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Issue 11, 2012
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Methylation using dimethylcarbonate catalysed by ionic liquids under continuous flow conditions

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Abstract

The ionic liquid, tributylmethylammonium methylcarbonate, has been employed as a catalytic base for clean N-methylation of indole with dimethylcarbonate. The reaction conditions were optimised under microwave heating to give 100% conversion and 100% selectivity to N-methylindole, and subsequently transferred to a high temperature/high pressure (285 °C/150 bar) continuous flow process using a short (3 min) residence time and 2 mol% of the catalyst to efficiently methylate a variety of different amines, phenols, thiophenols and carboxylic acid substrates. The extremely short residence times, versatility, and high selectivity have significant implications for the synthesis of a wide range of pharmaceutical intermediates, as high product throughputs can be obtained via this scalable continuous flow protocol. It has also been shown that the ionic liquid can be generated in situ from tributylamine, which has the net effect of transforming an ineffective stoichiometric base into a highly efficient catalyst for this broad class of reactions.

Graphical abstract: Methylation using dimethylcarbonate catalysed by ionic liquids under continuous flow conditions

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Article information


Submitted
03 Aug 2012
Accepted
19 Sep 2012
First published
20 Sep 2012

This article is Open Access

Green Chem., 2012,14, 3071-3076
Article type
Paper

Methylation using dimethylcarbonate catalysed by ionic liquids under continuous flow conditions

T. N. Glasnov, J. D. Holbrey, C. O. Kappe, K. R. Seddon and T. Yan, Green Chem., 2012, 14, 3071
DOI: 10.1039/C2GC36226K

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