Halides degradation, reductive

Problem 18.8 Prepare ethylamine by (a) Gabriel synthesis, (6) alkyl halide amination, (c) nitrile reduction, (d) reductive amination, (e) Hofmann degradation. ... 

Biodegradation. Halogenated solvents are degraded under aerobic and anaerobic conditions. The anaerobic process is typically a reductive dechlorination that progressively removes one halide at a time,... 

EMDE DEGRADATION. Modification of the Hofmann degradation method for reductive cleavage of the carbon-nitrogen bond by treatment of an alcoholic or aqueous solution of a quaternary ammonium halide with sodium amalgam. Also used as a catalytic method with palladium and platinum catalysts. The method succeeds with ring compounds not degraded by the Hofmann procedure. 

The reductive photodehalogenation of aryl halides has been actively investigated in recent years. Special attention has been given to (poly)halobenzenes and (poly)halo-biphenyls. The reactions are of interest in view of their mechanisms, and because of the importance of chlorinated aromatic hydrocarbons as environmental pollutants and the possibility of their photoinduced degradation. The photochemistry of aryl halides and related compounds in general14 and the photochemistry of polyhaloarenes in particular18 have been reviewed. 

Polyhalogenated aromatic hydrocarbons (e.g. hex-achlorobenzene (HCB, CeCle) and polychorobiphenyls (PCBs)) are rapidly degraded by superoxide ion in DMF to bicarbonate and halide ions. Because halogen-bearing intermediates are not detected, the initial nucleophilic attack is the rate-determining step. The rates of reaction exhibit a direct correlation with the electrophilicity of the substrate (reduction potential) (e.g. CeCle, E° = -1.48 V vs. SCE ki/[S] = 1 X lO M- s and 1,2,4-C6H3C13, E° = -2.16 V ki/[S] = 2x 10-2 M- s ). 

The amine group in primary amines can be replaced by halogen by warming the benzoyl derivative with phosphorus pentachloride or phosphorus pentabromide. Oftentimes, the separation of the halide from the benzonitrile, which is also formed, is troublesome. The process has been applied mostly to high-moIecuIar-weight amines obtained by the Hofmann degradation of acid amides or by reduction of nitriles." Diamines lead to dihalogen derivatives." If N-benzoyl piperidines are treated, substituted pentamethylene halides are formed. An example is the synthesis of pentamethylene bromide by the action of phosphorus pentabromide on N-benzoyl piperidine (72%). ... 

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