Hydrogenolysis: of alkyl halides

Protodehalogenation.1 This hydride is the reagent of choice for hydrogenolysis of alkyl halides. Lithium aluminum hydride is somewhat less powerful, particularly for reduction of alkyl chlorides. 

The hydrolysis of alkylmagnesium halides (Expt 5.3), and the hydrogenolysis of alkyl halides and of alkyl methane- or toluene-p-sulphonates (Expt 5.4). 

THE HYDROLYSIS OF ALKYLMAGNESIUM HALIDES, AND THE HYDROGENOLYSIS OF ALKYL HALIDES AND OF ALKYL METHANE- OR T0LUENE-/P-SULRH0NATES... 

Superhydride has also been used for the hydrogenolysis of alkyl toluene-p-sulphonates, and an illustrative example is given in Expt 5.4 for the preparation of cyclooctane from cyclooctyl toluene-p-sulphonate. A sodium borohydride hydrogenolysis of alkyl halides and of alkyl methane- and toluene-p-sulphonates under PTC conditions provides an interesting variant of this reaction.9... 

Catalytic hydrogenolysis of alkyl halides is one of the classical methods of alkane syntheses. Among other catalysts, Raney Ni has proved to be quite effective for the hydrogenolysis of iodides (equation 39) . A relatively recent discovery is the reductive dehalogenation of alkyl halides under the conditions of ionic hydrogenation. 

Brown and his co-workers have compared representative simple and complex metal hydrides in order to assess their capabilities for the hydrogenolysis of alkyl halides. Of the reducing agents studied, lithium triethylborohydride is the most powerful, and is the reagent of choice for the hydrogenolysis of alkyl... 

The reactions of alkyl halides with Fe(II) deuteroporphyrin IX have been examined (Wade and Castro 1973). Three classes of reaction were observed (i) hydrogenolysis, (ii) elimination to alkenes, and (iii) coupling of alkyl free radicals. Further discussion has been given in Castro (1998). 

Hydrogenolysis of the toluene-4-sulfonate of an alcohol may be carried out with a nucleophilic hydride such as lithium aluminium hydride. There are also a series of radical methods based on the reduction of alkyl halides with tri- -butyltin hydride (BUjSnH). Finally, the source of the hydrogen may be the electrophilic proton, exemplified by the decomposition of organometallic reagents such as the Grignard reagent with water. 

The hydrogenolysis of aryl halides proceeds more readily than the cleavage of alkyl-halogen bonds. Aryl chlorides are rather stable to hydrogenolysis in neutral medium and bromides are dehalogenated only to a moderate extent 24,132 but iodides are readily lost. Aryl fluorides, however, are hydrogenolyzed only under... 

No direct data for the decomposition of alkyl halides by clean, active metal surfaces seem to be available. Campbell and Kemball [11], in their study of the hydrogenolysis of ethyl chloride, cite evidence for the dehydrochlorination reaction... 

Triethylsilane reduction of alkyl halides is even better in the presence of thiols, which act as polarity reversal catalysts for hydrogen atom transfer from silane to alkyl groups (equation 41). This reagent in the presence of AICI3 reduces even em-dichlorides to alkanes (equation 42) . The powerful hydrogen donor reagent tn s-(trimethylsilyl)silane has been introduced as a superior alternative to triethylsilane for the hydrogenolysis of... 

Hydrogenolysls of alkyl halides may be performed by usina NaBHi, in DMSO, and of aryl halides by LiAlHi, in THF, a method for generating organotin hydrides in situ for use in hydrogenolysis reactions of alkyl halides has been presented. ... 

The reduction of alkyl halides by iron(ii) porphyrins and heme proteins has been investigated, with three general transformations taking place, either (a) coupling, (6) hydrogenolysis, or (c) elimination of vicinal halides... 

Historically, simple Vz-alkyl ethers formed from a phenol and a halide or sulfate were cleaved under rather drastic conditions (e.g., refluxing HBr). New ether protective groups have been developed that are removed under much milder conditions (e.g., via nucleophilic displacement, hydrogenolysis of benzyl ethers, and mild acid hydrolysis of acetal-type ethers) that seldom affect other functional groups in a molecule. 

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