August, 1961
KOTES
entire course of the rcsction. KO change in rate was observed on varying the volume of solvent from 50 to 125 ml. The average rate constants, calculated in the usual manner from the slopes of the experimental logarithmic plots, are brought together in Table I. The parameters of the Eyring equation, based upon the data in Table I, are shown in Table 11, along with corresponding data for oxalic acid, oxamic acid and malonic acid.
mately equal. This suggests that the carbonyl carbon atoms of these two acids have approximately the same effective positive charges. The fact that, in quinoline, the entropy of activation of oxalic acid is approximately equal to that of oxanilic acid, in spite of the differences in the sizes of the two species, may be attributed to the greater tendency of the dicarboxylic acid, as opposed to that of the monocarboxylic acid, to associate through hydrogen bonding to form a "supermolecule" cluster.lo Further work on this problem is contemplated. Acknowledgment.-The support of this research by the National Science Foundation, Washington, D. C., is gratefully acknowledged.
TABLE I APPARENT FIRSFORDER RATE CONSTANTS FOR CARBOXYLATION O F
THE DEOK4NILIC ACID I N QUINOLINE AND IN &METHYLQUINOLINE
Temp.,
Solvent
o c . cor.
141.45 152.00 160.86 135.78 146.95 155.23
Quinoline
8-Methylquinoline
k X I?',
Av.
dev. 1.34 f 0 . 0 2 4.41 .02 11.41 .02 1.29 .Ol 4.28 .02 9.93 -02 SCC.
TABLE I1
1461
(10) W. Huckel, "Theoretical Principles of Organic Chemistry,'' Vol. 11, Elsevier Pub. Co.. New York, N. Y., 1958, p. 329 et seq.
PHASE EQUILIBRIA IN T H E BINARY SYSTEMS PuC13-RbCl AND PuClrCsCl' BY R. BENZAND R. M. DOUGLASS Uniuersitg of California, Loa Alamos Sckntific Lahoratory, Loa Alamos N e w Mexzco Received March $4, 1961
KINETICDATA FOR THE DECARBOXYLATION OF SEVERAL Phase diagrams deduced from analysis of cooling OHCIANIC ACIDSIN QUINOLINE AND IN ~METHYLQUINOLINE curves have been reported for solid-liquid equilibria -Quinoline7 AH*,
Solvent
kcal./ mole
Oxalic acid4.6 Oxamic acid7 Oxanilic acid Malonicacid'
38.9 47.0 38.6 26.7
AS+
e.u./ mole
+15.8 +37.5 $16.0 2.4
-
-8-MethylquinolineAH*,
kcal./ mole
37.7 36.8 35.6 24.4
AS*.
e.u./ mole
+13.7 +14.7 +10.0 -10.5
Discussion of Results I n the decarboxylation of oxanilic acid in quinoline and in 8-methylquinoline the positive inductive effect of the methyl group in the latter, as well as its steric effect, are demonstrated by the data in line 3 of Table 11. The AH* of the reaction decreases by 3 kcal./mole, and a t the same time the AS* of the reaction decreases by 6 e.u./mole, on going from quinoline to 8-methylquinoline. A similar trend is shown by the parameters for the other three acids listed in Table 11. The negative inductive effect of the phenyl group in oxanilic acid is revealed by comparing the data in lines 2 and 3 of Table 11. I n both quinoline and 8-methylquinoline the AH* for the decomposition of oxanilic acid is lower than it is for that of oxamic acid. Since the phenyl group attracts electrons, the +E effect of the nitrogen atom is smaller in oxanilic acid than it is in oxamic acid. Therefore, the effective positive charge on the carbonyl carbon atom involved in coordination with the amine is neutralized to a smaller extent in the case of oxanilic acid-this carbon, therefore, has a higher effective positive charge than that in oxamic, the attraction between acid and solvent is increased, and the activation energy or enthalpy decreases. It will be seen in Table I1 that the enthalpies OS activation for the decomposition of both oxalic acid and oxanilic acid in quinoline are approxi-
in the binary systems PuC13-LiClj2 PuC13-NaC12 and P u C ~ ~ - K C ~ In. ~this paper are presented results for the systems PuC13-RbC1 and P u c k
csc1.
Materials.-The PuC13 has been described .a Reagentgrade RbCl was purified by precipitation as RbIClz from an aqueous solution, recrystallization of the precipitate, thermal decomposition to RbC1, and recrystalliiation of the latter from aqueous solution as described by Archibald.* The product crystals were heated slowly to the melting point under an atmosphere of €IC1 (dried with Mg(ClOa)n), cast into stick form, and stored under vacuum. Analysis of this material gave, by weight, 70.6 f 0.5% R b (theoretical, 70.7%) and 29.4 f 0.1% C1 (theoretical, 29.3%) with 0.04% Cs and less than 0.002% Li, O . O l ~ oNa, 0.01% K and 0.02% I. Reagent-grade CECI, purified by the same method, gave, on analysis, 78.9 =k 0.5% Cs (theoretical, 78.9%) and 21.3. d= 0.1% C l (theoretical, 21.1%), with less than 0.002% Li, 0.01% Na, K or Rb, and 0.03% I. On examination under the polarizing microscope, all three starting materials were found to exhibit normal optical properties with no extraneous phases being detected. Apparatus.-The apparatus and procedure have been described.' A calibrated Pt-Pt,lO% R h thermocouple was used to determine the thermal arrests and a chromclalumel differential thermocouple was used to detect polymorphic transformations. Microscopic examinations of the products were carried out using a polarizing microscope mounted in a closed glove box which was continuously flushed by a stream of dry helium.
Results The results of cooling-curve analyses for the system PuC13-RbC1, confirmed by microscopic examinations of the quenched products, are summarized in Fig. 1. The existence of three double salts is indicated. (1) Work done under the auspices of the Btoinic Energy Commission. (2) C. W. Bjorklund, J. G . Reavia, J. A. Leary and K. A. Walsh, J. Phys. Chem., 63,1774 (1959). (3) R. Benz. RI. Kahn and J. A. Leary, ibid., 63, 1983 (1959). (4) E. H. Archibald, "The Preparation of Pure Inorganic Substances," John Wiley and Sons, Inc., New York, &-, Y . , 19J2.
1462 800
-
I
I
tive index is between 1.6 and 1.7, in agreement with the value 1.66 calculated as above. Rb3PuC16.-This compound melts congruently a t 774 3' and, on cooling, undergoes polymorphic transformation a t 398". The mean refractive index calculated as above is 1.62. The results of cooling-curve analyses for the system PuCls-CsC1, confirmed by microscopic examinations of the quenched products, are summarized in Fig. 2. The existence of two double salts is indicateud.
*
TOO
i 1
l
9 600 5
r.
I
" 1
' 3
500
e
400
0.4 0.6 0.8 PuC13 PuCla mole fraction. Fig. 1.-Phase diagram of the binary system PuCls-RbC1: (1) PuCla melting point, 769 f 2"; (2) RbPulCl-, polymorphic transformation, 374' (cooling); (3) peritectic point for the compound RbPuzC1,, 584' a t PuC13 mole fraction 0.64; (4)eutectic point, 504' a t PuCla mole fraction 0.50; (5)deritectic point for the compound RbsPuCl!, 5600 at Pu mole fraction 0.42; (6) RbaPuCls melting point; Ti4 f 3 " ; (7)Rb3PuCls polymorphic transformation, 398 (cooling); (8) eutectic point, 630" a t oPuC13mole fraction 0.14; (9) RbCl melting point, 721 f 2 .
RbCl
0.2
RbPupCly.--This compound melts incongruently a t 584" with the peritectic composition 0.64 PuC1, and, on cooling, undergoes polymorphic transformation at 374". Crystals of the room-temperature modification are long prismatic, transparent, and light blue to greenish blue by transmitted light. They are optically biaxial positive with moderate birefringence, parallel and inclined extinction, positive elongation, absorption Z > X , with moderate optic axial angle, and strong dispersion of the optic axes, ~ V ( TZ) > 2Vz (!), The mean refractive index is around 1.8, in agreement with the value 1.80 calculated from Lorentx-Lorenz molar refractivity of the end-member chlorides with linearly additive molar volumes. RbzPuClS.--This compound melts incongruently a t 560" with the peritectic composition 0.42 PuC13. The composition is chosen as being the simplest consistmt nith the data. Crystals are transparent, brownish or greenish yellow t o nearly colorlees by txansmitted light, and optically anisotropic Rith low birefringence. The mean refrao-
9
---
-
1
j
'
400 -
CPCl
I 0.2
* e
I
--i
* e
I
0.4 0.6 0.8 PILCli PuCb mole fraction. Fig. 2.-Phase diagram of the binary system PuC13-CnCl; (1) PuC13 melting point, 769 f 2'; (2) eutectic point, 011 a t PuCI3 mole fraction 0.70; (3) CsPuZCl7meltin point, 616 f 3'. (4) eutectic point, 504' at PuC& mole fraction 0.47; (5) ks3PuC1G melting point, 825 ?Z 3"; (6) Cs3PuCl~ polymorphic transformation, 410' (cooling); ( 7 ) eutwtic point, 592' a t PuC13 mole fraction 0.10; (8) CsCl melting point, 645 2 " ; (9) CsCl polymorphic transformation, 465" (cooling).
CsPuzCly.-This compound melts congruently a t 616 * 3". Crystals of this phase are transparent, pale blue in thinnest sections through greenish blue to deep green in thicker sections and not noticeably pleochroic. They are optically biaxial negative with large optic axial angle and moderate birefringence. Acicular crystals exhibit positive elongation and parallel extinction suggest-
August, 1961
SOTES
ing orthorhombic symmetry. The mean refractive index is 1.85 f 0.03, in agreement with the value 1.85 calculated as above. The differences in the optical properties suggest that this compound may not be isomorphic with the isoformular rubidium compound. Cs3PuC16.-This compound melts congruently a t 825 =t 3" and. on cooling, undergoes polymorphic transformation a t 410". Crystals of the roomtemperature modification are green in bulk by reflected light but, immersed in liquid of similar refractive index, are transparent and virtually colorless by transmitted light. They are optically anisotropic and exhibit very fine, complex, polysynthetic twnning. The mean refractive index is around 1.7, in agreement with the value 1.73 calculated as above. Discussion It is interesting to note the similarity between PuC13 and UCljb6in the formation of double salts with alkali chlorides. KO compounds occur in the binary systems involving LiCl or NaC1. There exist iLIPuzC17-type compounds, where hI = Rb or Cs, hlzPuCl5-type compounds where 31 = K or Rb, and R13PuC16-typecompounds where bI = K, Rb or Cs. Acknowledgments.-We are indebted to A. TIT. Morgan and J IT. Anderson for the plutonium metal, and to C . F. AIetz, W. H. Ashley, G. R. Waterbury, R. T . Phelps, C. T. Apel, &I. H. Corker, D. C. Croley, J. A. Mariner, 0. R. Simi, C. H. Ward, K.IT. Wilson and A. Zerwekh for the chemical and spectrochemical analyses.
polyphosphate, previously reported5 a t 25", evaluated a t 65'.
1463 iq
Experimental Materials.-Tetramethylammonium polyphosphates and imidophosphates in 99.9+ and 97+% puiitl , Iebpectively, were prepared as previously d e s c r ~ b e d . ~The water used for solution make-up was distilled and freshly boiled to remove dissolved COz. Other chemicals were C.P. grade. Procedures.-The aciditv constant determination at a constant temperature and ionic strength WBR carried out ab previously described.3 A Leeds and Sorthiop pH meter with glass and calomd electrodes T T ~ Sutilized, and aa. calibrated a t each temperature with huffer solutions having a pH of 4, 7 and 10 Calibration oi the pH meter nith one buffer solution gave readings ~ i t thr h other two buffers that agreed to within 10.01 pH unit, indicating lineaiity of the pH scale. Temperature B A S controlled to 10.1" using a heater in combination with a heat-sensing Thermotrol unit, manufactured by Hallikainen Instruments, Berkeley, California. In the experiments below room temperature, the solutions were placed in an ice-acetone bath, aith the heater supplying enough heat to maintain the desired temperature. During titration the solutions \\err maintained untie1 :i nitrogen atmosphere. The magnesium coniplr\ing I)\ p\ iophosphate and tripolyphosphate vas measiirrd ti\ the same procedui e described by Lambert and W a t t t ~ sexcvpt ,~ that the measurements \\-ere made a t 25 and 65'. The p H mrasurements in the presence of excess magnesium nere made within a few minutes to aboid precipitntion of niagnefiirim phoqphates
Results and Discussion Acidity Constants.-Stepwise titration curves with definite breaks for the weakest two hydrogens were obtained with all of the investigated acids. The other hydrogens were so strong that no inflection points ~ e r eobserved. The acid-base titration dhta, obtained at a constant temperature and total ionic strength, were fit to a least-squares program of an IB3I 704 computer, as previously (5) C J Baiton R J Shell A B milkerson and W R. Grimes. described.3 The resultant acid dissociation conORNL-2548 or E M Leiin and H F RZcMurdie, "Phase Diagrams for Ceramists Part 11, %m Ceram Soc , 1959. stants with the statistical 95y0 confidence limits (6) J J Katz and E Rabinowitch 'The Chemistry of Uranium are listed in Table I. Part I , N N E S Di\ V I I I , Vol 5, RIcGraw-Hill, New York, N Y.. pu'o attempt was made to extrapolate the acid 1951, p 480 dissociation constants to infinite dilution since they were only determined a t fewer than four ionic strengths. For the polyphosphoric acids (H0)zOP METAL CORIPLEXISG BY PHOSPHORUS CORIPOUKDS. T'. TEMPERATURE [ ~ H ] ~ - P O ( O € € ) 2with n varying from 0-60, D E P E S D E S C E OF ACIDITY AND MAGSESIUM COMPLEXISG CONSTA4NTS no significant temperature dependence of the dissociation of the weakest two hydrogens was obBY RIYADR. 1 ~ 4 x 1 served. with the apparent, molal AH for dissociation RrseaTch Department, Inorganir Chemicals Dzuzszon, Monsanto Chemibeing between -1 and 0 kcal. The apparent A H cal Company, St. Louzs 66, Missourz for the dissociation of the stronger hydrogens lies Received A p r i l 3 , 1961 between - 2 and 0 kcal. As was previously3 found The acidity c ~ n s t a n t s l -of ~ polyphosphoric and at 25', the ratio of the dissociation constants of the imidophosphoric acids hare been reported at 25'. two weakest hydrogens approaches the value of However, the evaluation of the temperature de- four7 as the chain length of the phosphate chain appendence of metal complexing at pH values where proaches infinity. two hydrogen forms of a ligand coexist4requires the The acid dissociation constants of imidodiphosavailability of acid dissociation constants in the phoric and diimidotriphosphoric acids show sigsame temperature range. nificant temperature dependence, as was observed I n the present study the aciditj constants of poly- with their calcium complexes. Thus, the apparent phosphoric and imidophosphoric acids are presented molal AH for the dissociation of the weakcst hydroa t several temperatures and ionic strengths. Rlag- gen ( K J at :in ionic strength of 0.1 is -6.4 and nesiuni complexing by pyrophosphate and tri- - 4.5 kcal. for imidodiphosphorir and diimidotriphosphoric acids, respectively, where "
"
(1) J. I. Watters, E. D. Loughran and S. M. Lambert, J . A m . Chem. SOC.,78, 4855 (1956). ( 2 ) S. M. Lambert and J. I. Watters. ibid.,79, 4262 (1957). (3) R. R. Irani and C. F. Calli@,J . P h y s . Chem., 6S, 934 (1961). (4) R. R. Irani and C. F. Callis, ibid., 64, 1398 (1960).
(5) S. ILl. Lambert and J. I. T a t t e r s , J. A m . Chem. Soc., 7 9 , 5608 (1957). (6) R. R. Irani and C. F. Callis, J . Phgs. Chem., SS,296 (1961). (7) S. W. Benson, J . A m . CAem. Soc., 80, 5151 (1958).
