T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
456
sulfonating carvacrol and oxidizing t h e sulfonic acid by means of potassium bichromate. The quinone thus produced was reduced by means of sulfur dioxide. The yields were very poor and since this compound, from preliminary determination, shows no advantage over ordinary quinol, work along this line was not further prosecuted. p-Aminothymol was also prepared, but this base did not seem t o be so satisfactory a developer as t h e corresponding carvacrol derivative. One disadvantage is the relatively low solubility of the free base in ,water. SUMMARY
p-Aminocarvacrol is a very satisfactori photographic developer, and its preparation and use for such a purpose would furnish a means of using a portion of the large amount of p-cymene which is not being utilized a t present. COLORLABORATORY BUREAUOF CHEMISTRY WASHINGTON,
D.c.
A METHOD FOR THE PURlFICATION OF CERTAIN AZO DYES B y HERBERT A . LUES Received February 24, 1919
.
I n the preparation of t h e direct cotton dyes of t h e benzidine group, the dye is usually precipitated from the solution by means of sodium chloride. The method is also used in the case of certain acid wool dyes. As a result of this procedure, commercial specimens of such dyes contain varying amounts of inert inorganic material. For certain pharmacological investigations it was desired t o obtain a dye of this sort as free from salt as possible. The method was originally developed for the purification of brilliant Congo R. I n order t o test the general applicability of the method, Congo red, brilliant orange R, cotton dyes, and azorubin, an acid wool color, were investigated. Because of the simplicity of the method as developed and its possible use t o those who wish to prepare dyes of this type free from inorganic and certain organic impurities, a brief description of t h e procedure used is given. PURIFICATION OF D Y E S
Fifty grams of crude brilliant Congo R , No. 370,’ are dissolved in I O O cc. of distilled water and filtered. The solution is heated to boiling and solid sodium acetate added until t h e dye is practically completely precipitated. This requires about 350 g. of the solid sodium acetate. The precipitate is sucked as dry as possible on a Buchner funnel, and then boiled with 250 cc. of g j per cent alcohol. The suspended dye is then removed from the alcohol by filtration. The digestion with alcohol is repeated several times. A comparatively small amount of dye is dissolved by t h e alcohol. One gram of crude dried material gave 02 7 per cent sulfated ash One gram of purified dried material gave 25 9 per cent sulfated ash Calculated as sodium, this corresponds t o 8.4 per cent. Theory for sodium is 8.4 per cent
11,
No. 5
Azorubin and Congo red were also purified by this method, and the following figures are given t o indicate the extent t o which the impurities are removed. AZORUBINNo. 163 One gram of crude dried dye gave 48.3 per cent sulfated ash One gram of purified dried dye gave 26.8 per cent sodium sulfate Sodium found, 8.8 per cent. Theory for sodium is 9.2 per cent CONGORED No. 307 One gram OE crude dried material gave 50.6 per cent sulfated ash One gram purified dried material gave 21.4 per cenz sodium sulfate Calculated as sodium, this corresponds to 6.9 per cent. Theory for sodium is 6.6 per cent
Besides removing inorganic impurities, t h e procedure described also removes certain organic impurities usually present in commercial dyes of this type. This fact is of special importance when t h e compound is t o be used for pharmacological purposes. For those dyes which cannot be purified b y other simpler procedures, this method is of general application if t h e sodium salts can be precipitated from aqueous solution by sodium acetate and if they are relatively insoluble in hot 9 j per cent alcohol. The amounts of sodium acetate and of alcohol to be used naturally vary with each dye. I n the case of those dyes which cannot be satisfactorily separated from the solution by filtration, centrifugalization should be of great assistance in securing a pure product. COLORLABORATORY BUREAUO F CHEMISTRY WASHINGTON. D. C.
INTERMEDIATES USED IN THE PREPARATION OF PHOTOSENSITIZING DYES. I-QUINOLINE BASES By
L. A.
J. K. STEWART AND Lours E. WISE Received February 24, 1919
MIKESKA,
A recent article’ from this laboratory outlined briefly t h e methods of preparation of a number of photosensitizing dyes and dye intermediates. Since then we have made a thorough study of t h e best conditions for t h e synthesis of intermediates required in t h e preparation of pinaverdol, pinacyanol and dicyanin, t h e three most important photosensitizing dyes. The methods of preparation are described in this and in the following paper. The four bases required in the preparation of these dyes are quinoline, quinaldine, p-toluquinaldine, and 2,4-dimethylquinoline. All of these are well-known organic compounds, whose syntheses are recorded in the patent and chemical literature. The most important of these may be briefly reviewed. T h e Skraup synthesis of quinoline is so well known t h a t i t requires no further description. Hitherto the most satisfactory synthesis of quinaldine (or toluquinaldine) has been t h a t of Dobner and Miller,2 which depends upon t h e condensation of paraldehyde with aniline (or toluidine) hydrochloride, and which is quite similar t o the process described in D. R. P. 24317 (1882). 2,4-Dimethylquinaldine is usually prepared by Beyers’8 method, in which ethylidene acetone (prepared from acetone, paraldehyde, and hydrogen 1
The number refers to Schultz, “Parbstofftabellen,” Weidmannsche Buchhandlung, 1914. 1
Vol.
2
3
Wise and Adams, THISJOURNAL, 10 (1918). 801. Ber., 16 (1883), 2465. J . p r a k t . Chem , [2] 33 (1886), 401.
May, 1910
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
chloride) interacts with aniline hydrochloride. Unfortunately all of the preceding methods are cumbersome and time-consuming, and in certain cases the purification of t h e bases is difficult and the yields are disappointing. Since our problem involved the production of the pure bases on a fairly large laboratory scale, the above methods were carefully studied and gradually simplified. After performing a large number of orientating experiments, we succeeded in modifying each method in t u r n so t h a t the products could be obtained far more expeditiously t h a n b y the older methods without materially decreasing their yield. I n all cases the tedious steam distillations, which made the older methods so burdensome, have been dispensed with. I n many cases extraction has been resorted t o in place of distillation. I n the purification of toluquinaldine and quinaldine certain precautions have been adopted which appear t o materially improve the quality of the product. The procedures which up t o the present have proved most satisfactory in our hands are given in detail in the following experimental part:
QUINALDINE,
03
-CHS-TWO
Sodium nitrite is then added t o the solution until this reagent is present in decided excess, whereupon an oil separates. (It is quite possible t h a t this is nitrosotetrahydroquinaldine, which would be formed a t this point if tetrahydroquinaldine were present in the crude oil.) The oil is removed by extraction with ether, precautions being takelz t o maintain a temperature of about o o C., so as t o prevent decomposition of the oil. The residual acid solution is then heated t o decompose the diazonium salts, cooled, and rendered strongly alkaline with aqueous sodium hydroxide. The quinaldine which separates in the form of an oil is removed by extraction with ether. The ethereal solution is dried with sodium sulfate, the ether removed, and the residual oil fractionally distilled under ordinary pressure. The greater portion boils a t ~ 4 3 - 2 4 4 ~(uncorrected) and is pure quinaldine. Calculated for CioHeN: N = 9 79 per cent, 9.64 per cent.
per
cent.
Found: N = 9.60
The yield is about 2 j per cent, calculated on t h e basis of the aniline used. Fairly large quantities of quinaldine can thus be prepared in two days. HsC--/\/\
p-TOLUQUINALDINE,
EXPERIMENTAL
457
-The
prep-
N
hundred
grams
N
of aniline are added gradually t o 400 g. concentrated hydrochloric acid, and the solution cooled. A mixture of 1 2 0 g. nitrobenzene and 300 g. paraldehyde is then slowly poured into the acid solution, which is constantly agitated during the addition. The reaction is exothermic, and the temperature must be controlled. so as not t o rise above 60' C. If this precaution is neglected, resinification may occur and the subsequent yield may be decreased. After the mixture has been well shaken, i t is heated for I hr. in a water bath. Further heating causes excessive t a r formation. The excess of nitrobenzene and certain other impurities should be immediately removed by extracting the heavy acid solution with ether (or other suitable immiscible solvents). The aqueous solution is then rendered alkaline, using a concentrated solution of crude sodium hydroxide, and controlling the temperature of the neutralization, whereupon a black oil, consisting of a mixture of quinaldine, aniline and tar, separates. (It is also probable t h a t this oil contains some tetrahydroquinaldine which has been formed during t h e course of the reaction.) The oil is extracted with ether, and the ethereal solution dried with sodium sulfate. The ether is then removed (and recovered) and the residue distilled a t about 2 0 0 mm. pressure. A distillate boiling a t 150-220° is thus obtained. The amount of crude oil obtained approximately equals the weight of aniline! taken. Since repeated fractional distillations of this oil invariably lead t o impure quinaldine, the following chemical procedure is adopted: The crude oil is dissolved in a n equal weight of concentrated hydrochloric acid, and the solution cooled t o o o C.
aration of p-toluquinaldine ' is essentially similar t o t h a t of quinaldine, with the exception t h a t the oxidizing agent is omitted from the initial mixture and t h a t p-toluidine is used in place of aniline. It is convenient t o use 190 g. of p-toluidine, 300 g. of concentrated hydrochloric acid, and 2 2 5 g. of paraldehyde. I n this case the paraldehyde may be added slowly t o the hot acid solution of p-toluidine hydrochloride. The methods employed for the removal of paraldehyde, separation and diazotization of the crude oil, and the purification of p-toluquinaldine are identical with those described under quinaldine. p-Toluquinaldine is obtained in the form of large, colorless crystals melting a t 55 O ; boiling a t 2 6 6 2 7 0 ~ ; rapidly turning brown on exposure to air or light. Calculated for CuHuN. N = 8.92 per cent, 8 83 per cent.
per
cent. Found: N = 8.87
The yield varies from 40 t o 4 5 per cent, calculated on the basis of the p-toluidine taken. QUINOLINE)
zc
-To
72
g. of nitrobenzene,
hvigorously boiling under a reflux condenser, is slowly added a mixture of 114 g. of aniline, 360 g. of glycerol, and 300 g. of concentrated sulfuric acid. The reaction carried out by this method' is much less violent than in the case of the Skraup 'synthesis. After the last portions have been added the heating is continued for 2 hrs. longer. The syrupy solution is then diluted with water, the excess of nitrobenzene removed by extraction with ether, and the aqueous mother liquor rendered alkaline. The crude oil which separates is extracted with ether, the ethereal solution dried with sodium sulfate, the ether removed, and 1
Walter, J pvakt Chem.. [ 2 ] 33 (1894), 549
4.58
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t h e residual oil distilled a t zoo mm. pressure. Unchanged aniline remaining in the distillate is removed by diazotizing' in hydrochloric acid and heating t h e solution. The acid solution is then rendered alkaline, the supernatant quinoline extracted with ether, the ether solution dried, the ether removed, and the residual oil distilled a t atmospheric pressure. Quinoline thus obtained boils a t 238' (uncorrected). The yield is 65 per cent of the calculated amount, based upon the weight of aniline taken. Calculated for COHIN:N = 10.86 per cent per cent, 10.69 per cent
2,4-DIMETHYLQUINOLINE,
Found: N = 10.73
0CT33
1
vON- C &
-A
mix-
ture of 1 2 0 g. of paraldehyde and 2 0 0 g. of acetone is saturated with dry hydrochloric acid and allowed t o stand for 24 hrs., care being taken t o exclude moisture. The mixture is then slowly added t o 2 0 0 g. of aniline dissolved in 400 g. of hydrochloric acid, and the syrup finally heated during I hr. (in a water bath) under a return condenser. On rendering alkaline, a yellow oil separates from the solution. The oil is extracted with ether, and the ether evaporated. The residue, without further purification, is dissolved in an equal weight of hydrochloric acid and diazotized. Here again precautions are taken t o remove nitroso compounds b y extraction of the cold acid solution with ether. The aqueous solution is rendered alkaline and the yellow oil extracted with ether. The usual procedure is followed in the final purification of t h e 2,4-dimethylquinoline. The compound, which is obtained in 2 5 t o 3 0 per cent yield, based upon the weight of aniline taken, boils a t 260-264 (uncorrected) under ordinary pressure. Calculated for CiiHnN: N = 8.92 per cent, 8.73 per cent.2
per
cent.
Found. N
8.78
The above procedure is very much simpler and far more rapid than t h a t outlined by v. B e ~ e r . ~ COLORLABORATORY BUREAUOB CHEMISTRY D. C. WASHINOTON,
INTERMEDIATES USED IN THE PFtEPARATION OF PHOTOSENSITIZING DYES. 11-QUATERNARY HALIDES By CARL H. LVNDAND LOUISE. WISE Received February 24, 1919
The second step in the synthesis of photosensitizing dyes is the formation of quaternary iodides from the bases described in the preceding paper. These compounds result from the direct addition of methyl, ethyl or other alkyl iodide t o t h e quinoline base. Many of these addition products have been described in the literature, but there is too little available information on the best conditions for the preparation of these compounds. 1 No special precautions are necessary. Tetrahydroquinoline is not present. * Our thanks are due t o Messrs. Jenkins and Ellis, of the Nitrogen Laboratory of the Bureau of Chemistry, for the analytical data given in this paper.
* Loc. cit.
Vol.
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No. 5
We therefore undertook a systematic study of t h e synthesis of the quaternary iodides with a view t o establishing the simplest conditions which would give satisfactory yields of the pure compounds. Our many experiments need not be described in detail. After carrying out the addition reaction under varying conditions-in pressure flasks, in flasks under reflux condensers, with and without the use of various solvents, and with varying amounts of the components -we find t h a t i t is best t o use equimolecular amounts of the alkyl iodide and the base and t o carry o u t the reaction in a round bottom flask surmounted by a worm condenser. The flask should never be filled beyond one-third1 of its capacity. Depending on the nature of the base used, the reaction may proceed spontaneously a n d violently (as in the case of quinoline methiodide) or i t may require external heating (as in the case of quinaldine ethiodide). The presence of an a-methyl group in the molecule appears t o decrease the rate of reaction. The product is usually obtained in the form of a solid cake, which may be gradually dissolved by treatment with hot alcohol. The iodide crystallizes from the alcoholic solution on cooling. I n general, the yields of t h e quaternary halide are satisfactory, varying from 6 0 t o 80 per cent of the theoretical. We have found, however, t h a t small amounts of impurities in the reagents may decrease these yields very materially. All the quaternary halides are crystalline compounds of a more or less pronounced yellow color. Many of them melt with decomposition. All of them are water-soluble and ionize in solution. The iodine content of any quaternary base may be rapidly and accurately determined b y a slight modification of the Volhard method. This method served a useful purpose in permitting us t o judge the purity of our products. From the standpoint of the producer of photosensitizing dyes t h e following quaternary halides are perhaps the most important : quinoline methiodide and ethiodide, quinaldine ethiodide, toluquinaldine methiodide, and ~,4-dimethylquinolineethiodide. We have prepared relatively large amounts of these compounds and small amounts of a few other analogous iodides, all of which are described in the experimental part. EXPERIMENTAL
QUINOLINE METHIODIDE--.When small amounts of this product-less than I O O g.-are required, the following procedure is convenient: Equimolecular amounts of methyl iodide and quinoline are mixed in a round bottom flask, and allowed t o stand a t room temperature under a reflux condenser. The mixture gradually becomes warm and crystals begin t o appear in the flask. Since the reaction is exothermic, the mixture finally reaches a temperature a t which the methyliodide boils vigorously. When this point is reached the flask must be cooled in an ice bath t o keep t h e reaction from proceeding too violently. After a 1 This simple precaution is necessary. Well-annealed flasks filled half full frequently cracked during the course of the reaction.
