NOTES
Feb., 1956 The break-through curves a t a constant flow rate of about 1 ml./min. were measured by radioactive tracer techniques using CslS7. Previous experiments have indicated that the effects of downstream diffusion in these columns are minimized at the flow rate used. The reduced volumes T for the several runs fall nearly on the same curve, but the results of the experimant are better shown otherwise. I n Table I are summarized the significant features TABLE I
KINETICS OF CLAY-ASBESTOS COLUMN FOR CESIUM EXCHANGE qG/Co c ( CS) /eo
0.335 X 2.446/0.0200 = 41.0
1 .Ooo
0.900 ,800 ,700 .600 .500 .400 .300 .200 . 100 .050
n(Cs)/no
A
1.OOO 0.980 .956 .933 .910 ,884 .846 ,798 .738 .652 .558
1.78 1:78 2.13 2.37 2.59 3.15 3.76 5.72 7.94 11.6 17.5
25 1
the pairs: copper-cadmium' and lead-zinc12 respectively, was shown'J to follow, in the pH range from 5 to 6, the rate expression 1-0
(Mem)(Mecz)Y) {kl++kz+ [HI
+"+-I
[HI
(21
if (MesY) = 0 and (Mea) >> (Mecu). The last term in equation 2 involving the rate constant k3+, can be interpreted1.2 in terms of the reaction sequence
+
Me(DY2H + Z Me(a)'+ Me(,,Y*Me(l)*+ Y H a -
+
+ YH*+ H+
(3)
Using the steady-state approximation, the following rate expression was derived2s3 for the reaction Path (3) ka
kb(Me(a))
+ k,(Mew 1 (MecoY)(Meco)IHI
(4)
It can be shown that the rate expression (4) is valid for any reaction path3 of the general form
+ H+
Met2)Y2-
stationary intermediates Me(p)'+ YHa- (5)
+
of the experiment together with the values of A ob- Me(l,*++ YHa- If stationary intermediates tained independently for each break-through curve Me(l)Y*- H + by empirically fitting the curve with the aid of the Thus the meaning of the constmts ka, k b and kc table of expi - (u u) ] ~ ( u , v due ) to B r i n k l e ~ . ~ This table is constructed in such a fashion that the in (4) is complex and depends upon the detail of curve fitting becomes quite simple. Since the ra- the reaction sequence assumed.2 The mathematitio of the arguments of the function in equation 1 is cal form of equation 4 allows the determination of independent of A and so is determined solely by ex- two independent parameters only, &s for example perimental quantities, and since xq/c is fixed in a ka/kc and kb/kc. Under the condition kb(Met2))>> k,(Me(p) exsingle experiment, one has only to try a few values to arrive a t a selection for A which gives a nearly pression (4)takes the form of the third term in (2). perfect fit, Le., a series of values for y at the tabu- This condition waa fulfilled in the previous investilated round values of BIBo which reproduces the ex- gations.'. It will be shown in the following that perimental curve. When these values of A are equation 4 is valid without any restriction regardplotted against (q/qo)/(c/co),the straight line of ing the concentrations of the competing metal ions. Experimental Fig. 1is obtained. (The zero subscripts refer to the Material, apparatus, technique of calibrations and measvalues for pure cesium solutions.) As is required by mechanism (A) this line passes through the ori- urements were described in our previous communication.' The rate of the exchange reaction between lead nitrate gin. The discrepancies for large A probably rep- and the zincEnta complex, as well as that between copper resent only difficulties in curve fitting. Evidently nitrate and the cadmium-Enta complex, was measured in the kinetics of the column are adequately described acetate buffered solutions j(Ac0Na) = 0.1 M) of ionic strength of one (made up w t h potassium ptrate) at a temby the liquid diffusion mechanism.
+
+
(4) 8. R. Brinkley, Jr., Report No. 3172, Feb. 2, 1951. Explosives and Physical Sciences Division, U. 8. Department of the Interior. Bureau of Mines. ~
THE KINETICS OF DISPLACEMENT REACTIONS INVOLVING METAL COMPLEXES OF ETHYLENEDIAMINETETRAACETIC ACID. I1 BYK. BRJL,S. BRILAND P. KRWMHOLZ Contribution from the Rseearch L ~ J O T of ~ ~ Orquima O P ~ X.A., Sa0 Paulo, Brwil Received August 4,1966
-
The initial velocity vo of the displacement reaction Me(,)z+
+ Me(z)Y*-
+
Me(z)z+ Me(l)Y*- (1)
where Y represents the ion of ethylenediaminetetraacetic acid (=Enta) and Meco and Me(z)stand for
perature of 25 f 0.1", using the streammg mercury electrode as an indicator electrode of the reaction progress. The initial velocity vo was determined in two dXerent ways. The best curve was drawn (on a large scale) through the experimental points, (Me) = f(t), and vo calculated from the tangent slope at 1 = 0. Alternatively the best straight line was drawn through the experimental points over a period of time corresponding to an exchange of about 10%. The slope of t h s line gave an a proxhate value U'O of the initial velocity. From a set ofv'o values an approximate rate law was established, which allowed the estimation of approximate values of the formal rate constants involved. Using this rate law, the variation of the
(1) H. Ackermann and G. Schwarzenbach. Rslr. Chim. Acta, 86,485 (1952). (2) K. Bd, 8. Bril and P. Krumholr, THIBJOURNAL,69, 596 (1955). (a) Equation 4 implieu that the proton eauilibria of YHS- are maintained throughout the exahange proaess. I t is also assumed that any intermediate particle participating simultaneously in (3) or (5) and in some other reaction path, is in equilibrium with the snalytiorrl reaotion pertnen.
NOTES
252
Vol. 60
I
30 I
reaction velocity over the first 10% exchange waa evaluated in every ex eriment, taking into proper account the influence of t f e back reaction (1) as previously described.* Accordingly, V'O was multiplied by a correction factor to give the "true value" of the initial velocity. Since the correction factor was in general small (1.05 to 1.15) it was not necessary to apply further corrections. Both evaluation methods gave consistent values for uo within about 5%.
Experimental Results I n Fig. 1 the initial velocity vo of the reaction between lead nitrate and the zinc-Enta complex, divided by the initial zinc-Enta concentration, is plotted against the reciprocal zinc concentration, a t I , I [HI = 2.48 X M and = (Pb) = 1.21 10' 104 2 x 104 A X M . The line drawn in Fig. 1 was calculo* 108 2 x 10' B lated according to equation 2, expression (4)being l/(Cd)o. substituted for the last term of this equation. Fig. 2.-uo/(CdY)O as a function of the reciprocal cadFollowing values4 of the constants were used: kl+ mium mtrate initial concentration; ionic strength = 1.00; = 0.34,kz+ = 2 X io4 (see ref. 2), k a / k b = 1.15 nitrate solutiona; acetate buffer; t = 25'; [HI0 = 2.54 X X loa and k,/kb = 3.7. The values given above 10-6 M ; (CU)O= 1.91 X 10-4 M ; (CdY)o concentrations should be correct within a t least 2070. Comparison in ndf per liter are: 0,0.134; e, 0.268, 0, 0.804. of equation 4 with the third term in (2)(valid for complex concentration, is plotted against the rekb(Zn) >> k,(Pb)) shows that k$kb is identical with ciprocal cadmium concentration, a t [HI = 2.54 X ha+; indeed the value of 1.15 X loa is in good M (Mecl,) = (Cu) = 1.91 X M. agreement with the value previously reported for The line and drawn in this figure was calculated accordka+ = 1.1 X io3. ing to equations 2 and 4. The following values of kz+[H] = 2.1, the constants were used: kl+ ka/kb = 1.25 x lo3and kc/Jcb = 1.35. For (Cd) = 0 we found experimentally VO/ (CdY) = (28 1) X in good agreement with the calculated value of 27.5 X
+
*
THE VAPOR PRESSURE OF ETHYL
trans-/3-(%FURYL)-ACRYLATE BY F. FROMMAND SISTER M. CONSTANCE LOEFFLER, R.S.M. 104 2 x 104 A 10' 2 x 10' B l/(Zn)o. Fig. l.-vo/(ZnY)o as a function of the reciprocal zinc nitrate initial concentration; ionic strength = 1.00; nitrate solutions; acetate buffer; t = 25'; [HI0 = 2.48 X 10-8 M; (Pb)o = 1.23 X 10-4 M; (ZnY), concentrations in mM per liter are: 0,0.134; 8, 0.268; 0, 0.671; cD,1.34; 8, 4.69.
Deportment of Chemiatry. Mount Mercy College, Pittshroh, Po. Received September 1% 1066
10' 102
Information about the volatility of the ethyl ester of trans-p-(2-furan)-acrylicacid was needed in studies of its phytotoxicityll but sufficient data could not be found in the literature. Accordingly, the vapor pressure of the compound was measured in a Ramsey-Young apparatus after preliminary experiments had shown that the Menzies-Smith apparatus was not suitable because the ester did Additional experiments show that at low zinc not stand the prolonged heating needed to reach concentrations the linear dependence of vo/(ZnY) equilibrium. Doubly distilled ethyl trans-furylupon the hydrogen ion activity previously reported2 acrylate, prepared by Claisen synthesis,2 was used. is still valid. The extrapolation to [HI= 0 a t (Zn) Table I gives the temperatures in "C. and the cor-L. 5 X M leads to kl+ = 0.34,in full agree- responding vapor pressures p in tmm. ment with the value previously reported.2 Equation 4 was tested further by studying vo at TABLE I 155 168 168 177 194 205 215 220 222 227 (Zn) = 0. According to this equation, the initial velocity of the exchange through path (3)should be p 62 98 99 133 234 341 437 502 546 603 independent of the lead concentration. Actually The constants A and B in the equation a t [HI= 2.48 X M and for (Pb) varying belogp=A/T + B tween 5 X M and 2.5 X M we found experimentally: vo(a)/(ZnY) = (7.8 f 0.8) X lo-', in which T is absolute temperature, were calculated whereas the value calculated according to eq. 4 is by the method of the least squares. A was found to 7.7 x 10-4. be -2.969 X los,and B was equal to 8.727. The I n Fig. 2 the initial velocity uo of the exchange reaction between copper nitrate and the cadmium- b.p. a t 760 mm. was extrapolated as 235' in agreeF. Fromm, Ciencia ( M W , 9,40 (1948); Acto eienlif. uensrol., Enta complex, divided by the initial cadmium-Enta in (1) prew. (4) Here and in the following the unite ueed are: mole, liter, second.
(2)
H.Posner. J . prakt. Chem., [218%,426 (1910).
