Indoles Reactions and Synthesis

Indole and the simple alkyl-indoles 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 (3-methylindole). Many simple indoles are available commercially and all of these are produced by synthesis indole, for example, is made by the high-temperature vapour-phase cyclising dehydrogenation of 2-ethylaniline. Most indoles are quite stable in air with the exception of those which carry a simple alkyl group at C-2 2-methylindole autoxidises easily, even in a dark brown bottle. 

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 (see 20.13), which were named indoxyl and oxindole indole itself was first prepared in 1866 by zinc-dust distiUation of oxindole. 

For all practical purposes, indole exists entirely in the l//-form, 3//-indole (indolenine) being present to the extent of only ca. 1 ppm. 3H-Indole can be generated in solution but tautomerises to IH-indole within about 100 seconds at room temperature.  

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