A chemist accidently discovered 'Mauveine' the first synthetic dye whilst searching for what?

Mauveine, also known as aniline purple and Perkin's mauve, was the first synthetic organic chemical dye, discovered serendipitously in 1856. It is also among the first chemical dyes to have been mass-produced.

In 1856, William Henry Perkin, then age 18, was given a challenge by his professor, August Wilhelm von Hofmann, to synthesize quinine (which is a medication to treat malaria and babesiosis). In one attempt, Perkin oxidized aniline using potassium dichromate, whose toluidine impurities reacted with the aniline and yielded a black solid—suggesting a "failed" organic synthesis. Cleaning the flask with alcohol, Perkin noticed purple portions of the solution.

Suitable as a dye of silk and other textiles, it was patented by Perkin, who the next year opened a dyeworks mass-producing it at Greenford on the banks of the Grand Union Canal in London. It was originally called aniline purple or Tyrian purple, the name of an ancient natural dye derived from mollusks. In 1859, it attained the name mauve in England via the French name for the mallow flower, and chemists later called it mauveine. By 1870, its great demand succumbed to newer synthetic colors in the synthetic dye industry launched by mauveine.