Alcohols, halogenating agents

Alcohols undergo nucleophilic substitution at the 8+ carbon atom when reacted with halogenating agents. 

PMMAs are attacked by strong acids, strong and concentrated bases, esters, ethers, ketones, aldehydes, aromatic and halogenated hydrocarbons, certain alcohols, oxidizing agents, and phenols. 

Oxygenated polyvalent iodine compounds are also useful halogenating agents. oc-Iodoepoxides are prepared by reaction of iodosylbenzene diacetate (IBDA) with allyl alcohols (equation 116)832. Iodosylbenzene, activated by triflic acid, adds to acetylenes (equation 1 17)833. PhI(OAc)2 simultaneously iodinates and etherifies phenols (equation 118)834. 

Tertiary halides, RR R"CX, are formed easily by reaction of the alcohol and aqueous hydrogen halide. Acetyl chloride or bromide has also been used as the halogenating agent, as illustrated by the synthesis of triphenylchloromethane and its derivatives. . ... 

Choline876 and potassium amide877 have also given good results as dehydro-halogenating agents. Nitro- and cyano-benzyl chlorides are mostly converted very smoothly into stilbene derivatives when treated with alcoholic alkali hydroxide, as exemplified by Walden and Kernbaum for 4,4 -dinitrostilbene 878... 

The reaction of chlorodimethylformiminium chloride with alcohols has been utilized to synthesize the corresponding alkyl halides (122,234,235 and only a catalytic amount of N,N-dimethylformamide is necessary for conversion of an alcohol into the corresponding alkyl halide, using carbonyl chloride or thionyl chloride as the halogenating agent ( 22.143 p j. example. 

Various halogenating agents in the presence of a chiral additive have been used as oxidant systems to prepare sulfoxides (usually in low ee). Thus, the combinations iodine/water/(+)-2-methyl-2-phenylsuccinic acid [80] or N-chloroamides/chiral alcohols [81-83] gave sulfoxides with -10% ee at best. Menthyloxysulfonium salts are prepared by oxidation of sulfides in presence of menthol. They can be isolated and recrystallized, with improvement of the diastereoisomeric excess. They are interesting intermediates for the synthesis of chiral sulfoxides, which are obtained by aqueous basic hydrolysis, with inversion of configuration at sulfur. Sulfoxide may also be obtained (in lower ee) by a one-pot reaction, without isolation of the sulfonium salt. Thus, 1-chlorobenzotriazole in the presence of (-)-menthol in methylenechloride oxidizes benzyl p-tolyl sulfide into the sulfonium salt (42a) (Figure 1.3). After crystallization and hydrolysis, (-)-benzyl p-tolyl sulfoxide is afforded in 87% ee [84]. A chiral derivative of N-chlorocaprolactam has been used to prepare some sulfoxides in low ee [85]. 

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