Dichloromethylene, carbene

The carbene CH2 derived by removal of two hydrogen atoms from CH4 is known as methylene, CCl2 is known as dichlorocarbene or dichloromethylene, and C(C6H5)2 is known as diphenylcarbene or diphenylmethylene. 

Carbenes are highly reactive species, practically aU having lifetimes considerably under 1 s. With exceptions noted below (p. 289), carbenes have been isolated only by entrapment in matrices at low temperatures (77 K or less). The parent species CH2 is usually called methylene, although derivatives are more often named by the carbene nomenclature. Thus CCI2 is generally known as dichlorocarbene, although it can also be called dichloromethylene. 

The nucleophilic character of triphenylphosphine and the electrophilic character of carbenes suggested to two groups of investigators that the two reagents should combine to form ylides of a new type to use in expansion of the Wittig reaction. Speziale et ai. found that triphenylphosphine on treatment in pentane with chloroform and potassium t-butoxide at 0° gives yellow triphenylphosphine dichloromethylene, which reacts with benzophenone to yield I,l-diphenyl-2,2-dichloroethylene (1). 

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