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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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position shifts the color of the entire series towards the red. tained from the unsubstituted sulfonic acid.6 The effect The para series is slightly redder than the corresponding of the sulfonic group in position 8 on position 1 is shown by ortho series. Both G salt and ~-naphthol-3,6,8-trisulfonic the marked difference in behavior of l-brom-2-naphthol-6acids couple with m- and p-methylbenzenediazochlorides. sulfonic acid and 1-brom-2-naphthol-8-sulfonicacid with diazo compounds.7 The bromine is readily replaced by the diazo CHLORAZO-P-NAPHTHOLSULFONIC ACIDS group in the former case and is not reacted on in the latter. The introduction of one chlorine atom on the benzene ring Similarly, Witt* showed that ~-naphthylamine-8-sulfonicacid in benzeneazo-P-naphtholsulfonicacids has very little effect on the color produced by the dyes. The entire series is reacts with diazotized sulfanilic acid to give the correspondslightly yellower than the corresponding benzeneazo-P- ing diazoamido compound and not the amidoazo product. This evidence suggests that a peculiar relationship between naphtholsulfonic acid series. The m-chlorazobenzene-Pthe hydrogen adjacent to the hydroxyl group and the rest naphtholsulfonic acid dyes are slightly yellower than the of the molecule is in some way induced by the hydroxyl corresponding ortho and para series. I n addition to causing group. The reactivity of the molecule is dependent upon a slight change in hue, chlorine enhances the brilliancy of all the colors, and appears to increase the affinity of the dyes for this relationship. The degree of this activity is also dependent upon the influence of other substituents and upon wool, since their aqueous solutions exhaust in the dye bath the position which they occupy with respect to the hydroxyl more readily and more completely than the solutions of group. The influence of hydroxyl on the reactivity of the corresponding benzeneazo-P-naphtholsulfonic acids. certain groups adjacent to it in the benzene series has been SULFOBENZENEAZO-P-NAPHTHOLSULFOXIC ACIDS pointed out by Gibbs and PrattSg R salt reacts with diazo-m-4-xylene chloride, but G salt The sulfonic group on the benzene ring in sulfobenzeneazo8-naphtholsulfonic acids shifts the color towards yellow in all does not. When a mixture of R and G salts is used to couple cases, having the greatest effect in the meta position. Ben- with a diazo compound that will react with both R and G zeneazo-p-naphthol is insoluble. m-Sulfobenzeneazo-P-naph- salts, the R salt couples first and apparently no G salt retho1 is quite soluble and gives an orange color in hue slightly acts with the diazo compound, a t least not so as to give a yellower than that produced by the p-sulfo compound. permanent stable dye molecule, until all the R salt has been The corresponding product from ~-naphthol-7-sulfonicacid removed by coupling from the solution. If there is only a gives aTmuchyellower color. The R salt dye produces an sufficient amount of diazo compound to couple with the R orange color while the corresponding G salt dye gives a yellow salt present, then no G salt couples, and it can be recovered color. All the p-sulfobenzeneazo products are redder than quantitatively. When all the R salt has been coupled out of the mixture, the remaining G salt will couple with the the corresponding meta products. same diazo compound, but a t a much slower rate than the R CHEMICAL CONSTITUTION AND REACTIVITY OF P-NAPHTHOLsalt coupled. That addition is the initial step in all chemical SULFONIC ACIDS reactions is shared in common b y many of the modern The marked difference in the reactivity of the two isomeric theories of chemical reactivity. The “force field” theory of P-naphtholdisulfonic acids, R, 2-3-6, and G, 2-6-8, has been Baly’o is particularly important, in view of increasing eviobserved by several investigators. The 2-3-6 isomer re- dence in its favor. The reaction between diazo compounds acts with nitrous acid to give l-nitroso-2-naphthol-3,6- and naphthols has been assumed to take place by direct disulfonic acid, while the 2-6-8 isomer does not react with addition of the diazo to carbon through the medium of connitrous acid, The former isomer reacts readily with diazo jugated double bonds,ll the reaction capacity of which is compounds, giving the corresponding dyes, while the latter intensified by the hydroxyl group and also through the pridoes not react under the usual conditions of coupling with mary formation of unstable oxonium compounds.12 Much certain diazo compounds-e. g., o-methyldiazobenzene chlo- evidence has been secured in support of the part the hydroxyl ride and diazotized m-Pxylene chloride in which one methyl group plays in such reactions.l8 group is ortho to the diazo group. Certain diazo compounds When R salt reacts with a diazo compound, the diazo react with both the R and G isomers, but at widely different compound adds to the naphtholsulfonic acid molecule through rates. Smith4 measured the comparative rates of reaction the weak position in the neighborhood of the hydrogen atom of R and G salts with p-diazotoluenechloride and found as soon as interlacing of the respective molecules takes place. that under the same conditions over 85 per cent of the G The resulting molecule then undergoes cleavage into the more remained unchanged when all the R had combined. stable molecular systems-the salt of benzeneazo-p-naphThe monosulfonic acids, Schaeffer (2-naphthol-6-sulfonic tholsulfonic acid and sodium chloride. R salt may then be acid) and crocein (2-naphthol-8-sulfonic acid), show similar said to have an “open reactive field.” I n the case of G salt differences in chemical reactivity. The influence of the the hydrogen atom adjacent to the hydroxyl group is stabilsulfonic group in position 8 on the reactivity is also shown ized by the sulfonic acid group in position 8 and the molecuby the 2-naphthol-3,6,8-trisulfonicacid, which behaves lar system is not so readily penetrated by the diazo molelike the 2-6-8 isomer, The influence of the sulfonic group cule. The G salt may then be said to represent a “closed in the peri, or 8, position on the reactivity of the hydrogen reactive field.” in position 1 has been ascribed to “steric hindrance,”6 but If the diazo group is also stabilized or its reactivity neuthis hypothesis does not satisfactorily explain the facts. tralized by its interrelation with an adjacent group, no addiOf the several hydrogen atoms in the P-naphtholsulfonic tion is possible between it and B molecule having a closed acid molecule, only that adjacent to the hydroxy group is field of reactivity until the field of reactivity is opened in one usually replaced by the diazo group with its attached radical or the other of the two molecules. If the diazo group is and also by the nitroso group. It is also the first to be re8 J . Chem. Soc. (London), 89, 1167 (1906). placed by other substituents, such as nitrous oxide, chlorine, 7 I b i d . , 89. 1505, 1167 (1906). bromine, and iodine. It has been shown that when the 8 Be?., 21, 3483 (1888). g Phihggine J . Sci., 8, 33 (1913). peri position is unoccupied by a sulfonic group, the sub10 J . A m . Chem. Soc., 37, 979 (1915). stituent in position 1 is replaced by a diazo group and the 11 A n n . , 398, 66 (1913); J. Chem. SOC.(London), 109, 1031 (1916); resulting compound has the same constitution as that ob- i i i , 958 (1917);i a i , 427 (1922). 4
J . Chem. Soc. (London), 89, 1505 (1906).’ 89, 1505 (1906).
6 Ibid.,
11 18
Ber., 47, 1286 (1914). I b i d . , 40, 2, 4, 40, 404,460 (1907);41, 4012 (1908); 60, 1534 (1917).
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free to add to the G salt molecule, a reaction will take place, but the reaction will be slower than the corresponding one with R salt. There are then three cases: 1-That of an open reactive field in both the diazo- and the naphtholsulfonic acid molecules-for example, diazobenzene chloride and R salt. 2-An open reactive field in but one-for example, (a) diazo-m4-xylene chloride and R salt, and ( b ) diazobenzene chloride and G salt. 3-A closed reactive field in both-for example, diazo-m-4xylene chloride and G salt.
I n the selective coupling of R salt out of a mixture of R and G t d t by diazobenzene chloride, the diazo compound itself, having an open reactive field, reacts preferentially with the naphtholsulfonic acid having an open reactive field-that is, the R salt. The G salt, having a closed reactive field, cannot form an addition product with the diazo compound until the R salt, which has an open reactive
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field, is wholly converted into dye through the formation of a preliminary addition product. The sulfonic group in the P-naphtholsulfonic acid molecule appears to affect the energy refationship of the OH group and the adjacent hydrogen atom with respect to the rest of the molecule, and this is manifested in both the reactivity of the sulfonic acid and the color of the dye it produces. The maximum bathychromic effect is manifested by a sulfonic group in position 3, adjacent to the hydroxyl group. The hue lightens with the shifting of the sulfonic to position 6 . The maximum hypsochromic effect is manifested by the sulfonic group in position 8, where it also has the maximum stabilizing effect on the diazo group in position 1, and where it has less stability than in the other positions on the ring, with the exception of position 1. These seem to be significant, and relate facts which, when supported by additional evidence, should lead to a better understanding of the mechanism of such reactions and their relation to color.
Naphthalenesulfonic Acids',' V-The
Quantitative Estimation of 8,6- and 2,7-Kaphthalenedisulfonic Acids By Herbert L. Haller and D. F. J. Lynch BURFAUOF CHEMISTRY, WASHINGTON, D. C .
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for estimating qualltitadisrzlfonates. tively the monosulfonic acids,3 and so far as can be ascertained no method has been suggested for determining quantit:ttively the disulfonic acids.4 It is well known that when naphthalene is sulfonated isomers are always produced. For example, when naphthalene is disulfonated a t 160" C., the 2,7-naphthalenedisulfonic acid that is first formed, under the influence of heat and excess acid, is slowly converted into the isomeric 2,6-disulfonic acid. Thus it will be seen that any method proposed for estimating quantitatively naphthalenesulfonic acids, in order to be serviceable, should determine not only the total sulfonic acids, but also the proportion in which the isomers are present. The usual method5 of isolating the sulfonic acids of naphthalene is to boil an aqueous solution of the sulfonation product with calcium carbonate and filter off the precipitated calcium sulfate. The filtrate, which contains the calcium salts of the sulfonic acids with some calcium sulfate, since tkie calcium salts of naphthalenesulfonic acids are excellent tolvents for calcium sulfate, is treated with sulfuric acid drop by drop as long as a precipitate is produced. The precipitate is filtered off and the aqueous solution of the sulfonic acid is evaporated to dryness. The dissolved calcium 1 Presented before the Division of Dye Chemistry a t the 65th Meeting of the American Chemica! Society, New Haven, Conn., April 2 t o 7, 1923. Received October 1, 1923. a Contribution No. 84 from the Color Laboratory, Bureau of Chemistry, Washington. D. C. 3 Eww, Rec. trav. chim., 28, 298 (1909). 4 Only those sulfonic acids t h a t are produced by direct sulfonation are here considered. 6 Ebert and Merz, Ber.. 9, 592 (1876).
tween isomers. I n an exhaustive study 011 the formation of the naphthalene-monosulfonic acid, Ewes3 devised a rather ingenious method for the determination of qand p-monosulfonic acids in the presence of one another. He prepared the lead salts of both acids and then determined the mutual influence of these salts on their solubility in water a t 25" C. An excess of the lead beta salt was always added to 100 cc. of water and to this definite weighed quantities of the alpha salt were added. The total solubility of the mixture was then determined. From the data obtained a curve was plotted, from which, after determining the solubility of a weighed quantity of an unknown mixture of lead salts of aand P-naphthalenesulfonic acids, the composition of the mixture could be ascertained. The method proposed in this paper is similar to the one mentioned above. Lead salts of 2,7-naphthalenedisulfonic acid and 2,6-naphthalenedisulfonic acid were prepared and the solubility of known mixtures of the two salts was determined. Since the two isomers contain different amounts of water of hydration, all calculations were made on the basis of the anhydrous salts. PREPARATION O F THE LEADS.4LTS O F THE TWO ACIDS Since the two lead salts accompany one another in the ordinary method of preparation, and since it is very difficult to separate them by the usual methods of crystallization, they were prepared through the sulfonic chlorides. These can be easily separated and prepared pure. Pfter purification they were converted into the free acid and these in turn converted into the lead salts.
