Kinetics of the dehydration of methylene glycol in aqueous solution

Abstract
Methods are described for measuring the velocity of the reaction CH$_2$(OH)$_2 \rightarrow$ CH$_2$O + H$_2$O in aqueous solution by making use of the rapid reaction of unhydrated formaldehyde with the scavenging reagents semicarbazide, hydroxylamine, phenylhydrazine, hydrazine and sulphite. The reaction exhibits general acid-base catalysis, and catalytic constants are given for 14 acids and 30 bases. Relations between acid-base strength and catalytic power extend over an unusually wide range of velocities and types of catalyst, and this behaviour is discussed in terms of reaction mechanisms. The catalytic behaviour observed shows unexpected contrasts with that reported for the hydration of carbon dioxide. It is shown that, contrary to previous reports, the rate of removal of formaldehyde from aqueous solution by a gas stream is not appreciably affected by the rate of dehydration of methylene glycol. A few experiments are reported on the application of the chemical scavenger method to measure the rate of the reaction CH$_3$CH(OH)$_2 \rightarrow$ CH$_3$CHO + H$_2$O, and the results compared with those obtained by other methods.