Dehalogenation phase-transfer

The yields of ketones, isolated from the reductive debromination of a-bromo-ketones by dicobalt octacarbonyl under basic phase-transfer conditions are good (Table 11.13), but are improved (>95%) by the use of stoichiometric amounts of the quaternary ammonium catalyst. Somewhat unexpectedly, in the case of the reductive dehalogenation of secondary benzylic halides, the yields of the coupled alkanes are... 

In a manner analogous to the formation of the other hydridometal complexes, the tricarbonylhydridovanadate anion is easily produced from r)5-cyclopentadienyl-vanadiumtetracarbonyl under basic phase-transfer catalytic conditions and it has been used in the reduction of nitro compounds and the reductive dehalogenation of a wide range of halides [ 12]. 

Alkylidynetricobalt nonacarbonyl complexes are an interesting class of clusters (78). They can be synthesized by treatment of a tri- or tetrahaloal-kane with cobalt carbonyl under phase-transfer conditions [e.g., 71] (28). Partially or completely dehalogenated by-products were often isolated from these reactions. 

Dehalogenation (1, 1089). Debromination of vfc-dibromides can be carried out conveniently in a two-phase system (H2O—toluene) using hexadecyltributyl-phosphonium bromide (5, 322-323) as phase-transfer catalyst. The combination of sodium iodide and sodium thiosulfate (4, 466) is used as the reagent sodium iodide is needed in catalytic amounts only, since it is regenerated by the thiosulfate. weso-Dibromides react faster than the dZ-isomers and afford only trans-alkenes the d/-isomers give mixtures of cis- and frani-alkenes. ... 

Dehalogenation of a-hromo ketones. Treatment of ot-halo ketones with 1 equiv. of Co2(CO)a under phase-transfer conditions yields the dehalogenated ketone in high yield and traces of the 1,4-diketone. Yields of the methyl ketone are somewhat lower when the metal carbonyl is used in catalytic amounts. ... 

Elimination reactions have been induced under phase transfer conditions by a variety of techniques [1, 2, 4, 5, 25—28]. Predominant among these is the dehydrohalogena-tion of alkyl halides or sulfonates [1, 2, 5] and the dehalogenation of vicinal dihalides [25]. In the former case, some elimination is observed as a side reaction of the intended Sn 2 halogen exchange reaction. The direct displacement of halide by halide (the... 

Vicinal dehalogenation has been reported under phase transfer conditions [25]. In this case, a series of vicinal dibromides was treated with an aqueous solution of sodium iodide and sodium thiosulfate in the presence of a quaternary ammonium catalyst. 1,2-Dibromooctane was thereby converted to 1-octene in 92% yield (see Eq. 9.8) [25]. It was found that the elimination reaction could be effected by sodium thiosulfate itself, but that this method was slower than when iodide ion was present. Only a catalytic amount of iodide ion was required in the reaction, it being continuously regenerated by reaction with thiosulfate. 

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