NOTES
1933
100
Some Observations on the Kinetics of Hydrogen Iodide Addition t o 1,3- and 1,4-Pentadienel
00
x = 30.70° C
60
by Kurt W. Egger and Sidney W. Benson
I
4
40 Department o j Thermochemistry and Chemical Kinetics, Stanford ReseaTch Institute, Menlo Park, California 94086 (Received September 81, 1066)
v)
aC2O 0
0246810
30 TIME (min.)
Figure 1.
physical properties of this gas. In this report one of these parameters, the solubility coefficients in three sea water chlorinities at seven temperatures per chlorinity, is given.
Experimental Section The microgasometric method used has been described in detail earlier.1211ae The absorption chamber has been enlarged to employ 8 ml of water in order to maintain the same accuracy as obtained using distilled water.lab Figure 1 shows the rate of solution of CO in the absorption chamber, illustrating that 30 min is ample time for equilibration to occur. The procedures used for obtaining gas-free sea water and the chlorinity determinations are detailed in an earlier work. lss The purity of the CO was determined using a Scholander 0.5-cc gas analyzer14 and microgasometric analyzer16showing the gas to be at least 99.7% pure. An independent method utilizing palladium chloride also gave a purity of greater than 99%.6
Results and Discussion The experimental solubility coefficients are listed in Table I. Smooth curves were fitted on these points from which the values from -2 to 30" were taken. From these values the relations between solubility and chlorinity were graphed and the values from -2 to 30" in chlorinities ranging from 15-21"/,, were obtained. These are given in Table 11. The only other solubility determinations of CO are those of Winkler for distilled water. 18,17 (12) E. Douglas, J . Phye. Chem., 68, 169 (1964). (13) (a) E. Douglas, ibid., 69, 2608 (1965); (b) for critical discussion of systematic errors refer to the original paper.12 (14) P. F. Scholander, J . B w l . Chem., 167, 235 (1947). (15) P. F. Scholander, L. Van Dam, C. L. Claff, and J. W. Kanwisher, BWZ. Bull., 109, 328 (1955). (16) L. W. Winkler, Z . Physik. Chem. (Leipaig), 55, 344 (1906). (17) "Handbook of Chemistry and Physics," 39th ed, Chemical Rubber Publishing Co., Cleveland, Ohio, 1957.
We wish to report some quantitative kinetic information on the addition of HI to olefins, obtained complementary t o reported studies of the iodine atom catalyzed isomerization2&rband dimerization20 of n-pentadienes in the gas phase. The rate of addition of HI to either 1,3- or 1,Cpentadiene was checked as a possible side reaction in these studies. We found that, during the isomerization of 1,4-pentadiene in the presence of iodine at temperatures between 420 and 515"K, 5-10Oj, monoolefins had been produced, according to diolefin
+ 2HI
olefin
+ 12
The mechanism of this over-all type of reaction has been shown to consist ofid 1
diolefin
+ HI JcRI -1
(slow)
(A)
(fast)
(B)
and
RI
+ HI
2 -2
RH
+ I:,
with kl as the rate-controlling step. The intermediate alkyl iodide reacts rapidly and almost quantitatively with HI, forming the parent saturated compound, and in the case of diolefin as starting material, monoolefin is produced. Equation B was shown to be, in fact, a composite of
RI
+ IJR.
+
(B1)
and
R.
+H I Z R H +I
032)
As both steps, BI and Bz, are fast compared to L, they do not alter the simple second-order kinetics. Rate constants, kl, were calculated from pressure measurements, as only the rate-controlling step A leads to a pressure change. The formulation given (1) This work has been supported in part by Grant No. AP00353-01 from the Air Pollution Division of the U. S. Public Health Service. (2) (a) K. W. Egger and S. W. Benson, J . Am. Chem. SOC.,88, 241 (1966); (b) K. W. Egger and 5. W. Benson, ibid., 87, 3314 (1965); (c) K. W. Egger and 8. W. Benson, unpublished data; (d) S. W. Benson, J. Chem. Phys., 38, 1945 (1963).
Volume 7 1 , Number 6 M a y 1967
NOTES
1934
Table I : HI Addition to Olefins
Temp, Olefin
2-Butene 1-Butene 1-Pen tene 1,4-Pentad iene
1,SPentadiene
V e s8 e1
2 1 2 3 3 2 2 1
OK
461.2 483.6 461.2 420.8 424.1 428.8 461.2 432.0
(Olefin)o,b torr
96.8 52.9 89.4 102.3 136.0 65.4 53.3 135.6
(HI)oVb torr
Time, min
torr
(Olefin)t, I, torr
97.5 134.1 136.6 74.8 80.6 83.8 84.8 194.5
170 36 1067 40 31 94 42 2
2.5 3.0 31.1 12.8 15.1 9.1 20.0 87.1
94.3 49.9 58.3 89.5 120.9 56.3 33.3 48.5
AP,C
-Log kiVd torr-1 8ec - 1
8.04 6.44 7.45 6.76 6.85 6.80 5.75 4.45
1, Unpacked "old" Pyrex glass reaction vessel used for a variety of reaction systems over a period of several months prior to use; 2, unpacked "new" Pyrex glass reaction vessels, TeflonizedZband coated with Dow Corning silicone oil 705; 3, aluminum vessel, covered with a 0.1-in. layer of Teflon, commercially applied. Subscript 0 denotes initial, f final concentration. Measured pressure difference. Based on measured pressure differences (S. W. Benson and G. R. Haugen, J. Am. Chem. Soc., 87,4036 (1965)).
'
in ref 3c was used to calculate kl. The back reaction, the decomposition of the alkyl iodides, could be neglected as we were working a t reasonably low conversions and in excess HI.3c (Furthermore, it was previously shown that the steady-state concentration of alkyl iodides in excess H I a t temperatures between 480 and 600°K is very Conversions ran between ll and 38%. The iodine buildup during the reaction, monitored spectrophotometrically, checks out within experimental error limits with the amount of saturated hydrocarbon or monoolefin, respectively (in the case of npentadiene), measured by gas-liquid chromatography. The measured pressure changes are in reasonable agreement with the iodine produced. The method and experimental procedures used have been reported in detail earlier.28*4 The results are summarized in Table I. 'The use of coated reaction vessels was prompted by the finding that HI additions to olefins can be surface sensitive. Consistent results, using thrte different reaction vessels, indicate that the measured kl values probably represent homogeneous reaction rates. The reliability of the rate constants measured for the n-pentadienes can be checked by comparison with the results obtained for 1- and 2-butene and 1-pentene. ~" Careful studies of H I addition to e t h ~ l e n e ,pr~pylene,~b i s ~ b u t e n evinyl , ~ ~ chloride, 3c and 2-butene5 have been reported in the literature and for 1-butene good estimates are a ~ a i l a b l e . ~The measured kl values for 1and 2-butene are in good agreement with the literature data. We cannot directly derive any meaningful Arrhenius parameters from such a limited number of experiments; therefore, activation energies have been calculated, The Journal of Physical Chemistry
using estimated A factors, based on an intrinsic A* factor of 107e4 f 0.7 for all but 2-butene. This value has been arrived at on the basis of the reported log A values for HI, adding to ethylene (8.52),5apropylene (7.9),3b 1-butene (7.7),5isobutene (6.50),3cand 2-butene (6.3).5c It is further supported by consistent and reasonable A factors for the unimolecular back reaction, the elimination of H I from the corresponding iodides. These values, reported in Table 11, are obtained Table TI : Activation Energies and Frequency Factors for the Addit,ion of HI to Olefins and for the Back Reaction HI
+ Olefin
1
RI -1 Log Ai, I./mole
Olefin
sec
trans-Butene-2 1-Butene 1-Pentene 1,4-Pentadiene" 1,SPentadiene (4-iodopentene-2)
6.3"
*
7.7 7.7 8.0 7.7
EJ,b
El, kcsl/mole
(21.1)" 20.7 (23.5)'20.9 22.0 19.3 14.7
Log A A , ~ kcall sec-1 mole
11.0 13.0 13.0 13.6 12.1
(37.5)" 40.8 42.0 39.3 29.8
"Average value from all experiments, reported in Table I for 421-429'K. and AH are computed for a mean temperature of 450"K, using the ACpo shown in Table 111. See ref 5.
(3) (a) A. N. Bose and S. W. Benson, J. Chem. Phys., 37, 2935 (1962); (b) A. N. Bose and S. W. Benson, ibid., 37, 1081 (1962); (c) A. N.Bose and S. W. Benson, ibid., 38, 878 (1963). (4) (a) D. M. Golden, K. W. Egger, and S. W. Benson, J . Am. Chem. SOC.,86, 5416 (1964); (b) K.W.Egger and S. W. Benson, ibid., 88, 236 (1966). ( 5 ) P. S. Nangia and 5. W. Benson, J . Chem. Phys., 41, 530 (1964).
NOTES
1935
Table 111: Thermodynamic Data' Used for Calculating the Equilibrium Olefin
HI Butene-l trans-Butene2 Pentene- 1 Pentadiene-1,4 Pentadiene-1,3 sec-Butyl iodideb ZIodopentane' 4Iodopentene-1 4Iodopentene-2*
7.0 20.5 21 .o 27.4 25.1 24.7 26.2 31.7 30.3 29.3
+ + HI + + HI + HI + HI
sec-Butyl iodide -* butenel HI --c trans-butene2 HI 2-Iodopentane --c pentene-1 4-Iodopentene-1 + pentadiene-1,4 + pentadiene-1,3 4Iodopentene-2 + pentadiene-1,3
1
RI 2
sa,
cpo.
cal/mole OK
Compounds
+ HI
1.8 0.8 2.7 1.8 1.4 2.4
cal/mole
AH!', OK
49.3 73.9 70.9 83.1 79.7 76.4 89.8 99.2 97.6 96.3
33.4 30.4 33.2 31.4 28.1 29.4
32.6 33.2 32.4 32.0 29.5 28.6
kcal/mole
6.2 0.0 -2.8 -5.0 25.2 18.6 -14.4 -19.4 10.7 8.5
20.6 17.8 20.6 20.7 14.1 16.1
Unless otherwise stated, values are taken from "JANAF Thermochemical Tables," Aug 1965, and API Tables. * See ref 5. Estimated from group additivity properties and values for allyl iodide (A. 5. Rodgers, D. M. Golden, and S. W. Benson, J . Am. Chm. Soc., 88, 3196 (1966)). Intrinsic entropy difference, corrected for symmetry contributions. O
' Estimated from group additivity properties and ref 5.
from estimates of the equilibrium constants, &.I, in the systems, based on thermodynamic quantities, shown in Table 111. For 2-butene the literature value of 6.3 for log A1 was used. From the narrow temperature range of 40' for the data of l,Qpentadiene, El is calculated aa 22.2 f 2 kea1 and log A1 (l./mole sec) as 9.4 f 1. These rough values from limiting slopes in the Arrhenius plot are to be compared to the more reliable values of 19.3 and 8.1, respectively, based on the discussed estimate of the A factor. The disagreement is not significant, considering the scatter in the data and the narrow temperature range. Table I11 shows all the data used in calculating the equilibrium constant, K-1, for the reaction system A and the values of K-1 are incorporated in Table 11. When combined with the measured rate constant, kl, these data yield the Arrhenius parameters for the back reaction, k-1, the elimination of H I from the iodides. Keeping in mind that all these values are based on few experiments at one temperature only, the values for E-1 and log A-1, shown in Table 11, are in good agreement with previous results reported in the literature. The log A-1 values are reasonable for unimolecular reactions (and are in line with the values for ethyl iodide [13.5 isopropyl iodide [13.0],abisobutyl iodide
[11.6],3c etc.). The activation energies for the H I elimination are consistent with the results in the series CzHJ (50 kcal), i-CaHd (43.5), t-BuI (36.4), and secBuI (37.5). While the activation energy for removing H I from 4-iodopentene-1 to form 1,Ppentadiene is about the same as for H I elimination from sec-butyl iodide, 1,3pentadiene clearly shows significantly lower activation energies for both addition and elimination reactions. The difference of 11 kcal in Ez between the nonconjugated 1,4-pentadiene and 1,3-pentadiene is taken up primarily by the extra conjugation energy in 1,3pentadiene of about 7 kcal. The difference in activation energy of the forward reaction E1 has to do with the lower barrier for the H I addition to a conjugated double bond as compared to an isolated double bond. In view of the recently proposed6 detailed reaction mechanism of a four-center addition reaction, controlled by simple electrostatic dipole-dipole interactions, this difference would have to arise essentially from a much more facile polarizability of the conjugated double bond. In their calculation of Hz addition to cyclopentadiene, Benson and Haugen assumed the longitudinal ground-state polarizability of the (6) See Table I, footnote d .
Volume 71, Number 6 M a y 1967
NOTES
1936
conjugated bond to be the same as in 2-butene and obtained very good agreement with the observed values. No calculations have been carried out as of today for straight-chain conjugated systems. A more careful and detailed study would have to give better experimental data for the HI addition to l,&pentadiene before any further conclusions can be drawn. There is no doubt, though, that H I adds much faster to the conjugated olefinic bond and we believe that this corresponds to the homogeneous reaction rate. However, more extensive studies are required to be certain of this point.
Table I: The Equivalent Conductances of Solution of KCI in H20and Dz0
Temp,
O C
Equiv oondct, A , cm2 ohm-1 equiv-1
Temp, OC
Equiv condot, A, om2 ohm-1 equiv -1
0.10 M KCl in HzO -1.72 f0 . 0 6 -0.80 f 0 . 0 4 +0.01 f0 . 0 4 +0.75
* 0.05
+ 1 . 5 0 f0 . 0 3 + 2 . 2 9 f0 . 0 4 + 3 . 0 0 f0 . 0 3
67.85 69.79 71.52
{ ::::: 1
The Electrical Conductivity of Potassium
74.58 76.21 77.60 77.53
$ 3 . 8 1 f0 . 0 3 + 4 . 5 8 f 0.02 + 5 . 5 2 f0 . 0 3 $ 6 . 4 1 f0 . 0 2 $7.20 f0.02 + 7 . 8 3 f 0.00 +8.39f0.02
{ 79,45 79.49 81.06 83.05
85.00 86.59 88.07 89.40
0 . 1 0 M KCI in Dz0
Chloride in Heavy Water i n the -2 to 12" Range 54.60 57.35 57.32 57.10 59.09 59.00
-2.00 f0 . 0 5
by R. A. Horne and D. S. Johnson Arthur D . Little, Incorporated, Cambridge, Massachusetts (Received September 8.2, 1966)
-0.35f0.04
+ 0 . 5 0 f 0.05 $1.00 f 0 . 0 3
The structure D 2 0 is very similar to that of H20; however, the hydrogen bond is somewhat stronger in the former medium and, as a consequence, it is somewhat more highly structured.1--3 This stabilization of the structured regions results in a displacement of the temperature of maximum density from 4 to 11°.2 In order to determine if this greater structure is reflected in the energetics of transport processes4 we have measured the temperature dependence of the electrical conductivity of solutions of KC1 in D2O in the -2 to 12" range. The results of the measurements of equivalent conductances of 0.10 M KC1 in H 2 0 and in DzO and 1.0 M KC1 in DzO are shown in Table I. The apparatus and experimental procedures have been described p r e v i o ~ s l y ;however, ~~~ the capillary cell used, unlike the high-pressure cell earlier described,6 bad widely separated filling and lead arms. General Dynamics Corp. 99.7% DzOwas used. The present value for 0.10 M KC1 in H2O at 0" is in agreement, with Jones and Bradshaw.' La Mer and Nachod* found that a 0.02 M KC1 solution in H20 is 1.28 and 1.20 times as conductive as in D10 at 5 and 25", respectively, which is to be compared with the present value of 1.21 times for 0.10 M KCI at 10". The Arrheriius activation energies of electrical conductance of aqueous alkali halide solutions, including sea water, exhibit maxima near the temperature of The Journal of Physical Chemistry
59.78 60.37 60.21
$1.39 f0 . 0 4 + 2 . 4 1 f 0.04
62.53 62.42 64.44 64.38 64.33
+3.30*0.03
-1.70 f0.04 - 0 . 8 1 f 0.06 I
-0.01 f0.04 $ 0 . 9 5 f0 . 0 4
{
$ 4 . 1 4 f0 . 0 4 $4.93 f0 . 0 3 $6.00 f0.02 + 6 . 9 l f 0.03 $ 7 . 5 8 f 0.04
$8.00f
0.02
$8.32 f 0.03 +9.05f0.02 +9.86 f0.03 $11.33 f0 . 0 2
1 . 0 0 M KC1 in D20 56.96 +5.00=!=0.05 58.22 59.49 59.47 + 5 . 7 3 f0.03 61.00 63.56
+2.50 f 0.03
{ 63,41
+ 3 . 4 4 f 0.04 $4.02*0.03
65.18 66.64
$ 6 . 5 5 f 0.04 $7.50 f0.02 +9.07 f0.03 $9.89fO0.O2 + 1 1 . 5 2 =!= 0 . 0 3
66.09 67.60
{ 67,69 69.71 71.53 72.68 73.02 73.00 74.04 75.29 75.24 76.73 79.50
{ 68,17 68.24
{ ::::: 71.11 73.02 76.23 77.95 81.33
(1) J. L. Kavanau, "Water and Solute-Water Interactions," HoldenDay, Inc., San Francisco, Calif., 1964. (2) I. Kirshenbaum, "Physical Properties and Analysis of Heavy Water," McGraw-Hill Book Co., Inc., New York, N. Y., 1951, pp 12-13. (3) R. C. Bhandari and M. L. Sisodia, Indian J . Pure Appl. Phys.,, 2 , 266 (1964). (4) R. A. Horne, R. A. Courant, and D . S. Johnson, EEectrochim. Acta, 11,987 (1966). ( 5 ) R. A. Horne and R. A. Courant, J . Phys. Chem., 68, 1258 (1964). (6) R. A. Horne and G. R. Frysinger, J . Geophys. Res., 68, 1967 (1963). (7) G. Jones and B. C. Bradshaw, J . A m . Chem. SOC.,5 5 , 1780 (1933). (8) V. K. La Mer and F. C. Nachod, J . Chem. Phys., 9, 265 (1941).
