The nitration of benzaldehyde produces mostly 3-nitrobenzaldehyde. Partly for this reason, 2-nitrobenzaldehyde is prepared by indirect routes.[2] The main routes to nitrobenzaldehyde begin with the nitration of styrene or cinnamic acid followed by the conversions of the resulting 2-nitrostyrene and 2-nitrocinnamic acids, respectively. Cinnamaldehyde can also be nitrated in high-yield to 2-nitrocinnamaldehyde.[3] This compound is then oxidized to 2-nitrocinnamic acid, which is decarboxylated to the 2-nitrostyrene. The vinyl group can be oxidized in a number of different ways to yield 2-nitrobenzaldehyde.[4]
2-Nitrotoluene can be oxidized to yield 2-nitrobenzaldehyde.[5][6]
Alternatively, 2-nitrotoluene as formed above can be halogenated to a 2-nitrobenzyl halide followed by oxidation with DMSO and sodium bicarbonate to yield 2-nitrobenzaldehyde, which is subsequently purified with the creation of a bisulfite adduct.[7]
Uses
2-Nitrobenzaldehyde is an intermediate in an early route to indigo, a water-insoluble dye commonly used to dye jeans and other fabrics. In the Baeyer–Drewson indigo synthesis, 2-nitrobenzaldehyde condenses with acetone in basic aqueous solution to yield indigo in a one-pot synthesis[8][9] The method was abandoned in the early part of the 20th century, being replaced by routes from aniline.[10]
Given its two relatively reactive groups, 2-nitrobenzaldehyde is a potential starting material for other compounds. Substituted 2-nitrobenzaldehydes can also be used to yield other important compounds based on indigo, such as indigo carmine.
