Am ethod for the aerobic oxidation of aldehydest oc arboxylic acids in water by using an inorganic-ligand-supported copper catalystw as developed. This methodw as performed with the use of atmospheric oxygen as the sole oxidant under extremely mild aqueous conditions, and furthermore, aw ide range of aldehydes with variousf unctional groups were tolerated. The copperc atalyst could be recycled and used in successive reactions at least six times without any appreciable degradation in performance. This method is operationally simple and avoids the use of high-costing, toxic, air/moisture-sensitive, and commerciallyu navailableo rganic ligands. The generality of this methodg ives it potentialtob eu sed on the industrial scale.Oxidation is one of the mostf undamental chemical transformations for the production of valuable chemicals,r emediation of pollutants, and generation of energy in biological systems. Amongv ariouso xidative processes,t he conversion of aldehydes into carboxylic acids is not only ac ritical biological process in nature but is also an important reactioninthe synthesis of fine chemicals. [1] Many well-established methods are available for this transformation, including those that use CrO 3 , [2] KMnO 4 , [3] KHSO 5 , [4] and KIO 4[5] as the oxidants. Despite the widespreadu se of thesep rocedures, they still suffer from undesirable features, for instance, the use of expensive or toxic stoichiometric reagents, subsequents eparation and disposal of metal waste, and the use of harmful organic solvents.Catalytic oxidation can potentially alleviatet hese problems, and tremendous advances have been made in the development of catalytic methodsf or the aerobic oxidation of aldehydes in water.I ti sw ell known that water is the most environmentallyf riendly solvent with its natural abundance and the fact that it is inherently greener than common organic solvents,w hich makes green chemistry an active field. [6] Recently, the catalytic oxidation of aldehydes by using metals with molecular oxygen as the terminal oxidanti nw ater has attracted much attention, because it offers as ustainable, environmentally benign alternative to traditional processes. For example, Li [1e, f] and co-workers reported the oxidationo fa ldehydes by using organometallic catalysts ystems ( Figure 1) and provided the first examples of the silver-or copper-catalyzed aerobic oxidationo fa ldehydes in water under mild conditions to afford the desired carboxylic acids with almost 100 %c onversion. Nevertheless, this transformation required commercially unavailablep hosphine ligandso rN -heterocyclic carbenes, both of whicha re susceptible to oxidative self-degradation;t his is a commonly encountered problem in transition-metal catalysis. Moreover, the recyclability of these catalysts was not demonstrated, which vastly limits the generality of this method.Polyoxometalates (POMs), [7] al arge class of well-defined unique metal-oxide anionic clusters with rich redoxp roperties, Figure 1. Catalyst systems in aldehyde oxidation. DIPEA = N,...