A Novel Hydrate Form of Sodium Dodecyl Sulfate and Its Crystallization Process

A novel hydrate form of sodium dodecyl sulfate (SDS) was firstly discovered through a hydrate screening with the use of organic solvents, while SDS is generally prepared solely in aqueous media. Surprisingly, a novel SDS hydrate form with needle-shaped crystals produced by adding acetonitrile to a 20 wt % SDS aqueous solution at a ratio of 3:1 (v/v) and further cooling to around 5 °C could be found with a trace amount in one of the two purchased SDS products that we examined. After comprehensive solid-state characterizations by powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR), Raman spectroscopy, dynamic vapor sorption (DVS), and elemental analysis (EA), it is also successfully made directly from the synthesis of SDS through esterification and saponification. Four times the equal proportion of acetone was added into the reaction solution at an interval of 5 min to separate the side product, sodium sulfate, from the mother liquor. The desired novel hydrate form of SDS was then obtained by cooling the filtered mother liquor to 5 °C and aged for 8 h for a preferential growth.