Pentaethylphenol (Not 2,6-di-tert-butyl-4-ethylphenol) verified as the primary product of guaiacol ethanol alkylation reaction

Abstract

Guaiacol ethanol alkylation (GEA), a model reaction of lignin solvolysis, has been intensively investigated. However, the product identification with gas chromatograph-mass spectrometer (GC-MS) was wrong due to the defect of the GC-MS databases. In this work, the main product was isolated with a flash chromatography technique and analyzed with ¹H NMR and was identified as ethyl fully substituted phenol (or pentaethylphenol), which is contrary to the reported 2,6-di-tert-butyl-4-ethylphenol in previous literature. The NMR analysis of the entire product mixture further confirms that the product only contains ethyl substituted molecules, with no existence of isopropyl or tert-butyl substituted products. The byproducts, including ethyl partially substituted phenols, i.e., tetraethylphenol and triethylphenol, ethyl partially substituted guaiacol, 2-ethoxyphenol, and pentaethylbenzene, were also speculated based on the MS spectra. These findings rectify a long-standing error in product identification and may offer critical insights for mechanism investigations.