labphoto:

Preparation of a 2-bromobenzoic acid derivative from an anthranilic acid derivative using the Sandmeyer reaction.

The Sandmeyer reaction is a chemical reaction used to synthesize aryl halides from aryl diazonium salts. It is named after the Swiss chemist Traugott Sandmeyer. The reaction is a method for substitution of an aromatic amino group via preparation of its diazonium salt followed by its displacement with a nucleophile, often catalyzed by copper(I) salts.

ArN₂⁺ + CuBr → ArBr + N₂ + Cu⁺

On the picture and gifs the solution of copper(I)-bromide is being added to the chilled, freshly prepared diazonium salt solution and as the the two reactants mix, almost instantly nitrogen gas forms and the reaction starts. 

Interesting thing is that the copper(I)-bromide is a colorless, nearly insoluble solid when pure, however when mixed with hydrobromic acid it dissolved rapidly and gives a deep purple colored solution as seen on the pictures.