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Book Review Aromaticity. By P. J. Garratt

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70 0 R 2
C0 0 R 2
X
X
I
R', R" = e.g. H, I, (cyclic) acylamino; RZ = e.g. H, lower alkyl;
X = e.g. -CO-N(C,H,)-alkylene,
single bond
of concentrated sulfuric acid and (excess) formaldehyde.
[DOS 2050217 ; Schering AG, Berlin and Bergkamen]
[PR 88 IE-NJ
In a new process for the production of chloropyridines, in
which there is no need to start with a preformed pyridine
ring, cheap E-caprolactam or cyclohexanone oxime is
allowed to react with chlorine in the vapor phase at a
temperature of least 250°C (400 to 600°C). The chlorine
and the caprolactam or cyclohexanone oxime are preferably
preheated separately. The starting materials may be
diluted withinorganicdiluents(N, or steam)orwithorganic
diluents that are inert to chlorine (CCI,). The new method
is particularly suitable for the preparation of pentachloropyridine, but chloropyridines having less than five chlorine
atoms can also be obtained, the proportion of these products depending on the quantity of chlorine, the reaction
temperature, and the residence time. In general, at least
5 mol of chlorine should be used per mol of caprolactam or
cyclohexanone oxime. If pentachloropyridine is desired as
the main product, 15-30 mol of chlorine are used per mole
of starting material. The preferred residence times for the
mixture in the reaction zone are between 10and 30 seconds.
In one example, E-caprolactam is allowed to react with
18 mol of chlorine per mol of caprolactam at 53OoC, with
a residence time of 20 seconds. In addition to 2,3,4,6- and
2,3,5,6-tetrachloropyridines,the product contains pentachloropyridine in a yield of 86%. [DOS 2141 632; Imperial
Chemical Industries Ltd., London]
[ m75 n-uj
Hydrogenation catalysts for the hydrogenation of polymers
in viscous solution at low temperatures and low hydrogen
pressures consist of a reaction product of at least one metal
chelate of the metals nickel, cobalt, and iron, the chelating
agent being bonded to the metal via a nitrogen atom and
an oxygen atom, with at least one reducing agent having
the formula MR,, where M is lithium, magnesium, or
aluminum, R is a hydrocarbon or alkoxy group containing
1 to 12 carbon atoms or hydrogen, and n is the valency of
M. The catalyst can be obtained by dissolution o r dispersion
of the metal chelate in an inert solvent and reaction with
the reducing agent; however, the catalytic components
may also be mixed with the polymer solution to be hydrogenated. The catalyst is used for the hydrogenation of
polymers that contain C=C double bonds, C=
triple
bonds, and C-N triple bonds. [DOS 1767832; Bridgestone Tire Co. Ltd., Tokio]
[PR 37 IE-E)
BOOK REVIEWS
Aromaticity. By P. J . Garratt. McGraw-Hill Book Co.,
London 1971, 1st. Edit., viii, 184 pp numerms figures,
bound €. 3.40.
In the course of a century the concept of aromaticity has
greatly promoted the synthetic and theoretical development
of organic chemistry. This process is described in the
present work, which is intended as a textbook. It first
explains in detail, by a discussion of the classic pair
benzene and cyclooctatetraene, the physical and chemical
differences between Hiickel systems with closed and with
open shells. This is followed by the treatment of annulenes, monocylic aromatic and antiaromatic ions,
annulenones, and fulvenes. The other chapters are devoted
to heterocycles, polycyclic compounds, homoaromatic
n systems, and finally the aromatic transition states of
pericyclic reactions.
A very large volume of material is presented within this
broad framework, often with the welcome inclusion of
spectroscopic, magnetic, kinetic, and structural data,
and the field is covered in part up to 1971. In line with the
textbook style, the references are mainly confined to
lists of secondary literature at the ends of chapters. The
consistent use of the Frost-Musulin formalism or the
Dewar PMO method for the determination of delocalization energies is didactically commendable, as it
makes these parameters, which are fundamental to the
252
understanding of aromaticity, accessible even to students
and chemists with no mathematical background. On the
other hand, the treatment of aromatic transition states in
four pages, where (incorrectly in this context) even homoaromatic ions are found as solvolysis intermediates, is
simply too short. This chapter, which is certainly not
out of place, should be rewritten and expanded in a new
edition. The opportunity should then be taken to rid the
book of errors.
The book is well written and abundantly provided with
reaction schemes. It will provide advanced students and
chemists specializing in other fields with a good survey
of the field that has benefited from the concept of
aromaticity. Moreover, it also represents a reasonably
priced reference work for those who are already conversant with this field.
Wolfram Grimme [NB 112IE]
Carbene Chemistry. By W Kirmse. Academic Press, New
York-London
1971. 2nd Edit. xi, 615 pp., numerous figures and tables, bond % 33.--.
One of the heuristic principles of the last few decades in
organic chemistry (which is certainly not short of ideas) is
the carbene concept, which was introduced in the early
Angew. Chrm. internat. Edit.
1 Vol. 12 ( 1 9 7 3 ) 1 No. 3
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