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.
In the presence of
inhibitors, methyl chloroformate decomposes at 425- 480� to methyl chloride and
carbon dioxide in a homogeneous molecular reaction. The rate constant is given
by
k1 = 10(14.26�0.20)exp[(-251000�2000)/8.314T] s-1
2-Chloroethanol decomposes
at 430-496� into acetaldehyde and hydrogen chloride with first-order rate given
by:
k1 = 1012.8�1 exp(-229700 � 4000/8.314T) s-l
The rate is slightly less
than that for ethyl chloride. That acetaldehyde is the product shows that a 1-2
shift of hydrogen has taken place and this is indicative of a polar transition
state.The acetaldehyde
subsequently decomposes to methane and this decomposition is catalysed by the
hydrogen chloride produced.
Hydrogen chloride catalyses the
decomposition of t-butyl ethyl ether at 320-428�. Isobutene is quantitatively
the product and the kinetic form is first order in the ether and in hydrogen
chloride. The Arrhenius equation:��������� k, = 1012'16exp( -30,60O/RT) (sec-l ml mole-=)
is followed. The mechanism
of the reaction seems similar to those of other hydrogen halide catalysed
decompositions of ethers and alcohols.
The decomposition of t-butyl methyl ether
catalysed by hydrogen chloride takes place at 337-428�. It is first order in
each reactant and the rate is not affected by increase in surface area or
inhibitor. The rate equation is:
K2 = 1012.46exp(-32100/RT)
(sec-l ml mole-l)
The reaction is believed to
be molecular and its properties are in accord with those of other such
catalysed decompositions.
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