Question

What is t-butyl hydroquinone?

Answer 1

Basically hydroquinone with a t-butyl group ortho to one of the hydroxy positions.

Explanation:

The systematic name is 2-(1,1-dimethylethyl)-1,4-benzenediol.
Hydroquinone is a benzene ring with two hydroxy -OH groups para to each other, i.e. in the 1 and 4 positions.

t-butyl hydroquinone has a t-butyl group adjacent to one of the hydroxy groups (i.e. in the 2 position).

It's mainly used as an antioxidant for preservative applications, for example in unsaturated vegetable oils. But it also has non-food applications, for example, it is often used in biodiesel as an antioxidant.