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Chemistry
and Chance: Part 1*
Peter E. Childs
Department of Chemical & Envronmental Sciences,
University of Limerick, Limerick
serial cracker key code
"Accidental
discoveries are common, one might say almost the rule, in
chemistry but rare in mechanical engineering. It is much
more likely that a chemist would fortuitously turn up
some new and surprising property in a known compound than
that an engineer would group together pieces of metal
with one idea in mind and discover he had stumbled across
a device of a kind that he had not been seeking."
The sources of invention John Jewkes,
David Sawers, Richard Stillerman 2nd. edition Macmillan
1969 p.98
Introduction
From a title like "Chemistry and Chance" some
of you may be expecting an erudite lecture on statistical
thermodynamics and probability; some of you may have
chaos theory and chemistry in mind. However, I'm afraid
I'm going to disappoint you as I want to look at another
aspect of chance, namely the role of accidental discovery
in the progress of chemistry, with particular reference
to synthetic chemistry. We pride ourselves that chemistry
is a science and therefore is a systematic search for
understanding of the material world. Sir Derek Barton
said, however, in introducing a seminar in Texas in 1984:
"You know, most of the important reactions in
organic chemistry were discovered accidentally."
More of Chemistry than we might like to admit is the
result of chance observations and accidents, and many
advances have been the result more of serendipity than of
systematic search. Serendipity is the name usually given
to these accidental but happy discoveries, after the
Princes of Serendip described by Walpole in 1754 who
"were always making discoveries, by accidents and
sagacity, of things they were not in quest of ..".
Walpole coined the new word serendipity to describe this
phenomenon. Another well-known expression of this is
Louis Pasteur's dictum:
"Dans les champs
de l'observation, le hazard ne favorise que les esprits
prepares."
or more familiarly:
"In the field of observation, chance only
favours the prepared mind."
The theme of accident and chance in science also raises
the topic of scientific creativity and imagination in
science. Is this the result of method and intelligence or
does it have an unpredictable, random side to it? I want
to concentrate tonight only on accidental discoveries
that have opened up new areas of chemistry. Pasteur's
epigram has been emphasised by many people - it is not
enough to have accidents, everyone has those, but we must
also be ready and in the right state of preparedness to
profit from the happy accident or it may just be washed
down the sink like many failed experiments and reaction
mixtures. Joseph Henry, the American physicist, said:
"The seeds of
great discoveries are constantly floating around us, but
they only take root in minds well prepared to receive
them."
I want to look at some
examples, mostly well known I presume, of serendipitous
discoveries in Chemistry but I also want to discuss how
we can develop the intellectual skills and attitudes that
enable us and our students to profit from the unexpected
occurrence.
An unexpected reaction
In 1842 Schoenbeim, a Swiss-German chemist, was
experimenting in the kitchen at home in England against
the express wishes of his wife. Not surprisingly she
didn't want her kitchen or equipment spoiled with
chemical mixtures and smells. But she was out and Schoenbeim
took the opportunity to pursue his experiments.
Unfortunately he spilled 2the mixture of conc. nitric and
sulphuric acids that he was working with. Not wanting to
be caught out by tell-tale stains he quickly grabbed his
wife's cotton apron and wiped up the spill. He hung the
apron up to dry in front of the fire and was amazed when
it disappeared in a smokeless flash of fire. Many of us
would have been grateful at that point that the evidence
had been destroyed, although there was still a missing
apron to explain. But Schonbeim didn't stop there. He
recognised that something significant had happened and
when on to investigate the reaction of the nitrating
mixture on cellulose. He ended up discovering and
patenting guncotton, the first of the smokeless
explosives.
Accidental breakthroughs
in chemistry
Sir Derek Barton, who surely knows better than I, has
said that most important organic reactions were
discovered by chance. The Friedel-Crafts reaction, the
Wittig reaction and hydroboration are three 'moderately'
important reactions that illustrate this. One could argue
that the reaction that started organic chemistry off was
Friedrich Woehler's attempt to make ammonium carbamate
which produced urea instead. It started the decline of
vitalism and encouraged the rise of organic chemistry as
a scientific discipline. The same discovery also pointed
Woehler and Berzelius to the idea of isomerism , which
they thought the most important finding.
Organometallic compounds
were first made by accident not design. Edward Frankland
was using zinc to make alkyl iodides and found he had
made an organic compound containing zinc as a by-product.
Metal carbonyl compounds were also discovered by accident
as Ludwig Mond and his assistants investigated why nickel
valves were corroded by carbon monoxide. One accident led
to another and they observed the formation of nickel
carbonyls as their apparatus cooled down. Further
research led to the synthesis of more metal carbonyls,
which Lord Kelvin described as "metals with
wings" and to the Mond nickel carbonyl process for
refining nickel.
In 1987, at the age of 83,
Charles J. Pedersen shared the Nobel Prize in Chemistry
for his discovery and development of crown ethers. He had
stumbled across them, by accident, at the age of 63 - two
years before he officially retired. An impurity in one of
the chemical s he was using led to the formation of
unexpected white, fibrous crystals which turned out to
have the amazing property of making metals soluble in
organic solvents. The rest, as they say, is history. A
friend of Pedersen, Herman Schroeder, said this:
"You should
understand the crown ether discovery in perspective.
Charlie was an acknowledged expert in coordination
chemistry ... He knew what could or couldn't happen; he
was, in a sense, prepared for the discovery. It wasn't
that he stumbled on it; rather, it was as if the compound
walked in front of him and he snapped it up. You need a
sharp, ready, and flexible mind for that."
(Roberts, p. 243)
Many of the elements were discovered by accident in
places that people didn't expect to find them: iodine in
seaweed, selenium in a copper smelter, helium in the sun,
argon in air, thallium in a sample of impure selenium and
so on.
Impurities have played a major role in important
discoveries - so much so, that one wonders whether our
modern, highly purified reagents have eliminated one
fertile source of new chemistry. It is amazing how many
discoveries have been made because of impurities in
reagents or contaminants in the process led to an
unexpected result. Crown ethers, the synthesis of indigo,
the industrial synthesis of vinyl chloride, polyethylene
... all discovered because of impurities in the starting
materials or dirty apparatus.
There are many other
examples like this where an accidental contaminant
produced the unexpected effect and this wasn't
reproducible until the contaminant was recognised.
Accidental discoveries of
dyes and pigments
Everyone is probably familiar with William Perkin's
discovery of the first synthetic dye at the age of 18,
which he made by accident at home during one of his
vacations from university. He was trying to make quinine,
valuable in treating malaria, because it was only
available from the bark of the cinchona tree. Perkin's
boss A.W. Hoffmann had thrown out the challenge to
synthesise quinine in one of his lectures and Perkin went
home to try an make it, using the knowledge of chemistry
that he had. Instead of the expected product when he
oxidised toluidine Perkin got a brown sludge and then a
black sludge using aniline, a not unfamiliar result for
chemists. While trying to wash it out of the flask he
noticed that it gave a purple solution and he went on to
try its effect as a dye on cloth. He found a way to
extract the purple dye from the black product and sent
samples off for testing.
"With the
enthusiasm of youth, Perkin decided to patent his dye,
build a factory, and go into the dye business."
(Roberts p.67)
His professor, A.W. Hofmann, tried to discourage him but
to no avail and Perkin went on to set up a successful
factory to manufacture the dye and made his fortune. He
was able to retire at the age of 36 and devote himself to
chemical research. Not only did he initiate the synthetic
dye industry but his accidental discovery is also
credited with being the start of the organic chemicals
industry. Not bad for a teenage chemist!
There are other accidental
discoveries in the area of dyestuffs. Indigo was
synthesised successfully on a commercial scale by Karl
Neumann at BASF following an accident by a chemist called
Sapper when a thermometer broke in a reaction mixture
containing naphthalene and fuming sulphuric acid.
Mercuric sulphate was formed and acted as catalyst to
produce phthalic anhydride, which was easily converted
into indigo. BASF started selling synthetic indigo in
1897 and the natural indigo industry, based in India,
never recovered.
More recently the
phthalocyanine pigments were discovered when A.G.
Dandridge at Scottish Dyes Ltd. (later to become part of
I.C.I.) noticed blue crystals on the side of vat which
contained molten phthalic anhydride. These turned out to
be complexes of iron, their structure was elucidated and
they were called phthalocyanines and they turned out to
be valuable pigments. Their structures are related to the
structure of haem in haemoglobin and chlorophyll. With
copper as the metal the pigment is known as Monastral
Blue and is the best blue pigment for three-colour
printing.
"Although the
existence of the phthalocyanines was not predicted, and
was perhaps not even predictable, yet now the discovery
has been made and the structure of the molecule
ascertained, no one can fail to remark the inevitability
of the compound. Its right of existence is almost
declamatory! It is remarkable how readily at the
appropriate temperature of reaction, and in the presence
of such a metal as copper, the four integral components
almost snap into position."
(C.J.T. Cronshaw, Endeavour, 1942)
The lesson that we can learn from these three
discoveries: don't throw away the unwanted mess too
hastily or disregard an unusual colour or crystals in an
unexpected place.
Collodion
"Significant inventions are not mere accidents.
The erroneous view is widely held. and it is one that the
scientific and technological community, unfortunately,
has done little to dispel. Happenstance usually plays a
part, to be sure, but there is much more to invention
than the popular notion of a bolt from the blue.
Knowledge in depth and in breadth are virtual
prerequisites. Unless the mind is fully charged
beforehand, the proverbial spark of genius, if it should
manifest itself, probably will find nothing to
ignite."
(Paul Florey, on receipt of the ACS Priestley Medal.)
Collodion figures in several serendipitous discoveries.
Collodion, a solution of cellulose nitrate in a mixture
of ether and alcohol, was popular as a treatment for cuts
in the mid-1800s. One day in 1875 Alfred Nobel cut his
finger and applied collodion to the cut to seal it. That
night Nobel could not sleep because of the pain and
started thinking again about how to combine
nitrocellulose and nitroglycerine into a safe but
powerful explosive. He thought of using collodion instead
of guncotton, which might be more workable. He
immediately got up at 4.00 a.m. and set to work. By the
morning he had the first jelly-like samples of blasting
gelatin, which after further testing and development was
patented and became widely used.
Another cut and the use of
collodion led John Wesley Hyatt to the first synthetic
plastic material. He found the bottle of collodion
knocked over, leaving a sheet of hard cellulose nitrate.
He thought of using collodion as a binder for sawdust and
paper instead of glue, as he was searching for a hard
substitute for natural ivory. Hyatt and his brother found
that a mixture of cellulose nitrate, camphor and alcohol,
moulded under pressure, produced an acceptable, if
occasionally explosive, substitute for ivory. They went
on the patent the new material under the name Celluloid
in 1870 and it became a very successful material for
collars, buttons, knife handles and many other uses.
Another spilled bottle of
collodion led to the first semi-synthetic fibre. In 1878
Hilaire de Chardonnet spilled a bottle of collodion and
when cleaning it up noticed that the viscous liquid
produced fibres. He was searching for a silk substitute
and this chance discovery led him to investigate further.
Within six years he had produced the first artificial
silk, which was called rayon in 1924. He made collodion
from a pulp of mulberry leaves, the natural food of
silkworms, and drew out fibres from the solution in ether
and alcohol, drying the fibres in hot air to evaporate
the solvent. This discovery led to xanthate and acetate
rayons and then to the range of synthetic fibres that we
enjoy today, such as nylon and polyester.
But the collodion story
isn't finished yet. Another accident with collodion led
to the invention of laminated glass. A French chemist
called Edouard Benedictus accidentally dropped a glass
flask on the floor of his laboratory in 1903. It
shattered of course but he noted that the bits didn't fly
apart and although broken, the flask retained its shape.
On looking closer he found that a film had coated the
inside of the flask, produced by the evaporation of a
solution of collodion, leaving a plastic film of
cellulose nitrate on the glass. He did nothing further
until he read of a car accident where a young girl had
been badly cut by broken glass, and then later of a
similar accident. He remembered his broken glass and set
to work to make a coating on glass that would prevent
such accidents. He took out a patent on the new glass in
1909 and it took several years to go from the idea in the
laboratory to production in a factory. But the accident
combined with Benedictus' ability and then his
application to solve the problem, resulted in an
invention which has saved lives and prevented much
industry.
Plastics by chance
Although collodion led to the first synthetic plastics
and fibres the principles of polymer formation were not
understood until much later in the 1920s and 30s.
Consequently chemists didn't understand fully what
chemicals could be polymerised or how this could be done.
Several significant breakthroughs in the history of
polymers occurred by accident: the discovery of teflon,
polyethylene, cold drawing of nylon, neoprene,
Ziegler-Natta catalysis, polyvinyl chloride,
poly(ethylene oxide) - all these involved an element of chance,
an accident or contamination.
Teflon is the tradename
for poly(tetrafluoroethene), most familiar to the public
in non-stick pans. It was discovered by accident by Roy
Plunkett, a young chemist fresh from his Ph.D. who was
working for Du Pont. He was trying to produce a nontoxic
refrigerant from gaseous tetrafluoroethene and one day he
opened a full cylinder of the 'gas' but nothing came out.
The weight showed that the cylinder was full, the valve
was working but nothing came out. Instead of looking for
a new cylinder Plunkett investigated further to find out
how an empty tank could still be full. He sawed the
cylinder in half, a risky venture in itself, and found
that the gas had been converted into a waxy, white
powder. Several polymers were known by then and he
realised what this meant, although no-one had polymerised
tetrafluoroethene before. They investigated further,
found out how to make it and this led to a multi-million
dollar industry.
Polyethylene has had probably more impact on our everyday
lives even than Teflon and it was one of the earliest
plastics to come into common use. It too was discovered
by accident due to leaky and dirty equipment. It was
first discovered by two I.C.I. chemists, Eric Fawcett and
Reginald Gibson in 1933 when they reacted ethylene and
benzaldehyde at high pressure. The reaction shouldn't
have happened as it was catalysed by a trace of oxygen in
the tube. The first samples of polythene were formed in
1933 but the experiments were difficult to produce. M.W.
Perrin and J.C.Swallow at I.C.I. tried again in 1935 with
better apparatus, and at a temperature of 180oC the
pressure dropped and more ethylene was pumped in. 8g of
solid polyethylene was made but they recognised that the
pressure drop was greater than expected and suspected a
leak. Swallow writes in his book The history of polythene
(1960):
"Here again the
element of chance played an important role, and it took
some months of intensive work by all those in the
research team to elucidate the full reasons as to why, if
the leak had not occurred, the experiment would probably
have been far less spectacular than it was, and might
have been a repetition of the earlier ones.
The success of the experiment in September was in fact
due to the additions to the reaction vessel of fresh
ethylene gas to replace that which had leaked out. The
ethylene contained by chance about the right amount of
oxygen to catalyse the formation of successive amounts of
the polymer."
Three years earlier the American polymer chemist Carl S.
Marvel had made polyethylene by a different method but
didn't follow it up because "nobody thought
polyethylene was good for anything". In fact it was
the demands of war and the need for a better insulator
for cables that stimulated the development of
polyethylene and it played a key role in the development
of radar. In a similar way the demands of the Manhattan
Project for seals and gaskets to resist uranium
hexafluoride led to the development of polytetrafluoroethene
from a laboratory curiosity.
Polyvinylchloride is
another well-known polymer first made commercially in the
1930's and the first synthetic polymer, predating Hyatt's
celluloid. It was discovered by accident in 1838 by a
French chemist Victor Regnault. He exposed samples of
vinyl chloride to sunlight and described the formation of
a white powder. In 1872 E. Baumann rediscovered it and
found it to be unaffected by solvents or acids. The
significance of their findings wasn't realised until much
later and society had to wait another 60 years for PVC to
be made commercially.
(This article will be
concluded in issue #51.)
* This article is based on
a after-dinner talk given at the Annual Congress of the
Institute of Chemistry in Galway in May 1995. It has also
been printed in Irish Chemical News Vol. X (III) Summer
1996.
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