Platinum-catalyzed Hydrogenation Research Articles

Heterogeneous, platinum-catalyzed hydrogenation of (diolefin)dialkylplatinum(II) complexes: kinetics

(Diolefin)dialkylplatinum(II) complexes ((Ol/sub 2/)PtR/sub 2/) are rapidly reduced by dihydrogen in the presence of platinum black catalyst: the organic groups are converted to alkanes, and the platinum(II) to platinum(0). This platinum(0) is incorporated into the surface of the platinum black catalyst. The reaction is a heterogeneous process catalyzed by platinum(0). Its rate is strongly influenced by mass transport and by the surface area of the catalyst. It is poisoned by dineopentylmercury, di-n-octyl sulfide, and tri-tert-butylphosphine. Because the catalyst surface is constantly renewed by deposition of platinum, the reaction is, however, less sensitive to poisoning than more familiar platinum-catalyzed reactions such as hydrogenation of olefins. The form of the kinetic rate law observed for reduction of (1,5-cyclooctadiene)dimethylplatinum(II) depends on the reaction conditions. Two limiting kinetic regimes are observed. In one, mass transport of dihydrogen to the catalyst surface is rate-limiting; in the second, a reaction occurring on the platinum surface is rate-limiting. The activation energy for reaction in the mass transport limited regime is approx. 3 kcalmol and that in the reaction rate limited regime is approx. 15 kcalmol. In neither regime is there a kinetic isotope effect: nu/sub H/sub 2//nu/sub D/sub 2// approx. = 1.0. Examination of the relative ratesmore » of reaction of a series of (diolefin)dialkylplatinum(II) complexes indicates that the structure of the diolefin has a greater influence on the rate of reaction than does that of the alkyl group. Competitive experiments show that rates are influenced by adsorption of the (Ol/sub 2/)PtR/sub 2/ complex to the catalyst.« less

Deuterium-labeling experiments relevant to the mechanism of platinum-catalyzed hydrogenation of (diolefin)dialkylplatinum(II) complexes: evidence for isotopic exchange via platinum surface hydrogen. The stereochemistry of reduction

Reduction of (diolefin)dialkylplatinum(II) complexes with dihydrogen over a platinum black catalyst is accompanied by interchange of hydrogen among the organic groups and gaseous dihydrogen. Exchange of hydrogens between an alkane solvent and these organic groups also occurs during the reaction, but only relatively slowly. An examination of the stereochemistry of reduction of (norbornadiene)dimethylplatinum(II) with D/sub 2/ indicates that the deuterium atoms add predominantly to the same (endo) face of the olefins as that coordinated to the dimethylplatinum moiety. Reduction of uncomplicated norbornadiene under the same conditions yields norbornane having primarily exo C-D bonds. These experiments are compatible with a mechanism for the reduction involving adsorption of the (diolefin)dialkylplatinum(II) complex on the surface of the platinum catalyst via its platinum atom, conversion of the organic moieties of the soluble (diolefin)dialkylplatinum complex to platinum-surface alkyls, and interchange of hydrogen atoms between these surface alkyls via a mobile pool of platinum-surface hydrogen atoms. Combination of the surface alkyls with surface hydrogen yields alkanes in a final irreversible step. Comparison of the evidence from deuterium-interchange experiments conducted under mass transport limited and reaction rate limited conditions is consistent with the hypothesis that the concentrations of hydrogen on the platinum surface is lower under massmore » transport limited conditions.« less

Platinum-catalyzed hydrogenation of graphite: Mechanism studied by the rates of monolayer channeling

Monolayer channeling on the basal plane of graphite was studied for the Pt-catalyzed CH 2 reaction using gold decoration transmission electron microscopy, at temperatures below 1050 °C, H 2 pressures below 1 atm, and Pt particle sizes below 5000 Å. The particle movement is driven by the adhesion forces between Pt and the {101̄1} zigzag edge plane of graphite. Larger particles channel faster but the gasification rate per Pt surface area is the same for all sizes. The rate is independent of H 2 partial pressure. The kinetic data suggest that the rate-limiting step is the reaction on the Pt surface between surface carbon and chemisorbed hydrogen at their equilibrium amounts. A comparison of the monolayer channeling data and those on multilayer channeling and bulk measurement indicates that there exists a similarity between the mechanisms. A further comparison of the kinetic data for the catalyzed CH 2 reaction and for the methanation reaction (from CO + H 2) suggests the likelihood of a common rate-limiting step.

Shape-selective reactions of zeolites. Selective metal-catalyzed hydrogenation and oxidation using ZSM-5

The ZSM-5 zeolite was shown to act as a shape-selective support for the platinum-catalyzed hydrogenation of olefins and for the copper-catalyzed oxidation of hydrocarbons.

Heterogeneous platinum-catalyzed hydrogenation of dialkyl(diolefin)platinum(II) complexes: A new route to platinum surface alkyls

Platinum metal catalyzes the reduction of dialkyl(diolefin)platinum(II) complexes by dihydrogen to alkanes and platinum(0). The reaction involves adsorption of the platinum(II) complex on the platinum(0) catalyst surface with conversion of the alkyl moieties to platinum surface alkyls; these appear as alkane products. The platinum atom originally present in the soluble organoplatinum species becomes part of the platinum(0) surface.

Some chemical transformations of 7-β- D-glucopyranosyltheophylline

Selective chlorination of 7-β- D-glucopyranosyltheophylline with an excess of methanesulphonyl chloride in N,N-dimethylformamide gave 7-(6-chloro-6-deoxy-β- D-glucopyranosyl)theophylline. Likewise, selective tosylation of 7-β- D-glucopyranosyl- and 7-β- D-galactopyranosyl-theophylline gave, after acetylationi in situ, the corresponding 7-(2,3,4-tri- O-acetyl-6- O-tosyl-β- D-hexopyranosyl)theophyllines. Treatment of the D- gluco 6'-toluene- p-sulphonate with the excessof methanolic sodium methoxide gave the 3',6'-anhydride, isolated as its acetate which was shown from 1H-n.m.r. studies to be conformationally unstable in solution. Treatment of 7-(2,3,4-tri- O-acetyl-6-deoxy-6-iodo-β- D-glucopyranosyl)theophylline with silver fluoride in pyridine gave, after deacetylation, 7-(6-deoxy-β- D- xylo-hex-5-enopyranosyl)theophylline. Platinum-catalysed hydrogenation of this 5'-ene was stereoselective and gave mainly 7-(6-deoxy-β- D-glucopyranosyl)theophylline.

New Compounds: Oxazolidines and Derived Amino Alcohols

Oxazolidines II and V were prepared from 1-methyl-4-piperidone (I) and from 2-naphthalenecarboxaldehyde or p-chloro-benzaldehyde (IV) and appropriate secondary 2-aminoethanols. Platinum-catalyzed hydrogenation of II and II V gave amino alcohols III and VI, respectively. These oxazolidines and the corresponding amino alcohols showed no carcinolytic activity in experimental tests. Compound IIIa had marginal antimalarial activity in the mouse, P. berghei screen.

Platinum-catalyzed hydrogenation and hydrogenolysis of acylated pyranosyl halides, tetra-O-acetyl-2-hydroxy-D-glucal and tri-O-acetyl-D-glucal

Platinum-catalyzed hydrogenation and hydrogenolysis of acylated pyranosyl halides, tetra-O-acetyl-2-hydroxy-D-glucal and tri-O-acetyl-D-glucal

Reactions of nitro sugars. V. Some reactions with methyl 3-deoxy-3-nitro-α-d-hexopyranosides

The acetylations and catalytic hydrogenations of derivatives of methyl 3-deoxy-3-nitro-α-d-hexopyranosides were compared with the analogous reactions previously performed in the β-anomeric series. The acetylation of methyl 4,6-O-benzylidene-3-deoxy-3-nitro-α-d-glucopyranoside (II) gave its 2-O-acetyl derivative III, which, upon base-catalyzed elimination of acetic acid, yielded the nitroolefin, methyl 4,6-O-benzylidene-2,3-dideoxy-3-nitro-α-d-erythro-hexopyranos-2-enide (IV), whereas acetylation of the corresponding α-d-talopyranoside XI proceeded with dehydration, giving directly the α-d-threo nitroolefin XIII. These courses of reaction had their counterparts in the β-series and are believed to depend on the configurations at C-4. On the other hand, palladium-catalyzed hydrogenations of the nitroolefins IV and XIII gave results that were similar to each other but different from those obtained in the β-series. Besides the expected saturated nitro glycosides with α-d-arabino (V) and α-d-lyxo (XV) configurations, two oximes (VI and XIV) were produced in yields of 49 and 30%, respectively. This may be attributed to a measure of steric interference by the glycosidic methoxyl group during the hydrogenation of the olefinic double bonds in IV and XIII. Amino glycosides were obtained from V and XV by debenzylidenation and platinum-catalyzed hydrogenation.

The direction of platinum-catalysed hydrogenation of an unsymmetrical anhydride in the norbornane series

The products of hydrogenation of 2-exo-methylbicyclo[2,2,1]hept-5-ene-2,3-endo-dicarboxylic anhydride (VI) have been shown to be the hemiacylal (VII) and the lactone (IX), both formed by reduction of the less hindered carbonyl group. These structures were assigned by consideration of the N.M.R. spectra of the hemiacylal (VII) and of its ring-opened anion (XI) formed with alkali in water or deuterium oxide. The anion (XI) has been shown to undergo slow base-catalysed isomerization (accompanied, in deuterium oxide, by deuteration at C 3) to give an equilibrium mixture from which has been isolated the trans-isomer, 3-exo-formyl-2-exo-methylbicyclo-2,2,1,heptane-2-endo-carboxylic acid (XIII).

Solvents of Low Nucleophilicity. V. Platinum-Catalyzed Hydrogenation of Ketones, Tertiary Alcohols and Esters, and Tosylates in Acidic Solvents Including Trifluoroacetic Acid1a

Solvents of Low Nucleophilicity. V. Platinum-Catalyzed Hydrogenation of Ketones, Tertiary Alcohols and Esters, and Tosylates in Acidic Solvents Including Trifluoroacetic Acid^1a

The Chemistry of Ilexol. III.

It has now been shown that: (a) treatment with either perchloric acid or sulfuric acid of ilexol acetate in a mixture of benzene and ethanol, and (b) treatment with platinumcatalyzed hydrogen of ilexol and ilexone, affords an isomeric alcohol designated as isoilexol, which has C30H50O, m.p. 177~178°, +41.66° (acetate, C32H52O2, m.p. 226~227°, +48.92°).Furthermore, it has been shown that: (a) treatment with hydrochloric acid and glacial acetic acid of ilexol acetate affords α-amyrin acetate, and, in addition, an acetate (Acetate A), C32H52O2, m.p. 212~213°, −22.70°, which is hydrolyzed to an alcohol (Alcohol A), C30H50O, m.p. 202~203°, −35.88°; (b) treatment with sulfuric acid and glacial acetic acid of ilexol acetate and (c) treatment with hydrochloric acid and glacial acetic acid of isoilexol acetate, affords only Acetate A respectively.The infrared and ultraviolet spectra of these isomerized compounds have been measured, and the results of which are discussed.

The Chemistry of Ilexol. III

It has now been shown that: (a) treatment with either perchloric acid or sulfuric acid of ilexol acetate in a mixture of benzene and ethanol, and (b) treatment with platinumcatalyzed hydrogen of ilexol and ilexone, affords an isomeric alcohol designated as isoilexol, which has C30H50O, m. p. 177_??_178°, [α]20D+41.66° (acetate, C32H52O2, m. p. 226_??_227°, [α]27D+48.92°). Furthermore, it has been shown that: (a) treatment with hydrochloric acid and glacial acetic acid of ilexol acetate affords α-amyrin acetate, and, in addition, an acetate (Acetate A), C32H52O2, m. p. 212_??_213°, [α]19D-22.70°, which is hydrolyzed to an alcohol (Alcohol A), C30H50O, m. p. 202_??_203°, [α]19D-35.88°; (b) treatment with sulfuric acid and glacial acetic acid of ilexol acetate and (c) treatment with hydrochloric acid and glacial acetic acid of isoilexol acetate, affords only Acetate A respectively. The infrared and ultraviolet spectra of these isomerized compounds have been measured, and the results of which are discussed.