CATALYTIC HYDROGENATION AUTOCLAVES

See other UNIT OPERATION OR UNIT PROCESS INCIDENTS See also CATALYTIC HYDROGENATION AUTOCLAVES... 

See other unit operation or unit process incidents See also catalytic hydrogenation autoclaves... 

The use of more complex or more costly articles of equipment, such as catalytic hydrogenation apparatus, autoclaves, polari-meters, ultraviolet absorption spectrometers, etc., has not been described, because the type of such apparatus employed indifferent laboratories varies considerably, and students must be taught the use of their own laboratory equipment. 

In continuation of a previous work (1), catalytic hydrogenation of cinnamaldehyde has been studied in slurry phase using a high-pressure autoclave. A series of carbon powder (CP)-supported Pt catalysts with widely varying Pt dispersion and Pt location on the support has been used in the study. The purpose has been to find out how the location of the metal on the support and its dispersion affect the two parallel reaction paths, namely the hydrogenation of the C=0 and C=C bonds. 

Studies initiated by the author in CSIRO (13) seek to throw light on the role of the various macerals by studying the conversion, under catalytic hydrogenation conditions, in Tetralin as vehicle, of maceral concentrates from a high volatile bituminous coal. Some preliminary results, given in Fig. 3, show conversions as almost complete for the hand picked vitrain (>90% vitrinite) from a high volatile bituminous coal (Liddell seam N.S.W., 83.6% carbon and 43% volatile matter both expressed on a dry ash-free basis). However, it is evident that the conversion of the whole coal increases rapidly with increase in hydrogen pressure (under otherwise similar conditions - batch autoclave, 4h. 400°C). 

Catalytic hydrogenation on 400 g scale at 34 bar under excessively vigorous conditions (250°C, 12% catalyst, no solvent) caused the thin autoclave without bursting disk to rupture [1]. Under more appropriate conditions the hydrogenation is safe [2], See other catalytic nitro reduction processes... 

Harak, J., Stud. Surf. Sci. Catal., 1986 (27, Catal. Hydrog.), 578-611 Measures and equipment needed for safe control of autoclaves used for laboratory, pilot plant, or industrial scale catalytic hydrogenation are discussed, including the need for early recognition of onset of hazardous conditions. 

Catalytic hydrogenations were carried out in a 250mL, mechanicaly stirred autoclave (1250 rpm), under 5MPa hydrogen pressure at room temperature. The reactor was filled with 2.5 mmol of substrate 1 dissolved in 130 mL of alcoholic solvent, 0.07 mmol of rhodium, and, optionally, EDCA with a molar ratio EDCA/Rh of ca. 3.5, except otherwise stated. Samples of the reaction medium were analysed by gas chromatography (J W DB1701 column). Initial rates were determined and the diastereoisomeric excess of the cis products 2 and 3 was calculated as d.e. (%) = l(%2 - %3) / (%2 + %3)l x 100. 

The solution of maleic acid after being decolorized may be used directly for the production of malic acid by hydrolysis, or of succinic acid by hydrogenation. To form malic add the solution is heated in aluminum-bronze autoclaves. This alloy is not suitable for the absorber but may be used here due largely to the absence of oxygen. l or small scale succinic add production the electrolytic reduction method of Norris is more useful, but for large scale operation catalytic hydrogenation has been found to be desirable. 

New equipment as well as new chemical and analytical methods are necessary to accommodate today s research needs. Scheme 1 summarizes the practical synthesis of a-1 agonist ABT-866 (1-4), which includes a catalytic hydrogenation. In the preparation ABT-866, we were required to rapidly evaluate an array of catalysts and conditions for a hydrogenation step in the synthesis of this clinical candidate. The limited amount of starting material in this project restricted the use of standard hydrogenation apparatus such as pressure bottles, autoclaves, atmospheric hydrogenation, and shakers. 

In the synthesis of L-acosamine, condensation of the predominant isomer 609 with the magnesium enolate of tert-hutyl acetate gives 610 in 54% yield. Acetylation to 611 (77% yield) and subsequent catalytic hydrogenation in an autoclave (70 Kg/cm ) furnishes 612 as a single isomer. Acid hydrolysis of the ketal, benzoylation under Schotten—Baumann conditions, and lactonization affords 613. Reduction of the lactone to a lactol with diisobutyl-aluminum hydride gives N- benzoyl-L-acosamine (614) as an anomeric mixture. 

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