The Journal of Physical Chemistry, Vol. 83, No. 25, 1979
Kinetics of Proton Transfer Reactions
3293
15) P. W. Moor, F. W. Ayscough, and T. G. Clouston, J. Polym. Sci., Chem., 15, 1291 (1977). 16) T. Sasuga, N. Morishita, A. Udagawa, Y. Kusama, and M. Takehisa, J . Polym. Sci-Chem., 14, 2575 (1976). 17) T. Sasuga and M. Takehisa, J. Macromol. Sci., phys., 13, 215 (1977). 18) A. Chapiro, "Radiation Chemistry of Polymeric System, Hgh Pobmer", Vol. XV, Interscience, New York, 1962.
C. Wailing, J. Polym. Sci., 48, 335 (1960). A. C. Toohey and K.E. Weale, Trans. Fara&y Soc., 18, 2439 (1962). V. M. Zhulin, M. G. Gonikberg, and V. N. Zagorbinina, Dokl. Akad. Nauk., 183, 106 (1961). (13) G. B. Guarise, Polymer, 7, 497 (1966). (14) G. B. Guarise, G. Paima, E. Siviero, and G. Taiamini, Polymer, 11, 613 (1970).
Kinetics of Proton Transfer Reactions. 6. Temperature-Jump Study of the Inosine-Indicator Systems Jean C. Thomas and John E. Stuehr" Department of Chemistry, Case Western Reserve University, Cleveland, Ohio 44 106 (Received April 9, 1979) Publication costs assisted by the National Institutes of Health
Kinetic measurements, by the temperature jump technique, are reported for inosine and the following indicator systems: chlorophenol red, phenol red, cresol red, and phenolphthalein,as well as for the two indicators phenol red and cresol red themselves. The results are interpreted on the basis of protolysis/hydrolysisof the various systems, and proton exchange between the indicator and inosine. All proton transfer reactions appear to be near or at the diffusion controlled limit. The indicator/inosine exchange rate constants correlate with the differences in pK between donor and acceptor.
In a recent series of papers,l we have focussed attention on the kinetics of divalent metal ion interaction with nucleotides, particularly those of adenine and cytosine. We are extending these studies to other coenzyme systems, such as the inosine phosphates. In the course of these studies we observed relaxation effects in metal-free systems of nucleosides. These relaxation effects are certainly due to proton transfer reactions involving the nucleoside plus indicator. Inosine is a particularly interesting system in that it can exist in two tautomeric forms. We decided therefore to characterize the proton transfer kinetics involving inosine and several pH indicator systems. Structures are shown for the three sulfonephthalein compounds (HIn). Phenolphthalein differs from phenol red only in that -C02- replaces -SO3-. R
R
0 HN
H
O
H
C
G
&So;
:Phenol Red
CH3:Cresol Red
OH OH
inosine
H In
Literature reports of indicator proton transfer reactions typically contain either the protolysis rate constant or the hydrolysis rate constant from rate studies in the acidic and basic region, respectively. In this study the pH was varied 3 units about pH 7; as a consequence, the rates were dependent on both protolysis and hydrolysis reactions. Experimental Section Inosine, phenol red, and cresol red (all from Sigma) were purified as needed. pK, values and concentrations were determined by potentiometric titration. Phenol red was purified by dissolving in aqueous NaC03H and recrystallizing from acid solution.2 All solutions were made by dissolving weighed materials in 0.1 M KNOB. 0022-3654/79/2083-3293$0 1.OO/O
The pK, of inosine was determined by potentiometric titration of 0.006 M inosine in 0.1 M KNOBwith 0.1 M KOH. Solutions were thermostated at 15 "C and bubbled through with nitrogen. The pH was measured with a Corning 103 potentiometer in conjunction with a Corning glass electrode and Orion calomel reference electrode. Standardized KOH was delivered from a 2.5-mL Gilmont microburet. Kinetic measurements at 15 "C were performed by the temperature-jump t e ~ h n i q u e .Test ~ solutions in 0.1 M KNOBwere placed in the T-jump cell thermostated at 10 "C prior to the temperature jump. The pH was adjusted by adding either 0.1 M HN03 or 0.1 M KOH and was measured before and after the T jump at 15 "C. For the inosine indicator systems, a single relaxation effect with a relaxation time about 10 ps was observed. The effect was fairly large and the relaxation times could be estimated to 5-10% uncertainty. Solutions containing 10-4-10-2 M inosine and (2-5) X M indicator in 0.1 M KN03 were studied a t pH 6.5-9.2, depending on the indicator. Two indicators themselves (phenol red and cresol red) were studied at pH 7.0-9.8 over the concentration range (2-5) X M. Uncertainties in 7 are estimated to be &lo%. The main source of error, however, is the pH: the necessity of carrying out measurements in unbuffered solutions near pH 7 resulted in pH drifts. These were as large as 0.1-0.2 units for the most dilute solutions. All observations were made a t or near a wavelength corresponding to the absorption maximum of the deprotonated indicator. Titration and kinetic data were analyzed by nonlinear computer minimization programs on a Univac 1108 computer. Results and Discussion Phenol Red and Cresol Red. A single relaxation effect was observed for each of these two indicator systems. Experimental relaxation times, on the order of 8-50 ps, were found to be strongly concentration and pH depend0 1979 American Chemical Society
3294
The Journal of Physical Chemistry, Vol. 83, No. 1
I
I
I
I\
I
\,
I
2-
-
o 5xm4y 2x10-~~_
‘\ ;
Thomas and Stuehr
I
I
\
3’
25, 1979
-
1
io5
7:-’ 1 35 -
0
SeC”
5
:
~
0 y~
.
~
~
-
7:-‘
sec-’
-
32.
io4
2-
-
10‘ I
5
6
7
I
1
0
9
1
1
0
-
5
PH
6
7
9
1
0
PH
a Figure 1. Variation of
0
b
with indicator concentration and pH for (a) phenol red and (b) cresol red. Solid lines are theoretical curves for T--’ calculated via eq I with the rate constants shown in Table 11. Part of the predicted pH dependence of T+-’ is shown for phenol red (dashed line). T-’
Scheme A
ionization of water, the latter by the slower indicator reactions. Algebraically, eq I reduces below pH 6 to 1/7- = k23([HI + [In]) + k32 and above pH 10 to 1 / ~=- k13,([HIn]+ [OH]) + k3q
ent, as shown in Figure 1. The pH dependence is complex and was difficult to establish due to the pH drift mentioned above. It is clear, however, that the data points increase numerically above pH 9 and pass through a maximum between pH 7 and 8. The maxima are clearly seen in the curves (Figure 1)for the 5 X 10“ and 2.5 X M solutions and occur at pH values somewhat below the pK. These results are quantitatively consistent with protolysis/hydrolysis steps coupled to the ionization of water (Scheme A). Reactions4 (2) + (3) and (3’) (1) represent the protolysis and hydrolysis reactions of the indicator; (4) + ( 5 ) is the neutralization of H20. Under our experimental conditions (neutral pH and HIn In, H OH) all three processes are important contributors to the net reaction. Two relaxation effects are expected from this reaction scheme. The expression for the two relaxation times, T + - ~ ,is given by
-
-
T*-’
=
0.5[(aii + a22) f [(ail + a d 2 - 4(aiia22 - ai~azi)1”~] (1)
where all = k1340Hl + k3’1 + k32 + kz3([H1+ [In]) a12 = k13,[HIn]- k2,[In]
+ k3q - k,,[OH] a22= k13,[HIn] + k45[H+ OH] + k54 a21 = kly[OH]
The plus sign in (I) corresponds to the larger ( T + - ~ ) values of the reciprocal relaxation time, the minus sign to the smaller (7--l). The former is determined primarily by the
These correspond, of course, to the isolated protolysis and hydrolysis reactions, respectively. Between pH 6 and 10 all terms in eq I contribute to the relaxation time expression. The relaxation time for the isolated water neutralization reaction is estimated to be about 70 p s at pH 7, and about 12 p s at pH 6 or 8. The behaviors of the two roots under our experimental and with k45, kZ3,k13, 108-1011 conditions ( [Inlo M-l s-l are such that T + - ~goes through a minimum at pH -7 (depending on the value of kZ3 and k1y) and rises sharply at the higher and lower end of the pH scale. On the other hand, the smaller root T - - ~goes through a maximum at the same pH as for the T + - ~minimum and exhibits minima on either side. The pH’s of the minima depend largely on the pK, of the indicator. The T-jump results correspond to the behavior of the slower root. Figure 1 shows the experimental results and theoretical curves of 7+-l and T - - ~ calculated with constants via a computer minimization procedure. Since all the equilibrium constants are known, only the forward rate constants k13‘ and k 2 3 need to be determined. The constants obtained for phenol red and cresol red systems are shown in Table 11. The fit is most sensitive to k13, in the basic region and to k23 in the acidic region, as is expected. kd6, the rate constant for the water neutralization reaction, was calculated from the known value 1.4 X 10l1M-’ s- at I = 0 , 2 5 0C,5to be 7 X 1Olo M-l s-l for our experimental conditions. In fact, 7*-l values proved to be insensitive to k45over the range 5 X lolo-1.4 X 1011M-ls-l. Analogous rate constants for these two indicators are nearly identical. This is not surprising, considering the similarity of their structures. The difference in their pK’s is reflected in the values of k32 and k3q. Where comparisons can be made, our results are in good agreement with earlier determinationskg when differences
-
-
The Journal of Physical Chemistry, Vol. 83, No. 25, 1979 3295
Kinetics of Proton Transfer Reactions
Flgure 2. Variation of T-' with inosine and indicator concentrations and pH for two inosine-indicator systems. Solid lines are theoretical for eq M; c, [L]' = 2.5 X lov3M, M, [In]' = 3 X 11. 6A) phenol red: a, [L]' = 1.06 X lo-* M, [In]' = 6 X lop5M; b, [L]' = 4.23 X M. (B) cresol red: a, [L]' M; e, [L]' = 2.12 X M, [In]' = 4 X M, [In]' = 8.4 X [In] = 4 X M; d, [L]O = 4.2 X M, [In]' = 5 X M; c, [L]' = 5.06 X M, [In]' = 4 X M; d, [L]' M; b, [L]' = 1.03 X = 5.6 X M, [In]' = 5 X M. = 5.07 X lo-' M, [In]' = 2.5 X
Scheme B
TABLE I : Kinetic Data for the Interaction of Inosine with Chlorophenol Red and Phenolphthaleina
[LI0 M X
103
10.5 10.5 5.25 2.10 1.05 0.525
S-'
10-5~-1,
[In lo M x l o 5 pHC expt Chlorophenol Red 4.0 4.0 5.0 5.0 5.0 5.0
6.88 6.54 6.90 6.84 6.85 6.81
0.711 0.543 0.463 0.268 0.223 0.143
calcdd 0.728 0.546 0.458 0.256 0.185 0.152
Phenolphthalein 3.57 10.0 8.80 2.30 2.91 3.57 10.0 9.10 2.05 2.67 3.15 10.0 8.90 2.29 2.60 1.73 10.0 8.85 1.86 1.84 1.73 10.0 9.09 1.83 1.80 1.57 10.0 8.77 1.82 1.77 1.02 10.0 8.93 1.51 1.44 0.785 10.0 8.60 1.34 1.30 0.785 10.0 9.04 1.56 1.32 0.45 10.0 8.95 1.33 1.12 0.389 10.0 8.69 1.29 1.03 0.389 10.0 9.11 1.37 1.13 0.389 10.0 9.18 1.41 1.17 0.315 10.0 8.81 1.20 1.00 0.173 10.0 9.04 1.27 0.95 a At 15 "C, I = 0.1 M. Overall concentration of inosine (pK = 8.956). a~ d u e s were corrected to CH by 7~ = 0.83. Values calculated from eq 11.
(2) (4) H
-k
(5)
OH+H,O
in temperature and ionic strength are taken into account (see Table 11). Inosine-Indicator. A single, somewhat slower relaxation effect was observed for the four inosine-indicator systems. As shown in Figure 2, 7-l shows a strong dependence on inosine concentration and some dependence on pH and indicator concentration. The indicator concentration affects the relaxation time noticeably only at low inosine concentrations. These results can be interpreted by a reaction scheme (Scheme B) that includes proton exchange between the two reactants and protolysis and hydrolysis reactions of inosine (L) and indicator (In). Table I shows
TABLE 11: Rate Constants for Proton Transfer Reactions in Inosine-Indicator Systemsa
protolysis, k,,
(M-I
s-')
hydrolysis, k I 3 ?(M-' s-I)
chlorophenol red phenol red (PKIn = 6.1) (pK1, = 7.85) Indicator Reactinns (2.1 i: 0.2) x 10'' (2.0 i: 0.5) x 10" (2.3 X 101O)d ( 3 * 2) x 10'0b (2.7 X (2.7 X 10'o)c f (3.5 ?I 0.2) x 109
cresol red (pK1, = 8.25)
phenolphthalein (PKIn = 9.4)
(2.0 * 0.5) x 10"'
f
(3.0 i: 0 . 2 ~x 109 ( 4 x 109)
(3.0 i 0.1) x 109
f
f
Inosine Reactions protolysis, k2,' (M-' s-I) hydrolysis, k,, (M-I s-l)
(3.2 f 0.2) x
loLo
f
> 5 x 109 > 5 x 109 f Exchange Reactions (2.0 i: 0.1) x l o 7 (1.7 f 0.1) x 10' k33p(M-' s-l) (5.9 i: 0.2) x 10' (2.4 i: 0.1) X 10' (3.3 ~t0.2) x 107 (7.1 i: 0.4)x 107 (4.3 i: 0.1) x 105 (1.9 f 0.1)x 107 k 3 ' , (M-I s - I ) References 5 and 8. e Corrected Reference 5. Corrected to I = 0.1 from data in ref 7. At 1 5 " C and 0.1 M KNO,. to I = 0.1 and 1 5 " C from data in ref 9. f Data not sensitive to this rate constant; see text.
f
3296
The Journal of Physical Chemistry, Vol. 83, No. 25, 1979
Thomas and Stuehr
experimental and calculated relaxation times for the inosine-chlorophenol red and -phenolphthalein systems. The exact solution to Scheme B generates three relaxation times via the determinant in eq I1 a , , - 7.'
a,,
'13
- 7-1
a21
a 31
=o
a23
a,,
a 32
(11)
- 7.'
where all
+ k d [ H I + [LI) + k2,[In1 + kd5[OH1 ai2 = -(kvz + b3dHI) + k45[Hl
= 123'2
a13
= k3'2
+ k23dH1 - k3z - k d H 1
+ k45EOHI a22 = k13([OHl + [HLI) + k31 + k13dHInl + k45[Hl a21 = ki3[OH] - k3i
+ k1y[OH] + k3q a31 = k3,[In] + k33r[HIn]+ kz3[In] a32 = -k,,[In] - ka3,[HIn] + k13,[HIn]
a23
a33
-
2
-
1
0
1
1
3
4
A PK
+
+
b [ H ] + kidOH1 + k3ti
A detailed analysis of eq I1 shows that the first two relaxation times correspond essentially to the two times for the inosine-free system (Scheme A). The third time, at least an order of magnitude longer than the other two, corresponds to the relatively slow relaxation time that we observe with inosine. This relaxation time has pH-and concentration dependences distinctly different from those for the faster processes. Over the pH range 7-9, the concentrations of H+ and OH- are small compared to HL, L, HIn, and In and can be considered to be in steady state. As a consequence, eq I1 reduces to the explicit solution for a single relaxation time: 1 / 7 = F(C1)
3
Flgure 3. Dependence of log k for the proton exchange reaction HIn L T= In HL for four indicators: (A)phenolphthalein, (0)cresol red, (0)phenol red, and (0)chlorophenol red. Dashed lines show unlt slope up to the diffusion-controlled limits.
= -k13[OH] - k31
= k d H I n 1 + [LI) + k3'3([Inl + [HLI) + k32
-
+ F(C2) 4- F(C3)
(111)
where
F(C1) = k33t([HIn]+ [L]) + k3!,([HL1 + [In]) F(C2) = (k23k3t2([HLl + [In]) + k3zkz34HInl+ ELI) + K ~ ~ ~ ~ Z [ O H ] ~ / h( ~ [ IZn ~] f~ k4dOHI) [LI F(C3) = (k3&13([Inl + [HLI) + h13tk31([Ll+ [HInl) + k3'lk46[H1 + ki3&1/(ki3[HLl + kidHIn1 + k45[H])
F(C1) represents the exchange reaction between the two acids. Below pH 7, only F(C1) and F(C2) are of importance; above pH 7 F(C3) also becomes important. In the vicinity of pH 7, F(C1) dominates, so that if we plot 7-1 vs. [HIn] + [L] + K3a([HL] + [In]) a nearly straight line results with a slope approximately equal to k33t. However, a t low reactant concentration the F(C2) and F(C3) terms become more important. In principle, all the rate constants can be determined by varying the concentration of both reactants and pH over a wide range. Since, under our reaction conditions, F(C1) is always important, the exchange rate constants k33:and k313 could be determined with a high degree of precislon for each indicator system. The experimental data were fitted to eq I11 by a nonlinear regression method. The observed relaxation times were sensitive to differing degrees to the protolysis/hydrolyses rate constants for inosine itself: kB, could be obtained from the inosine-chlorophenol red system, k13 from the inosine-phenol red or -cresol red systems (see Table I).
+
Figure 2 shows the pH dependences of the relaxation time: the solid lines are theoretical values calculated with these constants. Values of the slowest root calculated from the exact solution, eq 11, are less than f 2 % different from those calculated by the simplified eq 111; i.e., the steadystate approximation is valid in this case. Examination of Table I1 shows that the indicator second-order protolysis rate constants are all 2 X 1O1O M-l s-l, and show no trend with pK. They all appear to be diffusion-controlled values. Hydrolysis rate constants for phenol red, cresol red, and phenolphthalein are also identical. As we pointed out in an earlier paper,l0 the value k13t = 3 X lo9 M-l s-l is somewhat less than the diffusion-controlled prediction, and may result from structural changes in the indicator accompanying the removal of a proton. The rate constants for the exchange reactions follow the order expected for differences in donor-acceptor pK's. Figure 3 shows log k vs. ApK for the four systems. The limiting slopes for both directions approach unity. Proton exchange appears to be normal. k33tseems to approach the diffusion-controlled limit for large values of ApK, as one would expect. However, rate constants for phenolphthalein appear to be somewhat slower than one would predict from the difference in pK's. Since phenolphthalein is the only non-sulfonephthalein of the four indicators, it is possible that the smaller rate constant is due to some resonance and/or tautomeric change in phenolphthalein associated with proton transfer. This lowering in rate is not obvious in its hydrolysis rate constant because there the large difference in pK between phenolphthalein and water compensates for the energy required for reaction.6 Finally, we address the question of possible tautomerism in inosine (lactam or lactim). We had hoped that enough of the two forms were present to be observed in the proton transfer kinetics. Attempts to fit the present results by including two different protonated forms, as in the kinetic analysis of Dreyfus,l' were unsuccessful. Not only were the distinctive pH profiles obtained in that analysis not found, but also the fit to oyr data was not even statistically improved. We conclude that the lactim form constitutes less than 1% of the total. This observation is consistent with the conclusion based on Raman spectroscopy" that the lactam is the predominant form.
-
Acknowledgment. This work was supported by the National Institutes of Health in the form of a research
The Journal of Physical Chemistry, Vol. 83, No. 25, 1979 3207
Exchange Reaction between CIONOz and l5NO2
grant to J.E.S. (GM 13,116). References a n d Notes
M. Eigen, Angew. Chem., Int. Ed. Engl., 3, 1 (1964). G. Ilgenfritz, Ph.D. Thesis, University of Goettingen, 1966. M. Eigen and G. G. Hammes, J. Am. Chem. Soc., 82,5951 (1960). D. J. Lentz, J. E. C. Hutchins, and E. M. Eyring, J . Phys. Chem., 78, 1021 (1974). (10) M. C. Rose and J. E. Stuehr, J. Am. Chem. Soc., 90, 7205 (1968). (11) M. Dreyfus, "Proton and Ions Involved in Fast Dynamic Phenomena", P. Laszlo, Ed., Elsevier, New York, 1978, p 169. (12) G. C. Medeiros and G. J. Thomas, Jr., Biochem. Biophys. Acta, 238, l(1971). (6) (7) (8) (9)
(1) Most recent paper in this series: C. M. Frey and J. E. Stuehr, J . Am. Chem. Soc., 100, 139 (1978). sOc" 45' 486 (2) w' " Orndorff and F' w' Sherwood' J ' Am' (1923). (3) M. Eigen and L. DeMaeyer, Tech. Org. Chem., 8, 895 (1963). (4) The numbering system for A is based on the notation in scheme B. (5) M. Egen, W. Kruse, G. Maass, and L. DeMaeyer, Rog. React. Kinet., 2 (1964).
Pressure Dependence of the Exchange Reaction between CIONO:, and 15N02+ G. Schonle, H.-D. Knauth, and R. N. Schindler" Institut fur fhysikalische Chemie der Universitat Kid, 02300, Kiel, West Germany (Received March 2 f , 1979)
-
The kinetics of the reaction CIONOz + Nz C10 + NOz + Nz (-1) have been investigated at 313 and 333 K and total pressures from about 1 to 180 torr by infrared absorption measurements of C1015NOzformation in mixtures of C10N0z-'5N0z-Nz. No deviation from first-order [N,] dependence is observed for pressures 1120 = torr. The pressure dependence and the low order rate constant kl/cm3 mol-' exp(-11820/T) are in good agreement with the result of a former ClONO, decomposition study. Rate constants for the stratospheric relevant recombination reaction C10 + NO2 + Nz ClONOz + Nz (1)derived from this study by combination of klwith the known equilibrium constant for the reaction CIONOz = C10 + NOz are about three times smaller than the values obtained from discharge flow measurements. Possible reasons for the discrepanciesare discussed.
-
Introduction Chlorine nitrate formation in the stratosphere is suggested to slow down ozone consumption by tying up chlorine photoproduced from chlorofluorocarbons. On the basis of model calculations the CIONOzproduction could interfere with the catalytic O3 destruction in both the chlorine and the nitrogen oxide cycles. The recommended rate constant for the formation of chlorine nitrate (1) C10 + NO2 (+ M) ClONOz (+ M) is based on three studies carried out in flow systems in the low pressure region of up to 6 torr of Nz. Zahniser et al.' followed the reaction by indirect detection of C10. Upon addition of NO to the flow system C10 was quantitatively converted to C1 which was detected by resonance fluorescence at 134.7 nm. Leu et ala2reported on measurements in a discharge flow mass spectrometer apparatus. Birks et ala3employed a similar technique in their investigations. No experimental values are available on the rate of recombination reaction 1 a t higher pressures where the reaction might be in its falloff region. Substantial deviations from first-order [MI dependence at pressures larger than 10 torr were predicted by two theoretical falloff studies4s5for reaction 1. Zellner's4 falloff calculations are based on weak-collision models6 by use of reduced Kassel integrals with low-pressure and highpressure limiting rate constants as reference points. These points are taken from experimental data'-3 and model calculations,' respectively. Application of RRKM theory in conjunction with a modified Gorin transition state by Smith and Golden5yielded a falloff of 35% at the highest stratospheric pressure of 50 torr and a representative stratospheric temperature of 220 K.
-
N
'This paper is dedicated t o Professor Dr. W. Luttke, Gottingen. 0022-3654/79/2083-3297$01 .OO/O
The results of these calculations were not supported by a recent finding by Knauths who studied the thermal decomposition of ClONO, (reaction -1) in the presence of the OC1-scavengerNO. Deviation from the low-pressure region was found to be less than 5% at p(Nz) = 210 torr. At the highest pressure used, Le., p(NJ = 350 torr, a deviation of only 20% was observed. In the present work the rate of exchange of NOz was studied in the system C10N0z-15N0z-Nz as a function of reaction time, nitrogen pressure, and temperature. The formation of the product C1015NOzis described to result from a pathway consisting of (-1) followed by recombination reaction l a and direct exchange in a metathetical
-
C10 + 15N02(+ N,) ClONO,
+ l5NOZ
C1015N02(+ N,)
C10'5N02 + NOz
(la) (2)
step (reaction 2). Following the rate of formation of the labeled product with IR spectroscopy as function of reaction time, we obtained data which allowed the calculation of rate constants for steps l a and 2. No deviation from the low-pressure value was observed for nitrogen pressures up to 120 torr. Experimental Section Chlorine nitrate was prepared and purified as described previo~sly.~ The labeled nitrogen dioxide (99 atom %) was supplied by Amersham-Buchler. It was purified by recrystallization to remove impurities of NO and Nz03. Messer-Griesheim Nz (99.99%) was dried with magnesium perchlorate and passed through oxisorb. Handling of all gases was performed on a standard high-vacuum line equipped with a Texas Instrument pressure gauge. The stopcocks were lubricated with a halocarbon product. The thermostated reaction cell as well as the reference cell were equipped with sealed-on Si 0 1979 American Chemical Society
