On an industrial scale, is prepared by spontaneous oxidation of:
1-Ethylanthraquinone
2-Ethylanthraquinol
1-Ethylanthraquinol
None of the above.
is prepared by spontaneous oxidation of 2-ethylanthraquinol. The reaction is:

The by-product 2-Ethyl anthraquinone is reduced to 2-ethyl anthraquinol by in the presence of catalyst palladium.