Sulfur-33 NMR of Benzenesulfonic Acid

Abstract

For the general use of sulfur-33 NMR spectroscopy, measuring conditions for benzenesulfonic acid were examined. A 0.75M solution (deuterium oxide-water mixture in the ratio of 2: 1) adjusted to pH 6.5-10.5 gave a good signal with line width at half the peak height of 13.5Hz after 3h of data accumulation. The chemical shift [-11.5ppm relative to (NH₄)₂SO₄] did not vary with this pH range. Hardly any signal could be observed at a pH less than 3.6. Slight lowering of S/N ratio and minor line-broadening were caused by the addition of excess sodium hydroxide (pH>14). Thus possibly, tuning of the probe and use appropriate pulse conditions are essential for measuring sulfur-33 NMR, and the sample solution of sulfonic acids should be made neutral or alkaline.