Henry reaction heterogeneous

The Michael addition of nitroalkanes to election-deficient alkenes provides a powerful synthetic tool in which it is perceived that the nitro group can be transformed into various functionalities. Various kinds of bases have been used for this transformation in homogeneous solutions, or, alternatively, some heterogeneous catalysts have been employed. In general, bases used in the Henry reaction are also effective for these additions (Scheme 4.18).133... 

Bulbule, V. J., Deshpande, V. H., Velu, S., Sudalai, A., Sivasankar, S. and Sathe, V. T. (1999). Heterogeneous Henry reaction of aldehydes diastereoselective synthesis of nitroalcohol derivatives over Mg-Al hydrotalcites. Tetrahedron 55, 9325. 

Ballini, R., Bosica, G., Livi, D., Palmieri, A., Maggi, R., Sartori, G. Use of heterogeneous catalyst KG-60-NEt2 in Michael and Henry reactions involving nitroalkanes. Tetrahedron Lett. 2003,44, 2271-2273. 

Keywords Aldehydes, bromoniromethane, solvent-free, carbonate on silica, room temperature, Henry reaction, a-bromonitroalcohols, Amberlyst I5/AC2O, heterogeneous catalysis, dehydration, diastereoselectivity, (Z)-a-bromonitroalkenes... 

Sharma et al. reported on the synthesis and catalytic properties of bifunctional heterogeneous catalysts with basic and organometallic catalysts for efficient catalysis of two-step Sonogashira and Henry reactions [55]. With a solvent-assisted grafting method, two different catalytic groups— an organoamine and a palladium-organodiamine... 

A chiral bis(oxazoline) ligand was covalently functionahzed onto a hierarchically ordered mesocellular mesoporous silica and applied to the asymmetric Henry reaction between various aldehydes and nitromethane at ambient temperature. As a chiral heterogeneous catalyst, this functionalized mesoporous material showed excellent enantioselectivity in the asymmetric Henry reaction when the free silanol groups of the mesoporous silica were capped by trimethylsilyl groups. And also this catalyst could be magnetically separated from the reaction mixture without significant loss of reactivity or enantioselectivity [94]. 

The Henry s law constant in water was used in the McJilton et al. uptake model to determine the equilibrium concentration of ozone and sulfur dioxide at the surface of a simulated mucus film along the airways in Weibel s symmetric model.It is also used to determine the concentration of absorbed gas at the surface of the mucus when the pollutant gas undergoes a homogeneous or heterogeneous chemical reaction within the mucus layer. 

There is evidence from laboratory studies that heterogeneous reactions on sulfate particles may be important in the upper troposphere as well. For example, HCHO uptake into sulfuric acid solutions or ternary mixtures of sulfuric and nitric acids and water has been observed in laboratory studies (e.g., Tolbert et al., 1993 Jayne et al., 1996 Iraci and Tolbert, 1997). In sulfuric acid, the effective Henry s law constant at the low... 

The experimental quantity used to characterize heterogeneous reaction rates is the "reaction probablity", y, which is defined as the fractional collision frequency that leads to reactive loss. Kinetic data for the generally irreversible reactive uptake of trace gas species on condensed surfaces are expressed in terms of uptake experiments, where the disappearance of the species under consideration and/or the appearance of one or more reaction products has been observed. Such processes may not be rate limited by Henry s law constraints, however the fate of the uptake reaction products may be subject to saturation limitations. 

Heterogeneous reactions involving water droplets in clouds and fogs are important mechanisms for the chemical transformation of atmospheric trace gases. The principal factors affecting the uptake of trace gases by liquid droplets are tne mass accommodation coefficient of the trace gas, the gas phase diffusion of the species to the droplet surface and Henry s Law saturation of the liquid. The saturation process in turn involves liquid phase diffusion and chemical reactions within the liquid droplet. The individual processes are discussed quantitatively and are illustrated by the results of experiments which measured the uptake of S02 by water droplets. 

The reaction of OH radical with DMDS is fast and OH is moderately soluble in water (Henry s law constant is 25 M atm-1 at 25 C. But again, it depends on the concentration levels of DMDS in clouds and rainwater. In addition, the low solubility of DMDS in water makes heterogeneous oxidation in water droplets unlikely. 

The last term arises from Eq. (15.32) applied to species C, Eq. (15.27) applied to B, and the fact that aA = fA for species A in the gas phase. Since K depends on the standard states, the value of K is not the same as that obtained when the standard state for each species is chosen as the ideal-gas state at 1 bar. However, all methods theoretically lead to the same equilibrium composition, provided Henry s law as applied to species C in solution is valid. In practice, a particular choice of standard states may simplify calculations or yield more accurate results, because it makes better use of the limited data normally available. The nature of the calculations required for heterogeneous reactions is illustrated in the following example. 

Recently, a new one-pot process for the sequence (i)-(iii) has been realized under heterogeneous catalysis (Ballini et al 2007b). In fact, treating at room temperature according to the reaction in Figure 2.20 one equivalent of primary haloalkanes (57) and one equivalent of aldehyde, or conjugate enone, in the presence of IR A-402 nitrite and Amberlyst A-21, the nitroalkanols (60) or y-nitro ketones (61) were obtained, respectively, in a one-pot SN2-nitroaldol (Henry) or SN2-Michael reactions. 

Ballini, R., Barboni, L., and Palmieri, A. 2007b. A new heterogeneous one-pot process for both nitroaldol (Henry) and Michael reactions from primary haloalkanes via nitroalkanes. Synlett, 19 3019-21. 

One of the most significant points that we must consider in scientific studies, not limited to studies on photocatalysis, is distinction between evidence and consistency, as least as far as the author thinks. In other words, it is necessary to recognize every fact to be a necessary condition but not a sufficient condition in a strict scientific sense. For example, the fact that a reaction rate obeys the first-order rate law giving a linear relation in a plot of data as in Fig. 6 is only a necessary condition for a monomolecular reaction in homogeneous phase and also a necessary condition for heterogeneous photocatalytic reaction in diffusion-limited conditions or that in surface-reaction limited conditions with a Henry-type adsorption or a Langmuir-type adsorption in the lower-concentration region. 

These kinetic expressions can be useful in many situations, since they capture two key aspects of heterogeneous catalysis the rate of the reaction, and the saturation of the surface by the reactants. The values assigned to the various kinetic and adsorption parameters in this work produce rates that agree well with those reported in the literature. The liquid-phase components were considered nonvolatile. The saturation concentration of H2 was evaluated using Henry s law. All physical parameters were treated as constants. The catalyst properties were representable for a supported noble metal hydrogenation catalyst. 

Gai PL, Boyes ED, Helveg S, Hansen PL, Giorgio S, Henry CR (2007) Atomic-resolution environmental transmission electron microscopy for probing gas-soUd reactions in heterogeneous catalysis. MRS Bull 32 1... 

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