RORYMOREO’FERRALL AND SIDNEY I. MILLER
2440 [ CONTRIBUTIOX FROM
The
p-p
THE
VOl. 85
DEPARTMENT OF CHEMISTRY, ILLINOIS INSTITUTE OF TECHNOLOGY, CHICAGO 16, ILL.]
Relation and Transmission of Electronic Effects in the Reaction of Phenylacetic Acids with Diphenyldiazomethane BY RORYMOREO’FERRALL A N D SIDNEY I. MILLER RECEIVED JULY 19, 1962 Rate data for the reactions of thirteen substituted phenylacetic acids (p-NHz, P-CH,, p-CHaO, H, m-CH30, m-NOz, p-C1, P-Br, p - I , m-C1, m-I, m-Br, .+NO?) with diphenyldiazomethane ( D D M ) in ethanol have been obtained. The range of the activation parameters for A H * is 13.8 to 15.0 kcal. mole-’ and for A S * -8 to - 12 cal. deg.-] mole-’. Satisfactory Hammett lines have been calculated: a t 26.05”, log k = 0.340 - 0.0538; a t 35.6”, log k = 0.370 0.2523. X derivation of a p-p relation, p / p ’ = constant, has been given and a test of its validity has been initiated. The systems of interest are the pK’s of acids, R - G C O O H , which yield p’s and the rate constants of these acids in the D D M reaction which yield p ” s . For the solvent ethanol p / p ‘ E 2.0; this may be taken as a measure of the effectiveness with which the electronic demands of the site of the DDM reaction are relayed t o the substituent.
+
Considerable effort has gone into the dissection of the Hammett e q u a t i ~ n ~ , ~ log k = P O constant (1) Substituent constants u have proliferated and various viewpoints on their use have been expressed. p , which characterizes the reaction, the reaction conditions, and the ease of transmission of electronic effects from the substituent to the reaction center, has attracted somewhat less attention. In this paper we launch a phenomenological inquiry into the basis of p of eq. 1. A p-p relation is derived and it is then tested with kinetic data for the system
+
RCsH4CHzCOOCH(CsH5)z
t (C6Ha)zCHOCzHs
The
Relation.-Certain interpretations of p are inherent in the formalism of linear correlations. Previously it was shown t h a t for p-p
log k
= f ( u , XI,
X Z , X?
)
(3)
in which log k is separately linear in each of the structural or environmental factors u, z1 = u+, z2 = U T , etc. ; it followed rigorously for each z that and where a , b,, b2) and q are parameter^.^ To illustrate how the several factors governing p can be treated, two examples are given. For the reaction6 RCsH4COOCzHs
+ OH-
60% ___f
acetone RCsHaCOO
-
+ CZHSOH (6a)
89 rate constants in 1. mole-’ sec.-1 in the temperature range T = 273-313’K. are contained in log k = 8.145
+ 0 . 3 0 2 2 ~+ 319.1/T + 587.3a/T
(6b)
which by eq. 5 yields Ap =
587.3 A ( l / T )
(6c)
For the dissociations a t 2506 (1) Supported by the U. S . Army Research Office (Durham).
( 2 ) H . H . Jaffe, Chem R e s , 63, 191 (19.53) ( 3 ) I< P Hammett. J A m Chem. Soc , 69, 96 (1937); “Physical Organic Chemistry.” hIcGraw-Hill Book C o . , I n c . ,Xew York,X. Y . ,1940, C h a p V I I . (4) la) S.I . l l i l l e r . J . A m . Chem. Soc., 81, 101 (1959); (b) G . S Krishnamurthy and S I hliller, i b i d . , 83, 3961 (1961). ( 3 ) LJata are taken from ref. 2 , reactions 47h-47k of Table 2. T h e method of calculation is given in ref 4b. ( 0 ) J . H Elliott and hl. Kilpatrick, J . Phys. Chem., 46, 454, 466, 472 (19.11); h l Kilpatrick and R. D . Eanes, J . A m . Chem. Soc., 66, 689 (1943). For e q 7b the variance = 0.0116 and t h e confidence levels of t h e coefficients are 99. 90. and 9 7 % , respectively, a s given by Students’ t . l b
+
RCsH4COOH
RCBH~COO- H +
(7a)
67 Ki’s were measured in the range of dielectric constant 24-78.5 D. log K ~ / K H= 0.9019
+ 1.0370 - 2.602/0 + 9.1270/0
(7b)
A(l/D)
(7c)
and A p = 9.127
In the same way, the dependence of p on other factors x may be displayed. Hammett’ and Jaff6z,8independently noted that for pairs of processes, e . g . , acid dissociation and ester saponification P A ~ T ~ C O O E / P A ~ T I C O O C= P ~ P A ~ T z C O O R / P A ~ T ~ C O O C= Z B 77 ~
(8)
Jaff6 rationalized eq. 8 on theoretical grounds and provided most of the published examples of its use.8 Several groups have made comparisons of the typeg-ll P R G - C 0 0 E / P A r C O O H = ~ R - G - C O O C ~ H ~ / P A T C O O C= ~ H ~. . , (9) Typical series of compounds, ArTi- or RG-, are given in Table I. I t is worth noting that eq. 8 emphasizes the electronic demands of the reaction site as compared to the parent family of acids while eq. 9 compares the effectiveness of transmittal of electronic effects through any group G with t h a t of similar benzoic acid derivatives. The assumptions or requirements that eq. 8 be valid are instructive and can be made explicit from the analysis of a multiple variation as in eq. 4 and 5 . Now suppose that the factors which determine p can be lumped together in an independent variable termed s. Then log k = f(u,s) and, subject to the condition that log k is separately linear in u or s (10)
Ap/As = p
for a given reaction, e . g . , the pK’s of acids ArTiCOOH. For another reaction, e . g . , the hydrolysis of esters, ArTiCOOC2H5 (1la)
Ap’/As = p’
Therefore (P
-
PO)/(P’
-
PO‘)
=
a/!?’
(1lb)
in which pa and pa’ stem from the reactions of ArToCOOH and ArToCOOCsHe, respectively. The reduction of l l b to eq. 8, p l p ’ = T , is simple. There are many series in which the substituent is completely insulated or just too far away from the reaction site to be sensitive to its demands. Here the interposed group is To and PO = po’ = 0. Other approaches to this reduction will be given elsewhere.I2 (7) L. P. H a m m e t t , in lecture notes taken by S.I. M. a t Columbia University, 1948-1949. (8) (a) H. H. Jaffe, J . Chem. P h y s . , 11, 415 (1953); (b) S.Yeh and H . H . JaffC, J . A m . Chcm. Soc., 81, 3287 (1959). (9) E . Imoto, el ai.. N i g p o n Kagaku Zasshi, 80, 1021, 1024, 1293, 1297, 1300, 1307 (1959). (10) hf. Charton, J Org. Chem., 16, 735 (1961). (11) R. E . Dessy and J. K i m , J . A m . Chem. SOL.,8 8 , 1167 (1961) (12) J. D. S. Ritter and S. I. Miller, t o he published.
PHENYLACETIC ACIDSWITH DIPHENYLDIAZOMETHANE
Aug. 20, 1963
2441
TABLE I HAMMETT P - ~ ~ A L T J EFOR S REACTIOVS OF ACIDSOR pK, Hz0 250
R -G-COOH
1 2 3 4
XrCOOH ArCH?COOH ArCH2CH?COOH frans-.kCH=CHCOOH 5 rzs-ArCH-CHCOOH 6 XrCH=CHCOCOOH 7 p-.~r-C6H4COOH CHz
/
\
8 trans-ArCHCH?
/
1 00 0 51gh 212d 466 643d - 054 ( 34)h
. 182e
CHCOOH
THEIR
DERIVATIVES~
P K , 50% C~H~OH 250 ,
1 4-1 6
48)'
2 0 0 1 1 1 0
473d
0 . 812d
0 3Md
(
+
R-G-COOCtHa OH aa% C ~ H ~ O H300,
431 821 5gd 32d 122d 329 608
R-G-COOH
+
D D M , CzHsOH 30'
0 940 0 3Fjc
\
CHCOOH ( .32)h ,436 1 ,014d 9 &-4rCH------10 A r C e C C O O H ( .34)h .48' 1.1" 0.31' 11 5-Furanyl-COOH 1.3969 2.973' 1 .076g 2.437' 12 5-Thieny-COOH 13 K-(2-CH3CsH3)-COOH 1.28; 1 .673' 2.1; 0.946 14 K-(2,6-(CH3)2CsH2)-COOH 1.4k 0.69' 15 ArOCH2COOH 0.3l 1.1" Ref. 25. This study. LI p-Value from ref. 2, unless otherwise noted. Ref. 29. e E . N. Trachtenburg and G. Odian, J . A m . Chem. Soc., 80, 4018 (1958). Ref. 28. 0 Ref. 9. Estimated in Fig. 1 or 2. Ref. 30. 1 Estimated from d a t a in ref. 2 . Ref. 17. R . F. Brown and H . C. Newsom, J . Org. Chem., 27, 3010 1 S . V. Hayes and G. E. I;.Branch, J . A m . Chen?. Soc., 65, 1555 (1943). (1962): p-value at 0'. Ref. 14.
The preceding derivation appears to be valuable theoretically and eq. 8 may be useful empirically. Examples of the type eq. Bc and 7c should be illustrative of two s - f a ~ t o r s . However, ~ the ultimate question as to the nature of this factor s as it relates to Ar-T,- must be deferred. First, what is the experimental basis of eq. 8 and does it have utility? JVe believe t h a t both the successes and the failures in the experimental tests of eq. 8 will furnish important information on which a fundamental approach to s must be based. This is our present emphasis. Despite all of the work relating reactivity to structure, rate data taken under uniform conditions for a test of eq. 8 are scarce. Table I and Fig. 1 and 2 show p-p data for acids and their derivatives R-G-COS. In the figures, the abscissa consists of p ' s for the dissociations of acids R-G-COOH in water at 2.5' ; the ordinate consists of p ' s for any other reaction, e.g., the basic hydrolysis of the esters R-G-COOC2Hb in 88% ethanol a t 30'. This is line A, Fig. 1. Based on one or two reported p ' s , it is of course possible to sketch in many lines and thus attempt to predict many more p ' s . Line C, Fig. 2, is the beginning of a p - p relation involving the pK's of the acids R-G-COOH in 50% ethanol a t 2.5'. Line D, Fig. 2 , based only on data for ArCOOH, is a potential or predicted p-p relation for the reactionsI3 R-G-COOH
+ HKS +R-G-NHz + COz + Xz
(12)
Line B, Fig. 1, is the subject of the present study and will be discussed later. I t thus appears that the hydrolysis reaction, line A, Fig. 1, provides the only satisfactory test of eq. 8. As indicated earlier this line has been constrained to pass through the origin. For points 7 , 9, and 10 the abscissa had to be estimated. Otherwise, the data stem from many sources and it may be necessary to repeat some of the work.I4 Excluding point 6 for the benzylidenepyruvoyl group, the median deviation in p along the abscissa is =t0.1 and along the ordinate f0.2. This is (13) L. H Briggs and J. W . Littleton, J . Chcm. S o c . , 4 2 1 (1913). (14) For example, p for the hydrolysis of t h e ethyl phenylpropiolates has
been remeasured. Professor F. Fuchs (private communication) finds p = 1.1 as compared t o the older value of p = 1.9.15 (15) J . D. Roberts and R . A . Carboni, J . A m . Chpni. Soc., 77, 5554 (1955).
only slightly larger than t h a t found by JaffC in his survey of many p ' s 2 Of course, acid dissociation and ester hydrolysis involve the relay of electronic effects to two different reaction sites ilrT,COO-H and ArTiCO-OC2H5
In fact, the hydrolysis reaction involves one or more intermediates which may go on to form products or revert to reactants.I6 Although the over-all rate constants are composite, they did not lead to a complex or composite p , a t least in the hydrolyses of the methyl benzoates16: there is no assurance, however, t h a t this will remain true for all of the families of esters of Table I. Despite all of these potential sources of deviation from eq. 8; the correlation given by line A, Fig. 1, is moderately encouraging and p / p ' = 2.4 f 0.2 for line A.
Results The kinetics and mechanism of the reaction of the acids with diphenyldiazomethane (DDM) are reasonably well u n d e r ~ t o o d . ~This ~ , ~ reaction ~ has the advantage of involving the transfer of a proton from the car-
-
C2H60H R-GCOOH (C ~ H S ) ~ C X Z R - G - C O O C H ( C ~ H S ) ~ ( C ~ H ~ ) Z C H O C.f ZH N2 ~ (13)
+
+
boxylate to the a-carbon atom of the D D M in the ratedetermining step. Subsequent to this slow transfer, there appears to be a partitioning into paths leading either to ester or ethyl benzhydryl ether.'*" One may suppose, therefore, t h a t in the transition state there is partial breaking of the 0-H bond of the acid and t h a t the factors involved here will be closely related to those t h a t determine the pK of the acid. Conditions of temperature and environment being similar, this would seem to provide an especially simple case for an initial test of eq. 8. Rate data for eq. 2 are given in Table 11. Although we were satisfied with the precision of our rate con(16) hl. I-. Bender and R . J . Thomas, ibid , 83, 4189 (1961). (17) J . D. Roberts and C. M. Regan, i b i k , 7 6 , 939 (19%); J . 1). Roberts and J . A . Yancey, ibid , 7 3 , 1011 (1951). (18) (a) J. D . Roberts, W . Watanabe, and R . E McMahon, i b d , 7 3 , 760 (1951); ( b ) J . D . Roberts a n d , C . M . Regan, i b i d . , 74, 3695 (1932), ( c ) J I). Roberts and U'. Watanabe, ibid , 7 3 . 4869 (14.50)
2442
RORYMOREO'FERRALLA N D SIDNEYI. MILLER
VOl. 85
\
\ \ D 0
0.5
1.0
1.5
PR- G- conA. Fig. 1.-p-p relation: P R - G - C O S for reactions of acids or their derivatives 28s. P ~ - G for ~ the ~ pK's ~ ~ in water a t 25': A, upper curve, the basic hydrolysis of R-GCOOC$H, in 88y0 ethanol a t 30"; B, lower curve, the reaction of R-GCOOH with DDM in ethanol a t 30"; numbers refer to the acids in Table I.
stants, i t is fair to point out t h a t there are often unexplained discrepancies of the order of 10-2070 in the rate constants of the reaction of benzoic acid with DDM as published by different groups (see Experimental fcr details). For a wide range of phenylacetic acids, the rate constant changes by a factor of ca. 2. This of course leads to a narrow spectrum of activation parameters. Rate data for the phenylacetic acid series are particularly interesting in their relation to the effects of substituents on Because of the insulating effect of the methylene group, such data have been used to estimate the inductive effect of a given substituent. Carried over to other series in which conjugation is possible, this inductive effect can be subtracted from the total effect of the substituent to giye a measure of its resonance effect.20,21\Vith this in mind, we correlated our rate data with several types of substituent factors (Table 111). Clearly, whether one uses "standard" U ' S based on the pK's of benzoic acids,23 u n ' s based on selected benzoic acids in which mesomeric interactions are presumed to be minimal,24or the pK's of the phenylacetic acids,26good correlations are ob(19) F. H. Westheimer, J . A m Chem. S o c , 61, 1977 (1939). ( 2 0 ) G E. K . Branch and h l . Calvin, "The Theory of Organic Chemistry," Prentice Hall, I n c . , New York, S Y., 1941, Ch V I . 121) R W T a f t , Jr , J . P h y s . C h e m . , 64, 1805 (IQfiO),and related work ( 2 2 ) R 0. C Norman, G K . R a d d a , D . A . Brimacomhe, P. D. Ralph, and E lf Smith, J Chein. Soc , 3247 (1961). ( 2 3 ) D . H. IlcDaniel and H C . Brown, J . Ovg. Chem , 23, 420 (1958). 1'2%) H Van Bekkum, P. E . Verkade, and B hl. Wepster, Rec. Iraa. chim., 7 8 , 818 (1939). (2.5) A . F i s h e r , B. R . M a n n , and J. Vaughan, J . Chem. SOC.,1093 (1961).
\
\ I
I
1.0
PA~-G-COOH Fig. 2.-p-p relation: p R - c - c O s for the reactions of acids or their derivatives VLIS. pR-G-COoH for the pK's in water a t 25': C, the p K ' s of R-G-COOH in 5075 ethanol a t 25'; D , a predicted line, say for reaction 12, ref. 13; numbers refer t o the acids in Table I .
tained. In contrast, Taft's inductive constants u*, deriving from inductive effects in aliphatic compounds,26gave a distinctly poorer correlation. These results reinforce the view t h a t polar effects of R, even in two insulated systems RC6H4CH2COOHand RCH2COOH,are different.21 T h a t the polar effect of R was intimately related to its immediate structural en\wonment has long been evident-albeit in a different context -from the differences in alkyl-R and aryl-K dipole momentsz7 It is worth pointing out that several workers have analyzed the data for reactions in which conjugation between the reaction site and the aryl nucleus is precluded. For the pK's of phenylacetic acids, satisfactory correlations have been obtained with an.24,25 Making use of data for several insulated systems, Taft has devised a new scale. uo, which differs significantly from the scale a t the strongly electron-releasing end with more negative u's, e . g . , uo = -0.38 zrs. u" = -0.17 for the p-amino substituent. Making use of much the same data, Norman, et al., have proposed still another scale, U G , which differs significantly from the others on the electron-withdrawing side with diminished u ' s for the nitro and acyl substituents,22 \Vhile our DDSI rate data give satisfactory correlations either '
(26) R . W. T a f t , J r . , in M . S. Sewnian, "Steric Effectsin Organic Chemistry," John Wiley and Sons, I n c . , New Vork, N. Y . . 195R, Chap (27) Reference 20, p. 146.
PHENYLACETIC ACIDSWITH DIPHENYLDIAZOMETHANE
hug. 20, 1963
TABLE I1 RATECOSSTANTS AND ACTIVATION PARAMETERS FOR THE REACTION CzHsOH RC6H4CHaCOOH (CsH5)zCNz KC6H4CH2COOCH(CeH5)z CzH50CH( CsHs)z Nz
-
+
+
Substituent v k x I . mole-’ min.-’aK (20 05 2Z 0.1)’ (35.6 2Z 0.1)’
AH+,^ kcal. mole-’
+
cal. deg.-‘ mole-’
P-SHy 1.40 P-CH, 0.76 14.3 - 11 P-CH10 ,775 1 63 H 81 1.82d - 9 15.0 14.1 - 12 m-CH10 .901 1.93 - 10 14.4 p-CI 1.05 2.29 D-Br 1.08 14.3 - 10 P-I 1.10 2.39 14.4 - 10 m-CI 1.17 2 55 13.8 - 12 m- I 1.25 2.64 kBr 1 20 14.9 - 8 p-SO2 1.531 3 43“ m-SOs 1.59 a Uncertainty in kz: f 3 % , normally three runs. * Uncertainty < & I kcal. molecl. e Uncertainty: 1 1 . 0 cat. deg.-’ mole-’. Five runs. e Seven runs. f Four runs.
TABLE I11 HAMMETT-TYPE CORRELATIONS FOR THE REACTION OF DIPHESYLDIAZOMETHASE WITH THE PHENYLACETIC ACIDSIN ETHANOL T e m p . , Substituent ‘C factor
P
log koa
Yb
SC
.d
-0.0538 0.977 0 . 0 0 5 8 12 0.339 26 ua3 ,988 ,0032 11 .3i3 - ,0721 26 unZ4 ,890 ,0267 12 ,447 - ,1319 26 u*26 4.176 ,978 ,0052 12 26 pKZ6 ,754 ,967 ,0074 9 ,362 0 2718 36 uZ3 0.2523 ,985 ,0033 9 36 unZ4 ,401 Correlation coefficient. Standard a Intercept of eq. 1. Number of compounds used in correlation. deviation.
2443
one-half of those for simple dissociation. l n short, this predicts a common Bronsted a % 0.5 for eq. 2 for all of the acid families in ethanol. In drawing lines A, B, and C (Fig. 1 and a), we gave the points 13 for the 2-inethylbenzoic acids no weight so that any nonrandom deviations from the lines due to the proximity effects might be exaggerated. From pK data it is known that as a group the 2-methyl members are generally more acidic in water but slightly less acidic in 50% ethanol than corresponding benzoic These pK shifts may be ascribed to steric and solvent factors which include steric effects on conjugation and on solvation of the carboxyl group. In addition, the p-data and especially the p-p plots reveal differentiating rather than constant influences of the o-substituent. For the pK line C, the DDM line B, and the ester hydrolysis line A, the points 13 lie low. In the D D M case this differentiation may be marginal and in fact D D M rate data have been cited as evidence for the “normal” behavior of o-substituted benzoic acids.31 Taken together, the data suggest first that the proximity effect of a constant ortho group may vary within any family and second that the electronic characteristics of the ortho group may effectively enhance or diminish the relay of electronic effects to the reaction site. If eq. 8 is generally valid, then the preceding discussion suggests a way in which “abnormal” p-values may be detected and discussed in the context of the group T or the reaction type. Because of the form of the Hammett equation “exalted” p-values are the analogs of exalted u’s, e.g., u = 1.27 for u = 0.78 for the @NO2 group.2 Indeed the low p-values for the 2-methylbenzoic system display a “proximity effect” which otherwise might have been missed. In previous work, p-values have sometimes been used to discuss the modes of transmission of electronic effects. For example, inductive, field, and conjugative modes of transmittal of electronic effects have been proposed. Since the p-p relations test the consistency and validity of the linear free energy relations, they should also provide insights on the relation between structure and p. Moreover, i t is expected that the abnormal systems may be among the most informative. For this reason, we are examining other families of acids in the DDM reaction 13 to establish the limitations of the p-p relations.
with U O ’ S or U G ’ S yielding slightly different p’s, a change to these d s does not appear to be warranted a t this time. For use in the p-p relation, eq. 8, we used p = 0.35 interpolated to 30’ from the “standard” u-correlation of Table 111. -Moreover, the p’s of Table I are generally based on “standard” u’s. Now i t is possible to vary p somewhat by using different u-scales. But such a variation is within the uncertainty of the p-p relation and is Experimental not important in this application. This p-value can The phenylacetic acids used in this study were purchased or be compared with p = 0.94 for the D D M reactions of prepared by standard methods. Each acid was decolorized with the benzoic acids. The effect of a -CH2- group in charcoal if necessary, recrystallized a t least twice from water or reducing the transmission of electronic effects to a petroleum ether, and vacuum dried. The presence of traces of mineral acid in the starting material could raise the rate conreaction center by a factor of ca. 2.7 is well estabstants; for this reason our acids were recrystallized from neutral lished,20, * solvents. Table I V lists the acids and their properties. The present study of the phenylacetic acid-DDM Diphenyldiazomethane was prepared by a standard method reaction contributes point 2 (line B, Fig. 1). Together and recrystallized repeatedly from methanol a t ca. - I O 0 to m . p . 29-30” (lit.*ec29-30’), At X:l,lf6OH 525 m p , , E , , ~ obtained with the benzoic acids (point l), a working p-p relation on two separate preparations was 102 =k 1 which differs from the is established. Because p for the pK’s of the phenylpublished value of 94 f 0.5,180I t is known t h a t D D M decompropiolic acids was known only for 50’% e t h a n 0 1 , ~ * ~ poses ~ ~ slowly t o yield diphenylketazine and tetraphenylethene line C (Fig. 2) was used to estimate the p-value for which do not absorb a t 525 mp.l@ Fortunately, knowledge of emax of D D M was not essential in the rate measurements. water a t 25Oso that its position at 10 on line B, Fig. 1, The solvent for the kinetic studies was commercial absolute is an estimate. ethanol. We can also compare corresponding p-values for the Pseudo-first-order rate constants for eq. 13 were determined in pK’s of the acids with p’s for their reactions with D D M absolute ethanol by a standard The change in optical density of the D D M a t 525 mp, usually (-a. 0.8 unit, was in the solvent ethanol. For use in eq. 9, we note t h a t followed in a Beckman D K spectrophotometer. The temperafor the DDM reaction p is 0.94 and for acid dissociation ture within the reaction cell was held to f O . l O . Normally the p is 1.9G where p’s are for the benzoic acids in ethanoL2 acid to D D M concentration was greater than IO: 1, b u t in a few This implies that the electronic demands of the acids in runs it was as low as 6 : 1. T h e second-order rate constant inthe DDM reaction (degree of bond breaking) are about (28) I . Solomon and R . Filler, J . A m . Chem. Soc., in press. (29) (a) J . J . Bloomfield and R . Fuchs, J . O Y E .Chem., 26, 2991 (1961); (b) R. Fuchs, C. A . Kaplan, J . J . Bloomfield, a n d L. F . Hatch, ibid., 2 1 , 733 (1962), R Fuchs, private communication.
(30) D. Peltier, Bull S O C . sci. B i e l n g n e . 31, 9 (1956); B d i . SOC. rhim France, [SI 2 6 , 991 (1958). Some of Peltier’s d a t a have been examined.24 (31) N . B. Chapman, J. Shorter, and J . H P. Utley, J . Chem. So‘ , 1823 (1952); A . Buckley, N. B Chapman, and J Shorter, ibid , 178 (1903). ( 3 2 ) J. Hine and W Id. Bailey, J. A m . Chem. .SOL , 81, 207.5 (1959).
2444
JOHN
E. BALDWIN AND
TABLE IV MELTINGPOINTSA N D EQUIVALENTS OF SUBSTITUTED PHENYLACETIC ACIDS Substituent
Equiv. wt. Calcd. Found
M . p . , OC. Lit.
136.1 262.0 262.0 166 2 166.2 181.1 170.6 170.6 215.1 215.1 150.2 151.2 181.5
D. ROBERTS
Vel. 8.5
0.015 M ; the second-order rate constants were calculated directly by another method33 and agreed with those obtained from the pseudo-first-order runs. The activation parameters listed in Table I1 were obtained from the expression34
Found
76.5-77" 77-78 135-136b 13S140 P-1 m-I 129' 129-130 p-CH30 85-86b 86-87 m-CH30 67d 67-68 p-so2 152b 156-157 p-CI 10Sb 105-106 m-C1 76b 74-75 p-Br 114b 113-114 m-Br 100" 100-101 P-CH, 94' 91-92 P-NHz . . 199-200' 200-201 m-XO2 188.6O 120b 1 17- 1 19 a A . H . Jeffery and i\. I. l'ogel, J . Chem. Soc., 166 (1934). ' J. F. J . Dippy and F. R. Williams, ibid., 161, 1888 (1934). J . F. J . Dippy, F. R. Williams, and R. H . Lewis, ibid., 644 (1936); 343 (1935). R . Pschorr, Ann., 391,44 (1912.) e H. Berger, J . prakt. Chem., 133,331(1932). Ref. 22. g Thequantity available was insufficient for further purification. H
JOHN
135.1 259.8 256.8 165.6 165.1 180.2 167.7 169.9 213.8 210.8 147.4
creased roughly linearly by ca. 50% in the range 0-1 AT' acid.33 Therefore the present data are reported for solutions initially ca. 0.0025 M in D D M and 0.14 to 0.015 M in acid where the deviation from the infinite dilution value was within experimental error. Each acid was usually studied at three different concentrations except as indicated (Table 11). The slopes of plots of optical density us. time gave the pseudo-first-order rate constant which was converted to a second-order constant by division by the initial acid concentration. Additional runs were carried out with comparable phenylacetic acid-DDM concentrations of ca. (33) R. M O'Ferrall, unpublished results.
There is some discrepancy in the reported rate constants for DDM-acid reactions in absolute ethanol. For benzoic acid, the second-order rate constant in 1. mole-' min.? a t 30" has been found to be 0.99,31 1.08 (1.04),35 l.00,32 1.2OZ8; our interpolated value is 0.99; at 25' the rate constant of Taft and Smith appears to be high at 0.9636;our figure is 0.75 at 26.05'. The Taft and Smith rate constants36 for phenylacetic and phenylpropionic acids are also higher than those found in our laboratory, i.e., 1.47 a t 25" vs. 0.81 a t 26.05' and 1.01 us. 0.545 a t 25'. I t is possible t h a t the total change in optical density in their kinetic runs was too low, ca. 0.2 unit or less, and thus susceptible to potential error. Otherwise, our activation parameters indicate t h a t it would require rather improbable errors in the temperature to yield such deviations. The rate constant for the benzoic acid-DDM reaction increases linearly with the concentration of water (0-8 M ) added to the ethanoll8C; this also appears to hold true for phenylacetic acid.33 However, the magnitude of this increase is such that the presence of traces of water would not appear to be responsible for these discrepancies in the rate constants. Further, there seems to be no relation between the magnitude of the rate constants and whether the solvent ethanol was redried by the investigators. Until the reasons for these inconsistencies in the DDM-acid reactions are ascertained, some care is needed when the work of different investigators is being compared.
Acknowledgment.-\iTe wish to thank G. R. Ziegler for preparing some of the acids used in this work. (34) A. A. Frost and R G. Pearson, "Kinetics and Mechanism," John Wiley and Sons, Inc., New York, pi. Y., Chap. 5. (35) J . D. Roberts and C. M. Regan, J. A m . Chem. Soc., 75, 4102 (1953). (36) R . W , T a f t . J r . , and D . J . Smith, ibid., 76, 305 (1954); 11. J . Smith, B S. Thesis, Pennsylvania State College, J u n e , 1953.
[COSTRIBUTION NO. 2945 FROM THE GATES AND CRELLIN LABORATORIES O F CHEMISTRY, CALIFORNIA IsSTITUTE O F TECHNOLOGY, PASADENA, CALIF, A N D THENOYESCHEMICAL LABORATORY, UNIVERSITY OF ILLINOIS, URBAXA,ILL,]
Structure and Rearrangement of Neutral Phenylketene Dimer BY JOHN E. BALD WIN^
A N D JOHN
D. ROBERTS
RECEIVEDAPRIL2, 1963 Neutral phenylketene dimer has been identified as 3-hydroxy-2,4-diphenyl-3-butenoic lactone. converted in the presence of base to an acidic isomer, 2,4-diphenylcyclobutenol-3-one.
Introduction Base-catalyzed rearrangements of neutral phenylketene dimer t o an acidic isomer3 and of neutral methylketene dimer t o an acidic form4 have been reported. These rearrangements were interpreted in terms of conversion of I t o I1 by simple t a ~ t o m e r i z a t i o n s . ~ , ~
I
I1 R
CHa, CsHb
Since this early work, investigations of various ketene dimers have led t o fairly secure structural assignments for diketene5 (IIIa), neutral methylketene and other alkylketene dimers (IIIb),6 acidic methyl- and ethylketene dimers (IVb or Vb)', and ketoketene dimers (IVd, N e ) . * (1) Supported in part by the Sational Science Foundation. ( 2 ) Xational Science Foundation Predoctoral Fellow, 1960-1962; Department of Chemistry, University of Illinois, Urbana, Ill. (3) H. Staudinger, Bey., 4 4 , 533 (1911). ( 4 ) H Staudinger. "Die Ketene," Ferdinand Enke, Stuttgart, 1912, p, 4 2 H Staudinger. Ber , 63, 1085 (1920). ( 5 ) See V V Perekalin and T . A . Sokolva, Cspeckhi K h i m . , 16, 1351 (1956). and R. N . Lacey in "Advances i n Organic Chemistry," Vol. 2 , Interscience Publishers, l n c . , New York, N. Y . , 1960, pp. 240-241, for references t o t h e original structural studies.
IIIa, R I = Rz = H IV b, R1 = H1, RP = alkyl c, R1 = H, R2 = aryl
I t was
Vd, Rl = Rz = alkyl e, R I = R P = aryl
Two new representatives of this series of compounds have been reported recently : cyclobutane-1,3-dione (which exists as the enol Va)9 and 3-hydroxy-2,2,4-trimethyl-3-pentanoic lactone (IIId, R = CH3). l a From the evidence now available it seems clear that the neutral dimers reported by S t a ~ d i n g e rare ~ , ~likely t o be lactonic-type dimers and, if so, then the reported ( 6 ) J . D. Roberts, R. Armstrong, R. F. Trimble, Jr., and M. Burg, Soc , 71, 843 (1949); C. D . Hurd and C. A . Blanchard, ibid., 71, 1461 (1950); R . L. Wear, ibid., 73, 2390 (1951); A. S. Spriggs, C . M.
J . A?n. Chem.
Hill, and G. W . Senter, ibid., 74, 1555 (1952); J . R . Johnson and V . J Shiner, ibid., 76, 1350 (1953); J. Bregman and S. W . Bauer, ibid., 77, 1955 (1955). (7) (a) R . B. Woodward and G . Small, Jr., ibid., 71, 1297 (1950): (b) E . B. Reid and S. J. Groszos, ibid., 76, 1655 (1953). (8) W . E , Hanford and J. C . Sauer in "Organic Reactions," Vol. 111, edited by R. Adams, John Wiley and Sons, Inc., Kew York, N . Y., 1946, p. 127 ff. (9) H . H . Wasserman and E . V . Dehmlow, J . A m . Chem. Soc., 84, 3786 (1962). (IO) R . H . Hasek, R. D . Clark, E. V. Elam, and J . C . Martin, J. Org. C h e m . , 17, 60 (1962).
