Alkaline Scission

With sodium methoxide, methyl 2,6-dimethyl-3,4-anhydro- 8-D-alloside (XXIII) gives a mixture of methyl 2,3,6-trimethyl-/3-D-gluco8ide (XXII) and methyl 2,4,6-trimethyl-/3-D-guloside. This result provided the first 

In many earlier examples, the isolation of only one of the two possible products of alkaline cleavage has been recorded. It is not clear whether this is due to the omission of a search for a second constituent or whether, in some cases, the scission is 100% in one direction.  

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Some examples will illustrate the applicability of this generalization in so far as it concerns alkaline scission. 5,6-Anhydro-l,2-isopropylidene-D-glucofuranose with alcoholic sodium hydroxide gives a mixture of isopropylidene-D-glucose and isopropylidene-L-idose. The latter results from inversion on C5, the former presumably by inversion on the non-asymmetric C6.7 3,4-Anhydro-l,2-isopropylidene-D-psicose (or allu-lose17) (XX) when treated with sodium hydroxide yields a mixture of products among which 1,2-isopropylidene-D-fructose (XIX) was detected (in the representations inversions are denoted by circles above the arrows and the carbons inverted are noted below the arrows). With sodium methoxide, however, l,2-isopropylidene-4-methyl-D-sorbose (XXI) is the chief product and results from inversion on C4.1S... 

Hoffman Degradation. Polyacrylamide reacts with alkaline sodium hypochlorite [7681-52-9], NaOCl, or calcium hypochlorite [7778-54-3], Ca(OCl)2, to form a polymer with primary amine groups (58). Optimum conditions for the reaction include a slight molar excess of sodium hypochlorite, a large excess of sodium hydroxide, and low temperature (59). Cross-linking sometimes occurs if the polymer concentration is high. High temperatures can result in chain scission. 

Heliotrine, CigH2,05N, m.p. 125-6°, [ajn — 75° (CHCI3), yields a methiodide, m.p. 108-111°, and contains one methoxyl group, two hydroxyl groups and a tertiary nitrogen atom. On alkaline hydrolysis it forms heliotridine (p. 607) and heliotric acid (p. 613). In presence of platinic oxide it absorbs two molecules of hydrogen and affords, as scission products, heliotric acid and hydroxyheliotridane (p. 607). 

Whereas the cleavage of /S-poly(L-malate) at neutral pH is at random [2], alkaline hydrolysis reveals characteristic patterns of the cleavage products, which is due to nonrandom chain scission (Fig. 3). The phenomenon is explained by an autocatalytic ester hydrolysis. Assuming that one (or both) of the polymer ends bends... 

The hydrolytic depolymerisation of PETP in stirred potassium hydroxide solution was investigated. It was found that the depolymerisation reaction rate in a KOH solution was much more rapid than that in a neutral water solution. The correlation between the yield of product and the conversion of PETP showed that the main alkaline hydrolysis of PETP linkages was through a mechanism of chain-end scission. The result of kinetic analysis showed that the reaction rate was first order with respect to the concentration of KOH and to the concentration of PETP solids, respectively. This indicated that the ester linkages in PETP were hydrolysed sequentially. The activation energy for the depolymerisation of solid PETP in a KOH solution was 69 kJ/mol and the Arrhenius constant was 419 L/min/sq cm. 21 refs. 

Peroxomonophosphoric acid (PMPA) oxidizes dimethyl sulphoxide in high yield in water and aqueous ethanol . In neutral solution the reaction mechanism was thought to be very complex but actually occurs by two different mechanisms that are very similar to those for sulphoxide oxidation by peracids in acidic and basic media. In an alkaline medium the mechanism involves nucleophilic attack by a phosphorus-containing species (probably POs ) on the sulphur atom of the sulphoxide, followed by O—O bond scission yielding the sulphone (equation 24). In acidic solution, on the other hand, the sulphoxide is the nucleophilic species as detailed in equation (25). It should be noted however that there is some evidence that these mechanisms are oversimplified since there are other nucleophilic species (such as H2P05 and HPO ") present in aqueous solutions of PMPA over a wide pH range . 

The coordination- and spin state of HRP C are dependent on pH, although little change occurs between pH 4 and pH 10. At pH 3.1, the resting state enz5mie is a 5-c HS form in which His 170 has been replaced as ligand by a water molecule (104). The scission of the Fe-His bond occurs from a 6-c intermediate with a water molecule boimd at the distal site. At high pH values, a transition to an alkaline form occurs... 

Significant volumes of low oxidized starch are used at the size press. These starches are made by treatment in alkaline suspension with sodium hypochlorite so that from 1 to 2% active chlorine acts on the starch. The reaction is simple to perform. However, the reaction products are complex. Chain scission occurs at the same time that carboxyl and carbonyl groups are formed in the starch. It is most desirable to prepare the highest ratio of carboxyl to carbonyl as possible and this reaction is a function of the pH in the slurry. 

It has been shown that the transformation 254 - 251 -t- 253 proceeds with first-order kinetics and that increase in solvent polarity is associated with an increase in the rate. It is proposed that the reaction involves a novel unimolecular heterolytic scission of the sulfur—sulfur bond in the symmetrical disulfide (254). The kinetics of the alkaline hydrolysis of anhydro-2-mercapto-4,5-diphenyl-l,3,4-thiadiazolium... 

Alkyl hydroperoxides. Peroxymercuration of alkenes proceeds cleanly and in good yield. These products previously were reduced to the desired alkyl hydroperoxides with alkaline sodium borohydride. This reduction proceeds in reasonable yield in the case of terminal alkenes, but scission to form epoxides of the original alkene predominates among products from nonterminal alkenes. This difficulty is now overcome by use of tri-n-butyltin hydride for reduction.18... 

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