Dimethyl carbonate does not
decompose at temperatures up to 390�. At 300-400� ethyl methyl, diethyl, ethyl
propyl and dipropyl carbonates yield carbon dioxide, the alkene and the alcohol
at similar rates with E (kJ mol-1) 182.0, 195.0, 181.6, 182.0 and
log A (s-1) 11.72, 13.06,
11.89, 11.97, respectively. With ethyl propyl carbonate, ethylene is the
slightly favoured alkene.
Mechanisms already proposed
or formally possible for the decomposition of n-propyl bromide as a
312-order reaction are shown to be unsatisfactory, and the reaction has been
reinvestigated. Two reactions occur simultaneously: (a) a first-order reaction
identifiable with the maximally inhibited reaction and presumably molecular; (b) a reaction second order
in the initial concentration and somewhat autocatalysed as the
reaction proceeds. The rate constant is given by
k2 == 1018.1exp(-49300/RT)sec-1ml mole-1
Reaction (b) is catalysed
by hydrogen bromide and inhibited by propene, and a bromine atom chain
mechanism with hydrogen bromide catalysed initiation is proposed.
Bromine-catalysed decomposition has also been studied. The mechanism of the
inhibition is discussed.
In the presence of hydrogen
bromide at 407�, methyl trimethylacetate decomposes to isobutene,
carbon monoxide, and methanol. Isopropanol reacts
with an intermediate to form isopropyl trimethylacetate,
which decomposes quickly to propene. Methanol
competes effectively with isopropanol. Some ratios of
individual rate constants are obtained from the rate reductions in the
competition reactions.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.