reactive than methyl chloride and certainly much more reactive than n-butyl chloride. T h e phenyl and vinyl groups, being capable of delocalizing positive or negative charge a t the reaction site carbon, facilitate SN2 reactions. Except for the allyl chloride-sodium salicylate system, no iodide catalysis was required to obtain high yields of product. T h e allyl chloridesodium salicylate reaction is a n exception of some magnitude. T h e explanation that, in general, the salicylate anion was the least reactive nucleophile studied does not rationalize this discrepancy. Side reactions depleting starting materials are not the primary cause for the low allyl salicylate yield, because 91% of the allyl chloride and 7870 of the sodium salicylate not consumed in ester formation were recovered. Considerable effort was expended in varying reaction conditions in the attempt to gain some insight into this discrepancy. T h e yields in all cases remained low whenever sodium iodide catalysis was avoided. We are a t present engaged in studying the reactions of substituted allyl chlorides with a variety of carboxylate anions to see if this is a general or specific phenomenon. T h e results of this work will be reported later.
Literature Cited
Badische Anilin- und Soda-Fabrik, German Patent 268,261 (Dec. 22, 1913). Brown, H. C., Cope, 0. J., J . Am. Chem. SOC. 86, 1801 (1964). Conant, J. B., Hussey, R. E., J . Am. Chem. SOC.47,476 (1925). Criegee, R., Dimroth, P., Schempf, R., Chem. Rer. 90, 1337 (1957). Emerson, W. S., Heyd, J. W., Lucas, V. E., Lyness, W. I., Owens, G. R., Shortridge, R. W., J . Am. Chem. SOC. 69,1905 (1947). Gould, S . E., “Mechanism and Structure in Organic Chemistry,” p. 276, Henry Holt, New York, 1959. Hoffman, F. W., Weiss, H. D., J . Am. Chem. SOC.79, 4759 (1956). Jeffrey, G. H., Vogel, A. I., J . Chem. SOC.1948,p. 658. Kester, E. B., Gaiser, C. J., Lazar, M. E., J . Org. Chem. 8, 550 11943). Ma, T.-S., Hoo, V., Sah, P. P. T., Science Repts. Natl. Tsinghua Univ. A2, 133 (1933); C. A. 28, 133 (1934). Mills, R. H., Farrar, M. W.. Weinkauff, 0. J., Chem. Znd. (London) 1962. D. 2144. Rueggdderg, W. H. C., Ginsberg, A., Frantz, R. K., Znd. Eng. Chem. 38, 207 (1946). Thorp, I. D., Nottorf, H. A., Herr, C. H., Hoover, T. B., Wagner, R. B., Weisgerber, C. A., Wilkins, J. P., Whitmore, F. C., Znd. Eng. Chem. 39, 1300 (1947). Yamashita, Y., Shimamura, T., Kogyo Kagaku Zasshi 60,423 (1957) (English transl.). RECEIVED for review February 13, 1967 ACCEPTED July 14, 1967
A NEW SYNTHESIS OF 3-ETHYLPYRIDINE JEAN HERZENBERG, ROMANO C O V I N I , MARCELLO P I E R O N I , AND ADRIANO
NENZ
Centro Ricerche di Bollate, Montecatini-EdiJon S.P.A., Milan, Ztaly
A new, simple and economic synthesis of 3-ethylpyridine is the water vapor oxidative demethylation of 2-methyl-5-ethylpyridine (MEP), an inexpensive commercial product obtained from acetaldehyde and ammonia. The use of a Ni-AIz03 catalyst (containing 41% Ni) with a Hz0-MEP molar ratio of 60 to 80, at about 3 7 0 ” C., and with a contact time of 90 to 110 seconds (referred to MEP alone), gives 3 4 to 41% conversion with the high selectivity of 9 3 to 95% of 3-ethylpyridine. Side reactions give 3.9 to 2.6 mole of 2-picoline, up to 0.4 mole % of pyridine, and less than 2% ring cleavage. 3-Ethylpyridine has not found a technical use, probably because of the lack of an inexpensive synthesis; when produced at a relatively low price it could become the starting material for other pyridine derivatives, such as 3-vinylpyridine.
Ethylpyridine, a minor component of the lighter coal tar 3 - f r a c t i o n s , is also a degradation product of some alkaloids (Stoehr, 1882; Woodward et al., 1944), like brucine, cinchonine, and nicotine, and a by-product in the synthesis of other pyridine derivatives (Chichibabin, 1903 ; Gechele et al., 1960; Mahan, 1956; Mahan et a / . , 1957; Stoehr, 1882, 1891). I t results from the dehydrogenation of 3-ethylpiperidine (Ladenburg, 1898), and from the cyclization of 2-ethylglutaric dialdehyde with hydroxylamine (Chumakov et al., 1965) ; it may be produced with 24% yields from tetrahydrofurfuryl alcohol, monoethylamine, and ammonia (Butler et a/., 1966), or with 51% yields, from 2,6-diethoxy-3-(l-ethoxyethyl) tetrahydropyran (Chumakov et al., 1964). T h e synthesis of 3-ethylpyridine may be conveniently carried out, starting from simpler pyridine derivatives. A possibility is to methylate 3-picoline with methyl chloride in liquid ammonia and in the presence of Na amide; yields are 39 to 54% (Brown and Murphey, 1951). Or nicotinic acid may be used, which after esterification with ethyl alcohol, Claisen condensation with ethyl acetate, and subsequent hydrolysis, gives 3-acetylpyridine (Brown and Murphey, 1951 ; Burrus and Powell, 1945 ; Camps, 1902 ; Gilman and Broadbent, 1948; Kollof and Hunter, 1941); the latter may be suitably reduced, according to Fand and Lutomsky (1949). One of the most promising starting materials should be 2-methyl-5-ethylpyridine (MEP), which is a commercial
product much cheaper than pyridine and the picolines, and which can yield 3-ethylpyridine by elimination of the 2-methyl group. T h e point is to find highly selective conditions, so that the ethyl group can be preserved. I t has been suggested that the methyl group of M E P be condensed with formaldehyde, the hydroxyethyl derivative oxidized, and the resulting 5-ethylpicolinic acid decarboxylated (Koenigs and Hoffmann, 1925). This same acid may be obtained in 76% yields by direct oxidation of MEP, using selenium dioxide as an oxidizing agent (Jerchel et al., 1955). Decarboxylation yields are as high as 90%. I n previous work (Nenz et al., 1966, 1967), we studied the thermal hydrodealkylation of MEP, and found that 15% yields of 3-ethylpyridine may be obtained, with various amounts of pyridine, 2- and 3-picoline, and 2,j-lutidine. T h e present work deals with the oxidative demethylation of M E P in the presence of water vapor and a Ni-A1203 catalyst. An example of oxidative dealkylation of substituted pyridines due to water vapor is the conversion of a technical grade 2picoline to lower boiling materials, carried out by Meerwein et al. (1931) with 52% yields on cerium chromate, a t 620’ to 640’ C. A nickel on alumina catalyst was used by Balandin, Zamyshlyaeva, and coworkers to demethylate the isomeric picolines and 2,G-lutidine (Balandin et al., 1956 ; Zamyshlyaeva et al., 1965a, 1965b, 1 9 6 5 ~ ) ; in the case of 2-picoline, 60% conversion and 83y0 yields of pyridine were obtained. VOL. 6
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M E P oxidized with water vapor in the presence of a Ni on A1203catalyst gives nearly quantitative yields of 3-ethylpyridine (93 to 95 mole %), the oxidation occurring with high selectivity on the 2-methyl group, leaving the 3-ethyl group almost una1tered.
100
-
$80
Y
-
Figure 1. Ternperature dependence of the over-all conversion
z
$ 60 -
Experimental
A stainless steel reactor of 3-cm. internal diameter was packed with 240 ml. of catalyst consisting of 47% NiO on A1203 (C 13-C catalyst, Catalysts and Chemicals, Inc., Louisville, Ky.). Prior to each experiment the catalyst was treated 1 hour a t 450' to 500' C. and 1 hour a t 700' C. in a stream of hydrogen. Water and M E P (Montecatini-Edison S.p.A., 98% purity) were evaporated, preheated, and passed through the nickel on alumina bed. At the end of each run carbonaceous materials on the catalyst were burned a t 400' to 430' C. in a stream of nitrogen containing 10 to 20% air (2 hours), and subsequently in air (1 hour). The same charge of catalyst was used in all the work, without loss of activity. In a single experiment 10 to 50 grams of MEP and 100 to 500 grams of water were used over a period of 50 to 60 minutes. The gaseous reaction products were measured and analyzed. The liquid products collected in a low temperature condenser formed a two-phase mixture; for the sake of simplicity, they were dissolved in acetone, prior to analysis. Pyridine bases were determined by vapor phase chromatography on a 3-meter X 4-mm. stainless steel column, packed with Carbowax 1500, 25% on Celite. A Perkin-Elmer Model 116 Fractometer was used, equipped with a flame ionization detector. Results and Discussion
I n the demethylation of M E P with water vapor and a Ni-Al203 catalyst the methyl group is eliminated by oxidation to CO2 and C O . This type of reaction has been studied on 2-picoline, first by Meerwein, and later by Balandin (Meerwein et al., 1931; Balandin et al., 1956). In their work, evidence is given that demethylation occurs via oxidative attack of water vapor on the methyl group; the latter is mainly converted to COz H2, while generally minor amounts of C O are also found in the reaction gases. We found that water vapor oxidation of M E P in the presence of a Ni on A1203 catalyst occurs with high selectivity on the 2-methyl group, and the 3-ethyl group is almost unaltered. According to our results and those of Meerwein and Balandin, the reaction goes mainly through the following scheme :
+
a W > E40 u
-
20
-
Contact time 50 seconds, HzO/MEP molar ratio 55
t
.375
425 450 T E M P E R A T U R E ["C] 400
which !ead to the cleavage of the pyridine ring. Analytical determinations carried out both in the acetone solution and in the gases leaving the low temperature condenser show that the cleavage of the ring gives ammonia with nearly quantitative yields. An obvious indication of the reported results is that a n increase in contact time, like an increase in temperature, enhances the over-all conversion ; a t high conversion, however, cracking side reactions become very important. The waterM E P ratio, on the other hand, has no apparent effect, a t least within experimental limits. 3-Picoline and 2,5-dimethylpyridine were not found in the reaction products. Apparently, oxidation of the ethyl group, when it occurs, leads only to a complete elimination of the substituent, hence to formation of 2-picoline. On the other hand, differences between yields of 2-picoline and 3-ethylpyridine indicate a much higher reactivity in the 2-position. Zamyshlyaeva and coworkers (1965a, 1 9 6 5 ~ came ) to the same conclusion, comparing the behavior of the isomeric picolines, in a work published when our research (Herzenberg et al., 1964) had been completed. The highly selective oxidation of the 2-methyl group according to our experiments must be connected with the use of a Ni-Al203 catalyst. A few runs performed by us a t 440' C. in a reactor packed with inert material (ceramic rings), while giving very low conversion, yielded considerable amounts of 3-picoline, showing that the noncatalytic reaction can follow a different pattern. Furthermore, a Ni-Al203 catalyst enhances the formation of 3-ethylpyridine also when M E P is dealkylated by hydrogen, although with a much lower selectivity than in the oxidative process. T h e thermal hydrodealkylation gives mainly pyridine and 2-picoline (Nenz et al., 1966, 1967); in the course of the present work, we found that by hydrodealkylating M E P in the presence of a Ni-Al203 catalyst, with H2-MEP molar ratio of 15 to 20, about 50% conversion and u p to 55 to 60 mole %
H5c2nm f 2H20 -c.
N
H5c2Q
+
CO, f 3H2
The above equation is supported by our results, which show that Hz, COZ,and CO are the main components of the gaseous reaction products, when cleavage of the ring takes place to only a limited extent. A first set of experiments (Figure 1) indicated that conversion reaches a significant value a t 370' C. (30%) and is close to 100% a t 430' C. At these two temperatures, more experiments were performed, to make clear the influence of contact time and water-MEP ratio on the extent of conversion and selectivity. In Table I contact times refer to M E P alone; yields are expressed as moles per 100 moles of converted starting material. Over-all yields of pyridine bases range from 65 to 98%; the balance to 100% is a measure of cracking side reactions, 196
I L E C PRODUCT RESEARCH A N D DEVELOPMENT
Table 1.
Temp., O
c.
370 370 370 405 430 430 430 450
Oxidative Dealkylation of MEP with Water Vapor Yields on Converted MEP, MEP H20/ Mole yo Contact M E P Conuer2-Pico- 3-Ethylsion, PyriMolar Time, line pyridine Sec. yo dine Ratio 57 89 107 48 30 35 48 42
54 57 70 60 79 118 54 55
32 34 41 81 77 80 94 100
1.7
...
0.4 4.0 5.8 3.1 8.6 8.2
4.4 3.9 2.6 1.2 4.5 2.8
1.o
...
90.5 92.6 95.3 80.3 77.1 75.0 55.5 60.2
of 3-ethylpyridine on converted starting material may be obtained. These experiments were carried out a t 420' to 430' C., o n a catalyst containing 3.6% Ni; higher Ni contents cleave the ring even a t 300' C. Conclusions
While other alkyl and alkenyl pyridines are being produced on a commercial scale, 3-ethylpyridine has now only a scientific importance, probably because of the lack of a simple and economic synthesis. T h e procedure just described provides a very high selectivity and makes use of a relatively cheap, easily available starting material. Compared with other methods which involve MEP (Jerchel et al., 1955; Koenigs and Hoffmann, 1925), it has the advantage of proceeding through a one-step reaction, using a cheap oxidizing agent, and requiring a commercial catalyst, easily regenerated, and therefore has a long life, especially if used in a moving bed. When produced a t a relatively low price by the process described, 3-ethylpyridine may be a n interesting starting material for the synthesis of other useful pyridine derivatives; among them, 3-vinylpyridine is a n interesting one, for it polymerizes a t a lower rate than its 2- and 4-isomers. By now, 3vinylpyridine can be obtained only via 3-acetylpyridine, as 3methylpyridine does not undergo formaldehyde condensation (Scejnkman et. a/., 1963). literature Cited Balandin, A. A., Sovalova, L. I., Slovokhotova, T. A., Dokl. Akad. Nauk SSSR 110,79 (1956). Brown, H. C., Murphey, W. A., J . Am. Chem. SOC.73, 3308 (1951). Burrus, H. O., Powell, G., J . Am. Chem. SOC.67, 1468 (1945). Butler, J. D., Doodsworth, J. H., Groom, A. T., Chem. Commun. 1966, No. 2, 54.
Camps, R., Arch. Pharm. 240, 345 (1902). Chichibabin, .4. E., Ber. 36, 2709 (1903). Chumakov, Y. I., Martynova, E. N., Zinov'eva, L. M., Khimchenko,T. V., Zh. Obshch. Khim. 34 (lo), 3511 (1964). Chumakov, Y . I., Shorstyuk, V. P., Dzygun, E. P., Ukr. Khim. Zh. 31 (6), 597 (1965). Fand, T. I., Lutomsky, C. F., J . Am. Chem. SOC.71,2931 (1949). Gechele, G. B., Nenz, A., Garbuglio, C., Pietra, S., Chim. Ind. ( M i l a n ) 42,959 (1960). Gilman, H., Broadbent, H. S., J . Am. Chem. SOC.70,2755 (1948). Herzenberg, J., Covini, R., Pieroni, M., Nenz, A. (to Societl Edison), Belg. Patent 667,477 (Nov. 16, 1965); Italian Appl. July 27, 1964. Jerchel, D., Bauer, E., Hippchen, H., Ber. 88,156 (1955). Koenigs, E., Hoffmann, F. K., Ber. 58,194 (1925). Kollof, H. G., Hunter, J. H., J . Am. Chem. SOC. 63, 490 (1941). Ladenburg, A,, Ann. 301,117 (1898). Mahan, J. E. (to Phillips Petroleum Co.), U. S. Patent 2,769,811 (Nov. 6,1956). Mahan, J. E., Turk, S. D., Schnitzer, A. M., Williams, R. P., Sammons, G. D., Ind. Eng. Chem., Chem. Eng. Data Ser. 2, 76 (1957). Meerwein, H., Schoeller, W., Schwenk, E. (to Schering-Kahlbaum A. G.), Ger. Patent 529,628 (July 15, 1931). Nenz, A., Covini, R., Pieroni, M., Chim. 2nd. ( M i l a n ) 49, 259 (1967). Nenz, A., Covini, R., Pieroni, M., Herzenberg, J. (to Societl Edison), Belg. Patent 672,048 (March 1, 1966). Scejnkman, A. K., Rozenberg, B. A., Artamanov, A. A., Khim. Prom. 1963 (3), p. 181. Stoehr, C., J . Prakt. Chem. 45, 20 (1882). Stoehr, C., J . Prakt. Chem. 43, 153 (1891). Woodward, C. F., Eisner, A., Haines, P. G., J . Am. Chem. SOC. 66, 911 (1944). Zamyshlyaeva, L. I., Balandin, A. A., Solovokhotova, T. A., Izv, Akad. Nauk SSSR, Ser. Khim. 1965 (2), p. 330 (a). Zamyshlyaeva, L. I., Balandin, A. A., Slovokhotova, T. A , , Vestn. Mosk. Univ. Ser. I I , Khim. 20 ( l ) ,38 (1965b). Zamyshlyaeva, L. I., Slovokhotova, T. A., Balandin, A. A., Vestn. Mosk. Univ. Ser. II, Khim. 20 (4), 39 ( 1 9 6 5 ~ ) . RECEIVED for review December 19, 1966 ACCEPTED May 11, 1967
THERMAL CRACKING OF LOW TEMPERATURE LIGNITE PITCH J O H N S. BERBER, R I C H A R D L. R I C E , A N D D E L M A R R . F O R T N E Y
Morgantown Coal Research Center, Bureau of Mines,U S . Department of the Interior, Moigantown, W.Va. The thermal cracking of low temperature lignite pitch has proved to be an effective means of upgrading the pitch. Four products are obtained by the thermal cracking. About 15 to 2570 of the pitch is converted to coke, about 20 to 407, is recovered as cracked pitch, about 20 to 3Oy0is recovered as oil, and the balance is recovered as gas. The oil, upon distillation to 400" C., gives a distillate rich in aromatics which can be oxidized to phthalic and maleic anhydrides. The oil distillation residue has good binding qualities for carbon electrodes. The gas contains 10 to 15% ethylene as well as hydrogen and methane. The coke was calcined and used with the oil distillation residue pitch as a binder to produce a metallurgical electrode made totally from lignite coal tar products. HE
tar used in this study was produced by the Texas Power
& Light Co. from a Texas lignite carbonized a t about
500'C. in a fluidized bed. T h e pitch, as used in this research program, is the tar distillation residue boiling above 350'C. and is about 40 to 50y0 of the crude tar. Pitch is a complex resinous mass of polymerized and polycondensed compounds (Berber et ai., 1967). I t is a n amorphous solid material and brittle a t room temperature. T h e pitch analyses average 84% carbon, 8% hydrogen, 5% oxygen, and 1% each of nitrogen and sulfur. I t is chemically similar to the tar from which it is prepared, being mainly mixtures of the higher homologs of the compounds contained in the distillable fractions of the tar. T h e pitch is potentially useful as a binder in the manufacture of products such as roofing cement, metallurgical electrodes,
and pitch fiber pipe, if its characteristics can be modified by physical and chemical techniques to approximate those of asphalt and bituminous binders (Greenhow and Sugowdz, 1961). Researchers of the Bureau of Mines, U S . Department of the Interior, have investigated three methods for changing the lignite pitch characteristics. Air-blowing, used to treat bituminous pitch by lowering the hydrogen content and increasing the softening point and the penetrability, was not too effective with lignite pitch (Berber and Rice, 1964; Chelton et al., 1959). Catalytic dehydrogenation (Rice and Berber, 1966) was effective in reducing the hydrogen content of the pitch, but catalyst cost per pound of treated pitch is high, and the catalyst-recovery cost would be prohibitive. Thermal cracking has proved to be the most effective in changing the pitch characteristics. This report covers the VOL. 6 N O . 3
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