close

Вход

Забыли?

вход по аккаунту

?

Hans Meerwein the Teacher and the Man.

код для вставкиСкачать
In conclusion let us consider a few reactions having the
common feature of the transfer of a hydride ion (and
in many cases of an alkoxide or cyanide ion) onto
a carbonium ion. These include the well-known Meerwein-Ponndorf reacticn, discovered by Meerwein and
Schmidt [201 in 1925 and later extended by Ponndorf and
Verley.
This reaction involves the exchange of oxidation states
between an aldehyde or ketone and a primary or secondary alcohol under the catalytic action of an aluminum
alkoxide. This forms a complex with the carbonyl component; the “activation by complex formation” consists in the formation of a latent electrophilic center on
the carbonyl C-atom, to which the hydride ion migrates,
presumably by a cyclic mechanism:
@ FH3
RO,@,O=CH
B
A1
RO‘ ‘O-ClH
R’
C-D
0 FH3
RO,@,O- C H
H
R O 0-C;H
P?
R‘
The reverse of this reaction has also become important
as the Oppenauer oxidaticn.
A still more versatile class of reactions is that of the
intermolecular anion shifts [211. The acceptors are carbonium or diazonium ions; on loss of the anion, the
donor is converted into a resonance-stabilized cation.
The last of these reactions ~ 2 is1 noteworthy in that the
well-known reduction of diazonium salts is carried out
with ethers or acetals instead of alcohols. The yields are
[20] H. Meerwein and R. Schmidt, Liebigs Ann. Chem. 444, 221
(1925).
[21] H. Meerwein, K. Wunderlicli, and K. Zeuner, Angew. Chem.
74, 807 (1962); Angew. Chem. internat. Edit. I, 613 (1962).
[22] H. Meewein, H. Aiienddrfer, P . Beekmann, F. Kuridert,
W. Morschel, F. Paweleck, and K. Wunderlicli, Angew. Chem.
70, 211 (1958).
appreciably better, since no phenol ethers can be formed
as by-products.
(CsH5)3C@ +
<:[ -
(CBHS),C-OR
0 OR
A r N ? + R-CHz-O-CHzR
+ [qC-H
0
0
+
ArH
+ Nz + R-CH-O-CH2R
0
Much of Meerwein’s work has only been hinted at in
this survey and much (e.g. the Meerwein reaction, i.e.
the arylation of a$-unsaturated nitriles, esters, ketones,
etc., with diazonium salts [ * 3 9 has not even been mentioned. However, it is not the volume, but the substance
of his work that is important, i.e. the perception of
the courses of many reactions, the discovery of ionic
processes in organic chemistry, the recognition of the
role of complexing agents as catalysts and initiators, and
the extension of our knowledge of the carbonium,
oxonium, and diazonium ions. Meerwein is justifiably
regarded as one of the originators of theoretical organic
chemistry. He also showed that nothing is of greater
practical use than a good theory, since his own theory
led him to m.any new methods, including even industrial
processes.
The description of Meerwein’s scientific work and the
reference to his extensive literary activity also sheds
some light on his personality, but the picture gleaned in
this way is not complete. To appreciate fully the infectiousness of his enthusiasm one must have discussed
with him and listened to his lectures, in which every
sentence was clearly formulated, and which held his
audience from beginning to end. This is how he will be
remembered by all his friends, colleagues, and students.
May the flame of enthusiasm for our science that he has
kindled in all of them be handed on to future generations
like an Olympic flame.
Received: January 28th, 1966
[A S04/2SS IE]
German version: Angew. Chem. 78, 341 (1966)
Translated by Express Translation Service, London
[23] H. Meerwein, E. Euchner, and K. van Emster, J. prakt.
Chem. [2]152, 237 (1939).
Hans Meerwein, the Teacher and the Man
BY PROF. DR. K. DIMROTH, MARBURG (GERMANY) [*I
Hans Lebrecht Meerwein died suddenly on October 24th,
1965. Among the few personal belongings found in his
office at the University Chemical Laboratories of Marburg was a small black notebook. It lay in the drawer
of his desk, together with some of the many medals and
[ * ] Address given at a mcmorial scwice held at Marburp University on January 15th, 1966.
338
awards that had been bestowed upon him during the
later years of his life.
This notebook relates his association with the family
home in Hamburg, an association that flourished to
the end of his days. The entries are inscribed in the
beautifully clear hand of his father Wilhelm Emil Meerwein whom he always held in high regard. They relate
Angew. Chem. internat. Edit.
1 VoI. 5 (1966) No. 4
the history of the Meerwein family. The story unfolds
like an exciting novel, telling of his father’s development
from the student of architecture with only a casual
interest in his subject, to the highly respected and honored master-builder and citizen of the Hanseatic city of
Hamburg. Having begun this chronicle at the age of 59,
Wilhelm Emil Meerwein laid down his pen when he
was 81 years old, having added to the tale at intervals
of five or ten years. The last two pages are written in
another hand, evidently after his death, and contain
additions based on notes which had come to light.
At the beginning we find a sentence which seems to me
so typical of the relationship between different generations as to merit quotation:
Even though today my children show no great inclination to
acquaint themselves with their family’s history, may the
time come one day when one or the other of them will be
glad to learn from the past.
Huns Meerwein was 26 when his father wrote these
words in 1905. At the beginning of that year he had
taken up his first position as an assistant lecturer at the
Chemische Institut at Bonn, under Professor Richard
Anschiitz. On the subject of this appointment his father
wrote:
Although the salary was modest I advised him to take the
post, since I think that he is better suited to a career in
science than to the practical life.
Having spent his youth in Hamburg, Huns Meerwein
always looked upon it as his home town. His father,
who came from a southern part of Germany, first
settled there in 1873, setting up business as an architect
in partnership with Bernhurd Hunssen, his friend from
student days. It was through the latter that he met his
future wife , Hunssen’ s sister-in-law Mu t h ilde Schmilinslcy, whom he married in 1877. Her maternal grandfather
had owned a well-known iron foundry and the family
had been long established in Hamburg. Its name is
familiar to its citizens through a generous foundation,
unfortunately deprived during World War I1 of the
large orphanage built by the elder Meerwein, as well as
through the Schmilinsky-Strasse, named in honor of
the founder, an uncle of Meerwein’s mother.
While Huns Meerwein was still at school at the Hamburger Gelehrtenschule Johanneum, his father set up
for him a small chemical laboratory. Here at home he
was able, as he himself related afterwards, to carry out
all the fundamental experiments known to chemists of
that time. Nevertheless, when he graduated from school
in 1898, he did not go immediately to a university, but
first spent three semesters at the Wiesbaden College of
Chemistry run by Heinrich and Wilhelm Fresenius,
where he studied analytical theory and practice. There
he obtained a basis which proved to be invaluable for
his later work. The careful development of simple
methods of qualitative and quantitative analysis
characterizes much of Huns Meerwein’s scientific work,
and it was precisely this approach which enabled him
to gain a clear insight into the often complicated course
of chemical reactions.
He enrolled at Bonn University in the summer semester
of 1900. Not long afterwards he commenced work for
Angew. Chem. internot. Edit.
Vol. 5 (1966)
No . 4
his doctorate with Ceorg Schroeter, who was some
ten years older than himself and had only recently
qualified as a lecturer. In February 1903, after only six
semesters of university work, Meerwein successfully
defended his thesis “On nitrated p-phenylglutaric
acids”. After studying for some time in Berlin-Charlottenburg, he returned to Bonn early in 1905, at the
invitation of the then director of the Chemische Institut at Bonn, Professor Richard Anschiitz, to take up
the assistant lectureship already referred to.
Huns Meerwein remained in Bonn until 1923. For many
years he must have moved in a stimulating circle of
artists and other high-spirited companions. He frequently looked back with pleasure to this period.
Gradually, however, his duties increased. Having
qualified in 1908 with his inaugural dissertation “On
the condensation reactions of a$-unsaturated aldehydes”, he took over in 1910 the position of his former
tutor Georg Schroeter who had gone to Berlin as Professor of Chemistry at the Veterinary Academy.
During his years in Bonn Meerwein cmcentrated his
work on organic rearrangements, particularly in the
terpenes and in camphor derivatives. He taught a great
many students, with most of whom he established a
firm and lifelong friendship. I shall single out only one
of them, Karl Freudenberg, who passed the practical
laboratory courses under him and who was to be for
many years the director of the Chemische Institut at
Heidelberg. In honor of Freudenberg’s 80th birthday on
January 29th, 1966, Meerwein dedicated to him a
paper entitled “On chlorodimethylsulfonium salts”.
When sending the manuscript to the editor of Liebigs
Annalen der Chemie, Professor Richard Kuhn, on
January 22nd, 1965 he wrote that it would probably be
his last paper. It was published in the 688th volume of
Liebigs Annalen on October 7th, 1965, just two weeks
before Huns Meerwein died. It was indeed the last
contribution to this great man’s work.
In 1923 Huns Meerwein was invited to take the Chair of
Chemistry at Konigsberg. He accepted the position at a
difficult time, when the Institute had become practically
ineffectual through the ravages of war and inflation.
Nevertheless, he succeeded within a short time in
restoring the institute to a high standing. He had a
relatively small number of students, many of whom
were later to reach high positions in the chemical
industry, thanks to the excellent training they had
received under him. With their assistance he explored
two new domains, and in doing so laid the foundation
for his future scientific renown: the theory of “cryptoions” as intermediates of many organic reactions, and
the formation of complex ions and acids, the “ansolvo
acids”, as he called them. The reduction of unsaturated
aldehydes, named after him, also dates back to those
years; it was developed in collaboration with the
chemical industry and for some time used in the production of important pharmaceuticals.
Admittedly, much of Meerwein’s work received scant
recognition at that time. The great chemists of the
period were engaged in the elucidation of natural
products. Interest was concentrated on the discovery
339
of vitamins and hormones and the study of their
relationship with the enzymatically catalysed processes
in organisms. This may be the explanation for the
rejection by a leading scientific journal of one of Meerwein’s pioneering papers on the ionic mechanism of
many organic reactions, on the grounds that it was
too speculative. Meerwein, who was never a fighter,
yielded, though he never doubted the correctness of his
views. He knew that in any case the truth would prevail
sooner or later. For many years he published no papers
in that periodical and preferred to write for the Journal
fur Praktische Chemie. Partly for similar reasons, he
published his fundamental work on complex anions in
the “Abhandlungen der Konigsberger Gelehrtengesellschaft,” and only parts of this still highly interesting
paper appeared in more readily accessible journals at a
later date. Consequently, many years passed before he
received the recognition that was his due. We must
confess with some shame that his work has only been
fully appreciated in Germany after the end of World
War 11, and then largely as a result of the high regard
in which he was held by American chemists, who consider him as one of the founders of modern organic
chemistry. Meerwein was fortunate enough to live to
witness this change.
Nevertheless, his reputation even in those early years
was such that in 1928 he was almost simultaneously
offered a professorship at the Universities of Leipzig
and Marburg. It seems typical of the man that he gave
preference to the smaller university, where he had fewer
distractions to fear from administrative and representative duties.
His scientific achievements as a successor to Karl von
Auwers in the 23 years during which he was head of the
Chemische Institut at Marburg, and in the 13 years
which followed his retirement from his chair, are unique.
To the very end of his life he continued to develop
original ideas, and only three weeks before his death
he engaged a new post-doctoral assistant at his laboratory with the intention of approaching an old problem,
connected with his dissertation, using new concepts and
methods.
The discovery of the oxonium salts, the polymerization
of tetrahydrofuran and consequently the discovery of
cationic polymerization, the discovery of nitrilium salts,
the use of carbonium ions instead of protons, which led
to new syntheses and reactions of acetals, lactams, and
orthoesters, the reactions of alkyl halides with silver
fluoroborate or those of diazomethane and aromatic
diazonium compounds, are just some of the many
topics he studied.
In his teaching capacity, Hans Meerwein introduced
generations of students to chemistry and guided their
progress in their daily laboratory work. His fascinating
lectures, supported by brilliant demonstrations, were
an unforgettable experience. He had mastered the
knack of building up suspense in his listeners ta the
point when, usually in a startling and unexpected
manner, the solution to the problem struck them as if
of its own accord.
340
He advised his students and co-workers also to use the
element of surprise in their lectures. It was better, he
said, to lecture less frequently, but then to present to
the audience new and unexpected material.
Whenever a chemist attracted Meerwein’s attention by
his originality and acumen, he invariably received the
fullest measure of encouragement. The scientific achievements of many young chemists received his support,
frequently even without their being aware of it. He did
everything he could to bring on the rising generation of
chemists, never hesitating to recommend gifted and even
very young men for responsible and challenging positions.
To this period at Marburg also belongs the rebuilding
of the Chemistry Laboratory after the last war. A new
building had been approved at about the time of his
appointment. However, by the time he had completed
the plans, prepared with all the talent inherited from his
father, it was too late: the political circumstances at the
universities after 1933 led to a decline in student
numbers, and to the rescinding of the earlier approval.
Thus it happened that the bold plans for the building
were never put into practice. Nevertheless he did have
the opportunity of demonstrating his architectural skill,
albeit on a much more modest scale, during the rebuilding of the Institute after its destruction in World
War 11. Thanks to his splendid planning, the new Marburg laboratory was for many years considered as one
of the foremost with regard to design and equipment.
Even today, it is only lack of space which necessitates
the replacement of the present facilities by a new building at another location.
On numerous occasions Meerwein has been concerned
with literary work falling somewhat outside his own
field. The first instance was when he succeeded Schroeter
in the preparation of the 11th edition of Richer-Anschiitz, the most comprehensive textbook of organic
chemistry of its day. After the last war he worked with
Eugen Miiller, Otto Buyer, and KarI ZiegIer on the new
edition of Houben-Weyl, Methoden der Organischen
Chemie. Twenty volumes have appeared to date, and
only those intimately involved in the work know the
full extent of his own efforts. We are indebted to him
not only for many useful suggestions, but also for a
number of contributions on his own particular fields of
interest. As with all his published work, they are models
of clarity and precision. He continued working on this
project to the last: on his desk were found new drafts
for a chapter on condensation reagents, which never
ceased to interest him and which had been the subject
of much thought and discussion with others.
I have not yet referred to his last work. It was found
hidden among other and quite unrelated papers in his
otherwise meticulously ordered office. Meerwein, who
was always glad to talk about his current work, who
never missed an opportunity to discuss the problems
which occupied his mind, spoke to no one about this
last manuscript. It is a comprehensive account of his
own life’s work. This account, on which he worked to
the last day of his life and the last pages of which, just
as his father’s chronicle, lay unfinished upon his desk,
will be his crowning achievement. It is to appear in
Angew. Chem. internut. Edit.
Vol. 5 (1966)
1 No.
4
Chemische Berichte, successor to the Berichte der Deutschen Chemischen Gesellschaft, which had once shown
a lack of appreciation by rejecting one of his most
important papers. In this way the man to whom
chemistry was his life and who has more than any
other in our time disseminated new ideas among
chemists all over the world, has continued his father’s
work in his own way by dedicating himself to research.
In so doing he has created for himself the finest memorial.
Received: January Zlst, 1966 [A 505/291 IEI
German version: Angew. Chem. 78, 353 (1966)
Translated by Express Translation Service, London
Scrambling Equilibria and Analysis of Labile Mixtures
BY DR. J. R. VAN WAZER A N D DR. K. MOEDRITZER
CENTRAL, RESEARCH DEPARTMENT, MONSANTO COMPANY, ST. LOUIS, MISSOURI (U.S.A.)
In this brief’ review, it is attempted to point up the importance of chemical equilibria in
structural inorganic chemistry and to show how the kind and yield of various molecules may
be treated quantitatively. Because of the importance of kinetic control in organic chemistry
and because the chemistry of carbon compounds is by far the most advanced branch of
general and descriptive chemistry, preparative inorganic chemists have often overemphasized the value of’reaction-mechanism theory to their studies and have thereby neglected the
powerful quantitative approach of thermodynamics which may be used in equilibrated
systems. The general theorems for treating in terms of small molecular segments the multitude of equilibria present in families of compounds are surveyed superficially with the hope
that the interested reader will turn to the original papers for details. Not only physicalinorganic chemists, but also those interested solely in preparative work can advantageously
employ the theoretical ideas discussed,
I. Introduction
Reactions involving only carbon compounds are generally kinetically controlled (i.e., the structure of the
products is determined by the reaction mechanism).
However, compounds having elements other than carbon in the spine of the molecule are often quite labile,
so that the amounts and kinds of reaction products may
be thermodynamically controlled (i.e., by the position
of an equilibrium), with different reaction mechanisms
leading to identical products and product distributions.
Most oligomeric compounds not based on C-C backbones are easily disrupted and therefore, under suitable
conditions, readily undergo “scrambling” reactions involving exchange of parts between the same or adjacent
molecules [I]. It is these scrambling reactions that complicate separations, lead to unreliability in elucidation
of structure by degradation or syn.hesis, and cause many
preparations of supposedly pure compounds to consist
of mixtures of molecules at or near equilibrium with
respect to exchange of parts among them.
In these cases the usual postulates as to reaction mechanism are no longer fruitful for explaining reaction
products, and must be replaced by the mathematically
more complicated approach of thermodynamics and
its underlying statistics of molecules (statistical mechanics and stochastic theories of molecular structure
and configuration).
[ I ] J. R. Van Wazer, Amer. Scientist 50, 450 (1962).
Aiigew. Chem. internat. Edit. ! Vol. 5 (1966) / No. 4
Of course, we d o not wish t o imply that reaction mechanisms
are always inapplicable t o the rationalization of reaction
products in inorganic chemistry. There are a number of areas
(e.g., the square-planar platinum complexes) in which the
energetics along the reaction coordinate are ideally suited to
present-day interpretative techniques of reaction-mechanism
theory. However, when reaction products are t o be ascribed
t o kinetic control the examples 121 must be carefully selected
when working with compounds based on elements other
than carbon.
II. Techniques of Experimentation and
D a t a Treatment
1. Analysis of Mixtures
a) N u c l e a r M a g n e t i c R e s o n a n c e
During the last 10 years, high-resolution NMR spectroscopy 131 has become a major analytical tool. At
present, the most suitable nuclei for quantitative NMR
measurements are IH, 19F, and 31P. Nuclei exhibiting
quadrupole moments, such as IlB, are ill-suited for
quantitative assay of mixtures (using the magnetic-field
strengths obtainable with non-superconducting magnets)
because of excessive line broadening. Problems of line
broadening may also De introduced by paramagnetic
[2] H . Taube, Chem. Rev. 50, 69 (1952).
[3] J . A. Pople, W. G. Schneider, and H . J. Bernstein: High-
resolution Nuclear Magnetic Resonance. McGraw-Hill. New
York 1959.
34 1
Документ
Категория
Без категории
Просмотров
1
Размер файла
450 Кб
Теги
hans, teacher, man, meerwein
1/--страниц
Пожаловаться на содержимое документа