Trichloromethide anion

The actual formylation process is preceded by the formation of dichlorocarbene 3 as the reactive species. In strongly alkaline solution, the chloroform is deproto-nated the resulting trichloromethide anion decomposes into dichlorocarbene and a chloride anion ... 

Step 1 Take a proton away. Treatment of chloroform, which is somewhat acidic because of its three electron-withdrawing chlorine atoms, with potassium fert-butoxide gives the trichloromethide anion. 

In solid-liquid phase transfer processes, i.e., those reactions in which a solid reagent is phase transferred by a crown [46] or occasionally by a tertiary amine, a cosolvent is ordinarily used, regardless of whether or not the substrate is a solid. In principle, any solvent which does not itself undergo reaction (unless this is the desired end) is acceptable. The most commonly used solvents for solid-liquid phase transfer processes have been benzene (and other hydrocarbons), dichloromethane and chloroform (and other chlorocarbons) and acetonitrile. The latter solvent can be successfully utilized in solid-liquid systems whereas it should be unacceptable in liquid-liquid systems because of its miscibility with water. Chloroform and dichloromethane are commonly and successfully used, although both undergo reactions the former being readily deprotonated to yield either trichloromethide anion or carbene [38], and the latter suffering nucleophilic displacement [19b, 53, 54]. 

Despite the many advantages of the phase transfer method for generating dichlorocarbene, it should be noted that the reactive species arises from the trichloromethide anion as it does in most other methods. Because of this, attempted reactions with electron poor olefins will yield products arising from Michael addition of ClaC" to the olefin instead of, or in addition to, cyclopropanation products. The thermal decomposition of trihalomethyl metal compounds remains the unique method for generating dihalocarbenes without prior formation of a trihalomethyl anion [8]. 

Reaction of diclilorocarbene with substituted benzaldehydes affords the corresponding mandelic acids. It might be supposed that this reaction does not involve dichlorocarben but rather its precursor, the trichloromethide ion. Nucleophilic addition of the trichlorc methyl anion to benzaldehyde should yield phenyl trichloromethyl carbinol. In control experiments, however, phenyl trichloromethyl carbinol was not hydrolyzed to mandelic acid under the reaction conditions. It was suggested that the reaction involves dichlorocarbene addition to the benzaldehyde carbonyl to form 2,2-dichloro-3-phenyloxirane followed by rearrangement to a-chlorophenylacetyl chloride which then is hydrolyzed as shown in equation 3.16. Mandelic, 4-methylmandelic, and 4-methoxymandelic acids were produced in 75%, 80%, and 80% yields, respectively [24]. 

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