Ionic liquids Henry reactions

Dupont et al. [60] studied the same reaction, but used [BMIM][PF6] and [BMIM][BF4] as ionic liquids. A special focus of their investigations was on the influence of H2-pressure on conversion. The Henry coefficient solubility constant was determined by pressure drop experiment in a reactor, which is a known procedure to measure gas solubilities [93]. The values reported by these authors were FC=3.0xl0-3 mol IT1 atm1 for [BMIM][BF4]/H2 and 8.8x10 4 mol L 1 atm-1 for [BMIM][PF6]/H2 at room temperature, which differ significantly from those determined by the 1H-NMR technique (see Table 41.2) [59]. However, their values indicated that molecular hydrogen is almost four times more soluble in [BMIM][BF4] than in [BMIM][PF6] under the same pressure. According to the authors, this is reflected by the values of conversion (ee), which were 73% (93% ee) for [BMIM][BF4] and 26% (81% ee) for [BMIM][PF6] at 50 bar H2 pressure (Table 41.9, entries 2 and 4). 

Ionic liquids have been used for many other reactions. Examples include Friedel-Crafts acylation (Tetrahedron Leu. 43 5793,2002), osmylation (Tetrahedron Lett. 43 6849,2002), Heck coupling (Tetrahedron Lett. 44 8395,2003), and Henry reaction (Tetrahedron Lett. 45 2699,2004). 

When aliphatic nitro compounds are used instead of aldehydes or ketones, no reduction occurs, and the reaction has been referred to as a Tollens reaction (see 16-43). However, the classical condensation of an aliphatic nitro compound with an aldehyde or ketone is usually called the Henry reaction or the Kamlet reaction, and is essentially a nitro aldol reaction. A variety of conditions have been reported, including the use of a silica catalyst, Mg—A1 hydrotalcite, a tetraalkylam-monium hydroxide,proazaphosphatranes, " or an ionic liquid.A solvent free Henry reaction was reported in which a nitroalkane and an aldehyde were reacted on KOH powder. Potassium phosphate has been used with nitromethane and aryl aldehydes. The Henry reaction has been done using ZnEt2 and 20%... 

Abstract The possible utilization of room temperature ionic liquids (RTILs), instead of volatile organic compounds (VOCs), in the electrochemical procedures of organic synthesis has been discussed. The synthesis of p-lactams, the activation of carbon dioxide and its utilization as renewable carbon source and the carbon-carbon bond formation reactions via umpolung of aldehydes (benzoin condensation and Stetter reaction) and via Henry reaction have been selected as typical electrochani-cal methodologies. The results, related to procedures performed in RTILs, have been compared with those performed in VOCs. The double role of RTILs, as green solvents and parents of electrogenerated reactive intermediates or catalysts, has been emphasized. 

The Henry reaction is performed, in the presence of catalysts (organic or inorganic bases, quaternary ammonium salts, etc.), protic and aprotic organic solvents [161], water [162], supercritical fluids [163] or ionic liquids [164], Nitroalkenes can be obtained as by-products, via dehydration of p-nitroalcohols. Considerable efforts have been made to increase the yield and selectivity and to control the basicity of the medium and the reaction time. 

Feroci M, Elinson MN, Rossi L, Inesi A (2009) The double role of ionic liquids in organic electrosynthesis precursors of N-heterocycUc carbenes and green solvents. Henry reaction. 

Ionic liquids have numerous applications in organic synthesis. Some of the important reactions have proved that ionic liquids are truly versatile catalysts. Reaction media include, esterification reaction [67, 68], aldol condensation [69, 70], hydrogenation [71], Friedel-Crafts reactions [72,73], oxidation [74-76], Henry reaction, cross-coupling reactions [77,78], and some enzyme reactions [79, 80]. 

The solubilities of H2 [181] and CO [182] in many different ionic hquids have been measured in this context by Dyson and coworkers using high-pressure H- or C-NMR spectroscopy. CO solubility at ambient conditions (Henry s law constants) were found to be in the range of 8.05-0.67 x 10 MPa which were in the same range than those measured for H2 in the same ionic hquids (about 6.6-0.7 X 10 MPa). In order to establish the effect of the CO solubihty on the rate of hydroformylation reactions, the same authors studied the [RhH(CO)(PPhj)3] catalyzed hydroformylation of 5-hexen-2-one comparing catalyst activities in the different ionic liquids with the determined gas solubilities. 

Polynitroalkanes undergo Henry and Mannich reactions in ionic liquids. TMS-methylenenitronate (75) reacts with aliphatic and aromatic aldehydes to give Henry reaction products, with scandium(III) triflate as catalyst. ... 

Scheme 6 Cathodic generation of N-heterocyclic carbene in ionic liquid and its catalytic use for Henry reaction...

The impact of these liquid phase reactions on the phase equilibrium properties is thus an increased solubility of NH3, CO2, H2S and HCN compared with the one calculated using the ideal Henry s constants. The reason for the change in solubility is that only the compounds present as molecules have a vapour pressure, whereas the ionic species have not. The change thus depends on the pH of the mixture. The mathematical solution of the physical model is conveniently formulated as an equilibrium problem using coupled chemical reactions. For all practical applications the system is diluted and the liquid electrolyte solution is weak, so activity coefficients can be neglected. 

Catalyst 5-Hydroxypentylammonium acetate (5-HPAA reusable task-specific ionic liquid) Keywords Alkyl/aryl/heteroaryl aldehydes, nitromethane, trialkylphosphites, 5-HPAA, solvent-free, room temperature, one-pot tandem Henry-Michael reaction, multicomponent reaction, terminal vinylphosphonates... 

Phosphonium ionic liquids exchanged with bicarbonate and methylcarbonate anions have been found to catalyse efficiently the Henry addition of nitroalkanes to different aldehydes and ketones under solventless conditions. These ionic liquids not only allow the selective formation of nitroaldols but also unlock a novel high-yielding access to dinitromethyl derivatives of ketones. The reaction mechanism plausibly involves the transformation of the initial catalytic species [MeP(Octyl)3+ ROCOO R= Me, H] through reversible loss and uptake of carbon dioxide. 

In the literature, there are reports of work concerned with the measurement of oxoacidic properties of ionic melts by gravimetric measurements of the solubility of acidic gases in these media [76, 77], The solubility of sulfur(VI) oxide in molten sodium phosphates was determined by the gravimetric method [76], A correlation was obtained between the melt basicities and the solubility of gaseous acid S03 in them. Iwamoto reported the estimation of the basic properties of molten salt by measurements of acidic gas solubilities (carbon dioxide and water) in them [77], However, similar methods cannot be used widely, owing to two factors. The first of these consists in the fact that the solubility of any gas in a liquid phase obeys Henry s law. Let us consider the following system of reactions ... 

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