PREPARATIONS 201 Set aside (preferably overnight), and then filter off the acid, wash it with water and dry. Yield of crude acid, 12 g.; m.p. 223-226°. For purification, transfer the acid to a 150 ml. flask containing 60 ml. of water, boil the mixture under reflux, and then add acetic acid in 5 ml. portions down the condenser until almost all the solid has dissolved: avoid an excess of acetic acid by ensuring that the solvent action of each addition is complete before the next portion is added. A small suspension of insoluble impurity may remain. Add 2 g. of animal charcoal, boil the solution again for 10-15 minutes, and then filter it through a preheated Buchner funnel. Cool and stir the filtrate, which will deposit pale cream-coloured crystals of the acid. Collect as before and if necessary repeat the recrystallisation. Yield of pure acid, 9 g.; m.p. 227-229°. 4(or />)-Bromobiphenyl. BrC 6 H 4-C 6 H 5 . (Gomberg Re-action.) When an aqueous solution of a diazonium salt is added to an alkaline solution
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