Platinum-on-carbon, catalyst

Du Pont uses a Hquid-phase hydrogenation process that employs a palladium —platinum-on-carbon catalyst. The process uses a plug-flow reactor that achieves essentially quantitative yields, and the product exiting the reactor is virtually free of nitroben2ene. 

Ignition occurred when methanol was charged into an unpurged autoclave containing platinum-on-carbon catalyst. 

According to the figure below, reacting 2,6-dimethylanilme with the acid chloride of pyridine-carboxylic acid first gives the 2,6-xylidide of a-picoUnic acid (2.2.4). Then the aromatic pyridine ring is reduced to piperidine by hydrogen in the presence of a platinum on carbon catalyst. 

The resulting 2,6-xylidide a-pipecolinic acid (2.2.5) is methylated to mepivacaine using formaldehyde with simultaneous reduction by hydrogen in the presence of platinum on carbon catalyst [15]. 

Labetalol Labetalol, 2-hydroxy-5-[l-hydroxy-2-[(l-methyl-3-phenylpropanol)amino)] ethyl] benzamide (12.1.12) is synthesized by the WaUcylation of iV-benzyl-Af(4-phenyl-2-butyl)amine 5-bromacetylsalicylamide and forming aminoketone (12.1.11), which is further debenzylated by hydrogen using a palladium-platinum on carbon catalyst into labetalol (12.1.12) [28-30]. 

Bragin and co-workers found that over platinum-on-carbon catalysts, both paraffins and alkylaromatics follow zero-order kinetics. Activation energy for C5-dehydrocyclization in which the new bond is formed between two sp3 hybridized atoms is substantially less than the activation energy of cyclization in which the new bond is formed between one sp3 hybridized atom and the sp2 hybridized carbon atom of the aromatic ring. Over one batch of platinum-on-carbon catalyst, Bragin and co-workers obtained 20 kcal/mol and 27.5 kcal/mol activation energies for the dehydrocyclization of paraffins and monoalkylbenzenes, respectively (6). Another batch of platinum on carbon (which differed only in some minor details of preparation from the first batch), gave 14 kcal/mol for the cyclization of l-methyl-2-ethylbenzene and isooctane, and 29 kcal/mol for the cyclization of secondary butylbenzene ( ) (Fig. 1). 

Over platinum-on-carbon catalyst at relatively low temperature (310°C), C5-cyclization of alkylbenzenes probably proceeds by direct closure of the ring between the carbon atoms of the side-chain and the benzene ring, bypassing dehydrogenation to olefins (25-27). However, at higher temperatures and on platinum-alumina or platinum-on-silica C5-dehydro-cyclization could involve olefinic intermediates (7,13, 28). 

C6-dehydrocyclization does not (50). As a consequence, over nonacidic platinum catalysts above 400°C, C6-dehydrocyclization predominates over C5-dehydrocyclization (27). Furthermore, the phenanthrene/anthracene ratio is independent of catalyst acidity (52). The effect of reaction temperature is, however, very interesting. Over platinum-on-carbon catalyst between 350°C and 400°C, more anthracene is formed than phenanthrene. Above 450°C phenanthrene is the main product (55). Phenanthrene is also the main product over chromia-alumina between 360°C and 440°C whereas, as seen above, anthracene is formed in this temperature range over platinum-on-carbon catalyst (54). 

There appear to be two C5-dehydrocyclizations over platinum-on-carbon catalyst. Activation energy differences suggest that the reaction involving an sp2 and an sp3 carbon atom (a cyclization in which the new bond is formed between an aliphatic and an aromatic carbon atom) is different from cyclizations involving two sp3 carbon atoms (in which the new bond is formed between aliphatic carbon atoms of two side-chains). 

P. C. C. Smits, B. F. M. Kuster, K. Van der Wiele, and H. S. Van der Baan, The selective oxidation of aldoses and aldonic acids to 2-ketoaldonic acids with lead-modified platinum-on-carbon catalysts, Carbohydr. Res., 153 (1986) 227-235. 

H. E. van Dam, A. P. G. Kieboom, and H. van Bekkum, Platinum/carbon oxidation catalysts. 7. Glucose-1-phosphate oxidation on platinum-on-carbon catalysts side-reactions and effects of catalysts structure on selectivity, Reel. Trav. Chim. Pays-Bas, 108 (1989) 404 107. 

Rimantadine may be also prepared by refluxing of the 1-adamantylmethylketone and ammonium formate in diethylene glycol or by hydrogenization of 1-adamantylmethyl ketoxime in the presence of a platinum on carbon catalyst at a room temperature and pressure. 

A solution of 4.7 g. of frcms-chlorohydrido-bis(triethylphosphine) platinum(II) in 25 ml. of ethanol is added to a stirred, chilled suspension of 2.1 g. of p-fluorobenzenediazonium tetra-fluoroborate in 50 ml. of ethanol, as in Sec. C. The mixture is then allowed to warm to room temperature over a period of 20 minutes. A 0.10-g. portion of 5% platinum-on-carbon catalyst is added, and hydrogen is bubbled through the mixtime for 2 hours. The mixture is cooled to 0°C. and is filtered to collect... 

Figure 3a. Platinum on Carbon catalysts in 190 °C phosphoric add. Compilation of specific activities for oxygen reduction versus platinum crystallite separation from Watanabe7 et al. M Giordano et al. —maximum values only24 ] Buchanan et aL 8[0] and Giordano et al. 15 16[D]. Function of upper tine is abestfittothe Buchanan values and the lower tine is a best fit to the Giordano values, (a) Data for crystallite separations up to 325 mn. (b) Data below 60 nm crystallite separations.

The oxidation of D-glucose to D-gluconic acid is also readily carried out by use of a platinum-on-carbon catalyst (a substantially more-active catalyst) in the presence of an equivalent of alkali. With the aid of the same catalysts, n-galactose, D-mannose, D-xylose, and L-arabinose can be converted to the corresponding aldonic acids. By this method, the pentoses are oxidized more rapidly than the hexoses. A reaction time of only 45 minutes is required at 22°, whereas the oxidation of D-glucose is complete only after five hours. 

The application of more-severe reaction-conditions, such as a reaction temperature of 50° with a platinum-on-carbon catalyst, results in attack on the primary hydroxyl group at C-6 thus, a 54% yield of D-glucaric acid is obtained from D-glucose. Aldoses are selectively attacked at the carbonyl group at room temperature, whereas, at higher temperatures, the hydroxyl group on C-6 is also oxidized, with the production of a glycaric acid. 

L-Ascorbic acid, the oxidation of which is catalyzed by such metal ions as iron or copper, is very readily oxidized under very mild conditions in the presence of a platinum-on-carbon catalyst. At 0°, it is transformed into dehydro-L-ascorbic acid by exposure to air for 80 minutes. The reaction is quantitative and affords no substantial amount of byproduct. ... 

Long reaction-times, 7 to 8 days at 55 to 60°, were required for oxidizing methyl 2-deoxy-a-D-am5fno-hexopyranoside to the corresponding uronic acid, using a platinum-on-carbon catalyst according to the method of... 

Under analogous conditions, galactitol is converted to DL-galactose, isolated as the phenylhydrazone in 30% yield. In the presence of 2 moles of sodium hydrogen carbonate per mole and a platinum-on-carbon catalyst at 61°, galactitol is readily oxidized to galactaric acid. ... 

Weygand and Bergmann investigated the oxidation of certain derivatives (known as Amadori products) of l-amino-l-deoxy-n-fructose. The oxidation of 1-deoxy-l-p-toluidino-n-fructose in 2 V ammonium hydroxide at 50° in the presence of a platinum-on-carbon catalyst led to the degradation of the compound to n-arabinonic acid, presumably according to the following sequence. 

Both (iea axial hydroxyl groups which would be expected to be oxidized at the same rate, the same oxidation products being formed in each case. Thus, the catalytic oxidation of deairo-inositol (37) gives pure (+)-vibo-inosose (38), and that of lewo-inositol (42), pure (—)-w o-inosose (43). The oxidations are carried out at 85-90°, in the presence of a platinum-on-carbon catalyst, by passing air through the reaction mixture. The bacterial oxidation of each of these inositols leads to a diketone. 

Catalysts suppliers as Johnson-Mattey (ref. 12), A.G. Degussa (ref. 13) or Heraeus provide special platinum on carbon catalysts at industrial scale. 

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