1398
T
U
0
v
x
INDUSTRIAL AND ENGINEERING CHEMISTRY
temperature, R. internal energy, B.t.u. per mole velocity, feet per second specific volume, cu. feet per pound = ratio of ZAP,t o 2Ap3
(4)
Vol. 44, No. 6
Lewis, B., and von Elbe, G., J . Chem. Phys., 11,75 (1943). Lichty, L. C., "Thermodynamics," pp. 303, 324, 326, 331, New York, McGraw-Hill B o o k Co., 1948. Smith, F. A . , and Pickering, 9. F., J . Research Natl. Bur. Stand-
ards, 17, 7 (1936). ( 5 ) von Elbe, G., and Mentser, J., J . Chem. Phys., 13,89 (1945).
REFERENCES (1)
Lewis, B., and von Elbe, G., "Combustion, Flames, and Explosions of Gases," pp. 238-41, New Y o r k , Academic Press, 1951.
RECEIVED for review May 22, 1961. ACCEPTED January 4, 1952. Presented before the Division of Petroleum Chemistry, Symposium on Combustion Chemistry, a t the 120th Meeting of t h e AXERICANCHEMICAL SOCIETY, Cleveland, Ohio.
ononitrati n of 0-Xvl d KENNETH A. KOBE AND PHILIP W. PRITCHETT University of Texas, Austin, Tex.
URING World War I1 considerable quantities of mixed xylenes were nitrated and reduced t o xylidines to increase the octane rating of aviation grade gasoline (3,16, 18). The increased production of xylenes by the hydroforming process used by the petroleum industry and new separation processes that permit the isolation of the individual hydrocarbons in a relatively pure form have aroused interest in the pure nitroxylenes. Of further interest is the effect of the position of the methyl groups on the relative ease of nitration and orientation of the entering nitro group. PREVIOUS WORK
Jacobson ( 1 4 ) was the first t o nitrate o-xylene by dropping it into ten times its weight of cold fuming nitric acid. He reported only the 4-nitro-o-xylene. Nolting and Forel ( 1 7 ) were the first to use sulfuric-nitric acid mixtures. They reported an SO% yield consisting primarily of the 3-nitro isomer. Later workers (5, 8) used different amounts of acid and reported various yields and ratios of isomers (Table I). Adams et al. ( 1 ) reported processes operated by the I. G. Farbenindustrie for the nitration of o-xylene a t Leverkusen and a t Griesheim. At Leverkusen, 1 part of o-xylene was mixed with 5.95 parts of mixed acid composed of 9% to 10%nitric acid, 68% 40 70% sulfuric acid, and 20% t o 23% water. The temperature wasincreasedfrom 15" t o 35" C. during the 3 to 4 hours required for the nitration. The yieldof crude nitro-o-xylene was 85y0to 90%. At Griesheim 1 part of o-xylene was diluted with 0.78 part of an inert hydrocarbon solvent and then were added 2.05 parts of mixed acid composed of 28% nitric acid, 58% sulfuric acid, and 14% water. The temperature was maintained at 0" t o 5 " C. during the 4 5 hours required for the addition of the acid, but $.was allowed t o rise t o 10" t o 15" C . during the 1 hour of additional agitation. The yield of crude product was T3.2%, but of the purified nitroo-xylene was 62.3%. The purified compound was separated by distillation into 3-nitro and 4-nitro isomers in a ratio of 55 to 45. The general patents in the field by Batchelder et al. ( 2 ) and Castner ( 4 ) have been reviewed by Kobe and Levin (16). The data of all investigators are summarized in Table I.
Kobe and Levin (15) studied the effect of the process variablcs on the yields of mononitro-p-xylene. A maximum yield of 90% was obtained a t 30" C., 2.4 moles of sulfuric acid per mole of p xylene, initial sulfuric acid concentration of 79.670, 111% theoretical nitric acid, and 30 minutes for the addition of the mixed acids. These workers, how!ver, used the dehydrating value of the sulfuric acid (D.V.S.) as a process variable, rather than the amount and concentration of sulfuric acid. The importance of these two separate items as process variables was pointed out by Haun and Kobe (13) in their work on the mononitration of cumene. They formulated two new process variables: the ratio of sulfuric acid to hydrocarbon and the initial concentration of the sulfuric acid, H2S04/(H2S04 H,O),on a nitric acid-free basis. I t is one of the purposes of this work to test and extmd the use of these variables to the nitration of o-xylene.
+
APPARATUS AYD MATERIALS
The nitrator was that used by Kobe and Levin (16)for pxylene. The rate of stirring %-asincreased from 1400 to 4000 r.p.m The steam-distillation apparatus for the separation of the mononitro-o-xylene was t h a t used by Haun and Kobe (15). The o-xylene used in most of this work was obtained from the Oronite Chemical Co. and had a nominal purity of 90%. The impurities were largely aliphatic and naphthenic compounds boiling in the same 1O temperature range, so that separation by fractional distillation was impossible A fractional crystallization operation was carried out in which 75% of the initial charge was crystallized and the final 26% rejected as containing most of the impurities. This material was considered to be 95% pure o-xylene. The refractive index a t 20" C. of the 90% commercial material was 1.49662, of the purified material 1.49973, and the h'ational Bureau of Standards pure o-xylene 1.50524 (10). Two nitrations (runs 29 and 30) were carried out on 99 mole % pure o-xylene obtained from the Phillips Petroleum Co. The sulfuric and nitric acids were analytical grade acids. The acid content was determined by chemical analysis. ,METHOB O F NITRATION
A nitrator acid and a mixed acid were prepared for each nitration using the proper mixture of sulfuric acid, nitric acid, and water. The nitrator acid consisted of 60% of the total sulfuric acid used plus sufficient water to give the desired initial R YPREVIOUS WORK TABLE I. S U M ~ I A OF acid concentration. The mixed G. H&01 acid consisted of 40% of the Ratio of Isomers Temp., per G. Concn. of "01, Yield, total sulfuric acid, all of the 3-nitro 4-nitro C. +Xylene HzSO4, % Theo. % Theo. % Investigator nitric acid, and sufficient water a 80.0 83.3 1.96 108 0 Nolting and Forel ( 1 7 ) 11 to make the concentration of 61.8 1.94 ... 0 Crossley and Renouf (6) 8 : 85.6 s3:2 112 1.94 -10toO Emerson and Smith (8) the sulfuric acid on a nitric 4 1 . 4 83.2 112 -10toO 1.94 Farmer and Sutton (9) acid-free basis the same as the 87.9 78.4 110 43.3 2.17 Batohelder et al. ( 2 ) . . . . 85 to 90 100 7 5 . 8 4.87 15 to 35 Leverkusen plant ( I ) concentration of the nitrator crude mix acid. Particular care was taken 55 45 7 2 . 3 crude 97 1,lQ 80.6 0 to 15 Griesheim plant (1) 6 2 . 3 purified t o measure the water to the 5 Investigator reported only this isomer. nearest 0.1 gram and acids t o 0.5 gram or less. O
INDUSTRIAL AND ENGINEERING CHEMISTRY
June 1952
I n all nitrations (except Nos. 29 and 30) 170 grams of purified o-xylene was added t o the nitrator. The cooled nitrator acid was added from the dispensing buret with stirring and cooling t o keep the temperature about 5" C. below the nominal temperature of nitration. Following this, t h e mixed acid was added at the desired rate t o give a n addition time of 60 minutes. An additional 15 minutes of agitation and temperature control was allowed t o ensure completion of the reaction. On addition of the mixed acid the temperature rose rapidly and within 1or 2 minutes reached the operating temperature, which was maintained within limits of 1" C. At the same time the hydrocarbon and acids layers became emulsified. The difficulties reported by Doumani and Kobe ( 7 )for p-cymene were not encountered here.
1399
and rate of stirring are important process variables. The rate of stirring was maintained constant at 4000 r.p.m. t o obtain the best possible emulsification of reactants. The amount of sulfuric acid initially in the nitrator may vary from none, in which case all is in the mixed acid, t o all, in which case only nitric acid is added during the nitration. Preliminary nitrations made using no sulfuric acid or 60% of the sulfuric acid in the nitrator gave yields t h a t were essentially the same. However, with 60% of the sulfuric acid in t h e nitrator there was no induction period in starting the reaction and temperature control was easier and more accurate; hence this amount was used in all other nitrations. The concentration of t h e sulfuric acid (nitric acid-free basis) was the same in both nitrator and mixed acids. The data for all nitrations other than the preliminary ones are given in Table 11. IO0
+ 150
200
250 300 350 400 450 TOTAL SULFURIC ACID I N GRAMS
500
6 90 V (L
w
a
Figure 1. Effect of Amount of Sulfuric Acid on Nitration of o-Xylene 170 grams of o-xylene, 25" C., 80.4% sulfuric acid, 15.7% excess nitric acid, @-minute addition time
A t the conclusion of the total time allowed, the stirring and cooling were stopped and the contents of t h e nitrator were drained into a 2-liter beaker containing 350 grams of chipped ice. The emulsion broke immediately. The mixture was placed in a separatory funnel, the bottom acid layer removed, and the upper organic layer placed in a 5-liter flask for steam distillation ( I S ) . The organic phase lighter than water was considered unreacted o-xylene and the phase heavier than water was taken as mononitro-o-xylene. Each was dried over Drierite, filtered, and weighed. PROCESS VARIABLES
Z -
80
0
>
70
fin "V
74
76
78
80
82
84
SULFURIC ACID CONCENTRATION I N PERCENT
Figure 2.
Effect of Acid Concentration on Nitration of o-Xylene
170 grams of o-xylene with 347.3 grams of sulfuric acid and 15.8% excess nitric aoid added in 60 minutes at 6 O , 2 5 O , and 35' C.
SULFURIC ACID. The ratio of sulfuric acid t o hydrocarbon was investigated t o determine the minimum amount t h a t would give Nitration with mixed acid involves four chemicals (aromatic hyessentially complete reaction. The results are shown in Figure 1, drocarbon, sulfuric acid, nitric acid, and water), so that their relative amounts can be expressed as three ratios. The concentration An increase in t h e amount of sulfuric acid increases the yield of the nitric acid in the nitrator is never high unless a large excess of mononitro-0-xylene until 300 grams of sulfuric acid are used. of nitric acid is used; hence the acidity may be expressed in terms of the sulfuric acid concentration on a nitric acid-free TABLE11. SUXMARIZED DATA AND RESULTSFOR NITRATIONOF 170 GRAMSOF basis. The concentration c o n s i d e r e d 95% 0-XYLENE may be the initial concentration of the Yield of MononiHzSOI Reaction Time, Min. - tro-o-xylene Run HzSOI, Concn., acid added t o the nitrator, the acid reNo. G. % % ', "Os, Theory T."?.' Add. Total Grams % maining in the nitrator a t the end of the 496.3 115.8 25 60 75 206.3 89.7 2 80.4 reaction, or any value between these two. 75 198.8 3 80.4 248.1 115.8 25 60 86.4 75 205.6 60 4 80.4 347.3 115 8 25 89.4 The use of final concentration is em75 60 185.5 5 80.4 198.5 115.8 25 80.7 6 60 90 204.0 80.4 347.3 115.8 25 88.7 bodied in the dehydrating value of sul60 75 204.7 80.4 115.8 25 7 297.7 89.0 furic acid ( I d ) . This is calculated on 60 75 164.9 74.4 347 I3 115.8 25 71.7 8 75 9 60 193.9 84.4 347.3 115.8 25 84.3 the basis of a theoretical yield of the de75 204.4 10 60 78.4 347.3 115.8 25 88.9 60 11 75 201.8 82.4 347.3 115.8 25 87.7 sired nitro compound, though the amount 60 75 204.6 79.4 347.3 115.8 25 12 89.0 of water produced depends on the actual 75 203.4 35 13 60 88.4 79.4 347.3 115.8 75 204.5 79.4 115.8 15 60 14 88.9 347.3 degree of completion of the reaction and 60 75 15 179.8 78.2 84.4 347.3 115.8 35 206.9 115.8 60 75 16 90.0 79.4 347.3 25 the nature and extent of the side reac207.3 79.4 115.8 30 40 17 90.1 347.3 25 tions. The initial concentration of sul105 205.1 89.2 116.8 25 18 90 79.4 347.3 79.4 199.5 105.3 19 60 75 86.7 347.3 25 furic acid is chosen as the process vari203.2 6 60 75 79.4 88.3 347.3 115.8 20 60 75 79.4 198.0 86.1 115.8 able in this work, as in previous work( IS). 42 347.3 21 183.9 94.7 60 26 75 79.4 80.0 347.3 22 The ratio of sulfuric acid t o hydrocar75 204.6 89.0 60 126.3 26 79.4 347.3 23 115.8 35 75 74.4 173.1 7 5.3 60 24 347.3 bon is a second process variable, being 6 196.6 60 116.8 75 84.4 85.5 347.3 25 25 15 115.8 18 79.4 206.1 89.6 expressed as the weight of sulfuric acid 26 347.3 6 115.8 154.8 60 75 74.4 63.7 347.3 27 required for 170 grams of o-xylene. The 25 115.8 75 206.5 60 79.4 89.8 347.3 28 60 25 110.0 75 79.4 218.2 90.1 29a 347.3 amount of nitric acid, expressed as the 60 25 117.0 75 79.4 203.3 89.3 306 347.3 percentage of the stoichiometric amount, 0 170 grams of 99% o-xylene used. is a third variable. Temperature, time b 159.8 gram8 of 99% o-xylene used. required for addition of the mixed acid,
'
1400
INDUSTRIAL AND ENGINEERING CHEMISTRY 100
nitration temperature near the end of the nitration. The nitric acid-sulfuric acid-water diagram of Gillespie and Millen ( 1 1 , I S ) shows the concentration of nitryl ion must be rather low, even below the spectroscopic limit of detectability, a t the optimum conditions for nitration of 0-xylene. I t thus appears that the nitryl ion concentration need not be high, so long as it is replenished rapidly.
I-
5
90
W
a
z
Vol. 44, No. 6
80
a 70
100
I l l
t
60
6
IO
Figure 3.
15
20 25 30 35 REACTION TEMPERATURE I N ' C
42
Effect of Temperature o n Nitration of o-Xylene
170 grams of o-xylene with 347.3 grams of sulfuric acid and 15.8 % excess nitric acid added i n 60 minutes
70
Beyond this amount the rate of increase of yield drops off markedly and beyond 350 grams there is no appreciable increase. For the remainder of the nitrations 347.3 grams of 97% sulfuric acid were used (actual concentration later shown to be 96.34%). ACID CONCENTRATION. The acid concentration was varied from 74.4 to 84.4%, when a constant amount of sulfuric acid was used. The results are shown in Figure 2. A maximum yield of 90.0% was obtained with 79.4% acid a t 25" C. Holding all other variables constant, nitraTEVPERATURE. tions were made a t temperatures from 6" to 42" C. Because temperature and sulfuric acid concentration are important interrelated variables, nitrations were made at three temperatures (6", 2 j 0 , and 35" C.) with three sulfuric acid concentrations (74.4, 79.4, and 84.4%). Results are presented in Figure 2 to show the effect of concentration' and in Figure 3 t o show the effect of temperature.
74
76
76
60
02
64
90
100
110
120
130
NITRIC ACID I N PERCENT O F THEORETICAL
Figure 5.
Effect of Amount of Kitric .4cid on Yield
Nitration of 170 grams of o-xylene with 347.3 grams of sulfuric acid a t 80.4 A concentration, 25' C., and 60-minute addition t i m e
EXCESS NITRICilcrn. The amount of nitric acid used was varied over the range of 94.7 to 126.3% of that stoichiometrically required for the mononitration of the o-xylene used. Figure 5 shows a maximum yield of 90% a t 16% excess nitric acid. Two nitrations %-eremade with 99 mole % of o-xylene to ascertain the effect of purity on the nitration. With the purified commercial oxylene some unreacted material was always recovered, which amounted to 5.9 i 0.67, of the initial charge for those nitrations which gave high yields. Sulfonation by the method of Patterson et al. ( 1 9 ) shomed a residue of 5.1%. Graphical comparison of the yields of mononitro-o-xylene from the 99% pure hydrocarbon and the purified commercial material showed that the latter contained not more than 95% o-xylene, and this value was used in calculating percentage yields for all nitrations in which this material was used. The agreement between the corrected yields and those for the 99% o-xylene is shown in Figure 5 .
86
SULFURIC ACID CONCENTRATION I N PERCENT
Figure 4. Effect of Temperature and Sulfuric Acid Concentration on Yield 170 grams of o-xylene with 347.3 grams of sulfuric acid with 15.8% excess nitric acid added i n 60 minutes
The data of Figures 2 and 3 are presented in a new form that shows simultaneously the effect of concentration and temperature on the yield. This is done by making a cross plot in which the yield is used as the parameter and contours of constant yield are plotted (Figure 4). Figure 4 shows that neither the temperature nor the sulfuric acid concentration is as important as the proper interrelation of these variables. Within limits, either the temperature or sulfuric acid concentration may be fixed arbitrarily and a satisfactory yield obtained by proper adjustment of the other variable. The generally negative slope of t h e yield contours indicates that a more dilute sulfuric acid concentration is suitable a t higher temperatures. This is the basis for industrial practice of raising the
0
30
60
90
ADDITION TIME I N MINUTES
Figure 6 .
Effect of Time of Addition of Mixed Acid on Yield
Nitration of 170 grams of o-xylene with 347.3 grams of sulfuric acid at 80.4 % concentration, 15.8vo excess nitric acid a t 25' C.
TIMEOF ADDITION. The time required for the addition of the mixed acid was varied from 15 to 90 minutes, with roughly proportional total times. Figure 6 shows that the maximum yield of 90.1% is obtained with an addition time of 30 minutes and a total time of 40 minutes.
1401
INDUSTRIAL AND ENGINEERING CHEMISTRY
June 1952
’
SUMMARY
OF STEAM-DISTILLED NITROXYLENES TABLE 111. COMPOSITION o-Xylene has been nitrated with a yield of 90% mononitro-+ DETERMINED BY VACUUM DISTILLATION xylenes using the following conditions:
Volume yo 1.2 45.6 17.0 33.6 1.4 1.2 100.0
Light ends 3-Nitro-o-xylene Mixed isomers 4-Nitro-o-xylene Residue
-
Losses
(45.6) 3-Nitro-o-xylene = 45.6 4-Nitro-o-xylene = (33.6) 45.6
(100) 33.6 57‘6% (100) = 42.4% 33.6
+ +
PROPERTIES OF NITRO-0-XYLENES TABLE IV. PHYSICAL Property
3-Nitro-o-xylene
Densit g./ml. 31° 15” C. 30’ C,. Refractive index, nn 200 c. 25’ C. Boiling point, C. 760 mm.
8:
758.2 mm. 569 mm. 91 .Omm. 29 mm. 21 mm. Melting point,
1,1274 1.146 (f7)
..
1.5436 1.5416 248.3 240 ( 6 ) 247.6
....
172.5 136 ( 6 )
4-Nitro-o-xylene 1.1286
1 , iik’ (14)
....
1.5543 264.1 254 252.0
....
C.
The precision of the data was determined from nitrations conducted under identical conditions. Runs 16 and 28 give yields agreeing within 0.2%, but run 12, because of poor control, agreed within 1%. It is believed that the results are reproducible within 1%, but possibly greater variation is found under conditions giving low yields. REACTION BY-PRODUCTS
From each nitration a black, tarry residue remained in the steam distillation flask. From run 30 this amounted t o 12.2 grams. At 100’ C. the residue was a viscous liquid and a t room temperature it was a sticky, semisolid amorphous mass. Attempts t o crystallize dinitro compounds from this residue dissolved in several solvents were unsuccessful. SEPARATION OF ISOMERS
The mononitro compound from runs 2, 4, and 6 was combined and a 500-ml. sample was distilled at 88 mm. of mercury for 6.5 hours. The residue from the distillation was steam-distilled, giving 7 ml. of black, tarry residue much like that remaining from previous steam distillations. A distillation curve was prepared and the significant points were taken from it. The amounts of the various components are given in Table 111. The orientation was determined from the amounts of isomers separated. The amount of mixed isomers is rather large (17.0%), but even if t h e amounts of isomers in it were equal, its separation would make a difference of only 1.2% in the orientation reported. The orientation reported here is in substantial agreement with German industry as reported by Adams et al. ( 1 )and at variance with reports of previous workers (6,8,9). A center cut of product from the distillation of each isomer was redistilled under vacuum with a rejection of initial and final fractions. The physical properties of t h e purified materials were determined and are given in Table IV in comparison with other valdes reported in the literature. Crossley and Wren (6) prepared 3-nitro-o-xylene free from the 4-isomer by the conversion of 3nitro-o-xylidine. The pure compound melted sharply at 15’ C. They prepared a melting point curve for small amounts of the 4isomer in 3-nitro-o-xylene.
Sulfuric acid-o-xylene weight ratio Concentration of sulfuric acid, % Nitric acid-p-xylene mole ratio Temperature, C. Nitration time, minutes
2.15 79.4 1.16 25 30
The effect of changing these process variables on the yield is shown graphically. A new method of plotting contours of equal yields shows the interrelationship of sulfuric acid concentration and temperature; with more dilute acid higher temperatures can be used t o Becure equal yields. The orientation is found t o be 58% 3-nitro- and 42% 4-nitroo-xylene. LITERATURE CITED
Adams, D. A. W., Harrington, T., and Livingstone, A. Y . , I. G. Farbenindustrie, “Separation of o-, m-, and p-Xylene and Manufacture of Derived Nitroxylenes and Xylidines,” British Intelligence Objectives Sub-committee, F i n a l Rept. 1146. Batchelder, G. W., Nagle, W. M., Vyverberg, J. C., and Willis, J. M., U. S. Patent 2,400,904 (May 28, 1946). Brown, C. L., Smith, W. M., and Scharman, W. G., IND. ENQ.CHEM..40. 1538-42 (1948). Castner, J. B.,.’U. S. Patent 2,385,‘128(Sept. 18, 1945), 2,438,204 (March 23, 1948). Crossley, A. W., and Renouf, N., J . Chem. Soc., 95, 202-18 (1909). Crossley, A. W., and Wren, G. H., Ibid., 99,2341-5 (1911). Doumani, T. F., and Kobe, X. A , , IND. ENG.CHEM.,31, 257-63 (1939). Emerson, 0. H., and Smith, L. I., J. Am. Chem. Soc., 62, 141-2 (1940). Farmer, E. H., and Sutton, D. A., J . Chem. Soc., 1946, 10-13. Forziati, A. F., Glascow, A. B., Jr., and Willingham, C. B., J . Research Natl. B u r . Standards, 36, 129-36 (1946). Gillespie, R. J., and Millen, D. J., Quart. Rev. ( L o n d o n ) , 2, 277306 (1048). Groggins, P. H., editor-in-chief, “Unit Processes in Organic Synthesis,” 3rd ed., pp. 25, 66-71, New York, McGraw-Hill Book Co., 1947. Haun, J. W., and Kobe, K. A,, IND.ENQ.CHEM.,43, 2355-62 (1951). Jacobson, Oscar, Ber., 17, 159-62 (1884). Kobe. K. A,. and Levin. H.. IND. ENG.CHEM..42.352-6 (1950). Kuno, J. F.. Jr., Howell, W. C., Jr., and Star;, C: E., Jr.; Ibid., 40,1530-8 (1949). Nolting, E., and Forel, S., Ber., 18, 2668-81 (1885). Okie, J. P., and Roberts, L. M., Chem. Eng., 55, No. 10, 124-6 (1948). Patterson, T. S., McMillan, A., and Somerville, R., J . Chem. SOC.,125, 2488-90 (1924). RECEIVED for review July 16, 1951. ACCEPTED January 25, 1952. Presented before the Division of Industrial and Engineering Chemistry, Sixteenth Unit Process Symposium, a t the 120th Meeting of t h e AMEHICAN CHEMICAL SOCIETY, New York, N. Y.
Corrections I n the article on “Maturing and Bleaching Agents Used in Producing Flour” [IND.ENG.CHEM.,44, 95 (1952)l caption B of Figure 7 should have read “nitrogen trichloride” instead of “nitrogen dioxide.” I n the acknowledgment on page 100 t h e first name mentioned should have been G. C. Thomas. C. G. HARREL
. . .. . , .
In the paper “Soiling and Soil Retention in Textile Fibers. Cotton Fiber-Grease-Free Carbon Black Systems” [Compton, Jack, and Hart, W. J., IND.ENG.CHEM.,43, 1564-9 (1951)], the average particle sizes of the carbon blacks were erroneously stated t o be in microns instead of the correct units, millimicrons. JACKCOMFTON
