Question

$~2{{C}_{6}}{{H}_{5}}-X+2Na\xrightarrow{Dry~Ether}A+2NaX.$ What will be the product A obtained in the reaction?
A.${{C}_{6}}{{H}_{5}}Cl$
B.${{C}_{12}}{{H}_{10}}$
C.$\,{{C}_{6}}{{H}_{5}}-\,{{C}_{6}}{{H}_{5}}$
D.${{C}_{6}}{{H}_{5}}Na$

Answer 1

We know that the reaction of alkyl halide with aryl halide and sodium metal in presence of dry ether to form substituted aromatic compounds by formation of new carbon–carbon bond is called Wurtz–Fittig reaction. It is a coupling reaction. It is a modified form of Wurtz reaction. Wurtz reaction is also a coupling reaction of organometallic chemistry in which two alkyl halides react with sodium metal in presence of dry ether to form a higher alkane by formation of new carbon–carbon bond.

Complete answer: Wurtz – Fittig reaction is best for formation of asymmetrical products if halide reactants are different in their relative chemical reactivity. The reaction is basically used for alkylation of aryl halides, but it can be used for production of biphenyl compounds by the use of ultrasound. The radical approach involves the sodium - mediated aryl radical and alkyl radical formation. According to these mechanisms sodium metal acts as a mediator and formation of alkyl radical and aryl radical takes place. Then alkyl radical and aryl radical combine to form a substituted aromatic compound. This mechanism is supported by formation of side products which cannot be explained by organo-alkali mechanism. For example, Bachmann and Clarke found that in reaction of sodium and chlorobenzene, one of the many side products is triphenylene whose formation can be explained by free radical mechanism only
$2{{C}_{6}}{{H}_{5}}-X+2Na\xrightarrow{Dry~Ether}{{C}_{6}}{{H}_{5}}Cl+2NaX.$
Therefore,the correct answer is option A.

Additional Information: Also the Wurtz – Fittig reaction is useful in the laboratory for synthesis of organosilicon compounds. For example, t-butyl trimethoxysilane can be prepared by Wurtz – Fittig reaction. In this $40$yield is obtained. Applications of Wurtz Fittig reactions are limited. It is not used at large scale for industrial purposes. However, it is useful in laboratory synthesis of substituted aromatic compounds.

Note:
Note that the organo - alkali approach involves the formation of an intermediate organo – alkali compound by reaction of aryl halide with sodium metal. According to this approach, first aryl halide reacts with sodium metal and forms an organo – alkali compound then nucleophilic attack of alkyl halide takes place. This mechanism is supported by indirect evidence such as many investigators observed that an organo – alkali intermediate is actually formed during the reaction.