Palladium, calcium carbonate, catalyst hydrogenation

C. [18]Annulene. In a 300-ml. conical flask fitted with a side arm (with a closed stopcock) and a 3.5-cm. Teflon -coated magnetic stirring bar is placed 1 g. of a 10% palladium-calcium carbonate catalyst (Note 20) and 30 ml. of benzene (Note 10). The flask is attached to an atmospheric pressure hydrogenation apparatus, and the air in the system is replaced by hydrogen by evacuating the flask and refilling with hydrogen three times. The catalyst suspension is stirred until no more gas is absorbed. One-third (390 mg., determined spectroscopically)... 

The use of catalytically activated hydrogen as an analytical tool for the dehalogenation of organic compounds was discovered by Busch and Stowe (106), who used a palladium-calcium carbonate catalyst. Later, Kelber (107) reported a similar procedure, using a reduced nickel catalyst. Whitmore and Revukas (108) observed that, in the reductive splitting of substituted azo compounds with hydrogen in the presence of Raney... 

Aldehydes can be obtained homogeneously from ozonides by reductive cleavage, which can be effected either by zinc in glacial acetic acid or by catalytic hydrogenation of the ozonide118,119 in the presence of a 1 19 palladium-calcium carbonate catalyst.120 Adipdialdehyde has thus been obtained from cyclohexene in 60-70% yield 121... 

It is very well documented that the carbon-carbon triple bonds (e.g., alkynes) on catalytic hydrogenation gives the completely reduced product, viz. alkanes. Alkynes can also be reduced partially to give z-alkenes by palladium-calcium carbonate catalyst which has been deactivated (partially poisoned) by the addition of lead acetate (Lindlar catalyst) or Pd-BaSO deactivated by quinoline. The lead treatment poisoned the palladium catalyst, rendering it less active and the reaction is more selective. Some examples are given (Scheme 98). 

A benzene solution of the cyclic dimer 61 when refluxed with a saturated solution of t-BuOK in BuOH gave a red solution of the bisdehydro[20]annulene 63 [62]. The cyclic trimer 62 was rearranged similarly to tridehydro[30]annulene 64. Both species show characteristic UV-vis spectra [62]. The bisdehydro[20]annulene was partially hydrogenated in benzene solution over a Lindlar catalyst (quinoline-poisoned palladium calcium carbonate catalyst). This procedure led to the [20]an-nulene 65. Similarly, the reduction of tridehydro[30]annulene 64 with Lindlar catalyst yielded the [30]annulene 66 [62]. 

The reduction of quinazolinone 242 with hydrogen at 3 atm in the presence of a palladium-on-calcium-carbonate catalyst furnished perhydroquin-azolinone 243. The stereochemistry of 243, with four chiral centers, was not investigated (70M1767). 

Methyl />-acetylbenzoate has been prepared by the esterification of -acetylbenzoic acid with methanol in the presence of hydrogen chloride,6 by the hydrogenation of methyl -trichloro-acetylbenzoate in the presence of a palladium on calcium carbonate catalyst,6 and by the air oxidation of methyl / -ethyl-benzoate.4... 

A solution of 20 g of desoxycorticosterone in 190 ml of absolute ethanol was stirred in an atmosphere of hydrogen in the presence of 1.68 g of 25% palladium on calcium carbonate catalyst. After 20 hours, approximately 1 molar equivalent of hydrogen had been absorbed and hydrogen uptake had ceased. The catalyst was removed by filtration and the filtrate evaporated in vacuo to yield 20 g of nearly pure product, MP 135°C to 140°C. The crude product was demonstrated to be free of starting material by paper chromatography. A highly purified product was obtained by recrystallization from acetone-water with cooling in an ice bath, yield 14.5 g, MP 152°C to 154°C. The product was characterized by analysis and by absence of ultraviolet absorption. 

Both objectives have been met by designing special hydrogenation catalysts The most frequently used one is the Lindlar catalyst, a palladium on calcium carbonate combi nation to which lead acetate and quinoline have been added Lead acetate and quinoline partially deactivate ( poison ) the catalyst making it a poor catalyst for alkene hydro genation while retaining its ability to catalyze the addition of H2 to the triple bond... 

Lindlar catalyst (Section 9 9) A catalyst for the hydrogenation of alkynes to as alkenes It is composed of palladium which has been poisoned with lead(II) acetate and quino line supported on calcium carbonate... 

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