Monohalogen compounds

A few examples of dangerous reactions of monohalogen compounds will now be listed ending with the polyhalogens. The table on p.278 provides a general idea. 

The reduction of the dibromo derivatives is thought to occur via zinc organic species [42], whereas radical intermediates are apparently involved in the reduction of the monohalogen compounds [43],... 

In a subsequent step, the enzyme adduct then detaches the alkyl group as an alcohol product. Sometimes, monohalogenated compounds act as growth inhibitors because the adduct formed is difficult to hydrolyze and thereby incapacitates the enzyme (recall suicide metabolites). However, assuming the adduct can be hydrolyzed, then the enzyme is prepared to serve again. 

Reaction LXXXV. Simultaneous Oxidation and Hydrolysis of Monohalogen Compounds. (A., 22, 1 143, 186.)—When benzyl chloride or one of its derivatives is heated with an aqueous solution of a mild oxidising agent, such as copper nitrate, lead nitrate, etc., combined hydrolysis and oxidation occurs, and benzaldehyde or one of its derivatives is obtained. 

Monohalogenated compounds, activated by carbonyl groups, also undergo cyclization giving five-, six- or seven-membered rings in reasonable to good yields (equation 130)290,683,733,783. Iodides may react without activation in some cases780,782,784,785. 

By far, the most studied chlorinating peroxidase is CPO (in particular that from Caldariomyces fumago, which is involved in the biosynthesis of the chlorometa-bolite caldariomycin). CPO is able to halogenate (Cl, Br) activated C-H bonds, such as those of 1,3-dicarbonyl compounds. The reaction can afford both the monohalogenated compound and the dihalogenated product (and also mixed chloro/bromo compounds) [89-92] (Fig. 6.8a). 

In fact, it is difficult to avoid these products when the a-halo dicat-boxylic acid is desired. Preparation of the monohalogenated compounds is accomplished by treatment of the ester acyl chloride with bromine or sulfutyl chloride in thionyl chloride solution (88-98%). ... 

The Wurtz-Fittfe synthesis. When a monohalogen compound is reduced by sodium under anhydrous conditions, the resulting rad-... 

So far, we have focused our discussion on the relative nucleophilicities of natural nucleophiles. Let us now consider how certain structural features of the organic molecule (i.e., type of leaving group, type of carbon skeleton) determine the kinetics of nucleophilic substitution. In Table 3, the (neutral) hydrolysis half-lives are given for various monohalogenated compounds at 25°C. Also indicated are the postulated reaction mechanisms with which these compounds undergo SN reactions. As can be seen from Table 3, the carbon-bromide and carbon-iodine bonds hydrolyze fastest, about one to two orders of magnitude... 

Substituted phthalimides are prepared by heating g. of potassium phthalimide with i cc. of a monohalogen compound usually in a sealed tube (150°-200°). The resultant derivatives are insoluble in dilute alkali, and thus can bo separated readily from unchanged phthalimide. 

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