Catalytic reduction with Adams platinum oxide catalyst

CATALYTIC REDUCTION WITH ADAMS PLATINUM OXIDE CATALYST 

Adams platinum oxide catalyst is readily prepared from chloroplatinio acid or from ammonium chloroplatinate, and is employed for catalytio hydrogenation at pressures of one atmosphere to several atmospheres and from room temperature to about 90°. Reduction is usually carried out with rectified spirit or absolute alcohol as solvents. In some cases (e.g., the reduction of benzene, toluene, xylene, mesitylene, cymene and diphenyl ), the addition to the absolute alcohol solution of 2-5 per cent, of the volume of rectified spirit which has been saturated with hydrogen chloride increases the effectiveness of the catalyst under these conditions chlorobenzene, bromobenzene, o-, m- and p-bromotoluenes, p-dichloro- and p-dibromo-benzene are reduced completely but the halogens are simultaneously eliminated. Other solvents which are occasionally employed include glacial acetic acid, ethyl acetate, ethyl acetate with 17 per cent, acetic acid or 8 per cent, of alcohol. In the actual hydrogenation the platinum oxide Pt02,H20 is first reduced to an active form of finely-divided platinum, which is the real catalyst allowance must be made for the consumption of hydrogen in the process. 

Method 2. From chloroplatinic acid. Dissolve 3 5 g. of the purest commercial chloroplatinic acid (3) in 10 ml. of water contained in a 250 ml. Pyrex beaker or porcelain casserole, and add 35 g. of A.R. sodium nitrate (1). Evaporate the mixture to dryness by heating gently over a Bunsen flame whilst stirring with a glass rod. Then raise the temperature 

Method 3. From platinum metal or platinum residues. Dissolve the platinum metal or platinum residues in aqua regia, evaporate just to dryness several times with concentrated hydrochloric acid, dissolve the final residue in a little water and precipitate as ammonium chloro-platinate with excess of saturated ammonium chloride solution. Filter and dry the precipitate at 100°. Then proceed according to Method 1. 

The hydrogenation is conveniently conducted in a wide-mouthed bottle H of 250 ml. capacity, provided with a head carrying a 50 ml. 

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Catalytic reduction, with Adams platinum oxide catalyst, 470 with copper-chromium oxide, 873 with Raney nickel, 566 Cation exchange resin, for esterification, 381, 387, 388 Cellosolve, 170, 265, 444 butyl, 170, 444 methyl, 170, 444 Cellulose, 458 ... 

Support for this suggestion comes from many quarters. Reduction of the jS-carboline anhydro-bases with sodium and alcohol or with tin and hydrochloric acid gives the 1,2,3,4-tetrahydro derivatives, as does catalytic reduction over platinum oxide in an alkaline medium. On the other hand, catalytic reduction with platinum oxide in acetic acid results in the formation of the 5,6,7,8-tetrahydro-j3-carbolinium derivatives (see Section III,A,2,a). It should be noted, however, that reduction of pyrido[l,2-6]indazole, in which the dipolar structure 211 is the main contributor to the resonance hybrid, could not be effected with hydrogen in the presence of Adams catalyst. 

It is well established that oxygen in the presence of platinum (Adams catalyst) can achieve specific oxidation of secondary alcohols by a preferential attack upon hydrogen in an equatorial position (25). Catalytic oxidation of methyl a- and /3-D-galactopyranoside (26), fallowed by catalytic reduction with hydrogen, led to the formation of methyl a- and /3-6-deoxy-D-galactopyranoside (D-fuco-pyranoside) in 15% and 35% yield, respectively. This oxidation-reduction sequence with selective oxidation at carbon 4 as the initial step is structurally closely related to the above described pathway for TDPG-oxidoreductase. 

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