Die katalytische Hydrogenisation organischer Verbindungen mit unedlen Metallen bei Zimmertemperatur. Die Entfernung von Halogen aus organischen Halogen‐verbindungen

The Function of Base in the Catalytic Dehalogenation of Aliphatic Halides. Reduction of Dichloromethylmethylcyclohexanones in the Presence of Potassium Hydroxide and Triethylamine

“…and chloride ion produced (1.0), as well as its broad melting point (45-60°), v.p.c. retention time, and infrared spectrum, appeared to be a mixture of the stereoisomeric 4-dichloromethyl-4-methylcyclohexanols (8). This structure assignment was shown to be correct by comparing the physical properties mentioned before with those of an authentic sample prepared from the dichloro ketone 2 by reduction with sodium borohydride.…”

“…Caled, for CgHuOCls (8b): C, 48.75; , 7.16. Found: C, 48.85; H, 7.23. Hydrogenation of 4-Dichloromethyl-4-methylcyclohexanol (8). A.…”

“…In the gas phase, inhibition of dehalogenation by halogen acids has been reported,10 but this is not surprising since the catalysts were in the form of metallic films which are notably susceptible to poisoning.11 In solution studies utilizing supported catalysts, only the dehalogenations of aromatic halides containing a basic nitrogen atom and certain aliphatic halides with adjacent unsaturation were impeded by acids and then merely to the extent of reducing the rates to those of compounds without such activating groups. 8 Finally, the use of base in excess of that necessary for. neutralization of the halogen acid has been found to accelerate the rate of reduction.3 8 These observations suggest that the sole function of base in catalytic dehalogenations is not, as has been assumed, the destruction of halogen acid, but rather that the base plays a direct role in aiding the reductive cleavage of the carbon-halogen bond.18 If the previous hypothesis is correct, then the ease of removal of aliphatic halogen atoms in basic solution may be related to any of a number of properties of the base such as its type (Lewis or Br0nsted), nucleophilieity, ionization constant, ionization potential, etc.…”

“…8 Finally, the use of base in excess of that necessary for. neutralization of the halogen acid has been found to accelerate the rate of reduction.3 8 These observations suggest that the sole function of base in catalytic dehalogenations is not, as has been assumed, the destruction of halogen acid, but rather that the base plays a direct role in aiding the reductive cleavage of the carbon-halogen bond.18 If the previous hypothesis is correct, then the ease of removal of aliphatic halogen atoms in basic solution may be related to any of a number of properties of the base such as its type (Lewis or Br0nsted), nucleophilieity, ionization constant, ionization potential, etc.…”