July, 1924
INDUSTRIAL A N D ENGINEERINGiCHEMISTRY
this change, deterioration was negligible in carbon dioxide. On the other hand, the fact that neither stock deteriorated to any such extent as in the oxidation test indicates again that oxidation is the predominant factor involved. GASEOUS OXIDATIONPRODUCTS The presence of gaseous products, such as carbon dioxide or sulfur dioxide and water, was investigated by passing the total volume of gas in the bomb, after treating the litharge stock with 300 pounds of oxygen for 16 hours at 60" C., through an absorption train containing successively calcium chloride, soda lime, and calcium chloride. A control test was made without the rubber present. Based on the rubber content of the stock oxidized, only 0.19 per cent of COZ, SOr, or so3 and no HzO were recovered by absorption. With this very small recovery of COz, SO2, or 503 the gain in weight of the stock during oxidation was 5.5 per cent, based on the rubber content. Since no visible products in liquid or solid form were found in the oxidation chamber, and since so little COZ, SOZ, or SO3 was recovered, almost the complete reaction involved is represented by the gain in weight. PRESENCE OF OXYGENIN THE PRODUCTS Since oxidation is the chief phenomenon involved, and since so little carbon dioxide was recovered from the gaseous products, it is almost certain that compounds containing oxygen are present in the solid product, Furthermore, since it has been shown that the acetone extract is an approximate index of the deterioration, it is of interest to determine (1) whether substances containing oxygen are present in the acetone extract, :tnd if so ( 2 ) whether the acetone extract contains all the oxidation products. T o determine this in a preliminary way, the original stock, the oxidized stock before extraction, the oxidized stock after extraction, and the acetone extract itself were tested for levulinic aldehyde (also certain dialdehydes, cliketones, and ketone-aldehydes) by the pyrrole reaction. This test was made in a manner similar to that first recommended by BruniZ5-i. e., the sample was heated with ammonium acotate, a pine wood splinter moistened with concentrated hydrochloric acid held in the ascending fumes, and the appearance of a crimson color noted. Both the litharge and the diphenylguanidine stocks were tested in the form of (1)the original vulcanized stocks, ( 2 ) the same stocks after oxidation under pressure, (3) the same stocks after oxidation and after extraction with acetone, and (4)the acetone extracts of the oxidized stocks. A negative reaction was obtained with the original stocks and with the oxidized stocks after extraction with acetone. A positive reaction was obtained with the oxidized stocks before extraction, and with the acetone extract itself. These results show that the original stocks contain no oxygen compounds responding to the pyrrole reaction, that such conipounds are formed during the high pressure oxidation, and that these compounds are completely extractable with ace1one. To correlate this phenomenon with natural aging, the red jar rings and the fire hose tubes, already described as having deteriorated badly under normal conditions, were subjected to the pyrrole test. A positive test (intense crimson color) was obtained for each stock in the deteriorated condition, whether this deterioration was the result of natural aging or of oxidation under pressure. A negative test was obtained with the same compounds newly vulcanized. BIBLIOQRAPHY
1-J. Chem. SOL.(London), 18, 44 (1865). 2 - I b i d , 18, 273 ( 1 8 6 5 ) . 3-J. Soc. Chem. I n d , 2 , 119 ( 1 8 8 3 ) .
717
4-Ibid., 4, 710 (1885). 5-Chem. Ztg., 19, 235, 382 ( 1 8 9 5 ) . 6-Gummi-Zlg., 20, 6 2 8 , 945 ( 1 9 0 6 ) . 7 - J . SOC.Chem. Ind., 31, 1103 ( 1 9 1 2 ) ; 32, 179 ( 1 9 1 3 ) ; 37, 55 ( 1 9 1 8 ) . S-KoZZod-Z., 13, 4 9 (1913). 9-caOUtChouC b gUlta-pef'Lha, 12,8724 (1916). IO-J. Sac. Chem. I n d . , 88, 339 (1919). 11-Ibid., 31, 251 (1920). 12-Rubber Age, 8 , 271 (1921). 13-India Rubber J . , 63, 742 (1922). 14--lbid., 63, 4 1 5 , 814 ( 1 9 2 2 ) . 15-Giorn. chim. ind. applicata, 5, 122 ( 1 9 2 3 ) ; Rubber Age, 13, 4 3 3 (1923). 16-Chem. N e w s , 6 2 , 192 (1890). 17-Movskoi Sbovnik, 1892, 5 7 ; J . SOC.Chem. Ind.. 11, 929 (1892). 18-Chem. Zlg., 18, 329 ( 1 8 9 4 ) . 19-India Rubber Would, BS, 127 ( 1 9 1 6 ) . 20-India Rubber J . , 61, 1163 ( 1 9 2 1 ) ; Rubber A g e , 11, 345 ( 1 9 2 2 ) . 21-Compf. Rend., 169, 1068 ( 1 9 1 9 ) ; 170, 26 ( 1 9 2 0 ) ; 174, 258 ( 1 9 2 2 ) ; 176, 127 ( 1 9 2 2 ) ; 176, 6 2 4 , 797 ( 1 9 2 3 ) ; Bull. SOC. chim., 81, 1152 ( 1 9 2 2 ) ; British Patents 141,361 a n d 181,365. 22-Comfit. rend.,177,204 ( 1 9 2 3 ) . (See Compt. rend., 176, 127 ( 1 9 2 2 ) , f o r bibliography on oxidation inhibitors, beginning with the work of Berthollet in 1797.) 23-Giorn. chim. z n d . applzcutu, 6 , 59 (1924). 24-J. Soc Chem. I n d . , 31, 251 ( 1 9 2 0 ) ; I n d i a Rubber J . , 61, 310 ( 1 9 2 1 ) . 25-India Rubber J . , 63, 415 (1922).
Decomposition of Anthraquinone by Heat''z By Harry F. Lewis and Sherman Shaffer CORNEU COLLEGE, MT. VERNON, I A .
NTHRAQUINONE has been prepared commercially for many years b y the oxidation of anthracene, the oxidizing agent being dichromate and sulfuric acid. The crude oxidation product contains such volatile impurities as anthracene and phenanthrene, etc., and nonvolatile organic chromium compounds. This crude product may be purified by sublimation. I n this process the necessary heat may be obtained either by superheated steam or directfired kettles. The temperature of sublimation varies from 200' to 350' C., and the temperature in case of local overheating may go much higher. I n this connection, it is interesting to know the rate of decomposition of anthraquinone a t elevated temperatures under differing conditions.
A
METHODS The anthraquinone used was of high purity, as indicated both by analysis and the melting point of 285.5' C. (cor.). The absence of anthracene was shown by the lack of charring with 15 per cent oleum. A sample weighing 4 grams was placed in a Pyrex bomb tube, sealed either at atmospheric pressure and room temperature, or evacuated a t room temperature and the pressure determined with a manometer before sealing, or, in the experiments carried out under water vapor pressure, the required amount of water added to obtain the desired vapor pressure and the tubes evacuated and sealed. The heating was carried out in a Carius furnace so constructed as to insure even heat, and the temperatures were determined with a standard thermometer. The reaction products were removed mechanically and tested for anthraquinone by the following modification of the zinc reduction method: The sample was finely ground, a 0.2-gram sample weighed and added to 50 cc. of 5 per cent sodium hydroxide solution. The temperature was raised Received December 29, 1923. A portion of the thesis submitted t o Cornel1 College by Mr. S h a f f e r in partial fulfilment of the requirements for the degree of master of arts. 1
2
INDUSTRIAL A N D ENGINEERING CHEMISTRY
718
to about 90" C. and about 0.5 gram sodium hydrosulfite added. The reduction was allowed to proceed for 10 minutes, the solution filtered rapidly, and the filter paper washed with a hot 1 per cent solution of hydrosulfite in alkali. This washing was carried out until the red color disappeared from the filtrate. Sufficient sodium peroxide was added to the filtrate to reoxidize the anthraquinone, as indicated by the disappearance of the red color. The anthraquinone was then filtered through a weighed Gooch crucible, washed with a small amount of dilute alkali, a little hot, dilute hydrochloric acid, and finally with water, dried a t 80" to 90" C., and weighed. In heating the anthraquinone, the following variables were studied: ( a ) temperature-a range of from 300" to 500' C.; ( b ) time--3, 8, and 24 hours; (c) the influence of air, oxygen, and water vapor. The results of these experiments are shown in Tables I and 11. TABLE I-DBCOMPOSITION O F ANTHRAQUINONE B Y HEAT I N AIR AND OXYGEN In the following runs the tubes were filled with oxygen a t atmospheric pressure a n d 25' C. in the oxygen runs; or sealed under the same conditions in air for the air runs, except for Expts. 19 a n d 20, where the tubes were evacuated and sealed a t 25 mm. and 25' C. Anthraquinone Temperature Time in Product Expt. c. Hours Per cent Air 1 300 3 99.6 2 325 100.1 3 4 5 6 7 8 9 10 11 12 13 14 15 16
350 375 400 425 450 475 500 300 350 400 450 500 350 500
17 18
350 500
19 20
350 500
8
24 Oxygen
8
Air
99.6 97.9 97.9 97.0 95.0 93.3 89.4 99.8 98.8 98.3 94.8 26.8 97.4 8.5 97.9 8.1 96.4 4.8
TABLE 11-DECOMPOSITIONO F ANTHRAQUINONE B Y HEAT I N WATER VAPOR In these runs t h e bomb tubes, of 240 cc. capacity, were charged with 4 grams anthraquinone and 0.18 gram of water and evacuated t o 25 mm. a t 25' C., and sealed. Exot
.
Temperature
c.
Time Hours
Anthraquinone in Product Per cent
In none of these experiments was there to be noticed any considerable pressure when the tubes were opened. Water was noticed on the walls of those tubes, which indicated much charring.
INVESTIGATION OF DECOMPOSITION PRODUCTS Three products were investigated-the charred material formed in the tubes heated at higher temperatures, a very soluble red substance found in certain of the tubes, and finally an alkali-soluble, brown material formed from the decomposition of the red substance in air. The tarry material composited from. Tubes 16, 18, 20, and 27, upon analysis for carbon and hydrogen by combustion, was found to contain 93.4 per cent carbon and 3.9 per cent hydrogen, by difference, 2.7 per cent oxygen. This would indicate that the material contains a large amount of carbon from the decomposition, mixed with the intermediate products. This is to be expected from the amount of charred material that has to be removed at times from the bottom of. the subliming kettles.
Vol. 16, No. 7
The red material was found to be present in those tubes which showed a trace of decomposition, indicating that it is an early step in the process. Under long periods of heating at temperatures from 350' to 400" C., and a shorter time a t higher temperatures, it was formed and easily separated, in an impure condition, from the portion of the product, on account of its great solubility in such solvents as ethyl acetate and acetone. This substance is very unstable and tends to decompose in air to give the brown product mentioned before. It was found to be stable in carbon dioxide, however, and whatever work was done was carried out in an atmosphere of this gas. This made the work of purification difficult, and consequently molecular weight work was of little value. AQalysis for carbon and hydrogen showed 81.3 per cent carbon and 4.6 per cent hydrogen. Anthraquinone contains 80.77 per cent carbon and 3.87 per cent hydrogen. Indications based upon molecular weight work point to a loose combination of two molecules of anthraquinone with the elimination of an atom of oxygen. The brown substance is either largely anthraquinone, or a t least a product which upon reduction and subsequent oxidation gives anthraquinone, for 88 per cent of it can be recovered as anthraquinone by reducing with hydrosulfite and oxidizing with sodium peroxide. The remaining 12 per cent is soluble in alkali and is precipitated by acidification, yielding a yellow precipitate which is completely soluble in ether. Indications point to the presence of a hydroxyl group. The amounts obtained were too small to serve for identification. CONCLUSIONS 1-Anthraquinone begins to decompose appreciably a t about 450" C., and to a slight extent a t even lower temperatures. This decomposition is not, in the main at least, oxidation, since the products obtained are poorer in oxygen than the original anthraquinone. The rate of decomposition is not materially different in the presence of air, water vapor, or oxygen, which substantiates the foregoing statement. 2-Sublimation of anthraquinone should be carried out a t temperatures no higher than 400" C., and care should be taken to eliminate local overheating. 3-In the decomposition the first product isolated is very unstable in air and tends to form a second, more stable product. Both of these are soluble in alkali, the unstable form with a reddish purple color. This unstable product seems to be composed of two anthraquinone molecules from which have been taken one or two oxygen atoms. Upon decomposition in air the second brown substance is formed, which, upon reduction and subsequent oxidation, goes largely into anthraquinone with a small amount of alkali-soluble product. Much time and careful work have been spent acquiring this little information with regard to the products of decomposition. Possibly a further insight into the reaction would explain some of the mysteries connected with the preparation of anthraquinone intermediates and dyestuffs. ACKNOWLEDGMENT The authors are indebted to the National Aniline and Chemical Company for aid in carrying out this work. The tenth annual convention of the American Cereal Chemists' Association was held a t Minneapolis, Minn., June 9 to 14. There were more than one hundred and fifty cereal chemists in attendance. Visits were made to many of the milling*plants in and about the city. M . J. Blish, of Lincoln, Nehr., is president of the association. Scientific instruments and apparatus of interest to the cereal chemist were on display.
