Wurtz - Fittig reaction is an extended approach by Wilhelm Rudolph Fittig on the Wurtz Reaction given by Charles Adolphe Wurtz in 1855. This is the reason, this modification of Wurtz – Reaction is named after Charles Adolphe Wurtz and Wilhelm Rudolph Fittig as Wurtz – Fittig Reaction. It is one of the important reactions of organic chemistry which is used to synthesize carbon – carbon bonds.
What is Wurtz – Fittig Reaction?
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. Reaction is given below –
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. Wurtz Reaction is given below –
2R – X + 2Na 🡪 R – R + 2NaX
Where R = alkyl group
X = Halide ion
Wurtz – Fittig reaction is best for formation of asymmetrical products if halide reactants are different in their relative chemical reactivities. 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.
Mechanism of Wurtz – Fittig Reaction
Mechanism of Wurtz – Fittig reaction is not certain as there are two approaches available to describe the mechanism of Wurtz – Fittig reaction and empirical evidence are available for both approaches. Both the approaches are listed below –
Organo - alkali mechanism
The radical approach involves the sodium - mediated aryl radical and alkyl radical formation. According to this mechanism 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. Reaction mechanism is given below –
Organo - Alkali Mechanism
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, 1st aryl halide reacts with sodium metal and forms 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. Reaction mechanism is given below –
Use of Other Metal in Place of Sodium
Wurtz – Fittig reactions can be carried out using other metals such as copper, iron, potassium and lithium than sodium metal. When we use lithium in place of sodium, the reaction gives appreciable yield, but the reaction takes place only under ultrasound. It takes place by free radical mechanism.
Wurtz Reaction, Fittig Reaction and Wurtz – Fittig Reaction
Generally, students get confused between Wurtz reaction, Fittig reaction and Wurtz – Fittig reaction. So, we are giving here a comparative study of these all three reactions in a tabular form –
Applications of Wurtz – Fittig Reaction
Wurtz – Fittig reaction is useful in the laboratory for synthesis of organosilicon compounds. For example, t-butyltriethoxysilane 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.
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