1985
Mercury( 11)- and Thallium (111)-Catalyzed Hydrolysis of Isopropenyl Acetate Peter Abley, James E. Byrd, and Jack Halpern* Contribution from the Department of Chemistry, The University of Chicago, Chicago, Illinois 60637. Received August 6, 1971 Abstract: The hydrolysis of isopropenyl acetate in aqueous solution was found to be catalyzed by organomercury(I1) and bis(organo)thallium(III) ions, i.e., RHg+ and R2T1+,respectively, where R = CH3COCH2,CHI, CBHS,etc. Kinetic and equilibrium measurements are interpreted in terms of an oxymetalation-deoxymetalation
+
+
+
+
+ +
mechanism, it., M+ C H d ( O A c ) C H 3 HzO $ MCH2C(OH)(OAc)CH, H+ + M+ CH3COCHa HOAc (where M+ = RHg+ or R*Tl+). Kinetic measurements on the reaction, Hgz+ CH2=C(OAc)CH3 HzO+ HgCH2COCH3+ HOAc, and on the corresponding reactions of Tl3+ and TlCHzCOCH32+ leading to the and TI(CH*COCH&+,respectively,also are reported. formation of T1CH2COCH32+
+
+
e have recently reported that Hg2+ reacts with isopropenyl acetate (1) in aqueous solution form the mercuriacetone ion (2) according to eq 1,
W to
TP+
+ CH-C
/OAC
\
ks + Hz0 +
CHa
0 HgZ+
+C
H A
/OAC
\
II
+ Hz0 + kl
TlCHzCCHa'+
CHa
(5)
+ HOAC
(6)
0
1
[ Lc1
II
TlCHzCCH32+
0
II + H+ ---t HgCHzCCH3+ + HOAc 2
HgCH-A-CHs
+ HOAC
ks + C H A ,/OAC + HzO + \
CHa
(1)
0
II
Tl(CHaCCHa)z+
and that 2, in turn, catalyzes the hydrolysis of excess isopropenyl acetate t o acetone (eq 2).l C H d
1
/OAC
\
+ HzO +CH3
CH3
+ HOAC
(2)
CH3
In this paper we report extensions of these studies which demonstrate that the catalysis of reaction 2 is effected also by other organomercury(I1) ions, RHg+ (where R = CH3, CsH6,etc.), as well as by bis(organo)thallium(II1) ions, RzTl+. Kinetic and equilibrium measurements are described, the results of which support the general mechanism depicted by eq 3 and 4
/ M+ + CHFC \
OAc
+ HzO
ka k -a
CH3
3 0
3
+ H + -% M+ + CHI! CHI i + HOAc
(4)
(where M+ = RHg+ or R2T1+), corresponding to that previously proposed for the HgCH2COCH8+-catalyzed hydrolysis of isopropenyl acetate. We also report the results of kinetic measurements on reaction 1 and on the corresponding reactions (eq 5 and 6 ) leading to the (1) J. E. Byrd and J. Halpern, Chem. Commun., 1332 (1970).
formation of TlCH2COCH32+and Tl(CH2COCH3)2+, respectively, Experimental Section Materials. The following organomercury and organothallium halides were obtained from Eastman or Alfa Inorganics and recrystallized from methanol: CH3HgCl, C6HjHgC1, p-CH3C6H4HgC1, (CH&TlCl, (CsHs)2TlCl. p-C1C6H4HgC1(mp 238-240", lit.z mp 240") and p-NOzCeH4HgC1(mp 261": lit.z mp 265") were synthesized from p-C1C6H4NH2 and p-NO2C6H4NHZ,respectively, by the procedure of Nesmeyanov.? p-NH2C6H4HgC1was prepared from p-NH2C6H40Ac (Eastman) according to Nesmeyanov.2 Solutions of HgCH2COCH3+, TICHZCOCH~~+, and Tl(CH2COCH&+ were prepared by the stoichiometric reactions of isopropenyl acetate with Hg?+ and T13+ in aqueous perchloric acid solution according to eq 1, 5 , and 6, respectively. Solutions of the other organomercury(I1) and bis(organo)thallium(III) ions (RHg+ and R2T1+,as their perchlorate salts) were prepared from the corresponding halides RHgX and RzTIX (obtained as described above) by the following procedure. A solution of the halide in aqueous methanol, to which were added an equivalent amount of reagent grade silver perchlorate and sufficient perchloric acid to prevent hydrolysis, was warmed and stirred. The precipitated silver halide was separated by filtration and the filtrate was evaporated at room temperature under reduced pressure with successive additions of water until all the methanol was removed. The resulting aqueous solution was chilled overnight, filtered, and diluted to the desired concentration. Solutions of mercury(I1) perchlorate and thallium(II1) perchlorate were prepared by dissolving HgO and Tl(OH)3 (each of which had been precipitated from an aqueous solution of the corresponding perchlorate salt with ammonia and washed thoroughly with distilled water) in aqueous perchloric acid. (2) L. G. Makarova and A. N. Nesmeyanov, "The Organic Compounds of Mercury," North-Holland Publishing Co.,Amsterdam, 1967, and references therein.
Abley, Byrd, Halpern / Hydrolysis of isopropenyl Acetate
1986 Sodium perchlorate was prepared by neutralizing reagent grade perchloric acid with sodium carbonate and recrystallizing the precipitated salt from distilled water. Perchloric acid and isopropenyl acetate (Aldrich, >99%) were reagent grade chemicals. Distilled water was used for the preparation of all solutions. Isolation and Characterization of Products. The products of reaction 1 were characterized by pmr, the product solution having the following spectrum: 6 2.1 (s, 3, HOAc methyl), 6 2.3 ( s , 3, CH, of 2), 6 3.0 (s, 2, CH, of 2). 2 was also isolated as the chloride, CHaCOCH*HgCI, by addition of sodium chloride to the product solution. The resulting product (mp 103-104", ]its3mp 104") was identical with a sample of CHKOCHgHgCI prepared from the reaction of isopropenyl n-butyl ether with mercury(I1) acetate according to Nesmeyanov., The product of reaction 5 , i.e., TlCH2COCHa2+,exhibited the = 53 Hz, CHI), 6 4.44 following pmr spectrum: 6 2.53 (d, 3, JTI-H (two doublets, 2, J ~ ~ ~ T=I 729 - H Hz, J~OSTZ-H = 723 Hz, CHz); M511: 2@3TIrelative abundance -3: 1. Attempts to isolate the acetate, (AcO)*TlCH2COCHS, yielded a rather unstable, lightsensitive product (ir: YC-o (Nujol) 1660 cm-'). The product of reaction 6, i.e., T1(CH2COCH&+, exhibited the following pmr spectrum: 6 2.47 (d, 6, JTI-H = 12.5 Hz, CH,; broadened presumably due t o unresolved 203T1and 205Tlcoupled signals), 3.60 (two doublets, 4, J~OETI-H = 393 Hz, JZO~TI-E = 387 Hz, CHz). Addition of sodium chloride to a cu. 1 M product solution yielded, on cooling, a precipitate of the chloride (CHICOCH&TlCl which was separated by filtration, washed successively with chilled water, ethanol, and ether, and dried over P 2 0 5 B z uucuo: mp 180-185" dec; ir Y C - o (Nujol) 1685 cm-1. Anal. Calcd for C6Hl~O2C1T1: C, 19.36; H, 2.84; 0, 9.04; C1, 10.02. Found: C, 19.37; H, 2.71; 0, 9.16; C1, 10.56. The course of reaction 2 was followed and the organic products (i.e., acetone and acetic acid) were identified and quantitatively determined by pmr (confirmed by gplc): 6 2.18 (s, 6, acetone), 6 2.10 (s, 3, HOAc methyl). Kinetic Measurements. The kinetics of reaction 2 were studied by pmr, monitoring the reactant (using the signal at 6 2.15 due to the acetate protons of 1) as well as each of the two products (using the 6 2.18 signal due to the methyl protons of acetic acid). These 1". measurements were made in the nmr spectrometer at 40 Control experiments were performed to determine the contribution from the acid-catalyzed hydrolysis of 1, and, in the few cases where this contribution was significant, an appropriate correction was made; this correction never exceeded 10% of the rate due to the mercury(I1)- or thallium(II1)-catalyzed reaction. The kinetics of reactions 1, 5 , and 6 were studied spectrophotometrically by monitoring the increases in absorbance accompanying these reactions at 250, 215, and 280 nm, respectively. The kinetics of reaction 4 for several RHg+ and R2Tl+ions, as well as the corresponding equilibrium constants, were also determined spectrophotometrically from the measured absorbance changes in the 270310-nm regions. All the spectral measurements were performed in a Cary 14 spectrophotometer with a cell compartment thermostated at 25 i 0.5". The treatment of the kinetic data for these reactions (as well as of the kinetic data for reaction 2 which is complicated by the accompanying occurrence of reaction 4) will be described later.
Results and Discussion Kinetics of the Hydrolysis of Isopropenyl Acetate. Kinetic measurements on reaction 2, performed as described above, typically encompassed the following initial concentration ranges: 0.1 to 0.3 M CH2= C(OAc)CH3, 0.05 to 0.5 M H+ (as HC104), and ca. 1 X to 1 X MRHg+ or R2T1+. The ionic strength was maintained at 1.5 M with NaC104. The kinetic results in each case could be accommodated by the general mechanism depicted by eq 3 and 4 and previously reported for the CH3COCH2Hg+catalyzed reaction. Both the spectral changes accompanying reaction 3 and the kinetic behavior described below supported the conclusion that under the prevailing reaction conditions the equilibrium of step 3 is rapidly (3) A. N. Nesmeyanov, I. F. Lutsenko, and N. I. Vereshchagina, Izc. Akad. Nauk S S S R , Otd. Khim. Nauk, 451 (1949).
Journal of the American Chemical Society
established compared to the ensuing product-forming step 4. On the basis of this assumption and in view of the large excess of 1 over M+ (justifying the neglect of [3] compared to [l]), the following relations may be derived, where K3 (= k3/k--3) is the equilibrium constant of reaction 3 and [M+Itot represents the total ( i e . , stoichiometric) catalyst concentration [M+ltot
rate
=
=
[M+l
-d[l]/dt
+ PI
=
(7)
k4[3][H+]
(9)
Combining eq 8 and 9 yields
Upon integration, this becomes
where [lI0 is the initial concentration (i-e., at t = 0) of 1. The half-life of the reaction, to.5(Le., the time at which [l] = 0.5[1],), is, accordingly, given by
In accord with eq 12, the kinetic measurements yielded linear plots, such as those depicted in Figures 1 and 2, of to.5us. [M+]tot-l and of t o . 5 us. [Hi-]-'. The slopes of these plots and the intercepts of the latter plots yielded internally consistent values of K3 and k4 which are listed in Table I. The values of K3 and k4, Table I. Equilibrium and Kinetic Data at 40" a
M+ 1.5b 0.11 0.22 0.29 0.60 0.35 0.44 0.90 14 1 .o 2.6 a Ionic strength maintained at 1.5 M with NaC104. by addition of 0.05 M HOAc.
2.5* 0.32 1.05 1.30 1.42 1.45 1.95 3.3 0.25 0.03 0.20 Unaffected
thus determined, could be used, in turn, t o simulate the complete rate plots (Le., plots of [l] us. t according t o eq 11) for the individual kinetic experiments. The agreement between such computed rate plots and the corresponding experimental ones, illustrated in Figure 3 for M+ = CH3COCH2Hg+,is seen to be satisfactory. Stoichiometry and Kinetics of Reactions 1, 5, and 6. The addition of CH2=C(OAc)CH3 (1) to solutions of Hg2+ and TI3+ resulted in rapid initial spectral changes which provided quantitative evidence for the formation of CH3COCH2Hg+, CH3COCH2Tl2+,and (CH3COCH2)2Tl+in accord with eq 1, 5, and 6 , respectively. The initial spectral changes accompanying the addition of 1 t o a solution of Hg2+ were in quantitative
1 94:6 1 March 22, 1972
1987 0.20
I
2000 I
l i
0.16
3
6 0.12 0)
s
t
8 0.08 a U 0.04 I
I
I
I
200
400
600
800
I 1000
Time, sec. Figure 3. Rate plots for the CHsCOCH2Hg+-catalyzed hydrolysis of isopropenyl acetate at 40": initial [I], 0.19 M ; [M+]tot = 4.2 M . Curves are calculated according to eq 11 using K3 = X 1.5 and ka = 2.5 M-1 sec -1. Points are experimental data ( [ l ] ~ M H + ; 0 , 6.25 = 0.19 M , [M+]tot = 4.2 X 10-3): 0, 3.12 X X 1W2MH+;A,0.125MH+;0,0.50MH+.
[Mf-Jtot-', M-'. Figure 1. Representative plots of io.: us. [M+]tot-' according to eq 12 (temperature 40"; ionic strength 1.5 M ; initial [l], 0.1-0.2 M ) : 0,CH3COCHzHg+ (0.33 M H+); 0, (CH3COCH&Tl+ (0.2 M H+); A, CeHaHg+(0.05 MH+); 0, (CeH~)zTl+(0.1MH').
0.4
Y
I
I I
0.3
i
Lo
N IC c O
g
0.2
c
0
c
Hd
0.1
I
/d
zooP -
,OOt
0
Added CCH7=C(OAc)CHal Initial CHg2'l or CTI"1
OO
5
10
20
LH'I" , M.'.
Figure 2. Representative plots of t o . 5 cs. [H+]-1 according to eq 12: M M+, 0.19 M 1); 0,CsHsHg+ 0,CH3COCH2Hg+ (4.2 X M M+, 0.1 M 1); 0, p-NOzCsHaHg+(1 X loW3M M+, (1 x 0.1 M 1); 0,p-ClCeHdHg+ (2.8 X M M+, 0.1 M 1); 0, M CF3C6HaHg+(1.47 X M M+, 0.1 M 1); V,(CH3)*T1+(3 X lO-'MM+,0.3Ml);A,CH3Hg+(S X 10-'MM+,0.3 M l ) .
agreement with the stoichiometric formation of CH3COCH2Hg+ according t o eq 1. This is illustrated by Figure 4 which depicts the results of a spectral titration at 275 nm (where the absorption spectrum of CHICOCH2Hg2+exhibits a maximum with E 3.6 X l o 2 M-I cm-l) with an end point at a [1]:[Hg2+] ratio of 1.o. Similar spectral changes, associated with the successive stoichiometric formations of CH3COCH2T12+and (CH3COCH2)2T1+[the absorption spectra of which con-
M Hg2+(0)and 4.2 X Figure 4. Spectral titrations of 1.0 X 10-4 M T13+(0)with CHz=C(OAc)CH3 at 275 and 290 nm, respectively (0.1 MHClOa, 1-cm light path).
tain bands centered on 292 nm (emsx 3.3 X IO2 M-I cm-l) and 287 nm,,,E( 8.6 X l o 2 M-' cm-l), respectively], characterized the addition of 1 to a solution of TI3+. Figure 4 depicts the results of a spectral titration at 290 nm which reveal end points at [1]:[Tl3++1ratios of 1 : 1 and 2 : 1, corresponding to the quantitative occurrence of reactions 5 and 6, respectively. The spectral changes described above were utilized to study the kinetics of reactions 1, 5, and 6 , each of which was found to obey a rate law of the form d[Mi+]/ dt = ki[M,][l] where MI = HgZ+,M6 = TI3+, and Ms = CH3COCH2T12+, respectively. Kinetic measurements (in which the formation of Mi+ was monitored spectrophotometrically at wavelengths of ca. 275, 215, and 280 nm, respectively) were performed under Abley, Byrd, Halpern / Hydrolysis of Isopropenyl Acetate
1988
2 a
0
2
4
8
6
0
IO
102[CH2=C(OAc)CH3], M. Figure 5. Absorbance change at 270 nm accompanying the addition of CH2=C(OAc)CH3 to a 1.0 X 10-3 M CH3COCH2Hg+ solution containing 0.05 M HClOc. Curve is computed for the equilibrium described by eq 3 using K3 = 1.26.
pseudo-first-order conditions with [Milinitial x M and [llinitial 5 X IOd4 to 3 X le3 M and [H+] = 0.1 M . These yielded the rate constants, kl = 2.6 X l o 4 M-I sec-I, ks = 1.2 X lo2 M-I sec-1, and ks = ca. 5 M-I sec-I, all at 25". Equilibrium and Kinetics of Reaction 4. The further increases in absorbance, beyond the 1 :1 [ l ] :[Hg"] and 2: 1 [1]:[T13+]end points of the spectral titration plots in Figure 4, can be identified with the reversible formation of 3 [Le., of CH3COCH2HgCHzC(OAc)(OH)CH3 and (CH3COCH2)2TlCH2C(OAc)(OH)CH3, respectively], according to eq 3 . The determination of the equilibrium constants for these reactions (i.e., the values of K3 listed in Table I) from kinetic data has already been described. The spectral changes associated with these reactions provided the basis for an independent direct estimation of K3 and, hence, for a test of the earlier kinetic interpretation. At sufficiently low H+ concentrations (
