Thermally stable compound

The main difference between field ionization (FI) and field desorption ionization (FD) lies in the manner in which the sample is examined. For FI, the substance under investigation is heated in a vacuum so as to volatilize it onto an ionization surface. In FD, the substance to be examined is placed directly onto the surface before ionization is implemented. FI is quite satisfactory for volatile, thermally stable compounds, but FD is needed for nonvolatile and/or thermally labile substances. Therefore, most FI sources are arranged to function also as FD sources, and the technique is known as FI/FD mass spectrometry. 

Table 15 summarizes anion-cation ratio for different types of fluorotantalates. Thermally stable compounds that can be prepared using the hydrofluoride method are noted in bold. 

Fluorine appears in hydroxides in the form of ammonium oxyfluoro-metalates, yielding ammonium fluoride upon decomposition during thermal treatment. Ammonium fluoride is not a thermally stable compound and... 

In the vast majority of gas-solid reactions, gaseous or evaporated compounds react at the surface of a solid catalyst. These catalytic processes are very frequently used in the manufacture of bulk chemicals. They are much less popular in processing of the large molecules typical of fine chemistry. These molecules are usually thermally sensitive and as such they will at least partially decompose upon evaporation. Only thermally stable compounds can be dealt with in gas-solid catalytic processes. Examples in fine chemicals manufacture are gas-phase catalytic aminations of volatile aldehydes, alcohols, and ketones with ammonia, with hydrogen as... 

This is a relatively new technique that is used for PCBs and other nonpolar, volatile and semi-volatile organic compounds. Typically, a small aliquot of soil sample (0.5-20 g) is used for the extraction. Soil samples are extracted with one or more organic solvents using microwave energy at elevated temperature (100-115 °C) and pressure (50-175 psi). This method uses less solvent and takes significantly less time than Soxhlet extraction but is limited to thermally stable compounds. 

For non-volatile sample molecules, other ionisation methods must be used, namely desorption/ionisation (DI) and nebulisation ionisation methods. In DI, the unifying aspect is the rapid addition of energy into a condensed-phase sample, with subsequent generation and release of ions into the mass analyser. In El and Cl, the processes of volatilisation and ionisation are distinct and separable in DI, they are intimately associated. In nebulisation ionisation, such as ESP or TSP, an aerosol spray is used at some stage to separate sample molecules and/or ions from the solvent liquid that carries them into the source of the mass spectrometer. Less volatile but thermally stable compounds can be thermally vaporised in the direct inlet probe (DIP) situated close to the ionising molecular beam. This DIP is standard equipment on most instruments an El spectrum results. Techniques that extend the utility of mass spectrometry to the least volatile and more labile organic molecules include FD, EHD, surface ionisation (SIMS, FAB) and matrix-assisted laser desorption (MALD) as the last... 

El and Cl are the most commonly used ionization techniques for the analysis of volatile, nonpolar, low molecular weight (up to 700 900 Da) and thermally stable compounds. These techniques can be also useful for studying non highly volatile molecules, but in these cases, preliminary chemical reactions, such as derivatization, have to be performed in order to obtain derivatives with increased volatility. 

The use of bulky organic groups permitted the isolation of several thermally stable compounds containing double bonds between arsenic, antimony, or bismuth.8 9 56 Examples of homonuclear dimetal compounds, that is, diarsenes,... 

In several cases the >j -coordinated diyne ligand can be displaced by other ligands. The pentane-soluble, thermally stable compounds Ni(L2) (HC2C2H) (n= 1, 2 L2 = dippe, dippp) react with P(OPh)3 to give Ni P(OPh)3 4 with liberation of diyne and the bis-phosphine. The reaction of Ni(dippp) 2(/z-/ M- -HC2C2H) with four equivalents of CO resulted in polymerization of the butadiyne released from the metal center and the formation of Ni(CO)2(dippp). ... 

Other interferences which may occur in flame AAS are ionization of the analyte, formation of a thermally stable compound e.g., a refractory oxide or spectral overlap (very rare). Non-flame atomizers are subject to formation of refractory oxides or stable carbides, and to physical phenomena such as occlusion of the analyte in the matrix crystals. Depending on the atomizer size and shape, other phenomena such as gas phase reactions and dimerization have been reported. 

Thiepane (35) has been purified by distillation at normal pressure (b.p. 170-174 °C) and may therefore be considered a thermally stable compound. At higher temperatures (400 °C) and in the presence of an aluminum silicate catalyst, however, thermal decomposition does occur to give hydrogen sulfide as one product (72HC(26)573). 

Less volatile but thermally stable compounds can be thermally vaporized in the direct inlet probe (DIP) situated close to the ionizing molecular beam. This DIP is standard equipment on most instruments. An electron-impact spectrum results. 

The first silver(I) poly(pyrazolyl)borate complexes were reported in 1975.150 Since then, a number of silver complexes of the type Ag(L)(R B(pz)4 ) have been isolated and characterized.151,152 They were prepared by the reaction of the poly(pyrazolyl)borate anions with silver(I) salts, usually the nitrate, in the presence of donor ligands, L, and were isolated as white, thermally stable compounds. In most cases they were either insoluble, or at best only sparingly soluble, in common organic solvents. 

A versatile approach to 1 -heteroarylsilatranes is the cleavage reaction of tetraheteroaryl-silanes (equation 42) which are hydrolytically and thermally stable compounds. The latter are more easily available compared with trifunctional heteroarylsilanes. The reaction is effectively catalyzed by CsF135. 

Chemical interferences arise from the formation of thermally stable compounds such as oxides in the flame. The use of electrothermal atomization, a hotter nitrous oxide-acetylene flame or the addition of a releasing agent such as lanthanum can help reduce the interference. 

Chemical interference arises when the determinant element forms a thermally stable compound with one or more concomitant ions or molecules present in the sample solutions.9 The best known examples are the interference of phosphate,... 

Because chemical interference depends upon the formation of thermally stable compounds, it is to be expected that the extent of the interference will be reduced if a hotter flame, such as nitrous oxide-acetylene, is employed. In many cases, unless the interferent and determinant concentrations are both high, the use of the hotter flame may be sufficient to prevent interference from occurring at all. Not all interferences are completely eliminated, however. 

Enamides R2C=CHNRCOR (N-acylated enamines) are thermally stable compounds under neutral or basic conditions. However, they show sensitivity to aqueous acid, hydrolysing to form aldehydes or ketones and amides. The photocyclization of enamides has been used to form a wide variety of natural products because it gave higher yields than the conventional thermal syntheses620-623. 

In subsequent related work [44], the less thermally stable solid compound [Au(CO)2]+[UF6] was prepared quantitatively by oxidation of elemental Au with UF6 in HF under a pressure of CO. UFg, the reduction product of UF6, is, presumably, just sufficiently weakly basic to stabilise the bis(carbonyl) cation, whereas the more weakly basic Sb2Fjj gave a thermally stable compound. 

U(OR) compounds (R = alkyl or aryl) exist in oxidation states between +3 and 4-6 in addition, there are some uranyl alkoxides. An unusual feature is the number of thermally stable compounds in the otherwise unstable and rare 4-5 state. 

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