Acid-catalyzed hydrolysis of sodium dodecyl sulfate.

The acid-catalyzed hydrolysis of sodium dodecyl sulfate (1) and the effect of 1-dodecanol (2) on this hydrolysis were investigated. The rate of hydrolysis was followed by measuring the rate of production of HSO-4 using a pH-stat. The rate constant (kH+) below the critical micelle concentration (CMC) increased with increasing concentrations of 2, up to a mole ratio of 0.5 for 2 to 1, after which the hydrolysis rate was independent of the concentration of 2. These results suggest the possible formation of a complex between 1 and 2. A micellar solution of pure sodium dodecyl sulfate (20 mM) hydrolyzed 50 times faster than that of a premicellar solution at the same pH. Plots of log k versus pH were linear with a slope of -1 at pH less than 4.3. At a constant pH, the addition of NaCl resulted in a decrease in the rate of hydrolysis of a micellar solution. This is probably due to the reduction of concentration of protons at the micelle surface. Furthermore, kH+ was also decreased by the addition of 2 in the region where 2 is solubilized in the micelle; again, this was probably due to the reduction of the charge density (sigma) on the surface of the micelle.