Purpurin (PP)

Purpurin, is an anthraquinone. It is a naturally occurring red/yellow dye. It is formally derived from 9,10-anthraquinone by replacement of three hydrogen atoms by hydroxyl (OH) groups. Purpurin is a crystalline solid, that forms orange needles melting at 259 °C, but becomes red when dissolved in ethanol, and yellow when dissolved with alkalis in boiling water. It is insoluble in hexane but soluble in chloroform, and can be obtained from chloroform as reddish needles. Unlike alizarin, purpurin is dissolved by boiling in a solution of aluminum sulfate, from which it can be precipitated by acid. This procedure can be used to separate the two dyes. Pupurin has a purgative action, although only 1/20 as effective as 1,2,7-trihidroxyanthraquinone (anthrapurpurin).Purpurin is a fast dye for cotton printing and forms complexes with various metal ions. However it fades faster than alizarin on exposure to sunlight.