text: Taurates were first obtained by the Schotten-Baumann method which is the reaction of long-chain carboxylic acid chlorides with aqueous solutions of the sodium salt of N-methyltaurine.
  The formation of (at least) equimolar amounts of sodium chloride is problematic, as they worsen the properties of surfactant mixtures with such taurates. The high salt content also makes the resulting taurates hygroscopic and corrosive. Another disadvantage of the Schotten-Baumann method is the hazardousness of the raw materials (such as phosphorus trichloride) and the intermediates (the acyl chlorides) and the accumulation of large amounts of waste materials, such as phosphonic acids. This synthesis pathway for taurates is therefore complicated and expensive. An advantage of the Schotten-Baumann method, however, is the very low content of free fatty acids in the end product. Taurates are also accessible by direct amidation of N-methyltaurine or its sodium salt with the corresponding fatty acid for 10 hours at 220 °C under nitrogen.
  The excess fatty acid (added for a favorable equilibrium) usually remain in the product, which can interfere with some applications. The decomposition of N-methyltaurine already begins At temperatures above 200 °C and the resulting taurates darken and develop an unpleasant smell. Therefore, more recent variants of the direct amidation aim at gentler process conditions using suitable catalysts, such as sodium borohydride, boric acid or zinc oxide.