Southwest Retort, Volume 13, Number 6, February 1961 Page: 8
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Catalysis by Complex Ions
Allylic alcohols react in the presence of
catalytic amounts of chloroplatinic acid
to yield diallyl ethers, and mixtures of
them with saturated alcohols when simi-
larly treated give alkyl allyl ethers as
well as the diallyl ethers. Physical-organic
evidence indicates that reaction occurs
while these reactants are attached as lig-
ands in a platinum (II) complex ion, and
that a key intermediate involves an allyl
carbonium ion so attached.
In the experiments with allyl alcohols
and alkanols the ratio of alkyl allyl ether
to diallyl ether increases with the basicity
of the saturated alcohol (with ethenol giv-
ing more of the alkyl allyl ether, than 2-
methylpropanel-2 does.) With homalog-
ous allylic alcohols (erotyl alcohol or n-
methylellyl alcohol), this platinum cat-
alyst system gives a different ratio of
allylic isomers than is obtained when such
reactions are effected with sulfuric acid
(which is required in much larger con-
centrations). In general, other said cat-
alysts (DNOj-AgNOs, HCl-FeClI, p-
toluene sulfonic acid) are not effective
at the low concentrations at which the
chloroplatinic acid is operative.
The reaction of allyl alcohol in the
presence of chloroplatinic (II) acid to
give diallyl ether is of first order in allyl
alcohol. This experimental fact suggests
that the rate determining step is the for-
mation of the complex ion in which allyl
alcohol or allyl carbonium ion is attached
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to platinum. This reaction system is sim-
ple enough to permit detailed study of
this example of an important reaction
Free Radical Rearrangements
Recent study of the reactions of free
radicals in solution has revealed many
instances of rearrangement of free radical
intermediates. Apparently, the driving
force for these rearrangements is less than
that of analogous ionic rearrangements.
This generalization accounts for the fact
that known examples of free radical re-
arrangements are less numerous than ionic
ones. Further, free radical rearrangements
involve energies of activation higher than
those of ionic rearrangements with the
experimental consequence that the extent
of rearrangement in free radical reactions
is dependent upon conditions. For example,
the photobromination of 1,1,1-trichloro-
propane gives more of the product of re-
arrangement (1,2-shift of chlorine),
1,1,2-trichloro- 1-bromopropane, than the
unrearranged product, 1,1,1,-trichloro-2-
bromopropane, at higher temperatures and
lower bromine concentrations.
Many interesting free radical examples
of other 1,2-shifts of chlorine from carbon
to carbon and of aryl groups from carbon
to carbon and carbon to oxygen are
known. With the latter aryl migrations,
migratory aptitudes are different than
those observed in ionic rearrangements and
are less dependent upon stereochemical
Two examples of free radical rearrange-
ments involving unstable Ar15 and
Ar2(; intermediates have been discovered
recently. The reaction of 4-phenyl-4-
methylpentanal with t-amyl peroxide at
1000 gives isocaprophenene and 4,4-di-
methyltetrelene among other products.
The descriptive chemistry and reaction
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American Chemical Society. Dallas/Fort Worth Section. Southwest Retort, Volume 13, Number 6, February 1961, periodical, February 1961; [Dallas, Texas]. (digital.library.unt.edu/ark:/67531/metadc111077/m1/8/: accessed September 24, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; .