Salicylaldehyde

Salicylaldehyde, or 2-hydroxybenzaldehyde, is the chemical compound with the formula C6H4CHO-2-OH. This colourless oily liquid has a bitter almond odor. Salicylaldehyde is a key precursor to a variety chelating agents, some of which are commercially important. It can be prepared from phenol and chloroform by heating with sodium hydroxide in a Reimer-Tiemann reaction.

Salicylaldehyde is a common highly functionalized arene that has often been exploited as a precursor to still other chemicals, which are shown in the figure.
 * Salicylaldehyde is converted to chelating ligands via condensation with amines. With ethylenediamine, it condenses to give the popular diprotic ligand H2salen. Hydroxylamine gives salicylaldoxime.
 * oxidation with hydrogen peroxide gives catechol (1,2-dihydroxybenzene).
 * condensation with diethyl malonate gives a derivative of the heterocycle coumarin.
 * etherification with chloroacetic acid followed by cyclisation gives the heterocycle benzofuran.

General reading

 * Merck Index, 11th Edition, 8295.