Selectivity hydrogen chloride effect

The purpose of the present work is to study the precursor (metallic chlorides or carbonyl compounds), particle size and support (silica, magnesia and titania) effects in the selective hydrogenation of carvone employing rhodium as active metal. 

Table 1 Selected diastereoisomers and their corresponding hydrogen chloride salt melting points for agents effective as ORLj receptor inhibitors. Optical activities for entries 5 and 6 provided by author...

In view of its industrial importance, a number of homogeneous catalysts have been examined for use in selective hydrogenations of nitroalkanes to amines.Tris(triphenylphosphine)ruthenium(II) chloride is particularly effective. The mechanism of this hydrogenation is known to involve nitronate anion formation. ... 

The effect of trace contaminants on the reaction has been investigated carefully. All uncondensed effiuent gases were recycled to the reactor, except for the amounts present in the streams taken off for analysis or flashed upon depressuring of the organic phase. Aqueous phase from the separator containing the water soluble by-products has been used as the water feed to the reactor. Hydrogen chloride containing chlorinated hydrocarbons and acetylene was used in all operations. In addition, certain possible impurities were tested for their effect on the kinetics and selectivity of the process. Paraffins, carbon monoxide, sulfide, carbon dioxide, alkali, and alkaline earth metals were found to be chemically inert. Olefins, diolefins and acetylenic compounds are chlorinated to the expected products. No deleterious effects of by-product recycle were observed even when some of the main by-products were added extraneously. 

Precipitation or coprecipitation methods are also often used. Suh et al. [40] analyzed the effect of the oxygen surface functionalities of carbon supports on the properties of Pd/C catalysts prepared by the alkali-assisted precipitation of palladium chloride on carbon supports, followed by liquid-phase reduction of the hydrolyzed salt with a saturated solution of formaldehyde. They observed that the metal dispersion increased with increasing amount of oxygen surface groups. Nitta et al. [41] also used a deposition-precipitation method, with sodium carbonate and cobalt chloride or nitrate, to prepare carbon-supported Co catalysts for the selective hydrogenation of acrolein. 

As electronic effects of additives have been claimed for the selective hydrogenation of a,p unsaturated aldehydes [9-14], the influence of metal salts was examined in the hydrogenation of acrolein with Co/silica-alumina catalysts. As shown in Table 2, a small amount of Fe (II or III) chloride added into the hydrogenation mixture exerted a favourable effect on the selectivity to allyl alcohol. TTie other metal chlorides examined were less effective on the catalyst performance. Therefore, not chloride anion but Fe cation seems to have positive effects on the hydrogenation of carbonyl group as illustrated by Richard et al.[12j. 

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