MadSci Network: Chemistry

Re: What are the chemical structures of artificial colors?

Date: Mon May 10 08:09:55 2004
Posted By: Keith Allison, , dept: New Product, Technology & Development, Binney & Smith, Inc. (Crayola)
Area of science: Chemistry
ID: 1079831630.Ch

Dear Aaron,

"Artificial color" is another way of describing synthetic dyes (man-made colorants). Syntheitc dyes vary greatly in their molecular size and shape. However, there are some common features among their structures that makes them colorful. Virtually all synthetic dyes have benzene rings in their structure. Benzene rings are the most efficient way to make the other critical feature of these synthesized molecules: alternating double bonds (double-single-double-single, etc.) Electrons in these types of structures become highly delocalized (able to freely move about the entire molecule).

As for the reaction part, dyes indeed do react with their substrates (objects or materials to be dyed)and the type of dye/substrate determines the type of bonding. Typically, these reactions are either ionic (where the dye is typically negatively charged and the substrate is positive and they combine to form a salt), or covalent (electrons are shared as opposed to transferred). In the fabric industry, most of the reactions utilize a specific kind of covalent bonding called "coordinate-covalent", because the fabrics must be pretreated with a "mordant" (a metal salt) which helps to anchor the dye to the fabric through coordinating metal bonds.

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