3. The polycondensation o f dicarboxylic acids with hydrazine at a molar ratio of one of the acid to two and more of the hydrazine under pressure leads to the formation of a " p o l y a m i n o t r i a z o l e . " 4. A m e c h a n i s m was proposed for the formation of polymers containing 4 - a m i n o - 4 - H - 1 , 2 , 4 - t r i a z o l e units. LITERATURE

CITED

[1] V. V. Korshak, G. N. Chelnokova and M. A. Shkolina, Bull. Acad. Sci. USSR, Di,,, Chem. Sci. 1959, 925. [2] V. W. Fisher, J. Appl. Chem. 4, 212 (1954).

Received

ADSORPTION

O. Y a .

OF V A R I O U S

IONS

FROM

AQUEOUS

September 18, 1958

SOLUTIONS

Samoilov

N. S. Kurnakov Institute of General and Inorganic Chemistry of the A c a d e m y of Sciences of the USSR

T h e c o n c e p t of the translational m o v e m e n t of m o l e c u l e s and ions in a solution as a c t i v a t e d jumps from one t e m p o r a r y position to equilibrium to a neighboring one has been applied in the study of the hydration of ions in solutions [1]. This concept will probably be found to be useful in an e x a m i n a t i o n of the question of the adsorption of various ions from aqueous solutions by, for e x a m p l e , a solid surface. Let us e x a m i n e the case of the adsorption of ions from f a i r l y dilute aqueous solutions. Let the concentration of ions be low, not only in the bulk of the solution, but also in the surface layer, so that effects due to the filling of the surface with ions and to interaction between ions do not p l a y any substantial part. ~lso, we sha~_l consider only f e e b l y hydrated ions (ions close to the boundary between positive and negative hydration [11). Let the surface of the solid be such that it adsorbs cations, but not anions, from solution, but let the action of the surface be so weak that i t c a n be regarded as a c t i o n on the thermal, m a i n l y translational, motions of the ions and m o l e c u l e s of water in the solution. It is c l e a r that the a c t i o n of the surface m a y be c h a r a c t e r i z e d by a quantity AEs, which is s i m i l a r to the previously introduced quantity AE, a quantitative c h a r a c t e r i z a t i o n of the c l o s e - r a n g e hydration of ions [1]. T h e quantities AEs and AE denote changes in the a c t i v a t i o n energies for jumps of particles as c o m p a r e d with the activation energy (E) for the jump of a water m o l e c u l e in water. Let AEs > 0 for ions of kind i . This means that these particles b e c o m e less m o b i l e near the surface than in the bulk of the solution: the average t i m e for which an ion of kind i__remains in a position of t e m p o r a r y equilibrium near the surface (ris) is greater than the corresponding t i m e in the bulk of the solution ( r i l ) . It is probable that the case AE s < 0 is also possible. In this case particles close to the surface b e c o m e more m o b i l e than in the bulk of the solution. In adsorption, e l e c t r i c a l neutrality is ensured by the formation of a double layer, which in this case has an e x t r e m e l y diffuse structure. It m a y be considered that the presence of such a double layer has a r e l a t i v e l y small effect on the exchange of p a r t i c l e s of the solution at the surface: the translational motion of particles near the surface ( a c t i v a t e d jumps of ions and m o l e c u l e s of water) is associated m a i n l y with short-range forces and in the case under consideration occurs in presence of a m e a n distribution of ions corresponding to a diffuse double layer inside it, in f a c t - probably just as i f it did not exist. Such an assumption, like the whole of the proposed approach (in particular, the use of the quantities AE s and AE), can be m a d e , of course, only when the above l i m i t a t i o n s are t a k e n into account.* * If the action of the surface cannot be regarded as sufficiently s m a l l , the proposed approach can be applied to the solution apart from one of two layers of particles that are c o m p a r a t i v e l y f i r m l y bound to the surface.

897

Let us e x a m i n e the movements (activated jumps) of ions of the kind i to and from the surface. Let cis and Cil be the concentrations (mole fractions) of iota of the kind i__ in the surface layer and the bulk of the solution, respectively. It is c l e a r that ~is

cis cu

Jil

--'~iz

--

/is

(1)

'

in which Jis and Jil are the average numbers of activated jumps from and to the surface per second. For an ion to leave an equilibrium position not close to the surface i t must have an energy of E + AE, and for an ion to leave an equilibrium position close to the surface in the direction away from the surface i t must have an energy of E + + AEs + ( 1 - a ) A E , in which 0 < a < 1. T h e coefficient ( l - a ) i s associated with the p a r t i a l "dehydration" of the ion when it goes onto the surface, i.e., the reduction in the average number of water molecules adjacent to the ion below the coordination number of the ion in the bulk of the solution. Hence, for Jis and Jil we m a y write the equations /is

.0 - - [ E + A E ==lis e

and

_/o

/il --

il

s

+ ( l - - a ) AE]/RT

e-- (E + a~)/nr

J

in which J~ and J~ are preexponential coefficients. Substituting these values in equation (1) we have:

r

Cil

--

/0 il A E s / R T e - a A E / R T .o e lls

~

Ae

-- a AE/RT

(2)

in which, of course, A > 0. As a > 0, it follows from (2) that

C{s

oil'

increases as AE diminishes ( ]AE[ diminishes in the case of positive AE and increases in the case of negative AE), i.e., it follows that, e . g . , in the series of a l k a l i - m e t a l cations, adsorption increases as we pass to cations of larger radius. In view of the assumption of the small effect of the surface on the particles of the solution, it m a y be assumed that the preexponential factors in the expression for the frequency of activated jumps of ions are approxi m a t e l y independent o f whether the ion vibrates around an equilibrium position close to the surface or around one that is not. This assumption is similar to that made previously [1]. At low AEs the coefficient A is a p p r o x i m a t e l y unity and we have, a p p r o x i m a t e l y , cis -Cil

~ e--

a ~E,/RT

in which a > 0. From the last equation it follows that r i,s

--->

I,

if

A I : < O,

if

AE > 0.

tril

and

Ci 8 Cil

898


This result has been obtained on very limited and, perhaps, somewhat artificial assumptions, but it probably explains in some measure the relation ,between the adsorption and hydration of ions: it indicates that, under certain condhions, there is preferential adsorption Of ions showing negative hydration (e.g., K+, Rb+ , Cs+, but not Na+) from dilute aqueous solutions of electrolytes. It is very interesting that Frumkin, Damaskin, and Nikolaeva-Fedorovich, in a study of the more than 'equivalent adsorption of various cations on a negatively charged mercury surface, showed that there was a certain, though small, specific adsorption of the cations of larger radii [2, 3]. SUMMARY 1. An examination is made of the relation between the adsorption of various ions from dilute aqueous solutiom and the close-range hydration of the ions. 2. Under certain conditions ions showing negative hydration are preferentially adsorbed from solutions. LITERATURE CITED [1] O. Ya. Samoilov, Structure of Aqueous Solutions of Electrolytes, and the Hydration of Ions, Izd. AN SSSR, Moscow, ] 957. [2] A. N. Frumkin, B. B. Damaskin and N. V. Nikolaeva-Fedorovich, Proc. Acad. Sci. USSR 115, No. 4, 751 (1957); a21, No. 1, 129 (1958). , [3] A. N. Frmnkin and N. V. Nikolaeva-Fedorovich, Bull, Moscow State Univ. No. 4, 169 (1957).

Received September 20, *1958

TRIALKYL ORTHOVANADATES

N. F. O r l o v

a n d M. G, V o r o n k o v

Institute of Silicate Chemistry of the Academy of Sciences of the USSR

Orthovanadic esters OV(OR)s have received very little study. They were first prepared in 1887 [1] by reaction of alkyl halides with silver vanadate. Prandtl and Hess [2] found that these esters are formed when vanadium pentoxide is treated with boiling alcohols taken in considerable excess: V,z05 i- 6110|1 ~ 20V (Oll)a -t- 31120: As this reaction is reversible, only small yields of trialkyl orthovanadates were obtained. Until recently no other

methods for the synthesis of orthovanadic esters had been developed [3, 4], but a proposal has now been made [5] to prepare them for the reaction of vanadyl trichloride with alcohols in presence of ammonia. In the present investigation our object was to synthesize some trialkyl orthovanadates by the reaction of VzO~ with alcohols. The reaction was carried out under conditions ensuring the removal of the water formed by continuous azeotropic distillation with benzene (boiling of vanadium pentoxide with excess of the alcohol and benzene under a reflux condenser fitted with a water trap), This procedure was found to be very convenient for the preparation of orthovanadic esters from alcohols boiling about 100". In this way we synthesized Six trialkyl orthovanadates (see table), two of which were previously unknown. Although the yields were low (2095%), the method of synthesis is so simple and convenient that it is to be preferred to the more complicated synthesis from VOC1s [5], which gives better yields. We mnst point out that the yield of OV(OR).~ is appreciably affected by the activity of the vanadium pentoxide used. The yields given in the table were obtained by the

899