ABSTRACT
Indole and the simple alkylindoles are colourless crystalline solids, with a range of odours from naphthalene-like, in the case of indole itself, to faecal in the case of skatole. The word indole is derived from the word India: a blue dye imported from India was known as indigo in the sixteenth century. Chemical degradation of the dye gave rise to oxygenated indoles. That 2-methylindole is a stronger base than indole can be understood on the basis of stabilisation of the cation by electron release from the methyl group; 3-methylindole is a somewhat weaker base than indole. Indole itself can be nitrated using benzoyl nitrate as a non-acidic nitrating agent; the usual mixed acid nitrating mixture leads to intractable products, probably because of acid-catalysed polymerisation. Under neutral conditions and at low temperature indole reacts with a mixture of formaldehyde and dimethylamine by substitution at the indole nitrogen; it seems likely that this reaction involves low equilibrium concentration of the indolyl anion.
