MERCURIC NITRATE WITH NORMAL CHAINALKYLAND ARALKYL BROMIDES
Oct. 20, 1953
5037
[CONTRIBUTION FROM THE DEPARTMENT OF CHEMISTRY OF THE UNIVERSITY OF KANSAS]
Relative Reactivities of Organic Halides in Displacement Reactions. 11. Reaction of Mercuric Nitrate with Some Normal Chain Alkyl and Aralkyl Bromides’ BY SHIGERU O A EAND ~ CALVIN A. VANDERWERF RECEIVED MAY21, 1953 Rate constants, heats of activation and entropies of activation have been determined for a series of bromoalkanes and of (w-bromoalkyl)-benzenes in their reaction with mercuric nitrate in aqueous dioxane. N o alternation effects were observed; the results are explainable simply on the basis of hyperconjugation and inductive effects.
Introduction
to the driving force derived from the energy of Conant and co-workersa have shown that for a formation of a mercury-halogen bond. Later Benfey’ used this reaction in his study on series of normal chain alkyl and aralkyl chlorides, the reactivity in the typical S Nreaction ~ with po- ethyl bromide, 1-bromopropane, 1-bromo-2-methtassium iodide in acetone solution shows a definite ylpropane and bromocyclohexane and found that alternation effect as the number of methylene the reaction occurred by the rate-determining atgroups between the functional group, such as a tack of mercuric ion on halogen, with an equilibphenyl or ketone group, and the chlorine atom is rium governing the relative concentrations of increased. In the (w-chloroalky1)-benzene chlo- mercuric ion, mercuric monobromide ion and merrides, for example, the alternation in rate is appre- curic dibromide. Of the three mercuric species ciable up to (7-chloroheptyl)-benzene with benzyl involved, only the first contributed perceptibly to chloride the most, and (2-chloroethyl)-benzene the the rate. Benfey explained the experimentally deleast, reactive compound in the series. A similar termined rate sequence ethyl > n-propyl > isobutyl phenomenon was observed in esters and ethers, and on the basis of a hyperconjugation effect. In the present studies on bromoalkanes and the general concept of “alternate polarity” has become quite firmly established in the literature.4 (a-bromoalky1)-benzenes we have calculated the Dew& has more recently offered an explanation of heats of activations and have confirmed the results the alternation effect, as observed in Conant’s and explanation offered by Benfey. No alternation effect was observed in the (w-bromoalky1)-benwork, based on second-order hyperconjugation. Since, however, the effect has been reported only zene series. for S Nreactions, ~ there is still doubt as to whether Experimental or not it is merely electronic in nature. If the Materials.-Eastman Co. C.P. 1,edioxane was effect were entirely electronic, a similar alternation purified in 2-1. quantities Kodak by the method of Beste and Hamin reaction rates in a homologous series of alkyl mett.8 The simple bromoakanes as well as benzyl bromide, halides might be expected in reactions of the ioniza- (2-bromoethyl)-benzene and (8-bromopropyl)-benzene were all Eastman Kodak white label products. All the bromides tion mechanism or S N type, ~ as well. washed with concentrated sulfuric acid, water, 10% The present paper deals with the reaction of mer- were sodium carbonate solution, again with water, then dried curic nitrate with benzyl bromide and (2-bromo- over calcium chloride and finally fractionally distilled just ethyl)-, (3-bromopropyl)-, (4-bromobutyl)-, (5- before use. 1-Bromopropane was prepared from 1-probromopentyl)- and (6-bromohexyl)-benzene, as panol by treatment with sodium bromide and sulfuric acid. (4Bromobt1tyl)-benzene.-To the Grignard reagent prewell as ethyl bromide, 1-bromopropane,l-bromobu- pared by reaction of 18.5 g. (1 mole) of (2-bromoethy1)tane and 1-bromopentane. Roberts and Ham- benzene with 25 g. of magnesium in 500 ml. of anhydrous metts have presented convincing evidence in the ether, 60 g. (1.4 moles) of well-cooled ethylene oxide was Then half of case of benzyl chloride that the reaction proceeds by added dropwise over one hour a t -10-0’. the ether was removed by distillation, the same volume of way of a rate-determining formation of a carbo- benzene was added, and the mixture was distilled until nium ion the temperature of the distillate reached 60’. The reaction
+ R-Cl + HgC1+ + R +
mixture was decomposed with ice-water, neutralized with dilute sulfuric acid, and the product extracted several times followed by a fast step to form the alcohol or alkyl with ether. The combined extracts were neutralized with nitrate. The rate of reaction of alkyl halides in sodium carbonate, washed and dried over Drierite. Fracdistillation of the residue after removal of solvent ionizing solvents is accelerated by a factor of several tional yielded 106 g. of 4-phenyl-1-butanol, b.p. 124125’ (14 hundred on addition of small concentrations of mm.). A mixture of 76 g. of the alcohol, 102 g. of freshly premercuric nitrate. This acceleration is attributed pared thionyl bromide9 and 100 ml. of chloroform was (1) First paper in this series, S. Oae and C. A. VanderWerf, TUIS heated on a steam-bath for 2 hours. The chloroform and JOURNAL ‘76, 2724 (1953). excess thionyl bromide were removed a t the water-pump, (2) Institute of Scientific and Industrial Research, Osaka University, and the residue was washed with 10% sodium carbonate Sakai City, Osaka, Japan. solution, then with water, and dried over calcium chloride. (3) J. B. Conant and W. R. Kirner, THIS JOURNAL, 46, 232 (1924); Fractional distillation gave 60 g. of crude (4-bromobutyl)J. B. Conant, W.R. Kinner and R. E. Hussey, ibid., 47, 488 (1925). benzene, b.p. 98’ (2.5 mm.). The crude product was (4) See, for example, (a) G. M. Robinson and R. Robinson, J. washed three times with concentrated sulfuric acid to remove Chem. SOC.,128, 532 (1923); (b) Lapworth, M c m . Proc. Manchester unreacted alcohol, then with water, 10% sodium carbonate Lit. and Phil. Soc., 64, No. 3 (1920); (c) E. Muller, “Neuere Ansolution, and again with water, then dried over calcium schauungen der Organischen Chemie,” Julius Springer, Berlin, 1940, chloride and finally distilled. The fraction which distilled Hg++
pp. 66-78. (5) M.J. S. Dewar, “The Electronic Theory of Organic Chemistry,” Oxford University Press, London, 1949, pp. 157-159. (6) I. Roberts and L. P. Hammett, TEIS JOURNAL,69, 1063 (1937).
(7) 0. T. Benfey, ibid., 70, 2163 (1948). (8) G. W. Beste and L. P. Hammett, ibid., 63,2481 (1940). (9) R. C. Elderfield, et al., i b i d . , 68, 1516 (1946).
SIIIGERU OAE AND CALVINA. VANDERWERF
5038
Vol. 75
TABLE I ~-BROMOBIJTANE-MERCURIC NITRATEREACTION IN 70% DIOXANE AT 25' [Ilg(?;03)2]= 0.02471 N; [ C H ~ C H Z C H ~ C H Z=B0.0250 ~] N ; [HNOa] = 0.0245 N; N = -dx/[RBr]xdt, x, [RBr] and dx all expressed in N ; K = 4; [Hg++]/x calculated by eq. 2. By extrapolation kl = 0.0665 mole-' min.-l 1.
min, min. Ax
0
t,,
($(I
60 116 0 001201 0 000921 02411 .02305 X5 [RBr ](mole/l )" 02440 ,02334 n0340 ,0306 0324 ,0310 N C W Hg++/x ,488 .466 ki = Noor/Hg++/x ,0665 .0665 a Mean value of the concentrations at ti and t?. t2,
116 230 0.001573 ,02190 .02209 .0287 .0295 .441 .0669
230 442 0.002296 .01987 ,02016 ,0270 ,0270 .402 .0672
442 647 0.001598 ,01792 ,01821 .0239 ,0245 ,363 .0675
647 1393 0.003869 .01519 .01548 .0220 ,0210 .317 .0662
The equilibrium controlling the concentrations of the two at 107-107.5° (6 mm.) was collected and used for the kimercuric ion species is netic experiments. Anal. Calcd. for CtoH13Br: C, 56.4; H , 6.2; Br, 37.5. H g + + HgBrz 2HgBr+ Found: C, 56.6; H, 6.0; Br, 37.6. K = [HgBr+l2/[Hg++][HgBrz] (SBromopentyl)-benzene .-To the Grignard reagent prepared from 200 g. of (3-bromopropyl)-benzene and 25 g. Following the method of Benfey,' in the special case of magnesium in 500 ml. of anhydrous ether, 60 g. of ethyl- where K = 4 ene oxide was added and the product treated as described [HgBr+]jx = 1 -X/XO, [Hg++]/x = 1/2x/xo (2) for (4-bromobutyl)-benzene t o yield 86 g. of 5-phenyl-lpentanol. Reaction of the alcohol with an equivalent where xo is the initial concentration of mercuric ion in quantity of thionyl bromide gave the crude bromide, b.p. equivalents. Values of N, calculated from equation 1, were 123-125' (7 mm.) in 70% yield. After the usual sulfuric plotted against the mean X/XO, and a smooth curve drawn acid treatment, the fraction of pure (5-bromopentyl)-ben- through the points to give the corrected values of N . The zene distilling a t 123-125' (7 mm.) was collected. rate constant k1 was calculated from the ratio Anal. Calcd. for CllHlsBr: C, 58.2; H , 6.6; Br, 35.3. i~rom/[Hg++l/x k1 Found: C, 58.2; H , 6.8; Br, 35.3. Data for a typical run in the study of the reaction of 1(6-Bromohexyl)-benzene.-6-Phenyl-l-hexanol, b.p. 128130' (2.5 mm.), was obtained in 57% yield by treatment of bromobutane with mercuric nitrate are shown in Table I. the Grignard reagent of (4-bromobutyl)-benzene with ethylResults and Discussion ene oxide by the general method previously described. Conversion of the alcohol to the bromide, b.p 113-114' (2 mm.), The rate-constants, calculated as described, towas accomplished in 64% yield. gether with the heats of activation, AH*, and enAnal. Calcd. for C12H17Br: C, 59.8; H , 7.1; Br, 33.1. tropies of activation, AS*,for the reactions studied Found: C,60.1; H, 7.2; Br, 32.9. The refractive indices, n%, of the (w-bromoalkyl)-ben- are listed in Table 11. zenes were as follows: (2-bromoethyl)-benzene, 1.5560; T a B L E 11 (3-bromopropyl)-benzene, 1.5438; (4-bromobutyl)-benzene, 1.5382: (5-bromoDentvlbbenzene. 1.5318: and (6-bromo- RATE CONSTANTS OF REACTION OF ALKYL A N D ARALKYL hexyl):bhnzene, 1.3295: ' BROMIDES WITH MERCURIC SITRATE Kinetic Determinations and Calculation of Rates.-The Temp., k (mole-$ AH*, AS*, kinetic measurements were made by following the producCompound OC. see.-! I.) kcal. e.u. tion of bromide ion according t o the method described in 25.23 2.47 X detail by Roberts.*O Dioxane (70% by volume) was used Ethyl bromide throughout as solvent. Mercuric nitrate and nitric acid 37.12 7.93 X 15.3 0.21 were added t o bring the concentration of each t o approxi- 1-Bromopropane 25.23 1.35 X mately 0.025 N ; the exact concentrations were determined 40.60 5.03 X 15.8 .36 by titration. Exactly 100 ml. of the freshly prepared solu1-Bromobutane 25.23 1 . 1 2 X tion was placed in a 250-ml. stoppered flask and was kept immersed in a thermostat until the temperature of the solu40.60 4.22 X 15.9 .39 tion was identical with that of the bath. Then an amount 1-Bromopentane 25.23 1.11 X 10-3 of organic bromioe required t o make the solution approxi40.60 4.17 X 15.9 .39 mately 0.025 N in that reagent was weighed into a 1-mi. weighing bottle and was added with vigorous shaking t o the Benzyl bromide Too fast to be measured, even a t 0' reaction flask. At measured intervals, after this initial (2-Bromethy1)25.23 5.02 X time, 10-ml. samples were pipetted into 5 ml. of 0.1 iV pobenzene 40.60 2.07 X 17.0 .G4 tassium chloride solution. The excess chloride ion was titrated against 0.025 N mercuric nitrate solution with di- (3-Bromopropyl)- 25.23 4.48 X benzene 40.60 1.75 X 10-8 16.7 .60 phenyl carbazide as indicator in a solution made sufficiently acidic with nitric acid. (4-Bromobutyl)- 25.23 7.53 X Rate calculations were made by the method of B e n f e ~ . ~ benzene 40.60 2.90 X 16.2 .48 Values for N were calculated from his equation (5-Bromopenty1)- 25.23 7.87 X -dx/ [RBrIxdt = k1 [Hg++]/n kp [HgBr+]/x = N (1) benzene 40.60 3.03 X 16.2 .47 in which kk and kl are the velocity constants for the possible (6-Bromohexy1)reactions, respectively, and x is the concentration of total benzene 25.23 7.80 X lo-' mercuric ion at time t.
+
+
ki + Hg++ + R + + HgBr+ ka R R r + HgBr+ --+ R + + HgBrz RBr
(10) I. Roberts. I n d . Eng. C h o n . . Anal Ed , 8 , 365 (1936).
No hint of an alternation effect was observed in the reaction of either the 1-bromoalkane or the (w-bromoalkyl)-benzene series with mercuric nitrate. The rate sequence ethyl bromide > l-bromopropane, as well as the lower heat of activation
Oct. 20, 1953
c~s-@-ARoYL-~AND @-METHACRYLIC ACIDSAND RELATED COMPOUNDS
for the reaction of the former, may be explained by the increase in hyperconjugative resonance stabilization of the transition state with an increase in the number of available p-hydrogen atoms.' Differences in the rate constants for 1-bromopropane, 1-bromobutane, and 1-bromopentane, all of which have two @-hydrogenatoms, are very slight. The rapid reaction of benzyl bromide is of course, explained by resonance stabilization of the transition state through participation of the phenyl group. In (2-bromoethyl)-benzene, the tendency of phenyl group to destabilize the transition state, presumably because of its electron-withdrawing inductive effect, is apparently not overcome significantly by the possible neighboring group interaction of the @-phenylgroup." From the heat of activation sequence,- (2-bromoethvl)-benzene > (3. bromopropf1)-benzene > (4-bromobutyl)-benzene, -
it is seen that the electron-withdrawal effect of the phenyl group is diminished with an increase in the number of carbon atoms through which it must act, apparently disappearing altogether in the lastnamed compound. Even here, however, the phenylsubstituted bromide reacts more slowly than l-bromobutane, indicating that the phenyl group inhibits the reaction through another mechanism, as well. It may be that mercuric ion, as was observed for silver ion, forms a loose complex12with the phenyl group in which its electrophilic character, and therefore the rate of its reaction with the bromides, is considerably decreased. Acknowledgment.-The authors are grateful to the Research Corporation for a grant which made this and continuing work possible.
I
71,3863 (1949); S. Winstein (11) See D. J. Cram, THISJOURNAL, and co-workers, i b i d . , 74, 1113, 1140 (1952).
[CONTRIBUTION FROM THE CHEMICAL
5039
(12) L. J. Andrews and R. M. Reefer, ibid., 71, 3644 (1949); 72, 3113'5034 (1950)'
LAWRENCE, KANSAS
LABORATORIES O F THEUNIVERSITY O F TEXAS AND
THE UNIVERSITY OF V I R G I N I A ]
The cis- and trans-p-Aroyl-a- and P-methylacrylic Acids and P-Aroyl- a-metbylenepropionic Acids BY ROBERTE. L u T z , PHILIP ~~ S. B A I L E Y ,CHI-KANG ~~ D I E N ' ~AND .~
JAMES
W. R I N K E R ' ~ , ~
RECEIVED APRIL 11, 1953 Ultraviolet absorption studies on the cis-8-aroyl-a- and p-methylacrylic acids and related compounds show that the cis compounds in solution are cyclic but are open-chain in the form of the anions. The cis-p-benzoyl-a- and &methyl compounds and both p-aroyl-a-methylenepropionic acids have been made, respectively, from citraconic and itaconic anhydrides by Friedel-Craf ts reactions. The structures and configurations have been demonstrated. The trans isomers are the stable forms; the cis isomers are labile; and the 8-aroyl-a-methylenepropionic acids also are labile and the least stable of the three types. Interconversions of the various isomers are described.
This paper deals with the extension of earlier work and represents a joint effort which is basic to three fields of interest, the study of ring-chain tautomerism of compounds containing groups capable of interacting when sterically favorable circumstances are involved,2 the influence of configuration and substitution on the effectiveness of the whole or parts of conjugated and the reactions and 1,3-hydrogen shifts during reactions of systems of the type -COCH=C(CH
