3- propenal, solvent effects

Considering that the activity of a Lewis acid depends strongly on the stability of the acid-base complex and that the complexation is notoriously hampered by chemically hard solvents like water, it is clear that reactions of bidentate dienophiles can be catalysed very efficiently36. Prototypical are the derivatives of 3-phenyl-l-(2-pyridyl)-2-propen-l-ones (vide infra). Their Diels-Alder reactions (Table 24) clearly show that the accelerating solvent effect of water is still present in the Lewis acid catalysed reactions, and that the Lewis acid activity is not necessarily hindered by the solvent301. While... 

As an example of application of the ASEP/MD method described in the previous section, in this section we proceed to the discussion of solvent effects on radiative and non-radiative processes in acrolein. Acrolein or propenal is the smallest a,(3-unsaturated carbonyl compound. The presence of the carbonyl group and the C=C double bond makes it a compound of marked interest from a spectroscopic and photochemical points of view. In solution, acrolein displays a strong absorption band corresponding to a transition and a weak band, at lower frequencies asso-... 

Solvent effects have not been greatly studied but Ingberman et al. [271] observed increases in rates of polymerization of propene by a/7 TiCls/AlEtj Cl in the order n heptane < toluene < chlorobenzene < o-dichlorobenzene. These data were interpreted in terms of the ability of the solvent to desorb impurities from the catalyst surface. However, polymerizations were conducted at constant propene pressure and individual monomer concentrations were not reported. In agreement with other reports the polymerization rate was reduced by the presence of AlEtClj. 

Cobalt. Solvent effects on hydroformylation of propene and of pent-l-ene catalysed by CoH(CO)4 have been investigated by product distribution analysis. Effects of temperature and pressures of hydrogen and carbon monoxide on the mechanism of hydroformylation of propene in the presence of Co2(CO)8(PBu8)a have similarly been probed by product analysis. The reaction of (36) with methanol or ethanol (R OH) produces CHR(COaRi)2. ... 

Ionic liquids have already been demonstrated to be effective membrane materials for gas separation when supported within a porous polymer support. However, supported ionic liquid membranes offer another versatile approach by which to perform two-phase catalysis. This technology combines some of the advantages of the ionic liquid as a catalyst solvent with the ruggedness of the ionic liquid-polymer gels. Transition metal complexes based on palladium or rhodium have been incorporated into gas-permeable polymer gels composed of [BMIM][PFg] and poly(vinyli-dene fluoride)-hexafluoropropylene copolymer and have been used to investigate the hydrogenation of propene [21]. 

Transition metal oxides or their combinations with metal oxides from the lower row 5 a elements were found to be effective catalysts for the oxidation of propene to acrolein. Examples of commercially used catalysts are supported CuO (used in the Shell process) and Bi203/Mo03 (used in the Sohio process). In both processes, the reaction is carried out at temperature and pressure ranges of 300-360°C and 1-2 atmospheres. In the Sohio process, a mixture of propylene, air, and steam is introduced to the reactor. The hot effluent is quenched to cool the product mixture and to remove the gases. Acrylic acid, a by-product from the oxidation reaction, is separated in a stripping tower where the acrolein-acetaldehyde mixture enters as an overhead stream. Acrolein is then separated from acetaldehyde in a solvent extraction tower. Finally, acrolein is distilled and the solvent recycled. 

It was shown that room-temperature molten salts derived from the combination of 1,3-dialkylimidazolium chloride and A1C13 can be used as solvents in two-phase catalytic dimerization of propene to give hexenes catalyzed by Ni(II) compounds (125). The effects of phosphane ligands coordinated to nickel and operating variables were also investigated (126). The dimerization products separate as an organic layer above the molten salt. This reaction has been carried out with n-butenes as the reactant and cationic nickel complex catalysts dissolved in organochloroaluminate liquids (127). 

Different metallic acetates [221] have also been used in acetonitrile, which acts not only as a solvent but also as a dehydrating agent to eliminate the effect of any water produced during the reaction. In this way, the thermodynamic equilibrium could be shifted and the yield of CCs improved. By using 1,2-propene glycol as the reactant (100 mmol) and anhydrous zinc acetate (2.5 mmol) as catalyst in acetonitrile (10ml) with a C02 reaction pressure of 10 MPa, at a reaction temperature of 343 K and a reaction time of 12h, the yield of 1,2-propene carbonate was shown to be 24.2% and the conversion of 1,2-propene glycol 38.9%. 

Adsorption of a high-boiling solvent onto a high-surface-area microporous solid yields a supported liquid phase that can be removed from the sohd only by extraction with a second solvent or by distillation at high temperature under vacuum. Under typical reaction conditions, a solid that contains a supported liquid phase looks and behaves as a solid, yet it can dissolve small quantities of a metal complex into the supported phase. One of the first examples of this arrangement was achieved with the immobilization of Rh(CO)(PPh3)2Cl in benzyl butyl phthalate on silica. The supported complex was successfiilly used to effect the gas-phase hydroformylation of propene. 

The hydroxylation of n-hexane on TS-1, in contrast to the epoxidation of propene, reached its maximum rate in the least polar solvent, t-butanol (Table 18.13). Acetonitrile behaved quite similarly to methanol and water [24, 25, 169]. On the assumption that t-butanol was comparable to i-propanol for the effects on adsorption, a clear relationship between rates and partition coefficients was lacking. Considering that hydroxylation and epoxidation involve different active species and mechanisms, a diverse role of the solvent in the two active species could contribute to the differences, whereas the partition coefficients alone could not... 

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