NOTES
Dee., 1960 Z(CHaT+CD3T) in all samples containing deuterated methanes is lower than that observed by Wolfgang, et ai., for CHa, and confirmed by us in comparable experiments, leading to the conclusion that the more important factor contributing to the observed HT/DT ratios is that a larger fraction of CHdT complexes leads to HT than of CD4 to DT. Qualitatively, it appears that “hot” reactions with CHI and with CD, are approximately in proportion to the mole fraction of each present, although a precise measure of this proportion requires separation and assay of CHaT and CD3T. The HT/DT ratios observed in the CH,D, systems represent solely the relative ease of abstraction of H or D in the reaction of a recoiling tritium atom with a given methane molecule. The observed ratio, except in the presence of excess reactive scavengers, is approximately 1.4 and is hence in excellent agreement with the ratio of the C-H/C-D bond vibrational frequencies. In each system, as the mole fraction of oxygen becomes quite large, the HT/DT ratio drops toward unity, and the ratio of total hydrogen activity to total methane activity is sharply reduced. In the presence of 02, a large fraction of atoms will react with O2 instead of methane, and will form HTO eventually rather than either labeled hydrogen or methane. The total observed activity in hydrogen and methane is also decreased by factors of as much as 5 of the high scavenger concentrations. The probable explanation for the change in HT/DT ratio is that tritium atoms reacting with methane in mixtures of high scavenger content have a higher average energy at the time of reaction than tritium atoms reacting in mixtures with low or zero scavenger content. This increase in average energy at reaction would tend to eliminate isotopic preferences in the abstraction reaction, and apparently also strongly favors the substitution reaction to form labeled methane vis-&vis the abstraction reaction t o form labeled hydrogen in “hot” reaction with methane. NOTE ON THE FUOSS-KRAUS EQUATION FOR T H E CONDUCTANCE OF SOLUTIONS CONTAINING ION-TRIPLETS BY E. C. BAUGHAN Chemistry Department, Royal Military College of Science. Sh?ivenham, Berks, England Received M a y 8, 1960
Many electrolytes, particularly in solvents of low dielectric constant, show a minimum in the equivalent conductance A as C increases. In 1933 Fuoss and Krausl explained this in terms of bilateral ion-triplet formation, thus: M X M+ X’, M X M+ M2+X, MX X’ MXZ’; they showed that, if certain approximations are legitimate, this explanation leads to the equation A = A + BC (1) where A and B are constant for a given solventsolute system at a given temperature. This equation has been widely applied, and most modern treatises discuss it at length. The author
+
+
z/c
+
1951
hopes therefore that the following simple mathematical consequencemay prove useful. All systems obeying equation 1 will show the same curve if the logarithms of A and C are plotted against one another, and this curve is symmetrical as log C varies about the log of the concentration C , at which A has its minimum value A,. The proof is easy. From equation 1 A has a minimum A, at a concentration C,, and
A,dZ
= 2BCm = 2A
(2)
Consider the value A, of A at some other concentration C, where
c;
=
xc,
(3)
It may easily be shown that (4)
so that a plot of log A against log C gives the same curve for all electrolytes if the points (log Am, log C,) are superposed. The proof of symmetry easily follows since
This check on equation 1 is easy as the curve can once and for all be plotted on a transparency. And it is probably the most satisfactory way of fitting 1 to experimental data since the errors in A are usually proportional rather than absolute and since C is usually varied over a wide range, so that it is difficult to give due weight to both the dilute and concentrated solutions. (1) R.M.Fuoaa and C.A. Kraus, J . A m . Chem. Soc., 65,2387 (1933).
FORMATION CONSTANTS OF 6-METHYL3-PICOLYLAMINE WITH COPPER, NICKEL, CADMIUM AND SILVER IONS BY HARRYR. WEIYER~ AND W. CONARD FERNELIUS Department of Chemistry, the Penns lvanio State Uniueraity, L’niversity Park, benna. Rem‘ned June #4,1960
Formation constant data €or complexes of 2picolylamine, 2-picolylmethylamine and 2-(2-amino ethyl)-pyridine with several metal ions were reported recently.a These data are now augmented by similar data for 6-methyl-2-picolylamine with copper, nickel, cadmium and silver ions (Table I). No values for zinc could be obtained because of precipitation. For cobalt(I1) the values for both log KI and log K2 varied with the value of E chosen for calculations; approximate values a t 40’ are 3.5 f 0.2and3.0 f 0.2. Discussion 6-Methyl 2 picolylamine is a slightly stronger base than 2-picolylamine although the effect of substitution of methyl for hydrogen on the pyridyl nucleus is not as great as the effect of substitution on the primary amine group. However, the forma-
- -
(1) Holder of a National Scienoe Foundation Researoh Partioipatioa Award for the Summer of 1969. (2) D. E. Goldberg and W. C. Fernelius, Tar8 JOURNAL, 68, 1240 (1859).
XOTES
195'
Vol. 64
TABLE I
\
T
FOR THE ~
THERMODYNAMIC ~ ~ ~ QUANTITIES ~ LOG K,, AND
10,
c.
10
H+
9.18
f0 . 01 20 30 40
10-40
10 20 30 40
9.83 10.01 8 70 fO.O1 8.48 fO.O1
40"
OF
- AF,, - AHn A N D AS,
INVOLVED IN THE REACTION AT 10, 20, 30
SEVERAL METALIONS WITH 6-METHYL-2-PICOLYLAMINE
a-
cu++
Ni++
7.18 10.01 6.95 fO.01 6.81 f0.01 6.69
log K1 5.05 f0.04 4.85 10.02 4.71 f0.03 4.64 fO.O1
4.22 f0.05 4.09 fO.01 4.01 f0.06 3.89 -10.05
4.40 f0.04 4.14 10.08 3.97 f0.05 3.73 f O .04
5.86
4.52
9.34
Cd++
fO.O1 AH1 (kcal./mole)
Ag
+
2.9 fO.l 2.9 fO.l 2.9 f O .1 2.9 fO.l
CU"
Ni++
6.03 10.01 5.79 kO.01 5.65 fO.O1 5.51 f0.01
log K i 3.23 f0.04 3.05 f0.06 3.02 f0.05 2.85 f0.05
Cd++
2.84 fO.08 2.74 10.05 2.69 f0.08
Ag
3.47 f0.07 3.46 10.08 3.45
f O .09 3.39 f O . 11
- AHz (kcal./mole)
9.3
6.86
9.2 9.2 9.1 9.1
AS1 (cal./mole-deg.) 8.6 2.4 3.3 8.4 2.2 3.3 8.5 2.2 3.4 8.7 2.5 3.4
7.23
4.99
-0.52
1.07
ASz (cal./mole-deg.)
-12.9 -12.9 -12.7 -12.8
tion constant values for 6-methyl-2-picolylamine with various metal ions are significantly less than the corresponding values for 2-picolylamine. For Cu++ the difference between the two amines is >2 in both log K 1 and log Kz; for Ni++ it is > 2 in log K1, but >3 in log K2; for Cd++ it is very small in log K1 but > I in log Kz. Further, no values for log K3could be measured for Cu++, Ni++ or Cd++. It is obvious that the steric effect of methyl substitution on the pyridine nucleus is much greater than substitution on the primary amine group. The findings with Ag+ are especially interesting. In view of the inability of both nitrogen atoms of the ethylenediamine molecule to coordinate to the same silver ion3 it is unlikely that both nitrogens in 6-methyl-2-picolylamine coordinate to the same silver ion. The magnitude of the log K n values supports the view that coordination is through the primary amine nitrogen rather than through the heterocyclic n i t r ~ g e n . ~However, in a plot of log K us. ~ K Athe H values recorded here lie well above the line of proportionality found for simple amines. Further, t.he value for log KZ is less than that for log K 1 which is unusual among silver complexes with monodentate ligands. Experimental The preparation of solutions of metal ions as perchlorates, measurements and calculationR were performed as described previously.1 6-Methyl-2-picolylamine (Aldrich Chemical Company, Inc.) was distilled twice a t 75-75.6", 6-7 mm. before preparing solutions. (3) G. Schwarzenbach, B. Maissen and H. Aokermann, Helv. Chim. Acta, 86, 2333 (1952); G. Sohwarzenbach, H. Aokermann, B. Maissen and G . Anderegg, ibid., 85, 2337 (1952); G . Sohwarzenbaoh. ibid., 36, 23 (1953).
(4) R . J. Bruehlmann and 5'. H. Verhoek, J . A n . Chem. ~ o c . 70, , 1401 (1948).
SHOCK TUBE EXPERIMENTS ON THE PYROLYSIS OF ACETYLENE BY GORDON B. SKINNERAND EDWARD M. SOKOLOSKI Monsanto Chemzcal Company, Research and Engineering Divtsion Rezearch Deparlment. Dayton, Ohzo Rerewed June % 9 , 1960
2.0 1.8 2.0 2.1
-2.9 -3.1 -2.6 -2.9
14.8 14.3 14.1 14.9
12.1 12.2 12.2 12.1
Shock tube studies on the pyrolysis of acetylene have been reported by Greene, Taylor and Patterson,l who have also mentioned some of the earlier work on acetylene pyrolysis by other techniques. Actually, the shock tube experiments are in a class by themselves with respect to temperatures, heating times and wall effects, and comparisons with other work are difficult to make. The present paper agrees with Greene's results in some respects, and disagrees in others. Experimental The single-pulse shock tube described earliers was used, with identical techniques and methods of calculation. As before, helium-nitrogen mixtures were used as "driver gas." Experimental temperatures were corrected for variations in temperature due to minor pressure fluctuations during the runs, and for heat effects from chemical reaction. Vapor chromatographic analyses were made for Hi, CZHa, CiHr and CzHS in all of the experiments, fo? CS and C4 hydrocarbons in most, and for CH4 and CO in a few. Experiments were carried out with the gas mixtures listed in Table I. Total reaction pressures were five atmospheres, and dwell times two milliseconds. Matheson acetylene, washed with concentrated sulfuric acid and passed through an Ascarite-Drierite column, and Airco helium, nitrogen, hydrogen and argon, were used without further purification. The gas mixtures always were analyzed before reaction. A trace of vinylacetylene was found in mixture I, but none in the other mixtures since the acetylene content was lower.
Results For mixtures 1 and 2, the chief pyrolysis products were hydrogen and vinylacetylene, although small amounts of CzH4, CH4, C3H8 and CO also were found. Carbon was deposited in the shock tube in the higher temperature runs. The amount of acetylene decomposing increased from about 2% a t 1150'K. to about 50% at 1800°K., for mixture 1. Below about 1500'K. no hydrogen was found, and the amount of vinylacetylene produced corresponded fairly well with the acetylene which disappeared. Above 1500'K. hydrogen formed, but (1) E. F. Greene, R. L. Taylor and W. L. Patterson, Jr., THIS JOURNAL, 68, 238 (1958). (2) G . B. Skinner and R. A. Ruehrwein, rbzd., 88, 1736 (19591.
