Solvents heterogeneous hydrogenation

Apart from the chemical effects of solvent as hydrogen donor, being heterogeneous systems, an important role of solvent is to provide appropriate reaction sites on the balance of solvent interactions with base polymer and growing graft chain. For the study of solvent effects, AM is not an adequate monomer since it is scarcely soluble in non-polar solvents. Instead, acrylic acid(AA) was employed and photografting was conducted as shown in Figure 8. 

We have found that the development of such a process is more demanding than a classical heterogeneous hydrogenation reaction because so many additional reaction parameters are involved. The use of statistical optimization methods can be of advantage and in addition, rigorous quality control (substrates, catalyst, solvent etc.) is necessary to garantce reproducibility. 

For certain metal systems, the chemical properties of bimetallic DENs include selective extraction from the dendrimer interior into organic solvents. Catalytic properties include homogeneous hydrogenation catalysis heterogeneous hydrogenation and oxidation catalysis have also been examined. Homogeneous hydrogenation studies indicate that... 

The use of dense gases for heterogeneous hydrogenations is attractive given the ease of product purification and the significantly enhanced rates. " Other solvent... 

There are numerous studies concerning solvent effects on selectivity in heterogeneous hydrogenations (1). Similar effects are observed in oxidation or acid catalysed reactions. In addition, molecular sieves can be viewed as solvents for the species that they contain (2) and therefore, even in vapor phase reactions, modifications of activity or selectivity can be attributed to solvent effects. 

The supported nanoparticle catalyst system was used for solvent-free hydrogenation reactions of cydohexene, 1-hexene, and 1,3-dicydohexadiene, respectively, and compared with a similar biphasic ionic liquid system and with a heterogeneous supported nanocatalyst (Table 5.6-6). 

The classical Chichibabin reaction is normally to be carried out on heating (>100°C) in a media, which is inert towards sodium amide (aromatic hydrocarbons, AT,iV-diaIkylanilines, a mineral oil), or without any solvent at all. The aminatirm under these heterogeneous conditions is supposed to proceed on the surface of sodium amide particles, which are insoluble in all abovementioned solvents. Vigorous hydrogen gas evolution and intense red color are typical indicators of the reaction progress. 

G. (2004) Pd Nanoparticles immobilized on molecular sieves by ionic liquids heterogeneous catalysts for solvent free hydrogenation. Angew. Chem. Int. Ed., 116, 1421-1423. 

Pd-catalyzed heterogeneous hydrogenation may be carried out without any solvent. In many cases, however, the use of solvents is desirable or even necessary. A wide range of solvents ranging from nonpolar hydrocarbons, (e.g., hexane) to highly polar water, HOAc, MeOH, EtOH, and DMF as well as various others of intermediate polarity, such as THF, dioxane, EtOAc, acetone, and MeCN, have been used. 

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