Hydrogenolysis halogen effect

Water does not dissolve many organic compounds but it can be used as a solvent, especially in hydrogenations of acids and their salts. It may have some deleterious effects for example it was found to enhance hydrogenolysis of vinylic halogens [66],... 

Solutions of low-valence titanium chloride (titanium dichloride) are prepared in situ by reduction of solutions of titanium trichloride in tetrahydrofuran or 1,2-dimethoxyethane with lithium aluminum hydride [204, 205], with lithium or potassium [206], with magnesium [207, 208] or with a zinc-copper couple [209,210]. Such solutions effect hydrogenolysis of halogens [208], deoxygenation of epoxides [204] and reduction of aldehydes and ketones to alkenes [205,... 

Bases are added frequently as promoters in catalytic dehalogenations to neutralize the liberated halogen acid that may inhibit the action of catalyst.196 Denton et al. studied the effects of added potassium acetate to the rates of hydrogenolysis of various halogen compounds with a Pd-C as catalyst in methanol (Table 13.8).196... 

TABLE 13.8 Effects of Added Potassium Acetate on the Rates of Hydrogenolysis of Halogen Compounds 1 ... 

Finally, hydrogenolysis of the halogen atom of a-halocarbonyl compounds can be carried out at noble metal catalysts. Palladium is frequently used for this purpose. Selective removal of just one of the halogen atoms in the dihalides (32) can be effected in NaOAc/HOAc over a palladium catalyst. ... 

Defunctionalization. Removal of halogen atoms from bromo and iodo compounds, deoxygenation of alcohols, and deamination can be achieved by free radical chain processes. The reaction employs diphenylsilane as the hydrogen source to effect the hydrogenolysis alcohols and amines must be derivatized as xanthates and isocyanides, respectively. 

Hydrogenolysis of the carbon-halogen bond is an important reaction, both from synthetic and from environmental points of view. The results of the early experiments with [HCo(CN)5] as catalyst are summarized in Ref [4], A variety of organic halides could be effectively dehalogenated with aqueous sodium formate with [PdCl2L2] (L= various sulfonated phosphines) [57], [RuCl2(TPPMS)2]2 and [Ru(H20)3(PTA)3] + [63], and [Ir(bipy)(Cp )(H20)] [64] catalysts. 

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