Baeyer–Drewsen indigo synthesis

The Baeyer–Drewsen indigo synthesis (1882) is an organic reaction in which indigo is prepared from 2-nitrobenzaldehyde and acetone 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.



The reaction is classified as an aldol condensation. As a practical route to indigo, this method was displaced by routes from aniline.

Note
In the English literature this reaction is sometimes called Baeyer–Drews o n reaction, although the author of the original paper was spelled Drews e n.