Halogeno acids, elimination reactions

Cyclization. Halohydrin. The elimination reaction of ethylene halohydrins on solid catalysts gives ethylene oxide or other products depending on the nature of the catalyst. Acetaldehyde was obtained using a solid acid catalyst supported on silica gel by halide-ion abstraction, ethylene from the less polar sites on metal surfaces by halogen-atom abstraction, and ethylene oxide from the basic sites by proton abstraction. Among some of the more unusual epoxides which have been formed by base treatment of the corresponding halohydrin are the polyfluorinated epoxides (89) and the C-labelled l-halogeno-2,3-epoxy[3- K )]propane (90) (X = Cl, Br, or I). 

Several papers report on the nucleophilic reactivity of dithiocarbamate ions towards alkyl halides, 1,2-dibromoalkyl compounds, alkyl and aryl chloroformates, chloroacetic acid, chloroacetates, 3-halo-genophthalides, sulphenyl chlorides, sultones, and trialkylam-monium compounds. Examples of a similar reactivity of dithiocarbazate anions have also appeared. " A series of papers deal with addition or addition-elimination reactions of dithiocarbamate - or dithiocarbazate anions with w-nitrostyrene, 2-thioxo-, 2-oxo-, and 2-imino-5-methoxycarbonylmethylidene-4-thiazolidones, dimethyl acetylenedicar-boxylate, and NN -dialkyl phenylpropiolamidines. S-Monoalkylated N-cyanodithioimidocarbonates (492) underwent oxidative ring-closure to give 3-halogeno-l,2,4-thiadiazole sulphides (493) on treatment with halogenating agents. ... 

The use of a reagent bearing a basic center or the addition of a base to the reaction mixture was recognized as necessary to prevent the acid-catalyzed elimination of the elements of water from the intermediates. Since the publication of this work, a number of similar intermediates have been isolated from thioamides and a-halogeno carbonyl compounds (608, 609, 619, 739, 754, 801), and as a result of kinetic studies, the exact mechanism of this reaction has been well established (739, 821). 

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