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Handbook of Free Radical Initiators. Edited by Evguenii T. Denisov T. G. Denisova and T. S

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Angewandte
Chemie
Handbook of Free Radical
Initiators
Edited by Evguenii T. Denisov, T. G.
Denisova and T. S.
Pokidova. John
Wiley & Sons,
Hoboken 2003.
879 pp., hardcover
E 329.00.—ISBN
0-471-20753-5
Free-radical initiators are compounds
that produce reactive free radicals by
unimolecular breakdown or by a bimolecular reaction. They are used for
initiating polymerizations or chemical
syntheses, or for the modification of
polymers, and are of great technological
importance. These compounds typically
work by a thermal mechanism, but
photoinitiators have also gained in
industrial importance recently. However, the latter are not covered in this
book, apart from a brief mention of the
photochemistry of azo compounds, and
therefore a better title would have been
“Handbook of Thermal Free Radical
Initiators”.
One expects a handbook on this
subject to give comprehensive mechanistic, reaction-kinetic, and thermochemical data on the formation of free
radicals by all the different classes of
initiator compounds, mainly in the form
of tables, accompanied by explanatory
text, and that is what the book contains;
it is a work of 879 pages which includes
about 250 lengthy tables. Unfortunately,
however, there are no illustrations or
diagrams, even in cases where they
would have been very appropriate and
could have been reproduced from the
literature. The coverage of the literature
up to about 1995 is reasonably comprehensive, but for later years it is only
selective. A useful aspect is that it
includes many Russian publications,
especially some early ones, which are
not widely known in the western world.
In addition to the central subject of freeradical initiators, the book also contains
some information about important reactions of the radicals that they generate,
although that is not evident from the
Angew. Chem. Int. Ed. 2004, 43, 274 – 276
title. Wider aspects of the subject are
also touched on to some extent, apparently so that the kinetic model developed by the authors for interpreting the
rates of formation of free radicals can
also be applied to other reactions.
The book is divided into three parts.
Part 1, “Initiators”, is the longest
(420 pp.), and deals with the generation
of free radicals by the unimolecular
breakdown of compounds with weak
single bonds. It begins with three introductory chapters of a general nature,
discussing breakdown mechanisms, the
cage effect, and experimental methods
for investigating reaction kinetics. These
are followed by chapters describing the
main types of initiators: dialkylperoxides and alkylhydroperoxides, diacylperoxides, peroxyesters and related compounds, polyoxides, azo compounds, and
other compounds with weak single
bonds. Each chapter contains tables
listing practically all the known compounds in the class concerned, with
information about their synthesis, physical properties, trade names, and enthalpies and entropies of formation, as well
as kinetic breakdown constants and
their temperature-dependence, in the
Arrhenius form. The sources are cited.
Regrettably, however, apart from a few
exceptions, the experimental error limits
for the data are not given, and consequently the user of the handbook must
go to the original publications for information about the reliability of the values
listed. Nevertheless, this part of the
book is extremely useful, as it collects
together, in a concise and comprehensive form, a mass of information that is
scattered throughout the literature.
The uniform style of the preceding
chapters changes abruptly at the beginning of Part 2, “Bimolecular Reactions
of Free Radical Generation” (233 pp.),
with a very long description of a semiempirical model for interpreting and
predicting rate constants for bimolecular reactions. This “intersecting parabolas model” (IPM) developed by Denisov
has been described by him in a number
of publications, including applications to
a wide variety of reactions. The parameters needed for using the model are
listed in tables. That is followed by
chapters along the lines of those in
Part 1, describing the various bimolecular free-radical-forming reactions that
www.angewandte.org
involve molecular oxygen, ozone,
hydroperoxides, olefins, halogens, or
nitrogen dioxide, and lastly the important class of redox reactions using transition-metal ions. As before, experimental data are given, but many values
predicted by the Denisov model are
also listed and accorded the same status.
Part 3, “Reactions of Free Radicals”,
is concerned with reactions that are not
really relevant to the main subject of the
book: isomerizations and breakdown
processes of free radicals, dehydrogenations and substitutions, additions to
multiple bonds, and termination reactions. Here the literature coverage is
fragmentary, and much space is devoted
to tables of rate constants calculated by
Denisov from his model. Although it is
stated frequently that the calculated
values are in good agreement with
experimental data, the latter are not
given. The calculated rate constants for
the addition of methyl and tert-butyl
radicals to alkenes (Tables 19.13 and
19.15) can be compared with experimental values (mostly from published
work by this reviewer), which are, however, not explicitly cited in the book.
One then finds differences that are
seldom less than a factor of two, and
even exceed two orders of magnitude in
individual cases. In view of such discrepancies, there must be doubts about
whether the many tables of results
from the IPM model (which comprise
one-third of all the tables in the book)
are meaningful. Moreover, Part 3 contains serious errors in the citing of
results from other authors and in the
descriptions of their theoretical models,
as well as some formulas that are simply
incorrect [e.g., formulas (19.16) and
(20.3)]. This part has evidently been
written very hurriedly.
To summarize, Part 1 is very useful,
and so is Part 2 to some extent, but Part
3 will be disliked by all free-radical
chemists other than the few adherents of
Denisov's intersecting parabolas model.
The style of the English is passable but
sometimes a little awkward. Here and
there the reader will smile on finding
expressions such as “rentgen structural
analysis” or “sinomime shell diazenes”
(azo compounds). The classification of
silyl and phosphoryl peroxides under the
heading “Organometallic Peroxides” is
* 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
275
Books
rather unusual, as also is the description
of halogen compounds as “haloids”.
Despite the book's shortcomings,
especially the fact that photoinitiators
are not covered, the absence of error
limits in the data, and the undue emphasis on the IPM, the book will be useful to
all users of free-radical initiators as a
276
source of data and literature references.
Parts 1 and 2 give a good up-to-date and
comprehensive description of this extensive and important field. Part 3, and all
the reaction constants that are merely
* 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
calculated values, are extras that one can
confidently ignore.
Hanns Fischer
Physikalisch-Chemisches Institut
Universit5t Z7rich (Switzerland)
DOI: 10.1002/anie.200385035
www.angewandte.org
Angew. Chem. Int. Ed. 2004, 43, 274 – 276
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