Organic Lab Reactions 231

Organic Lab Reactions 231 - 226 THE PREPARATION OF...

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226 THE PREPARATION OF UNSYMMETRICAL BIARYLS diazohydroxide reacts. The overall reaction may be written in the following manner. Br— i > />—N 2 +C1- + ( v /) + NaOH -> N 2 + NaCl'+ H 2 O The second step is carried out by adding a 15-40% aqueous solution of sodium hydroxide dropwise to a well-stirred mixture of the cold dia- zonium salt solution and the aromatic liquid until a slight excess of alkali is present.' This procedure avoids the isolation of the unstable, explosive diazohydroxides of Bamberger, 1 which are formed from the diazonium salt and the alkali. The diazohydroxide is extracted by the aromatic liquid as it is formed. The biaryl reaction takes place in the organic liquid and is complete when evolution of nitrogen ceases. In the example given, 4-bromobiphenyl is obtained in 35-46% yield. A variation in the procedure for certain amines is to add the diazonium salt to sodium hydroxide in an amount sufficient to form the sodium diazotate. The biaryl compound is formed when the aqueous solution
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