The Methclnolysir of Acetal
A chemical kinetics a n d g a r chromatography experiment
Nashville,
Tennessee
The methanolysis of acetal and gas chromatography complement perfectly to provide a rare and interesting experiment for the physical chemistry student. The reaction of acetal with methanol is a consecutive reaction in which diethyl acetal (aretal) replaces its two ethoxy groups with methoxy groups forming methy1et)hylacetal first and dimethyl acetal in the second step. Investigating the reaction kinetics for this type of reaction mas almost impossible before the advent of gas chromatography (I). There are many advantages to using the methanolysis of acetal in this study: Sufficient data for a complete analysis can be collected within three hours. The reaction requires reagents which are readily available in high purity. The reactants, intermediate, and products are liquids at temperatures easily accessible for kinetic runs. The primary reactant, intermediate, and product are sepe rated rleanly on a typical gas chromatographic column. The peak heights are linear with concentration in the range studied (2). Analysis of the data affords an application of firshorder kin~ticsand the steady state hypothesis. The experiment presented herc is an adaptation of the detailed study of the reaction by Juvet and Chiu (2), who have shown it to be acid catalyzed and first order in diethyl acetal and methylethyl acetal. By decreasing the elution time, modifying the mathematics for calculating the rate constants, and simplifying the preparation of the HCI-methanol solution, it is now possible to complete the reaction sufficiently aud to obtain the data within three hours.
The Experiment
Conn.) containing 30% dioctyl phthalate (Matheson). Chromosorb W can also be used as the solid support. The temperature of the
