Hexafluoromonothioacetylacetone-A New Ligand for Gas Chromatographic Separation of d*-Metals Ernst Bayer, Hams Peter Muller, and Robert Sievers Chemisches Institut der Universitat Tiibingen, Germany
Hexafluoromonothio-acetylacetone (HFAS) has been synthesized as a new ligand for the preparation of volatile chelates. HFAS shows completely different analytical selectivity compared to its oxygen analog hexafluoroacetylacetone.With the divalent metal ions of Cu, Zn, Fe, Ni, Pt, Pd, Cd, and Pb, volatile chelates from HFAS have been prepared. The identification of these chelates i s possible by means of their characteristic mass spectra. The conditions for gas chromatographic separation of the chelates of Ni(ll), Pt(ll), and Pd(ll) are described.
THEAPPLICATION of gas chromatography in inorganic metal analysis is quite common for several metals. Fluorinated pdiketones such as 1,1,1,5,5,5,-hexafluoroacetylacetone and l,l,l,-trifluoroacetylacetoneform chelates with many metal ions, which are sufficiently volatile, soluble, and thermally stable for gas chromatographic metal analysis ( I ) . The fluorinated /3-diketones contain oxygen as a n electron donor. Different donor atoms such as sulfur, selenum, and nitrogen should show different metal specificities and should make other transition metals applicable for gas chromatographic analysis. Martin ( 2 ) has shown in the case of acetylacetone that sulfur and selenum as donor atoms significantly change the properties of the metal complexes formed as compared to the analog oxygen compounds. Acetylacetonates can be used especially for trivalent hexacoordinating metal ions. I n the case of HFAS we expected selectivity toward divalent ds-metals. Livingstone (3) was the first t o synthesize a monomer monothioacetylacetone ligand, namely 1,l ,l-trifluoro-4-mercaptopentene-2-one (TFAS). We have recently reported the synthesis of hexafluoromonothioacetylacetone (HFAS) ( 4 ) . Starting from hexafluoroacetylacetone (HFA) we obtained a p-ketoenolchloride by reaction with thionylchloride. Further reaction with sodium hydrogen sulfide or sodium sulfide yielded the sodium salt of hexafluoromonothioacetylacetone (HFAS Na). Addition of a dry solution of hydrogen chloride in ether resulted in a monomer hexafluoromonothioacetylacetone (H FAS).
The free thioenol HFAS as well as the sodium salt HFAS Na readily form the metal chelates in relatively strongly acidic solution by reaction with metal salts of strong acids. These complexes are volatile and can be analyzed gas chromatographically.
( I ) R. W. Moshier and R. E. Sievers, “Gas Chromatography of Metal Chelates,” 1st ed., Pergamon Press, Oxford, England,
1965. ( 2 ) R. L. Martin, Ails/. J . Chem.. 22, 891-904 (1969). ( 3 ) R. K. Y. Ho. S. E. Livingstone, and T. N. Lockyer, ibid., 19, .
I
1179-1185 (1966). (4) E. Bayer and H. P. Muller, Terrukedrorr Lett., 1971, 533. 2012
EXPERIMENTAL
Instrumentation. For gas chromatographic and mass spectrometric investigations a n LKB 9000 G a s Chromatograph-Mass Spectrometer was used. The total ion current was measured as a detector signal. The accelerating voltage was 3.5 kV. The ion source temperature was 250 “C. Reagents. 2-Chloro-1,l ,I ,5,5,5-hexafluoro-4-oxopentene(2)-(HFACI) was prepared in the following way: 100 ml of carefully purified thionylchloride and 2 ml of dimethylformamide are heated a t 40-50 “C in a three-neck flask, equipped with condensor, drying tube, and funnel. At this temperature, 52 grams (40 ml, 0.26 mole) H F A are slowly added during 3 hours. The formation of a gas (HCI, SOp) can be observed. The reaction mixture is heated at 90-100 “C for 3 hours. The reaction product H F A Cl can be distilled as an azeotropic mixture out of the reaction mixture (bp 65-75 “C). The product is added to ice water. After hydrolysis of the excess thionyl chloride, the organic layer is washed with water and dried over MgS04. The fractionation over a 20-cm Vigreux column yields 31.2 grams of enol chloride (bp 75-78 “C). H F A C1 is a narcotically smelling, irritating, mobile, green-yellow liquid, bp 77-78 “C. Yield: 31.2 grams (53 %). Anal. Calcd for C5HOF6C1 (226): C , 26.61; H, 0.44; CI, 15.86; F, 49.79. Found: C, 26.78; H , 0.54; CI, 16.09; F, 49.58. Hexafluoromonothioacetylacetone (HFAS): 22.4 grams (0.4 mole) of sodium hydrogen sulfide ( 5 ) are dissolved in 250 ml of dry ethanol in a four-neck flask, equipped with a stirrer, funnel, condenser, and drying tube. Under nitrogen atmosphere, 45.2 grams (0.2 mole) of H F A CI in 50 ml of dry ethanol is slowly added during one hour. The reaction mixture turns yellow and red while H2S is developed. The mixture warms up at 40-50 “C and sodium chloride precipitates. After the addition of H F A CI is completed the reaction mixture i s stirred for one hour under nitrogen atmosphere. The cooled, dark red solution is quickly filtered off the sodium chloride (G 3 frit) and the solvent is evaporated on a rotatory evaporator. The remaining red oil is taken up in dry ether and again filtered through a G 3 frit. Dry HCI gas is bubbled through the ether solution for one hour. The solution turns yellow and sodium chloride precipitates. After about one hour, the formation of NaCl is completed. The ether solution is once again filtered through a G 3 frit, the ether is quickly evaporated in a rotatory evaporator, and the remaining yellow oil is fractionated in cacuo (12 mm Hg). The main fraction, hexafluoromonothioacetylacetone boils at 75-78 OCjI 2 mm Hg. Yield: 16.5 grams ( 3 7 7 3 Anal. Calcd for C5H20SF6(224): c , 26.82; F , 50.94; S, 14.38. Found: C, 26.90; F, 50.91; S, 14.33. There are two ways for the preparation of metal chelates. IN AQUEOUSSOLUTION.The aqueous 0.001M solutions of the metal salts are added to an aqueous solution of HFAS N a . aq (0.001 M ) with stirring. The formed metal chelates immediately precipitate. The product is filtered off, washed
___ _ ( 5 ) G.
_ _ ~ _ _ _ - _
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Brauer, “Handbuch der praparativen Anorganischen Chemre,” Ferdinand Enke Verlag, Stuttgart, 1960, S. 325.
ANALYTICAL CHEMISTRY, VOL. 43, NO. 14, DECEMBER 1 9 7 1
(HFASbNi
DODECANE
TETRADECANE
--
!
1
I
1200
1362
14 00
- [Fl
Figure 1. Gas chromatogram of (HFAS), Ni
1
3-m glass column, 1% SE 30, column temperature, 100 "C; 16 ml He/min carrier gas
M-19
P A L L A D l UM
NICKEL
P L A T i NUM
533
t M-69
483
'*cr;
2 60 1280
1445
14 80
0
223
Pd'
Figure 2. Gas chromatographic separation of Ni-, Pd-, PtHFAS chelates 1.5-m glass column, 3 x OV 17, column temperature, 80 "C; 18 ml He/min carrier gas
Figure 4. Mass spectrometric fragmentation of (HFAS), Pd Table I. HFAS Metal Chelates
79-80
with HzO, and recrystallized from pentane or chloroform in an open crystallization dish. IN ETHANOLSOLUTION.A solution of 0 . o 1 mole of HFAS Na . aq in 10 ml of pure ethanol is added t o a 0.001M solution of the metal salt in 30 ml of 5 0 x ethanol with stirring. The reaction mixture is stirred for 12 hours. After addition of water, the complexes are extracted with two 30-ml portions of chloroform. The chelates readily crystallize from pentane solution.
77-78 107- 109
RESULTS AND DISCUSSION
Melting
Sample CU" ZnI1 Fell
red-brown
68-69 54-55 88-92
Ni" AuT1*
dark green-brown red
73-75
red
Color green-brown yellow
point, "C
yellow-green
Hglr Pt" Pd"
dark red
red yellow red orange (enolate)
Cd" Pb" Nal
96-98
Reactivity of the Ligand. The ligand HFAS predominantly reacts t o chelates with metal ions having a d* electron con-
175-1 78
rxlO I
1 I
/
-co
+
329
I
I
M -69
@Po ,'
132
36 1
I
4
I
I
I
I,
II 300
dl
I1
400 450 Figure 3. Mass spectrum of (HFAS)e Pd
403
I $1
M-19
533
1 1
mlc
-
J~,I
ANALYTICAL CHEMISTRY, VOL. 43, NO. 14, DECEMBER 1971
11 550
2013
10 0 'I.
Y'
k
l g 5 Pt
641
223
1
I
239
4 622
hill
1
107 210
25 0
1
I I 300
350
450
550
L
600
mle-
Figure 5. Mass spectrum of (HFASh Pt figuration (Ni, Pd, Pt). Of the d1o elements, zinc and cadmium form hexafluoromonothioacetylacetonates. The Hg complex, however, decomposes shortly after its formation under precipitation of mercury sulfide. All trivalent metals, which tend to change their valence state, oxidize the ligand to the disulfide. N o metal chelates are formed by these metal ions. An exception is trivalent gold. It forms an intensively red complex with HFAS Na in ethanol solution. We have not been able t o isolate this complex so far, because it decomposes under formation of metallic gold. The chelates synthesized so far are shown in Table I. Gas Chromatographic Investigations. HFAS metal chelates are extremely volatile and thermally very stable. The gas chromatographic conditions and the selection of a proper column have first been tested with (HFAS)*Ni. The chromatogram of the nickel complex is shown in Figure 1. The retention index of (HFAS)? Ni (1362) has been determined according to Kovats (6). The metal chelate can be analyzed on a glass column packed with 1 % SE 30 on chromosorb W/AW at a relatively low temperature. The separation of the hexafluoromonothioacetylacetonates of Pd, Pt, and Ni was achieved on a 1.5-m glass column packed with 3 x OV 17 on chromosorb W/AW (Figure 2). In this experiment, 30 p1 of hexane solution of a mixture of equal amounts of the metal complexes was injected (concn ~ 0 . 0 0 0 5mgiml). An exact quantitative statement is not possible, because of the application of a quite selective molecule separator in the gas chromatograph-mass spectrometer. It can be estimated, however, that in this gas chromatographic noble metal analysis, microgram amounts can easily be detected and exactly identified. The retention indices have also been determined according t o Kovats (6). They are: Ni (HFAS)*, 1280; Pd (HFAS)?, 1445; and Pt(HFAS)n, 1480. The gas chromatographic separation of the metal derivatives of Ni, Pd, and P t on OV 17 was achieved at a column temperature of only 80 "C.
( 6 ) E. Kovats, Helc. Chim. Acta, 41, 1915 (1958).
2014
Mass Spectrometry. The gas chromatographically separated metal chelates can be easily identified in the combination instrument. The known relative abundance of the natural nuclides allows a simple and exact mass spectrometric analysis. Figure 3 shows the upper mass range of the mass spectrum of (HFAS)2Pd. The molecular ion can easily be detected; for 106Pd it appears at m/e 552. Fragments M-19 and M-69 are also observed. Significant fragments appear at mje 361, 329, 260, 232, and 223. The base peak in the spectrum of (HFAS)? Pd appears at m / e 223, resulting from one intact ligand. The complete mass spectrometric fragmentation scheme is shown in Figure 4. In this scheme, only the mass numbers of the Pd isotope lo6Pdare accounted for. The fragmentation pattern of the Pt chelate (HFAS)?Pt equals that of the Pd chelate. Figure 5 shows the mass spectrum of the Pt chelate. CONCLUSIONS
The synthesis of hexafluoromonothioacetylacetone (HFAS) can be achieved by using the P-ketoenol chloride of hexafluoroacetylacetone (HFA) as an intermediate. With thionylchloride, the enol chloride is obtained. The reaction with sodium hydrogen sulfide or sodium sulfide yields free hexafluoromonothioacetylacetone (HFAS) or its sodium salt, respectively. Further reaction of HFAS with various transition metals as Ni", Pd", Pt", etc. results in the formation of volatile chelates, which can be favorably separated by gas chromatography. For the first time, volatile Pd and Pt complexes have been synthesized, which can be separated by gas chromatography. ACKNOWLEDGMENT
The technical assistance of Mr. G . Nicholson is acknowledged. RECEIVED for review July 23, 1971. Accepted August 20, 1971, We thank the Bundesministerium fur Wissenschaftliche Forschung for supporting this work.
ANALYTICAL CHEMISTRY, VOL. 43, NO. 14, DECEMBER 1971
