REDUCTION OF 2-NITRO-PCYMENE THOMAS F. DOUiMMIINI AND KENTUETH A. KOBE IJniversitr of \Vnslringtorr, Smattlc, M'asb.
Separation of the mixture of 2-nitro-pcymene and p-nitrotoluene formed in the mononitration of p-cymene b y fractionation is difficult. The corresponding amines are Far more easily separated; however, the complete reduction of the mixture hy standard laboratory methods is not easily carried out. Pure 2-nitro-p-cymene is rcduced without clifficulty. To elrect complete reduction, a laboratory shaker equipped with a heater, flask, and condenser, with provision for slowly arlding hydrochloric acid to the mixture of nitro compounds, iron powder, and sand has been found very convenient. This apparatus is useful for carrying out numerous ht~terogeneonsreactions.
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S 'ITIF, previous paper on the motionitration of p-cyrrienc (page 257), it v a s shown that the nitratiori product, consisted of a mixture of 2-nitro-p-cymene and p-nitrotolirene tha.t is difficult to separate by fractionation. 2-Cyinidine (2-amimo-p-cyriiene) ic: miidi easier to purify by fractionation arid is also niore usrfiil for tlie preparation of derivatives. Previoiis in\vst.igators used various mixtures for this TCduction. Iron-acet.ic acid was lound muatisfactory by Barlow (8). Zinc-hydror hlorio acid, acoonlirig to Siiderb;ium sild M'idman ( l l ) ,gaarr a prmliict almnst entirely solublr in acid. Tin-ii~riroeliloricacid \\as used by bhc following: Wheeler and Solithey (12) with ii yield of 80 per cent; Dernonlrreuii arid Kremers (31, 75 per cent; and Kirriurn (7), FO-77 per cent. Activated iroii m u used by Carrhqly and 1,eFevr.e ( 5 )and by LeFevre ( 8 ) ; tlie former obtained TO per cent and the latter, niore than 93 per cent. Iron-hyilroclilorie acid was u s d by Andrew (1) wit!) quantitative yields; Dorier and Ikrt (4, 90 per cent; Ifixson and Cauwcnberg (S),88.8 per cent; Phillips ( I O ) , 80-85 per cent; and Demonbreun and Kremers (8)with a rriaxiiriuiii yield of 09 per cent. Since tire ease of rcduct.ion and yields vary witli the purity of the 2-nitro-p-cymcne, wliicli is generally not given by the previously cit.ed investigators, their conditions arc, of little value. Only recently lias (I-nitrotoluene heen noted as an impurity always associated with the 2-rritni-p-cynene. Tin-hyrlrochloric acid, zinc-hydrochloric acid, aiid ironhydrochloric acid IWTO tried as rt:ducing ageiits. The latter agent was found to be tlic most effective and economical, arid was consequently used for this reduction. In ttii. work the fallowing products from the mononitration of (I-cymene were rccliiced: (a) the iiiiilistillerl nitration jiruoducts after wasliing, (6) the iriixt.iire of pnitrot.oluene and 2-11itro-pcyrnene ol~tained by simple distillation in vacuo from the crude nitration products, and ( c ) pure 2-nitro-~~-cymer1c. 264
Apparatus and Materials A laboratory shakcr (Figure I ) , adjusted by the cccentric for
and t h c condenser ~r-cresecurely held by suit.alile clam$=. As a safety tube, two air condensers woi'c used in series, held by an cxternd iron stand and ronnectcd to the top of thc eondoncer 1)y a short, piece of rubber tubing. A XIO-ml. dispensing hori%,/, held by an iron stand ~l'nsused for nddiiii: tlie hydroelrloric wid t o the reaction mixture; t,hc tip of thc huret, was ronnactcd by a short piece of rubher tubing to tho inlet, tuba on the flask.
The hydrochloric acid >vas of technical grade, the iron was a powder (;\Iallinckrodt Clieiriical Works) of the screen analysis given:
The iron powder was shaken witli a mixture of ether and alcohol to remuve any oil or grease before it was uscd.
Method of Reduction The following conditions were foiilld suitable for the reduction: one-hundred granix of pure 2-nitro-p-cymene, 100 rrrl. of water, 200 grams of the iroo powder, 25 grains of sand (about 65 nresh), and 10 nil. of hydrocliloric acid are rriired in a 2-liter Erlenmeyer flask. The heat evolved is sufficient only to warm the m:tsc; it is now heated to boiling in the shaking apparatiis (Figure 1). To avoid excessive re-
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flux a t first, 1-ml. portions of hydrochloric acid are added every 3 minutes for 12 minutes. Five hundred milliliters of hydrochloric acid are now added a t the rate of about 8 ml. per minute with continued external heating. This operation requires one hour, after which heating and shaking are continued for another hour. The reaction mixture is transferred to a 5-liter round-bottom flask, made alkaline with sodium hydroxide solution, and steam-dktilled. The oily liquid floating above the water is separated; the aqueous layer is saturated with sodium chloride and extracted with petroleum ether. The extract plus the 2-cymidine are dried with calcium chloride and distilled in vacuo. The weight is 77.5 to 80.0 grams (boiling point a t 17 mm., 123.8' C., uncorrected). The cymidine is now tested for nonbasic impurities by acidifying a small portion with hydrochloric acid and steam distilling. The distillate is acidified before inspection to dissolve any hydrolyzed 2-cymidine hydrochloride. The residue in the flask may be tested in exactly the same manner. Under these conditions none is found. Pure cgmidine is found to have a refractive index (n") of 1.54050; boiling point a t 10 mm., 110.2" C., and a t 760 mm., 242.0' C. Mann, Montonna, and Larian (9) give nz: = 1.5395; boiling point a t 10 mm. = 112.2" C.
Yields Using pure 2-nitro-pcymene the yields of rec o v e r e d p u r e 2-cymidine amount to 93-96 per cent of the theoretical. Owing to the difficulty of obtaining pure 2-nitro-p-cymene by fractionation, the reduction of a product of varying degrees of purity was carried out. The purer the product taken for reduction, t h e higher were the yields; the p-nitrotoluene interferes with the ease of reduction. The
FIGURE 1. REDUCTION APPARATUS
b
chloride with the iron as used in the commercial reduction of nitrobenzene were unsuccessful with both the crude nitration products . and the mixture of 2-nitro-p-c~mene and p-nitrotoluene. The addition of a few milliliters of hydrochloric acid to the nitro compounds mixed with the iron powder (200 grams) and water (100 ml.) would only react sufficiently to warm the mixture and consequently would require external heating. Sitrobenzene treated in exactly the same manner reacted violently and required external cooling. The crude nitration products contain a material which, upon distillation in vacuo, remains as residue (tarry matter) in the flask. I n reducing the crude nitration product, this material is quantit a t i v e l y decomposed and does not N 'D" appear in the product. The small a m o u n t of u n changed p-cymene after the reduction I54200 can be easily separated by fractiona154160 tion. The lower yield obtained by '54100 r e d u c t i o n of a crude 2-nitro-pcymene has been 0 2 4 8 a IO reported by DePERCENT PARA-TOLUIDINE. monbreun a n d FIGURE 2. COMPOSITION-REFRACKreiners (3). TIVE INDEX DIAGRAN FOR 8-CYMIDINE I n fractionating PLUSp-TOLUIDINE crude cymidine to obtain the pure product, the refractive index-composition diagram (Figure 2) may be used. This method of reduction is characterized by the steady production of hydrogen from the surface of finely divided iron which is being constantly thrown through the boiling solution by the shaking mechanism. Stirring has been found less effective and convenient than shaking. This apparatus is suitable for carrying out various heterogeneous reactions, both organic and inorganic. I n applying heat externally, i t is important that the solid matter in the flask be sufficiently mobile with the liquid upon shaking to prevent superheating cracking of the flask. ~~
Literature Cited dndrews, C. E., J. IND. ENG.CHEM.,10, 453 (1918). Barlow, J., Ann., 98, 245 (1856). Demonbreun, 1%A., '. and Kremers, R. E., J . Am. Pharm. Assoc., 12, 296 (1923).
Dorier, P. C., and Bert, M. L., Compt. rend., 182, 63 (1926). Ganguly, S. N., and LeFevre, R. J. W., J . Chem. SOC.,1934,
mixture of 2-nitro-p-cymene and p-nitrotoluene gave a yield of about 90 per cent on reduction. I n order to minimize the labor and time necessary in producing 2-cymidine for the preparation of various derivatives, the reduction of the undistilled nitration product was carried out directly. The yield based on the original weight of crude p-cymene taken for nitration was about 80 per cent. This yield is equivalent to an 87 per cent yield based on the nitro compounds present. Attempts to obtain complete reduction using a very small amount of hydrochloric acid or equivalent ferric MARCH, 1939
852.
Hixson, A. W., and Cauwenberg, W. J., J . Am. Chem. Soc., 52, 2120 (1930).
Kimura, S., J . Soc. Chem. In,d. Japan, 37, suppl. binding, 4 (1934).
LeFevre, R. J. W., J . Chem. Soc., 1933, 977. Mann, C. A., Montonna, R. E., and Larian, M. G., ISD.ESG. CHEM.,28, 598 (1936). Phillips, M.,J . Am. Chem. SOC.,45, 1490 (1923). Soderbbum, H. G . , and Widman, O., Ber., 21, 2127 (1888). Wheeler, A. S., and Smithey, I. W., J . Am. Chem. SOC.,43, 2611 (1921). RECEIVED November 2, 1938.
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The glass-linedsteam-j aclteted still a t the right is used by Eli Lilly and Company in the preparation of ethyl mercuric chloride, an intermediate in the manufacture of Merthiolate. In the real center is a 14-square-foot glass-lined condenser which serves as a reflux for the still during the reaction Courtesy, The Pfaudler Company
The photograph a t the left shows the apparatus used in the catalytic purification of the nitrogen-hydrogen gas mixture for the synthetic production ‘of ammonia, using electrolytic hydrogen. Nitrogen Engineering Corporation process Courtesy, Chemical Construction Corporation
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