Electrochemical production of alkoxy-substituted phenols

The electrochemical oxidation of hydroquinone and substituted hydroquinones has been studied over graphite and platinum electrodes in different alcohol media. The results have shown that good yields of the corresponding alkoxy-substituted phenols can be obtained with high selectivities towards the hydroquinone monoalkyl ether. A mechanism is put forward to explain the formation of the alkoxyphenol through the creation of a quinhydrone complex, formed between the hydroquinone and benzoquinone, which is then attacked by the alcohol acting as a nucleophile. In this study, the effect of sulfuric acid as supporting electrolyte and acid catalyst was compared with that of methanesulfonic acid. It was found that sulfuric acid gave the best yield for different alkoxyphenols. The alcohols under investigation were C-1-C-8, and it was found that the longer the chain length of the alcohol, the slower the tendency to produce alkoxyphenols. Branched alcohols such as secondary and tertiary alcohols showed no reactivity towards the quinhydrone complex. Some of the yields obtained are as follows: 4-methoxyphenol (97%), 4-ethoxyphenol (71.4%) and 4-propoxyphenol (81.1%). (c) 2008 Elsevier Ltd. All rights reserved.