James C. Hindman Argonne National Laboratory Lemont, Illinois
Neptunium and Plutonium
Neptunium and plutonium occupy a unique place among the chemical elements. Neptunium was the first of the transuranium elements to be discovered (1). The Np239isotope, found by McMillen and Abelson, is the precursor of PuZa9,the plutonium isotope of such great importance in the atomic energy field. The first plutonium isotope to be discovered, PuZa8,was produced in 1940 by Seahorg, McMillen, Kennedy, and Wahl (9). The principal isotopes of chemical interest are the a-emitters, NpZS7(3) (till = 2.2 X 108y) and PuZ38(tql = 24, 360y). Since these early discoveries the chemistry of these elements has been intensively investigated. Plutoninm, in particular, can he classed among those elements whose chemistry is well understood. The amount of information available precludes any complete discussion in a short review. The present summary is therefore confined to a consideration of only the salient features of the chemistry of these elements with particular reference to the more recent literat,ure. For more extensive discussions and further literature, reference should be made to various reviews (4-8).
have the conventional sign. If the phase espauds on heating, the resistance decreases. Much less is known about Npo. I t has t\vo and possibly three allotropic modifications belolv its meltiug point (648'C). Its density is variable betn-een 18 and 20.45 g/cc.
able
Phase
1. Some Properties of Plutonium Metal (9)
Density, g/cc
Temp Linear Resistiv- coeffiit?, cient Temp. expsnsian of phase eoeffip X loB of trsnsieient," (ohm- resistiva X 10' cn~) ity" tion
Chemistry of the Solid State There is a large amount of information available on the solid compounds of neptunium and plutonium. Examination of the literature reveals much of the data rests on the pioneer microchemical preparations of Fried and his co-workers and on the X-ray identiThe Oxides. The common oxides are NpOP and fications of Zachariasen. Reference to this work will PuOZ. They are formed by ignition of the hydroxides, he found in the reviews cited (6-8). oxalates, peroxides, nitrates, etc., of any oxidation Some aspects of the chemistry of the more important state of these elements. A careful examination of the solid componnds are summarized in the following properties of PuOp prepared from different sources paragraphs. has been made (10). It has been found that oxide The Metallic State. Both NpO and Puo are silveiy prepared by ignition a t 1200° is stoichiometric. If white. reactive metals. NDO is ~renared bv the reduction of NpFa or N ~ with' F ~ B ~ aOt l i 0 0 ~ ~ . prepared by ignition of plutonium salts a t 870°, the molecular formula varies from P u O ~ . ~ ~ - P UdependO~.~~, PuOcan he similarly prepared by reduction of PuF3 ing on the starting material. Low temperature igwith Can. Plutonium metal deserves special mention nition of different compounds also results in material because of its unique properties. It is known to exist differing in color and physical appearance. in six allotropic forms below the melting point (63g°C). No higher oxides of plntonium are kno~vn. NepSome of the physical properties are given in Table 1. tunium is intermediate in behavior between uranium Particularly interesting and puzzling are the contracand plutonium, having an oxide NpsOa, isomorphous tions which the delta and delta-prime phases undergo U3O8, but no oxide corresponding to UOa. SpaOl; with with increasing temperature. Also noteworthy is the is only formed under special conditions, e.g., by the fact that for no phase do both the coefficient of thermal action of dinitrogen tetroxide on neptunium(1V) and ex~ansionand temDerature coefficient of resistivitv (V) compounds, ( t = 421°C), or by the ignition of Presented ss part of the Symposium on the New Elements before neptunium(V) hydroxy compounds a t low temperature the Division of Chemical Education at the 133rd Meeting of (275425°C). A lower plntonium oxide, Pu203, is the American Chemical Society, San Francisco, April, 1958. known. This appears to he a phase of variable comBased on work performedunder the auspices of the U. S. Atomic position with a possible upper limit of PurOr. Energy Commission, 22
/ Journal of Chemical Education
The Halide?. One of the most important classes of compounds of these elements is the halides. The kno~r-n halides are given in Table 2. Shown for comparison are the halides of uranium. This table illustrates the decreasing stability of compounds of the higher metal oxidation states with the heavier halide5 as one progresses from uranium to plutonium. Practical use can he made of the stability differences. For example, a separation process has been based on the sublimation of NpCla from the less volatile PuCIJ (11). Table 2.
Halides of Uranium, Neptunium, and Plutonium
Metal oxidation state +4 +5
+3 UF? KpFs PuF. UCI, NpCl, PuC~J URr7 i%pBr8 PuBr* UI, NpIt Pula
UF,
UFI NpF, PuF, UCI' NpCL
UCl,
+6
-
UFO
I\'pF. PoFe UC1e
UBn NpBr, PuOx
UI4
2Pu02
Typical preparative conditions for the fluorides can be illustrated by the equations for the formation of t,heneptunium salts.
NpF,
+ Fr
5cQ0C
NpFs
(3)
The analogous plutonium compounds require slightly higher trn1prl.at11rc.sfor thrir prtp~rntio~i. Thr hesnfluoridw :we of nrtnirnlar rhrmirril imrrcst and have been the subject of much recent experimental investigation (18-16). Like the higher fluorides of the transition elements, e.g., MoFs and WF6, the hexafluorides of uranium, neptunium, and plutonium are Ion. melting, low boiling compounds of ext~aordinaryvolatility. Their physical properties are summarized in Table 3. The strength of the hexafluorides as fluorinating agents appears to increase from uranium to plutonium, PuFe being capable of conrerting BrFa to BrF6 while BrF3 can be employed to make UF6from uranium compounds. Table 3.
dioxide with CClr a t 500°C. Treatment of PnOz with powerful halogenating agents such as CC14, PC]&,and SC4 yields PuCla. NpBr4 is prepared by treatment of the dioxide with AIBr3 (300-400°C). With excess AlO, the tribromide is produced. Np13 is similarly obtained with A113. PuBr3 and Pn13 are conveniently made by the action of the anhydrous gases, HBr and HI on PrO. Various oxyhalides are known hut their properties have not received recent attention. Other Compounds. There are a large number of other compounds known, e.g., hydrides, sulfides, carbides, silicides, nitrides, etc, (6, 7, 8). Most of these have not been investigated in detail. In particular, conditions for the preparation of a relatively pure single phase have not been determined. Some recent work has been done on the carbides (17). These are of interest because of their refractory nature. The conditions for the preparation of the carbides are:
+ 3C + 7C
180O0C
+ 2CO Po.C8 + 4C0
PuC
1850°C
(5) (6)
Both PuC (mp 1850") and Pu2C3 (mp 1900') are reactive, easily hydrolyzed compounds. There is some evidence for a higher carbide. Although the analogous neptunium compounds, NPC2, Np,C,, and NpC have been reported, little is known of their properties. In addition to those compounds prepared by vacuum line techniques, there are a large number of compounds that have been prepared from solutions. The most important of these are given in Table 4. It is of interest to note that no neptunium(II1) compounds are listed. This is due to the fact that Np(II1) is unstable with respect to air oxidation. Undoubtedly snch compounds could be prepared by suitable techniques. Table 4. Some Insoluble Inorganic Compounds of Neptunium and Plutonium Precipitated from Aqueous Solution
Physical Characteristics of Hexafluorideso
Property Color (solid) Colof (gas) Xlelt~ngpoint ('C) Boiling paint ('C) Vapor prwsure (25'C), mm Hg
UFs
NpFe
PuFe
White Orange Dark brown Colorless Colorless Brown 64 54.4 50.8 56.5 55.2 62.2 111.9
126.8
104.9
" Data courtesy, J. G . Malm, B. Weinstock, and E. E. Weaver (18).
The other halides are prepared by a variety of methods. NpClr can be made by treatment of the
" M is either neptunium or plutonium. Chemistry i n Aqueous Solution
Various aspects of the solution chemistry of these elements have received attention in recent years. More precise values of the formal oxidation potentials have been obtained. A limited number of quantit,ative investigations of complex ion equilibria have Volume 36, Number 1 , January 1959
/
23
-
been reported. I n particular, the field under most active investigation a t the present time is the study of the reaction kinetics of these elements. The present discussion will be confined to these more fundamental aspects of the solution chemistry. For extensive discussion and review of various separations and purification methods for these two elements reference should be made t o other sources (8,11,18,19). The O d a t i a Slates. Both neptunium and plutonium have oxidation states of +3, +4, +5, and +G in aqueous solution. The ions are of varying stability as indicated by the values of the formal oxidation potentials for 1M HCIOa. Formal Oxidation Potentials of Neptunium Couples in 1 M HClO, (80) Npo 1.83 Np+"0.155 Np+' -0.739 NpO,+ -1.137 NpO,++ --0.938-0.677 -
I
1
Formal Oxidation Potentials of Plutonium Couples in 1 M HClO, (dl)
Examination of these potential schemes reveals the following features of interest: One is the highly electropositive nature of the metals. A second is the stability of the neptunium(V) state. Another is the separation of the potentials for the different oxidation states of neptunium. I n contrast, examination of the plutonium potentials reveals that P u + ~P, u + ~ , and PuOz++can co-exist in 1M HC104. Furthermore, although unstable in 1 M HCIOI, PuOz+ becomes increasingly stable as the acidity decreases because of the strong hydrogen ion dependence of the couples. Conditions therefore exist for the stabilization of all four oxidation states in solution. Although various reagents (4, 7) can be employed in the preparation of the oxidation states of these two elements for chemical study, special mention should he made of the controlled potential electrolytic technique. This has been found particularly useful since solutions of a single oxidation state can be made without the introduction of extraneous reagents (22). Solutions of the different oxidation states of these elements have characteristic absorption spectra of varying degrees of complexity. Surprisingly, complete spectra covering the wavelength region from 0.2 to 1.85 microns are only available for neptunium (25,24). They have beeu of great analytical value in studies of equilibria, complex ion formation, and reaction kinetics. Attempts have also beeu made to analyze the spectra in terms of the electronic configurations (25,26). Hydrolysis and Complex Ion Formation. Hydrolysis and complex ion formation can have a marked effect on the relative stabilities of the different oxidation states. Despite the importance of these phenomena they have received relatively little recent attention. The general hydrolytic behavior of these elements has been reviewed by Kraus (27). Approximate 'hydrolysis constants based on the assumption of the formation of monomeric hydrolysis products are given in Table 5. The heat of the plutonium(1V) 24
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Journol of Chemical Education
Table 5.
Hydrolysis Reactions of Neptunium and Plutonium a t 25'C (ClOn- Medium)
Reaction
Kh
Pu+'+HnO~PuOH++HH+ Put" H 2 0e P u O H t a H + H,O NpOzOH NpOzf H Pu02+ H 2 0 PuOnOH H+ PuO:++ HzO PuO.Ht H
+
+
=
+
=
+
" AH
=
++ + +
Conditions
7 5 Y 100.054"
p=0.07 p = 2.0
9 X 10-
p =
3 X 10.'
3 X
p =
3 X
1 . 9 5 X 10-e
p = 1. 0
lo-'
13.3 keal mole-', AS = 19 eal deg-' mole-' (88).
reaction has been measured (28). Polymerization processes are extremely important but little information exists (27). Plutonium(1V) has been reported to form soluble polymers with molecular weights as high as 10'' (29). There are also comparatively few systems for which quantitative information on complex ion formation is extant. Qualitatively, it is known that univalent anions with the exception of fluoride form relatively weak complexes with the ions of all oxidation states. Higher valent anions are known to form relatively strong complexes. An example is sulfate, which complexes neptunium(IT3 and (VI) ions strongly enough to make the Np(V) states unstable with respect to disproportionation. The magnitude of the association constants for sulfate complexes of the +4 states of neptunium and plutonium are given in Tahle 6. Toble 6.
The Sulfate Complexes o f NeptuniumWJ and Plutoniurn(lVJ
Reaction
+
=
+
M+4 HSO, MS04++ H t MS04++ HSO, 6 M ( S 0 4 ) ~ ~ H+ HSO: s M(SOA M(S04)r- H + a
+ ++
+
Assoc. Assoc. constant constantb (M = NpP ( M = Pu) 270 740 11
60
..
5
In presence of 2 M C10,- (50). In presence of 2.3 M C1- (31).
Qualitatively, it is also known that the relative stabilities of complexes of a given anion decrease in the order M+4 > M+a > Mop++> M o p +
The only quantitative data illustrating this point have been obtained from a combination of spectrophotometric and potentiometric observations (52-54). These are given in Table 7. Toble 7.
The Chloride Complexes of Plutonium, t A,
-
= 1.0
= 25'C
Reaction
+
Puf3 CI- s PuCI+~ CI PuCl+= Put' C1 G 2 Pu02CI I'oOlt Po02++ C1- s P"02CI+
++ = +
Other available data on the complexit" constants are given in references 6, 7, and 8.
Equilibria and Kinetics. I t is of obrioui; concern how rapidly mixtures of ions of different oxidation states of neptunium and plutonium approach the
equilibria determined by their oxidation potentials. The principal neptunium reactions of interest are the Np(1B) Np(V1) + 2Np(V) reaction and the Kp(V) + 2Np(IV) reaction. The principal Np(II1) plutonium reactions are the disproportionation reaction of plutonium(1V) and the reactions leading to equilibrium between all four oxidation states. The fundamental information on these reactions is summarized in the following paragraphs. Additional information on activation energies, etc., may be obtained from the original papers. In perchlorate solution the equilibrium
a t O°C, p = 2.0, k, = 43.3111-2sec-L (36). One of the most important reactions involved in the establishment of equilibrium in solution of plutonium is the disproportionation reaction of plutonium(1V) (37-40). The equilibrium is
lies far to the right. At 25' in 1 M HC104, K = 5.45 X 10B. The rate of formation of Np(V) is slow. The form of the rate law
However, because of the maintainence of the equilibrium involving all four oxidation states
+
+
3PuC'
+ 2H90
Kt = 2Put"
f01++ + 4Ht
(11)
a t 25OC, in 1 M HC104, K , = 8.4 X 10-3. Kinetic studies indicate that the fundamental mechanism involves the formation of Pu(II1) and Pu(V) according to the equation
the rate law assume the form indicates that the mechanism is complex (55). At ionic strength (p) = 2.2 and 25', k = 4.27 X 10-2 M sec-' and h = 5.04 X lo-= M 2 sec-'. As a consequence of the formation of sulfate complex ion, the equilibrium in reaction (7) is shifted so that both for\vard and reverse rates can be measured. The dat.a on the kinetics have been interpreted in terms of reactions involving sulfate complex ions of Np(1V) and iYp(V1) (55). Examination of the potential diagram shows that the formation of Np(1V) is also highly favored according to the equilibrium spo2+
+~
p +f v~
K
e +
+
2 ~ p + 4 ZH~O
(9)
I n 1 M HC10a a t 21°C, K = 10lO. The forward reaction is rapid (56). The rate law for the forward reaction is
Table 8.
2Kp(V)
-
Np(1V)
2Pu(V)
Np(IV)
+ Np(VI)
+ Np(V1) -2Np(V)
A
-+
Pu(IV) A
,
--
+ Pu(V1)
+
-a - Pn
+ "
+
k[Put3] [Pu02++] k, [PuSO,+Is[O21 k2 [PuS04+l[Pu(SOd-10: Np03+ k P Kpl a PPu8 k[Z Pu]
+
-
Table 9.
Reaction
Specific rate constant, see -1
+
I'u(llr)' Pu(V) O? Po(1V) Pu(II1) NpO?;: PnO?
25'C
[NpO~+IP[kl[HSO,-] + k21HS04-]2] kt = 4 . 3 X AT-* kr = 2 . 3 X M-a ko[Np+41~[Np0~++l[H+l-P k. = 4.48 X 10-2M I hlNpSOdf+l [NpOzt+l k, = 7 . 1 2 X 10-2M-' k2[-L-pSOlt+1[NpO?SO,Il k2 = 1 . 1 9 X 10-'M-' lkl[Ht1-a k41H+i-31 ka = 3 . 6 M 2 k4 = 1.7 M3 k[PuOl+]'[H+] k = 3.6 X
+
P n.(\l T T 1, I P n..l B,T.1, + A
Other Reactions of Neptunium and Plutonium Ions a t
Form of kinetic equation
Reaction
The rate of the reverse reaction (12) can be determined from the relation (k-l)/Kz = kl/Kl. At 25"C, P = 1.0 in C104-, KI = 8.4 X K2 = 13 and kl = 3.4 X lo-= M 2sec-'. The rate of disproportionation is increased in chloride solution. The rate of attainment of equilibrium in reaction (13) has been measured. Kinetic data on this and other recently investigated reactions of neptunium and plutonium are given in Tables 8 and 9. The following comments can he made about the reactions listed in these tables. Although plutonium(V) disappears primarily by the reverse of reaction (12), a t low concentrations of Pu(II1) it is possible to observe the disproportionation reaction of Pu(V). Kinetically the reaction is similar to the disproportionation of U(V).
Conditions 2.2, C10&HSO; p = 2.2, ClodHSOIp =
=
(35) (~5) ..
......
.. ..
1.0, CI04-
tli)
..... . ... ...
p
Reference
k = 1.3Md' k, = 5 . 5 X 10-PM-1 2ltrn-I k2 = 0.355 M-I atm-I k = 3 1 X 10-Qsee-L k = 1.7 X 1 0 ' e l sec-I
Exchange Reactions in Perchlorate Solution
Rate law
Specific rate constants sec-1
Conditions
Reference
Volume 36, Number I, January 1959
/
25
Despite the fact that the lower states of neptunium and plutonium are unstable with respect to oxidation by air the only reaction thus far measured is the oxidation of Pu(II1) in sulfate solution. In this case the reaction intermediate appears to involve sulfate ions. A special kind of reaction that occurs for these elements is that induced by the reaction the a-particles on the aqueous solutions (Table 9). For neptunium, reduction has not been observed to proceed past the +5 state (44). For plutonium the maintenance of the various equilibria already discussed results in the gradual lowering of the average oxidation number in the solution (57). The final steady state is Pu(II1) with a small concentration of Pu(1V). Finally, a number of exchange reactions have been investigated (Table 9). Examination of the data shows that, with the exception of the Np(1V)-Np(1V) exchange, all of the reactions are rapid. In addition to their general kinetic interest, information on these reactions is of practical concern in the proper design of tracer experiments. Literature Cited (1) MCMILLEN,E., A N D ABELSON,P., Phys. Reu., 57, 1185 (1 * - ,. ,-44n) (2) SEABORG, G. T., MCMILLEN, E. M., KENNEDY, J . W., AND WAHL,A. C., Phys. Reu., 69, 366 (1946). ~ C., A N D SEARORG, G. T., Phys. Reu., 73, 946 (3) W A H A. ,,O"Q\
\'YIU,.
(4) CONNICK, R. E., Chap. 8, "Oxidation States, Potentials, Equilibria, and Oxidation-Reduction Reactions of Plutonium" in Vol. 14A, "The Actinide Elements," National Nuclear Energy Series, McGraw-Hill Book Ca., New York, 1954. J. C., Chap. 9, "Ionic and Molecular Species of (5) HINDMAN, Plutonium in Solution," Vol. 14A, "The Act,inide Elements," National Nuclear Energy Series, MeGraw-Hill Book Co., New York, 1954. B. B., Chap. 10, "Preparation and Properties (6) CUNNINOHAM, of the Comnounds of Plutonium." Vol. 14A. "The Aetinide Elements," National Nuclear Energy Series, McGraw-Hill Book Co., New York, 1954. (7) CUNNINGHAM, B. B., AND HINDMAN, J . C., Chap. 12, "The Chemistry of Neptunium," Vol. 14A, "The Actinide Elements," National Nuclear Energy Series, McGrawHill Book Co., New York, 1954. G. T., "The Chemistry of the (8) KATZ,J. J., A N D SEARORO, Actinide Elements." John Wilev $Sons. New York. 1957. . 23,365 (1955). (9) JEWS, E. R., J. ~ h e kPhys., J. L., AND WELCH,G. A,, J . Chem. Soe., 1957, (10) DRUMMOND, 4781. I. K., AND VOROBYEV, A. M., Paper P/674, (11) SHVETSOV, Proceedings of the Internationd Conference on the Peaceful Uses of Atomic Energy, Geneva, 1955, 7,304 (1956). I. R., A N D LEMONS,J. F., (12) FLORIN,A. E., TANNENBAUM, J. Inorg. Nuel. Chem., 2,368 (1956). (13) MANDLEBURG, C. J., ET AL.,J. I n o ~ gNuel. . Chem., 2, 358 (1956). B., A N D MALM,J. G., J. Inorg. Nuel. Chem., 2, (14) WEINSTOCK, 380 (1956); J . Chem. Phys., 27, 594 (1957).
26
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Journal of Chemical Education
B., AND CLAAGSEE~, H. H., J . (15) MALM,J . G., WEINSTOCK, Chem. Phys., 23, 2192 (1955). B., AND WEAVER, E. E., "The (16) MALM,J. G., WEINSTOCK, Preparation and Properties of NpF@;a eomperison in the PuF.." To be published. (17) DRUMMOND, J. L., ET AL., J . Chem. Soc., 1957, 4785. J.. AND S I L L ~ N L., G., Acta Chem. Scand., 9, 1241 (18) RYDBERG, (1955). L ~ m o s ~ S., r , Paper P/823, Proceedings of the International Conference on the Peaceful Uses of Atomic Energy, Geneva, 1955, 9,575 (1956). COHEN,D., AND H I N D ~ N J., C., J. Am. Chem. Soe., 74, 4679 (1952); 74,4682 (1952). RABIDEAU, S. W., J. Am. Chem. Soc., 78, 2705 (1956). HINDMAN, J . C., COHEN,D., AND SULLIVAS, J. C., Proceedings of the International Conference on the Peaceful Uses of Atomic Energy, Geneva, 1955, 7, 345 (1956). SJOBLOM, R., A N D HINDMAN, J. C., J. Am. Chem. Soe., 73, 1744 (1951). WAGGENER, W.C., J. Phys. Chem., 62,382 (1958). EISENSTEIN, J. C., AND PRYCE,M. H. L., PTOC.Roy. Soc., 238A, 31 (1957); 229A, 20 (1955). J@RGENSEN, C. K., Dan. Mat. j y s . Medd., 29, Nos. i and 11, (1955); J . Chem. Phys., 23, 399 (1955). KRAUS,K. A,, "Hydrolytic Behavior of the Heavy Elements," Paper P/731, Proceedings of the International Conference on the Peacefnl Uses of Atomic Enereu. -. . Geneva, 1955, 7, 245 (1956). S., J. Am. Chem. Soc., 79, 3675 (1957). (28) RABIDEAU, D. W., A N D WELCH,G. A,, J. Chem. Soe., 1956, (29) OCKENDEN, 1152
(30) SULLIVAN, J. C., AND HINDMAN, J. C., J . Am. Chem. Soc., 76, 5931 (1954). (31) SULLIVAN, J . C.. AXES,D. P., AND HINDMAY, J. C., unpublished observations. (321 . . 2 .. . . WARD.M.. A N D WELCH.G. A.. J . I n o ~ o .S I ~Chern.. 395'(1956). S. W., J . Am. Chem. Soe., 78, 2705 (1956), in(33) RABIDEAU, cluding unpublished observations of T. Seuton. (34) NEWTON, T. W., AND BAKER,F., J . Phys Chew, 61, 934 iIC57) ,L"".,. (35) SULLIVAN, J . C., COHEN,D., AND HINDMAS, J . C., J . A!% Soe., 79, 4029 (1957). J. C.. SULLIVAN, J. C., A N D COHEX, (36) . . HINDMAN. . D.,. J. Am. Chem. ~ o c . 1958, , in press. (37) KASHA,M., Paper 3.100, "The Transuranium Elements," National Nuclear Energy Series, MeGra~--HillBook Co., New York, 1949. R. E., A N D MCVEY,W. H., J . Am. Chem. Soe., (38) CONNICK, 75, 474 (1953). S. W., AND COWAN, H. D., J. Am. Chem. Soc., (39) RABIDEAU, 77, 6145 (1955). S. W., J. Am. Chem. Soc., 75, 798 (19%). (40) RABIDEAU, (41) Ibid., 79, 6350 (1957). J. Ph~ls.C ~ P R L60, . , 812 (42) OOARD,A. E., A N D RABIDEAU, (195fi). ~ -
~
~
~
,
(43) NEWTON,T. W., AND BAKER,F. B., J . Phvs. Chem., 60, 1417 (1956); 61, 381 (1957). (44) ZIELEN,A. J., COHEN,D., AND SULLIVAN, J. C., unpublished work. (45) SULLIVAN, J. C., COAEN,D., A N D HINDMAS, J. C., J. Am. Chem. Soc., 79, 3672 (1957); 78, 1543 (1956); 77, 4964 (1955); 76,4964 (1955). T. K., J. Am. Chem. Soc., 78, 2339 (1956); J. (46) KEENAN, Phvn. Chem.., 61. 1117 (1957). (47) S ~ L I V A J. N ,C., COHEN,D., A N D HINDMAN, J . C., J. Ant. Chem. Soc., 76, 4275 (1954).
.
