Supercritical Amines

In all cases the metal ion was monovalent and the compounds contain no Q-Q bonds. In most cases the compounds are valence precise, diamagnetic, narrow bandgap semiconductors or semimetals. 

A much more extensive series of compounds can be prepared by including mixed group 15/16 compounds as the starting materials. This leads to quaternary compounds, A M EyO (A = K, Rb, Cs, Tl M = Cu, Ag E = P, As, Sb, Bi Q = S, Se, Te) wiA tri- and pentavalent atoms creating additional linkages and greater structural complexity. Thus were isolated and characterized an enormous series of structurally fascinating quaternary phases [121-123]  

Product formation is extremely sensitive to reaction conditions and, with the large number of reaction parameters available, there appears to be no end to the number of new phases that can be made. However, in virtually all cases, the compounds are valence precise, diamagnetic semiconductors with bandgaps between 1.8-2.8 eV. Thus their electronic properties are of minimal interest. 

For all preceding chalcogenide compounds prepared in supercritical amines, the metal centers are always monovalent. This includes both the alkali metal and the transition metal. In attempts to make more electronically interesting compounds, the inclusion of polyvdent metal ions with open shells in the chalcogenide framework was attempted. This was done by replacing the alkali metal cations with divalent cations or trivalent rare earth cations. However, 

This preferential coordination of ammonia to the metal center occurs with alkaline earth cations as well  

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The problems of properly characterizing the compounds from ammonia solutions caused a major hiatus in the exploration of the cluster anions. However, in 1970 Kummer and Diehl reported that liquid ammonia may be replaced by more easily handled and considerably more stable polyamines, most conveniently by tetraethy-lenediamine (en). Extraction of sodium-tin alloys in en and subsequent precipitation with THE or monoglyme yields the reasonably stable compound (Na+)4(Sn9 ) 6-8en. Kummer and Diehl pointed out the analogy between Sn9" and the previously characterized cluster cation Bi9 , and a partial structural characterization was reported for (Na+)4(Sn9 ) 7 en. However, in terms of the synthesis of well-defined, stable cluster compounds, the route pioneered by Kummer and Diehl left a lot to be desired. Nevertheless, supercritical amines have recently been found to be good reaction media for the synthesis of extended chal-cogenide structures. 

The principal solvents that have been used are alcohols such as ethanol, methanol, and propanol, and organic acids such as formic or acetic acid, but other solvents iaclude esters, ethers, phenols, cresols, and some amines. Even solvents such as CO2 and NH in the supercritical fluid state have been tried as solvents. 

Alkyne-nitrile cyclotrimerization is a powerful synthetic methodology for the synthesis of complex heterocyclic aromatic molecules.118 Recently, Fatland et al. developed an aqueous alkyne-nitrile cyclotrimerization of one nitrile with two alkynes for the synthesis of highly functionalized pyridines by a water-soluble cobalt catalyst (Eq. 4.62). The reaction was chemospecific and several different functional groups such as unprotected alcohols, ketones, and amines were compatible with the reaction.119 In addition, photocatalyzed [2+2+2] alkyne or alkyne-nitrile cyclotrimerization in water120 and cyclotrimerization in supercritical H2O110121 have been reported in recent years. 

Iridium(III) hydride forms complexes with DIOP, BDPP (2,4-bis(diphenyl-phosphino)pentane), NORPHOS, and BINAP ligands to produce amines in 11 -80% ee.679 Similar modest results are obtained in the reduction of N-arylketimines with an iridium(HI) complex with (2S,3 S) -C HIRA PHOS as the chiral ligand.680 The indium complexes with chiral phosphinodihydrooxazoles catalyze the enantioselective hydrogenation of imines in supercritical carbon dioxide with up to 80% ee, but generally lower ee values are observed in... 

Problematic functional groups, however, are thioethers and disulfides [28] as well as free amines which poison catalysts of type 1 [4c]. In case of amines this problem is easily solved by choosing either an appropriate protecting group for nitrogen (e.g. amide, sulfonamide, urethane), or simply by protonation since ammonium salts were found to be compatible with 1 [4c]. As will be discussed in Sect. 4, free amines can also be metathesized in supercritical C02 as the reaction medium [7]. 

Supercritical extractions such as that illustrated in Procedure 12.3 have been used to extract phenols, organochlorine, organophosphate compounds, and amines from soil [9,10,12],... 

Ashraf-Khorassani M, Taylor LT, Zimmerman P. Nitrous oxide versus carbon dioxide for supercritical fluid extraction and chromatography of amines. Anal. Chem. 1990 62 1177-1180. 

The carcinogenic aromatic amines released from azo dyes in leather were investigated by using microwave-assisted extraction (MAE) or supercritical fluid extraction (SFE) followed by RP-HPLC. The chemical structures of dyes and aromatic amines are listed in Fig. 3.69. The flow schemes for SFE and MAE are shown in Figs 3.70. and 3.71. 

White recently illustrated the use of fast supercritical fluid and EFLC for drug discovery and purification [46]. The optimized isocratic separations used to scale up to preparative-scale separations were often EFL mixtures. For example, Figure 9.13 shows the optimized conditions for the separation of a drug candidate included 30% methanol (with 0.2% isopropyl amine)/C02 on a Chiralcel OJ-H column at 5 mL/min [46]. His work also illustrates by using gradients that start in supercritical conditions and then move into EFL mixture conditions provides efficient and fast separations. 

Oostdyk TS, Grob RL, Snyder JL, et al. 1995. Supercritical fluid extraction of primary aromatic amines from characterized soil samples comparison with sonication extraction. J Environ Sci Health A30(4) 783-816. 

Oku, T. and Arita, Y. and Tsimeki, H. and Ikariya, T. (2004). Continuous Chemoselective Methylation of Fimctionalized Amines and Diols with Supercritical Methanol over Solid Acid and Acid-Base Bifunctional Catalysts. J. Am. Chem. Soc., 126, 7368-7377. 

The single largest use of ammonia is its direct apphcation as fertdizer, and in the manufacture of ammonium fertilizers that have increased world food production dramatically. Such ammonia-based fertilizers are now the primary source of nitrogen in farm soils. Ammonia also is used in the manufacture of nitric acid, synthetic fibers, plastics, explosives and miscellaneous ammonium salts. Liquid ammonia is used as a solvent for many inorganic reactions in non-aqueous phase. Other apphcations include synthesis of amines and imines as a fluid for supercritical fluid extraction and chromatography and as a reference standard in i N-NMR. 

A comparison of extraction methods for primary aromatic amines including 1,4-phenylenediamine, 2,4-diaminotoluene, benzidine, 4,4 -methylenebis (2-chloroanilme), 3,3 -dimethylbenzidine, and 3,3 -dichlorobenzidine from solid matrices was conducted. Supercritical fluid extraction (SEE) was evaluated and compared with the classical method, sonication extraction (Oost-dyk et al., 1993). 

Supercritical Fluid Extraction of Amine Surfactant in Hexagonal Mesoporous Silica (HMS)... 

Supercritical carbon dioxide modified with 10 vol% methanol has been employed for the removal of the amine surfactant in hexagonal mesoporous silica (HMS). The effects of temperature and pressure on the extraction efficiency have been extensively studied. It has been found that within an hour, as high as 96% of the amine surfactant can be extracted at a relatively mild condition of 85°C and 100 bar. At constant pressure, high extraction efficiencies are obtained at 50 and 85°C while at constant temperature, high efficiencies occur at 100 bar and 250 bar. This work establishes the feasibility of using supercritical fluid extraction (SFE) for the removal of the amine surfactant. In fact, it has been discovered that SFE produces EIMS of more enhanced mesoporosity as compared to that of calcination. 

As such, supercritical fluid extraction (SFE) has been proposed for the removal of the amine surfactant. In this work, 1.8 ml/min of CO2 modified with 0.2 ml/min of methanol has been employed for the extraction purpose. Through SFE, recycling of surfactant can be accomplished while generating minimal liquid solvent (methanol) for disposal. Supercritical CO2, which forms the solvent bulk, can be easily separated from the extract (and methanol) via depressurisation and the resultant gas can then either be recycled or be released into the atmosphere. 

Extraction of the amine surfactant using pure CO2 at 65°C and 150 bar has been attempted, but it has been found from TGA that there is completely no extraction at all. In 1985, Dandge et al. [4] have reported that the solubility of amines in supercritical CO2 generally decreases with increasing basicity (Kb). The threshold basicity, above which the compound becomes insoluble in CO2, was found to be about 10 9. As such, it is a foregone conclusion that the surfactant dodecylamine (Kb 10 4) is insoluble in pure supercritical CO2. This explains the zero extraction observed and thereby justifies the need of a modifier (methanol in this case). 

Flotation - [AMINES - FATTY AMINES] (Vol 2) - [FLOTATION] (Vol 11) - [FOAMS] (Vol 11) - [METALLURGY-SURVEY] (Vol 16) -dye water effluent treatment [DYES, ENVIRONMENTAL CHEMISTRY] (Vol 8) -isopropyl xanthates for [PROPYL ALCOHOLS - ISOPROPYL ALCOHOL] (Vol 20) -of lead ore [LEAD] (Vol 15) -formica [MICA] (Vol 16) -m paper recycling [RECYCLING - PAPER] (Vol 21) -ofpotassium chlonde [POTASSIUM COMPOUNDS] (Vol 19) -silicates for [SILICON COMPOUNDS - SYNTHETIC INORGANIC SILICATES] (Vol 22) -use of copper composition [COPPER COMPOUNDS] (Vol 7) -usmgSCFs [SUPERCRITICAL FLUIDS] (Vol 23)... 

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