ANALYTICAL CHEMISTRY, VOL. 50, NO. 11, SEPTEMBER 1978 (16) M. L. Bender, "Mechanisms of Homogeneous Catalysis from Protons to Proteins", Wiiey-Interscience, New York, N.Y., 1971, p 159. (17) J. F. Kirsch and W. P. Jencks, J . A m . Chem. Soc., 86, 833 (1964). (18) R. Wolfenden and W. P. Jencks, J. A m . Chem. Soc., 83, 4390 (1961). (19) K. A. Connors. "Reaction Mechanisms in Oraanic Analvtical Chemistrv". Wiley-Interscience, New York, N.Y., 1973,-pp 598-601, (20) J. L. Cohen and G. P. Fong, Anal. Chem.. 47, 313 (1975). (21) S.A. Lapshin, V. A. Dadali, Y. S. Sirnanenko, and L. M. Litrinenko, Zh. Org, Khim., 13, 586 (1977) I
1545
(22) H. Takaku, Y. Shimada, and K. Aoshinia, Chem. Pharm. Bull. Jpn., 21, 2068 (1973).
/
RECEIVED for review March 27,1978. Accepted June 29, 1978.
This work was supported in part by NSF Grant No. CHE78-06603.
Vacuum Sublimation Behavior of Various Metal Chelates of 4-Anilino-3-pentene-2-one, Acetylacetone, Dithiocarbamates, Oxine and Its Derivatives, Dimethylglyoxime, Dithizone, 1-(2-Pyridylazo)-2-naphthol, and Tetraphenylporphyrin Takaharu Honjo,
Hisanori I m u r a , Shigeki Shima, and Toshiyasu Kiba
Department of Chemistry, Faculty of Science, Kanazawa University, Marunouchi, Kanazawa, Ishika wa 920, Japan
A vacuum sublimation apparatus with continuous temperalure gradient (30-320 "C) along its length (0-65 cm) is described. Samples are inserted Into the high temperature end of the sublimator and are heated for about 4 h under low pressure (1.5-3 X lo-* Torr). The metal chelates recrystallize on the walls of the glass tube, and the high temperature end of the zone is sharply defined. The sublimation-recrystallization zone temperatures are reported for metal chelates of 14 chelating reagents. The temperatures at the start of sublimation of labeled chelate compounds of six chelating reagents are also determined by using another type of a vacuum sublimator. Diethyldithiocarbamates and oxine were found to offer the greatest promise for the purification and separation of metals as their chelates by the vacuum sublimation method.
Sublimation is a very useful method for purifying analytical reagents or reference standards, separating solid mixtures into constituents, and concentrating very small traces of impurities in a solid substance (1). Recently, vacuum sublimation behavior of various metal chelates of 8-hydroxyquinoline ( 2 ) , phthalocyanine ( 3 ) ,and P-diketones with aliphatic groups (acetylacetone (4-8) and dipivaloylmethane (6)) and fluoromethyl groups (trifluoroacetylacetone ( 6 ) , hexafluoroacetylacetone ( 6 ) , benzoyltrifluoroacetone ( 7 ) , thenoyltrifluoroacetone ( 7 ) ,and monothiothenoyltrifluoroacetone (9)) has been investigated, and many metal chelates are isolated and purified with the use of the vacuum sublimation method. Radiochemical a n d hot-atom chemical studies on metal chelates of phthalocyanine (10) and P-diketones with acetylacetone (11, 12) and dipivaloylmethane (13-15) have also been carried out by means of t h e vacuum sublimation technique. T h e purpose of this study is to find suitable chelating reagents for the purification and separation of metals by sublimation, and various chelate compounds have been treated in a vacuum sublimator with a continuous temperature gradient under low pressure. Some aspects of t h e behavior of the chelate compounds in vacuum sublimation will also be discussed.
EXPERIMENTAL Apparatus. Hitachi Vacuum Pump, Type 3VP-C3; Shimadzu Pirani Gauge, Model PM-12; Hitachi Recorder, Type 056; Yamato 0003-2700/78/0350-1545$01.OO/O
Denki Mantle Heater, Type CL; Kubota Voltage Regulator, Type 1A-100;Hitachi Voltage Stabilizer, Type FPW-4; Iwaki Shaking Machine, Type V-S; Kubota Centrifuge Machine; Hitachi-Horiba pH Meter, M-5; 323 Hitachi Recording Spectrophotometer; 239 Hitachi Digital Spectrophotometer; Kobe Kogyo NaI(T1) Well-Type Scintillation Counter, Model EA-14; and Toshiba 200 Channel Pulse Height Analyzer, Type EDS-34208A were used. Materials. Metal low. The guaranteed-grade or reagent-grade metal salts of AgNO,, A1C13.6H20,HAuC14.4H20,BeCl,, Bi(N03)3*5H20,CaCl2-2Hz0,CdCl,, CoC 12.6H20,K2Cr20j, CuS04. 5H20, (NH4)2Fe(S04)2.6H20, FeC12.6H,0, HgC12, In(NO3I3, MgS04.7H20,MnC12.4Hz0, (NH4)6hIo7024.4H20, H2M04.H20, NiC12-6H20,Pb(N03),, PdCl,, RhCl,, TeO,, U02(CH3C00)2.2Hz0, NH4V03, and ZnCl,, were dissolved in distilled water or in a slightly acidic hydrochloric or nitric acid solution to make a lo-' M aqueous solution of each metal ion. Each of the high-purity metals, such as Cd, Cu, Fe, Mn, Pb, Se, Sn, T1, and Zn, was also dissolved in a minimum amount of concentrated hydrochloric or nitric acid, heated almost to dryness, followed by diluting it with a slightly acidic solution to make each 113-' M stock solution. A s 2 0 3 was dissolved in an aqueous solution of sodium hydroxide, and the solution was neutralized with sulfiiric acid to make a lo-' M solution. The chlorides or the nitrates of the radioisotopes, @ C ,o' 59Fe,'03Hg, and 65Zn,were purchased from the Radiochemical Centre (England), and the New England Nuclear Corporation (U.S.A.). Chelating Reagents. The reagents obtained commercially were all guaranteed-grade materials. Dithizone and l-nitroso-2naphthol were purified by recrystallization from chloroform with petroleum ether, while other reagents of the reagent-grade materials were used without further purification. DDTC (sodium diethyldithiocarbarnate), PDTC (ammonium pyrrolidindithiocarbamate), oxine (8-hydroxyquinoline), dibromooxine (5,7-dibromooxine),thiooxine (8-mercaptoquinoline), PAN (1-(2-pyridylaz0)-2-naphthol), dithizone (diphenyldithiocarbazone), dimethylglyoxime, MBT (2-mercaptobenzothiazole), diphenylcarbazone, and toluene-3,4-dithiol, were purchased from the Wako Junyaku Kogyo Co. Dichlorooxine (5,7-dichlorooxine), methyloxine (2-methyloxine), nioxime (1,2-cyclohexanediondioxime), a-benzildioxime, cupferron (N-nitrosophenylhydroxylamine), and N-benzoyl-N-phenylhydroxylaminewere purchased from the Tokyo Kasei Kogyo Co. Ethylxanthate (potassium ethylxanthate) and I-nitroso-2-naphthol were obtained from the Katayama Kagaku Kogyo Co. BDTC(sodium di-n-butyldithiocarbamate) was synthesized by the method of Klapping and Van der Kerk, that is, by the reaction of di-n-butylamine with carbon disulfide in an aqueous solution of sodium hydroxide on cooling (16),and was purified by recrystidhation from chloroform. @-Ketoimine(4-anilino-3-pentene-2-one) was synthesized by the C 1978 American Chemical Society
1546
ANALYTICAL CHEMISTRY, VOL. 50, NO. 11, SEPTEMBER 1978
L 100cm 1
Samole tube'
Sublimation tube
Pirani g a u g e
-
0 5 cm
---9
I
To v a c u u m DUmD
Ammeter
Figure 1.
Stabilizer
Vacuum sublimation apparatus with continuous temperature gradient
method of Roberts and Turner, that is, by the reaction of acetylacetone with aniline in benzene in the presence of a small quantity of concentrated sulfuric acid on heating (171, and was purified by recrystallization from benzene. T P P (tetraphenylporphyrin) was also prepared by the method of Alder et al., in which freshly distilled benzaldehyde and pyrrole were added to propionic acid under refluxing ( I @ , and was purified by sublimation under low pressure. 2-Nitroso-5-diethyl-aminophenol was a gift from Kyoji Toei of Okayama University in Japan. Preparation of Chelating Compounds. All metal chelates were prepared with the use of the following three conventional methods under conditions of excess or deficient chelating reagents. ( 1 ) Liquid-Liquid Extraction Method (Soluent Extraction). A buffer solution (2-3 mL) adjusted to a desired pH with or without 2 X 10-2-10-1 M chelating reagents was added to 10-*-10-' M metal salt solution (I mL), and the mixture was shaken with pure chloroform or with 2 X 10-*-10-' M chelating reagents in chloroform for a time enough to complete the extraction of the metal chelates. Then, the organic solution was washed with the buffer solution and distilled water. After centrifugation, 1 mL of the organic phase was taken into the sample tube in a reduced pressure desiccator, and the excess solvent was evaporated off in air under low pressure by using an aspirator. (2) Aqueous Solution Method (Precipitation). Each of a 1V2 M chelating reagent in acetic acid solution, in ammonium solution or in ethanol solution was added to lo-' M metal salt solution adjusted to a desired pH. After aging it for 30 min on heating, the product was filtered off, washed with distilled water, followed by drying it in a desiccator under low pressure. Then the products were purified by recrystallization from chloroform or by sublimation under low pressure. ( 3 ) Nonaqueous Solution Method (Precipitation). T P P chelates were prepared by the method of Alder et al., that is, by heating T P P and an excess of metal salt in refluxing dimethylformamide for 30 min to 10 h (19, 20). The dimethylformamide was removed by evaporating it under low pressure, and the product was dissolved in benzene. The residue in benzene was then filtered to remove unreacted metal salt. The benzene was evaporated off in air, and the crude product was purified by recrystallization from chloroform. The labeled metal chelates of 6oCo,59Fe,203Hg,and &Zn were also prepared by the liquid-liquid extraction method mentioned above. The y activity of the chelate compounds was about 1-10 x lo4 cpm/mg. Sublimation Apparatus a n d Procedure. V a c u u m Sublimation Apparatus u'ith Continuous Temperature Gradient for Fractional Sublimation. A schematic diagram of the vacuum sublimation apparatus with continuous temperature gradient is shown in Figure 1. The sublimator consists of a Pyrex glass tube (3 cm in outer diameter; 100 cm in length) covered with a mantle heater having a continuous temperature gradient (30-320 "C) along its length by definite settings of the powerstat under low pressure (1.5-3 X lo-' Torr). A small glass sample tube (0.7 cm in inner diameter; 5 cm in length) containing individual chelate (0.1-30 mg) and an attached long glass tube (0.5 cm in outer diameter; 60-80 cm in length) are inserted into the high temperature end of the sublimator and are heated for about 4 h. The
3
o-o-o-
120
80
41 ----O--o-o-o-o-
r C I L L , - L 0
1
I
2 Healing
3
,
, 4
1
lime l n r l
Rate of rise in temperature along vacuum sublimation apparatus. Distance from the high temperature end of the sublimator: (1) 0 cm, (2) 10 cm, (3) 30 cm, (4) 50 cm Figure 2.
temperature is checked by placing a thermometer inside the sublimator, and by reading its scale directly just after removing the mantle heater from the apparatus. The pressure inside the sublimator is determined by means of a Pirani gauge. The pressure inside the sublimator is always held at approximately 1.5-3 X Torr with or without temperature gradient. The system is evacuated to this pressure within 15 min, and the pressure remains constant about 5 h, and heating begins. The rate of rise in temperature along the sublimation apparatus is shown in Figure 2. The sublimator seems to require about 2 h to reach its thermal equilibrium. Therefore, the sublimation is carried out for 4 h throughout this investigation. The typical continuous temperature gradient along the sublimator after thermal equilibrium was obtained as shown in Figure 3. The temperature gradient is in the region of 30 (room temperature) to 320 "C, and its deviation falls within * 5 "C. The sublimate zones are examined microscopically, spectrophotometrically, as well as gravimetrically. In most cases, the high temperature end of the zone is rather sharply defined. The sublimate is confirmed by dissolving it in an appropriate solvent with the reference of the initial compound by measuring its visible and ultraviolet spectra or mass spectra after cutting out a part of the glass tuhe corresponding to the desired compound. The percentage of the amount remaining is determined from the loss in weight of the initial sample after the sublimation. Other types of fractional sublimator with a temperature gradient have also been used in the sublimation analysis of various solid materials (5, 21-24). Vacuum Sublimation Apparatus for Measurement of the Temperature at the Start of Sublimation. A schematic drawing of the vacuum sublimation apparatus for the measurement of the temperature at the start of sublimation of the chelate compounds
ANALYTICAL CHEMISTRY, VOL. 50, NO 11, SEPTEMBER 1978
*
1547
Table I. Volatility of Various Chelate Compounds in the Torr Region of 30 to 300 " C under 2 x I _ _ _
320
metal chelatesa
280
vola tile
chelating reagents
200
nonvolztile
Na, V, Cr, R h , As, Se, M o , Ag, Fe, Co, Ni, Cu, Sb, Te, A u , U, Zn, Pd, Cd, Sn, E t J H l Hg, T1, Pb, Bi BDTC Na, Cr, Cu PDTC NH,, Cr, Co, Cu, Zn Mg, V, Cr, Mn, Oxine H, Al, Fe, Co, Pd, Cd, Pb, Bi, Ni, Cu, Zn, u Mo, In dichlorooxine H, Cu dibromooxine H, Cu methyloxine H, Cu thiooxine H, Mn, Fe, Co, Pb Cu, Zn, Mo, Rh, Pd, Hg V , C!o, Ni, Zn, U 4-anilino-3-pentene- H, Be, Mn, Cu 2-one TPP H, Be, Ca, N[n, Fe, Co. Ni, CU; zn; PCI, Cd, Hg, Pb H, V, Co, Ni, PAN Cu, Zn, Ptl, Hg Cu, Pd dithizone H,Zn, Hg Fe, Cu dimethylglyoxime H, Ni, Pd nioxime H, Ni cu a-benzildioxime H cu K, Ni ethylxanthate Co, cu 1-nitroso-2-naphthol H co 2-nitroso-5-diethyl- H aminophenol V , Fe, Co, Cu, &Io cu pferron "4 cu H MBT cu n-benzoil-n-phenyl- H hydroxylamine cu diphenylcwbazone H M0 toluene-3,4-dithiol chelating reagents. a H, Na, K, NH,, Et,",: DDTC
2 4C
9
i
0 1 0
IO
20
30
40
50
60
70
Dlstonce lcml
Figure 3. Continuous temperature gradient along sublimation apparatus
is shown in Figure 4. The small sample glass tube containing the labeled metal chelates is placed in a definite position inside the sublimator. The voltage of the mantle heater is set at 46-49 V. The temperature inside the apparatus shows about 288 O C after heating for about 67 min. Temperature was read directly with a thermometer placed inside the sublimator. Pressure inside the sublimator is measured with the use of a Pirani gauge connected to a recorder. The y activity of the labeled chelate compounds during sublimation is also recorded every 20 s by means of a NaI(T1) scintillation counter connected to a 200channel Multi Channel Scaling equipped with a recorder. The temperature at the start of sublimation is determined by analyzing the plot of the increase of the net count of y activity of the chelate compounds during sublimation against the temperature ascending inside the sublimator. The change of pressure inside the sublimator during sublimation is also checked by means of Pirani gauge under the same condition.
RESULTS AND DISCUSSION T h e volatility of various chelate compounds in milligram amounts (0.1-30 mg) on heating over the temperature ranges from 30 to 300 "C under 2 X lo-* Torr is summarized in Table I. Most of t h e volatile chelates of DDTC, oxine, and their derivatives with aliphatic and halogenic groups, and dimethylglyoxime sublimed quantitatively without thermal decomposition. T h e thermal decomposition during t h e sublimation process was very conspicuous for P-ketoimine, thiooxine, and dithizone chelates. The PAN and TPP chelates were thermally stable, b u t did not sublime completely. This fact may be caused by t h e rate of sublimation of the chelate
--
compounds, which depends upon t h e temperature set at the high temperature end of the sublirnator. In general, compounds that were volatile a t reasonably low temperatures did not have large dipoles or high vapor pressure. nor did they exhibit adduct formation, polymerization, or hydrogen bonding (25). By taking advantage of the difference in volatility under t h e given condition, some separations of metals as their volatile and nonvolatile chelates may be possible with the chelating reagents listed in Table 1. 'The Multi Sca Iinq
,v,
Sublimotian tube Pirani gauge
1
I
Mantle heater
I
100 v W
Lead block
Voltage regulator
Figure 4. Vacuum sublimation apparatus for the measurement of temperature at the start of sublimation of chelate compounds
ANALYTICAL CHEMISTRY, VOL. 50, NO. 11, SEPTEMBER 1978
1548
2DTCL
viv: CrllllI
-
--
L
---
Mnilll~
FeIIiII CDilIlI
1
-____ -__
1
Nllli L
_L__
-
;
:"(ll;
Znill8
5
"dll!~ Cdllll
~ S " f I l [
Snl1i.r Hgllli
TI.0
~
I-
i
.
! Pbll 1
a,illii
I
-
-LLL-_LLLLL.I_AI
300
260
220
I80
140
I00
60
20
i
TemperolureiDCl
Figure 5. Sublimation-recrystallizationtemperature for various metal
, 300
260
diethyldithiocarbamates (DDTC compounds) sublimation-recrystallization temperatures for various diethyldithiocarbamates are graphically presented in Figure 5 . In cases where the recrystallization zone was not a uniform pattern, the deposition zones in large amount of chelates were shown as a thicker line. After sublimation of the chelates of V(V), Bi(III), and Sn(I1, I\'), a little residue remained in the sample tube. All other chelates exhibited a remarkable volatility without thermal decomposition. T h e remarkable stability of t h e metal-to-sulfur bond and the particular four-membered chelate rings probably may account for the high volatility of these chelate compounds (26-29). From the mass-loss curves and the vapor pressure measurements, it was also seen that most of the metal diethyldithiocarbamates were highly volatile (30). T h e difference in t h e recrystallization zone temperatures was observed among the DDTC chelates of Zn(I1) and Fe(III), and a mixture of these chelates could be resolved by sublimation. The sublimation-recrystallization temperatures for various metal oxinates and thiooxinates are shown in Figure 6. Oxine and its chelates of Fe(III), Co(II), Zn(II), and In(II1) sublimed almost completely. The divalent metal chelates sublimed in different temperature range, while t h e trivalent metal chelates sublimed in almost the same temperature range. Similar behavior of metal oxinates on heating under 10-5Torr has also been reported (2). Thiooxine and its chelates of Fe(III), Rh(III), and Hg(I1) also sublimed completely. Other chelates of oxine and thiooxine sublimed only partially with a considerable thermal decomposition. Each of the oxine chelates of Zn(I1) and Cu(I1) was recovered quantitatively from a binary mixture. Thiooxine chelate of Hg(I1) could be separated easily from other chelates by sublimation. The sublimation--recrystallization temperatures for various 8-ketoimine and TPP chelate compounds are shown in Figure 7. Remarkable thermal decomposition was accompanied with t h e sublimation of P-ketoimine chelates; however, the sublimation-recrystallization temperatures of these chelates were found in the lower temperature region of all chelates studied. These chelates were generally unstable on heating and exposing to air. Therefore, the decomposition of the chelates may depend upon the rate of the sublimation and of the rise in temperature inside the sublimator under low pressure. T h e sublimates were ascertained to be pure chelates by spectrophotometry. The TPP chelates were only slightly volatile without thermal decomposition. No substantial difference in recrystallization zone temperatures was
220
180
I40
_- - I
loti
GO
2C
TernperoIure!'iI
Flgure 6. Sublimation-recrystallizationtemperature for various metal oxinates (Ox compounds) and thiooxinates (TOx compounds)
-
Calli!
-
CdlllI
1
Hgllil Pb(l,J
r
2
..........
-
C.L--&
L-L-
300
250
220
I80
_L-L-L--
140
I00
50
20
TemperoturePCi
Figure 7. Sublimation-recrystallization temperature for various metal 4-anilino-3-pentene-2-one compounds (fi-ketoiminecompounds)and
tetraphenylporphyrin compounds (TPP compounds) observed among the chelates studied, and the mutual separation of these chelates was impossible. T h e effective purification of the chelating reagents of P-ketoimine and TPP was possible under the same conditions. T h e TPP can also be purified by vacuum sublimation in a horizontal furnace using vacuum ion pumping and a thermal gradient (31). T h e sublimation-recrystallization temperatures for various metal chelates of PAN, dithizone, and dimethylglyoxime are shown in Figure 8. T h e metal chelates of dithizone and dimethylglyoxime sublimed quantitatively, while those of PAN were only slightly volatile without thermal decomposition. Even though the mutual separation of these chelate mixtures was impossible, the effective purification of the chelating reagents was achieved. Effect of ligands on the sublimation-recrystallization temperatures for various chelate
ANALYTICAL CHEMISTRY, VOL. 50, NO. 11, SEPTEMBER 1978
CP
cu
=
co clr
D
1549
-
i
-
t
-
.... 141
l
5
ZI
8
Zn
-
:C" t
6cu
-
51
-
I-
L
, 350
, 260
,
1
220
,
I
16'
,
180
, 140
1
, IO0
,
, 60
,
L
20
Temperoture IT1
3CO
260
220
I80
140
I00
60
Figure 10. Separation of each metal chelate from a mixture of metal diethyldithiocarbamates and of metal oxinates. Metal chelates (mg): (1) Fe 2.6,Zn 4.3; (2)Co 1.5, Cu 2.1; (3)Co 18.0, Cu 11.5; (4) (Temperature at the end of sample tube: 162 "C) Co 5.4,Cu 4.3;(5) Zn 1.5,Cu 3.1; (6)Zn 3.2,Cu 5.8
20
Temperoturel'C!
Flgure 8. Sublimation-recrystallization temperature for various metal 1-(2-pyridylazo)-2-naphtholates (PAN compounds), dithizonates (Dz compounds), and dimethylglyoximates (Dx compounds)
-
DDTC
$
PDTC
;
DDTC
1
I
- PDTC 0
DDTC
BDTC PDTC
O*
< MeGx ci20x E
--z B r n 0 x j T0x
AcAc ?Keto. imine
PAN TPP 0
DDTC
2 PDTC I
,
N
300
260
220
180
I40
I00
L
1
60
20
Temperoture ('C1
Flgure 9. Effect of ligands on the sublimation-recrystallization temperatures for various chelate compounds of cobak(III),copper(II), and zinc(I1)
compounds of cobalt(II), copper(II), and zinc(I1) are shown in Figure 9. T h e sublimation-recrystallization zones for various metal chelates of Cr(III), Co(III), Cu(II), and Zn(I1) generally increased in t h e next order: P-ketoimine (4anilino-3-pentene-2-one), 8-diketone (acetylacetone) < dithiocarbamates (with diethyl group < with dibutyl group < with pyrrolidine group) < oxine and its derivatives (with 2-methyl group < oxine < thiooxine < with dichloro group < with dibromo group) < P A N < TPP. T h e polarization phenomenon, formation of dipoles, and dipole interactions caused by t h e effects of t h e terminal groups of t h e ligands (electron withdrawing or releasing effect, resonance effect, and steric effect), and of t h e electronegativity of coordination atoms (oxygen, sulfur, and nitrogen) may play a n important
role on t h e sublimation of these chelate compounds. Sublimation-recrystallization zone temperatures, recovery, and color of various chelate compounds after sublimation under 2 X Torr are summarized in Table 11. In general, the sublimation-recrystallization zones can be definitely observed a t the higher temperature side, while the tailing of the zones appears at the lower temperature side. The strength of t h e adhesive forces between metal chelates and t h e glass wall determines the "deposition temperature", i.e. the temperature where adsorption begins to dominate over desorption ( 3 2 ) . T h e sublimation-recrystallization temperatures of individual chelates geinerally increased in t h e following order: Be(I1) < Cu(I1) < Mn(I1) for 4-anilino-3pentene-2-one, Fe(II1) < Cu(I1) for acetylacetone, Cu(I1) < In(II1) < Zn(I1) < Ni(I1) < Al(II1) < Fe(II1) < Co(II1) < Co(I1) for oxinates, Hg(I1) < Zn(I1) < Cu(I1) < Fe(II1) < Rh(II1) < Mo(V1) < Pd(I1) < Co(II1) < Mn(I1) for thiooxinates, Pd(I1) < Ni(I1) for dimethylglyoximates, Tl(1) < Tl(II1) < Zn(I1) < Cu(I1) < Hg(I1) < Cd(I1) < Pb(I1) < Pd(I1) < Ni(I1) < V(V) < Mn(II1) < Fe(II1) < Sn(I1) < Sn(1V) < Co(II1) < Cr(II1) < Bi(II1) for diethyldithiocarbamates, Zn(I1) < Cu(I1) < Co(II1) < Cr(II1) for pyrrolidinedithiocarbamates, Cu(I1) < Cr(II1) for di-n-butyldithiocarbamates, Hg(I1) < Zn(I1) for dithizonates, Hg(I1) < V(V) < Cu(1I) < Zn(I1) < Ni(I1) < Pd(1I) < Co(I1) for PAN chelates, and Hg(I1) < Cd(I1) < Ca(I1) < Be(I1) < Ni(I1) < Co(I1) < Cu(I1:) < Zn(I1) < Mn(I1) < Pd(I1) < Fe(1I) < Pb(I1) for TPP chelates. The configuration of the metal chelates (octahedral, tetrahedral, and planar) depends upon the coordination bonds formed between the metals and the chelating ligands. This will have a n effect on the molar heats of sublimation of the chelate compounds. The sublimation-recrystallization temperatures described above will be a reliable guide for predicting the separability of various metals as their chelates. Therefore, we attempted the mutual separation of binary mixtures of various quantities of metal chelates of DDTC and oxine. Separation of each chelate from a mixture of the diethyldithiocarbamates and of the oxinates is shown in Figure 10. With the increase of t h e relative amounts of chelates vn sublimation, the overlap of t h e sublimates occurred; however, the separation of each chelate from a mixture of t h e metal chelates of Co, Zn, and Cu was possible. Sublimation-recrystallization temperatures of copper(I1) chelate compounds of oxine, diethyldithiocarbamate, and 4-anilino-3-pentene-2-one in varying quantities are shown in Figure 11. In general, t h e sublimation-recrystallization temperatures gave higher values with increase in quantity of the chelates u p to 20 mg and remained es-
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ANALYTICAL CYEMISTRY, VOL. 50, NO. 11, SEPTEMBER 1978
Table 11. Sublimation Recrystallization Zone Temperature, Amount Remaining, and Color of Various Chelate Compounds Torr after Sublimation at 2 X chelate recrystallization metal com. taken, zone temperature, pound remetal chelates 'C color maininp mg 4-aiiilino-3-pentene-2-one bright yellow none i 30 12.3 Be (I1) much 108-55 pale yellow orange 1.8 Mn(I1) much 4.0 198-149 deep orange Cu(l1) 3.8 100-60 dark orange a little acetylacetone Fe(II1) none 98-38 red 1.9 CU(I1) none 100-65 blue 4.6 sodium diethyldithiocarbamate much 262-109 white 8.5 a little dark yellow green 264-140 3.3 V(V) Cr(II1) none 199-147 blue 4.5 I\lln(III none 186-108 dark purple 3.9 Fe(1II) none 192-11 1 dark yellow green 1.4 c 0 (II I )2' none 204-140 1.9 green Ni(I1) 166-84 none green 2.7 Cu(I1) none 3.0 129-70 dark yellow orange Zn(I1) 4.1 120-70 none white Pd(I1) none yellow 2.6 183-84 Cd (11)b 182-80 none white 3.0 Sn(I1) 3.9 26 2-127 none pale yellow orange Sn (IV )c a little pale yellow orange 4.6 245-129 none white 4.1 129-108 H!q 134-60 none 2.8 pale yellow orange TU1 1 140-51 none yellow 6.7 none white 4.5 180-84 222-172 a little 6.6 yellow (oil) ammonium Fyrrolidinedithiocarbamate none 10.0 decomp. white Cr(II1) 3.5 none blue 256-186 Co(II1j 4.0 252-168 none green Cu(1I) none 3.0 201-172 brown zn ( I1 ) 4.0 190- 107 none white sodium di-n-butyldithiocarbamate 10.0 254- 21 8 much white (oil) Cr(I!I) 5.2 21 3- 1 7 3 none blue Cu(I1) 4.5 180-108 none brown oxine < 31 none white 9.6 AI(II1) much yellow 246-18 2 1.2 Fe(lI1) none dark yellow green 2.5 252-1 8 3 CO(1I y none 2.5 288-176 brown CO(!Ii)~ 6.2 289-182 much brown Ni(1I) much 1.9 256-177 yellow CU(I1) 1.8 196- 1 60 none dark yellow green Zn(1I j none yellow 246-1 7 7 2.8 In(I?i; none 242-177 1.6 yellow dichlorooxine 100-34 none white 10.1 Cu(I1) 237-176 much dull yellow 2.7 dibromooxine 194-59 none pale yellow orange 12.6 Cli(11) 2.60 much 240- 17 6 dull yellow 2-methyloxine white < 30 none 9.7 Cu(J1) 179-91 much 1.8 brown thiooxine 2.1 177-99 none yellow Mn(1J) 2.8 254-204 much dark yellow orange Fe(IL1) a little deep orange 9.6 237-173 Co(I11)l 1.9 248-222 much dull yellow cum) a little 1.7 232- 17 3 deep orange Zn(I1) 190-144 much 2.9 yellow Mo ( v I ) 257-186 much black 8.3 I1 h ( I11) none orange 1.7 257-182 Pd(I1) 5.1 a little deep orange 249-218 180-77 much bright yellow 0.5 WII) dimethylglyoxime 13.4 none white 68-26 Ni(I1) 288-117 a little orange 5.1 PdCl) none 2.2 29 1-108 orange dithizone 11.2 a little 123-40 orange Zn(I1) a little 1.3 288-204 red none 0.7 190-174 red Hg(I1) 1-(2-pyridy1azo)-2-naphthol 8.5 130-40 a little orange V(V) 0.7 much red purple 293-156 Co(J1) much 0.6 293-186 red Ni(I1) 0.8 278-171 much purple Cu(1I) 2.5 258-165 much dark orange Zn(II) 1.1 none red purple 27 9- 190 Pd(I1) 0.9 much green 284-190 194-176 red 0.4 much WII) te traphenylporphyrin purple 262- 23 2 3.1 none
ANALYTICAL CHEMISTRY. VOL. 50, NO. l'i, SEPTEMBER
1978
1551
Table I1 (Continued) metal chelates
recrystallization zone temperature, "C
chelate taken, mg
color
metal compound remainin$
0.4 290-213 purple Be(I1) 1.6 287-213 blue Ca(I1) dark yellow green 1.4 305-218 Mn(I1) 5.8 30 5- 218 brown Fe(I1)' 2.8 301-213 purple Co(I1y' 0.9 295-213 blue Ni(I1) strong red purple 2.0 293-218 Cu(I1) strong red 4.0 305-220 Zn(I1) 0.4 30 6-2 18 purple Pd(I1) 1.8 270-213 purple Cd(I1) 286-208 green 1.8 Hg(II 1 294-218 dark yellow green 0.4 Pb(I1) b j Oxidation number of metals before the preparation of 'None, 0-10%; a little, 10-3096; much, ~ 3 0 % . Ascertain the (111) valent metals by mass spectrometry. compounds.
much much much much much much a liitle much much much much much the chelate
_ _ I _ _ -
Table 111. Temperature at the Start of Sublimation of Various Chelate Compounds recrystallizatemperature tion zone at at the start the higher of sublima- temperature metal chelates tion, C side, " C acetylacetone Fe(II1) sodium diethyldithiocarbamate Fe(II1) Co(II1) Zn(I1) W I I1 ammonium pyrrolidinedithiocarbamate Co(II1) Zn(I1) oxine Fe(II1) Co(I1) thiooxine Fe(II1) Zn(I1) HdIII 1-(2Pyridylazo)-2-naphthol Zn(I1) a
chelate taken, mg
su Himation, %
75
98
1.9
99.5
183 172 102 105
192 204 120 129
7.9 5.8 4.0 6.0
240 174
252 190
9.4 4.0
99.5 99.3
272 201
252 288
2.5 24.1U
90.8
245 200 151
23 7 190 180
9.6 13.4
85.9
252
279
7.2
95.9
99.3 100
99.3 100
With oxine.
sentially constant in quantity from 20 to 200 mg. In this case, all chelates sublimed quantitatively without thermal decomposition, and t h e sublimation-recrystalIization temperatures gave higher values in the order of the metal chelates of P-ketoimine, DDTC, and oxine. T h e sublimation-recrystallization zones of 109 mg amount of copper(I1) oxinate appeared a t the higher temperature side with rise in temperature along vacuum sublimstion apparatus and remained constant over 4 h. Pressure and y activity inside the apparatus with increasing temperature during sublimation of each labeled chelate of Fe(II1) and Zn(I1) are shown in Figure 12. When the sublimation of t h e chelate compounds began, the pressure inside the apparatus gave higher value, while y activity of the sublimate increased. T h e temperatures a t the start of sublimation of various chelate compounds determined by analyzing these d a t a are summarized in Table 111. T h e temperature at the start of sublimation of individual chelates generally increased in the order: Hg(I1) < Zn(I1) < Co(II1) < Fe(II1). The temperature at the start of sublimation of the chelate compounds increases in t h e following order: acetylacetonate < diethyldithiocarbamate < oxinate for Fe(III), and pyrrolidinedithiocarbamate < thiooxinate < PAN chelate for Zn(I1). This phenomenon may be due to differences in vapor pressure, molecular weight, and surface area of the chelate compounds. The change of pressure was also observed
280
40
0
1
I
'
I
M
' 0
20
40
60
,
,
SO
IOC
A -
1?3
146
16u
IS0
230
Meto, c o m p o " n e i I r n ~ 1
Figure 11. Sublimation-recrystallization temperature of copper(I1) chelate compounds in various quantities. LigaGds: (1) oxine, (2) diethyldithiocarbamate, (3) 4-anilino-3-pentene-2-one
in systems 1, 2. and 3 during sublimation of the chelate compounds. while the peak appearing in systems 5 and 6 may correspond to the sublimation of the !chelating reagents. The
1552
ANALYTICAL CHEMISTRY, VOL. 50, NO. 11, SEPTEMBER 1978
\
1 -
1
-
crystallization temperature. T h e sulfur-containing chelates of diethyldithiocarbamates were also reported to be the most stable with respect to "flash" volatilization (33). According to the Langmuir equation ( 3 4 ) ,t h e rate of evaporation of a subliming substance in vacuum at a given temperature should be a function of t h e vapor pressure, molecular weight, and surface area of the substance. Q = P f t'2sMRT, where Q is the evaporation rate per unit area, P is the vapor pressure of the compound, M is the molecular weight, R is t h e gas constant, and T i s the absolute temperature. Therefore, the difference in volatility of various chelate compounds may be due to the difference in vapor pressure, molecular weight, molar heats of sublimation correlated with the space arrangement (octahedral, tetrahedral, and planar), and surface area of these chelate compounds. However, a number of fundamental experiments must be undertaken in order to obtain enough information to be able to theoretically predict t h e vacuum sublimation behavior of chelate compounds.
121
13
E u a
16)
1 / 0
50
I50
103
200
250
300
H e a l i n g ternperolurei°C
Figure 12. Pressure and y activity during sublimation of e a c h metal chelate in vacuum sublimation apparatus with rise in temperature. Chelate compounds: (1) 59Fe(AcAc) , (2) 65Zn(PDTC),, (3) 59Fe(DDTC),, (4) 65Zn(TO~),, (5) "Zn(PAN),, (6) "Fe(OX)3
/ -~ 3 50 ~
~
-,~l0i
~
-
2
I53
Healirg temperature
~
2130
I P ~ -
250
300
feci
Figure 13. Pressure and y activity during sublimation of a mixture of Zn(DDTC), and Fe(DDTC), in vacuum sublimation apparatus with rise in temperature. Chelate compounds: (1) "Zn(DDTC),, Fe(DDTC),; (2) Zn(DDTC),, 59Fe(DDTC)3; (3) 65Zn(DDTC)2,59Fe(DDTC)3
change of pressure was negligibly small during sublimation in high temperature region like systems 5 and 6. Pressure and y activity during sublimation of a mixture of Zn(DDTQ2 and Fe(DDTC), vs. rise in temperature are shown in Figure 13. I n mixed chelate systems, the temperature a t the start of sublimation of each chelate was almost the same temperature. As seen from the figure, mutual separation of DDTC chelates of Zn and Fe was ascertained from the change of pressure and y activity during sublimation. In conclusion, of all the chelating reagents studied, diethyldithiocarbamates and oxine were found to offer the greatest promise for the purification and separation of various metals as their chelates by vacuum sublimation, because these chelate compounds gave a great thermal stability during vacuum sublimation and, moreover, showed a considerable difference in the sublimation-re-
ACKNOWLEDGMENT We acknowledge Kyoji Toei of Okayama University for his kind gift of the reagent of 2-nitroso-5-diethylaminophenol. Thanks are also due to Masanobu Sakanoue of Kanazawa University for his helpful advice and discussion.
LITERATURE CITED (1) E. C. Kuehner and R. T. Leslie, "Sublimation-Encyclopedia of Industrial Chemical Anatysis", F. D. Snell and C. L. Hiiton, Ed., Interscience P u b l i s , New York, N.Y.. 1966, p 572. I R. G. Chales and A. Langer. J . Phys. Chem., 63, 603 (1959). I C. Hamann. Krist. Tech.. 6. 491 (1971). S. Saito, M. Kinoshita, and 1. Kamii, Sginku Kagaku, 12, 252 (1964). E. W. Berg and F.R. Hartiags, Jr., Anal. Chim. Acta, 33, 173 (1965). E. W. Berg and J. J. C. Acosta, Anal. Chim. Acta, 40, 101 (1968). E . W. Berg and K. P. Reed, Anal. Chim. Acta, 4 2 , 207 (1968). E. W. Berg and A. D. Shendrikar. Anal. Chim. Acta, 44, 159 (1969). E . W. Berg and K. P. Reed, Anal. Chim. Acta, 36, 372 (1966). K. Endo and M. Sakanoue, Radiochem. Radioanal. Lett., 9, 255 (1972). H. Kawazu and M. Sakanoue, Radixhem. Radioanal. Lett., 16,363 (1974). R. Amano and M. Sakanoue, Radixhem. R a d b m l . Lett., 20, 227 (1974). R. Amano, H. Nio, and M. Sakanoue, Radiochem. Radioanal. Leff., 23, 63 (1975). Y. Shirota and M. Sakanoue. Radixkern. Radhnai. Lett., 23, 111 (1975). M. Sakanoue and R. Amano. "Proceedings of 4th International Transplutonium Element Symposium'', W. Muller and R. Lindner, Ed.,Nofth-Holhnd Pubiishing Company, New York. N.Y., 1976, p 123. H. L. Klopping and G.J. M. Van der Kerk, Recl. Trav. Chim. Pays-Bas, 70, 917 (1951). E. Roberts and E. E. Turner, J . Chem. Soc.. 1927, 1832 A. D. Alder, F. R. Longo, J D. Finarelli, J. Goldmacher, J. Assour, and L. Korsakoff, J . Org. Chem., 32, 476 (1967). A. D. Alder, F. R. Longo, F. Kampas, and J. Kim, J. Inorg. Nucl. Chem., 32, 2443 (1970). K. S.Hui, B. A. Davis, and A. A. Bouiton, J. Chromtogr., 115, 581 (1975). H. Kawazu and M. Sakanoue, Radkhem. R a d h m l . Left, 16,373 (1974). E. Shibata and S. Saito, Nippon Kagaku Zasshi (in Japanese) 80, 604 (1959). J. F. Thomas, E. N. Sanborn, M. Mukai. and B. D. Tebbens, Anal. Chem., 30, 1954 (1958). J. Merinis and G. Bouissieres, Anal. Chim. Acta, 25, 498 (1961). R. W. Mosher and R. E. Severs, "Gas Chromatography of Metal Chehtes". Pergarnon Press, Oxford, 1965, p 11. M. Bonamico, G. Dessy, G. Mazzone, A. Mugnoli, A . Vaciago, and L. Zarnbonelli, Atti. Accad. Naz. Lincei, Rend. GI. Sci. f i s . . Mat. Nat., 35, 338 (1963). R. M. Golding, W. C. Tennent, C. R. Kanekar, R. L. Martin, and A. W. White, J . Chem. Phys., 45, 2688 (1966). M. Bonamico, G. Dessy, A. Mugnoli, A. Vaciago, and L. Zambonelli, Acta Cvstallogr., 19, 886 (1965). M Bonarnico, G. Mazzone, A. Vaciago, and L. Zambonelli, Acta Crystallogr., 19, 898 (1965). G. D.'Ascenzo and W. W. Wendlandt, J , Thermal Anal., 1, 423 (1969). A. D. Aider, J . Inorg. Nucl. Chem., 32, 476 (1970). L. Westgaard, J . Inorg. Nucl. Chem., 31, 3747 (1969). D. C. Hilderbrand and E. E. Pickett, Anal. Chem., 47, 424 (1975). I.Langmuir, J . Am. Chem. SOC.,38, 2221 (1916).
RECEIVEDfor review March 22,1978. Accepted June 8,1978. We thank the Ministry of Education for its Scientific Research Grant to one of us (T.H.).
