Reimer–Tiemann reaction

This interaction favors selective ortho-formylation, consistent with other electrophilic aromatic substitution reactions.

Hydroxides are not readily soluble in chloroform, thus the reaction is generally carried out in a biphasic solvent system.

In the simplest sense this consists of an aqueous hydroxide solution and an organic phase containing the chloroform.

This can be achieved by rapid mixing, phase-transfer catalysts, or an emulsifying agent such as 1,4-dioxane as solvent.

Using carbon tetrachloride instead of chloroform gives a carboxylic acid product instead of an aldehyde.