The gas-phase decomposition
of 2,3-dimethylbutan-2-ol into 2,3-dimethylbut-1-ene, 2,3-dimethylbut-2-ene,
and water, catalysed by hydrogen bromide at 303-400�, is described. The rate is
first-order in each reactant and the Arrhenius
equation
k2 = 1011.88 exp(-26490/RT) sec-l ml
mole-1
is followed. The olefins
appear to be in their equilibrium proportions. The effects of substitutions in
the alcohol at Cα and Cβ on the rate are discussed.
Hydrogen bromide catalyses
the decomposition of methyl formate into carbon monoxide and
methanol at 390-460�. The radical chain decomposition product, methane, is
formed in only a small amount that is further reduced by the addition of
inhibitor. The reaction is homogeneous and molecular, is first order in each
reactant, and follows the Arrhenius equation:
k2 = 1012.50exp(-32200/RT)sec-1
ml mole-1
It is not reversed by added
methanol.
Hydrogen bromide and
hydrogen chloride catalyse the decomposition of methyl trimethylacetate
into isobutene, carbon monoxide, and methanol at 370-442� and 450-48O�,
respectively. The kinetic form, which is basically 1 : 1, is severely modified
by the effect of methanol either produced in the reaction or added initially.
Water or alcohols react with an intermediate in the catalysed decomposition of trimethylacetic acid or its methyl ester in esterification-like reactions; some of the resultant esters
subsequently decompose to olefin and acid.
Hydrogen bromide catalyses
the gas-phase decomposition of 1,1- dimethoxy-ethane at 233-322� into methyl
vinyl ether and methanol. The reaction, first-order in each reactant, is
believed to be homogeneous and molecular. ��� The Arrhenius equation
������ �����������k2 = 1.3x1013exp(-22160/RT)
s-1 cm3 mol-1
is followed. This
decomposition is much faster than the analogous reactions of alcohols and
ethers. The catalyst is effective when present in only 1% proportion.
Hydrogen iodide catalyses
the decomposition of isopropanol into propene and water at 356 to 457�, viz. �������������������������� i-C3H7OH+HI
→ C3H6+H2O+HI
This is followed by the
faster reactions
�������������������������� C3H6+HI
→ i-C3H7I
����� ��������������������i-C3H7I+HI
→ C3H8+I2������������������������ i-C3H7OH+I2
→ (CH3)2CO+2HI
The rates of the initial
reaction fit the Arrhenius equation
����������������� k2 = 1012.24
exp(-31900/RT) sec-1 ml mole-1
and it is believed to be
homogeneous and molecular. It is faster than the corresponding reactions with
hydrogen chloride and hydrogen bromide in the ratios 100 : 1 and 5 : 1,
respectively. For the overall reaction the amounts of the products formed to
70% reaction, computed with the use of rate constants of the individual
reactions, agree well with the amounts found by analysis.