2706
T'ol. GG
NOTES
Table I also shows that the values of S, for different electrolytes in formamide are much smaller than the corresponding valuetin water. A detailed examination of Voand Svfor different electrolytes and of other related aspects of ionsolvent interaction will be taken up when more extensive data have been obtained. R. K. S. is grateful to the Scientific Research Grants Committee, Uttar Pradesh Govt., for the financial support. Our thanks also are due to the Head of the Chemistry Department and the authorities of the Lucknow 'C'niversity for providing the necessary facilities.
4.5
SPECIFIC ADSORPTION OF ISOTHIOCYANATOCHROMIUM( 111) COMPLEX IONS AT THE MERCURYAQUEOUS SOLUTION INTERFACE BY
EISHINKYU.I.0, GEN SAT^, REITATAMAMUSHI
NOBUYUKI TANAK-4,
ASD
Department of Chemistry, Faculty of Science, Tohoku Cnznerszty, Sendai, J a p a n Recezved March id, 1DG2
Only a few examples have been reported on the specific adsorption of inorganic cations a t the mercury-aqueous solution interface. The specific adsorption of thallium(1) ion at the mercury-solution interface has been reported by several Laitinen and Randles reported that the anomalous faradaic impedance of a dropping mercury electrode in a solution of tris-(ethylenediamine)-cobalt (11) and -cobalt (111) complex ions was attributed to the adsorption of these ions.5 Recently, specific adsorption of [Cr(NCS)6IJ- ion a t the mercury electrode surface was pointed out by Fischerov6 and E'ischer from the measurement of capacity current.6 I n the systematic investigation on the polarographic behavior of chromium(II1) complex ions, we have noticed that some of them have an extraordinary adsorbability a t the mercury-aqueous solution interface. These complexes were prepared and their electrocaDillarv curves were examined : [Cr(NH&]Ch, [CrCl(NHs)b]Clz, [Cr(ox)("&IC1 .nHZO,' [CrK,(,\THJ5](NO3)2, [Cr(en)3]CL.3.51320, [Cr(SCS) (NH&] CIZ, cis- [Cr(KCS)2(-\TH3)41C1, trans- [Cr(?iCS)z(en)z]Cl.€LO, trans- [Cr(?JCS)2(pn>zIC1. H207, trans-NH4 [Cr(?JCS)4(NII3)2]2/3HzO, and K3[ C r ( ~ C S ) 6 ] . 4 H z 0 Electrocapillary . curves were obtained by the measurement -of the drop-time of a dropping mercury electrode in a solution containing 1 mM complex ion, 0.1 41 sodium acetate, 0.1 M acetic acid, 0.9 ilf potassium
-
(1) A. Frumkin and A. Titievskaja, Ruas. J . P h y s . Chem., 31, 485 (1957). (2) A. Frumkin and N. Poljanovskaja, ibid., 32, 157 (1958). (3) A. Frumkin, "Surface Phenomena in Chemistry a n d Biology," Pergamon Press, London, 1958, p. 189. (4) R. Tamaniushi and N. Tanaka, Z. physik. Chem. (Frankfurt), 28, 158 (1961). ( 5 ) H. A. Laitinen and J. E. B. Randles, Trans. Faraday SOC., 51, 54 (1955). (6) E. Fisclierovl and 0. Fischer, Colleclion Czech. Chem. Commun., 26, 2570 (1961). (7) New compounds; the method of preparation f u r these compounds will IIC rprmrted elsewhere.
y
1 8
1
-0.6 -1.0 -1.4 E, v. us. 8.c.e. Fig. 1.-Electrocapillary curves of isothiocyanstochromium(II1) complexes at 25'; supporting electrolyte, 0.1 M NaOAc 0.1 M HOAc 0.9 111 KC1 0.005% gelatin (for Ka[Cr(NCS)e].4Hz0, 1 M KCl 0.005% gelatin wag used): -c-, tr~ns-[Cr(NCS)~(pn)2]Cl.H20; -e+, [Cr(NCS)(NH&] Cln; m-, tr~ns-[Cr(NCS)z(en)~}Cl. HzO; -0-, ~~U~~-NH~[C~(NCS)~(NHI),].~/~HZO; -El-, as[ C ~ ( N C S ) Z ( N H J ) ~ ]-@, C ~ ; Ks[Cr(NCS)6].4HzO (1 M KCl 0.005% gelatin); , 0.1 M NaOAc 0.1 M HOAc 0.9 M KC1 0.005% gelatin; ---, 1 M KSCN 0.005% gelatin. -0.2
+
+ +
+
++
+
+
+
chloride, and 0.005% gelatin, unless otherwise stated. In the case of K3[Cr(NCS)s], 1 M potassium chloride solution containing 0.005% gelatin was used as the supporting electrolyte. The first five complexes did not show any marked adsorbability under the experimental conditions, whereas the other complexes, which have KCS- coordinated, exhibited remarkable effects on the drop-time as shown in Fig. 1. Their adsorbability must be attributed to the sulfur atom rather than to the nitrogen atom of the KCS- ligand, because the azido complex ion was not adsorbed. The structure of crystalline STlc[Cr(SCS)4(SHs)2].2/3H20 has been determined; the "28ligands are coordinated to the cent'ral ion through the nitrogen atoms.8.9 The same structure has been assumed for [Cr(KCS)(NH3)S](X03)2and trans-[Cr(NCS)z(en)~]C1.H~0 in the solid state.I0 On the other hand, Linhard, Siebert, and Weigel suggested that the XCS-ligand of [Cr(r\;CS)(NH3)5]2+ ion is bonded with the sulfur atom from the absorption spect'rum of its aqueous solution." The present results, however, lead to the conclusion that these rhodanatochromium(II1) complex ions may have the Cr(III)-YCS st'ructure in aqueous solutions. The extremely high adsorbability of these isothiocyanatochromium(II1) complex ions may be realized when the electrocapillary curves of these com(8) Y. Saitu, Y. Takeuchi, and R. Pepinsky. Z. Kn'st., 106, 476 (19.55). (9) Y. Ttlkeuchi and Y . Saito, Bull. Ciiem. SUC.Japan., 30, 319
(1957).
(IO) J. Fujita, K. Sakamoto, and AI. Iiobayaslii, J. A m . Che7n. Soc., 78, 3295 (l95G). (11) M. Linhard, 13 Siebert, and M. Weigel, Z. anorg. aligem. Chem. 278, 287 (193.5).
NOTES
Dec., 1963
plex ions are compared with that of potassium thiocyanate; l mM of these complex ions gave an effect on the drop-time comparable to that given by 1 M potassium thiocyanate (Fig. 1). Coordination of NCS- ion to Cr(II1) seems to increase the affinity of the sulfur atom in NCS- ion to mercury. The electrocapillary curves of [Cr(nTCS)(NHJb]2+, C ~ ~ - [ C ~ ( N C S ) ~ ( N Hand + ] + ,trans-[Cr(NCS)z(en)z]+ ions clearly indicate that these cations are strongly adsorbed in the positive branch of the electrocapillary curve. In this respect, they exhibit the character of capillary-active anions. The adsorbability of these complex ions seems to depend on the local charge distribution rather than on the total charge of the complex ion. Figure 1 also shows that trans- [Cr(NCS)*(en)?]+ ion has much higher adsorbability than trans- [Cr(NCS)z(pn)z]f ion. This difference may be due to a kind of steric effect. The current-potential curves of these complex ions also were obtained, which indicated clearly that anomalies on the electrocapillary curves are closely related to the reduction or oxidation of these complexes. The current-potential curve of trr~ns-[Cr(NCS)~(en)~]+ ion showed a sudden increase in reduction current a t -0.92 volt vs. s.c.e., where the electrocapillary curve shows an anomaly as seen in Fig. 1. On the current-potential curve of [Cr(NCS)6l3- ion a small anodic wave appeared at -0.15 volt us. s.c.e.,6where an anomalous change is observed also on the electrocapillary curve in Fig. 1. These relations suggest, in turn, that the adsorption of reacting species plays an important role in the electrode reactions. The present results provide not only interesting examples of electrocapillary phenomena of inorganic ions, but also some important experimental data pertinent, to the discussion of the structure of complex ions in solution and their electrode reactions. Acknowledgment.-The authors thank the Japan Society for the Promotion of Science for the financial support granted for this research.
2707
However, the reaction under study may be controlled by vapor phase diffusion. Naphthalene and picric acid were purified by sublimation in vacuo and fractional crystallization with ethanol, respectively. The melting points were 80.3 and 121.4O, respectively. The reaction in the solid state was studied in the following way. Experimental Clean thick-glass capillaries ( 5 in. long) with uniform diameters (internal 3 mm. and external 9 mm.) were taken. Finely ground naphthalene was introduced in the capillary with a clean metal rod from one side while picric acid waa introduced from the other side in a similar manner and the position of the interface wa.a noted. The capillaries were sealed from either side with a paste which hardened after some time. These capillaries were kept in air-thermostats maintained at suitable temperatures but below the eutectic temperature. The temperature fluctuations were of the order of &lo. A scale was attached to these capillaries. The start of the reaction was indicated by a change in color a t the naphthalene-picric acid boundary. The distance through which the boundary moved was noted a t different time intervals. The induction period at room temperature was found to be only 7 to 10 min. It also was observed that picric acid did not diffuse through product layer whereas naphthalene did. This is schematically shown below.
1
I 1
Naphthalene AB Picric acid - A B
1
t
In this case it appears that the phase-boundary processes are so rapid that equilibrium is established at the boundaries during the entire course of reaction. The diffusion in the product layer is alone rate determining as happens in the case of tarnishing reactions so that if 5 is the thickness of the diffusion layer2 kt (1) where k is a certain constant and t is the time. Modification has been made in the above relationship to account for the heating at the interface due to poor thermal conductivities of the solids. For such a case it has been shown that (2
=
t2 = 2k,t exp(-Pi)
(2)
where
KINETICS OF i m i c r m ~ BETWEEK NAP€ITHSI,Eh’E AND PICRIC ACID I N THE SOLID STATE BYR. P. RASTOGI,* I’ARMJIT S.BASSI,*A N D S.L. CHADHA Chemzstry Department. Panjab lln?zcrs?t$i,Chandauarh. I n d i a
Racezved lllareh ID, 1962
Reactions in the solid state are a class by thcmselves. Because of difficulties in analysis of the composition of the solid phase, studies have been confined mainly to those cases where the course of reaction could be followed by X-ray crystallographic methods or by measuring the amount of gas evolved in suitable reactions.‘ The present note describes a new technique for studying the kinetics of reaction between naphthalene and picric acid in the solid state by following the movement of the colored interface which apparently gives worthwhile results. * Chemistry Department, Gorakhpui University, Gorakhpur, India. ( 1 ) S. W. Benson, “The Foundations of Chemical Kinetics,” XIcGraw-Hill Gook Co., Inc , New York, N. Y..1960,p. 616.
l;, C
= = =
E P
T,,,
= =
C exp(-E/RT,,,) certain constant energy of activation proportionality constant maximum temp. attained instantaneously in the mixture
In this derivation it is assumed that Ti - T = k’t where k’ is another constant so that P = k’E/ RTiT; Ti is the initial temperature and T is any temperature intermediate between T , and Tma,. Equation 1 did not satisfy the data. For testing eq. 2 log [/t was plotted against $. Straight lines were obtained a t all temperatures of observations, justifying the validity of eq. 2. This is shown in Fig. 1. It is interesting to note that all the curves have approximately the same slope, indicating thereby that P has the same value, which should be the case. Further, with increase in the value of T i , k i also (2) G. Cohn, Chem Reu , 42, 527 (1948).
