Azo chemistry is one of the most widely used methods of making synthetic dyes

and pigments. The term azo refers to a nitrogen double bond within the mole-

cule. The discovery of nitrogen is attributed to Daniel Rutherford who was the

first to isolate the gas and demonstrated that it was an asphyxiant and did not

support combustion. Azo is abbreviation for azote, the name proposed by French

chemist Antoine Lavoisier for the element nitrogen. Azote derives from the

Greek a (not) and zoe (to live).

William Henry Perkin is credited with the discovery, albeit accidental, of the first

synthetic organic dye called mauvine in 1856. The key to synthesis of mauvine

was analine, an aromatic amine. In the 1800s, the burning of coal became an im-

portant source of heat and light in many European and American cities. Burning

of coal leaves behind a viscous, brown liquid that was called coal tar because it

resembled the pine tar.

In failed experiments aimed at making quinine, Perkin created the bright purple

dye from coal tar derived benzene. During a time when most fabric dyes were

based on natural sources that were expensive to produce and highly variable in

quality, Perkin patented the dye making process and promptly reigned from col-

lege in order to set up the business of manufacturing the dye.

Many new dyes were synthesized from aniline, eventually leading to the devel-

opment of azo dyes. Synthetic organic pigments are sometimes referred to as

coal tar dyes today, but the term is outdated as modern cosmetic dyes are pre-

pared from petroleum distillates. Azo pigments account for most of the red, or-

ange, and yellow pigments used in cosmetics including Red 6 and 7 Lakes.

A quick look at the FDA’s reports on total pounds certified reveals Red 6 and 7

lakes are the most widely used. This is due to their bold hues, excellent econom-

ic value, and good stability properties. They are the two main colorants used to

create bright red lipsticks and nail polish with Red 6 being a yellow-shade red

and Red 7 a blue-shade.

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