Palladium, on carbon, catalyst

C. Palladium on carbon catalyst (5 per cent. Pd). Suspend 41-5 g. of nitric acid - washed activated carbon in 600 ml. of water in a 2-litre beaker and heat to 80°. Add a solution of 4 1 g. of anhydrous palladium chloride (1) in 10 ml. of concentrated hydrochloric acid and 25 ml. of water (prepared as in A), followed by 4 ml. of 37 per cent, formaldehyde solution. Stir the suspension mechanically, render it alkaUne to litmus with 30 per cent, sodium hydroxide solution and continue the stirring for a further 5 minutes. Filter off the catalyst on a Buchner funnel, wash it ten times with 125 ml. portions of water, and dry and store as in B. The yield is 46 g. 

The palladium on carbon catalysts should be dried at room temperature or the carbon may ignite. These catalysts are first dried in air and then over potassium hydroxide (or calcium chloride) in a desiccator. 

Preparation of 7-amino-3-chloro-3-cephem-4-carboxylic acid To a solution of 750 mg (1 55 mmol) of p-nitrobenzyl 7-amino-3-chloro-3-cephem-4-carboxylate hydrochloride in 20 ml of tetrahydrofuran and 40 ml of methanol was added a suspension of 750 mg of prereduced 5% palladium on carbon catalyst in 20 ml of ethanol and the suspension was hydrogenated under 50 psi of hydrogen at room temperature for 45 minutes. The catalyst was filtered and washed with THF and water. The filtrate and catalyst washes were combined and evaporated to dryness. The residue was dissolved in a water-ethyl acetate mixture and the pH adjusted to pH 3. The insoluble product was filtered and triturated with acetone. The product was then dried to yield 115 mg of 7-amlno-3-chloro-3-cephem-4-carboxylic acid. 

Of this material 1.0 g is dissolved in 150 ml of warm 95% ethyl alcohol. To the solution is added 1.0 g of 5% palladium on carbon catalyst, and the mixture is hydrogenated at room temperature and atmospheric pressure by bubbling hydrogen into it for 3 hours with stirring. The hydrogenation product is filtered. The solid phase, comprising the catalyst and the desired product, is suspended in ethyl acetate and water and adjusted to pH 2 with hydrochloric acid. The suspension is filtered to remove the catalyst. The aqueous phase is separated from the filtrate, and is evaporated under vacuum to recover the desired product, 7-(D-a-aminophenylacetamido)cephalosporanic acid. 

To the reduction mixture was then added 3.5 g of 5% palladium on carbon catalyst and the mixture was hydrogenated under a hydrogen pressure of 50 psi at room temperature for 12 hours. The catalyst was removed by filtration and the filtrate was evaporated to a small volume. The concentrated filtrate was dissolved in diethyl ether and the ethereal solution was saturated with anhydrous hydrogen chloride. The reduction product, 3,4-dimethoxy-N-[3-4-methoxyphenyl)-1 -methyl-n-propy 11 phenethylamine was precipitated as the hydrochloride salt. The salt was filtered and recrystallized from ethanol melting at about 147°C to 149°C. 

Bj Pivaloyloxymethyl D(—)-Ot-aminobenzylpenicillinate. hydrochloride To a solution of pivaloyloxymethyl D(—)-a-azidobenzylpenicillinate (prepared as described above) in ethyl acetate (75 ml) a 0.2 M phosphate buffer (pH 2.2) (75 ml) and 10% palladium on carbon catalyst (4 g) were added, and the mixture was shaken in a hydrogen atmosphere for 2 hours at room temperature. The catalyst was filtered off, washed with ethyl acetate (25 ml) and phosphate buffer (25 ml), and the phases of the filtrate were separated. The aqueous phase was washed with ether, neutralized (pH 6.5 to 7.0) with aqueoussodium bicarbonate, and extracted with ethyl acetate (2 X 75 ml). To the combined extracts, water (75 ml) was added, and the pH adjusted to 25 with 1 N hydrochloric acid. The aqueous layer was separated, the organic phase extracted with water (25 ml), and the combined extracts were washed with ether, and freeze-dried. The desired compound was obtained as a colorless, amorphous powder. 

Hydrogenation of the vinyl ether (49) in ether solution in the presence of palladium-on-carbon catalyst afforded 6-deoxy-2,3-0-isopropyli-dene-/ D-arafemo-hexulofuranose (53) (17) as the only product. As with the vinyl ethers (39) and (43), reduction of the double bond occurred from the least hindered side of the molecule, namely opposite to the isopropylidene ring. 

It is well known that palladium on carbon catalysts are poisoned by hydrogen cyanide and thiol products or hydrogen sulfide (6). Therefore, it was of interest to investigate the reduction of perfluoroalkyl thiocyanates as a function of tin concentration, keeping the concentration of palladium and reaction conditions constant. Figure 15.1 delineates the % conversion vs. Sn/Pd ratio, under the same reaction conditions of 175°C, 700 psig H2 for 2 hours with 5% Pd on carbon catalysts in ethyl acetate solvent at a 1000 1 substrate catalyst molar ratio. The increase in... 

Similarly, 1,2-cyclononadiene in methanol with 10% palladium on carbon catalyst gave cis-cyclononene122. The cis isomer is not necessarily the primary product of allene hydrogenation, since the initially formed trans isomer is rapidly isomerized under the reaction conditions. Bond and Sheridan showed that allene resembles acetylene in its ease of hydrogenation123. They suggested that it is selectively adsorbed and held more strongly by the catalyst than 1-propene. Allene was selectively hydrogenated with Pd, Pt and Ni in the presence of 1-propene without its further reduction. 

As outlined above a purity of only 99.5% is not sufficient for a polymer feedstock and the mono-acid intermediate has to be removed either by oxidation under more forcing conditions (Mitsubishi) or reduction (Amoco). In the Amoco process (not shown) the crude di-acid is dissolved in water (275 °C) (15 % weight) and hydrogenated over a palladium on carbon catalyst. The intermediate 4-formylbenzoic acid is hydrogenated to 4-toluic acid which has a much higher solubility and does not cocrystallise with terephthalic acid. The solution is carefully cooled while the product crystallises and the by-product remains in the water. The final content of 4-formylbenzoic acid is as low as 15... 

The a-substitution product from oxidation of methylbenzenes in acetic acid can be eliminated by electrochemical hydrogenolysis at the cathode. An undivided cell is used and a palladium on carbon catalyst is suspended in the medium. The necessary hydrogen is generated by reduction of protons at the cathode. In this way, the... 

Tetracaine Tetracaine, the 2-diethylaminoethyl ester of 4-butylaminobenzoic acid (2.1.6), is also structurally analogous to procaine, in which the amino group of the benzene ring is replaced by a butylamine radical. The methods for its synthesis are the same as the above-mentioned methods for procaine or chloroprocaine, with the exception of using 4-butylaminobenzoic acid in place of 4-aminobenzoic acid. There is also a proposed method of synthesis that comes directly from procaine (2.1.1). It consists on its direct reaction with butyric aldehyde and simultaneous reduction by hydrogen using a palladium on carbon catalyst [6]. 

Loperamide Loperamide, l-(4-chlorophenyl)-4-hydroxy-iV,iV-dimethyl-a,a-diphenyl-l-piperidinebutyramide (3.1.55), proposed here as an analgesic, is synthesized by the alkylation of 4-(4-chlorophenyl)-4-hydroxypiperidine (3.1.50) using iV,A-dimethyl(3,3-diphenyltetrahydro-2-furylidene)ammonium bromide (3.1.54) in the presence of a base. The 4-(4-chlorophenyl)-4-hydroxypiperidine (3.1.50) is synthesized by reacting l-benzylpiperidine-4-one (3.1.48) with 4-chlorophenylmagnesiumbromide, followed by debenzylation of the product (3.1.49) by hydrogenation using a palladium on carbon catalyst. 

Methamphetamine Methamphetamine, (+)-N-a-dimethylphenylethylamine (8.1.2.3), can be synthesized by the reduction of ( )-ephedrine by hydrogen using a palladium on carbon catalyst [8]. 

Tetracycline Tetracycline, 4-dimethylamino-l,4,4a,5,5a,6,ll,12a-octahydro-3,6,10,12,12a-pentahydroxy-6-methyl-l,ll-dioxo-2-naphthacencarboxamide (32.3.3), is synthesized by reducing chlorotetracycline with hydrogen using a palladium on carbon catalyst. However, it can be synthesized microbiologicaUy using the actinomycete Streptomyces viridifaciens, as well as a certain mutant S. aureofaciens [206-214]. 

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