Trihexyl (tetradecyl) phosphonium tetrafluoroborate was found to be an active catalyst for the introduction of fluoride by nucleophilic aromatic substitution. With a decomposition temperature above 300 degrees C, this ionic liquid is suitable for reactions at high temperatures. The addition of 1 mol% of the ionic liquid relative to KF increased the initial rate for the fluorination of 1,2-dichloro-4-nitrobenzene six-fold compared to the uncatalysed reaction. The highest reaction rate was observed at 20 mol% ionic liquid relative to KF. Ease of handling without the need for stringent drying conditions and reuseability make this ionic liquid a useful phase transfer catalyst. (C) 2012 Elsevier B.V. All rights reserved.