Selective monoalkylation of hydroquinone in the presence of SO 3 H-functionalized ionic liquids as catalysts
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ORIGINAL PAPER
Selective monoalkylation of hydroquinone in the presence of SO3H‑functionalized ionic liquids as catalysts Priyanka V. Bhongale1,2 · Sunil S. Joshi1,2 · Nilesh A. Mali1,2 Received: 24 February 2020 / Accepted: 26 May 2020 © Institute of Chemistry, Slovak Academy of Sciences 2020
Abstract A process aiming at O-alkylation of hydroquinone (HQ), where ionic liquids (ILs) act as catalyst is objectively described. Five SO3H-functionalized ILs having different cations were prepared and characterized by NMR and FTIR techniques. The acidity and thermal stability of ILs were determined by Hammett function and thermogravimetric analysis (TGA), respectively. The catalytic activity of these ILs were tested for O-alkylation of HQ with methanol in 4-methoxyphenol (4MP) in the presence of small amount of benzoquinone (BQ). The effect of reaction parameters such as temperature, time, catalyst loading and substrate concentration on the conversion of HQ and product distribution was examined and optimized to maximize the yield of 4MP using 1,3-disulfonic acid imidazolium hydrogen sulfate (IL2) catalyst. Maximum yield of desired product 4MP 93.79% was obtained at 338 K temperature, 5.45 × 10–2 mol HQ, 8.33 × 10–3 mol BQ, and 10.37 mol% catalyst loading in 120 min reaction time. Single-product formation was observed up to 338 K temperature but higher temperature (above 338 K) and longer reaction time resulted in the formation of 2,4-dimethoxyphenol (24DMP) as a by-product. Catalyst recyclability was also established up to the fifth run which showed no declination in its activity. Keywords O-alkylation · Ionic liquids · 4-Methoxyphenol · Hydroquinone · Benzoquinone Abbreviations HQ Hydroquinone BQ Benzoquinone 4MP 4-Methoxyphenol 24DMP 2,4-Dimethoxyphenol IL Ionic liquid IL1 1-(4-Sulfonic acid) butyl-3-methylimidazolium hydrogen sulfate Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11696-020-01230-1) contains supplementary material, which is available to authorized users. * Sunil S. Joshi [email protected] Priyanka V. Bhongale [email protected] Nilesh A. Mali [email protected] 1
Chemical Engineering and Process Development Division, CSIR-National Chemical Laboratory, Dr. Homi Bhabha Road, Pune 411008, India
Academy of Scientific and Innovative Research (AcSIR), CSIR-Human Resource Development Centre, Campus Postal Staff College Area, Ghaziabad 201002, India
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IL2 1,3-Disulfonic acid imidazolium hydrogen sulfate IL3 3-Methyl-1-sulfonic acid-imidazolium hydrogen sulfate IL4 1-(4-Sulfonic acid) butylpyridinium hydrogen sulfate IL5 N-(4-Sulfonic acid) butyl triethylammonium hydrogen sulfate H2SO4 Sulfuric acid DMSO-d6 Deuterated dimethyl sulfoxide FTIR Fourier-transform infrared NMR Nuclear magnetic resonance TGA Thermogravimetric analysis KBr Potassium bromide H0 Hammett acidity min Minute mg Milligram K Kelvin mM Millimolar µM Micromolar
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Introduction Selective synthesis of O-alkylated products of p
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