[7440-06-4] · Pt · Platinum (Sulfided) on Carbon · (MW 195.08)
Solubility: insol all organic solvents.
Form Supplied in: typically 5 wt % of Pt on black powder or granules poisoned with S; in dry or 50 wt % water wet form; commercially available.
Analysis of Reagent Purity: atomic absorption.
Handling, Storage, and Precautions: can be stored safely in a closed container under air but away from solvents and potential poisons such as sulfur- and phosphorus-containing compounds; pyrophoric in the presence of solvents; general precautions for handling hydrogenation catalysts should be followed; the catalyst must be suspended in the organic solvent under an atmosphere of N2; during filtration the filter cake must not be allowed to go dry; if a filter aid is necessary, cellulose-based materials should be used if catalyst recovery is desired. Use in a fume hood.
Sulfided platinum on carbon is a deactivated catalyst which gives useful selectivity in hydrogenation of polyfunctionalized compounds. Because of the deactivation, hydrogenation reaction conditions needed with this catalyst can be quite vigorous sometimes. Even so, many functional groups, including aromatic rings, ketones, aryl halides, sulfides, nitriles, amides, and esters, are stable under these conditions.
The reduction of halogenated nitrobenzenes to amines was effected without dehalogenation. Both chlorine (eq 1)1 and bromine (eq 2)2 survived the reduction conditions.
Appropriately substituted nitro compounds may lead to cyclized products after amine formation (eq 3).3
The catalyst is also insensitive to poisons. Even in the presence of a sulfide, a nitro group was reduced readily to the amine (eq 4). The benzhydryl (diphenylmethyl) protecting group was stable to the reaction conditions and was not hydrogenolyzed.4 The diamine was reacted directly with alloxan monohydrate to give 10-[2-(diphenylmethylthio)ethyl]isoalloxazine in 51% yield.
Aryl disulfides are hydrogenolyzed to thiophenols and no further reduction to the hydrocarbons and hydrogen sulfide was observed.2
The low reactivity of this catalyst towards ketone hydrogenation and hydrogenolysis allows the reductive alkylation of amines or amine precursors and ketones in excellent yields with no competitive reduction of the ketone to an alcohol.5 The absence of ketone reduction is further illustrated in eq 5. When compared with Palladium on Carbon and Platinum on Carbon catalysts, which gave the nitro alcohol and the amino alcohol, respectively, Pt(S)/C is by far the most selective catalyst.
Anthony O. King & Ichiro Shinkai
Merck & Co., Rahway, NJ, USA