Man-Made Molecules THOMAS MIDGLEY, JR. Ethyl Gasoline Corporation, Detroit, Mich.
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N THE beginning God created t h e heaven and the earth . . . and God said, Let the earth bring forth THOMAS MIDGLEY,JR. grass, the herb yielding seed, and the fruit tree yielding fruit after his kind, whose seed is in itself . . . . And God said, Let the waters bring forth abundantly the moving creature that hath life, and fowl that may fly above the earth . . , . .And God said, Let the earth bring forth the living creature after his kind, cattle, and creeping thing, and beast of the And God said, Let us make man in our image, earth . after our likeness; and let them have dominion over the fish of the sea, and over the fowl of the air, and over the cattle, and over all the earth, and over every creeping thing that creepeth upon the earth.” These excerpts from Genesis present the simplest and most commonly accepted explanation of those alchemistic processes which gave us our universe and the earth on which we live. They present the picture of creating simply by divine edict Unfortunately this method is not susceptible to experimental demonstration, and those of us whose minds are closed to any other form of truth than that which can be substantiated by reproducible experiment must seek a different explanation. Scientific fantasy suggests a series of events even more astonishing than the edicts of Genesis. Its basis is probability. For is it not probable that during the last 1300 million years nearly every molecule that can exist upon earth has come into existence a t some time or other due to purely accidental causes? Thus may we picture the accidental formation of a protein molecule possessing the properties of the tobacco mosaic virus (recently demonstrated by Stanley) in that it was procreative in the medium in which it occurred. And so more of its kind came into existence, and an assemblage thereof resulted in the first living cell. After continued multiplication some of these cells arranged themselves into the f i s t organism. Differentiation soon accounted for many varied forms. These first organisms depended upon the sun’s radiation for their energy supply and carbon dioxide for their food. If any of these forms possessed a consciousness of its existence, we are unaware of it. When the process of utilizing carbon dioxide, converting the carbon into organic substances, and exhaling oxygen had proceeded to establish a reasonable quantity of oxygen in the atmosphere, other forms of life began to appear which made use of the substance of their predecessors for food and oxidation of some of this food for energy. These creatures required mobility to obtain food. Mobility needed senses for its guidance. Soon some began feeding on others of their kind. The senses were then required to give warning of an enemy’s approach so that the individual might escape to preserve its existence. Such action has been defined as the instinct of self-preservation. Yet there is a deeper implication than is covered by this definition. The very act of trying to escape indicates a consciousness of existence which must be accepted as the f i s t evidence of dawning intelligence.
These early forms grew to be giant reptiles, which in turn gave place to mammals with ever-increasing intelligence. Finally in one of these creatures the original functions of the five senses were converted from mere mechanisms for the preservation of life into a complicated device which we call “mind” and which speculates upon the nature of the universe, its own existence, and the causes, reasons, and usefulness thereof. Thus intelligence of the kind which we recognize as really worthy of the name, has came into existence in this creature which now calls itself “man.”
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ESSENTIALLY there is little difference in the story of Genesis and the scientific fantasy which has just been presented. The major events and their chronological order are in close agreement. I n neither case do we understand the forces or motives that produced these events so that whether one chooses to be a fundamentalist, believing in edicts without motives, or a scientist, accepting accidents without cause, he must necessarily admit much ignorance. We can, however, all accept the fact that when man came into exisb ence there had been prepared for him a world made up of many and varied molecules over the origins of which he had exerted no control. These molecules were the elemental units from which primitive man’s environment was built, Many of them were essential to his very existence, others contributed to his safety, comfort, and pleasure. One of the commonest of human characteristics is a desire to alter environment. We often refer to such changes as material progress. Early genus homo did little to alter his environment save in its physical form and by the building of fires. It was not until the appearance of our own species, some 30 thousand years ago, that we find any evidence of man altering in any way the molecular nature of his environment. This consisted principally in the cooking of food. Some ten thousand years ago additional impetus was given environmental change by the discovery of the reduction of metallic oxides. For a considerable period of time these were the only chemical reactions of sufficient importance to cause any great changes. It was not until the days of alchemy during the Middle Ages that any further advances worth noting were made in man’s ability to alter molecular forms. During this time man was learning that he could change chemical constitution but actually made little use of this knowledge towards bettering himself. Gunpowder alone seems to be the outstanding development. This is essentially a mixture of naturally occurring substances, rather than a new molecular form. Chemistry emerged from alchemy and for some time consisted only of the study of the constitution and reactions of existing nature-made molecules. As these compounds and their reactions were better understood, it became possible for the chemist to direct the synthesis of many of them, first in the inorganic field and then in the organic, with synthetic indigo as a classical example. During all this time much was being learned about the generalizations of synthesis to the end that molecules could be, were, and are being produced which, to the best of man’s knowledge, have never occurred in nature. Such molecules truly can be thought of as entirely man-made.
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THE term “man-made molecule” in an exact sense means the product of any chemical reaction carried out by man. For the purposes of the present discussion, however, i t is intended to refer only to those molecules, conceived by the brain of man, which do not occur in nature and which serve some useful purpose-for example, novocaine.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
JANUARY, 1938
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1097
1917
1937
YEAR
FIQURE1. TRENDOF MAN-MADEMOLECULES FOR PASTCENTURY
THE
I n discussing this class of substances and pointing out their ever-increasing importance in the material progress of the world, it is not intended to detract from the importance of sfnthesizing many of the naturally occurring molecules such as camphor, or to minimize the difficulties encountered in effecting such syntheses, or to obscure the obvious importance of such work in the future. I merely wish to emphasize how the progress of chemistry has placed in man’s hands tools for adjusting his environment to his changing needs in a fashion that is not possible by extracting from or copying naturally occurring substances. As long as man was limited by lack of chemical knowledge to confine his alterations to changing the physical form, the location of, or the proportions of naturally occurring substances, “material progress” had definite finite limits. It is true that in many fields, such as the applications of the hormones, we are still far from even approaching these boundaries. Yet we do recognize that they exist. However, the use of hormonelike substances, synthetically produced never occurring in nature, opens such vast possibilities that we can truly say that the only limitation conceivable is our own ability to apply them. Thus man-made molecules provide new elemental units for environmental construction that far transcend in possibilities the wildest dreams of alchemy. We are usually inclined to glorify the present accomplishments and forget the past. Thus we might overlook the fact that cooking, soap, and glue manufacture are examples of man-made molecules which are extremely ancient, as are also the curing of leather and the making of steel. Yet there is a difference in their origins from the processes in use today to accomplish similar results. This difference is seen by the comparison of discovery by fortuitous accident (man-made, if you please, but fortuitous and accidental nevertheless) with the use of the inventive process which conceives h s t of a desired result and then proceeds to discover or determine a method of obtaining it-i. e., the difference which exists between the discovery of a primitive savage that the carcass of a rabbit tasted better after having been heated by a forest fire and the development of a synthetic resin for holding two pieces of glass together to make automobiles safer. I asked a group of my friends t o submit lists of important man-made molecules, and was careful to ask them to include tetraethyllead and organic fluorides in their lists so that I may have some material with which I have had personal contact to use in this address. From the answers the lists in Table I were compiled in chronological order. There is
a decided increase in the numbers of such molecules as we approach the present time. Figure 1 indicates that we may confidently expect many more such molecules to make their appearance in the future. TO APPRECIATE how recent the applications of manmade molecules are, let us look back a century and briefly picture the conditions which surrounded Doctor Chandler when he was only a few months old. The materials used in the construction of the house in which he lived were derived directly from natural sources without any essential molecular alterations. The clothes which he wore were all woven and spun from natural fibers. The colors which brightened his surroundings were all of simple vegetable or mineral origin without chemical change. The fuel for lighting his evenings was an extract from animal fats. The medicines his parents used to ease his infant illnesses included no man-made molecules. The industry that supported the community in which he lived consisted principally in directing nature to make useful molecules from carbon dioxide and water. And when the family went to church to christen their newest born, the motive power was a horse which drew a vehicle composed entirely of naturally occurring molecules. Nor was i t possible in that day for the neighborhood soothsayers to visualize the impending changes that were about to take place in man’s environment due to man-made molecules, nor to predict the important part that Baby Chandler was to play in this advance. And yet it was only two years later that Goodyear discovered the vulcanization of rubber.
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IULES TABLEI. DATESOF APPLICATION OF MAN-MADE MOLEC
Prechemistry Era Cooked foods Steel (not iron) Glass (1) Soaps Tanned leather Bronze Brass Glue
Name Vulcanized rubber Coal tar dyes Nitroglycerin Nitrocellulose hTitrocellulose Phenolic resins Rubber accelerators Tetraethyllead Nitrocellulose lacquers Rubber antioxidants Cellulose acetate Cellulose acetate Alkyd resins Organic mercury Ethylene glycol Urea resins Gasoline antioxidants Organic polysulfides Chloroprene polymer Cellulose acetate
Copper phthalocyanine Ethyl ether Chloroform Iodoform Acetyl salicylic acid Barbitols Arsphenamine Novocaine Hexylresorcinol Divinyl oxide p-Aminophenylsulfamide
Inorganic
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Silver bromide Sluminurn
Magnesium Sodium chlorate (weed eradicator) Tungsten carbide Organic Trade h-ame Use Numerous ...... Coloring Explosive ceiiiioih Plastic Smokeless powder Explosive Molding material Bakelite
Textile Preservative Molding
Date 1839 1856 1866 1874 1898 1912 1912 1923 1924 1925 1925 1926 1927
Fungicide Antifreeze Molding material Preservatives Rubber substitute Rubber substitute
1928 1928 1929 1830 1930 1931
......
EthYi Duco
......
‘‘
V i G G ‘rayon
Cellophane Dulux, Glyptal Semesan, Ceresan. Lignasan Prestone Beetle, Plaskon Neoprene Tci;ibi;dl’
Plastacele, Tenite Freon Vinylite Gardinols Lucite Monastral Medicinal
...... ......
Aspirin Veronal, Amytal, Luminal Salvarsan
...... vihk’thk’ne Prontylin
1864 1888 1898 1900 1905 1912 1914 1918 1927 1928
hntiknock Paint
......
1931 1931 1932 1933 -substitute Pigments
1936 1937
Aneathetic Anesthetic Antiseptic Hypnotic Hypnotics and soporifics Specific against syphilis Local anesthetic Antiseptic Anesthetic Specific against coccuses
1846 1847 1880 1900 1904 1910 1916 1927 1932 1936
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The automobile of some twenty-five years ago exhibits man-made molecules in the steel and rubber used in its construction-a goodly proportion of the whole, t o be sure, but compare this with the vehicle of today. T o the rubber have been added preservative materials called "antioxidants," whose molecular construction is unknown in nature. The paint, instead of being natural oils mixed with natural pigments as was the case twenty-five years ago, is now cellulose nitrate containing coal-tar dyes. If we look under the hood we find synthetic resins and chlorinated naphthalene in the electrical system, polyisobutylene in the lubricating oil, ethylene glycol in the cooling water, and tetraethyllead in the gasoline. The glass in the body is no longer a simple inorganic compound such as was made by the Egyptians, but contains an internal layer of a transparent synthetic resin. Inside the car the steering wheel is made of, and much decorative finishing is accomplished by, other synthetic resins. The upholstering, if of the leather variety, comes from an autoclave instead of a cow. Not only have these man-made molecules increased our comforts and conveniences but their production has created new industries, new demands for raw materials, and new opportunities for individual initiative to such an extent that today they are the very lifeblood of chemical industry. I n four of the many divisions of the chemical industry which are founded on man-made molecules we find in 1936 the production of coal-tar dyes employing some 15 thousand men to produce 120 million pounds of material worth 62 million dollars; synthetic resins employing 12 thousand men producing 100 million pounds worth 50 million dollars; nitrocellulose and cellulose acetate employing 3 thousand men producing 30 million pounds worth 23 million dollars; and the explosives industry (for peace time purposes only) employing 5 thousand men, producing 400 million pounds worth 40 million dollars. These four industries annually account for 50 thousand employees, and 650 million pounds of products worth 175 millions of dollars, without the inclusion of intermediates, heavy chemicals, or raw materials. It is safe to assume that a similar number of employees in these accessories owe their jobs to the demands of the Simon-pure man-made-molecule industries. S o r are these four the only branches of chemical industry founded on man-made molecules. Tetraethyllead alone compares favorably in poundage with some members of this group. ORGAXIC fluorides and tetraethyllead fulfill the definition of man-made molecules. I happened to be intimately connected with the development of the applications of both. ' The discovery that organic fluorides were ideal refrigerants took place in the following manner: One morning I received the following telephone message: "Midge, I was talking with Lester Keilholtz last night and we came to the conclusion that the refrigeration industry needs a new refrigerant if they ever expect to get anywhere. So I told Lester that I would call you and have you see him to talk it over. H e is leaving for Dayton tonight." Mr. Keilholtz informed me that a nontoxic, nonflammable refrigerant was needed imperatively for the further expansion of air conditioning; the desired substance must have a boiling point between 0" and -40" C. and be stable. International Critical Tables gave us a partial summary of the volatile organic compounds. Recognizing International Critical Tables to be very incomplete, we decided to bring the periodic table into play t o see if the desired volatilities could be related to it. It takes but a fraction of a second to see that this is true. I n an arrangement according to vacant places the elements on the right-hand side are the only ones which
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make compounds sufficientlyvolatile for the desired purpose. I n fact, only a certain number of these need be considered. Volatile compounds of boron, silicon, phosphorus, arsenic, antimony, bismuth, selenium, teIIurium, and iodine are all too unstable and toxic to consider. The inert gases are too low in boiling points. Consider the remaining elements. Every refrigerant used has been made from combinations of these elements. Flammability decreases from left to right. Toxicity, in general, decreases from the heavy elements a t the bottom to the lighter elements a t the top. These two desiderata focus on fluorine. It was an exciting deduction. Seemingly, no one previously had considered it possible that fluorine might be nontoxic in some of its compounds. This possibility had certainly been disregarded by the refrigeration engineers. If the problem before us were solvable by the use of a single compound, then that compound would almost certainly contain fluorine. The heats of formation between the halogens and carbon were checked. They increase from iodine to fluorine, thus indicating a high degree of stability for fluorine-carbon compounds. Everything looked right except that old fear of hydrofluoric acid burns. As it turns out, hydrofluoric acid burns are a special case. Next came methods of preparation. Carbon tetrafluoride seemed rather hard to make. And then how could dichlorodifluoromethane boil a t -20" C. and carbon tetrafluoride a t -15" C.? It just didn't make sense. Plots of boiling points, hunts for data, corrections, slide ruks, log paper, eraser dirt, pencil shavings, and all the rest of the paraphernalia that takes the place of tea leaves and crystal spheres in the life of the scientific clairvoyant, were brought into play. We decided that carbon tetrafluoride boiled a t about -136" C. or else it was a very special kind of substance. (Not long after this time a publication on the subject appeared. Carbon tetrafluoride boils a t -128" not -15" C.) Feeling pretty certain that -15" C. was wrong and that it was a sizable research problem to make carbon tetrafluoride, we selected dichloromonofluoromethane as the starting point for experimentation. I called one of the chemical supply houses by telephone and ordered five 1-ounce bottles of antimony trifluoride. The five bottles arrived. One was taken a t random, and a few grams of dichloromonofluoromethane were prepared. A guinea pig was placed under a bell jar with it and, much to the surprise of the physiciaii in charge, didn't suddenly gasp and die. While it is conceivable that under some rare series of accidents dichloromonofluoromethane may have been formed in nature, it is certainly not a recognizable product of nature which can be secured by some refining process. It is distinctly a manmade molecule and serves a function which cannot be performed by any naturally occurring substance now known. The expansion in air conditioning which has occurred during the past decade has rested largely upon the ability of the engineer to secure a refrigerant free from hazard. Thus we see our physical environment continuing to change because of the application of this man-made molecule. THROUGH the medium of man-made molecules man has the means of altering his environment as he chooses. What that choice shall be is not for the chemist alone to decide. Steel may be used for building and transportation or for guns and shells, high explosives for mining and construction or for the killing of women and children, and the same tools that make dyes will make poison gases. May I therefore ask you to join with me and with chemistry, in the name of the man whose memory we honor here, in doing all within our power to see that these man-made molecules are applied exclusively to the pursuit of happiness? Thus may we comply with God's edict in Genesis that Man shall be in His likeness and have dominion over all the earth.
