The 1,4-benzoquinone-bromine photoreaction is investigated with UV/Vis spectroscopy, mass spectrometry, and H-1 NMR methods. The absorption and mass spectra suggest that 1,4-benzoquinone in aqueous solution reacts with bromine only in the presence of light, which leads to the production of brominated-1,4-hydroquinones. Parallel experiments performed with illuminated and unilluminated 1,4-hydroquinone-bromine reactions indicate that the bromination of the benzene ring takes place during rather than after the photoreduction of 1,4-benzoquinone. The results provide an explanation for the subtle photosensitivity seen in a number of acidic bromate-aromatic compound reactions. (C) 2007 Elsevier B.V. All rights reserved.