A P . , 1914
T H E J O U R N A L O F I r I T D U S T R I A L A N D E N G I N E E R I N G CHE.VISTRI’
inforce a diet poor in flesh food,” yet he says further “we arc inclined to believe t h a t the maximum amount of cottonseed meal which should enter into the diet is two t o three ounces per d a y ; t h a t the conditions under which such a diet may prove injurious must be established. . . . . . . . . . , . and t h a t only experience and experiments can tell us the part which cottonseed flour should play in nutrition and under what conditions i t may prove unwholesome:“ The writer has eaten for some time in his own home cakes and bread of various kinds containing a portion of cottonseed flour without experiencing any ill effects from its use.
339
It should be said, however, t h a t while therc arc no reported cases of injury from the use of the meal as a food for man, it is possible and indeed quite probable t h a t this is due to its so far limited use for this purpose. The assumption of its unwholesomeness for man naturally grows out of the well known injurious effects which it produces when fed t o stock. Investigations are now under way t o ascertain the true nature of cottonseed meal toxicity. If this can be done, cottonseed meal or flour may be given to the world as a new and exceedingly inexpensive food with an almost unlimited source. C H E M I S T R Y LABOR.4TORY. GEORGIA EXPERIMENT STATIOX
WILLIAM H. NICHOLS MEDAL AWARD The Nichols Medal was conferred upon Professor AI. Gomberg, of the University of Michigan, in recognition of his distinguished researches on triphenylmethyl and its analogues. The medal meeting was held in Rumford Hall, The Chemists’ Club Auditorium, on Friday evening, March 6, 1914, with n r . ,411en Rogers, Vice-president of the Section, in the chair. The presentation address was made by Dr. Bernhard C. Hesse. Professor Gomberg, in acknowledgment of the medal, presented a n address on “ T h e Existence of Free Radicals,” in which he gave the first complete review of his eighteen years’ investigations and drew his conclusions based upon the results of his work. A large number of papers representing the stages of these investigations’have been published in the Journal of the Society, and a complete review of the work t o date is now in course of preparation. Professor Gomberg has prepared an abstract of his address which is published below, together with the presentation address by Dr. H e s s e . - - . [ E ~ ~ ~ o ~ j _ _ ~
PRESENTATION ADDRESS By BERNHARD C. HEW$
T h e purpose of this meeting of the New York Section of the American Chemical Society, is to present the William H . Sichols Medal t o the author of what has been determined by the Jury of the U’illiap H. hTichols Medal, to be the best original paper contained in the publications of the American Chemical Society during the year 1 9 1 3 . The purpose of the William H . h’ichols medal is the stimulation of research in chemistry. Research has latterly become a topic with which to conjure. I t is regarded by many as a panacea for the disabilities of chemistry, applied and pure. Yet there is no magic in research; no marvels arc performed by it. Y o u get out of research precisely what you put into it. You no more get something for nothing in research than in any other effort. There is, however, a divergence of opinion is to what does constitute research. As I view it, research is the orderly, systematic development of and addition t o science; science is nothing more nor less than the orderly, systematic and coordinated record of human experience. Purely accidental or random addition t o our knowledge without causal connection with what precedes and with what follows, however valuable or beneficial the addition may itself be, is not research. Yet, tesearch is not wholly independent of accident nor of chance; the systematic, orderly and planned exploitation of t h a t which chance or accident may have thrown into the path of him who is engaged in research, together with the carrying out of the original plan brings research t o its highest state of efficiency and t o its ample justification. Chance, without system, leads to chaos. System, even without chance, leads t o an orderly and coordinated statement of what we know and of what we know not to be. A-egative information, if true, has the same value as positive information. 1
Chairman h7ew York Section of the Smerican Chemical Society.
He who engages in research must have not only a working knowledge of what has gone before, but also :L norking know1 edge of all the tools a t his disposal; he must have a creative imagination, so that he may set himself the problem and for? cast with greater or less certainty that which may hr espccted; hc must be prepared t o deal with and to recognize the i i i i e x pected or unforeseen; he must have within himsclf ii sterlinfi quality of rigid self-analysis and a stern judgment of that which is of his own creation. Without a creatil-e imagination, balanced by a knowledge of the uncertainties of hypothesis and of theory and without balance by a knowledge and an appreciation of the imperfections of all human effort, he who engages in research is led into the highways and by-ways of confusion. Research information which is incorrect or confusing and work that leads to it are worse than useless, and he who knowingly produces such results is false not only to hiinself but to the hest and highest traditions and aims of research. Thosc who engage in research must have a thorough and an ahiding desire for truth a t all costs and must ha satisfied with nothing as trur which has not been demonstrated to he true by evc’rg test that can he reasonably applied. The more fundamental the nature of that which is believed to be new, the greater the necessity and responsibility for rigid scrutiny and inquiry as to its accuracy. Power of observation without the ability or without the quality of character to scrutinize and test the results of observation as to accuracy and certainty, is useless in research. Successful research requires a happy blending of many of the qualities of those who have explored and made our earth habitable, namely, daring, tempered with caution, and imagination, balanced by judgment. Those acquainted with the published wm!i of Professor Gomberg, our guest of honor this evening, recognize that his work fulfills and typifies the highest ideals of research. Starting out to obtain a n answer t o a definite problem in a carefully planned and definite way he came across something new, unexpected and unusual. His patient, laborious and ingenious examination of this led to the work which has consumed much of his time and effort for the past eighteen years and has given t o chemistry a new class of substances---triphen4-lmethyl a n d its derivatives. Professor Gomberg, it is my privilege as Chairmzti of t h e X e w York Section of the American Chemical Society now to place in your hands this, the tenth gold impression of the IVilliam H. Sichols Medal RS a token of the appreciation and esteem in which we hold your work as a chemist and the encouraging example you h a r e thereby given for all who engage in research.
THE EXISTENCE OF FREE RADICALS By It,GOMBERG
From the time when Kekule and Franchimont first prepared triphenylmethane, numerous attempts were made t o prepare the analogous compound tetraphenylmethane, but seemingly without succesj. The assumption \vas made that this substance
T H E J O U R N A L OP I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
340
must be very unstable and consequently incapable OC existence under ordinary conditions. I n 1897, a reactior, wns worked out by the writer by means of which a hydrocarbon, supposedly tetraphenylmethane, was produced. The compound proved quite stable, melting a: 280' C., and distilling undecomposed at 430' C. I n order to obtain more evidence as t o the constitution of this hydrocarbon an attempt was made to prepare, for comparative study, the next higher completely phenylated analogue,. namely, hexaphenylethane. Accordingly triphenylchlormethane was subjected to the action of metals-silver, mercury, zinc, sodium-with the full expectation that the reaction would proceed normally and gil-e rise to hexaphenylethane: (C6Hs)sC:Cl
I
+Agi (CeHs)aCiC1 . . . .i
+
(C&)3C I
(C&)& A hydrocarbon possessing the requisite composition (C = 93.8 per cent, H = 6.2 per cent) was actually obtained. But the proneness of this new compound to enter into the most varied chemical reactions, and its strikingly unsaturated character, precluded the natural inference that the conipound a t hand was a c t u a l l y h e x a p he n y l ethane. The opinion was 'expressed t h i t here was a n instance of 3 compound with one atom of carbon in the trivalent state, i. e., t r i p h e w y l m e t h j l , (CSHj13C, a free radical. Subsequently it was found that many analogues of triphenylmethyl are capable of existence. In other words, there is 3 large class of such free radicals-a class of triarylmethyls. Geizeral Reactioii and Method of Preparation\Vhen a triarylmethyl halide, dissolved in benzene, is treated with some M. GOMBERG, WILLIAM H. metal in the absence of oxygen, the halogen is t a k n out by the metal and the unsaturated triarylmethyl is formed. RzC AgCl RaCCl Ag
+
+
The solution is invariably colored, the nature of the color depending upon the nature of the three groups in combination with the central carbon atom. The colored compound is extremely sensitive to the oxidizing influence of the air, consequently when the colored solution is exposed to the air, the color disappears. In order to prepare a triarylmethyl pure the essential conditions are: exclusion of moisture-to prevent the hydrolysis of the triarylmethylchloride itself ; absence of oxygento prevent the oxidation of the resulting unsaturated hydrocar-
Vol. 6, No. 4
bon. A convenient form of a n apparatus which assures the above conditions was described by the writer' some years ago. It permits of the preparation, recrystallization, filtration, washing and drying the final product without ever exposing it to the oxidizing influence of the air. Physical Properties-The simple representative, triphenylmethyl itself, is in the solid state undoubtedly colorless, but goes into solution wit4 the production of a distinct orange-yellow color in any solvent whatsoever. We are forced to conclude that the compound in dissolving must undergo a change in molecular structure. To Schmidlin belongs the credit for the proof that even in solution the two modifications, colorless and colored, exist side by side in equilibrium with each other. In the solid state triphenylmethyl can be kept for years without change. I t melts at 145' C. The unsaturated character of triphenylmethyl is evidenced by its avidity to unite with a variety of solvents, taking them up as solvents of crystallization, and easily losing, them a t slightly elevated temperatures. It unites with aromatic and aliphatic hydrocarbons, with ethers, aldehydes, esters, ketones, nitriles, carbon disulfide, chloroform, etc. The composition of these various additive products is quite uniform, being I molecule z(C6H&C solvent. Another striking characteristic of triphenylmethyl is itf capacity to function as an electrolyte. When dissolved in liquid sulfur dioxide, a very good ionizing solvent, it conducts the electric current well, and its molecular conductivity increases with dilution. Chemical Prop e r ti e sF o r e m o s t among the chemical reactions of triphenylmethyl and all its analogues is the readiness NICHOLS MEDALIST. 1914 with which they unite with oxygen. Triphenylmethyl in benzene takes up oxygen from the air a t the rate of 60 cc. in one minute for I gram of the hydrocarbon. The compound formed in this reaction is colorless, fairly stable, and has the constitution of a peroxide: 2 (CeHa)sC f 0 2 ----f (CaH6)sC-o-o-c(CaHa)s As these peroxides are but little soluble in the usual organic solvents their purification presents no difficulties. Consequently the isolation of a peroxide in a reaction as described, is sufficient proof that a compound containing a trivalent carbon atom is present. Next to the combination with oxygen, the behavior of tri-
+
1
B e . , 37 (1904). 2033.
-
AV.8 1914
T H E JOCRNAL OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
phenylmethyl towards halogens is very striking. It unites instantly with iodine, even in very dilute solutions, giving almost quantitatively triphenylmethyl iodide:
+ *
341
other saturated hydrocarbons, is, or rather ought to be, preeminently unstable; (3) Jacobson’s quinol formula :
Hxz>
= CRg. Each of these three explanations had R3C followers, but undoubtedly the free radical idea was most favored, and was most widely adopted. (CeHdC H --3 (CeHs)sCH Constitution, Second Period, 1905-Io-We now enter upon I t also adds on nitrogen oxide as well as nitrogen dioxide, giving the second period of our hypothesis. These questions presented themselves: Is i t possible by experimental evidence t o show nitroso and nitro-triphenylmethane : whether a hydrocarbon of the type of hexaphenylethane i s or (C6HS)aC-NO and (C6H5)~C-N02 i s not stable? Is it possible to test experimentally the validity I n addition t o all the various additive reactions it also reacts of Jacobson’s suggestion? with phenols, amines, and hydrocarbons, giving tetraphenylOne of the fundamental arguments in favor of the probable methane derivatives, and is readily affected by light, suffering instability of hexaphenylethane was the well known fact t h a t auto-oxidation. the unsymmetrical tetraphenylethane seemed impossible of Constitution, First Period, Igoo-rpo5-It is obvious that the preparation. Anschiitz proved definitely that all methods, entire chemical behavior of triphenylmethyl finds its most con- perfectly logical and reasonable in themselves, t h a t have been sistent and most plausible explanation in the hypothesis that employed by the many investigators in order to obtain the unthis hydrocarbon is a free radical containing a trivalent carbon symmetrical tetraphenylethane, invariably resulted in giving the atom. This explanation when first advanced was received symmetrical compound : without open opposition, but none the less with hesitancy. (C&)ZCH-CH(C~H~)Z The hesitation to acquiesce in the hypothesis of the trivalency Symmetrical tetraphenylethane of carbon received later its main support from the fact that the (CsHs)sC-CH,(CeHs) molecular weight of triphenylmethyl was found to be not 243, Unsymmetrical tetraphenylethane but double that. Here then was the dilemma: The chemical behavior of the unsaturated hydrocarbon speaks forcibly, almost The conclusion became prevalent that the unsymmetrical hydroexclusively, in favor of the trivalency of carbon. The only carbon could not exist, owing to its instability. From thepresumed instability of the unsymmetrical tetraphenylethane it was argument against this interpretation is the dimolecular state of further surmised that the more complex homologous hydrocarthe compound, one single physical constant. It did not seem, however, impossible to reconcile this apparent contradiction bons, pentaphenyl- and hexaphenylethane, may reasonably be exbetween the molecular weight on the one hand and the entire pected to be still more unstable and consequently less likely t o chemical behavior of the compound a n the other hand. We have exist as such. And yet, by the application of the more modern numerous examples among inorganic as well as organic compounds method, the use of the Grignard reaction, we were able to obwhere substances in solution possess abnormally high molecular tain any amount of the long sought-for hydrocarbon, i. e . , the weights, double and triple that demanded by the composition unsymmetrical tetraphenylethane: (C6Hs)3CC1 CIMgCHGHs + (C~H~)~C-CHZ(CBHS) and constitution of the compounds in question. We say under such circumstances that the compound exists in the associated It turned out to be a very stable substance, beautifully crystalline, state, i. e., several molecules unite to form a single aggregate. and showed no resemblance to triphenylmethyl. Is not water itself polymolecular, the size of the aggregate The next step was to prepare pentaphenylethane, and here varying with the temperature? Are not the organic nitriles, a number of difficulties were encountered. Finally, however, the acids, the acid-amines, di- or poly-molecular in solution? this hydrocarbon was also prepared by the action of magnesium To quote from a paper of ten years ago: “The depressions in simultaneously upon a mixture of triphenylchlormethane and the freezing point obtained with naphthalene as a solvent at diphenylbrornmethane : the elevated temperature of 79-80’ C., suggest the probability (C&)sCC1 Mg BrCH(C&)2 + (cd%)~C-cH(CsHd~ that a t this temperature triphenylmethyl exists partially in the We encountered no difficulties in recrystallizing pentaphenyldissociated, mono-molecular state, as the molecular weights ethane from the various solvents; no oxidation on exposure to obtained in this solvent are 40 7-420 against 486 calculated. air was observed, and neither iodine nor bromine added on. On the assumption that such dissociation may exist, be it to ever The successful preparation of the two higher phenylated ethanes so small a n extent, the behavior of the hydrocarbon becomes above mentioned made it seem more probable than ever that intelligible: through the action of oxygen or of iodine the monothe hypothetical hexaphenylethane ought also to be a stable molecular form reacts first, the equilibrium is thus disturbed compound and that it could be prepared if only the conditions and it can only be restored through further and further dis- requisite for the process could be found. Alas, neither we nor sociation of the dimolecular triphenylmethyl until all of the anyone else of the many who have tried it, have found these compound has reacted.”’ conditions. Hexaphenylethane still remains a figment of the The dimolecular state of the hydrocarbon was, however, the imagination. And so the idea began to take root more and more occasion for the suggestion of various structures for triphenyl- generally that, after all, there is no difference between the SOmethyl all intending to do away with the interpretation involving called triphenylmethyl and the hexaphenylethane, that the former the existence of a free radical. hfarkownikoff, Heintschel, is in reality the latter. Add t o this the insistent emphasis which Vorlander, Chichibabin. P. Jacobson, Baeyer, Fliirschheim Chichibabin laid upon his discovery (1907)that pentaphenyland others took part in the discussion, each suggesting a some- ethane is decomposed by hydrochloric acid a t 170’ C., and that what different structural formula for triphenylmethyl. i t absorbs oxygen a t its melting point, 180’. and you have a t Thus, then, stood the question of the constitution of triphenyl- least a formal analogy, if not a real one, between pentaphenylmethyl a t the end of 1905: (I) The idea of the associated ethane and triphenylmethyl. These two factors taken together, molecule, associated but none the less in equilibrium with the the failure to prepare a stable hexaphenylethane and the apparent monomolecular free radical: RaC; ( 2 ) the hexaphenyl- lesser stability of pentaphenylethane than was attributed to it, thane view, which assumed that hexaphenylethane, unlike all these two factors had much to do with shaking the confidence of chemists that hexaphenylethane as such ought t o be a stable 1 Ber., 87 (1904), 2049.
(CE&)~C I (CsHd3CI Triphenylmethyl also combines with hydrogen in the presence of finely divided platinum :
+
+
+ +
T H E J O C R X A L O F I Y D C S T R I A L d;VD E N G I N E E R I N G C H E M I S T R Y
342
substance, unlike triphenylmethyl. Henceforth the hexaphenylethane constitution for triphenylmethyl began t o appear in the literature more frequently, a t least as one of the more probable constitutions Quinol Formula of Jacobson-Competing with the hexaphenylethane structure for recognition as the constitution of the dimolecular triphenylmethyl was the quinoid formula, suggested by Jacobson in 1905. I n subjecting the validity of this constitution t o the test of experiment the writer was guided by the well known fact t h a t the quinoid nucleus means a much less stability than the benzoid ring. And it was possible to prove by a n extensive series of quantitative experiments that “triphenylmethyl” actually behaves as if it contained a quinoid nucleus. Quinocarbonium Salts-The probable quinoid character of triphenylmethyl threw a flood of light on many phenomena which were at t h a t time the subjects of much debate. Baeyer strenuously opposed Kehrmann’s view that the colored solutions of triphenylcarbinol in strong acids are due to the formation of quinoid salts of the type:
Benzoid
Quinoid
I n the light of the results with triphenylmethyl our adherence to Baeyer’s view began t o waver. The verdict of our experiments was positive; these salt-like bodies were proved to be quinoid in their constitution. While the sulfates were found to exist only as intensely colored and quinoid, the chlorides were proved to exist in the two modifications: (CBHS)BC-C~ Colorless, benzoid
(Cs&),c =
