Preparationof Zirconium ,&Diketonate Complexes from Zirconium Ores S. Tsuge, J. J. Leary, and T. L. Isenhour Department of Chemistry, Universify of North Carolina, Chapel Hill, N . C . 27514 ZIRCONIUM is widespread in nature (about 0.028% of the Earth's crust) and is well known as one of the best construction materials for nuclear reactors because of its high transparency to thermal neutrons. Zirconium is also becoming important in the tanning industry ( I ) and in metallurgy because of its resistance to corrosion and the mechanical strength it gives alloys at low and elevated temperatures. In natural rocks and ores, zirconium is mostly found as baddeleyite (ZrOs) and zircon (ZrO?.Sios) which are among the most refractory minerals. Metal P-diketonates are very promising materials for the production of high purity metal oxides (2). Of equal importance is their potential in the field of trace metals analysis. Although several investigators (3-6) have previously reported the synthesis of zirconium P-diketonates, the starting material in these syntheses has usually been pure zirconium(1V) chloride (ZrC14). No method, applicable to the refractory minerals utilizing volatile P-diketonates for the analysis of zirconium has been reported. In this note, a new more general method is described for the synthesis of zirconium P-diketonates in which the very intractable mineral, ZrOz.Sios, as well as ZrOv and ZrCll can be converted into the volatile chelates. This method involves a borax fusion of the minerals, followed by sequential reactions with carbon tetrachloride (CC14) at 400 "C and with the P-diketone at 110 "C in a sealed glass capillary tube. Such a general preparative method is necessary when the trace analysis of zirconium in unknown minerals is to be performed via gas chromatography or mass spectrometry of the volatile P-diketonates. EXPERIMENTAL Reagents. Trifluoroacetylacetone [H(tfa)], benzoyltrifluoroacetone [H(bta)] and octafluoroheptanedione [H(fod)] were obtained from Pierce Chemical Company. These ligands are subsequently designated as L. These chelating agents were either distilled at reduced pressure or used without further purification. Zirconium chloride was supplied by Ventron Ltd. Specpure grade zirconium oxide was obtained from Johnson Matthey Chemicals Ltd. Baddeleyite and zircon were kindly supplied by P. D. Fullager of the Geology Department of the University of North Carolina, Chapel Hill, and used after grinding to a fine powder in agate and boron carbide mortars. Reagent grade sodium borate (decahydrate) was obtained from J. T. Baker Chemical Company. Reagent (1) K. C. Montgomery and J. G. Scroggie, J . Soc. Leather Trades Chem., 54, 361 (1970). (2) L. A. Ryabova, Ya. S. Savitskaya, and R. N. Sheftal, J . Appl. Chem. USSR.,38, 1817 (1965).
(3) M. L. Morris, R . W. Moshier, and R. E. Sievers. h r e . Chem.. 2, 411 (1963). (4) . , R. E. Sievers. B. W. Ponder. M. L. Morris. and R. W. Moshier. ibid., p 693. ( 5 ) S. C. Chattoraj, C. T. Lynch, and K. S . Mazdiyasni, ibid., 7 , 2501 (1968). (6) M. G . Allcock, R. Belcher, J. R. Majer, and R. Perry, ANAL. CHEM.,42, 776 (1970). 198
grade carbon tetrachloride was dried with freshly activated Molecular Sieve 5A (50/60 mesh). Synthesis of Chelates. Fuse about 20 mg of borax (NaaBiOi.10H20) in a small platinum crucible (volume, 1 ml). Place on top of the fused mass about 0.1-1.0-mg sample of the finely powdered mineral and fuse again for 10 minutes over a Meker burner at about 900 "C while stirring with a platinum wire. After cooling the crucible, dissolve the melt with 0.3 ml of 2 : 5 HCI and digest on a hot plate at 80 "C until complete dissolution. Transfer the dissolved solution into a borosilicate glass tube (140 mm X 5 mm i d . ) one end of which has been flame sealed. Evacuate the tube first at room temperature and finally at 450 "C until complete dryness is obtained. Add about 200 p1 of CC14 to the tube and seal it. Place the tube in an explosion shield and heat in an oven at 400 "C for 2 hours. A satisfactory explosion shield is a five-inch length of 1/2-inch0.d. stainless steel tubing closed at one end. After cooling to room temperature, carefully open the tube in a hood by applying a flame to the sealed tip. Evacuate the tube to near-dryness to remove gaseous products such as phosgene and hydrogen chloride. After substituting the atmosphere in the tube with dried argon, cool the tube to below -30 "C using a chloroform-dry ice bath and add a slight excess of chelating agent dissolved in dried CC1+ Remove the cooling bath and the chelating reaction will take place as the frozen reagents melt. After the evolution of hydrogen chloride subsides, cool the tube to freezing again in the cooling bath, and again replace the atmosphere with dried argon. Reseal the tube and heat at 110 "C for 30 minutes to ensure complete reaction. Analysis. Mass spectra of the synthesized chelate compounds were taken on an Associated Electronics MS-902 high resolution mass spectrometer equipped with a direct insertion probe and precise peak-matching circuitry which was used to identify the molecular ion, when possible, and other important peaks in the spectra. All spectra were run between 130-160 "C with probe tip extended, and accelerating voltages of either 6 or 8 kV as required. RESULTS AND DISCUSSION
Although zirconium chloride reacts with most 0-diketones, zirconium oxide and zircon have not been found to react directly with any of these chelating agents. Moreover the chelating reaction between zirconium chloride and P-diketones should be carried out under anhydrous and inert conditions for the following two reasons. Zirconium chloride is easily hydrolyzed in the presence of water to the stable oxychloride (ZrOC1,.8H20) which is sometimes not suitable for the synthesis of the P-diketonates. Some of the formed zirconium P-diketonates decompose in open air ( 5 ) . Although zirconium oxide can be decomposed with hydrofluoric acid, zircon is generally not attacked by acidic reagents. Knox et a / . ( 7 ) proposed one promising procedure to convert metal oxides to the anhydrous chlorides using CCli at high temperatures in a sealed borosilicate glass tube. This method (7) K. Kiiox, S. Y . Tyree, Jr., R. D. Srivastava, V. Norman, J. Y . Bassett, Jr., and J. H. Holloway, J . Amer. CIrem. Soc., 79, 3358 (1957).
ANALYTICAL CHEMISTRY, VOL. 45, NO. 1, JANUARY 1973
I II
Pt4
33.0
34.7
P+5
6.2
5.6
Pt6
5.9
6.3
x1
2 r( b t a)4 R e l . Mass Abundance P = Z r ( b t a ) i (7 3 5 . 0 0 )
l
obs.
cal.
100.0
100.0
Mass R a t i o ( P t i / P ) P
obs. 1.001360
I
( c a l . i.001361)
Pt1
58.3
54.9
Pt2
48.4
46.9
__+
4
(ZrL,-
m
F)+
2 r ( f od R e l . Kass Abundance
.
Zr ( fod ) ( 9 7 5 0 7 ) obs
cal.
100.0
100.0
14.8
12.4
Mass R a t i o ( P t l / P )
P
o b s . ;.001026
Pt3
Figure 1. Portions of mass spectra of Zr(tfa)4, Zr(bta)4, and Zr(fod), at the base peak and the parent peak regions
+
+
is applicable quantitatively to ZrOs (Zr02 2CC14+ ZrC14 2COCL) but zircon does not react with CC14. Borax fusion, as recommended by Lundell and Knowels (8):is suitable for the decomposition of both zirconium oxide and zircon. The resulting sodium zirconate (NalZrOB),which is present after the fusion, is reactive enough to form a colored complex with alimrin whirh i c i i c ~ d_.I in the _- ciilfnnate ---.--, .._.__ .. ..l.c r l n c c i r n l cnertmnhntornetric determination of zirconium ( 9 ) ; however, the zirconate is not directly reactive enough to form any of the pdiketonates. Therefore, the zirconate was converted into a more reactive form by means of the carbon tetrachloride reaction at 400 "C in a sealed glass capillary tube. A possible reaction is ..y".Lvy"v
_._I^_^ I-._
NanZrOs
+ 3CCl4
--L
ZrCll
+ 3COC1, + 2NaCI
(1)
(8) G. E. F. Lundell and H. B. Knowels, ibid.,42, 1439 (1920). (9) L. Silverman and D. W. Howley, ANAL.CHEM., 28, 806 (1956).
Following this step, direct reactions were carried out with various p-diketones, including H(tfa), H(bta), and H(fod). The identification of the formed chelate compounds was confirmed by mass spectrometry. Natural zirconium has five stable isotopes: 90Zr(51.46 %), g1Zr(11.23z),92Zr(17.11 94Zr(17.40x),and 96Zr(2.8073;
z),
hpnrp the yu"v~.I.I., n c c n r i a t p r l phplatp rnmnnltnAc eyhihit *.-..--, .... vprv LI1-
cLI-L...I
'"'L.y"ULLU"
_ I
.,I-
,W.J
rharar-...,...,.-
teristic mass spectra. In most chelate compounds studied, the base peak is goZrL3+ and the parent peak, goZrL4+, is usually two orders of magnitude less intense than the base peak. It should also be noted that the ratio of the intensities of ZrL3+/ZrL4+is a very strong function of the source temperature. Figure 1 illustrates portions of the observed mass spectra covering the base peak (ZrLs+)and the parent regions. There are no major zirconium containing peaks between (ZrL4-F)+ and ZrL3+. Hafnium, however, is present in all zirconium
ANALYTICAL CHEMISTRY, VOL. 45, NO. 1, JANUARY 1973
199
Table I. Reactivity of B C h , B O s , and ZrOZ.Si02 Zr 0 2 . Compounds ZrC14 ZrO: Si02 Direct reaction with L Borax fusion (Alizarin test) + Reaction of borax-fused sample
+
with L
Conversion to ZrCh with cc14 Conversion to ZrClr after boraxfusion with CCla
-
+
+
+
-
__ -
+ +
+
ores and therefore the hafnium base peak, l*oHfL3+,is observable 90 mass units above the zirconium base peak at about one hundredth the intensity of the latter peak. The theoretical relative abundance at the cluster of ZrL3+ which was calculated considering the stable isotopes of zirconium, carbon ( l ZC and C ) and oxygen (l 60 and IsO) is also given. 2H and 1 7 0 were neglected in this calculation because of their low abundances. The observed and theoretical mass ratios between the first and second peak in the ZrL3+clusters are also shown in Figure 1 for the sake of rapid, accurate identification of mass number without the need of a standard which can often complicate the analysis of very small samples. Rapid identification of a peak is particularly important in trace analysis using the stable isotope dilution method (IO, 11).
Table I shows a summary of the reactivities of zirconium chloride, zirconium oxide, and zircon. This method for preparing the zirconium P-diketonates has the following advantages. First, it is applicable to most compounds containing zirconium. Second, an almost completely anhydrous state can be obtained during reactions because Small amounts of water present in the reagents, which may cause hydrolysis of ZrC14 and decomposition of the formed j3-diketonates, are converted into COCh and HCI. These gaseous products are easily removed from the reaction system and do not interfere in later chelating reactions. Third, a sealed glass capillary is suitable for the preparation of the chelate samples for trace analysis of zirconium by mass spectrometry or gas chromatography. This procedure is also applicable to the synthesis of j3-diketonates of many other metals. Throughout this work, parallel synthesis of the corresponding hafnium compounds has been carried out, with further work on the trace analysis of zirconium and hafnium in rocks and ores currently in progress. ACKNOWLEDGMENT
The authors gratefully acknowledge the assistance of David Rosenthal for his cooperation and for the use of the facilities of the Research Triangle Center for mass spectrometry, which is supported by the Biotechnology Resources Branch of the NIH under Grant Number PR-330.
~~
(IO) J. K. Terlouw and J. J. De Ridder, Z . Anal. Cheni., 250, 166 (1970). (11) N. M. Frew, J. J. Leafy, and T. L. Isenhour, ANAL.CHEM., 44, 665 (1972).
RECEIVED for review May 12, 1972. Accepted August 11, 1972. Work supported by Materials Research Center, University of North Carolina, under Contract Number DAHCIS67-(2-0223 with the Advanced Research Projects Agency.
Simple Separation of Vitamins D from Sterols and Retino1by Argentation Thin-Layer Chromatography David Sklan and Pierre Budowski Faculty o j Agriculture, The Hebrew University of Jerusalem, Rehovot, Israel THE SEPARATION OF CALCIFEROLS from accompanying materials prior to their physicochemical determination is of paramount importance in the determination of vitamins D in pharmaceutical preparations, enriched food and feeds, and biological materials. The main compounds to be removed are sterols and retinol which accompany vitamins D in tissues and many enriched products, and interfere especially with the antimony trichloride color reaction. Retinol is readily retained by Florex columns, and this separation technique is being used in combination with column partition chromatography ( I ) or digitonin precipitation of sterols ( 2 , 3). Conversion of vitamins D to jsotachysterol (4-6)
(1) United States Pharmacopeia, 17th Rev., Mack Publishing Co., Easton, Pa., 1965. p 891. (2) P. P. Nair, C. Buchana. S. De Leon, and D. A. Turner, ANAL. CHEM., 37, 63 1 (1965). (3) J. Eisses and H. De Vriess. J . Ass. Ofic.Agr. Chem., 52, 1189 (1 969).
200
provides additional possibilities of removal of interfering substances prior to gas-liquid chromatography (GLC) of isotachysterol esters. An adsorption chromatographic procedure on thin layers of silica gel G has been described, which however, does not separate vitamins D from retinol (7). This is achieved by partition thin-layer chromatography (TLC) (8), but the calciferols are not well separated from each other. The problems of efficient separation of vitamins D becomes particularly acute in low potency materials such as foods and (4) T. K. Murray, K. C. Day, and E. Kodicek, Biochem. J . , 98, 293 (1966). (5) A. J. Sheppard, D. E. La Croix, and A. R. Prosser, J . Ass. Ofic. Agr. Chem., 51, 833 (1968). (6) P. P. Nair and S. De Leon, Arch. Biochem. Biophys., 128, 663 (1968). (7) H. Janecke and I. Maas-Goebels, Freselzius’ Z . A d . Chem., 178, 161 (1960). (8) H . R. Bolliger, in “Thin-Layer Chromatography,” E. Stahl, Ed., Springer, Berlin, 1965, p 223.
ANALYTICAL CHEMISTRY, VOL. 49, NO. 1, JANUARY 1973
