Molybde num(Vl) Nicoti nylhydroxa m ic Acid Chelate RONALD ROWLAND]. and CLIFTON E. MELOAN Department of Chemistry, Kansas State University, Manhattan, Kan.
b Mo(VI) forms a ‘I:2 chelate with nicotinylhydroxamic cicid at p H 3.0. The absorption maxirrium is at 350 mp and the chelate has a molar absorptivity of 1.60 X 10+3, a t a concentration of 1.2 X 10-4M. Extraction studies were made as were interferences and effect of pH. The stability constants were found to b e 5 X lo-’ for Kal arid 2 X lo-’ for Ka2. The Ka for nicotinylhydroxamic acid is 8.2 X lop9.
T
of liydroxamic acids with various metals to form chelates have been found in many cases to be of analytical importance ( 2 ) . Nicotinylhydroxamic acid (Figure 1) has been shoan to chelate with Mn(II1) to form a red-violet chelate a t pH’s more basic than 9 ( 2 ) . Traces of iron have been determined spectrophotometrically as the golden colored chelate of nicotinylhydroxamic acid itt a pH of 4.5 to 6.0 a t 440 mp (3). Vanadium and molybdenum both form yellow nicotinyl hydroxamics.
ml. of water and stirred for 5 minutes. T h e p H of each solution was adjusted with N a O H or HCl to cover the p H range of 2 to 12. RESULTS A N D DISCUSSION
The results are shown in Table I. From the results obtained in Table I it was decided to investigate the Ti(IV),
Table I.
Ion Fe+2 Fe +g Mn + 2
H E REACTIONS
Figure 1 .
Nicotinylhydroxamic acid
Since nicotinylhydrcixamic acid does chelate with the fore-mentioned metal ions, possibilities existed for chelate formation with other transition metals.
Mo +6 Ti
+,
v
+6 +5
Investigation of Metal-N.H.A. Chelate Formation
Compound FeClz FeCI3 MnS04 (SH4)zhloOn K2TiO(C204)z UOS(YO3)2 SaV03
Solvent Ililute HC1 Dilute HC1 Ililute HISO, Dilute HCI Dilute HC1 Ililute H S 0 3 Dilute HCI
?IIo(T.’I),and V(V1) in more detail since the chemistry of these has not been reported. The Ti(V1) and V(T’1) work will be reported in future papers. The following ions produced no a1)parent chelation: Xg+l, As+b, Cd+2, Ce+4, Cr+s, Crfe, Ge+‘, In+3, La+S, S i + 2 , Pb+2,Rh+3, Sn+2,Te+4,W + e , Y+3, Zr+4 Effect of pH. I n order to determine the effect of pH on the transniittance of t h e solutions, the chelate3 were prepared a t p H interval3 of one unit. These solution3 were placed in a cell of a Iieckman DI3 spectrophotometer and the spectrum recorded from 700 mp to 320 mp Water \!as used as a reference solution The result\ (Figure
EXPERIMENTAL
Apparatus. Beckman DB spectrophotometer equipped with matched 1.00-cm. cells; Becltman potentiometric- recorder; I3ecliman zeromatic p H meter: I.B.M. 16120 computer. Reagents. Solutions of approuimately 0.01M of the ions were prepared from reagent g a d e chemicals. Xicotinylhydroxamic acid, 0.01J1, Nutrition:il 13iochemicals. Sodium hydroxide, 3 J f , 0.01J.11. Hydrochloric acid, 351, O . O I J f . (NH4)J\107024.4H201
2 ) show that the yellow molybdenum (VI) chelate has a maximum absorption at 350 mp and at ,,H of 3.0, Structure Studies. Job’s method (4) of continuous variation was applied to the system a t DHof 3. The results indicate a 1 : 2 ratio of metal to ligand. Conformity to Beer’s law. 1Iolybdenum nicotinylhydroxamate solu-
Results Red soln. for pH 2 5-6 0 Red soln. for pH 2 5-6 0 l‘iolet soh. for pH 9-12 Yellow soln. for pH 2-8 Golden soln. for pH 3-9 Yellow s o h . for pH 3-11 Pink soh. fcir pH 3-9
tions were prepared at various concentrations a t a pH of 3 and a 5 : 1 ligand to metal ratio. Table I1 shows the results. Table II. Beer’s Law Studies .Molar concentration Ab.\Zolar of .\10(11) sorbance absorptivity 0 . 4 x lo-‘ 0 071 1.77 x 10-8 0.8 0 134 1 68
1.2 1.6 2.0 3.0 4.0
0 0 0 0
192 246 304
1 60 1 54 1.52 1 45 1.41 1.34
435
0.565
5.0
0.668
100-
80-
/
0.01.11.
Procedure. CHELATEFORMATION. T o 2 ml. of each metal solution, 10 ml. of the ligand were added. T h e resulting solution was diluted with 25 Present address, D o w Chemical Co., AIidland, Nich.
I 300
400
Figure 2.
I
I
500
I 600
Effect of pH on chelate absorbance VOL. 36, NO. 10, SEPTEMBER 1964
1997
This could undoubtedly be improved by increasing the ligand to metal ratio. Extraction of the Chelate. I n previous work with hydroxamic acids, advantage has been taken of the fact t h a t some chelates are considerably more soluble in organic solvents t h a n in aqueous solution. I n some cases the color of the chelate is more intense in the organic phase t h a n in the aqueous phase. Thus, Wise and Brandt (5) have developed a method for determining vanadium(V) by extracting vanadium benzohydroxamate with 1-hexanol and measuring the absorbance. The molar absorptivity for the chelate in the aqueous solution is 1 x l o 3 while in 1-hexanol it is 3.5 X 103. Since nicotinylhydroxamic acid is quite similar to benzohydroxamic acid, an attempt was made to find an appropriate organic solvent for extracting
the chelate. Visual examination revealed that none of the organic solvents tried would extract the chelate. Those solvents tried were: benzene, bromoethane, carbon tetrachoride, chloroform, diethyl ether, diisobutyl ketone, ethyl acetate, ethyl benzoate, heptaldehyde, n-hexanol, isoamyl alcohol, skelly B, and toluene. This is in keeping with Feigl's rule. Effect of Foreign Ions. T h e interfering ionu have been studied quite extensively by Dutta (S) with regards to the &In system. It should be pointed out that uranium(V1) and Ti(1S') interfere a t all concentrations employed. This is in addition to Dutta's work. Stability Constants. The stability constants were determined by the method of Bjerrum ( I ) . The K n of the at ligand, was found to be 8.2 X an ionic strength of 0.1. Kai and Kaz for the Mo(V1) chelate were 5 X
and 2 X These values are also for an ionic strength of 0.1. The calculations aere made with an 113111 1620 programmed for a constant pH increment. The experimental conditions employed were a 10: 1 ligand to metal ratio, 0.01JI solutions, 25' C.. and ionic strength adjusted with SaC104. LITERATURE CITED
( I ) Bjerrum, "Metal A4mmineFormation in *Aqueous Solution," P. Haase and Son, Copenhagen, 1941. ( 2 ) Dhar, S. K., Das Gupta, A. K., J . Sci. Ind. Res. (Indiu) 11C 500 (1953). (3) I h t t a , R. L., J . Indian ('hem. SOC. 34, 311-16 (1957); Ibid., 35, 243-50
ij 19581. -.-_, ( 4 ) Job, P., Ann. Chim. 10, 113 (1928). (5) Wise, W. M., Brandt, W. W., AXAL. CHEM.27, 392 (1955).
RECEIVEDfor review A n d 29. 1963. Resubmitted July 1, 1664. '4ccepted July 1, 1964.
Determination of Cesium and Rubidium after Extraction with 4-sec- Butyl-2(a-met hylbe nzyl) phen01 W. J. ROSS and J. C. WHITE Analytical Chemistry Division, Oak Ridge National laboratory, Oak Ridge, Tenn.
b Methods have been developed for radiochemical and flame photometric determinations of cesium and rubidium. These elements are selectively extracted from basic tartrate solutions, after removal of the alkaline earth elements, with 1M solutions of 4-sec butyl 2(a methylbenzy1)phenol (BAMBP) in cyclohexane. Cesium and rubidium can be measured directly in the organic solution or after being back-extracted into 1 M HCI.
-
I
-
in the recovery of heavy alkali metals from their ores and in the separation of radioactive Cs'3' from spent nuclear fuels has resulted in additional attention being given t,o analytical methods for isolating and determining cesium and rubidium. Cronther and Moore (4) have recently discussed the advantages of liquidliquid extraction as a means of separating cesium and presented a method based on the extraction of cesium with t'henoyltrifluoroacetone (TTA). C r h l this time gravimetric ( 5 ) and extraction (8) methods using tetraphenylboron have been t'he most popular means for isolating cesium. Recently, Horner et al. (1,1, 6 ) demonstrat)ed the feasibility of extracting cesium from alkaline solutions with substituted phenols, especially with 4 - sec - butyl - 2 - ( a - methylbenzyl) NCREASED INTEREST
1998
ANALYTICAL CHEMISTRY
phenol or BAMBP. Subsequently, Arnold (3) has efficiently separated cesium from other alkali metals through a continuous extraction process employing BAMBP. The novelty and efficiency of the separations reported by these workers have given impetus to an investigation of the analytical potentialities of BAMBP. This paper describes a rapid and efficient method for extracting tracer and milligram amounts of cesium and rubidium from all other elements that interfere either in radiochemical or flame photometric determinations of these alkali metals. EXPERIMENTAL
Apparatus. A\ll extractions were performed manually in glass extraction funnels. The gamma activities of single radionuclides were measured with a single-channel pulse-height analyzer coupled with a well-type XaI(T1) crystal. The gamma activities of multicomponent system? were resolved and measured with a multichannel pulse-height analyzer equipped with a 3-inch X 3-inch NaI(T1) crystal. Flame photometric measurements were made with a Jarrell-Ash spectrophotometer with flame attachment. Reagents. Radiotracers of X a z 4 , K4*, Ca47, Srs5, RbS6, and Cs13' were obtained in aqueous solutions from the Isotopes Division of the Oak Ridge Kational Laboratory.
Gamma-emitting radionuclides of and all other elements were produced by activating microgram amounts of the natural element for 16 hours in a reactor neutron flux of 8 X 10" neutron per sq. cm. per second. Solutions of 1 M BAMUP were prepared by dissolving 25 grams of the phenol in 100 ml. of cyclohexane. This reagent, 4-sec-butyl-2(a.methylbenzyl) phenol, was obtained from Dow Chemical Co. and was used without further purification. Radiochemical Procedure. Pipet an aliquot of a neutral, aqueous sample into a 50-ml. centrifuge tube. Add 1 ml. of 5% N a O H and evaporate to incipient dr) ness to expel ammonia. Add 1 ml. of 1'11 tartaric acid and dilute to -3 ml. with HzO. Add 1 ml. of strontium carrier (10 nig. of Sr) and 1 ml. of 1 X ?;azCOs solution. Precipitate SrC03 by warming the solution in a water bath (50' to 70" C.) for 10 minutes. Separate the precipitate by centrifugation and decant the supernatant liquor into a 25-ml. separatory funnel. Add 5 ml. of 1JI BXMBP and extract for 1 minute. Repeat the extraction with 5 ml. of fresh E h M B P solution if quantitative separation of rubidium is desired. Combine the extracts. Remove an aliquot of the organic phase and count the activity of cesium and rubidium. If interference from radionuclides of sodium or potassium is observed, backwash the organic phase with 5 ml. of 131 S a O H solution and recount an aliquot of the organic phase.
