William Henry Perkin studied and worked at the college under von Hofmann, but resigned his position after discovering the first synthetic dye, mauveine, in 1856. Perkin's discovery was prompted by his work with von Hofmann on the substance aniline, derived from coal tar, and it was this breakthrough which sparked the synthetic dye industry, a boom which some historians have labelled the second chemical revolution. His contribution led to the creation of the Perkin Medal, an award given annually by the Society of Chemical Industry to a scientist residing in the United States for an "innovation in applied chemistry resulting in outstanding commercial development". It is considered the highest honour given in the industrial chemical industry.
What discovery by von Hoffman was prompted by his work with Perkins?