An alternative synthesis and mobile phase ion chromatography of alkanedisulfates

Abstract

Preparation of alkane disulfates using chlorosulfonic acid results in a crude product containing significant amounts of chloride, sulfate, and hydroxyalkanesulfates. This paper describes an alternative synthesis using trimethylamine:sulfur dioxide complex in anhydrous pyridine. Workup with sodium hydroxide and washing in acetone results in a crude product with less than 1% inorganic impurity and ~0-3% hydroxyalkanesulfate. Recrystallization from acetone reduces the inorganic impurity to less than 0.1%. Alkanedisulfates can be separated from the corresponding hydroxyalkanesulfates, chloride, and sulfate using mobile phase ion chromatography with tetrabutylammonium hydroxide (TBAOH) as the ion-pairing agent and acetonitrile as the organic modifier. With the crude octanedisulfate and decanedisulfate product mixes, the alkanedisulfate is retained more strongly by the ion-pairing effect; but with the tetradecane species, hydrophobic interaction dominates and the tetradecanedisulfate elutes before the hydroxytetradecanesulfate. The choice of acetonitrile gradient and TBAOH is particularly important for the separation of the dodecane derivatives because the opposing effects of polarity (hydrophobic effect) and electrostatic interaction with TBAOH are of similar strength.