July, 1962
THERMAL REACTIONS OF ORGANIC KITROGEN COMPOUNDS
1245
THERMAL REACTIONS OF ORGANIC NITROGEN COMPOUNDS. 11. 1-n-BUTYLPYRROLE BY I. A. JACOBSON, JR.,AND H. B. JENSEN Laramie Petroleum Research Center, Bureau of Mines, U.X. Department of the Interior, Laramie, Wyoming Recezved NovemFer 6, 1961
Thermal reactions of 1-n-butylpyrrole were investigated in the 460 to 570’ range by a flow method and in the 360 to 400” range by a static method. 1-n-Butylpyrrole isomerized to 2-n-butylpyrrole which then isomerized by a reversible reaction to 3-n-butylpyrrole. The Arrhenius equation for the isomerization of 1-n-butylpyrrole is Ici = 3.10 X 1013 e-57~900 * 1 ~ 0 0 ’ R T sec.-l. The 2- and 3-n-butylpyrroles decompose to form pyrrole, 2- and 3-methylpyrroles, 2- and 3-ethylpyrroles, 2- and 3vinylpyrrolea, pyridines, and hydrocarbons.
Introduction This paper is the second resulting from a continuing study of the thermal reactions of compounds occurring :in shale oi1.l About half of the compounds in Colorado shale oil contain nitrogen, and most of these are thought to be pyridine and pyrrole types. Only a 1:imited amount of the literature on thermal reactions of organic nitrogen compounds deals with pyrrolic compounds,*-7 with the majority of the pyrrole papers appearing more than 50 years ago. The only alkylpyrroles studied were methyl and ethyl substitut’ed. The first paper of this study of shale-oil compounds described the thermal reactions of 1-methylpyrrole. To obtain information on the thermal reactions of other alkylpyrroles, 1-n,-buty1p;yrrole was selected as a moderately long straight-chain alkylpyrrole. Experimental Material.---1-n-Butylpyrrole was synthesized by the thermal decomposition of the dibutylamine salt of mucic acid* and was purified by distillation, refluxing with calcium hydride, and redistillation. The final product had a purity of 99.5 mole %, as determined by the freening point method. To protect the purity of the material it was kept under either vacuum or a nitrogen atmosphere. Apparatus.-The experimental work was performed in a flow system and a static system. The equipment used for the flow studies was the same as that previously described . l For the static work the heating bath was a salt mixture with a melting point of 109”; it was composed of 40% sodium nitrite, 7% sodium nitrate, and 53y0 potassium nitrate. The bath wa,s heated by two electric heaters controlled so that the bath temperature was maintained within &5’ of the desired temperature. The reaction vessel was a 300-ml. round-bottom Pyrex flask. The flask had a neck 15 mm. 0.d. and 5 cin. long, which was sealed on the end. A side arm, 7 mm. o.d., was attached a t right angles to the neck of the flask. This sidearm ended in a “T,” and one arm of the “T” was sealed t o form a sample well 5 em. long. The other arin of the “T” was used to introduce the sample and to evacua,te the flask. Procedure.-Flow studies were performed using the general procedure previousty described.’ Flow runs were made between 460 and 570 ; several residence times were used a t each temperature studied. Most of the runs were made in the presence of a diluent gas (purified nitrogen) and in an unpacked reaction tube. Runs also were made -.
(1) I. A. Jacobson, Jr., H. H. Heady, and G. U. Dinneen, J . P h y s . Chsm., 62, 1b63 (1958). (2) .:C Ciamician and P. hlagnaghi, Bar., 18, 1828 (1885). (3) G. Ciamioian and P. Silber, ibid., 20, 698 (1887). (4) E’. Crespioux and A. Pictet, ibid., 28, 1904 (1896). ( 6 ) A. Piotet, i b i d . , 37,2979 (1904); 38, 1947 (1905). (6) A. G. Oosterhuis and J. P. Wibaut, REC.trav. chim., 66, 348 (1936).
(7) W. Reppo, Ann., 696, 80 (1955). (8) I,.C. Craig and R. M. H i x o n , J . Ana. Chem. Soc., 63, 187 (1931).
without the diluent gas, or in a packed reaction tube, or with added nitric oxide. For all flow runs the products were assed through a liquid nitrogen trap. The product that :id not condense was collected in an evacuated gas bulb. After the completion of a run the gaseous material that was condensed in the liquid nitrogen trap was collected in another evacuated gas bulb by raising the temperature of the frozen products to room temperature. The reaction vessel for the static work was flushed with purified nitrogen, and 0.5 g. of sample was introduced into the sample well from a hypodermic syringe. The sample then was degassed by the freeze-thaw technique, and the flask was evacuated and sealed. The flask containing the sample was immersed in the salt bath for a predetegmined time. Static runs were made between 360 and 400 , with several residence times used at each of the temperatures studied. Analysis.-For the flow work the following analytical techniques were used: (1) Unreacted 1%-butylpyrrole in the liquid product was determined by infrared spectroscopy. The spectra of the products in a benzene solution were run between 7.0 and 8.5 p: and the absorbance of the 7.9 p peak was determined. This peak is unique to 1-n-butyl yrrole in these reaction roducts. (2) Concentration o? other components in the [quid product was determined by gasliquid chromatography from the peak areas. Emergence times and sensitivities were determined for most of the components. (3) Composition of the gaseous hydrocarbons was determined by mass spectral analyses. The products from the static runs were analyzed only for unreacted I-n-butyl yrrole. The same infrared technique was used as for the &w work.
Results General.-Table I, a tabulation of the data from the flow runs, lists the nitrogen-compound distribution and hydrocarbon formation, The analytical results were normalized to 100% recovery. Residence times reported in Table I were calculated as follows: The effective volume of the end elements of the reactor was determined by the method of Hillenbrand and Kilpatrickg and was added to the volume of the reactor a t run temperature to give the total-effective volume of the reactor; the apparent residence time was calculated by dividing the total-effective volume of the reactor by the flow rate of gaseous material entering the reactor; this apparent residence time then was corrected by the method of BrinkleylO for the increase in flow rate due to decomposition. Table I1 lists the analytical results obtained from the static runs. The residence time for each of these runs was the length of time that the reaction vessel remained in the heating bath. Isomerization.--Table I lists the nitrogen-compound distribution in the reaction products. Pre(9) T. L. Hillenbrand, Jr., and M. L. Kilpatrick, J. Chem. Phys., 2 1 , 625 (1949). (10) S. R . Brinkley, Jr., Ind. Eng. Chem., 40, 303 (1948).
I. A. JACOBSON, JR.,AND H. B. JENSEX
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Vol. 66
TABLE r COMPOSITION OF PRODUCTS FROM THE THERMAL REACTIONS OF ~ - ~ - B ~ T Y L P Y RUSING ROLE THE FLOW SYSTEX Product analyses, wt. 70 Ttmp,,
C.
Cor. residence times, BBC.
------m-Butylpyrrole 12-
1
3-
Pyridine
Other nitrogen productsQ
462
Total hydrocarbon formed
394.8 97.1 2.1 0.03 0.1 0.5 325.6 95.4 3.3 .3 .I .7 483 337.5 85.7 10.3 1.2' .4 1.5 265.9 85.3 10.2 1.4 .4 1.9 189.3 89.7 7.9 .8 .3 1.2 160.5 91.2 3.5 .2 .7 2.9 501 202.9 66.6 19.3 4.1 1.1 6.5 197.2 74.7 15.4 3.5 0.9 3.8 165.3 73.3 15.6 3.0 .9 5.3 108.5 78.7 12.2 1.1 .6 5.8 56.5 84.4 7.7 1.2 .2 5.4 48.9 89.9 6.7 .6 .2 1.9 188.6b 74.0 15.7 4.1 .6 4.0 49.5b 86.7 6.5 1.o .2 4.4 525 186.8 44.3 27.3 9.3 3.1 10.2 139.1 53.5 23.3 7.2 2.3 9.1 97.7 61.5 20.0 5.6 1.7 7.6 48.4 69.6 14.5 1.8 1.1 9.8 550 159.7 15.0 25.2 10.8 6.4 26.0 133.9 17.7 26.6 11.6 5.4 24.3 98.1 26.2 28.3 11.6 4.5 18.5 51.1 44.5 19.4 9.3 2.8 11.0 31.5 57.5 22.3 6.4 1.9 7.9 157.8" 23.2 9.5 5.9 26.4 18.7 26.6 10.8 4.6 19.2 109 7' 27.1 74.4' 24.2 9.0 3.2 14.7 41.3 17.7 7.8 7.0 33.2 142.7d 13.5 19.7 8.1 6.0 24.6 125.Od 25.6 20.1 8.3 5.1 19.5 34.3 90. Od 52.2* 44.0 23.1 9.0 3.5 12.4 5.6 29.2 159.gb 12,7 23.7 11.5 5.7 23.7 13.4 28.8 14.1 132,8b 3.8 17.4 13.2 30.3 90.1* 25.6 1.8 8.4 45. Ob 8.8 50.2 26.0 8.8 42.9 5.7 11.8 572 99.0 4.7 7.1 34.3 8.3 70.6 12.5 17.4 6.0 26.3 10.8 42.8 25.9 15.6 20.3 36.9 25.8 9.2 3.7 15.7 a These include 2- and 3-methylpyrroles, 2- and 3-ethglpyrroles, and 2- and 3-vinylpyrroles. Runs Runs made in a packed reaction tube. added nitric oxide. Runs made without nitrogen diluent gas. I
TABLE I1 UNREACTED BUTYLPYRR PYRROLE IN THE PRODCCTS USIKGTHE STATICSYSTEN Temp., O
c.
360
375
Residence time, see. X 10-4
79.5 44.9 29.1 14.2 27.6 15,Q 14.8 6.06 5.56 3.36 1.44 .63
1-wButylpvrrole in produc&,-wt. %
76.7 83.7 92.2 96.3 78.5 87.4 84.9 93.9 78.6 77.6 93.2 97.0
0.2 .3 .8 .9 .6 1.6 2.4 1.8 1.9 1.6 1.1 .7 1.6 1.3 5.9 4.7 3.6 3.2 16.7 14.4 10.8 13.0 4.0 16.4 11.6 7.7 20.9 16.1 12.7 8.0 17.2 14.3 9.8 4.6 26.1 20.3 15.5 8.8 made with
from the 1- to the 2-position on a pyrrole ring was irreversible and also demonstrated the reversibility of the 2- to 3-isomerization. These data indicate that the only route by which 1-n-butylpyrrole disappeared was by isomerization to 2-n-butylpyrrole. First-order rate equations mere used for the kinetic calculations of the initial isomerization reaction, based on the disappearance of l-n-butylpyrrole. The first-ordgr rate equation ki = (l/t) In C d C ,
was evaluated at each temperature by a least squares method using the origin as a fixed point. Table I11 lists the resulting specific reaction rate 400 constants. All composition and time data were given the same weight for the calculations. The limits shown in Table I11 are for 95% confidence. The izomerization of 1-n-butylpyrrole was not viously reported work on 1-methylpyrrolesl dem- affected by changes in run conditions. Increasing onstrated that the isomerization of alkyl groups the area-to-volume ratio from 2.24 to 19.88 with-
July, 1962
THERMAL REACTIONB OF ORGANIC NITROGEN COMPOUNDS
TABLU I11 SPECIFIC REACTION RATECONSTANTS FOR THE IBOMERIZbTION O F 1-n-BUTYLPYRROLE Temp., C. Reaction rate, k ~ m.-I , X 106
360 375 400
46il 483 501 52:) 550
57il
By static method 0.317 f 0.042 0.917 zk 0.171 5.16 f 2.52 By flow method 103 f 431 532 3t 127 1820 4 300 4630 f 11’70 12700 4 900 32400 =k 9100
1247
hi
1-n-butylpyrrole -+ (2-n-butylpyrrole kd
3-n-butylpyrrole) ---t decomposition products
Two limiting conditions were imposed for these calculations: (1) both 2- and 3-n-butylpyrrole decompose at the same rate, and (2) all nitrogencontaining decomposition products were grouped together and treated as a single product. For the decomposition this mathematical treatment gave the following Arrhenius equation kd
a
5.48 x
1013 ~ - S O , U l O & 11,20O/RT
sec,-l
The decomposition is heterogeneous, as evidenced by the increase in the amount of decomposition products when the reaction tube was packed (Table I). Nitric oxide addition produced no effect. The appearance of pyridine in the products is of interest because of the formation of a six-membered ring from a five-membered-ring starting material. It is postulated that the pyridine is formed directly from C-butylpyrroles
out affecting the isomerization rate indicates that the isomerization is a homogeneous reaction. The addition of nitric oxide had no inhibiting effect on the isomerization, showing that it is not a chain reaction. The isomerization is first order and also unimolecular, as is evidenced by the fact that the presence of the diluent gas had no effect on the isomerization. The data from all of these runs were, thercfore, used to calculate the specific reacH tion rate constants. Two activation energies for the isomerization N N reaction were calculated: (1) using only the flowH method data, and (2) using only the static-method Summary.-1-n-Butylpyrrole isomerizes by a data, The energies thus calculated showed no significant difference so data from both the flow first-order reaction to 2in-butylpyrrole, which subseand static work were used in evaluating the Ar- quently isomerizes, by an equilibrium reaction, to rhenius equation. Activation energy was calculated 3-n-butylpyrrole. The isomerization reaction is by a least squares method weighting the specific not changed by packing the reactor, by eliminating reaction rate constants inversely to their variances. the diluent gas, or by adding nitric oxide; this The Arrhenius equation for the isomerization of indicates that the reaction is unimolecular, homogeneous, and non-chain. The isomerization reac1-n-butylpyrrole was evaluated to be tion is consistent when observed by either the o/~~ ki 3.10 x 1Oia e - ~ i , ~ o o ~ i , i a ~ec,-i %owor the static method. The C-substituted n-butylpyrroles are thermally Decomposition.-The butylpyrroles decompose in a complex manner to produce pyrrole, 2- and 3- unstable and decompose to form pyrrole, 2- and 3methylpyrroles, 2- and 3-ethylpyrroles, 2- and 3- methylpyrroles, 2- and 3-ethylpyrroles, 2- and 3vinylpyrroles, pyridine, and hydrocarbons. The vinylpyrroles, and pyridine. The decomposition is absence in the products of any detectable l-sub- heterogeneous but is not affected by the addition stituted pyrroles, exclusive of the starting mate- of nitric oxide. rial, is indicative that decomposition takes place Acknowledgment-Thanks are extended to API after isomerization. The appearance of the de- Research Project 52 for the purification and purity composition products is essentially a first-order determination of 1-n-butylpyrrole. The work was process. The decomposition was, therefore, math- done under a coijperative agreement between the ematically treated 2s a consecutive first-order reac- University of Wyoming and the Bureau of Mines, tion. U.S. Department of the Interior.
