INDUSTRIAL A N D ENGINEERING CHEMISTRY
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Vol. 16, No. 3
Contact Catalysis and Photochemistry’ By Wilder D. Bancroft CORNELL UNIVERSITY, ITHACA, N. Y.
HE greatest difficulty about a problem is often the formulation of it, and this has been strikingly true of
fatal blow. That is the view held by Kruyt and van Duin.2 On this view contact catalysis is a most unsportsmanlike contact catalysis, each period of development being thing. It is equivalent to hitting a man, not only when he marked by a new formulation. The classification by Ber- is down, but when he is held by somebody else. That is not zelius of a group of phenomena under the general head of an argument either way, because chemical reactions may catalysis ushered in the first period, which was essentially follow the laws of the gang even though Professor Taylor has qualitative. Osttvald’s sharper definition introduced a period postulated intelligent molecules in order to account for of quantitative measurement of reaction velocity. Colloid negative catalysis. chemistry brought the realization that there were two groups The other possibility is that, as the bond between the adof phenomena, one in which definite, intermediate chemical sorbed substance and the adsorbing agent makes and breaks compounds were formed, and one in which there was adsorp- during dynamic equilibrium, we have temporarily an actition and the intermediate formation of indefinite chemical vated radical, which may react with another activated radical compounds, meaning thereby, complexes that are not de- or with an ordinary molecule. On this assumption the scribed by the law of definite and multiple proportions. The reaction will take place chiefly a t the inner or adsorbed end attempt to determine in which group a particular reaction of the molecule, the catalytic agent functioning as a beneffalls has led to the brilliant work a t Princeton on catalysis icent agent which enables the molecule to throw off the restraints that ordinarily hamper its action or reaction. a t an interface. It is hoped that this symposium will mark the beginning The experiments of D. Berthelot and Gaudechon3 indicate of the study of the fundamental question-how the activation that ultra-violet light of suitable wave lengths will bring occurs. This paper will be limited to cases dealing with about the same reactions that we get with different catalytic adsorption. Any action between so-called saturated com- agents, such as the decomposition of ethyl alcohol into acetalpounds involves either a preliminary dissociation which means dehyde, ethylene, etc. Under these conditions there can be the breaking of a regular bond, or a preliminary association no captive molecules and consequently the reactions must which means the opening of a contravalence or residual be between free radicals. Until some proof to the contrary valence. Nef believed that all reactions were preceded by is found, it is simpler to postulate that the reactions in presdissociation, while Michael defends the view that all re- ence of solid catalytic agents are reactions of free radicals and actions are preceded by the formation of addition compounds. not of captive molecules. Since there can be no formation The real truth probably lies somewhere between these two of definite or indefinite intermediate compounds between extreme views, and it is very much to be hoped that the or- alcohol, for instance, and light, it must be concluded, until ganic chemists will go over their field and point out definitely further notice, that the formation of definite or indefinite in which cases we are justified in saying that we have pre- chemical compounds with the solid catalyst is not in itself liminary dissociation, in which cases we know we have pre- the essential thing, but is merely the step in the formation liminary association, and what is lacking in the other cases of the free radical which is the real reacting substance. to enable us to decide where these cases belong. A comThe problem on the photochemical side is to determine mittee to do this has been appointed by the National Re- what radicals are formed and what ultra-violet rays produce search Council. them. The step after that is the really fascinating one. The next problem in contact catalysis is therefore to If, as seems probable, each chemical bond corresponds to determine in each case which bonds have been broken or one or more absorption lines, which will lie in the ultra-violet opened. To simplify matters this problem will be discussed or infra-red in the case of colorless compounds, it should be solely on the assumption that adsorption involves dissociation. possible, theoretically, to break or open any desired bond in It will be a simple matter for anybody to translate this into any given substance by the use of suitable monochromatic terms of opening contravalences. We owe to Langmuir the light of sufficient intensity under favorable conditions. I n important conception of oriented adsorption, meaning that other words, we see the possibility of developing an absolutely acetic acid, for instance, when adsorbed by charcoal may new technic for organic chemistry. One of the things that worries the thoughtful physical attach itself by the methyl carbon, by the carboxyl carbon, or by either of the oxygens. If we are dealing with associa- chemist, if this is not a tautological phrase, is the apparent tion, it may also attach by any of the hydrogens. Langmuir difference between inorganic and organic reactions. Several has been very definite as to what he means by oriented ad- years ago the attempt was made to bridge the gap by possorption in the case of oil films on water, but he has been tulating that all reactions in organic chemistry were ionic very indefinite with regard to what he means in the case of reactions, but that postulate was so obviously wrong that it did not get anywhere. The reasoning put forward with recontact catalysis, even though he has given one picture. After postulating oriented adsorption and the opening of gard to reactions between saturated compounds applies just particular bonds, there are still two ways in which reaction as much to inorganic as to organic reactions. We must may take place. The adsorbed or captive molecule may be postulate a preliminary dissociation or association. On this bombarded effectively by a free molecule, in which case the basis the ordinary reactions in dilute aqueous solutions at outer end of the molecule is the reacting one and the catalytic once become a part of the general plan. We are dealing agent merely holds the victim in place until it receives the with activated molecules which have become activated by dissociation into electrically charged radicals, to which we I Presented as a part of the Intersectional Symposium on Catalysis at
T
a joint meeting of the New Haven, Connecticut Valley, Rhode Island, and Northeastern Sections of the American Chemical Society, Cambridge, Mass., January 12, 1924.
Rec. tuav. chim., [4]2, 249 (1921). 150, 1169, 1327, 1517, 1690; 151, 395, 473,1349 (1910); 153, 262,376, 522; 165, 383 (1911). 2
* Compt. rend.,
March, 1924
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
give the name of ions. I n organic chemistry we get activation and reaction as a result of the formation of radicals, using the word in its broadest sense to mean the products obtained when a regular bond is broken or a contravalence is opened. If these radicals are charged electrically, we call them ions just as in inorganic chemistry. It seems probable, however, that in many and perhaps in most cases the organic radicals are electrically neutral. A Consideration of the photochemical work of D. Berthelot and 1Gaudechon led, on the one hand, to the conclusion that
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the function of the solid catalyst is to bring about the formation of free radicals, the reaction probably not taking place in general with the captive molecule a t its outer end. On the other hand, a consideration of this same photochemical work has led to the possibility of an entirely new method of making organic compounds. The conclusion to be drawn from both sets of considerations is that the organic chemistry of the future will deal with the reactions of radicals instead of the reactions of molecules.
Color and Constitution’ I-Preliminary Paper. Effect of Isomerism on the Color of Certain Azo Dyes By M.L. Crossley and P.V. Resenvelt THECALCOCHEMICAL Co., BOUNDBROOK, N. J.
acids towards INCE 1868, when Graeber and Liebermann2 first by all the o-nitrobenzeneazo-P-naphtholsulfonic suggested a relationship between color and chemical red, the entire series being redder than the corresponding constitution, many theories have been advanced to benzeneazo-P-naphtholsulfonic acid series. o-Nitrobenzeneaccount for the p h e n ~ m e n o n . ~The available evidence, when azo-~-naphthol-6-sulfonic acid gives a very red-orange color, correlated, suggests that color is related to some intra- the corresponding 7-sulfonic isomer an orange color, the R molecular dynamic change associated with certain groups. salt product a scarlet, the G salt isomer a yellow-orange, and It is the purpose of this investigation to study the effect of the 3,6,S-trisulfonic acid product an orange color about isomerism on the color of certain azo dyes. This preliminary equivalent in hue to a blend of the colors produced by the paper deals only with the colors produced on wool by cer- corresponding R and G salt dyes. tain azo dyes made from benzenediazonium chloride and The corresponding m-nitrobenzeneazo-P-naphtholsulfonic substituted products by coupling with the salts of P-naph- acids give colors much yellower than the ortho products, tholsulfonic acids. The results of the absorption spectra and, in fact, much yellower than the colors of the benzeneazoP-naphtholsulfonic acid series. work will be reported a t some future time. This influence of the meta position is true for all the subRENZENEAZO-P-NAPHTHOLSULFONIC ACIDS stituents studied. The same relative differences in hue of The sodium salt of benzeneazo-~-naphthol-6-sulfonic acid, the members of the series are maintained. The R salt prodmade by coupling Schaeffer salt with diazobenzene chloride, uct gives the deepest and the G salt the lightest hue. dyes wool from an acid bath a red-orange color. The isoThe p-nitrobenzeneazo-P-naphtholsulfonic acid series is meric product having the sulfonic acid group in position 7 slightly redder than the corresponding o-nitro series, but the gives a much yellower color, and the corresponding isomer difference is not very marked. This close similarity between having the sulfonic acid group in position 8 gives the yellowest the colors produced by the ortho and para isomers is true color of the three. The introduction of a second sulfonic in all the cases studied. acid group in position 3 on the ring already containing one METHYLBENZEXEAZO-P-NAPHTHOLSULFOYIC ACIDS sulfonic acid group in position 6 shifts the color back towards red. R salt, the salt of 2-naphthol-3,6-disulfonic acid, The methyl group affects the color of the dyes of the coupled with diazobenzene chloride gives a color much redder benzeneazo-P-naphtholsulfonic acid series to a less extent than that of benzeneazo-~-naphthol-6-sulfonicacid. If than the nitro group, The influence of the position of the the two sulfonic acid groups are in positions 6 and 8, as in methyl group is consistent with the results obtained with the the case of G salt,, the salt of 2-naphthol-6,8-disulfonic acid, nitro group. Of the substituents studied the methyl group then tho resulting dye, benzeneazo-~-naphthol-6,S-disulfonicis exceptional in its influence on the reactivity of the diazo acid, gives a color which is the yellowest of the series, the group. o-Methyldiazobenzene chloride does not react with color being shifted in the yellow beyond that of the benzene- G salt and the salt of /3-naphthol-3,6,8-trisulfonic acid under azo-~-naphthol-6-sulfonic acid. This striking difference in the usual conditions of coupling. It reacts slowly with G the color produced by R and G salt dyes holds true for all salt a t temperatures above 25” C., with accompanying dethe products so far studied and runs parallel with the differ- composition of the diazo compound. The writers have not ence in the reactivity of the two isomers. yet succeeded in coupling the trisulfonic acid with any diazo The dye obtained by coupling ~-naphthol-3,6,8-trisulfoniccompound containing a methyl group in an ortho position acid with diazobenzene chloride gives a color about midway to the diazo group. The o-methylbenzeneazo-@-naphtholbetween the colors produced by the R and the G salt dyes. sulfonic acid series gives redder hues than the corresponding benzeneazo-P-naphtholsulfonic acid series. The dye from R NITROBENZENEAZO-P-NAPHTHOLSULFONIC ACIDS salt again gives the reddest hue of the series; that from the The introduction of a nitro group on the benzene ring in 2,7-sulfonic acid a yellower hue than that from the 2,6a n ortho position to the diazo group shifts the color produced sulfonic acid. The last two are red-orange and the former is 1 Presented before the Division of Dye Chemistry at the 64th Meeting a scarlet. The introduction of the methyl group in a of the American Chemical Society, Pittsburgh, Pa., September 4 t o 8, 1922. meta position to the diazo group shifts the color of the entire Revised manuscript received December 10, 1923. series towards yellow, but the change is not so pronounced, a Ber , 1, 106 (1868). as that caused by a nitro group. The methyl group in para 8 Watson, “Colour in Relation to Chemical Constitution,” 1918.
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