"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