[CONTRIBUTION FROM THE WM. H. CHANDLER
LABORATORY OF LEHIGH UNIVERSITY]
HALOGEN REACTIVITIES. IV. KINETIC STUDY OF THE DISPLACEMENT REACTIONS OF BROMOTHIANAPHTHENES WITH PIPERIDINE KAY R. BROWER
AND
E. D. AMSTUTZ
Received August 7, 1969
Previous papers in this series have dealt with the kinetic study of several halopyridines (l), the bromonaphthalenes (2), and the haloquinolines (3) in reaction with piperidine. In each case it was possible to relate the reactivity of the halogen in terms of activation energy with the effective electron density at that position. The energies of activation of bromide displacement from 1- and 2-bromonaphthalene are the same and equal to 25 f 1.0 Kcal. (2). Since naphthalene hydrocarbon may be regarded as the isosteric parent of a number of benzoderivatives of heterocyclic compounds we felt that an investigation of 2- and 3-bromothianaphthenes under the same conditions might provide much interesting information. Any pronounced differences between the halonaphthalenes and halothianaphthenes might be ascribed to the inductive and mesomeric effects of the sulfur atoms. 2-Bromothianaphthene was found to react smoothly with piperidine to yield 2-~iperidinothianaphthene, and the E,t. calculated from the pseudo-unimolecular rate constants listed in Table I was found to be 20.2 f 0.6 Kcal. The fact that this value is so much lower than that of 2-bromonaphthalene may be explained by the inductive removal of electrons from the 2-position by the sulfur atom. This effect also was noticed in the lowering of the activation energy for 3-bromoquinoline relative to that obtained for 2-bromonaphthalene (2). Unfortunately, 3-bromothianaphthene did not react with piperidine to produce 3-piperidinothianaphthene. A temperature of 255' was required to liberate bromide ion at a rate great enough for convenient measurement (half-life of approximately 24 hours), and under such conditions the products obtained were 2-piperidinothianaphthene and thianaphthene together with small quantities of ammonia and other decomposition products. The reactivity of this isomer contrasts markedly with that of 2-bromothianaphthene and 2-bromonaphthalene which react a t convenient rates at 185" and 200" respectively. If, as seems most likely, the unreactivity of 3-bromothianaphthene at temperatures below 250' indicates that the direct substitution reaction has an unusually high activation energy, an explanation can be found in the nature of the interaction of the sulfur
atom and the 3-position as illustrated above. The low reactivity follows from the requirement that formation of a transition state involving spa hybridization a t 411
412
K. R. BROWER A N D E. D. AMSTUTZ
TABLE I PSEUDO-VNIMOLECULAR
THE REACTION O F 2-BROMOTHIANAPHTHENE PIPERIDINE
RATECONSTANTS FOR WITH
T ("C.)
183.0 f 0.2 193.7 jc 0.2 202.6 3.z 0.2 214.2 j, 0.2
I
k (hr.-l)
0.0162 .0268 .0412 .0659
.0002 f ,0006 =k .0006 f .0009 =k
413
HALOGEN REACTIVITIES. IV
tion yielded 4.3 g. of nearly pure product which, after recrystallization from alcohol, melted a t 99-100". A n a l . Calc'd for C I ~ H I ~ NC, S :71.8; H, 6.97. Found: C, 72.2; H, 7.16 2-Piperidinothianaphthene was also obtained in 20% yield by heating 30 g. of 3-bromothianaphthene with 40 g. of piperidine a t 250-260' for 46 hours. After cooling and opening the tube, the pale yellow semi-solid reaction mixture evolved approximately 100 cc. of ammonia. The excess piperidine and piperidinium bromide were removed by adding water, making the mixture barely acidic, and extracting with ether The 2-piperidinothianaphthene was extracted from the ether with several portions of 20% hydrochloric acid and was precipitated by neutralization with alkali. Recrystallization from alcohol and mixture melting point determination established that the products obtained from 2- and 3-bromothianaphthene are identical. The ether layer referred to above was concentrated, steam-distilled, and fractionally distilled a t reduced pressure to yield 1 g of thianaphthene, b.p.3.; 95-loo", and 13 g. of 3bromothianaphthene, b.p.o.8 90-91". The two substances were identified through their picrates n-hich had melting points of 145-147", and 113-114", respectively. The recorded m.p.'s are 149" (8) and 114-115" (9). Degradation of 2-piperidinothianaphthene.A 2-g. portion of 2-piperidinothianaphthene was dissolved in 8 ml. of concentrated hydrochloric acid and refluxed for four hours. An oily layer which separated during the heating was taken up in ether and extracted first with concentrated hydrochloric acid, and then with 10% sodium hydroxide solution. Acidification of the basic extract yielded 0.5 g. of oil which solidified on cooling and had m.p. 40-45". The m.p. reported for 2-hydroxythianaphthene is 44-45" (10). The 2-hydroxythianaphthene obtained above was saponified by refluxing with 10% sodium hydroxide for one hour. Acidification yielded crystals of 0-mercaptophenylacetic acid, m.p. 95-96", recorded m.p. 96-97" (11). The material was analyzed for mercaptan sulfur by electrometric titration with silver nitrate solution. A n a l . Calc'd for CeHa02S: S, 19.0. Found: S, 18.5. Rate determination procedure. The technique employed and the method of estimating the precision of the activation energy have been previously described (2). The result of a typical rate determination is as follows:
0 1.50 1.50 2.00 2.00 2.50 2.50 2.75 2.75 3 .OO 3 .OO
1.0016 1.068 1.066 1 .OS7 1 .OS6 1.110 1.105 1.123 1.122 1.132 1.134
0.0429 .0417 .0410 .0405 .0412 .0392 .0417 .0413 .0408 .0414
KaV,= 0.0412 f .0006 hr.-l Calculation of energy and entropy of activation. The pseudo-unimolecular reaction of 2-bromothianaphthene with piperidine was found to have Eaot20.2 f 0.6 kcal, Ssct -46.5 e.u. Analysis of the data was carried out by means of the Absolute Reaction Rate Equation : k = kT/h e e A S*/R, - A E*/RT
414
K. R. BROWER AND E. D. AMSTUTZ SUMMARY
2-Bromothianaphthene has been found to react smoothly with piperidine to produce 2-piperidinothianaphthene.The ESot.for the displacement is 20.2 f 0.6 Kcal./mole. At the temperatures necessary to attain workable rates with 3-bromothianaphthene (250°), side reactions became so important as to vitiate rate studies. It is probable that cin6-substitution is the important feature of the reaction of 3-bromothianaphthene with piperidine. BETHLEHEM, PENNSYLVANIA
REFERENCES (1) YOUNGAND AMSTUTZ,J . Am. Chem. Soc., 73, 4773 (1951). (2) BROWER AND AMSTUTZ,J . Org. Chem., 18, 1075 (1953). (3) BROWER, SAMUELS, WAY,AND AMSTUTZ, J . Org. Chem., 18, 1648 (1953). (4) KOMPPA AND WECICMAN, J . prakt. Chem., 138, 109 (1913). (5) BUNNET,CORMACK, AND MCKAY,J . Org. Chem., 16,481 (1950). (6) SHIRLEY AND CAMERON, J . Am. Chem. SOC.,74, 664 (1952). (7) KOMPPA, J . prakt. Chem., 122, 319 (1929). (8) MEYERAND MEYER,Bel., 62, 1249 (1919). (9) ETIENNE,Compt. rend., 223, 38 (1946). (10) MARSCHALK, J. prakt. Chem., 88, 240 (1913). (11) MARSCHALK, J. prakt. Chem., 88, 237 (1913).
