The Birch reduction is an organic reaction which is particularly useful in synthetic organic chemistry. The reaction was reported in 1944 by the Australian chemist Arthur Birch (1915–1995) working in the Dyson Perrins Laboratory at the University of Oxford, building on earlier work by Wooster and Godfrey published in 1937. It converts aromatic compounds having a benzenoid ring into a product, 1,4-cyclohexadienes, in which two hydrogen atoms have been attached on opposite ends of the molecule. It is the organic reduction of aromatic rings in liquid ammonia with sodium, lithium or potassium and an alcohol, such as ethanol and tert-butanol. This reaction is quite unlike catalytic hydrogenation, which usually reduces the aromatic ring all the way to a cyclohexane.

The original reaction reported by Arthur Birch in 1944 used sodium and ethanol.   Alfred L. Wilds later discovered that lithium gives better yields.  Also the use of tert-butyl alcohol has become common. The reaction is widely used in synthetic organic chemistry.

An example is the reduction of naphthalene:

Basic reaction mechanism

A solution of sodium in liquid ammonia consists of the electride salt [Na(NH₃)_x]⁺ e⁻, which has an intense blue color. The solvated electrons add to the aromatic ring to give a radical anion. The added alcohol supplies a proton to the radical anion and also to the penultimate carbanion; for most substrates ammonia is not acidic enough.