Tyrian Purple (6,6’-dibromoindigo) A New Twist on the Dye of Old

An Ancient Process The Current Way

The base chemical of 6,6’-dibromoindigo dye is Dow Chemical Company was the first company to make found naturally in mollusks and certain other crustaceans. Fabric can be dyed through synthetic indigo dye. 6,6’-dibromoindigo soon followed. Indigo direct dyeing, where the fabric or fiber is dyes (including 6,6’-dibromoindigo) are no longer made in the coated with the paste of the mollusk’s mucus U.S., because it is cheaper to import them from other countries. gland. The pasted fabric is allowed to sit in the Today, indigo dye is produced using laboratory chemical sun so that the purple can develop. Fabric can processes. These processes are highly efficient and cost-effective also be dyed using vat dyeing. In this process, the saliva of the mollusk is combined with for the companies that use them, but there are a growing paste of the mucus gland and allowed to dry. number of environmental concerns that are associated with their This residue is ground into a powder and put manufacture and use, as the dying process creates a large into a warm solution of sodium hydroxide or amount of chemical waste that must be disposed of carefully. At lye, away from sunlight, and fabric this time, both lawmakers and chemists are investigating simpler, is immersed in it. Finally, the dyed fabric is put through a finishing process (for safer, and more efficient ways to get the vividly colored clothing example, an acid wash), and washed with soap and water. In Rome, enormous vats of snails were left to decompose over a period of days, then boiled to we wear and love. concentrate the dye. After the mucus and saliva mixture was boiled down enough, fabric was immersed until the desired color was attained. Over the Rainbow A chemical reaction with multiple steps uses sunlight to turn the paste from the mollusk’s mucus gland from clear to the vivid purple we are all familiar with. The following list shows the reaction’s steps. Each chemical is color-coded to show its color during the reaction. 1. The removed mucus gland contains clear, colorless tyrindoxyl sulfate 2. When cells begin to die in the sun, tyrindoxyl sulfate is converted to tyrindoxyl 3. Tyrindoxyl oxidizes to form tyrindoleninone. 4. Tyrindoleninone reacts with tyrindoxyl to make tyriverdin. 5. Tyriverdin is actually yellow, but it decomposes into 6,6’-dibromoindigo and dimethyl disulfide, which smells like rotting fish or strong garlic. Tyriverdin appears green because the 6,6’-dibromoindigo and tyriverdin are always mixed. 6. Eventually, so much decomposition occurs that the gland appears purple.