Hydrogenation solvent-free

Usually metal-free phthalocyanine (PcH2) can be prepared from phthalonitrile with or without a solvent. Hydrogen-donor solvents such as pentan-l-ol and 2-(dimethylamino)ethanol are most often used for the preparation.113,127 128 To increase the yield of the product, some basic catalyst can be added (e.g., DBU, anhyd NH3). When lithium or sodium alkoxides are used as a base the reaction leads to the respective alkali-metal phthalocyanine, which can easily be converted into the free base by treatment with acid and water.129 The solvent-free preparation is carried out in a melt of the phthalonitrile and the reductive agent hydroquinone at ca. 200 C.130 Besides these and various other conventional chemical synthetic methods, PcH2 can also be prepared electrochemically.79... 

Diels-Alder reactions of vinylpyrazoles 45 and 46 only occur with highly reactive dienophiles under severe conditions (8-10 atm, 120-140 °C, several days). MW irradiation in solvent-free conditions also has a beneficial effect [40b] on the reaction time (Scheme 4.11). The indazole 48, present in large amounts in the cycloaddition of 45 with dimethylacetylenedicarboxylate, is the result of an ene reaction of primary Diels-Alder adduct with a second molecule of dienophile followed by two [l,3]-sigmatropic hydrogen shifts [42]. The MW-assisted cycloaddition of 46 with the poorly reactive dienophile ethylphenyl-propiolate (Scheme 4.11) is significant under the classical thermal reaction conditions (140 °C, 6d) only polymerization or decomposition products were detected. 

The oxidation of sulfides to the corresponding sulfoxides and sulfones proceeds under rather strenuous conditions requiring strong oxidants such as nitric acid, hydrogen peroxide, chromic acid, peracids, and periodate. Using MW irradiation, this oxidation is achievable under solvent-free conditions and with desired selectivity to either sulfoxides or sulfones using 10% sodium periodate on silica (Scheme 6.34)... 

Taking all criteria into consideration, aqueous two-phase techniques are very sound methods for homogeneously catalyzed processes such as hydrogenations or hydroformylations. Of the various alternatives to the conventional (and solvent-free) processes most progress in terms of ecological impact and economics has been attained by the aqueous biphasic approach (Figure 5.20). 

These Mo catalysts with a C2-tether connecting the phosphine and cyclopenta-dienyl ligand provide an example of the use of mechanistic principles in the rational design of improved catalysts, in this case based on information about a decomposition pathway for the prior generation of catalysts. The new catalysts offer improved lifetimes, higher thermal stability, and low catalyst loading. The successful use of a triflate counterion and solvent-free conditions for the hydrogenation are additional features that move these catalysts closer to practical utility. 

Solvent-free hydrogenations of 1-octene, 2-pentene, cyclohexene, and styrene were carried out with catalyst loadings as low as 0.05 mol.% of the dimer, in some cases with TOF values as high as 6000 IT1 [71]. Total turnover numbers of almost 2000 were obtained in most of these cases. Solvent-free hydrogenation of ketones such as Et2C=0, cyclohexanone, and diisopropyl ketone were also reported at the same temperature and H2 pressure, but with somewhat lower TOFs for the hydrogenation of C=0 compared to C=C hydrogenations. 

Polyphosphazene-based PEMs are potentially attractive materials for both hydrogen/air and direct methanol fuel cells because of their reported chemical and thermal stability and due to the ease of chemically attaching various side chains for ion exchange sites and polymer cross-linking onto the — P=N— polymer backbone. Polyphosphazenes were explored originally for use as elastomers and later as solvent-free solid polymer electrolytes in lithium batteries, and subsequently for proton exchange membranes. 

Coals covering a range of rank downwards from low-volatile bituminous were examined in solvent-free catalytic hydrogenation over the temperature range 300-400°C and for reaction times up to 60 min. The work discussed here specifically Involved four coals which were obtained form the Penn State Coal Sample Bank. These were a subbituminous coal PSOC-1403, and three hvAb bituminous coals, PSOC-1168, PSOC-1266 and PSOC-1510. 

Figure 1. Relationship of H2 consumption and 0/A ratio for hvAb coal, PSOC-1266 (solvent-free hydrogenation 400°C 1% wt sulfided Mo 7MPa H2 cold).

Figure 2. Variation in atomic H/C ratio versus chloroform-soluble yields from subbituminous (PSOC-1403) and bituminous (PSOC-1266) coals (solvent-free hydrogenation 300-400°C 5-180 min 1% wt sulfided Mo 7 MPa H2 cold) (data from refs 7 and 8).

Figure 6. Relations among fluorescence intensity, chloroform-solubles yield and Gieseler placticity for hydrogenated coal (PSOC-1510 solvent-free hydrogenation, 400 C 5-60 min 1% wt sulfided Mo 7 MPa H2 cold.

Figure 7. Comparison of fluorescence spectra of two components in chloroform-solubles fraction with oil and asphaltene fractions of hydrogenated coal (PSOC-1266 solvent-free hydrogenation 400 C 60 min 5% wt sulfided Mo 7 MPa H2 cold).

Figure 5. Effect of coal rank and sulphided Mo catalyst on yield of chloroform-soluble liquids in solvent-free hydrogenation at 400 C.

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