oxygen on the substrate (b) nucleophilic attack of the sulfate oxygen of the substrate on the aldehyde FGly yields a diester sulfoenzyme, which hydrolyzes into the sulfoenzyme monoester. Enzyme desulfurylation (c) elimination of inorganic sulfate leaves an aldehyde moiety, which is hydrated to give a gerr7-diol (d) nucleophilic attack of a nucleophile, such as water, yields the hydrated gerr7-diol FGly.

For inorganic chemistry, hydrolysis is usually the reverse of neutralization, hdt in organic chemistry its scope is broader. Here it includes, amoi other things, the inversion of sugars, the brealdng down of proteins, the saponification of fats and other esters, and the final step in the Grignard reaction, all of which can be carried on with water alone, albeit slowly and incompletely. For convenience, the meaning of the term has been extended to cover also the numerous cases in which an alkali is added to the water and in which the alkali salt of an acid is usually one of the final products ... 

The main reactions of hydrolytic cleavage (hydrolysis) are shown in Fig. 31.26. They are frequent for organic esters, inorganic esters such as nitrates, and amides. These reactions are catalysed by esterases, peptidases or other enzymes, but non-enzymatic hydrolysis is also known to occur for sufficiently labile compounds under biological conditions of pH and temperature. Such reactions are of... 

Overoxidation accompanied by release of inorganic phosphate or sulfate has been observed in the periodate oxidation of some hexose monophosphates or monosulfates, although the ester hydrolysis is largely obviated by use of dilute reaction mixtures. The products of the periodate oxidation of o-glucose 2-sulfate and o-galactose 2-sulfate suggest that the acyclic form of each is oxidized 3-sulfates are, however, oxidized normally. ... 

If the substituents are not stable during acid hydrolysis or methanolysis, the complementary substitution pattern can be determined after permethylation, as already noted. Examples are organic (acetates) and inorganic esters (sulfates), and benzyl and silyl ethers. " Such an approach was applied as early as 1964 to vinyl starches."" In contrast to the direct determination of the substituent pattern, incomplete methylation and consequently erroneous evaluations cannot be recognized from the product pattern obtained in the indirect methods. If the average DS is known from an independent determination, it allows at least a certain control. Therefore, the absence of OH absorption should be carefully monitored by IR spectroscopy. 

An ester is a compound that, on hydrolysis, yields an alcohol R OH and an organic or an inorganic acid (Fig. 1). The reverse reaction is called esterification. Carboxylic acids (R C02H) and phosphoric acid (H3PO4) are examples of common acids that participate in esterification in nature. In spite of mechanistic similarities, ester hydrolysis and esterification should not be mixed with the term transesterification. 

The hypothesis just outlined will be tested against the measurements of Llewellyn et al. (119,120) of the effect of a-deuteration on the rate of hydrolysis of alkyl inorganic esters, which are summarized in Table X. These results are part of the authors extensive and very... 

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