A selective hydrogenation

Nickel Arsenate. Nickel arsenate [7784-48-7] Ni2(As0 2 8H20, is a yellowish green powder, density 4.98 g/cm. It is highly iasoluble ia water but is soluble ia acids, and decomposes on heating to form As20 and nickel oxide. Nickel arsenate is formed by the reaction of a water solution of arsenic anhydride and nickel carbonate. Nickel arsenate is a selective hydrogenation catalyst for iaedible fats and oils (59). 

The first reactor is a selective hydrogenation reactor, which product is split into LCN and HCN. The LCN cut is substantially S-free and could be directed to etherification... 

Hydrisom A selective hydrogenation process offered by Phillips Petroleum. It is used in Argentina to upgrade C4 olefins before alkylation. 

KLP [Dow K Catalyst liquid phase] A selective hydrogenation process for removing acetylenes from cmde C4 hydrocarbons from ethylene cracking, with no loss of butadiene. The catalyst is based on either copper metal or alumina. Developed by Dow Chemical Company and first commercialized at its plant in Temeuzen, The Netherlands. The KLP licensing business was sold to UOP in 1991. 

A selective hydrogenation catalyst for alkynes was obtained with the PdCl2 complex of such immobilized pyridine. Diphenylacetylene was hydrogenated under 0.44 MPa H2 in ethanolic solution. At full conversion, the following selec-tivities were observed cis-stilbene 80.7%, trans-stilbene 16.1%, and only 3.2% 1,2-diphenylethane [90]. 

The reaction is rendered irreversible by hydrogenating the ethylene with a selective hydrogenation catalyst. 

A selective hydrogenation of conjugated dienes was carried out with a Pd complex which was preactivated with oxygen. Besides the conversion of dienes with good selectivity (98%), diene esters, ketones and nitro compounds were also hydrogenated with fairly good selectivities (equation 9)29. 

The first manufacturing route of the GEM side-chain relied on a-cyanoketone 125 however, the number of chemical steps from 125 to the final side-chain was reduced by one step (Noh et ah, 2004a). The sequence began with a selective hydrogenation with Raney nickel followed by double bond migration to enamine 131 (Scheme 4.25). The amino functionality of 131 was then monoprotected, and the double bond was reduced under hydrogenation conditions to afford pyrrolidine-3-one 133. Treatment of 133 with methoxylamine yielded methoxyoxime 129. Deprotection of the carbamate functionality was achieved with methanesulfonic acid to afford the C7-side-chain as the bis-methansulfonate salt. 

The proposed mechanism (Scheme 1) involves the mixed-valence compounds [Rh2" " ( Ji-cap)4(OH)] and [Rh2 (p.-cap)4(OOt-Bu)] formed from the homolytic cleavage of t-BuOOH. The t-BuOO radicals in the medium promote a selective hydrogen abstraction from the alkene to give the allylic alkenyl radical. This species traps the peroxide in [Rh2 (p.-cap)4 (OOt-Bu)] to produce the alkenyl hydroperoxide, which rapidly decomposes to the isolated products, thus regenerating the catalyst. 

Similar function can also be applied for the selectivity as well. In these formulas the bo and bi parameters can be determined if two corresponding d and a values are available. These values are usually arbitrary selected by the researcher, d can have values only between 0 and 1. Obviously, the higher the value of d the better the catalyst performance. For example, the acceptable d value (0.4) in a selective hydrogenation can be adjusted to 60 % of conversion, whereas the excellent d value (0.9) belongs to 80 % conversion. This selection always depends on the type of reaction investigated and the researcher itself The combined desirability function (D) is obtained by the determination of the geometrical average of d values calculated for conversion and selectivity ... 

A photography of a selective hydrogenation unit designed by the Institut Fran9ais du Petrole is shown in Figure 5.2-43 [62]. 

The selective hydrogenation of organic compounds which contain a C=C and a C=0 double bonds into unsaturated alcohols is a very challenging subject from an industrial and from a fundamental point of view. Recent studies have shown that some catalytic systems are suitable for a selective hydrogenation in particular bi or trimetallic supported catalysts but no clear conclusion could be drawn concerning the mechanism and the respective effects of the support and the alloying (ref.1). 

The product gases are cooled and compressed (4) to facilitate separation of products and by-products. The suction-side of the compressor ensures that upstream units operate at a low pressure. The product gases are first dried (5) and the cooled product passed to a cryogenic separator (6) which removes hydrogen from the system. Some is recycled with the other portion passed-on for other uses. A selective hydrogenation unit (7) removes dienes and acetylenes. A final distillation train removes light hydrocarbon (C2-), propylene product, propane, which is recycled, and a C4 by-product. 

Aminobenzonitrile is prepared by reduction of 3-nitrobenzonitrile by sodium disulfide in aqueous suspension (63%). This reagent causes some hydrolysis of the cyano group. A selective hydrogenation of the more reactive nitro group in the presence of the cyano group can also be done, e.g., in the preparation of p-aminobenzyl cyanide (7S>%). ... 

The extent of double bond isomerization also varies with the nature of the catalyst. The degree of isomerization over metal catalysts usually decreases in the order Pd > Ni > Rh > Ru > Os =Ir =Pt.5.6 The extensive double bond isomerization observed with palladium and, to some extent, with nickel catalysts can be attributed to the formation of the adsorbed 7t-allyl species with these catalysts. While double bond isomerization may not be important in a routine alkene hydrogenation, it may influence a selective hydrogenation because the isomerized olefin can have different adsorption characteristics from those of the... 

The use of copper chromite at 40°C and atmospheric pressure was not very effective for selective carbonyl group hydrogenation. Unsaturated alcohols were produced from unsaturated aldehydes in low yields at low conversions and not at all from methyl vinyl ketone. 28 With unconjugated, unsaturated aldehydes, copper chromite is effective as a selective hydrogenation catalyst. Hydrogenation of 46 at 140°-160°C and 200 atmospheres gave better than 70% of the diene diol, 47. Increasing the temperature to 240°C resulted in the complete saturation of 46 (Eqn. 18.28). 29... 

A selective hydrogenation of diacetyl to acetoin can also be carried out in an electrolytic cell using a cathode with a high hydrogen overvoltage [83], It is recommended to start with a solution consisting of... 

The environmental impact of the cyclohexane oxidation could also be reduced. An alternative is to start from benzene and make a selective hydrogenation to form cyclohexene. Ru-based supported catalysts working in the liquid phase and in the presence of a co-catalysts such as Zn (Asahi Chemical Industry process) are selective in the reaction, with yields up to about 60% [247], but with cyclohexane as the main by-product. Cyclohexene is hydrated in the liquid phase with an MFI zeolite as catalyst at moderate temperature (100-130 °C). This reaction is very selective (>99%). This route was primarily developed for the synthesis of adipic acid, but could be used also to reduce the number of products and separation costs in the production of cyclohexanone. 

CAMP was prepared by a selective hydrogenation reaction of 10 (Fig. 13) using a heterogeneous rhodium-on-carbon catalyst. It was important to monitor the reaction... 

Haptophilicity of the hydroxyl function may account for a selective hydrogenation. A difference of strain is responsible for the preferred reduction of one of two similarly substituted double bonds in 12 ... 

The influence of reactant pressures upon selectivity can be easily explained by the above mechanism the changes of selectivity essentially concern the complementary formations of unsaturated alcohol and hydrocarbons which i the re uk of competitive 1,2 and 1,4 additions of hydrogen. An increase of the partial pressure of prenal on the initially saturated surface, is likely to induce a change of the adsorption configuration of the molecule in favor of a 1,2 di-o adsorption and consequently of a selective hydrogenation of the C=0 bond. 

---