Deuteration of 2-methylnaphthalene and eugenol in supercritical and pressurised hot deuterium oxide

Abstract

The dramatic changes in the properties of water (e.g. density, relative permittivity, ionic product) near its critical point make high temperature water an attractive reaction medium in place of organic solvents. The suitability of deuterium oxide (D₂O) at high temperatures (200–450 °C) for the deuteration of eugenol and 2-methylnaphthalene was studied in this work. Deuteration was performed with pure D₂O and with D₂O containing several acid, base, salt and metal catalysts. As well, deuterium chloride and sodium deuteroxide were tested as catalysts. Reactions were carried out in batch-type reactors made of stainless steel or Hastelloy^® C-22. Gas chromatography-mass spectrometry (GC-MS) was used for the determination of reaction products. With 2-methylnaphthalene deuteration efficiencies were as high as 100% at 450 °C. Reactions with NaOH, NaOD and Na₂CO₃ catalysts produced most repeatable results (in the best conditions RSD<5%). In the case of eugenol, relatively good deuteration efficiency was achieved at lower temperatures, with use of D₂O alone, without any catalyst. With both compounds, small amounts of by-products were occasionally detected in the total ion chromatogram of GC-MS.