posted on 2012-02-17, 00:00authored byJohn P. Guzowski, Edward J. Delaney, Michael J. Humora, Erwin Irdam, William F. Kiesman, Albert Kwok, Amy D. Moran
The formation and fate of monomethyl sulfate (MMS) and
dimethyl sulfate (DMS) were studied by proton NMR for a sulfuric acid
catalyzed esterification reaction in methanol. The kinetic rate constants
for DMS and MMS were determined at 65 °C by fitting time-dependent
experimental data to a model using DynoChem. In refluxing
methanol, sulfuric acid was converted to monomethyl sulfate (MMS)
in nearly quantitative yield within 45 min. Once formed, the MMS underwent
a reversible esterification reaction to form DMS. Dimethylsulfate
reacted with methanol to regenerate MMS and form dimethyl ether. A
byproduct of the esterification reaction was water, which further
consumed DMS through hydrolysis. On the basis of derived rate constants,
in refluxing methanol, DMS would not be expected to exceed 4 ppm in
the reaction mixture at equilibrium. In the presence of the carboxylic
acid substrate, DMS was not detected in the reaction mixture. The
reaction pathways of this system have been systematically investigated,
and the results of this study will be presented.