Hydrolysis by water

Aconitine contains four methoxyl groups and three hydroxyl groups (triacetyl derivative, m.p. 207-8°). On hydrolysis by water under pressure, or by boiling with dilute acid, it loses 1 mol. of acetic acid and forms benzoylaconine, whilst hydrolysis by alkalis eliminates both acetic and benzoic acids and yields aconine. 

Ammonium complex fluorometalates are generally susceptible to hydrolysis by water formed in the course of the fluorination process (see 25). Such interactions, resulting in the formation of oxyfluoride metalates can be described as follows ... 

The very low rate of amide hydrolysis by water alone has been measured Kahne, D. Still, W.C. J. Am. Chem. Soc., 1988, 110, 7529. 

Fig. 4 Formulae of alkaloids wh Table 1. The rate (V) of the acetylthiocholine hydrolysis by water extracts (1 10 weight/volume) Equisetum arvense in the presense of allelochemicals -alkaloids and ozone...

Figure 1.82 The hydroxyl group of serine residues and the phenolate ring of tyrosine groups may be modified with succinic anhydride to produce relatively unstable ester bonds. In aqueous conditions these reactions are minor due to competing hydrolysis by water.

After isolation, the intermediate products were reacted with zinc in acetonitrile or a glyme solvent to provide the trifluorovinyl ether monomers. This reaction with zinc is also sensitive to the presence of protic substances in the reaction mixture, and forms the same tetrafluoroethyl ether by-product in an undesirable side reaction. The reaction of the 2-bromotetrafluoroethyl ether reactants with zinc involves the formation of zinc organometallic species as an intermediate, and this species is sensitive to hydrolysis by water or acidic substances (Figure 3.6). 

The potential for the preservation of lipids is relatively high since by definition they are hydrophobic and not susceptible to hydrolysis by water, unlike most amino acids and DNA. A wide range of fatty acids, sterols, acylglycerols, and wax esters have been identified in visible surface debris on pottery fragments or as residues absorbed into the permeable ceramic matrix. Isolation of lipids from these matrices is achieved by solvent extraction of powdered samples and analysis is often by the powerful and sensitive technique of combined gas chromatography-mass spectrometry (GC-MS see Section 8.4). This approach has been successfully used for the identification of ancient lipid residues, contributing to the study of artifact... 

These resins have adequate physical properties for most applications (Table 21.1), although they don t have good resistance to wet environments. In other words, they are prone to hydrolysis by water. This is probably due to the close proximity of the two-ester groups, being ortho to each other. 

The coupling led to the intermediate phosphite (step a) which was oxidized by TBHP (step b). The phosphate formed containing eight ethoxy groups was deprotected by trans-esterification using trimethylbromosilane and subsequent hydrolysis by water (step c). Two benzoyl groups were removed by basic hydrolysis (step d). The same tetrakis phosphate was prepared by phosphitylation with dibenzyl-h/,iSr-diisopropylphosphoroamidite in the presence of tetrazole (step c) followed by oxidation with CPBA (step f). The removal of all benzyl and benzoyl groups was achieved in one step by sodium in liquid ammonia (step g). 

The next operation consists in the reconversion of the esters into the amino acids. In the case of the lower boiling fractions, this reconversion is effected by boiling the esters with five to six voluiiies of water under a reflux condenser for six to seven hours, until the alkaline reaction has disappeared in the case of the higher boiling fractions, which contain the esters of aspartic and glutamic acids, the reconversion is effected by boiling with baryta water for one and a half to two hours hydrolysis by water alone only converts these esters into their acid esters. Phenylalanine ester is converted into its hydrochloride by evaporation to dryness with hydrochloric acid. 

To circumvent the problem of lower water solubility and fast hydrolysis by water, some authors have investigated peroxyoxalate emission in micellar environments ... 

Potassium peroxodicarbonate (K2C206) is readily prepared, for example by anodic oxidation of saturated potassium carbonate at — 20 °C, but attempts at complex formation have been hampered by its ready hydrolysis by water and low solubility in organic solvents. Vibrational spectral data for the dianion have been interpreted38 on the basis of the trans planar structure (5). 

In addition, oxygen atoms may act as the attacking nucleophile, such as those in water molecules. In aqueous solutions, hydrolysis by water is the major competing... 

The shorter-term exposure experiments show that some portion of the organically-bound chlorine, such as trichlorethane or its decomposition products, remains absorbed on a 304 stainless steel surface, even after heating at 35-40°C in a high vacuum. Conversion to an ionic species begins after a short contact period and can be detected using XPS. Formation of the ionic chloride is likely the result of hydrolysis by water also absorbed on the surface, and is perhaps catalyzed by the surface metal oxides. Further atmospheric exposure up to a few months increases the relative amount of the ionic form of chlorine. The composition of the surface oxide layer was altered, with chromium oxide replacing iron oxide as the major species. There was further evidence that chlorine was present as iron chloride, perhaps up to 5% of the surface film. The conditions under which oxidation of such surfaces occurred are quite comparable to those which could occur on steel surfaces in industrial usage. 

Ethereal salts or esters derived from the neutralisation of an acid by an alcohol also undergo hydrolysis by water and the fats, which are compounds of this type, are frequently decomposed m this way for the manufacture of glycerine, candles, or sogp the hydrolysis of such esters is catalytically accelerated by the addition of a mineral acid. 

A most important class of reactions in which PC15 plays a part is its hydrolysis by water or other compound containing the hydroxyl group with the substitution of chlorine for hydroxyl. Complete hydrolysis with an excess of water gives orthophosphoric and hydrochloric acids —... 

The oxides of a given element become more acidic with increasing oxidation state and the halides more covalent and susceptible to hydrolysis by water. 

As chemically summarised in Fig. 2, the compound behaves as a powerful oxidising agent and as a derivative of platinum(v). Its hydrolysis by water vapour to oxygen, platinum dioxide, and hydrogen hexafluoroplatinate(iv) resembles that of osmium(v), iridium(v), and ruthenium(v) fluoro-salts, which are similarly reduced to the acids of their 4+ ions e.g.,... 

Sulphur and selenium form dimeric chlorides and bromides. S2CI2, made by passing dry CI2 over molten sulphur, is an amber liquid whose vapour dissociates a little and becomes red. Hydrolysis by water is slow HCl, sulphur, SO2 and oxyacids, principally HgSgOg, are formed. Electron diffraction by the vapour indicates a non-planar structure analogous to that of hydrogen peroxide (p. 381) ... 

Scheme 4 The putative mechanisms for the two steps of the RNase A-catalyzed reaction. Despite the fact that after the initial transphosphorylation reaction to form the 2, 3 cyclic phosphate, His-12 and His-119 are in the correct protonation states to immediately catalyze its hydrolysis by water, the cyclic phosphate is released by the enzyme faster than it is hydrolyzed.

Hydrolysis by water to obtain the highest possible concentration of silanols... 

---