Synthesis of Oxalates and Carbonates

The palladium catalyzed oxidative carbonylation of alcohols yields the corresponding oxalates [171]  

The reaction was first developed by D. M. Fenton [75] in the presence of oxygen (or air) and copper cocatalysts unfortunately it was slow and scarcely selective. 

Addition of different water scavengers and different bases improved the results, but not enough for economic commercialization. 

The best results have been obtained by Ube [76, 77] who replaced the classical CUCI2/O2 redox couple by a RONO/O2 couple, the reaction thus becomes  

The three steps can be performed in the same reactor and the overall reaction conditions are mild. In the Uquid phase n-butanol gives dibutyl oxalate in excellent yields using a simple palladium on charcoal catalyst furthermore, the water/butyl nitrite azeotrope allows facile separation of the water formed. 

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