ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Selective monoalkylation of hydroquinone in the presence of SO₃H-functionalized ionic liquids as catalysts

Priyanka V. Bhongale, Sunil S. Joshi, and Nilesh A. Mali

Chemical Engineering and Process Development Division, CSIR-National Chemical Laboratory, Pune, India

E-mail: pv.bhongale@ncl.res.in

Received: 24 February 2020  Accepted: 26 May 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

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-020-01230-1

Chemical Papers 74 (12) 4461–4471 (2020)