May 5, 1952
%PHENYL-1-PROPYL ~-BROMOBENZENESTJLFONATE
[CONTRIBUTION FROM THE CHEMISTRY
DEPARTMENT, UNIVERSITY OF
2171
CALIFORNIA AT LOS ANGELES]
Neighboring Carbon and Hydrogen. XIII. The Solvolysis and Internal Rearrangement of 2-Phenyl-1-propyl p-Bromobenzenesulfonate1i2 BY
s. W I N S T E I N AND KURTc. SCHREIBER
In the case of 2-phenyl-1-propyl p-bromobenzenesulfonate, a fast primary arylsulfonate, the accompaniment of solvolysis by internal rearrangement to benzylmethylcarbinyl p-bromobenzenesulfonate is detectable through a n upward trend in acetolysis rate constant and by isolation of rearranged ester from partially solvolyzed reaction mixture. A thorough kinetic analysis of acetolysis of 2-phenyl-l-propyl p-bromobenzenesulfonate and synthetic mixtures of primary and rearranged secondary esters, designed to give constant first-order solvolysis rate constants, shows the rearrangement to be internal and uncomplicated by external p-bromobenzenesulfonate ion. Also, this analysis gives first-order rate constants for solvolysis and rearrangement of the primary ester. The importance of the internal phenomenon in acetolysis is comparable in the present case, two other unsymmetrical cases with neighboring aryl, the exo-norbornyl, the 3-phenyl-2-butyl and the a,adimethylallyl systems. The present data supply more orientation on the magnitude of driving forces due t o participation of carbon. ‘
The solvolysis of 2-phenyl-1-propyl p-bromobenzenesulfonate is of interest for several reasons. First, it furnishes another calibration point in the development of a picture of the order of magnitude of driving forcesadue to participation of neighboring groups in Wagner-Meerwein type rearrangement. Secondly, it is of interest in connection with internal rearrangements, symbolized by I + 11, which acR
sulfonate (111) and some related matters are reported in the present paper.
I
> CI p C a < I
0
0
\/ S
/\
0
Ar
I
I
0
B r C & I i \O I11
4
S ’‘
/\
Ar
0
I1
company solvolysis. In symmetrical cases such as that represented by exo-norborny14 and 3phenyl-2-butyP arylsulfonates, rearrangement of the sulfonate maintains structure and the rearrangement can be followed by comparison of polarimetric with titrimetric rates. In most unsymmetrical cases the rearranged sulfonate would solvolyze a t a rate too fast to observe the rearrangement, J t could be anticipated that 2-phenyl-lpropyl p-bromobenzenesulfonate (111) was a favorable case for the observation of internal rearrangement accompanying solvolysis for 2-phenyl- I propyl p-bromobenzenesulfonate (111) was expected3 to be a fast primary sulfonate, while the product of internal rearrangement involving migration of a phenyl group, namely, benzylmethylcarbinyl p-bromobenzenesulfonate (IV), was already known6 to be a slightly retarded secondary sulfonate. Therefore, the expected gap in solvolysis rate between the secondary and primary isomers was expected to be well below the usual value, possibly low enough to make observable the accumulation of secondary isomer starting with primary bromobenzenesulfonate. The results of our investigation of the kinetics of the solvolysis-rearrangement of 2-phenyl- 1-propyl p-bromobenzene(1) Research supported by Office of Naval Reseurch. (2) Presented before Organic Division of American Chemical Society, Boston, Mass., April 2-5, 1951, page 5 2 M of Abstracts. (3) S. Winstein, B. Morse, E. Grunwald, K. Schreiber and J. Cone, THISJOURXAL, 74, 1113 (1952). (4) S . Winstein and D. Trifan, ibid., 74, 1154 (1952). (5) S Winstein and K. Schreiber, ibid., 74, 2165 (1952). (6) S.Winstein. E;. Schreiber and M. Brown,ibid., 74, 1140 (1962).
\s.”
b
0
S ’‘
> c,-c.,< 0
CHoCH-CH1 I
I
0
R
I
k,_
CHaCH-CH2 I
Br CsH!
‘0 IV
.1k*
kp
Products
Products
First order rate constants k for the acetolysis of 2-phenyl-1-propyl p-bromobenzenesulfonate (111) calculated from equation 1 where a is the initial concentration : nI
a - x
=
kt
of the ester and x is the concentration of reacted material a t time t, rose rapidly. A representative run is given in Table I. Thus it is seen that in the solvolysis of 0.0306 M bromobenzenesulfonate the first order reaction rate constant rose from 2.07 to 7.53 X set.-'. In view of the experience with the symmetrical s ~ l f o n a t e s this , ~ ~ ~behavior suggests that indeed the rearrangement accompanying solvolysis is observable. Starting with the TABLE I RATE O F ACETOLYSISO F 0.03061 hf 2-PHENYL-1-PROPYL ~-BROMOBENZENESUI.FONATE AT 75.01 10-21,
0.0431 M
sec.
NaOAc, ml.
00 72 144 217 293 373 493 812 966 1107 1717 1969
0.000 ,051 .166 .250 .a0 .538 .SI8 1.412 1.825 1.979 2.508 2.744 3.551
m
lo‘$, sec.
.. 2.07 2.32 3.38
4.30 4.41 5.30 6.25 6.89 7.36 7.14 7.53
..
S. WINSTEINAND l i w r c'. SCHKEIBEK
21172
secondary isomer 1V on the other hand, extremely steady first order rate constants of acetolysis are obtained.6 Table IT presents the data for a typical run and it is clear that first order rate constants show no trend up to 937, solvolysis. Thus the secondary isomer is not developing primary material in solvolysis. r4BLE I < A l L O F AcEIoLYSIS O F
11
0 0301 M
NaO4c nil
10.
0i)OO
li
1'27
0
5%
77
1
14:
i 76
1 461 1 692 1 liL? 2 412 , 04x 1 (1.W 4 GB; 1 %l
; 87 '1 8.;
44581i YlOili) m
in the residual ester a t any time, t. The necessaq specific rate constants of benzylmethylcarbinyl p-bromobenzenesulfonate, k,, whose determination is illustrated in Table 11, are summarized in Table 111. The necessary specific solvolysis rate constants for 2-phenyl-l-propyl p-bromobenzenesulionate, K,, are the values of the instantaneous rate constant extrapolated to zero time. Because of the rapidly rising instantaneous rate constants, this is a difficult extrapolation and the values of k, obtained in this way tend to be high.
X sec
2700 6420 3520 10260 1:368il 160Sl) J4BfiO
From large scale plots of (a - x ) as. t values of the instantaneous rate constant, k, or (dx/dt)/(a - x) were obtained with the aid of a tangent meter. These then furnish what amounts to an analysis oi the remaining p-bromobenzenesulfonate a t any time, t , with the aid of equation 2, where F, denotes the inole fraction of I11
0 0296 -19HE N L Y L M E ? H Y L C A R R I ~ ~ J ,
p-BROMOBENZEKESULFOVATE A r 75 01 ' 1 , ,ec
Vol. $4
.i 0;) ; 'li > 01 i 90 (R, will begin a t zero and will climb until it approaches a value R equal to k ; / ( k , - kr - kp) a t infinite time. lo The instantaneous rate constant begins at the value of the primary ester, kp and climbs until it approaches the value (kr kp) a t infinite time. I n solvolysis of a mixture of I11 and IV with the original value of SIP less than R, SIP TABLE will tend to climb to R and the instantaneous ACETOLYSISOF 0 . 0 3 1 8 M ~ - P H E N Y L - ~ - P R O P YP-BROMOL rate constant will climb to the same final value BENZENESULFONATE AT 74.84' of (k, kp). When S/P is initially greater than Reaction, % 0.0234 M 0.03704 M 10-1, No salt R, SIP decreases in a run and approaches R while NaOAc added DPGHOBs sec. the instantaneous rate constant will start appropri1.26 1.46 1.54 6.3 ately high and decrease, approaching the same 2.41 3 . 1.3 3.09 9.9 limiting value, (kr k,) as before. For a mixture 4.31 5.73 5.58 15.3 with SIP initially equal to R,SIP is predicted to 6.02 5.30 6.09 17.1 remain perfectly constant, and the instantaneous 10.4 9.77 8.17 24.0 rate constant to remain constant a t the value 12.6 13.3 28.2 (k, kp), which is reached in the limit in the other 18.1 15.4 17.2 36.0 cases. When synthetic mixtures of I11 and IV 16.6 18.5 39.0 were solvolyzed, this prediction was verified. 26.0 23.6 24.9 50.4 This is illustrated in Table VI, where the first It also is clear that the rearrangement of I11 order constants, calculated from equation 1, in acetolysis of a 1:0.253 mixture of I11 and I V are into IV is not due to external r e t ~ r n . An ~ ~ ex~ seen to be very steady. L. Batrman, M. Church, E. Hugtics, C Ingold a n d K. Taher,
+
+
+
+
+
+
+
(8)
J . C h o n . S a ,979 (1940). (9) S. Winstein, E. Grunwald and €I Junes, THIS J O U R N A L , 73, 2700 (1951).
+
(10) For the case where ( k , k,) > k, the composition of residual 9-bromobenzenesulfonate aproaches pure S and the instantaneous solvolysis rate constant approaches k.
2-PElENYL-1-PROPYLp-BROMOBENZENESULFONATE
May 5, 1952
2175
TABLE VI ’ composition of the mixture and the observed rate constant, k p can be calculated using equation 2. RATEOF ACETOLYSS OF A 1:0.253 MIXTUREOF 2 - P B N n - 1 The d u e S of kp, thus derived, are shown as “10’ PROPYL AND BENZYLMETHYLCARBINYL @-BROMOBENZENESULFONATES AT 0.0411 M NaOAc, ml.
kp calcd.” These values are a little lower and more
99.96’
reliable than those in Table IV since the latter, obtained by extrapolation, tend to be high. Re000 0.311 .. treatment of the data of solvolysis of pure I11 003 .475 1.31 (Table IV) using the new values of kp leaves (kr 006 ,623 1.31 kp) virtually unchanged, since these are quite 012 .905 1.29 insensitive to the choice of kp. The values of 018 1,152 1.27 (kr kp) are given in Table VII, and by subtrac024 1.396 1.28 tion of kp from them, new values of kr, given in Table 030 1.615 1.27 VII, are obtained. The theoretical value of SIP 036 1.840 1.29 for a mixture with a constant rate constant, cal046 2.113 1.26 culated as k,/(k, k, kp), is given in Table VI1 060 2.500 1.26 in the column headed “ S / P calcd.” These values 081 2.976 1.28 are, of course, sensitive to the choice of k, and 105 3,298 1.24 differ somewhat in some cases from the “SIP 157 3,881 1.28 expl.” values, which were based on earlier estimates m 4.430 .. of k. Internal Rearrangement.-The internal rearMean 1.28 f 0.02 rangement of I11 into IV which the data demand In Table VI1 are summarized the data on the is still open to more than one kind of description, it seems solvolysis of synthetic mixtures of I11 and IV. but, in line with the previous discu~sion,~ lo%, aec.
10’k, (sec. -1)
+
+
- -
-
TABLEVI1 SOLVOLYSES OF MIXTURES OF 2-PHENYL-I-PROPYLAND BENZYLMETHYLCARBINYL #-BROMOBENZENESVLFONATES
&AfMARY OF
57%
Temp., OC.
75.01 74.92 74.90 74.90 74.90 99.96 99.86 99.78 4
Added salt
0.236 ,28? .243 .193 .243 .253 .252 .189
... ... 0.041 M NaOAc .037 M NaOAc .042 M DPGHOBs’
...
.041 M NaOAc .037 M NaOAc
+
10’k Obsd., sec-1
106kp 106(kr kp) Calcd., set.-' sec.-1
0.88 i 0.02 0.98 f 0.02 1.09 f 0.03 0.94 i 0.03 1.00 f 0.03 12.8 f 0.2 14.8 0.3 12.7 f 0 . 5
1.7 1.5 3.4 3.1 2.4 42 43 45
*
0.97 0.97 1.01 1.01 1.11 12.7 12.7 12.7
S/P
10‘kr sec. -1
Calcd.
8.0 8.2 6.7 7.0 8.7 85 84 82
0.273 .280 .211 .221 ,291 ,251 .202 .188
Diphenylguanidinium p-brornobenzenesulfonate.
The column “S/P expl.” lists the ratios used in the experiments and the column “10% obsd.” gives the observed first-order rate constants which were steady and showed no definite trend. From the
0 I
CH:-CH-CHa 0
k’
+
I
0
Q
0
)
Y
\s/
/\
0 CsH4Br I11
J. k1
0 I
CHc-yH-cH,
a t present best described in terms of internal ret ~ r n ~ 1On ~ *this ~ basis an ion-pair type of intermediate such as VI11 or IX is the one which can yield benzylmethylcarbinyl p-bromobenzenesulfonate (IV) by internal return. We can have k‘ represent the sum of the firstorder rate constants for reactions which either do not give return or do ,H,, CfI--?-->CH give some return, but only to very e or CH8-C+-CHa much more reactive bromobenzeneCHs 0- 0 0-Bs sulfonates than I11or IV. If k1represents the rate constant for formation VI1 from I11 of the intermediate which /\ or returns to IV (rate constant L1) 0 CsHdBr VI yields products and titrable p-bromobenzenesulfonic acid (rate constant or other products ~ S O H ) ?then the measured kr values (for I11 + IV) are represented in equation 6, and the measured kp values by equation 7.
or C H 8 - - c i i ~ ~ H ,
CH:-CH-CHs
I
OBs I V 0-
0
\d /\
0
C‘H‘Br
VI11
0- 0
s’\ ’0 b&IdBr IX
Products
0
/ ’
kr
(hk-i)/(k-i
+
+ +
~EOH)
(6)
KP a k‘ [hk8OH/(k-l k80H)I (7) Whether, on the present basis, the acetolysis of benzylmethylcarbinyl p-bromobenzenesulfonate (IV) is also associated with internal return, cannot yet be answered, The extent to
s. WINSTElN AND KURTc. SCHREIBER
'2 17(j
which an intermediate from IV resembles or differs from intermediate VI11 or IX from I11 in any solvent, taking into account the nearest and most important solvent molecules, we expect to decide from work now proceeding. An intermediate from TV can differ from one from 111, and therefore internal return could be more important in one case than another. It is interesting that the relative importance of the internal phenomenon is comparable in the several cases of acetolysis where internal rearrangement has been observed. Thus ( k ~ k , ) / k ~is ca. 3-4 for a,a-dimethylallyl chloride7 a t 25O, k,/ kt is 3.5 for exo-norbornyl p-bromobenzenesulfonate4 a t 25' arid ca. 4.5 for 3-phenyl-2-butyl p-toluenesulfonatei a t 00-75O, while ( k , k,)/kp is ca. 3-5 for 2-phenyl-1-propyl p-bromobenzenesulfonate (111) a1 i'3-100°. The situation is similar with two analogs of 111, mniely, X and XII, ' t s tllsclosed by preliininnry work.
+
+
CXHa
OCIII
Vol. 74
constants, 1V:III is similar in ethanol and acetic acid and, while a little smaller, is still 9 in formic acid a t 25'. In ethanol we ascribe the disappearance of the internal rearrangement phenomenon to solvent participation but shall defer more discussion of this matter until our investigation of the products and stereochemistry of solvolysis of I11 is more complete. In formic acid, the internal rearrangement has become sufficiently unimportant, relative to solvolysis, that a large trend in the solvolysis rate constant is no longer observed. In the case of 3-phenyl-2-butyl 9-toluenesulfonate, the change from acetic acid to formic acid decreased very markedly the ratio of polarimetric to titrimetric rate constants. Analogously in the present case, the change from acetic to formic acid solvent would decrease the ratio of (k, kp)/kp very markedly. This decrease was evidently sufficient to make the upward trend in rate constant [whichcan a t most go from k , originally to ( k , k,) a t infinity] during the portion of the reaction ordinarily scrutinized In a formolysis rate run too small to exceed ordinary random variations. 1
+
+
1 -\BLt \ 111
ICarbs
I CH~CH-CHZ
I
I
p
i.50 thdt iesidunl brornoberiienestdiriing 1, i t h piire ?\ rpproac lie5 p u r e rate cotistaiit . ~ p p r i ~ a c h ck,\ K u r l iclireillir i i - i ] > u t i l i i l i L d i t t i i 1, 1 , ,181ssystem ( k r
HCOOH IiCOOIi
C6H4Br
SSI
1ii acetolj-sis of 2-p-anisyl-1-propyl p-broinobenzenesulfonate ( X ) a t 49.60', the integrated first order rate constant begins in the region of 2 X 10-5 set.-' (kp) and rises to 3.2 X louJ sec. t t 95yo completion. The rate constant, k,, of p-methoxybenzylmethylcarbinyl p-bromobenzenesulfonate (XI), not yet available, can be estimated set.-' from the value for the p a t ca. 4 x toiuenesulfonate,6 1.20 X l o p J sec. a t 49.72'. Thus the gap between k , and 6, is very small. When a value for k, of ca. 4.2 X 10-j set.-' is used together with k , = 2 X set.-' in eyuation 2, a plot of in [a/(. - x)Fp]vs. t leads to a k p ) is cu. 3.60 X straight line. From this (k, IOF5 sec.-'so that ( k , k , ) / k p is cu. 3." The general climb in rate constant in acetolysis f 2,3-diphenyl-l-propyl p-bromobenzenesulfon"tel2 ( X I ) suggests a comparable importance of aternal rearrangement in this system, also. Ethanolysis and Formo1ysis.-In two other zclvents, namely, absolute ethanol and formic tcid, the solvolysis of 2-phenyl-1-propyl p-broinouenzenesulfonate (111) proceeds in ci first-order fashion with no certain trend in the rate constants, which i.ze suimnarized in Table VIII. Coinparison cf the rate constants of I11 in these solvents with those6 of IV shows that the failure to detect a trend is not largely due to a decreased gap in rate between 111 and IV, for the ratio of solvolysis rate ,i i i L n n
501\ e n t
rj
0
bitlA\OL\51S
A\D
F o R > f o L ~ b r SO F
PHENYL-
1-PROPI L P-BRQMOBENZENESULPoXAlE
CH--C€€-CH2
CH jCFI--&IL
01
t, C
75 75 75 24 14
01
01 01 96 06
ROBs 10%df
d 004 3 972 2 80-4
5 374 :3 3.21
l O g k , 5ec
4 48 & 0 4 20 i 0 -4 3 8 i 0 3 31 i:o 3 35+0
-1
08
09 06 09 16
Reactivity Considerations.-The rate data show that '2-phenyl-1-propyl p-bromobenzenesulfonate, with a primary leaving group, has a considerably enhanced reactivity to be ascribed to participation, Comparing ( k , kri with the rate constant for solvolysis of the corresponding neopentyl derivative3ti3(allowing a factor of 3 between a p-bromohenzenesulfonate and a p-toluenesulfonate), one obtains the sequences
+
.lcOlI, ; Y o ,
CI-I3CI1ICoM~)C€I,OBs,
40 > (CH~)~CCHIOBS, 1 IICOOtI, 2 j o , C1I3CH( C ~ l i 5)CIIZOBs, 50 > (CHz)sCCH20Bs, 1
These illustrate the rate enhancement even without consideration of correction factors previously discussed. The effect of a p-methoxy group in 2-phenyl-lpropyl p-bromobenzenesulfonate is very substantially rate-enhancing, as is expected. Comparing ( k , k,) values in XcOH a t 50' gives the sequence
+
CH?CI-I(C6I-I40CI-I3-~)CHzOBs, 112 > CH3CH(CaHa)CH2OBs, 1
This effect of the 9-methoxyl group corresponds to d p in Hammett's p b treatment'* of - 7.65. With the aid of the data presented in the present article and previously, it is possible again3 to illustrate the much decreased sensitivity of rate to a-methyl substitution for cases of participation.
i
LO
113) S \\.instein a n d €i hlarshnll Tins J O C R X A L 74, 1120 (1952) (14) IInmmett, ' Phvsiial Organic Chemlstr) McGrnm -11111 BooL Irii \ ~ nY o r l \ 1 1040 p 186
May 5, 1952
2-PHENYL-1-PROPYL ~BROMOBENZENESULFONATE
2177
ment to XI11 involving hydrogen migration (see VI or VII) would yield such a reactive isomer that the k, for this process would be included in the AcOH, 75"; CHaCH(CaH6)CH(OBs)CHa, designated as kp in the present work. 71 > C H ~ C H ( C ~ H ~ ) C H ~ O 1 B Sconstant , Similarly in the case of 3-phenyl-2-butyl p-tolueneHCOOH, 25"; CH&!H(C&)CH(OBs)CHa, sulfonate,j rearrangement to the tertiary ester 240 > CHaCH(CaH6)CHzOBs, 1 XIV would, for kinetic purposes, supply a conThese show that introduction of an a-methyl group into 2-phenyl-1-propyl p-bromobenzenesuffonate increases rate by only a factor of ca. lo2. I I This effect of an a-methyl group is even smaller OTs OTs when the substitution is in 2-p-anisyl-1-propyl XIV p-bromobenzenesulfonate. Comparing k , for 3-panisyl-2-butyl6 with k, for 2-p-anisyl-1-propyl in tribution to the titrimetric rate, included in the titrimetric rate constant, kt. 9cOH a t 50' gives the sequence
Comparison of 3-phenyl-2-butyl5 I (ha) with 2phenyl-1-propyl (kp kr) gives the sequences
+
CHaCH(C G H ~ O C H ~ - ~ OTs)CHa, )CH( Kinetic Appendix 28 > CH~CH(C~HIOCH~-P)CH~OTS, 1 Letting P and S denote the concentrations of primary and isomer I11 and IV, respectively, equations 8 and Complication Due to Internal Rearrangement.- secondary 9 express dP/dt and dS/dt in terms of P and S. For our understanding of molecular rearrangedP/dt = -(kr kp)P (8) ment, one of the worst complications arising from dS/dt = k, P - k, S (9) internal rearrangement is that the phenomenon may escape kinetic detection. For instance, Integration of equation 8 gives equation 10 for P as a funcconsider the situation if, in the case of 111, S had tion of time while substitution of this expression for P into equation 9 and solving the resulting differential equation been very much more reactive in solvolysis; in yields equation 11 for S as a function of time. In equations
+
+
other words k,>>(k, k,). Under these conditions, from the derivations in the Appendix, S/'P would quickly reach the steady state value substantially equal to k , / k , and the solvolysis rate constant starting with pure P would very quickly reach kr). In fact the steady rate conthe value (k, stant ( k , k,) could be reached before the first point in the kinetic run and then the measured steady rate constant would include reaction through S as an intermediate. Further, consider the hypothetical case where k, : kr : k, are of the order of 1Oj : lo2:1. The steady rate constant, reached too soon to observe a drift, would be 101 times k, and would measure solvolysis, 99% of which proceeded through the rearrangement product. It is, of course, possible, in general, for a substance to rearrange to a number of isomers, depending on which one of the b-groups migrate in a Wagner-Meerwein rearrangement, even without bringing up the more complex possibility of coupled shifts. As derived in the appendix for one case of originally pure material giving solvolysis and irreversible rearrangement to other species, more reactive in solvolysis, each ratio SuiP approaches a value R, and the solvolysis rate constant approaches a definite final value. Now in such a case the Sn/Pratios approach their steady values a t different rates. One or more of them may reach their steady values too soon to disturb the kinetics. Then, even the very initial solvolysis rate constant will be the sum of k , and those kr values relating t o the Su/Psteady states so rapidly established. For example, in the case of 2-phenyl1-propyl p-bromobenzenesulfonate 111, rearrange-
+
+
HI O-(j!-TH, CH3 OBs 111
0 I
CH3-C-CH3
I
OBs
XI11
p =
Poe-(kr+kp)t
(10) (11)
10 and 11, POand SOdenote initial values of P and S , respectively, to use the general case where a mixture of I11 and I V is solvolyzed. This gives for S I P the expression shown in equation 12.
I t is convenient to define R, ROand A by equations 13, 14 SIP from equation 12 in the form
and 15 and thus t o rewrite of equation 16.
R k,/(k. - k, - k,) (13) Ro 3 So/Po (14) A k , - k, - kp (15) SIP = (Ro - R ) e - A l + R (16) From equation 16, Fp,the mole fraction of primary ester 111 in the remaining ester a t any time, t , is given by equation 17 and from this equation and equation 2
the instantaneous first order rate constant, (dx/dt)/(a is given by equation 18. k = (dx,'dt)/(a - X ) = k , -
- cc),
For the general case where originally pure P isomerizes irreversibly to a number, n, of more reactive species, SI, S::. . ., S,,cach with a solvolysis rate constant ks,, ksz. . ., kin,an analogous treatment is possible. P is given a
P
=
- (kp + F k r ) f Poe
(19)
s. WINSTEIN AND R URT C. SCI~REIBER
2178
\'ol. i 4
Anal. Calcd. for CljH160aSBr: C, 50.71; H, 4.2G. Found: C, 50.84; H, 4.46. Benzylmethylcarbinyl p-Bromobenzenesulfonate.-This n Where ks, is greater than (kp Z k , ) , &/I' approaches the material was the same as previously describeda8 2-p-Methoxyphenyl-1-propylp-Bromobenzenesulfonate .1 2-Ani~ylpropionaldehyde~was reduced with lithium aluvalue Rn defined by equation 22. minum hydride. To a solution of crude 2-anisyl-propanol (5.4 g., 0.0326 mole) in pyridine (32 cc.) was added bromobenzenesulfonyl chloride (8.3 g., 0.0326 mole) with cooling and the mixture was allowed to stand overnight in the refrigerator. Isolation in the usual way yielded 5.2 g. (42%) Defining A , by equation 23, S J P becomes of 2-anisyl-1-propyl bromobenzenesulfonate, m. p. 87-88 ". Anal. Calcd. for Cl&I170aSBr: C, 49.88; H, 4.44. (kBn - k,, - 2 k r ) = 1., Found: C, 49.87; H, 4.29. Diphenylguanidinium p-Bromobenzenesu1fonate.-A expressible by equation 24 solution of 1.5 g. (0.0063 mole) of p-brornobenzeiiesulfoiiic acid in 100 ml. of dry ether \vas added with shaking t o ;t solution of 1.4 g. (0.0065 mole) of diphenylguanidiiie in 50 (24) nil. of c!ry cther. The mixture was kept overnight in the When all the ratios Sn/P have become equal to the R, values, refrigerator. Then the crystals were filtered, washed l v i t h cold ethcr and dried to yield 3.5 g. (90%) of material; m.p. the fractions of P , SI, etc., in the remaining toluenesulfonate after recrystallization from acetonitrile, 180.5-181.3". are given by equations 25 and 26. The rate Anal. Calcd. for C1SHlaX30jSBr: C, 50.90; H, 4.05. 1 = ----(231 7 Found: C, 50.84; H, 4.16. Isolation of Benzylmethylcarbinyl p-Bromobenzenesul1 S l l fonate (IV) from Partial Solvolysis of 2-Phenyl-1-propyl pBromobenzenesulfonate (III).-A solution of 2-phenyl-lR, propyl 9-bromobenzeiiesulfonate (24 g., 0.0675 mole) in FRn = ____ (26) dry acetic acid (1 1.) was heated at 99.7' for 95 minutes, 1 i ZRn cooled in ice and poured into a separatory funnel containing water (1 l.), Skellysolve "F" (500 cc.) and ether (500 cc.). constant for solvolysis at that time will be given by equation The aqueous layer was once extracted with a 1 : 1 mixture 27, of ether-Skellysolvc I;. The combined organic layers were neutralized with 10% potassium carbonate solution and k = - -dx/dt =---1 dried over potassium carbonate. After concentrating to a--2 ca. 200 cc. and cooling in ice, 7.8 g. of fairly pure 111, m.p. 1 $Rn 79.5-82" were obtained. On further concentration to ca. 50 cc. there was obtained a second crop (3.2 g.), m.p. 75-79', [kp Ribs, R&s2 . . . R&a,l (27) which still consisted largely of 111. After removal of the remaining solvent and standing in the freezing unit of a reExperimental frigerator for several days, a third crop (2.4 g.), m.p. 612-Phenyl-1-propyl p-Bromobenzenesulfonate.-2-Phenyl- 75", was obtained. This contained a substantial amount of propionaldehyde (8 g., 0.06 mole), was reduced with lithium IV. Procedure for Kinetic Measurements.-In acetolysisl5 aluminum hydride (1.2 g., 0.03 mole) in 70 ml. of anhydrous ether. The reaction mixture was poured into ice-water con- and ethanolysis,a the general procedure was the one pretaining 6 N sulfuric acid, and the carbinol was isolated in viously described. Lithium perchlorate was prepared and the usual way. The residue ( 8 g.) from removal of ethcr used in acetolysis runs as reported previously.le In formolyfrom the ethereal solution of the cxbinol was not purified, sis, the titration procedure was the one used before,13 the but immediately treated'with 60 cc. of anhydrous pyridine solvent was 0.08% in water by Karl-Fischer titration, and and 16 g. of p-bromobenzenesulfonyl chloride. The reac- the ampoule technique was employed. tion mixture was allowed to stand in the refrigerator for 24 Los ANGELES24, CALIF. RECEIVED JUNE 11, 1951 hours; then it was worked up in the usual way to yield 15.2 g. (73%) of 2-phenyl-I-propyl p-bromobenzenesulfonate, (15) S. Winstein, E. Grunwald and L. Ingraham, THISJOURNAL,70, m.p. 81.5-82.5'. The equivalent wt. of this material in 821 (1918). acetolysis was within 1.0% of theory. (18) S. \%i'nstein and R. Adams, ibid., 70, 838 (1948).
as a function of time by equation 19, the concentration of any one of the isomers, S, by the general equation -00 and S,/P by equation 21.
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