Adams catalyst hydration

Platinum in a finely divided form is obtained by the in situ reduction of hydrated platinum dioxide (Adams catalyst) finely divided platinum may also be used supported on an inert carrier such as decolourising carbon. Finely divided palladium prepared by reduction of the chloride is usually referred to as palladium black. More active catalysts are obtained however when the palladium is deposited on decolourising carbon, barium or calcium carbonate, or barium sulphate. Finely divided ruthenium and rhodium, usually supported on decolourising carbon or alumina, may with advantage be used in place of platinum or palladium for some hydrogenation reactions. 

Of the two chair conformations of an alkyl /S-D-arabinopyranoside (81), the IC form is the more stable. In this conformation, the hydroxyl group on C-4 is axial, and catalytic oxidation (in the presence of Adams catalyst, in neutral solution at 45°) proceeds smoothly to afford " the alkyl /8-D-starting material, because the oxidation product is obtained as an unstable sirup which isomerizes " and decomposes to give acids. A better starting material is benzyl /3-d-arabinopyranoside, which yields a relatively stable, crystalline mono-hydrate of a benzyl pentosidulose (82) this is obtained pure by recrystallization or by column chromatography. The structure of the product was determined by reduction with sodium amalgam to a mixture of D-arabinose and L-xylose. 

Hydrogenation of hydrated dihydrohumuiinic acid using Adams catalyst leads to 2,5-bis(3-methylbutyl)-3-hydroxy-2-cyclopentenone (142, Fig. 66) (43), which can also be obtained by Clemmensen reduction of dihydrohumuiinic acid (18,19,52) or by hydrogenation of isohumulinic acid in acetic acid containing hydrogen perchlorate... 

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