Alkali hydrolytic reactions

Interest in acid-fixing reactive dyes has remained active because of their environmentally attractive features (section 1.7). The freedom from competing hydrolytic reactions potentially offers exceptionally high fixation, extreme stability of the dye-fibre bonds and complete suitability of the unfixed dyes for recycling. In contrast to conventional reactive dyes, sensitisation problems arising from reaction with skin proteins are not anticipated. Unlike the haloheterocyclic reactive dyes, there is no risk of release of AOX compounds to waste waters. Heavy metals are not involved in the application of acid-fixing reactive dyes, nor are the electrolytes or alkalis that normally contaminate effluents from conventional reactive dyeing. 

Cleavage of carbon-carbon bonds in hydrolytic reactions is relatively rare, but those reactions that occur are important. The reagent is usually a concentrated solution of an alkali, and the starting material must contain a carbonyl group the first stage is addition of a hydroxyl anion to this group, and the resulting intermediate splits to a carbon anion and a carboxylic acid ... 

The use of alkali in aqueous solution leads naturally to another type of hydrolytic reaction, namely, aOcali fusion, wherein the proportion of... 

Excellent examples are found in the hydrolytic reactions of esters with alkalis, the interaction of alkyl halides with hydroxyl ions, the benzoylation of amines, and the union of tertiary amines with alkyl halides to give quaternary ammonium salts. Among gas-phase reactions the decomposition of hydrogen iodide, on the one hand, and the union of hydrogen with iodine on the other provide the classical examples. The absolute rates in this last case are rather closely given by collision number... 

Stannous tin (Sn ) behaves very much like Sn in its aqueous hydrolytic, reactions. When Sn solutions are neutralized with alkali carbonate or... 

The alkali metals only form monovalent ions in aqueous solution. Their low ionic charge and relatively large ionic radius lead to hydrolysis only at very high pH (near and above 14). For lithium, sodium and potassium, the ionic radii are 0.76, 1.02 and 1.38 A, respectively (Shannon, 1976). Consequently, lithium will have the strongest hydrolytic reactions due to its smaller size, but regardless all are very weak. As such, hydrolytic data are virtually only available for lithium, sodium and potassium. An upper limit for the formation of CsOH(aq) has been proposed (Baes and Mesmer, 1976), and a stability constant for this latter species has been given by Popov et al. (2002). 

The synthesis and surface-active properties of higher hydroxyalkanediphos-phonates are discussed in Ref. 67. Phosphorus-containing betaines as hydrolytically stable surfactants, free from alkali salt impurities, were prepared by a reaction of amidoamines and equimolar amounts of phosphonate esters with 1.5-2 eq of formaldehyde at 60-140°C in a polar solvent [72]. 

The course of the reaction has not been fully clarified. Hydrolytic and aromatization processes are probably responsible for the formation of colored or fluorescent deriva4 tives (cf. Potassium Hydroxide Reagent). For instance, sevin is converted to a-naphthalkali metal salt of the o-hydroxycinnamic acid pro- duced by hydrolytic cleavage of the pyrone ring is converted from the non-fluorescent cis- to the fluorescent trans-form by the action of long-wavelength UV light (X = 365 nm) [2]. 

Although organosilanes appear to react slowly (if at all) with water alone, in the presence of acids or bases (e.g., alkali metal hydroxides), reactions to give a silanol and H2 are rapid, with bases being particularly powerful catalysts. The evolution of H2 in this type of reaction may be used as both a qualitative and a quantitative test for Si-H bonds, and the mechanism of the acid and the base hydrolysis has been discussed in detail (30,31). This hydrolytic method is not very common for the preparation of silanols that are to be isolated, because both acids and bases catalyze the condensation of silanols to siloxanes, and therefore, only compounds containing large substituents are conveniently made in this way. If an anhydrous alkali metal salt is used, a metal siloxide may be isolated and subsequently hydrolyzed to give the silanol [Eq. (10)] (32). 

Nucleophilic attack at substituted ring carbon is probably the most common reaction of 1,3,4-oxadiazoles. However, few examples have been reported of nucleophilic attack at unsubstituted carbon since such compounds (19a) are relatively uncommon. The mechanism of the well-known conversion of 2-amino-oxadiazoles (in aqueous alkali) into triazoles has been studied in the case of the reaction where (19a R = NHPh) is converted to (20). This proceeds via the anion of semi-carbazide PhNHCONHNHCHO and is initiated by hydroxide attack at C-5 <84JCS(P2)537>. A similar nucleophilic attack by hydroxide on oxadiazole (19a R = 5-pyrazolyl) was followed by cyclization to the pyrazolo-triazine (21). Hydrolytic cleavage of 2-ary 1-1,3,4-oxadiazoles to aroyl-hydrazides allows use of the former as protected hydrazides. Oxadiazole (19a R = 4-... 

Aqueous alkali hydrolyzes lactones and the products, e.g. (287), are frequently unstable or recyclize, depending on other substituents present. Coumarin is hydrolyzed by dilute alkali first to the yellow cis acid (coumarinic acid) salt (288) which recyclizes to coumarin on acidification but when heated with alkali isomerizes to the trans acid (coumaric acid) salt (289). When it is desirable to identify the hydrolytic product of such a reaction it is better to incorporate a methylating agent so that the reverse reaction cannot then occur. Hot aqueous alkali converts methyl 3-bromocoumalate (290) into furan-2,4-dicarboxylic acid (73JCS(Pl)ll30). 

The proportion of 1,4-anhydroribitol formed by treatment of teichoic acids and synthetic poly(ribitol phosphate) with alkali is small, and the major hydrolytic pathway involves the cyclic phosphate sequence. No 1,4-anhydroribitol glycosides have been observed in the alkaline hydrolyzates of teichoic acids possibly, the presence of a glycosyl substituent makes the reaction sterically less favorable than when such substituents are absent. 

Hydrolysis can be defined as the decomposition of a compound by reaction with water, the water taking part in the reaction. The effect is enhanced by the presence of either acids or alkalis. The chemistry of polyurethanes leads to the probability of hydrolytic attack. The mechanism is illustrated in Figure 2.41. 

There is a substantial group of diazonium salts to which the alkaline formaldehyde method, or any other deamination process requiring alkaline conditions, should not be applied, inasmuch as they are unstable in the presence of alkali. This instability is merely an extension of the hydrolytic cleavage reaction previously noted (pp. 274-276). Comparatively few diazonium salts are converted to the diazo oxides in aqueous mineral acid. As the acidity of the solution is decreased, however, diazo oxide formation is facilitated, and finally on the alkaline side many diazo compounds that are stable in acid media undergo hydrolytic cleavage.96 96 Thus, while 2,4-dinitrobenzenediazonium acid sulfate is stable to dilute aqueous sulfuric acid, in neutral or slightly alkaline solution it readily yields the diazo oxide.6 The reaction is not quantitative a poorly defined insoluble product is also formed in 14 to 20% yields. 

The reactor is an enameled apparatus with an agitator and a water vapour jacket. The production of sodium dihydroxyphenylsilanolate is carried out in butanol and toluene or ethanol and toluene medium at 35-50 °C. The consumption of other components is calculated by the amount of the loaded condensation product. After loading the product of condensation, the reactor is filled with toluene and butanol (or ethanol and toluene) from batch boxes 10 and 11. The ratio of the solvents should be 1 1.4 to obtain 10% silanol solution. The calculation takes into account toluene contained in the product of hydrolytic condensation. The loaded mixture is agitated in the reactor for 30 minutes after that it receives 20% alkali solution from batch box 12 at agitation. The reaction forms sodium dihydroxydiphenylsi-lanolate and water. 

Approximately 150 different amino acid residues have been reported in proteins (1 5). At least half of these could undergo chemical deteriorations under the conditions of stress usually encountered. Many of these deteriorative reactions involve hydrolytic scissions, not only of peptide bonds but of the many different nonprotein substances added covalently to proteins postribosomally. These susceptible side chain groups are indole, phenoxy, thioether, amino, imidazole, sulfhydryl, and derivatives of serine and threonine (such as 0-glycosyl or O-phosphoryl), the disulfides of cystine, and, of course, the amides (such as asparagine and glutamine). With strong acid or alkali, other residues, such as serine and threonine, also are less stable. 

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