Dec., 1958
THERMAL REACTIONS OF 1-METHYLPYRROLE
to permit more reproducible activity measurements, and equilibrium catalysts that have been in actual use in a catalytic cracking unit. Because these catalysts have been subjected to different heat and moisture treatment, with resulting changes in their physical and chemical properties, the proportion of aluminum that reacts with fluoride should vary. The correlation shown by the line for steamed catalysts, Fig. 4, represents only the relationship between reactive alumina content and IRA for catalysts deactivated by the steaming technique used in these studies. To obtain a correlation for other than fresh and steamed catalysts, other variables such as pore dimensions and methods of manufacture must be considered. These factors are being studied.
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The ability of the reaction to measure the catalytically active aluminosilicate content of a catalyst becomes a liability in steamed or other deactivated catalysts, probably because not all the aluminosilicate contributes to activity. A milder reaction, which would not break down the catalyst structure and would measure only the aluminosilicate on the catalyst surface, should provide a more satisfactory correlation for deactivated catalysts. The reaction of sodium fluoride with natural cracking catalysts proceeds in a different manner from that with synthetic catalyst, and no correlation of reactive alumina with activity has been observed. Acknowledgment.-The assistance of J. W. Harlan is gratefully acknowledged.
THERMAL REACTIONS OF ORGANIC NITROGEN COMPOUNDS. I. 1-METHYLPYRROLE BYI. A. JACOBSON, JR.,H. H. H E A D YAND ~ G. U. DINNEEN Petroleum and Oil-Shale Experiment Station, Bureau of Mines, Laramie, Wgoming Received June 86,1968
The thermal reactions of 1-methylpyrrole were investigated by the flow method over the temperature range of 475 to 700". I n the temperature interval of 475 to 575' the reaction was found to be a homogeneous first-order isomerizatjon that may be represented as shown: 1-methylpyrrole + 2-methylpyrrole e 3-methylpyrrole. The Arrhenlus equation for this reaction, based on the disappearance of I-methylpyrrole, is IC = (2.39 & 0.11) x 1 0 % - ( 6 4 ~ 8 0 ~ * Above 575" there was decomposition to give a complex mixture of reaction products.
This investigation was part of a general study relating t o the nitrogen compounds in Colorado shale oil. About half the compounds in Colorado shale oil contain nitrogen, and the majority are thought to be of the pyridine and pyrrole types. The present study was designed to obtain information that will be useful for correlating the structure of the organic matter in oil shale with the compounds found in retorted shale oil. A limited amount of work has been reported on the pyrolysis of organic nitrogen compounds. Most of this was done over 50 years ago and dealt with 1-substituted pyrroles. Ciamician and Magnaghi2 reported the partial conversion of l-acetylpyrrole to a carbon substituted pyrrole when it was heated in a closed tube at 250 to 280". Liter data3 indicated that migration of the acetyl group had been to the 2-position. Similar rearrangements were reported for 1-phenyl- and l-pyridylpyrrole. The most extensive study of pyrroles was inade by Pictet5 who found that when 1-methylpyrrole was distilled through a dull-glowing combustion tube, the products were 2-methylpyrrole and pyridine. A clean reaction and a yield of about 10% pyridine were reported. When 2-methylpyrrole was the starting material, about 20y0 pyridine mas formed. 3-Phenylpyridine was formed when 1beiizylpyrrole was treated in the same manner. (1) Chemist, Bureau of Mines, Region 11, Reno, Nevada. (2) G. Ciamician and P. Magnaghi, Ber.. 18, 1828 (1885). (3) G.Ciamician and P. Silber, ibid., 20, 698 (1887). (4) P. Cresuieux and A. Pictet. ibid.,28, 1904 (1895). (5) A. Pictet, ibid., SI, 2979 (1904); 38, 1947 (1905).
Pictet continued his work to include indoles and carbazoles. Recently reported studies6 have verified the isomerization of 1-methylpyrrole. Kinetic studies have not been reported for pyrroles. Most of the kinetic work on nitrogen compounds has been limited to oxides of nitrogen, simple amines, nitromethane and some azo compounds. Hillenbrand and Kilpatrick' showed that for the decomposition of nitromethane the flow method gave kinetic results comparable to the static method. Experimental Material.-1-Methylpyrrole was synthesized by treating sodiopyrrole, made from pyrrole and sodamide in liquid ammonia, with methyl iodide8 and was purified by distillation, refluxing with calcium hydride and redistillation. The treated material had a purity of 99.9 mole % as determined by the freezing point method. Small quantities of 2- and 3-methylpyrrole were furnished by American Petroleum Institute Research Project 52. These samples were synthesized a t the University of Kansas and had a purity of 98 mole % as estimated by an examination of infrared and mass spectral data. The pyrroles were kept either in ampoules under vacuum, or in bottles under a nitrogen atmosphere. Apparatus.-The equipment employed for this study was similar to that of Thompson, et al.9 The reaction tube was quartz, 18.5 mni. i.d., and 91.5 cm. long, with t~ heated length of about 60 cm. A stainless-steel liner was used inside the furnace as a heat distributor. Sample introduction into the furnace was by means of a Monodrum unit and hypodermic syringe. By selecting appropriate syringe s (6) W. Reppe. Ann., 596,80 (1955). (7)T . L. Hillenbrand and M. L. Kilpatrick, J . Cham. Phys., 21, 525 (1953). (8) N. D.Scott, U. S. Patent 2,488,336(November 15, 1949). (9) C . J. Thompson, R . A. Meyer and .J. S. Ball, J . A m . Chem. Soc., 74, 3284 (1952).
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I. A. JACOBSON, JR., H. H. HEADYAND G. U. DINNEEN
I .5
I
I
I
0 RESULTS WITH H E L I U M
b
0 RESULTS WITHOUT HELIUM
I.o
.
" 0
u
Vol. 62
A temperature rofile of the reaction tube was determined by means o f a thermocouple (down the center of the reaction tube) and a potentiometer. Temperature measurements were made at 2.5 cm. intervals throughout the length of the heated zone with a sweep of helium through the reactor. The calibrating thermocouple was removed from the reactor before the runs. It was found that 49 f 1.5 cm. of the reactor length was a t the desired run temperature. Procedure:-Before each run, the system was alternately evacuated and filled with helium to flush out the air. Flushing in this manner was repeated at the end of the run to ensure a complete collection of the products. The majority of the thermal runs were made using helium as a diluent. For most of the runs, the reaction products were collected in about 20 ml. of solvent. For the other runs, the products were collected by freezing in liquid nitrogen. The nitrogen content of the products was determined by a macro Kjeldahl procedure.10 The relative quantities of the three isomeric pyrroles were determined from infrared spectra of the products using carbon tetrachloride or 2,2,4trimethylpentane as solvent. The analytical wave lengths used were: 15.10 p for 1-methylpyrrole, 9.75 p for %methylpyrrole, and 9.38 p for 3-methylpyrrole. These corresponded to absorption peaks for the three compounds. Quantitative calculations were accomplished with simultaneous equations.
Results Runs were made a t 25" intervals in the temperature range of 475 to 575". Several residence times were used at each tedperature. Table I is a comTABLE I ISOMERIZATION OF ~-METHYLPYRROLE L
Fig. 1.-Isomerization -3.0I
-9.0L-_ .-i .
I
-.
T-'X
Fig. 2.-Effect
of 1-methylpyrrole.
I
f
1 . I-----
I03,.':KO
of temperature on the rate constant for the isomerization of 1-methylpyrrole.
and speeds, the unit provided delivery rates from about 0.01 to 15.0 ml./min. Both the inlet and outlet of the reactor were wound with heating tape and maintained at about 150'.
Temp., QC.
Flow .rate ml./s&.
Av.. residence time, sec.
Concn. of pyrroles in products, 1Methylpyrrole
wt.
7%
9-
Methylpyrrole
3Methylpyrrole
95.1 4.9 0.8163 153.6 97.1 2.9 1.5521 80.8 91.9 8.1 500 0.8566 152.6 94.1 1.6231 5.9 80.5 96.6 3.4 2.5561 51.1 2.1 72.8 25.1 525 0.8857 146.6 1.1 82.9 1.4284 16.0 90.9 0.4 91.6 3.5177 8.0 36.9 0.2 3.0 96.8 8.9576 14.5 1:3 22.5 0.8454 153.5" 76.2 1.0 11.3 87.7 2.1880 59.3" 0.1 92.0 7.9 3.5493 36.6" 0.1 4.2 9.1405 14.2O 95.7 10.2 56.0 550 0.8939 144.7 33.8 5.7 42.2 52.1 1.4745 87.7 1.7 19.3 79.0 4.9739 26.0 1.1 12.0 9.4763 13.7 86.8 9.7 0.8731 55.1 148.2" 35.2 2.1 17.4 5.7639 22.4" 80.5 6.3 42.2 575 5.0499 25.8 51.5 3.2 9.5110 69.0 27.8 13.7 13.1 61.9 2.3363 25.0 55.7" 8.2 3.7219 43.7 48.1 35. 0" a Results obtained without the use of helium as a diluent. 475
pilation of the data obtained from these runs. The analytical results were obtained by infrared analysis of the products and have been normalized t o 100%. This normalization was considered valid because the nitrogen recovery, as determined by the macro Kjeldahl method, was between 98 and 102 weight yofor all runs. (IO) G. R. Lake, P. McCuhhan, R. Van Meter and J. C. Neel, AnaE. Chern., 23, 1634 (1951).
THERMAL REACTIONS OF 1-METHYLPYRROLE
Dec., 1958
The average residence times shown in Table 1 were calculated by dividing the total, effective volume of the reactor by the flow rate of gaseous material through the reactor, Effective volume of the end eIements of the reactor was determined by the method of Hillenbrand and Kilpatrick' and was added to the volume of the reactor at run temperature t o give the total, effective volume of the reactor which was 129 f 4 ml. When helium was used as a diluent it made up 35 to 60 volume % of the material flowing through the reactor. As can be seen from Table I, the presence or absence of helium did not affect the composition of the reaction products. For example, the composition of products at 525" and residence times of 36.9 seconds without helium and 36.6 seconds with helium are the same within experimental error; hence, runs both with and without helium were used for the kinetic calculations. Kinetics of the isomerization of 1-methylpyrrole were determined for the temperature range of 475 t o 575". All calculations were based on the disappearance of 1-methylpyrrole. A plot of log change in concentration us. log concentration inditated a first-order reaction so the first-order rate equation was applied. The analytical data of Table I were used t o obtain the lines shown in Fig. 1. Ln(Co/C,) was plotted against residence time to evaluate k (Table 11) in the rate equation kt = In (Co/C.)
k = specific reaction rate constant
= residence time Co = initial concn. of 1-methylpyrrole C. = concn. of 1-methylpyrrole at time 1 t
With the origin as a fixed point the best straight line through the rest of the data was obtained by the least squares equation. l 1 The effect of temperature on the rate of the reaction is shown in the Arrhenius plot in Fig. 2. For the isomerization of 1-methylpyrrole the line .gives an activation energy of 54.8 f 0.1 kcal. per mole. The Arrhenius equation was evaluated to be k = (2.39 & 0.11) X 1012e-(%W * 100)IRT To determine whether isomerization of l-methylpyrrole was an equilibrium reaction, several runs were made a t 550 and 575" using 2-methylpyrrole as starting material. The only detectable products from these runs were the carbon substituted pyrroles. These results proved that the isomerization of 1-methylpyrrole was irreversible. Runs made at 550 and 575" using S-methylpyrrole as starting material had only the carbon substituted pyrroles as products. The results from (11) W. E. Roseveare, J . Am. Chem. Soc., 63, 1651 (1931).
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TABLE I1 SPECIFICREACTION RATESFOR ISOMERIZATION OF ~-METHYLPY RROLE Temp.,
Reaction rate X 104.
OC.
see. -1
475 500 525 550 575
2.87 f 0.38 6.53 f 0.32 1.0 21.1 77.2 f4.0 250 f4
*
the 2- and 3-methylpyrrole runs and the fact that 3-methylpyrrole did not appear in the products from 1-methylpyrrole until 525" (Table I) lead t o the postulation of the following over-all reaction route for the isomerization of l-methylpyrrole 1-methylpyrrole -+-2-methylpyrrole
IT3-methylpyrrole
Only small amounts of 2- and 3-methylpyrrole were available so only a limited study could bemade using these compounds as starting materials. Using the data obtained, approximate equilibrium constants for the reversible reaction 2-methylpyrrole t o 3-methylpyrrole a t 550 and 575" were calculated t o be 0.3 and 0.2, respectively. Several runs were made a t 575" with the reaction tube packed with quartz tubing. The pack. ing increased the area-to-volume ratio from 2.2 t o 5.5. The reaction constant was not increased by the packing, indicating- that the reaction was homogeneous. A series of runs was made in the 600 and 700" range. I n these runs, there was decomposition in addition t o isomerization. No gas was formed up through 575" but gas production became evident a t the higher temperatures, amounting, for example, t o one per cent. a t 100 seconds residence time at 625". The gas consisted mostly of methane and hydrogen with some ethane and ethylene. The liquid products from these runs were subjected to mass spectral analysis. The majority of the products were the methylpyrroles, but traces of pyrrole, dimethylpyrroles, indoles, benzene and pyridines also were present. Because of the decomposition of l-methylpyrrole above 575", first order calculations did not hold in this temperature range. Acknowledgment.-This project was part of the Oil-Shale Program of the Bureau of Mines and was performed a t the Petroleum and Oil-Shale Experiment Station, Laramie, Wyoming. Thanks are extended to G. L. Cook for aid in the spectroscopic determinations and t o API Research Project 52 for purification of the 1-methylpyrrole and purity determinations on it. The work was done under a coorjerative agreement between the Universit,y of Wyoming and the Bureau of Mines, U. S. Department of the Interior.
