Explain how biphenyl (an undesired product) can be formed during the preparation of the Grignard reagent. How can the amount of biphenyl that is formed be minimized

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Explanation:

Biphenyl is formed by the reaction of two phenyl radicals. It is a major impurity ( undesired product) that is formed when some amount of phenyl bromide (bromobenzene) doesn't react solid magnesium in the formation of the Gignard reagent. In other words, it is formed when there is a coupling reaction between Grignard reagent  (Grignard reagent acts as a strong nucleophile) and bromobenzene

Biphenyl is usually produces when the concentration of bromobenzene is high and when there is increase in temperature during reaction. To minimize the amount of biphenyl, it is best to add the bromobenzene solution slowly so that the reaction boils gently, since the reaction is favorable at low temperatures.

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