352
INDUSTRIAL AND ENGINEERING CHEMISTRY
relations although sizes below a mean diameter of about 1 mm. have not been investigated. It is improbable that the predicted relation betn een these quantities would extend to very small granules. This would lead to the conclusion that a powdered catalyst or charcoal is more efficient than a granular solid in the removal of a toxic gas. The above ielation has been found to approach a limiting value with granules below 1mm. in diameter and to fail completely for very small granules in the case of carbon monoxide. Somewhat similar results indicating a limiting value for the case of the iemoval of phosgene by charcoal is shown by Klotz (7). The theory is not applicable in its present form to the initial breakdown of the catalyst when the escaping concentration is extremely small, although analytical difficulties may be in part responsible for the lack of agreement in this range. Some departures from t,he theory may also be expected if the temperature of the reacting bed increases owing to the fact that the heat of reaction is not conducted away instantly. Finally, the rrlation between the concentration of active cenieis and mean granule diameter is largely empirical. The kinetics provide a guide to the evaluation of the maximum surface activity of a catalyst and indicate the condition
Vol. 42, No. 2
when it is not possible to increase the rate of removal of gas by any further improvements in the surface of the granules. LITERATURE CITED
(1) Amundson, N. It., J . P h y s . & Colloid Chem., 52, 1153-7 (1948). (2) Benton, A. F., and Bell, R. T., J. Am. Chem. Soc., 56, 501-5
(1934).
(3) Bohart, G. S., and Adarns, E. Q.,I b i d . , 42, 523-44 (1920). (4) Danby, C. J., Davoud, J. G., Everett, D. H., HinsheIwood, C. N . , and Lodge, R. &I.,J. Chem. Soc., 1946, 918-34. (5) Katz, M . , and Grant, G., unpublished results. (6) Katz, M., and Katzman, J., Can. J . Reseurch, 26F, 318-30
(1948).
(7) Klotz, I. M., Clcem. Reus., 39, 241-68 (1946). (8) Lamb, A. R., Bray, W. C., and Frazer, J. C. TV., IND. ENG. CHEM.,12,213-21 (1920). (9) LMeckienberg, W., and Kubelka, P., 2. Elektrochem., 31, 488-95
(1925).
RECEIVED April 7, 1949. Presented before the Division of Physical and Inorganic Chemistry at the l l B t h Meeting of t h e Armmc.+x CHEMICAL SOCIETY, San Francisco, Calif.
ononitrati n of
p-
KENNETH A. KOBE AND HERMAN LEVIN Uniuersity of Texas, Austin, Tex.
T h e process variables i n the nitration of p-xylene to the mononitro-p-xylene have been studied. A maximum yield of 90% was obtained by carrying out the nitration at 30’ C. with a D.V.S. (dehydrating value o€ sdfuilric acid)
value of 3.0 and llyc excess nitric acid, the mixed acid being added in 30 minutes. The effect of the process variables, temperature, D.V.S. ratio, time, and excess nitric acid is shown graphically. No deallcylation was found to occur.
P
nitric acid t o p-xylene kept in an ice bath. I n 1885 mixed sulfuric and nitric acids vere first used by Nolting and Fore1 (21) ~ h added o the mixed acid t o p-xylene. Xonomalow and Gureiyitsch ( 1 7 ) nitrated a number of alkyl benzenes, including p xylene, with mixed nitric and acetic acids. Electrolytic nitration of xylene has been described by Atanasiu and Belcot (2) and by htanasiu ( I ) , who obtained best results a t 40” t o 50” C. with a ratio of acid to hydrocarbon of acid, 1; hydrocarbon, 2 to 3. Two recent patents describe the nitration of mixed xylenes. Batchelder et nl. (8) claim a mononitro product low in dinitro and by-product impurities. Vigorous agitation is maintained to secure “substantial emulsification” and hence “extremely intimate contact between acid and xylene.” For maximum yield a weight ratio of nitric acid (0.6 to 0.7) to xylene (1.0), representing a 10 mole % excess of nitric acid, and a D.V.S. (dehydrating value of the sulfuric acid) range of 2.60 to 2.95 for the mixed acid were recommended. The nitration was carried out in 35 minutes at 43.3” C. to give a yield of unpurified nitroxylenes that is 87.9% based on the initial weight of the xylene. This yield is high as no information is given concerning the amounts of unreacted xylene, dinitroxylenes, and oxidation by-products that were present in the unpurified reaction mixture. Whereas Batchelder et al. desired a high degree of emulsification of acid and hydrocarbon, Castner ( 8 ) took extreme care to avoid any such emulsification or even mixing between the two phases. Hence the term “interface nitration” can be applied to the process of Castner whereas “emulsification nitration” describes the process of Batchelder. Castner claims a greater control over the degree of nitration. The equipment used for interface nitration provides for a fixed interfacial level in the nitration, separate agitation within the acid, and hydrocarbon layers to
RIOR to World War I1 the nitration of the xylenes was carried out only on a small scale to produce solvents and chemical intermediates. However, during the war mixed xylenes were nitrated in a t least three governrnent ordnance works and reduced to xylidines n hich were used as an additive to increase the octane rating of aviation grade gasoline. The production during the war reached 150,000 pounds per day of recoverable specification grade xylidines a t the Esso Standard Oil Company plant a t Baton Rouge ( 7 )and other plants contributed additional amounts of xylidines. Sumerous uses were suggested for the surplus xylidines available at the end of the war, such aq for dyes and intermediates, wood preservatives, wetting agents, accelerators for rubber, and frothing agents for the flotation of ores. The production of xvlenes by the hydroforming process used for the manufacture of toluene from petroleum hydrocarbons makes available large amounts of these three isomeric hydrocarbons. Their nitration represents the application of one of the important unit processes to give a n intermediate compound for further chemical utilization. I n this work the para isomer was selected because only one mononitro compound exists, making easier its isolation from the nitration mixture. Also, previous work on the nitration of p-dialkyl benzenes had shown that dealkylation frequently occurred and it was desired to ascertain if this reaction was occurring with the first member of this series. PREVIOUS WORK
p-Xylene was first nitrated by Glinzer and Fittig (10)who prepared the mononitro and two dinitro-p-xylenes by adding p xylene to fuming nitric acid. Jannasch (IS) was unable to secure the mononitro compound by following the procedure of Glinzer and Fittig but later ( 1 4 ) prepared it by slowly adding fuming
February 1950
INDUSTRIAL AND ENGINEERING CHEMISTRY
give a continuous movement of fresh material to the interface for nitration, and a replacement of spent acid by fresh mixed acid during the course of the nitration. An example describes the nitration of xylene a t a temperature below 65" C. without stating the time required or the yield of products secured. I n the nitration of para-substituted dialkyl benzenes the replacement of one alkyl group Figure 1. Nitration Flask by a nitro group has been reported (90).Kobe and Doumani (9,15) report that in the mononitration product of p-cymene (1-methyl-4-isopropylbenzene) 8% by weight was p-nitrotoluene and 92% was 2-nitro-p-cymene. The isopropyl group was isolated as isopropyl alcohol from the spent mixed acid. Such a replacement has not been reported in t h e nitration of p-ethyltoluene (6) nor for p-tert-butyltoluene (4). This replacement has been observed with symmetrical dialkylbenzenes such as p-diisopropylbenzene, from which 48.5 mole %t of 4-nitroisopropylbenzene was obtained (19), and p-di-tertbutylbenzene, from which 13.5 mole % of 4-nitro-tert-butylbenzene was obtained (18). A further objective of this work was to investigate thoroughly the nitration products to ascertain whether or not a methyl group has been replaced by a nitro group during the reaction.
.
+
was always added to the less dense liquid using adequate stirring and cooling. Safety goggles or spectacles are always worn in the laboratory and a transparent face shield is worn during more hazardous operations. METHOD OF NITRATION
Preliminary work indicated there was little or no difficulty in obtaining an emulsion of the mixed acid and hydrocarbon phases. This is somewhat surprising in view of the difficulty encountered by Kobe and Doumani (15) in the nitration of p-cymene. Mixtures of sulfuric and acetic acid were tried in order to find their effect on emulsification. I n experiment 47, sulfuric acid was added to the p-xylene to form an emulsion before the nitrating acid was added. In this case the nitration reaction began immediately; however, the yield of product was lower than the experiments in which initial emulsification was not employed (see experiments 45 and 46). All nitrations (except experiment 47) were carried out by addmg the mixed acid [prepared from sulfuric acid (specific gravity, 1.84) and nitric acid (specific gravity, 1.42)] to the p-xylene. A constant stirring rate of 1400 r.p.m. was maintained. The reaction temperature and the amount of acid added were recorded every 5 minutes to ensure good temperature control and an even rate of addition of the acid. Tem eratures below 13.28' C. cannot be used because p-xylene solidiffes. In all experiments (except 47) 2 to 4 minutes were required to initiate the reaction and an additional 2 to 3 minutes to become vigorous. The longer times were required at lower temperatures, more dilute acid mixtures, or slower addition rates. A small amount of oxidation was observed during every nitration, being greatest at the higher temperatures, longer reaction times, and lower D.V.S. values. The presence and extent of the oxidation was indicated by the amount of brown fumes of nitrogen dioxide liberated during the reaction. The nitration mixture became reddish brown in color after 10 to 15 minutes, even though no fumes of nitrogen dioxide were evolved. After addition of all of t h e acid, stirring was continued for 1@ minutes, then the reaction mixture was slowly and carefully added to a beaker containing 350 to 400 grams of chipped ice. Separation of the two layers occurred within 10 to 20 minutes without the addition of sodium fluoride and kieselguhr recorn-
APPARATUS AND MATERIALS
&
i
*
The apparatus used for this nitration is shown in Figures 1and 2. The nitration flask, shown in Figure 1, was built from a 1-liter, 3necked glass flask. At A , a ground-glass joint contained a thermometer well which was immersed in the nitration mixture. At B a mercury sealed glass stirrer entered the flask. The stirrer was made of 0.125-inch stainless steel rod with a 6-bladed propeller, 1 inch in diameter, at the end. The stirrer was driven by a variable speed (300 to 4000 r.p.m.) motor. The propeller was laced close to the bottom of the flask and rotated so that the Kquid was moved upward at the center and downward at the walls of the flask. At C, a 100-mm. water-jacketed condenser allowed the escape of gases but condensed the vapors. A small glass thistle tube, T, was inserted through the condenser tube and its tip was bent so it would be directly above the blades of the propeller. Nitrating acid was added a t M through the thistle tube from a 500-ml. graduated buret from which the delivery rate could be controlled by the stopcock. Temperature control was obtained by insertin a single circular bank of 9 glass coils, 3 inches in diameter. fce water was circulated through the cooling coils by means of a small pump. In a few nitrations additional cooling was necessary. This was obtained by adding small pellets of solid carbon dioxide directly to the reaction mixture (16). A 2-mm. stopcock was attached to the bottom of the flask to allow the rapid removal of the nitration mixture. The condenser C was removed after the first five runs because no volatile by-products were sought in the nitration mixture. The p-xylene was obtained from the Oronite Chemical Company and was stated to contain 97.6% p-xylene. The remainder consisted of other xylenes and aromatic compounds as easily nitrated as p-xylene so that the material used was considered to be p-xylene and calculations were made on this basis. The other chemicals used were of reagent grade. The usual safety precautions were observed when working with mixed acid and nitration products. The more dense liquid
353
Figure 2.
Nitration Assembly
8 4
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY 100
counted for in the D.V.S. Although it might be more scientific to use a mole ratio rather than a weight ratio to express watersulfuric acid ratio, the fact that analyses of the reactants are given on a weight basis leads to a retention of D.T.S. as a plant operating value. The relationship can be calculated from the equations:
90
2
Vol. 42, No. 2
M t. of I-lzSOcused D.V.S. = --__xi. of HzO a t cnd of reaction
80
!e
&SOa) (98) = 5,444 moles R,SO, (moles HzO) (18) moles Ill0
- (17101('s
C 70
z
_ _ _ I _ _
w
V
U
2
60
The relative values of the two methods are given in the following tabulation for commonly used values:
50
D.V.S.
40
I
IO
I
I
I
15 20 REACTION
Figure 3.
I
I
I
I
I
I
30 35 40 TEMPERATURE IN "C.
25
I
1.0
1 . 5 2.0
2.5
mended by Batchelder et al. ( 3 ) . The two layers were separated snd the acid layer diluted with 200 to 300 ml. of water with stirring. A vigorous evolution of brown nitrogen dioxide gas occurred, confirming previous oxidation reactions. After further dilution and cooling, the solution (about 800 ml.) was extracted once with 200 ml. of petroleum ether to recover any organic material. The nitro-p-xylene layer was washed twice with 100ml. portions of water, 10% sodium carbonate solution, and finally with water. The combined washings were extracted once with petroleum ether which was then added to the ether extract of the acid layer. The combined petroleum ether portions were washed once with 200 ml. of water and evaporated on the Reaction eteam bath to secure 5 to 10 grams Temp.a, Run of liquid which was added to the washed NO. c. hydrocarbon. The nitro-p-xylene layer 1 40 was slowly steam distilled (20 to 24 hours) 2 40 3 30 until a white solid (the dinitro-p-xylene) 20 4 waa first observed solidifyinq a t the en10 5 trance to the condenser, The nitro-p40 6 40 xylene layer was decanted from the water 7 40 8 and dried with anhydrous calcium sulfate. 40 9 The nitro-p-xylene was distilled a t 40 10 45-mm. pressure through a %-inch Vigreux 40 11 12 40 column operated at a high reflux ratio. 13 40 The only boiling point for nitro-p-xylene 14 40 recorded in the literature is 238.5' to 15 40 30 16 239" C. at 739 mm. (21). The purified 17 30 compound made in this work diqtilled 18 30 a t 149a to 150' C. a t 45 mm. and 238 to 30 19 30 20 239" C. at 747 mm. The refractive index 30 21 at 32" C. in dayoiiyht was 1.5366 and 22 30 the density a t 32 C. was 1.116 grams 23 30 24 30 per ml. 20 25
I n this work the process variables Investigated were the temperature of nitration, the time of addition of the mixed acid, the ratio of nitric acid t o p-xylene, and the dehydrating value of the sulfuric acid (D.V.S.). The D.V.S. is defined by Groggins ( 1 1 ) as the actual sulfuric acid content of the mixed acid divided by the total water present when nitration is completed, both values being on a weight basis. Hence, water introduced with the reactants -mixed acid and hydrocarbon-and water formed in the reaction are both ac-
b C
3.5
4.0
6.48.210.913.616.4
45
Effect of Temperature on Yield of R Iononitro-p-x ylene
PROCESS VARIABLES
3.0
I
[email protected])S
The data for the various nitiations and the yields of nitro-pvylene are given in Table 1 and the results are shown in Figures 3 to 6. The reproducibility of the yield is 1yo,as shown by yields of $9.0, 89.0, and 90.1 % for runs 23,45, and 46. The effect of temperature is shown in Figure 3 in which runs for various times and dehydrating values of sulfuric acid are shown as a function of temperature. A maximum yield of 89% is secured at 30" C. Over the temperature range of 20" to 30" C.
TABLEI.
SUMMARIZED
Xitra-
tion Time b , Xlin. 30 23 40 61 115 90 90 90 60 60 60 30 30 30 90 90 90 90 60
DATAAiVD RESULTS
Mole Ratio,
Weight of p-Xylene Nitrated,
Weight of Recovered, p-Xylene
Rlozk&!p-
"01:
D.V.S. 3.94 3.94 3.94 3.94 3.94 3.0 2.0 4.0 4.0 3.0 2.0 3.0 4.0
2.0 4.0 2.0 3.0 4.0 2.0 2.0 60 4.0 60 2.0 30 3.0 30 30 4.0 2.0 90 3.0 20 90 26 4.0 90 20 27 2.0 60 20 28 3.0 60 20 29 60 4.0 20 30 30 2.0 20 31 3.0 30 20 32 4.0 30 20 33 30 3.0 13 34 30 3.0 26 35 3.0 35 30 36 3.0 15 30 37 3.0 45 30 38 2.5 30 30 39 3.5 30 30 40 30 3.0 30 41 30 3.0 30 42 3.0 30 30 43 3.0 30 30 44 3.0 30 30 45 3.0 30 30 46 3.0 30 30 47 Reaction temperature * l o C., except f Stirring continued for 10 minutes more. Basis: initial weight of p-xylene.
G. G. p-Xylene 1.11 170.0 4.8 1.11 170.0 6.0 2.1 1.11 170.0 0.0 1.11 170.0 0.9 1.11 170.0 15.3 1.11 170,O 170.0 41.6 1.11 6.0 1.11 170.0 170.0 6.8 1.11 6.4 1.11 170.0 38.2 1.11 170.0 170.0 2.1 1.11 170.0 1.7 1.11 26.6 1.11 170.0 6.8 170.0 1.11 41.7 1.11 170.0 2.1 1.11 170.0 0.0 1.11 170.0 42.5 1.11 170.0 1.11 170.0 0.4 0.0 1.11 170.0 40.8 1.11 170.0 0.0 1.11 170.0 0.0 1.11 170.0 47.6 1.11 170.0 3.4 1.11 170.0 170.0 0.0 1.11 44.2 1.11 170.0 3.8 1.11 170.0 0.0 1.11 170.0 52.7 1.11 170.0 1.7 1.11 170.0 0.0 1.11 170,O 2.1 1.11 170.0 1.3 1.11 170.0 1.3 1.11 170.0 0.0 1.11 170.0 0 .0 1.11 170.0 15.8 1.11 170.0 0.0 1.11 170.0 11.9 189 1.0 27.6 210 0.90 0.0 1.20 157 0.0 145 1.30 0.4 1.11 170 1.3 1.11 170 6.0 1.11 170 2' C. in runs 1, 2 , 4, 5 , 7, 37.
Weight, G.
%e
69.6
62.2
75.2 77.5 72.5 63.6 44.2 69.6 66.3 76.0 49.3 82.5 71.5 54.2 68.7 54.8 85.7 82.0 53.5 88.5 81.1 56.7 89.0 82.5 50.3 85.7 83.9 55.3 87.1 85.3 53 .O 88.0 83.0 86.5 88.5 87.5 85.3 88.5 79.3 87.9 82.1 73.8 88.1 87.4 89.0 90.1 77.0
INDUSTRIAL AND ENGINEERING CHEMISTRY
February 1950 100 1
I SYMBOL
TEMP. ("C.)
I
90
@ 80 j
w>. + z
70
W
V
u. 60
tion conducted at 30" C. for 30 minutes with a D.V.S. of 3.0. The maximum yield occurs with a 10% excess of nitric acid. The use of a larger excess of nitric acid causes a lowered yield due to oxidation, as well as being uneconomical in the use of nitric acid. The per cent yield can be calculated on the basis of the p-xylene charged, the p-xylene unrecovered or the nitric acid charged. Because of its relatively high cost large scale nitrations might be carried out more economically using only 5% excess nitric acid, for only a slight decrease in yield occurs and any unreacted pxylene can be recycled in the process. From the curves in Figure 6 the conditions for maximum yield can be selected as: Reaction temperature, ' C. Nitration time, min. D.V.S. "0s: p-xylene, mole ratio
50
40
15
Figure 4.
30 45 60 75 90 NITRATION TIME IN MINUTES
105
30 30
3.0 1.10
Under these conditions a maximum yield of 89% mononitro-pxylene is produced. This surpasses the 88% yield of unpurified product reported by Batchelder et al. (3).
Effect of Time of Addition of Mixed Acid on Yield of Mononitro-p-xylene
there is little change in the yield so that close control below the maximum is unnecessary. Batchelder et ai. (3) reported a temperature of 43" C. (1lOO F.) which is seen to be considerably beyond the best value and oxidation must have been considerable. The effect of time of addition of the mixed acid to the nitration mixture is shown in Figure 4. Time is not an important factor except a t higher temperatures and lower D.V.S. values. This indicates that the rate of dinitration and oxidation reactions that reduce the yield increase more rapidly with temperature than does the mononitration. T h a t D.V.S. exercises the greatest influence on the yield of mononitro-p-xylene is shown in Figure 5 . At every temperature used (20 O, 30 O, and 40' C.) a rapid decrease in yield occurs with decrease from a D.V.S. of 3.0. As D.V.S. is increased above 3.0 slight decreases in yield occur. This uniform behavior at D.V.S. less than 3.0 indicates that as the reaction proceeds the water formed dilutes the mixed acid sufficiently so that the nitric acid loses some of its nitrating value and becomes an oxidizing agent. At higher values of D.V.S. the concentration of nitric acid in the mixed acid becomes less, thereby decreasing the rate of nitration. The effect of excess nitric acid is shown in Figure 6 for the reac-
.
401!5
355
' ' '
A.
90
3!0 3.5 4.0 4!5 DEHYDRATING VALUE OF SULFURIC ACID
20
2!5
Figure 5. Effect of Dehydrating Value of Sulfuric Acid on Yield of Mononitro-p-xylene
0.90
IO0 1.10 I20 MOL RATIO OF NITRIC ACID/P-XYLENE
I30
Figure 6. Effect of Mole Ratio of Reactants on Yield of Mononitro-p-xylene at 30' C. for 30 Minutes, Dehydrating Value of Sulfuric Acid Is 3.0
0=
6
Initial weight of p-xylene
= Weight of p-xylene unrecovered = Initial weight of nitrio acid
REACTION BY-PRODUCTS
In order to determine whether or not a dealkylation reaction was occurring to produce p-nitrotoluene and methyl alcohol the spent acid layers from runs 1to 5 were examined thoroughly. N o qualitative tests could be obtained for methyl alcohol and so it was concluded that p-xylene does not dealkylate under the nitration conditions used in this work, as does p-cymene. The dinitro-p-xylene compounds formed were investigated by crystallizing from alcohol 4 grams of the solid residue remaining from the steam distillation of run 47. Assuming that under the relatively mild nitration conditions used in this work no 2,5dinitro-p-xylene is formed, the amounts of purified components separated and melting point of the unseparated components (6) show that a n approximate ratio is 75% 2,3- and 25% 2,6-dinitrop-xylene. There is no indication that any trinitro-p-xylene is formed under these nitration conditions. The only oxidation product found was p-toluic acid which was never present in amounts greater than 0.1 gram. I n those experiments where a large evolution of nitrogen dioxide had occurred the initial dilution of the spent acid solution caused a small amount of white solid to rise t o the surface. This was identified as p-toluic acid [found: melting point 178" to 180OC.; neutralization equivalent, 135; recorded values: melting point, 181' C. (1.9); neutralization equivalent, 136.11. Wahl (2.9,M)reported that 1 to 2% of the product obtained in the nitration of p-xylene was p-tolualdehyde and 2-nitro-ptolualdehyde. His conditions of nitration were not described fully but were more severe than those used in this work, for his
INDUSTRIAL AND ENGINEERING CHEMISTRY
356
final temperature was 50” C. N o such oxidation products could be found in the nitro-p-xylene layer formed in this work. SUMMARY
p-Xylene has been nitrated with a yield of 89% mononitrop-xylene using the following conditions: Temperature, C . Nitration time, min. D.V.S. “01: p-xylene, mole ratio
30 30 3.0 1.10
No dealkylation could be found in the nitration under these conditions. Only small amounts of dinitro-p-xylene are formed. LITERATURE CITED
(1) Atanasiu, I. A., BulE. Chim. SOC.Rom4ne Chim., 39, 71-82 (1937-38). (2) Atanasiu, I. A., and Belcot, C., Bull. sect. sei. acad. Roumaine, 19. 28-38 (1937). (3) Batchelder, G. W ; Nagle, W. M., Vyverberg, J. C., and Willis, J. M., U. S. Patent 2,400,904 (May 28, 1946). and Haeffely, P., Bull. soc. chirn., 35, 983 (1924). (4) Battegay, M., (5) Blankama, J. J., Chem. Weelcblad, 10,136-7 (1913). (6) Brady, 0. L . , and Day, J. 3.E., J . Chem. Soc., 1934, 115
Vol. 42, No. 2
Brown, C. L., Smith, TV. M., and Scharman, W. G., IWD. EWG. CHEIvf., 40, 1538-42 (1948). Castner, J. B., U. S. Patent 2,386,128 (Sept. 18, 1945); I b i d . , 2,438,204 (March 23, 1948). Doumani, T. F., and Kobe, K . A., J . Org. Chem., 7, 1-5 (1942). Glinzer, E., and Fittig, R., Ann., 136, 307-8 (1865). Groggins, P. H., “Unit Processes in Organic Synthesis,” p. 25, New York, McGraw-Hill Book Co., 1947. Heilbron, I. M., and Bunbruy, H. M., “Dictionary of Organic Compounds,” Vol. 3, p. 779, London, Eyre and Spottiswoode, 1943. Jannasch,P., Ann., 171, 81 (1874). Ibid., 176,55-6 (1875). Kobe, K. A., and Doumani, T. F., IND. ETG.CHEM.,31, 257-63 (1939). Kobe, K. A. and Doumani, T. F., Organic Sgntheses, 21, 98-8 (1941). Konowalow, M.,and Gurewitsch, Ch., J . Rzm. Phys. Chem. Soc., 27, 537-41 (1905); Chem. Zentr., 76, 11, 818 (1905). Legge, D. I . , J . Am. Chem. SOC.,69, 2086-90 (1947). Newton, A., I b i d . , 65, 2434-9 (1943). Nightingale, D. V.,Chem. Rem., 40, 117-40 (1947). Nolting, E., and Forel, S.,Ber., 18, 2680 (1885). Wahl, H., Ann. chim., [ l l ]5, 43-4 (1936). Wahl, H., Compt. rend., 198, 2107 (1934). RECEIVED September 30, 1948. Presented before the 13th Unit Prooesses Symposium of the Division of Industrial and Engineering Chemistry at the 114th Meeting of the AMERICAN CHEMICAL SOCIETY,St. Louis, Ma.
Nitration of Nitro-p-xylene KENNETH A. KOBE AND T. BROCKETT HUDSON University of Texas, Austin, Tex.
Nitro-p-xylene is easily nitrated to dinitro-p-xylene i n 95% yield in 15 minutes at a temperature of 80’ C., D.V.S. (dehydrating value of sulfuric acid) value of 8.0, and 10% excess nitric acid. The effect of these process variables is shown graphically. The orientation is anomalous, with 60 to 8070 of 2,3-dinitro and 40 to 20% 2,6-dinitro-p-xylene being formed.
P
REVIOUS work of Kobe and Levin (IO)in which a small amount of dinitro-p-xylene was produced indicated that
PREVIOUS WORK
Dinitro aromatic hydrocarbon may be made in either one or two steps (4,7), but it is more common to carry out the nitration in separate steps to reduce oxidation and also reduce the solubility of the product in the strong acid required for the one step process. For the nitration of nitro-p-xylene it would be expected that the mixed acid would be less concentrated than for the dinitration of toluene, but more concentrated than for the mononitration of p-xylene. Likewise, the temperature of nitration should be lower than for dinitration of toluene but higher than that used for the mononitration of p-xylene.
Most of the work previously reported on the dinitro compounds has been incidental to the nitration of p-xylene. Glinzer and Fittig (6) heated mononitro-p-xylene and fuming nitric acid to produce a solid mixture of dinitro compounds from which two compounds were separated, one melting a t 123.5’ and the other a t 93 C. Jannasch (8), Jannasch and Stunkel ( 9 ) ,and Choufoer ( 2 )all reported the preparation of dinitro-p-xylene and the formation of only these two isomers. However, in 1885, Lellmann (11) reported the three isomeric dinitro compounds, the 2,3- melting a t 93”, the2,6-meltingat 124”]andthe2,5-meltingat 147’to 148OC. His nitration method was to mix 25 grams of p-xylene and 100 grams of nitric acid (density] 1.51) and allow them to stand for several days. From 100 grams of solid product he separated only 2 grams of the 2,5-dinitro-p-xylene. Giua (6) nitrated p-xylene with mixed acid and found only the 2,3- and 2,6-isomers. None of these investigators reported any data on yields and gave little d a t a on the operating conditions.
SITRATOR. The nitration was carried out in a 1-liter flask having 3 necks (Figure 1). Through the central neck passed a stainless-steel propeller-type stirrer which turned in such a direction as to force the liquid downward. I t turned at 1725 r.p.m. The mixed acid was added through a thistle tube entering through a side neck. The acid discharged about 0.125 inch above the propeller so that it was mixed instantaneously with the reaction mixture. A thermometer entering through the other side neck was immersed in the nitration mixture near the propeller. The flask rested in a cradle made of 6 turns of 0.25-inch copper tubing spaced about 0.5 inch apart. The coil of tubing was placed in a round steel container] approximately 4 X 6 inches in diameter. The small amount of free space in the container was filled with water. The coil was so connected that either steam or water or both could be passed through the coil, giving a bath
approximately 75% was the 2,3- and 25% was the 2,6-dinitro-pxylene. This orientation is not that which would be predicted, hence it was decided to investigate the nitration of 2-nitro-pxylene to determine the optimum conditions for producing the dinitro compound and the effects of the process variables on the orientation.
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APPARATUS AND MATERIALS
