Volatile chelates acetylacetonate

Other fluorinated derivatives of acetylacetone are trifluoroacetylacetone (CF3COCH2COCH3) and hexafluoroacetylacetone (CF3COCH2COCF3), which form stable volatile chelates with aluminium, beryllium, chromium(III) and a number of other metal ions. These reagents have consequently been used for the solvent extraction of such metal ions, with subsequent separation and analysis by gas chromatography [see Section 9.2(2)]. 

Belcher and his colleagues examined bis chelates of R1CSCH2COR2 and found them to be mainly monomeric.95 Hexafluorothioacetylacetone formed a number of volatile chelates (63 M = Cd, Cu, Fe11, Ni, Pb, Pt and Zn) with quite low melting points ranging from 108 °C (Cd) to as little as 54.5 °C (Zn), and many satisfactory separations are reported. Monothiotrifluoro-acetylacetone has been used to determine Ni down to 10-u g.97... 

Blood, serum Sample after wet digestion converted to a volatile chelate usually with fluorinated acetylacetone GC/ECD 0.03 pg 0.5 pg 1.0 ng No data Fishbein 1984... 

In thermal ionization mass spectrometry (TI-MS), solid, inorganic compounds may be volatilized from a heated surface. TI-MS is the most precise method for the measurement of isotopic ratios of minerals and has been used to analyze 58pe in fecal samples collected from a human study (H). The major drawbacks of this technique are the costly instrument and the slow sample through-put. Conventional mass spectrometry produces ions by electron bombardment of the vapor of volatile compoimds. This is called electron-impact ionization mass spectrometry (EI-MS). Analysis of iron by EI-MS requires derivitization to volatile forms before introduction into the mass spectrometer. A method has been developed for the synthesis of volatile iron-acetylacetone chelates from iron in blood serxm (1 ). A tetraphenylporphyrin chelate has also been synthesized and used in an absorption study in which 54pe and 57pe were given orally (16). 

Hass et al. 65a) have observed no ion current from an emitter coated with hexaquocobalt(II)chloride, but on the admission to the ion source of gaseous acetylacetone (Hacac) the ion [Co(acac)Cl]+ was observed. Trifluoroacetic acid produced an analogous ion and when FeCl2 was coated on the emitter the corresponding iron chelate was observed. Sodium from sodium chloride has also been detected by volatilization with acetic acid. 

A large class of coordination compounds, metal chelates, is represented in relation to microwave treatment by a relatively small number of reported data, mainly p-diketonates. Thus, volatile copper) II) acetylacetonate was used for the preparation of copper thin films in Ar — H2 atmosphere at ambient temperature by microwave plasma-enhanced chemical vapor deposition (CVD) [735a]. The formed pure copper films with a resistance of 2 3 pS2 cm were deposited on Si substrates. It is noted that oxygen atoms were never detected in the deposited material since Cu — O intramolecular bonds are totally broken by microwave plasma-assisted decomposition of the copper complex. Another acetylacetonate, Zr(acac)4, was prepared from its hydrate Zr(acac)4 10H2O by microwave dehydration of the latter [726]. It is shown [704] that microwave treatment is an effective dehydration technique for various compounds and materials. Use of microwave irradiation in the synthesis of some transition metal phthalocyanines is reported in Sec. 5.1.1. Their relatives - porphyrins - were also obtained in this way [735b]. 

Despite the recent interest in the preparation and properties of thermally stable metal chelates, only a few attempts have been made to study in a systematic manner the chemical reactions that take place when metal chelates are thermally decomposed. The thermal stabilities of the acetyl-acetonates of a number of metal ions were compared by measuring the increase in pressure caused by the formation of volatile decomposition products in a closed system containing the metal acetylacetonate and nitrogen gas. A comparison of the data obtained at 191°C indicated that the rate and extent of decomposition were dependent on the nature of the metal ion. The acetylacetonates of Zr(IV), Co(III), Fe(III), and Mn(III) had the lowest thermal stability whereas the Li(I), Mg(II), Be(II), Cu(II), Ni(II), Ga(III), and Cr(III) chelates were among the most stable (44)- In contrast, acetylacetone itself does not decompose under the same conditions (4 ). 

The major breakthrough that transformed metal chelate GC into a useful analytical technique was the introduction of fluorinated beta-diketone ligands, which formed complexes of greater volatility and thermal stability. Trifluoroacetylacetone (l,l,l-trifluoro-2,4-pentanedione—HTFA) and hexafluoro-acetylacetone (l,l,l,5,5,5-hexafluoro-2,4,-pentanedione—HHFA) are the fluorinated ligands most frequently employed. HTFA extended the range of metals that may be gas chromatographed with little or no evidence of decomposition to include Ga3+, In3+, Sc3+, Rh3+ and V4+. An example of a recent application is the analysis for beryllium in ambient air particulates. After filter sampling and extraction/chelation, packed column GC with electron capture detection allowed ppm level beryllium quantitation in collected particulates which corresponded to levels of 2-20 x 10 5 pg/m3 in the sampled air. 

The /3-diketonates of di-, tri- and tetravalent metals have proved the most suitable and the ligands acetylacetone trifluoroacetylacetone and hexafluoro-acetone the most used. In general, the more fiuorinated the /3-diketone the more volatile the chelate also greater sensitivity can be achieved with the BCD. 

In inorganic chemistry, mixtures of metal ions in solution can be analyzed by electron-impact mass spectrometry. First the metal ions are complexed with an organic ligand (usually various substituted acetylacetonates) to form volatile metal chelates. If many metal ions are anticipated, the mixture is separated by GC and the separated fractions identified by mass spectrometry. Simple mixtures can be analyzed directly using the mass spectrometer. Because of the high sensitivity of mass spectrometry, trace analysis is possible. 

Thiopicolinamides are known to form chelates with metal ions. The synthesis of suitable bis(thiopicolinamides) to serve as ligands for polymer formation was reported in 1958 (2-4, 20). Heating a metal acetylacetonate with a stoichiometrie amount of a bis(thiopicolinamide) effects chelate exchange and the formation of polymer as a residue product (VIII-1). Acetylacetone is removed as a volatile by-product. Direct synthesis of these polymers from a metal acetate and the bis(thiopicolinamide) has been used more widely. Generally, methanolic solutions of the metal acetate are added to solutions of the bis(ligand) in dimethylformamide, benzene, or chloroform (8, 20, 26,31, 32). Almost always the polymer precipitates in quantitative yield, but in some cases, other isolation techniques have been required. 

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