Process-Focused Synthesis, Crystallization, and Physicochemical Characterization of Sodium Lauroyl Isethionate

There is a notable lack of published data concerning sodium cocoyl isethionate despite widespread application in the personal care industry. A specific homologue, sodium lauroyl isethionate (SLI), was therefore synthesized, purified by recrystallization, and then subjected to a detailed physicochemical examination. A purity of 98% was achieved via repeat recrystallization in methanol. A turbidimetric solubility analysis was then executed to identify both its crystallizability and metastable zone width as a function of temperature. Thermogravimetric analysis yielded decomposition onsets of 330 °C for the purified SLI. A dynamic vapor sorption study also demonstrated reversibility in the 2.3% mass gained when it was exposed to sustained humidity of 87%. Surface tension measurements of purified SLI yielded a critical micellar concentration (CMC) of 5.4 mM and a plateau surface tension of 38 mN/m at 20 °C. Both values are lower than the previously reported values for SLI in water, thus indicating the performance benefits of purified isethionates in personal care formulations. The single step synthesis was chlorine-, catalyst-, and solvent-free, thus improving process efficiency, safety, and throughput over existing SLI syntheses. The succeeding physicochemical analysis crucially provides much needed insight into the purification, properties, and perform ance of isethionate ester surfactants, all of which are strongly applicable to their commercial manufacture from biorenewable sources.