Dyestuffs as Field for Academic Research R. E. ROSE,E. I. du Pont de Nemours & Company, Wilmington, Del.
T
HE dyestuffs industry arose from work done by aca-
demic investigators, and for a long time the relation between the university laboratory and the industry was fundamental to the progress of the latter. But, as the industry grew, it came to rely more and more upon its own research workers, and also its problems became to a larger extent unsuited for treatment as academic research until the two drew almost completely apart. I n this country there was no dyestuffs industry until of late, so that a t no time was work on dyestuffs a subject, chosen for investigation by academic workers. Even in the reports of work done abroad, one rarely finds research based on the characteristics of dyestuffs. At most it is a case of determining the constitution of a natural color. Of commercial dyes one finds no word. This is unfortunate. If the academic chemist would only realize that dyes represent a magnificent collection of organic materials, a collection which is readily available for his use, and that among them he would find substances differing widely, he would realize that he is missing an excellent chance when he leaves them or, perhaps it would be more truthful to say, never reaches them. The reason for this condition is not far to seek. The chemistry of dyestuffs lies beyond the region of the ordinary and advanced courses in organic chemistry. These do not contain much more than a reference to the triphenylmethane colors, perhaps going so far in the advanced course as to discuss the constitutional formula of rosaniline, p-rosaniline, and the basic violets. There will be some description of the diazo reaction and of its use in making a dye, the example chosen being usually methyl orange. Add to this a full discussion of r o n Baeyer’s work on the constitution and the synthesis of indigo and you have most of the material furnished in the organic courses available with one exception-the work on the determination of the constitution of Turkey red. I am afraid both instructor and student believe that this is one of the most important of dyes. Formerly it was, but now real Turkey red would be hard to find in any store. This is not said in any spirit of criticism. After all, the whole field is much too broad to be covered in detail and there are many more adaptable chapters than those describing dyestuffs. Dyes merely as examples to illustrate monoazo, diqazo, and trisazo couplings are not very interesting. Indeed, there is no group less interesting if viewed merely superficially. I can remember my own consternation when I was forced to meet the dificulty of giving a course on dyes to an advanced class, The triphenylmethane group was not so bad; I could go ox-er the logic used by the organic chemists who determined the real constitution of these bodies. But the azo group was hopeless because it was merely a case of describing variants on a single reaction and stating that the product obtained was yellow, red, orange, or blue, as the case might be. The real subtlety of these materials escaped me entirely because I was not familiar with the dyer’s art and I could not see how every molecule that I described was actually an admirable material to meet the special needs of the user. Hedged around by the limit of commercial availability, the dye chemist had built marvelous molecules, each subtly different from the other, but I did not see clearly enough to read the meaning of those delicate variations in the choice of intermediates for special results. In fact I had a feeling that
dyes, being such practical materials, were a little beneath the mental ability of the synthetic organic chemist. I suffered from the delusion that a product synthesized in a chemical factory was in some way contaminated by the atmosphere of useful research instead of being born of pure academic genius. And the dyes themselves are another deterrent. They are not available on the shelves of the supply houses except for some few ordinary indicators and stains. They are not available as beautiful, chemically pure, crystalline substances. After all, what is there to make a student or his professor think of using a direct black azo dye for determining the effect of electrolyte concentration on the rate of diffusion of a colloidal organic substance? Again, dyes, are known by cryptic trade names. These alone are sufficient facts to deter the academic worker. CHEhlICALLY PURE DYES But these difficulties may be surmounted in order to reach the abundant treasure that is actually available. While i t is true that the chemical identity of dyes is not disclosed on the label nor is it found in the ordinary textbook, the identity can be established easily by taking a little trouble. The laboratories of the dyestuffs manufacturers and the pages of the Colour Index published by the Society of Dyers and Colourists are available for consultation. The dyestuffs manufacturers are willing to answer honest inquiries. They are glad to stimulate research in their field. Of course one cannot expect them to be willing to disclose the constituents of some specialty of theirs. I n most cases they will even go so far as to assist the academic worker by supplying him with generous samples of their products, provided this is not merely to furnish sample cases. Therefore, every commercially available dye is essentially on the stock room shelf of the academic worker and all but those whose constitution is either unknown or a subject of secrecy are just as well described as any other organic substance. There is no source of chemically pure dyes. Some of the basic colors are nearly chemically pure, provided the highly concentrated brands are used. I n the course of manufacture the azo colors all become mixed with salt, and in standardizing to a commercial strength more salt or Glauber’s salt is added. I n addition, if azo colors of considerable complication are examined, it will be found that they have a certain quantity of material other than the chief component, simply because it ic not possible to carry out a coupling quantitatively on a manufacturing scale. The purification of dyes is not particularly difficult in comparison with other complex organic substances. The literature contains descriptions of the best methods for purifying such dyes as Congo red. I can recommend a method which I have worked out. This is to precipitate the dye as an organic salt. The best base for this purpose I have found to be one of those aryl guanidines which are used as vulcanization accelerators. These are available a t a low cost and in a condition of great purity. I have found the most serviceable to be diphenyl- and di-otolylguanidine. Once in a while triphenylguanidine may come in handy because its salts are much less soluble. If a solution of the hydrochloride of such a base is mixed with the hot solution of the dye, a tarry precipitate is formed a t once. This can usually be collected on a glass rod, solidified on cooling, and, after cooling, be broken up, washed with water con-
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September, 1933
INDUSTRIAL AND ENGINEERISG CHEMISTRY
taining a little more of the hydrochloride, and finally dissolved in methanol. It can then be filtered and the alcohol evaporated off, or, in some cases, sodium methylate may be added in sufficient quantity to precipitate the sodium salt from the alcoholic solution. I n general I have found it better to evaporate the alcohol completely and add the theoretical quantity of sodium or potassium hydroxide. Alcohol can then be added until the sodium salt separates out. It is filtered off and extracted with alcohol until the liquor is colorless if the dye is really insoluble in alcohol or until the extraction has reached the stage represented by the maximum solubility of the sodium salt in alcohol. Going through this process once gives one a n extremely pure dyestuff but, if necessary, it can be repeated. The process eliminates the more soluble organic impurities that were formed as by-products in the process of manufacture, if it is carried out in such a way that the original dye is not completely precipitated by the guanidine salt. Some of these guanidine salts can be recrystallized from organic solvents, usurtlly alcohol, or alcohol and water. Assuming that we have purified our dyestuffs, what can we d o with them? What sort of problems are available?
PHYSICAL PROBLEMS 1. The physical properties of dyes have not been settled by any means. I should like to see the solubility of pure dyes, a t temperatures up to those employed in dyeing, determined quantitatively. This should include solutions containing the usual dyeing assistants-sodium chloride and sodium sulfate. 2. Practically nothing is known about the true solubilities of the calcium, magnesium, iron, and aluminum salts of dyes. 3. When dyeings of vat colors and azo colors are soaped, the hue is changed, and the fastness to light is distinctly improved, presumably because of a change in particle size. The actual mechanism of this process would furnish an excellent subject for research, even though a great deal has already been done, especially in connection with the azo colors. 4. The dyeing of acetate rayon is stated to be a case of solid solution. Something should be known of the real solubility of acetate rayon dyes in cellulose acetate, and whether they migrate in the fiber. 5 . It would be extremely interesting to dye a whole series of colors on the same material in equimolecular percentages. I n doing this care would have to be taken to consider the dyestuff left in the dye bath; for this reason very low concentrations should be used a t first. 6. The quantitative measurement of the equilibrium relation between the dye on the fiber and in the bath throughout the dyeing process in the case of rayon and cotton a t high and at lower temperatures needs investigation. 7 . It would be interesting to determine the properties of dyestuffs as applied to cotton, ~vool,and silk in other than aqueous solution-in liquid ammonia, sulfur dioxide, and organic solvents. For the latter the salts of organic bases can be used. 8. The diffusion rates of dyes under dyeing conditions and the use of the results to calculate the particle size of these substances has been investigated to some extent but there is a great deal still to be done. 9. The change in the equilibrium point between the dye in the dye bath and on the fiber which is produced by the addition of dispersing agents, such as glue, is of material interest to the dyer and has never been determined accurately. 10. The rate at which the final equilibrium between the
1029
dye in solution and on the fiber is reached is a characteristic of the dye which determines how it will behave in continuous dyeing, particularly when used in combination with other dyes. The dyer’s method of determining the rate of exhaust is practical. We should have a quantitative method which would describe the rate a t which the dye which goes on to the fiber is adsorbed and the total percentage of the available dye which is adsorbed. These two characteristics are quite independent. 11. I n the case of lake colors which are used in printing inks, one of the important characteristics is oil absorption. The underlying causes of the differences are practically unknown and yet one lake will make so stiff a n ink that it will be useless while another will be quite fluid. Presumably this is a matter of particle size, but it goes back to the Characteristics of the dye used in making the lake.
CHEMICAL PROBLEMS 1. The nature of the reaction by which “indigosols” undergo oxidation should be investigated. The “indigosols” are esters of reduced vat colors. They oxidize readily when treated with such substances as ferric salts or nitrous acid. The reaction then is a saponification and oxidation or the two steps in the reverse order. 2. During the printing of vat colors the pastes give off gaseous substances which are important in their effect on the development of the prints of certain colors. Yery little is known about these products. 3. Colors that are quite fast to light on paper or as paper dippings are sometimes extremely fugitive in nitrocellulose lacquers. This is particularly true of azo colors. Presumably the nitrocellulose acts as an oxidizing agent. The nature of the reaction is unknown. 4. A method for removing the sulfonic acid groups from the azo colori without destroying the dyestuff would be useful. If anyone is looking for something desperately difficult, here is the problem. 5. An interesting subject for research would be that of comparing the effects produced by a change in the position of one substituent a t a time on the finer physical characteristics of the dyestuff molecule. For example, in the case of benzidine coupled with two molecules of H acid, we are dealing with a direct blue which is distinctly colloidal in its characteristics. Sow, if we leave the H acid on one side but substitute Chicago acid on the other, we have done nothing but shift the position of two sulfonic acid groups. What differences will this cause in the behavior of the colloidal particle? Perhaps none, but so far as the writer knows, except for the variation produced in the hue of the dye, the differences have never been investigated. We have any number of colloidal substances but few of them allow of such delicate variations being played upon their chemical constitution. I n the case being used as a n illustration, we could next substitute one molecule of K acid in u-hich the two sulfonic acid groups are altered in their relative position, one occupying the same position as in the original H acid. N7e could go farther and choose compounds in which the position of the amino and hydroxyl groups differed. The variations are practically limitless and each change in constitution could be followed exactly. Again it would be just as easy to modify the benzidine by substituting tolidine or dianisidine while leaving the sulfonic acid groups in the H acid unaltered. There is a wonderful field for the physical chemist in such treatment of the constitutional variations which are possible in those colloids which are dyes. I n closing, I wish to advise the academic worker never to undertake research on any phase of dyestuff chemistry without consulting a competent dyestuff chemist. The pitfall.
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are so numerous that he is almost certain to overlook some one of them. He is apt to think, for instance, if he is unfamiliar with the field, that, if he gives the name of the dye, he has described it sufficiently minutely. As a matter of fact, this is not so, because dyes are not found in commerce as chemically pure substances. Also, while I am a great believer in the value of academic research and of its being untrammeled by any effort to make it practical, yet it seems foolish not to make academic work fit into the practical use of products if we can do so without causing the academic work t o suffer. For in-
Vol. 25, No. 9
CHEMISTRY
stance, I do not see any advantage in a study of lake formation using dyestuffs that are not sufficiently adapted to the production of commercial lakes to rank as lake colors. The idea of synthesizing valuable dyestuffs in the course of anything but long continued and specialized work in the field is bound to be disappointing. Synthetic work having for its object the production of useful dyes I would regard as the least promising of all fields for the academic worker. RECEIVED April 15, 1933.
Preparation of 1,2- and 2,3Diaminoanthraquinones P. H. GROGGINSAND H. P. NEWTOK,Bureau of Chemistry and Soils, Washington, D. C . I n the preparation of 3’,4’-dichloro-2-benzoylbenzoic acid, a study of the eflect of time, temperature, solvent ratio, and agitation on yield and purity of the product is reported. The m a x i m u m yield is 80 per cent. Cyclization of the keto acid by means of concentrated sulfuric acid gires in all instances a mixture of the isomeric dichloroanfhraquinones. Differ-
T
HIS report deals n i t h the utilization of 1,2-dichlorobenzene as a raw material for the preparation of 1,2and 2,3-diaminoanthraquinones. These isomeric conipounds have been previously prepared by more complex methods. Briefly, the procedure employed in this case was the condensation of phthalic anhydride with 1,2-dichlorobenzene, in the presence of anhydrous aluminum chloride, to yield 3’,4’-dichloro-2-benzoylbenzoicacid, which was cyclized to a mixture of the isomeric 1,2- and 2,3-dichloroanthraquinones. Conditions were found under which the separated isomers were aminated to the corresponding diaminoanthraquinones. A critical examination of the available technical 1,2-dichlorobenzene indicated the presence in practically all cases of varying quantities of 1,4dichlorobenzene, chlorobenzene, and traces of polychlorinated benzenes. By means of refrigeration and distillation, a relatively pure 1,2-dichlorobenzene was obtained, which contained as the only impurity a trace of 1,4dichlorobenzene. Carswell (3) reports the boiling point of pure 1,2-dichlorobenzene to be 180.3’ C. It was possible to secure for this work a special product which gave a distillation range of 179.5’ to 180.5’ C. PREPARATION
O F 3’,4’-DICHLORO-2-BENZOYLBENZOICACID
Senn (8), Phillips ( B ) , and later M. and N. Tanaka (9) reported the preparation of 3’,4’-dichloro-2-benzoylbenzoic acid by the condensation of phthalic anhydride with 1,2dichlorobenzene in the presence of anhydrous aluminum chloride. I n the present investigation a study was made of the effect of time, temperature, solvent ratio, and agitation, in an attempt to improve the purity and yield of the keto acid. The equipment employed is shown in Figure 1. Tables 1-111 illustrate the effect of the variables listed. The phthalic anhydride, anhydrous aluminum chloride, and 1,Zdichlorobenzene were mixed together and treated under the conditions
ence i n solubility of each isomer in sulfuric acid and also in ethanol indicates the quantitative relationship of 13 per cent 1,2-dichloroanthraquinoneto 87 per cent 2,3-dichloroanthraquinone. Ammonolysis of the corresponding dihalogenoanthraquinones, in the presence of copper, a n oxidant, and ammonium nitrate, results in the complete removal of chlorine. indicated in the tables. After the reaction was completed, the mass was hydrolyzed with cold dilute mineral acid, the excess of l,>dichlorobenzene was removed by steam distillation, and the aluminum was removed as a salt in solution. The soluble ammonium salt of the keto acid was obtained by treating the residue n i t h aqueous ammonia. This was passed through a filter to remove insoluble impurities, and the keto acid was reprecipitated by the addition of mineral acid. The 3’,4’-dichloro->benzoylbenzoic acid was then collected on a filter, washed, dried, and weighed. TABLEI. EFFECTOF SOLVEKT RATIOON PREPARATION OF 3‘,4’-DICHLORO-2-BENZOYLBEh’ZOICACID Phthalic anhydride 0.5 mole = 74.0 grams Anhydrous AlClr, {mole 10% = 147.8 grams l,2-Dichlorobenzene = 0.5 mole X ratio Solvent = excess 1,2-dichlorobenzene Theoretical yield = 147.5 grams Reaction time = 8 hours Reaction temp. 90’ C. M. p. of pure keto acid = 192.5’ C. M.p. of crude keto acid, all runs 190-191’ C.
+
-
-
SOLVENT TYPEOF EXPT. PHTHALIC ANHYDRIDE AQITATION Moles None 1 None 2 None 3 None 4 None 5 Continuous 1-A Continuous 2-A Continuous 3-.1 Continuous 4-A Continuous 5-.1
YIELD yo of theory 24.0 35.4 64.4 95.0 65.4 96.5 66.4 98.0 67.1 99.0 62.6 92.3 65.2 96.2 68.6 101.2 70.5 104.0 71.8 106.0
Grams
PREPARATION AKD SEPARATIOK OF ISOMERIC DICHLOROAKTHRAQUINONES
Penn (8) reported 87 per cent of 2,3-dichloroanthraquinone and 13 per cent of 1,2-dichloroanthraquinonefrom the cyclization of 3’,4’-dichloro-2-benzoylbenzoicacid. He made the cyclization with concentrated sulfuric acid and effected a separation of the isomers by the difference in their solubility
