Hydroquinone

From Silvergrain Labs

Hydroquinone is a very common developing agent, which has been in common use since late 1800s.

Manufacturing

Hydroquinone is commercially manufactured by process analogous to the Hock process (Hock and Lang 1944) but using diisopropylbenzene as the starting material. Diisopropylbenzene is oxidized with pressurized gaseous oxygen (or air) at a high temperature to generate its hydroperoxide form, which is then decomposed with sulfuric acid to obtain hydroquinone and acetone. This process is used by Eastman Chemical and Goodyear in the US.

Another method is hydroxylation of phenol, used by Mitsui Petrochemical and Sumitomo Chemical of Japan, Rhône-Poulenc of France and Enichem of Italy.

Before Hock method became commonly used after WWII, hydroquinone was produced by oxidizing aniline to p-benzoquinone with permanganate or dichromate acidified with sulfuric acid, then hydrogenating p-benzoquinone using iron and hydrochloric acid. The oxidation is usually carried out at a low temperature a few degrees above the freezing point of water. This process is currently used in China but it is no longer used in the United States and Japan due to the use of manganese and chromium based oxidizing agents.