The direction of addition of one mole of isocyanate to 2-mercaptoethanol is determined by the type of catalysis used. Basic catalysts lead to a series of S-urethans; uncatalyzed or acid- catalyzed reactions afford the corresponding series of 0-urethans. The 0-urethans of 2- mercaptoethanol polymerize rapidly under the influence of aqueous alkali to give polysulfides of general formula ArNHCOO (CH2CH2S)" H.
