The Reissert indole synthesis is a series of chemical reaction

Chemical reaction

A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, typically following the input of some type of energy, such as heat, light or electricity...

s designed to synthesize indole

Indole

Indole is an aromatic heterocyclic organic compound. It has a bicyclic structure, consisting of a six-membered benzene ring fused to a five-membered nitrogen-containing pyrrole ring. Indole is a popular component of fragrances and the precursor to many pharmaceuticals. Compounds that contain an...

 or substituted-indoles (4 and 5) from ortho-nitrotoluene 1 and diethyl oxalate 2.

Potassium ethoxide has been shown to give better results than sodium ethoxide

Sodium ethoxide

Sodium ethoxide is an alkoxide salt with the chemical formula C2H5ONa.-Preparation:It is commercially available as a white solid, or as a solution in ethanol. It is easily prepared in the laboratory by reacting sodium metal with ethanol:...

.

Reaction mechanism

The first step of the Reissert indole synthesis is the condensation of o-nitrotoluene 1 with a diethyl oxalate 2 to give ethyl o-nitrophenylpyruvate 3. The reductive

Redox

Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....

 cyclization of 3 with zinc

Zinc

Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...

 in acetic acid

Acetic acid

Acetic acid is an organic compound with the chemical formula CH3CO2H . It is a colourless liquid that when undiluted is also called glacial acetic acid. Acetic acid is the main component of vinegar , and has a distinctive sour taste and pungent smell...

 gives indole-2-carboxylic acid 4. If desired, 4 can be decarboxylated

Decarboxylation

Decarboxylation is a chemical reaction that releases carbon dioxide . Usually, decarboxylation refers to a reaction of carboxylic acids, removing a carbon atom from a carbon chain. The reverse process, which is the first chemical step in photosynthesis, is called carbonation, the addition of CO2 to...

with heat to give indole 5.