《有机化学》课程教学资源（文献资料）A Kinetic Study of the ortho-Claisen Rearrangement

July 5,1958 KINETICS OF Ortho-CLAISEN REARRANGEMENT 3277 Strong interaction of this nature is ssible sinc Claisen ent the effec the the o be most rbon of the allv 10r The existen or transi Th exp action and as a fina or ierent solvents.Ho ion ply,a nega t th t the dif e more than III is indi acby the obtai niza ed with the of th should increase the dielectric constant)in the the rence the ionizat ent is similar in magn ty of the benzyl Me cal. Altho this in b the itra utkin reactio e be ely polar in natur dical it is likely tha ica al rather chanist explanations for the bstituent and the electro ment sent the Diels-Alde sm is bilities stulated by Woodward E,J,Ce.R 6. be hybrid. stabil n H.O.Priteb rd andBad6859D CoLUMBUS 10,OHIO CONTRIBUTION FROM THE DEPARTMENT OP CHEMISTRY OF THB UNIVERSITY OF WISCONSIN A Kinetic Study of the ortho-Claisen Rearrangement BY HARLAN L.GOERING AND ROBERT R.IACOBSON RECEIVED IANUARY 27.1958 The relative ang hod fo 01 was raiPamioohea8i2tcreactao Inmany respects the ortho-Clais me as a ocess as ilu the Cla arrangemen E.F.Slve 77 R.H.J 01 s."Vol.II,John om is the .79,3464

July 5, 1958 KINETICS OF Ortho-CLAISEN REARRANGEMENT 3277 Strong interaction of this nature is possible since the carbons of the allyl group may lie in a plane directly over the aryloxy grouping so that the a￾carbon of the allyl group is over the oxygen of the aryloxy moiety, the P-carbon is over the 1-position of the ring, and the y-carbon over the 2-position. This places one terminal carbon of the allyl group over the oxygen from which it breaks away and the other over the o-carbon to which it becomes bonded. This complex must be very short-lived if it is to maintain its orientation. The substituent data are explained if structure I1 contributes more to the resonance hybrid than 111-a positive charge which is stabilized by electron donation is placed on the aromatic ring during reaction and as a final stage, if equation 2 is to apply, a negative charge is cancelled at the position meta to the substituent requiring electron withdrawal. That I1 actually would contribute more than I11 is indicated by the fact that the difference between the ionization po￾tential of the benzyl radical32 and the electron af￾finity of the allyl radical33 is about 17 kcal./mole greater than the difference between the ionization potential32 of the allyl radical and the electron af￾finity of the benzyl radical.33 Although this com￾parison is not precise because the actual system in￾volves a phenoxy radical rather than a benzyl radical, it is likely that the comparison is justified since the electron affinity of phenoxy radical34 is even less positive than that of benzyl radical by 14 kcal./mole. Finally, this latter mechanism is sup￾ported by an analogy to the Diels-Alder reaction for which a charge transfer complex mechanism has been postulated by W0odward.~5 Like the (32) D. P. Stevenson quoted by A. Streitwieser, Jr., Chem. Reus., (33) N. S. Hush and K. B. Oldham quoted by H. 0. Pritchard, ibid., (34) N. S. Hush quoted in H. 0. Pritchard, ibid., 62, 529 (1953). (35) R. B. Woodward, THIS JOURNAL, 62, 3058 (1942); R. B. 66, 571 (1956). 63, 529 (1953). Woodward and H. Baer, ibid., 66, 645 (1944). Claisen rearrangement, the effect of substituents on the Diels-Alder reaction of l-(p-X-phenyl)-1,3- butadienes and maleic anhydride has been found to be most suitably correlated by use of the u+ constants and a small, negative p.23.36 The existence of a polar intermediate or transi￾tion state in the Claisen rearrangement is demon￾strated not only by the substituent effects but also by the preliminary results on the effect of solvent (Table VI). A semi-quantitative treatment of the data is not possible since the dielectric con￾stants of these solvents have not been measured at the temperature of rearrangement, and the change of dielectric constant with temperature is different for different solvents. However, it is encouraging that the solvent of lowest dielectric constant at or￾dinary temperatures (n-octane) yields a rate one￾third to one-seventh that obtained with the other solvents, and that the addition of a salt to Carbitol (which should increase the dielectric constant) in￾creases the rate. The solvent rate effect observed for the Claisen rearrangement is similar in magni￾tude to that for the Menschutkin reactions of methyl iodide in benzene-nitrobenzene mixtures, 37 a reaction which is most definitely polar in nature. There are, therefore, at least three reasonable mechanistic explanations for the substituent and solvent effects observed in the Claisen rearrange￾ment. Unfortunately, at present, there is not enough experimental information available to de￾cide among these possibilities. (313) The effect of a y-methyl group in the allyl portion of the ether (footnote 30) can be explained as being due to a larger contribution by structure I11 to the hybrid. The additional methyl group should tend to stabilize 111. (37) H. C. Raine and C. iT. Hinshelwood, J. Chem. SOL, 1378 (1939); K. J. Laldler and C. N. Hinshelwood, ibid., 858 (1938). COLUMBUS 10, OHIO [CONTRIBUTION FROM THE DEPARTMENT OF CHEMISTRY OF THE UNIVERSITY OF I IS CONS IS] A Kinetic Study of the ortho-Claisen Rearrangement' BY HARLAN L. GOERING AND ROBERT R. JACOBSON RECEIVED JANUARY 27, 1958 The relative rates of the ortho-Claisen rearrangement of allyl phenyl ether, fifteen m- and p-substituted allyl phenyl A dilatometric The rela￾The relative reactivities of ethers and a-, 0- and y-methyallyl phenyl ether at 185 and 197" in diphenyl ether have been determined. method for following the reaction accurately using low concentrations (about 0.1 M) of substrate was developed. tive rates of rearrangement of allyl p-cresyl ether in twelve solvents also have been determined. the series of p-substituted allyl phenyl ethers can be correlated by the CT+ substituent constants. Introduction In many respects the ortho-Claisen rearrange￾ment2 is similar to the intramolecular (SNi') re￾arrangement of allylic ester^.^ Both of these reac￾tions are first-order intramolecular processe~.~,~ (1) This work was supported in part by the Office of Ordnance Rc￾search, U. S. Army, and in part by thP Research Committee of the Graduate School with funds given by the Wisconsin Alumni Research Foundation. (2) D. S. Tarbell in R. Adams, "Organic Reactions," Vol. 11, John Wiley and Sons, Inc., New York. N. Y., 1944, Chapt. 1. (3) (a) H. L. Goering and R. W. Greiner. THIS JOURNAL, 79, 3464 The relative positions of the atoms in the reactants and products are the same for the two reactions and in each case the over-all reaction can be sum￾marized as a six-membered cyclic process as illus￾trated by I and II.4 In the Claisen rearrangement (1957); (b) H. L. Goering, J. P. Blanchard and E. F. Silversmith, ibid. 76, 540b (1954); H. I. Goering and E. F. Silversmith, ibid., '77, 1129 (1955); (c) unpublished work of R. H. Jagow and M. M. Pombo. (4) It recently has been shown with 0'5-labeled esters that in the SNi' rearrangement of allylic esters the carbonyl oxygen atom in the reactant becomes the alkyl oxygen atom in the product as illustrated by 11; W. E. Doering, private communication (1955); E. A. Braude and D. W. Turner, Chemirlvy f-? Industry, 1223 (1955)

3278 HARLAN L.GOERING AND ROBERT R.JACOBSON Vol.80 d dienone is converted to the 0 0 0 0 epent dinethylphenv the other hand.it has been concluded that in the determin 2e CH CH CH: RCO- 之 C-OCOR develo 11b CH.CHCE ic centers ud t OH CHs -CHCH-CHCH Experimental roduct difter In another the tions 1.0 and and nat summarized b hasthe Sirear aihtePeentec 思

3278 HARLAN L. GOERING 4ND ROBERT R. JACOBSON Vol. 80 (I) the initially formed dienone is converted to the corresponding phenol. there is evidence that there is some covalent bond￾ing between the allylic carbon atoms and the oxygen atoms in VI. It has been suggested* that similar intermediates may be involved in other I1 It would appear that the stereochemical relation￾ship between reactant and product should be the same for the two reactions, however, there is evi￾dence that this may not be the case. It has been de~nonstrated~~J~ that in the rearrangement of trans-a, y-dimethylallyl esters (HI), the configura￾tion of the asymmetric carbon in the product is opposite that of the asymmetric carbon in the reac￾tant, ;.e., in this system the product and reactant are enantiomers as illustrated below. On the other hand, it has been conclude@ that in the H 13 li / H’ ‘11 11 rIIa IIlb Claisen rearrangement of optically active truns￾a, y-dimethylallyl phenyl ether (IV) ,6 the configura￾tions of the asymmetric centers in the reactant and CHaCHCHzCHCHa I product (V) are the same. If this conclusion is correct, the stereochemical relationship between reactant and product differs for the two cases. In another problem the relative configurations of IV and V are being re-examined to determine whether this apparent discrepancy is real. Considerable information concerning the timing and nature of the electronic shifts in the SNi‘ rear￾rangement summarized by I1 has been presented in earlier papers3 It appears that an intermediate VI (an “internal ion-pair” intermediate according to Winstein’s classification’) is involved in this reaction as follows. As indicated previouslyaa (5) H. Hart, THIS JOURNAL, 76, 4038 (1954). (6) E. R. Alexander and R. W. Kluiber, ibid., 13, 4304 (1931). (7) S. Winstein, E. Clippinger, A. Fainberg, R. Heck and G. Robin son, ibid., 78, 328 (1956). I K \,- I 12 intramolecular processes including the Claisen rearrangement. In order to obtain inforniation concerning mechanistic details of the ortho-Claisen rearrangement (I) we have examined the effects of substituents and variation of solvent on the rate of rearrangement. The results of this investigation are presented in this paper. The rates of the ortho-Claisen rearrangement of a few aryl allyl ethers in the absence of solvent have been reported previously.”l” Kinetic studies of the rearrangement of allyl /]-cresyl ether in di￾phenyl ether lo and allyl 2,l-diinethylphenyl ether in diethylaniline“ also have been described. In the latter two cases rather high concentrations of substrate were used (5-335; by weight of the reac￾tion mixture) and the reactions were followed by determination of the amount of phenol formed by quantitative acetylation. This method is liniited to non-hydroxylic solvents and probably could not be used with low concentrations of substrate. In the present work a dilatometric iiiethotl was developed which can be used to follow reactions at temperatures up to 200”. Previously dilatoiiietry has been used to follow reactions only at ternpera￾tures near room Tletails of this method are included in the Experimental section. \Vith it the ortho-Claisen rearrq+ncnt can be fol￾lowed with a high degree of accuracy at tenipera￾tures of iS3-800” using low concentratioiis of sub￾strate (about 0.1 111). lye have used this niethotl to deterniine (a) the relati1.e reactivities of allyl phenyl ether and eighteen substituted allyl phenyl ethers and (b) the relative rntes of rearrangenicnt in twelve solvents. Experimental Allyl Phenyl Ethers.-Except as iiotecl bel(^^ all of tlic ethers were prepared bj- the following tnethotl which is u modification of the method used by Claiseii.I3 A solutioti of 0.2 mole of plieiiol, 0.22 inole of ally1 brotnitlc atid 0.22 mole of potassium carbonate in 50 1111. of drl- acetoiie W:LS refluxed for 8 hours. hfter cooling, the reictimi inisture was diluted with 250 nil. of water aiid extracted with three 35-ml. portions of ether. The organic layer WIS ivashetl first with 105; aqueous sodium hydroside aiid then with water and dried over magricsiurn sulfate. .lfter reinoviil of the solveiit the residue was fractioiiatcd under rcdueetl (8) I) J. Cram, tbid , 74, 2129 (1952); 75, 332 (10;iX). (9) €1. Schrnid and K, Schmid, H~la. Chzin. .4c/ii, 35, 18i!l (1932). (10) J. F. Kincaid and D. S. Tarbell, 7‘rirs JOIJRNAI., 61, 30% (11) 1’. Kall,erer and H. Schrnid, 11~1:’. i’hiiii. tlclu, 40, 13 (1‘337) (12) (a) J. S. Brbnsted, el (IL, THIS JULIRNAI., 49, 2584 (liI27); 61, 428 (l!J?!I); (h) L. K. J. Tong and A. 12. Olson, ibid., 66, 1701 (19.43). (13) L. Claisen and 0. Eisleh, .41n>~, 401, 21 (1913). (1039)

Jly5,1958 KINETICS OF OrhO-CLAISEN REARRANGEMENT 3279 ERTIES OF Lit. 97.297,4 13 90 M.p.39-40 0.y 119-120 1.5199(20 -C 111 10e 07 21000 1.5100(28 -COCH, 00 0.6 14147 94.094 160 -6 M.p. 32-33° 1 3 87090 0 4 M.Megh in and H. a-CH 429-43. 1,078 0.7 18 5or3)-C00C:H. NLp.1-1 d the sa p-Ethoxyphe the trile. heny rest of the p ther (pre o.n the s nie m.p.115-116°.1 allyl -f b.p. have ectheestabd (W.M.Lauer and W.Wilbert.Tr Jou Com

July 5, 1958 KINETICS OF O?'thO-CLAISEN REARRANGEMENT 3279 Substituent P-NH2 P-OCzH, p-OCH3 P-CHB p-c1 p-Br None p-CHO P-COOCsH, p-COCH3 P-CN P-NOz WZ-OCH~ m-SOz p-CH3 -(-CHJ a, -,-Dimethyl TABLE I PHYSICAL PROPERTIES OF SUBSTITUTED ALLYL PHENYL ETHERS Obs. b.p. Lit. b.p. OC. bIm. Obs. ?$~SD OC. Mm. Lit. nb 97.2-97.4 1 1.5679 136 11 70.0-70,5 0.1 1.5249 119-120 13 119 11 M.p. 44.2-45.0" . . M.P. 39-40' 100.0-100.5 9 1.5157 65 4 1,5199 (200) 97.0-97.3 10 1.5348 106-107 12 110.0-110.1 10 1.5583 126 14 67.5-67.6 10 1.5196 73 11 1.5190 (26") 100.0-100.1 0.6 1.5258 156 10 106.0-106.5 2 1.5069 142 10 89-90 0.6 1.5525 146-147 10 1.5432 (45") 94.0-91.5 .3 M.p. 43.6-44.1" . . ALP. 43" 105-106 .4 1.5789 160 12 66.0-66.1 .5 1.5263 125-126 15 92.2-92.3 .6 M.p. 32-33' 136-137 8 M.p. 31,532' 75.2-75.8 10 1.5136 70 8 1.6168 (20') 87.1-87.5 8 1.5183 95-98 12 1.5187 (19') 59.8-60.0 0.4 1.5060 72 0.8 1.5110 (20') Ref. 16 35 13 13 16, 13 13 0 9, 10 ;> 13 35 i 9 6 a S. M. McElvain and E. L. Engclhardt, THIS JOURNAL, 66, 1077 (1944). C. D. Hurd and L. Schmerling, ibid., 59, 107 M. \ir. Partridge, J. Chew Soc., 3043 (1949). Mi. C. 9. R. Bartz, R. F. Miller and R. ;Idams, ibid., 57, 371 (1935). (1937). Wilson and R. Xdams, THIS JOURSA-., 45, 528 (1928). Q J. v. Braun and W. Schirmacher, Her., 56, 538 (1923). R. T. ilrnold and J. C. McCool, ;bid., 64, 1315 (1942). TABLE I1 PHYSICAL PROPERTIES ASD .~NALYTICAL DATA FOR ARYL ALLYL ETHERS AND SUBSTITUTED 2 allyl ether oc. him. ii25D formula Calcd. Found Substituted phenyl B.p. Empirical Carbon, % p-N(CH3)z 88.1-88.2 0.5 1.5500 CiiHlbNO 74.55 74.89 P-CZHL 96.0-9G. 8 9 1,5124 CiiH140 81.45 81.26 WZ-COOC~H~ 88.0-88.1 0.2 1.5169 C12H1103 69.89 69.80 a-CH3 42 9-43.0 0.8 1.5078 CioH120 81.04 80.70 Substituted 2-allylphenols 4-K(CH3)2 85 0.1 1.5681 CiiH1SNO 74.55 74.67 4-CzHj 63.0-63 5 0.2 1.5301 CilHliO 81.45 81.43 4-CN M.P. 83.0-84.0 5(or ~)-COOCZH~ M.p. 151-152 pressure with a short Vigreux column. The main fraction was refractionated prior to use in the kinetic experiments. The phenols were purified by distillation or recrystalliza￾tion. nz-Carbethoxyphenol and p-carbethoxyphenol were prepared by esterification of the corresponding liydroxy￾benzoic acids. p-Ethoxyphenol was prepared from hydro￾quinone and diethyl sulfate by the method used to prepare anisole from phenol and dimethyl ~u1fate.l~ @-Cyano￾phenol was prepared from p-aminoplienol by the method used previously to convert p-toluidine to p-tul~onitrile.~~ The rest of the plietiols are available commercially. Allyl p-aniinophenyl ether was prepared by hydrolysis of allyl p-acetaniitioplieiiy-1 ether.lG Allylic chlorides were used for preparing CY- and -,-methyl￾allyl and a,-,-dimethylallyl phenyl ether. These chlorides had the following physical properties: -pmeth>-lallyl chlo￾ride, b.p. 83-83.7", %%D 1.4325 (lit.I7 b.p. 83', nZo~ 1.4351); a-methylallyl chloride, b.p. 62.5-63.5', nlj~ 1.4125 (lit.17 b.p. 63.5", 1.4150); a,y-dimethylallyl chloride, b.p. 27" (30 mm.), TZ%D 1.4306 (lit." b.p. 18-20" (12-13 nim.), n% 1.43 11). Commercialll- available 0-methylallyl chlo￾ride was used to prepare P-methylallyl phenyl ether. Ethanol was used as the solvent instead of acetone for preparing allyl p-formylphenyl ether.13 Most of the allyl phenyl ethers used in the present work have been described previously. These are given in Table I together with the observed and reported physical properties. CioHsKO 75.39 75.55 CmH14Op 69.89 69.95 That the samules were homoneneous ALLYLPHENOLS Hydrogen, % 8.53 8.24 8.70 8.78 6.84 6.71 8.16 8.10 Calcd. Found 8.53 8.60 8.70 8.58 5.69 5.48 6.84 7.00 was indicated bv the fact that fractionation gave fractions having the -same physical properties. A11 of the samples had the correct chemical composition (carbon-hydrogen analysis) and the infrared spectra showed the samples to be free of phenol. The structures of these several substituted allyl phenyl ethers reported in Table I were confirmed by oxidationi8 to the corresponding aryloxyacetic acids-p-NHz (as its acetyl derivative), p-OC2Hj, p-OCHa, p-CI, p-Br, p-ii02, WL-OCH,~, nz-NO:! and -pCH.,. a,y-Dimethylallyl phenyl ether (presuinably the trans isomer6)), was oxidized to a￾phenoxyprupionic acid, m.~. 115-116O (lit.19 m.p. 115-116') in good yield. The structures of the p-COsC?H, p-CHO and p-CN phenyl allyl ethers were verified by conversion to p-allyloxybenzoic acid.13 The new allyl phenyl ethers are shown in the upper half of Table 11. The structure of a-methylallyl phenyl ether was established by reduction (palladium-on-charcoal) to sa￾butyl phenyl ether. The physical properties and infrared spectrum of this product were the same as for an authentic sample.20 The unsaturated ether also was oxidized to a￾phenoxypropionic acid, m.p. l15-l16°.19 1Vlien heated the ether rearranged to o-crotylphenol (isolated in 947, yield), b.p. 67-68' (0.6 mm.), phenylurethan m.p. 66-67" (lit.21 phenylurethan m.p. 65-66"). The structure of allyl p-ethylphenyl ether was established (14) G. S. Hiers and F. I). Hagcr, "Organic Syntheses," Coll. Vol. I, 2nd edition, John Wiley and Sons, Inc., New York, N. Y., 1941, p. 58. (15) H. T. Clarke and R. R. Read, ibid., 11. 514. (16) L. Claisen, A>tn., 418, 69 (1'31'3). (17) E. H. Huntress and E. E. Toops, Jr., "Organic Chlorine Con￾pounds," John Wiley and Sons, Inc., Sew York. N. y., 1948. (18) W. M. Lauer and W. F. Filbert, THIS JOURXAL, 68, 1388 (19) C. A. Bischoff, Bey., 33, 925 (1900). (20) M. M. Sprung and E. S. Wallis, Tiirs JOCJRNAI., 56, 1715 (21) I,. Claisen and E. Tietze, Be?., 59, 23-14 (1926). (1936). (1934)

3280 HARLAN L.GOERING AND ROBERT R.JACOBSON Vol.80 thyiphenoxyacetic acid,m.p.6.- c,62 Caled.for C:C.506.Found: 8p prev 5-78.0°0it. ly fo (a)Tn coiled at el of th aor near roo and the capillary (D)was th well in was aa G n the kinetic he dila 0 and the crature. d a gsd品oe7盘e lquid had B ate zero-tim as dete Fig.1.-Dilatometer used in kinctic experiments ter 19p tly the Wieland.(1)

3280 HARLAN L. GOERING AND ROBERT 12. JACOBSOS VOl. so by oxidation to fi-ethylpheiioxyacetic acid, 1ii.p. 96.3- 96.5' (lit.22 m.p. 97"). The structure of m-carbethoxyphenyl allyl ether was established by hydrolysis to nz-allyloxybenzoic acid, m.p. 80.0-80.5'. 23 Anal. Calcd. for CIDHIOO~: C, 67.40; H, 5.66. Found: C, 67.62; H, 5.59. The structure of the latter compound mas established by oxidation to nz-carboxyphenoxyacetic acid, m.p. 207-208" (lit.24 m.p. 206-207"). Allyl p-dimethylaminophen) 1 ether was prepared in 33 % yield by alkylation of the p-amino ether by a method that has been used previously for alkq lating aromatic amines.*j The structure of this compound was established by conver- sion to p-dimethylaminophenol, m,.p. 77.5-78.0" (lit.26 m.p. 78") by refluxing 1 g. of the dimethylamino ether in 7 tnl. of 48'/c hydrobromic acid for 5 hours. The amino phenol nas isolated in 757* yield. Rearrangement of Allyl Phenyl Ethers.-Four of the allyl phenyl ethers listed in Tables I and I1 rearrange to phenols that have not been described in the literature. These new phenols are included in Table 11. The phenols were ob￾tained from the ethers by the procedure given below for the conversion of allyl nt-carbetlioxyphenJ.1 ether to re- arrangement product. This is one of the tno cases where two rearrangement products are possible and the only case F 1 (22) Fig. S. RI. 1.-Dilatometer RlcElvain, "The used in kinetic experinients. Characterization L of Organic Com￾pounds," revised edition, The hlacmillan Co., R-ew York, S. Y., 1953, p. 268. (23) Evidently the melting point of 118O reported for this compound by Scichilone, Gazz. chim. dd., 12, 453 (1882), is incorrect. (24) R. Meyer and C. D. Duxzmal, Ber., 46, 3360 (1913). (26) W, L. Borkowski and E. C. Wagner, J. Oug. Chem., 17, 1128 (1932). (26) H. Wieland, Ber., 43, 712 (1910). in which two products are formed. .i solution of 3.0 g. of allyl m-carbethoxyphenyl ether in 6 g. of diphenyl ether was heated under nitrogen for 9 hours at 220'. After cooling, the solution was extracted with lOy0 sodium hy￾droxide and the aqueous layer was saturated with carbon dioxide and extracted with ether. Removal of the ether gave a residue, 2.95 g. (98%), which apparently was a mixture of the two possible rearrangement products, i.e., 2-allyl-5-carbethoxyphenol and 2-allyl-3-carbetlioxyphcnol. The higher melting component of the mixture was purified by several recrystallizations. This material is included in Table 11. The lower melting component was not purified. Kinetic Exper;ments.-The dilatometer used to follow the reactions at temperatures of 185 arid 197' is illustrated by Fig. 1. This dilatometer, which was designed for use at high temperatures, differs substantially from thosc used previously for following reactions at much lower teinpcra￾tures (near room temperature).12,27 The important features of this design are: (a) The coiled tube provides a high surface to volume ratio and thus temperature equilibration is rapid. This coil was constructed of 7 mm. thin walled Pyrex tubiug and had a capacity of about 30 nil. (b) The level of the reaction mixture (sealed in the dilatometer at or near room temperature) in the capillary (D) can be adjusted so as to be on scale at the reaction temperature. The capillary (D) was 10 inches long and had a precision bore 0.0224 inch in diameter. The length of the dilatom￾eter from the bottom of the coil to the top of the capillary was about 14 inches. During the kinetic experiments the sealed portion of the apparatus (from A to C) was immersed in the constant temperature bath and held in place by clamps attached to the two glass rods (E and F) which extended through its cover. The constant temperature bath consisted of a Pyrex jar in a well insulated box. The box had a double paned window for observing the scale on the dilatometer. Except when in use the window was covered by a well insulated door. The Pyrex jar (12" in diameter and 18" deep) contained 6 gallons of Dow KO. 550 silicone oil. The bath was heated by two 500 watt heaters. One of t1ie.e served as a constant heater and the other as the intermittent heater. The lattcr was connected in series with a 50-watt light bulb. The constant heater mas connected to a variable viiltage control and the current for this heater was controlled by :L Raytheon line voltage regulator. The temperature of the bath was controlled by a carefully selected Philadelphia type S\Y 912 thermoregulator. The bath was also provided with an eficient stirrer arid a tight-fitting cover. The tempera￾ture fluctuations of the bath were less than 0.003" during a rate run and during the period of its use the absolute tern￾perature varied less than 0.05'. In the kinetic experiments the dilatometer was fillcd as follows. Both A and C were sealed and the reaction mixture n-as added through B at room temperature. After filling to the top of the coil, B was sealed aud a scale with 2 mm. divisions was attached to the capillary tube. For emptying and cleaning the dilatometer A, B and C were opened. The level of tlic liquid in the capillary at the reaction temperature was adjusted as follows. The sealed tiilatom￾cter was placed in the bath which had previously been heated a few tenths of a degree abovc the operating tern￾perature. After the excess liquid had overflowed into the reservoir (G) the temperature was lowered to normal and the level of the liquid dropped to the top end of the scale. This operation required about 5 minutes. After equilibration for 10 minutes at the reaction temperature the zero-time reading (Ro) was taken and the rate of decrease in volume was determined. The total drop during a kinetic cxperi￾tnent varied from 50 to 90 mm. and the readings were re- corded to 0.2 mm. The readings were always taken at the same time during the heating cycle (;.e., when the inter￾mittent heater shut off) to minimize error? resulting from the temperature fluctuation of the bath. n'hen the dilatometer was filled with pure solvent the level fluctuated about 0.1 mm. However, when readings were taken at the same time during the heating cycle they agreed to within 0.2 rnm. Thus it appears that the readings in the kinetic csperiments are good to about *0.2 mm. (27) R. Livingston in A. Weissberger's "Technique of Organic Chemistry," Vol VIII, Interscience Publishers, Inc., New York, N. Y. 1953, ChaDt. 2

July5,1958 KINETICS OF tO-CLAISEN REARRANGEMENT 3281 were and the k er rate ter ten ha nghestordere t for the c exper of t OCH sho the ran of the of n duplic . two 84.85 ue RATE OF REA 8 2.69810 Time.10-1 kX10530. 0 Se ral of the constants in are of men ons th e rate const d ge values and of ab ants ging rom ility ms都eeo sisted AL.SO NyI.E th this X 104,see.- Allyl p-eresyl ethe cible Results Phe imately ants for the activa 1 0 ment of B.Ally!p-ecarbethoxyphenyl cthe Ethylene giyco B.4±0.6 odtomaeeandelraetepstdsterr Averag

July 5, 1958 KINETICS OF 0rh.J-CLAISEN REARRANGEMENT 3281 In the kinetic experiments the amount of substrate used was 1.5% by weight of the reaction mixture. This corre￾sponds to a concentration of about 0.1 molar. Theallylaryl ethers were freshly distilled and the solvents were purified as follows. Diphenyl ether was purified according to the method of Kincaid and Tarbell.10 N,N-Dimethylaniline was dried over fused potassium hydroxide prior to distilla￾tion and diphenylmethane was purified by fractionation. The other solvents (see Table V) were purified by standard methods. The specific first-order rate constants for the decrease in volume of the reaction mixtures were calculated by use of equation 1 in which Ro, R, and R.CO correspond to the readings at zero time, time t and "infinity" time (;.e., after ten half￾lives). Since with dilute solutions the change in volume is a k = (lit) In (Ro - I?-)/(& - Rm) (1) linear function of the percentage completion of the reaction,28 k is the first-order rate constant for the reaction. Usually about 25 readings were taken during a kinetic experiment and values of k were calculated for each of these readings. These values did not shov any trends over the range that the reactions were followed (to about 8 1% completion) and the average deviation was usually <2yo of the value of k. In duplicate experiments the values of k agreed within the combined average deviations. A typical kinetic experiment is summarized in Table 111. In this table only every third reading is recorded and thus the average value and average deviation may differ slightly from the value recorded in Table IV. TABLE I11 RATE OF REARRANGEMENT OF ALLYL +CRESYL ETHER IN DIPHENYL ETHER AT 184.85'" Time, 10-8 sec. Dilatometer reading k X 106 set.-* 0 67.2 . 2.70 65.2 2.05 5.40 63.3 2.05 8.00 61 .O 2.05 14.4 57.8 2.05 19.8 54.9 2.06 25.2 52.3 2.07 30.6 49.9 2.08 36 0 47.8 2.09 57.6 41.6 2.09 72.0 38.8 2.08 03 30.6 . Average 2.07 f 0.02 a The reaction mixture consisted of 1.5% by weight of the substrate in diphenyl ether. First-order rate constants fo- the rearrangement of all but two of the ethers listed in Tables I and I1 were deter￾mined by this method. Allyl m-nitrophenyl ether decom￾poses in diphenyl ether at th reaction temperature and thus the rate of rearrangement of this compound could not be determined. For some unknown reason a,?-dimethylallyl phenyl ether showed erratic behavior and the rate of de￾crease in volume of the reaction mixture was not reprodu￾cible. Results The results of the kinetic experiments are pre￾sented in Tables IV and V. In these experiments the concentration of substrate was 1.5% by weight of the reaction mixture (approximately 0.1 M). First-order rate constants for the rearrangement of nineteen ethers in diphenyl ether at 184.85 and 19'7.29" are given in Table IV together with the Arrhenius activation energies, Ea, and entropies of activation, AS*. Similar data for the rearrange￾ment of allyl 9-cresyl ether in benzonitrile are in- (28) J. A. Riddick and E. A. Troops In A. Weissherger's "Technique of Organic Chemistry," Vol. VII, Interscience Publishers, Inc., New York, N. Y. 1956. TABLE IV RATE CONSTANTS AND ACTIVATION PARAMETERS FOR THE REARRANGEMENT OF SUBSTITUTED ALLYL PHENYL ETHERS IN DIPHENYL ETHER "JLICUFUL aromatic rinr or suL':',.-' in ~.~. Ea, AS*,a allyl k X 106, set,-; k X 106, set,-; kcal / ral / portion 184.65 f 0.05 197.29 i 0.02 ~. mole degree p-N(CHs)i 14.3 f 0.2 38.7 f 0.5 34.3 - 2 P-NHa 10.0 f .2 27.4 f .2 34.7 - 2 fi-OCzH6 4.77 f .04 12.5 i .1 33.1 - 7 p-OCHa 4.58 f .Olb 12.2 f ,1 33.6 - 6 P-CHI 2.08 f .Ole 5.58 f .05 34.0 - 7 fi-CzH6 2.00 f .03 5.51 f .04 34.8 - 5 9-Cl 1.70 f .02 4.21 i .04 31.2 -13 p-Br 1.58 f .03 3.92 f .02 31.2 -13 None 1.52 f .0Zb 3.86 f .03 31.6 -12 fip-COOCzHa 1.115 + ,005' 2.80 f .04 31.5 -13 9-CHO 1.07 f .01 2.72 f .03 32.2 -12 9-COCHs 0.994 f .007 2.54 f .03 32.2 -12 p-CN 0.903 + ,007 2.285 zt .005b 32.0 -13 $-NO1 0,892 f .004' 2.26 f .02 31.9 -13 m-OCHs 4.92 f .05 11.9 f .02 30.4 -13 n-COOC1Hs 1.48 f .02 3.51 f .04 29.8 -16 a-CHa 21.1 f .2 52.5 f .7 31.4 - 8 @-CHI 1.32 f .02 3.29 + .03 31.5 -13 r-CHa 1.61 f .02 4.05 f .04 31.7 -12 #-CHE 2.49 f .03d 6.60 f .OSd 34.6d - jd Calculated for T = 184.85'. Average value (and average deviation) of two independent kinetic experiments. Average value (and average deviation) of four independent kinetic experiments. Reference 5 reports k = 2.69 X 10-6 sec.-l at 185.8', E. = 33.1 (14.2% solution). These data are for the rearrangement of the p-methyl ether in benzonitrile. cluded in this table. Several of the constants in this table are average values (and average devia￾tions) of more than one independent kinetic experi￾ment. As indicated by the magnitudes of these de￾viations the rate constants are generally reproduci￾ble to within 1%. The rest of the constants are average values (and average deviations) of about twenty-five values determined during the course of the reaction. Judging from the reproducility of the rate constants the activation energies are prob￾ably reliable to within 1 kcal. The entropies of activation (calculated from the frequency factor, TABLE V RATE CONSTANTS FOR THE REARRAN'GEMENT OF ALLYL 9-CRESYL ETHER IN SEVERAL SOLVENTS AND ALLYL p￾CARBETHOXYPHENYL ETHER IN ETHYLENE GLYCOL AT 184.85 O A. Allyl p-cresyl ether Solvent k X 106, sec.-l Ethylene glycol 18 i 1" Benzyl alcohol 9.7 f 1.0 1-Octanol 9 f2 Phenol 45 & lb Carbitol 3.6 f 0.3 Methyl salicylate 2.45 f .O1 Benzonitrile 2.49 f .03 N,N-Dimethylaniline 2.46 f .04 Acetophenone 2.41 f .12 Diphenyl ether 2.08 f .Ole Diphenylmethane 2.12 f .02 Decalin 1.56 f .O1 B. Allyl P-carbethoxyphenyl ether a Average of four independent determinations. Ethylene glycol 6.4 f 0.6 * Average of two independe it determinations