Baeyer–Drewsen indigo synthesis

The Baeyer–Drewsen indigo synthesis (1882) is an organic reaction in which indigo is prepared from 2-nitrobenzaldehyde and acetone[1][2] The reaction was developed by von Baeyer and Viggo Drewsen in 1880 to produce the first synthetic indigo at laboratory scale.

This procedure is not used at industrial scale.

[3] The reaction is classified as an aldol condensation.

As a practical route to indigo, this method was displaced by routes from aniline.

[4] In the English literature this reaction is sometimes called Baeyer–Drewson reaction, although the author of the original paper was spelled Drewsen.