1,4-Benzoquinone, commonly known as para-quinone, is a chemical compound with the formula C₆H₄O₂. In a pure state, it forms bright-yellow crystals with a characteristic irritating odor, resembling that of chlorine, bleach, and hot plastic or formaldehyde. This six-membered ring compound is the oxidized derivative of 1,4-hydroquinone. The molecule is multifunctional: it exhibits properties of a ketone, forming an oxime; an oxidant, forming the dihydroxy derivative; and an alkene, undergoing addition reactions, especially those typical for α,β-unsaturated ketones. 1,4-Benzoquinone is sensitive toward both strong mineral acids and alkali, which cause condensation and decomposition of the compound.

1,4-Benzoquinone is prepared by oxidation of diisopropylbenzene via a reaction related to the Hock rearrangement:

The reaction proceeds via the bis(hydroperoxide). Acetone is a coproduct.

Another major process involves the direct hydroxylation of phenol by acidic hydrogen peroxide: C₆H₅OH + H₂O₂ → C₆H₄(OH)₂ + H₂O Both hydroquinone and catechol are produced. Subsequent oxidation of the hydroquinone gives the quinone.

Quinone was originally prepared industrially by oxidation of aniline, for example by manganese dioxide. This method is mainly practiced in PRC where environmental regulations are more relaxed.

The oxidation of hydroquinone is rapid and convenient and therefore desirable for the laboratory. 1,4-Benzoquinone can be prepared from hydroquinone via a number of oxidation methods. One such method makes use of hydrogen peroxide as the oxidizer and iodine or an iodine salt as a catalyst for the oxidation occurring in a polar solvent; e.g. isopropyl alcohol.

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