Anwendungen der phasentransfer-katalyse—4: Halogenaustausch und reaktivitäten bei dibrom-, chlorbrom- und dichlorcarben

Exchange with external halogenide is possible in phase transfer catalytical generations of dihalocarbenes. CHBrCl₂ and CHBr₂Cl yield adducts of all three possible combinations, CBr₂, CBrCl and CCl₂. Consumption of haloform is accelerated by the presence of olefin, the amount of hydrolysis competing with carbene formation, however, is reduced thereby. Contrary to claims in the literature no optical induction is observed in CX₂ additions. These results support once more the intermediacy of free CX₂. CBr₂ is more reactive and electrophilic than CCl₂ under phase transfer catalysis conditions, again contrary to literature claims. An example of a differing mode of reaction of chloroform and bromoform is given.