[60-24-2] · C2H6OS · 2-Mercaptoethanol · (MW 78.15)
(synthesis of 1,3-oxathiolanes from ketones; reducing agent for fluorimetric assay of amino acids)
Physical Data: bp 157-158 °C; flash point 73 °C; d 1.114 g cm-3; n
Solubility: sol alcohols, Et2O, benzene; sparingly sol H2O.
Form Supplied in: liquid; commercially available.
Analysis of Reagent Purity: mp of 2-(2,4-dinitrophenylthio)ethanol is 101-102 °C.1
Preparative Methods: by reaction of ethylene chlorohydrin with Sodium Hydrogen Sulfide or Potassium Hydrogen Sulfide;2 by treatment of bis(b-hydroxyethyl) disulfide with zinc dust in aqueous alcoholic sulfuric acid at 40 °C;3 or by reaction of Ethylene Oxide (2 mol) and Hydrogen Sulfide (1 mol) in thiodiglycol at 45-60 °C.4
Purification: by distillation (bp 157-158 °C).
Handling, Storage, and Precautions: can be stored as colorless, odorous liquid in a refrigerator for several months without significant coloration developing. Toxic by inhalation, in contact with skin and if swallowed. Irritating to eyes, respiratory system, and skin. Stench; can be incinerated neat for disposal. Use in a fume hood.
The synthesis of 1,3-oxathiolanes from ketones constitutes one of the principal synthetic applications of 2-mercaptoethanol (eq 1). It was found that using 1 equiv of Boron Trifluoride Etherate in the reaction gave highest yields of 1,3-oxathiolanes. Reducing the amount of solvent below 750 mL per mol of ketone reduced yields of oxathiolanes and increased yields of polymeric materials.
2-Mercaptoethanol was introduced by Djerassi6 for the conversion of steroidal ketones to ethylenehemithioacetals (1,3-oxathiolanes) (eq 2). These are more readily reconverted to the ketone (using Raney nickel) than the similar ethylene thioacetals. The simplest procedure uses boron trifluoride etherate as catalyst.7
o-Phthaldialdehyde reacts with amino acids in alkaline medium in the presence of 2-mercaptoethanol, as reducing agent, giving rise to fluorescent compounds.8 This permits fluorimetric assay of amino acids down to the nanomolar range. The sensitivity is better than with ninhydrin procedures. The amino acids proline and hydroxyproline are not detected by the method.
J. Jonathan Knight
University of Bristol, UK