Due to the toxicity and possible carcinogenicity of these compounds, we initially chose the Beech synthesis instead, starting from o-nitroaniline ( 2). The traditional syntheses of 6 involve the use of p-toluidine, o-nitrotoluene, or their derivatives as starting materials or intermediates. This paper describes our efforts in developing a new, more attractive synthesis of Tyrian purple.įirst synthetic scheme for the preparation of dibromoindigo ( 1). In particular, we are interested in a synthesis which is amenable to production of relatively large amounts of the compound in an undergraduate student laboratory. A chemical synthesis of reasonable length, cost and safety is, therefore, still a very desirable research goal.

Synthetic Tyrian purple is commercially available today, but at a price nearly as high as the natural pigment. However, all known syntheses are either lengthy, inefficient, or involve expensive or hazardous starting materials or reagents. Įver since the dye was identified, chemists have been interested in developing practical syntheses of the compound.

Paul Friedländer, who in 1909 first identified the structure of the dye as 6,6′-dibromoindigo, required 12,000 Murex brandaris snails to produce 1.4 g of pure pigment. Due to the minute amounts of dye found in the snails, the dye has always been very costly. Structure of 6,6’-dibromoindigo ( 1, Tyrian purple).įrom ancient times the dye has been produced from secretions of various species of snails found off the Atlantic and Mediterranean coasts.

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