Hydrogen transfer over palladium

Reductions of nitronitriles situated to favor interaction are apt to involve both functions (S4,93). Hydrogenation of o-nitrobenzonitrile over either palladium or platinum gave o-aminobenzamide (78), with the amide oxygen transferred from the nitro group (66). On the other hand, l-amino-2-cyanonaphthalene gave the amino amide on reduction over Pt02, but the amino nitrile over palladium (82). 

Disproportionation is a special form of double bond migration in which the double bond is transferred from one molecule to another. Reactions of this type are especially liable to occur over palladium, and for this reason palladium sometimes is best avoided in olefin hydrogenation when the double bond is contained in an incipient aromatic system. Disproportionation activity in the hydrogenation of cyclohexene (and presumably other incipient aromatic systems will follow the same order) decreases with the metal in the order palladium >> platinum > rhodium (16). An example of the complication that can be caused by disproportionation during hydrogenation is found in the attempted reduction of... 

Johnson et al. (J3) suggest the use of the hydrogenation reaction of a-methylstyrene with a suspended palladium-alumina catalyst as an alternative test system to establish the effect of agitation variables on liquid-phase mass-transfer coefficients. They found the over-all hydrogen transfer coefficient to vary in a complex manner with agitator speed, and to increase with the 0.6 power of the superficial gas velocity up to a point beyond which the transfer showed no further change with gas velocity. 

Dehydrogenation. Newman and Lednicer found rhodium-alumina to be an effective catalyst for the transfer of hydrogen from hexahydrohexahelicene (1) to benzene to produce hexahelicene (2). Similar exchange over palladium catalyst... 

A Mdssbauer investigation of the reduction of iron oxide (0.05 wt % Fe) and iron-oxide-with-palladium (0.05 wt % Fe, 2.2 wt % Pd), carried upon 7 -Al203, reveals that supported ferric ion alone, under hydrogen, yields ferrous ion only at 500—700 °C this reduction takes place at room temperature with the bimetallic catalyst and proceeds to form a PdFe alloy at 500 °C. Similar effects are found in reduction by carbon monoxide, which yields iron-palladium metal clusters at 400 °C. The view is taken that migration over T7-A1203 is not involved but that activated hydrogen transfers only at bridgeheads on the contact line between the metal and iron oxide. 

Coke formation during acetylene hydrogenation over palladium catalyst could promote hydrogen transfer to acetylene and ethylene adsorbed molecules leading to a decrease in ethane selectivity and an increase in ethylene loss. 

The crude enamine is dissolved in 450 ml. of ether, and the solution is transferred to a 1-1. three-necked flask equipped with a sealed stirrer, a 250-ml. dropping funnel, and a two-necked adapter fitted with a calcium chloride tube and a thermometer immersed in the solution. A solution of 71-76 g. (0.85-0.90 mole) (Note 5) of methyl propiolate (Caution Methyl propiolate is a severe lachrymator and should he handled only in the hood.) in 150 ml. of ether is added dropwise. During the addition the temperature of the mixture is maintained at 25-30° by periodic cooling of the reaction flask in a dry ice-acetone bath. When the addition is almost complete, a white solid begins to separate. The mixture is stirred at 25-30° for an additional hour, cooled to 0°, and filtered to remove the solid. This is dissolved in 700 ml. of 6% hydrochloric acid (Note 6), the acidic solution is warmed at 55-60° for 1 hour, and the mixture is cooled and extracted with two 100-ml. portions of ether. The ether is removed on a steam bath, and the residue of crude methyl 10-oxocyclodec-2-ene-l-carboxylate is dissolved in 300 ml. of methanol and hydrogenated over 5 g. of 5% palladium-on-alumina catalyst at 40 p.s.i. pressure and room temperature. 

Rhodium(III) complexes [e.g. (i-Pr,P)2Rh(H)Cl2] in the presence of quaternary ammonium salts are excellent catalysts for the hydrogenolysis of chloroarenes under mild conditions [5] other labile substituents are unaffected. Hydrodehalogenation of haloaryl ketones over a palladium catalyst to give acylbenzenes is also aided by the addition of Aliquat [6]. In the absence of the phase-transfer catalyst, or when the hydrogenation is conducted in ethanol, the major product is the corresponding alkyl-benzene, which is also produced by hydrodehalogenation of the halobenzyl alcohols. 

Procedure. Hexene (Phillips Petroleum, pure grade, 99% ) was dried over sodium and filtered through a layer of A1203 (Merck, Aktivitatsstufe I) to remove peroxides. The alkene was dissolved in benzene (Baker analyzed) dried over sodium, and the reaction mixture was transferred to the reactor. The complex was placed in the jar and the system was closed. To remove all air dissolved in the liquid phase, the system was evacuated and flushed with hydrogen purified for possible 02 by passing a deoxo catalyst (palladium), under a pressure of 10 atm, and then passing a molecular sieve to remove H20 3 to 5 times under stirring. Adjustments permitted stabilization of the pressure in 1-2 min where the reaction rate was to be measured. 

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