Aqueous H2O2 is an ideal oxidant, when coupled with a tungstate complex and a quaternary ammonium hydrogensulfate as an acidic phase-transfer catalyst. It oxidizes alcohols, olefins, and sulfides under organic solvent- and halide-free conditions in an economically, technically, and environmentally satisfying manner.

Currently, the industrial production of adipic acid uses nitric acid oxidation of cyclohexanol or a cyclohexanol/cyclohexanone mixture. The nitrous oxide emission from this process measurably contributes to global warming and ozone depletion. Therefore, the development of an adipic acid production process that is less damaging to the environment is an important subject in chemical research. Cyclohexene can now be oxidized directly to colorless crystalline adipic acid with aqueous 30 percent hydrogen peroxide under organic solvent- and halide-free conditions, which could provide an ideal solution to this serious problem.

Hydration of unsaturated carbon compounds is one of the most straightforward and environmentally benign methods to form the carbon±oxygen bond. Synthesis of carbonyl compounds by the hydration of alkynes is an important variation in this category, which has been extensively studied. [1] Acidcatalyzed hydration of alkynes is long known. [2, 3] However, only electron-rich acetylene compounds, such as alkynyl ethers, alkynyl thioethers and ynamines react satisfactorily. [1d, 4] The reaction of simple alkynes is usually sluggish and needs cocatalysts, typically toxic mercury(ii) salts, to enhance the reactivity. [5] More recent interest lies in the use of transition-metal-complex catalysts containing Ru II , [6] Ru III , [7] Rh, [8] Pt, [9] Au III , [10] and other metal centers. [11] However, the process catalyzed by these complexes is not efficient either. The highest turnover frequency (TOF) is 550 h À1 claimed as the initial TOF for the hydration of 3-pentyn-1-ol catalyzed by [cis-PtCl 2 (tppts) 2 ] (tppts ¼ P(m-C 6 H 4 SO 3 Na) 3 ), but its overall TOF is no more than approximately 100 h À1 . [9c] Recently Teles and co-workers reported the addition of methanol to alkynes catalyzed by Au I species in conjunction with acidic cocatalysts. [12] Hydration of propargyl alcohol was also briefly mentioned in their patent application, [13] although the yield was quite low. [14] Herein we report that the Au I ±acid systems in aqueous methanol serve as powerful catalysts, [15] which promote the hydration of alkynes [Eq. (1)] and have turnover frequencies of at least two orders of magnitude higher than [cis-PtCl 2 (tppts) 2 ].In a preliminary experiment, a mixture of 1-octyne (1 mmol), [(Ph 3 P)AuCH 3 ] (0.01 mmol, 1 mol %) and concentrated sulfuric acid (0.5 mmol, 50 mol %) in aqueous methanol (1.5 mL, methanol:H 2 O ¼ 2:1 v/v) was heated for 1 h at 70 8C affording the corresponding Markovnikov hydration product, 2-octanone, in 95 % yield without anti-Markovnikov hydration, or possible methanol addition. [12] The reaction did not proceed in the absence of either the Au catalyst or sulfuric acid.The following aspects about the catalytic system are worth noting. First, the nature of the reaction medium significantly affects the reaction. The reaction run without using solvent (in otherwise the same conditions as the preliminary experiment) did not furnish 2-octanone. On the other hand, the use of 2propanol (71 %), dioxane (56 %), acetonitrile (53 %), or THF (11 %) resulted in a low yield, and the yield obtained with dichloromethane, DMF, or toluene was even lower. Thus methanol was the solvent of choice for this particular transformation. [16] Second, the efficiency of the catalyst was significantly enhanced by addition of appropriate ligands, which enabled the quantity of the precious catalyst used to be minimized. For instance, the control experiment run without ligand addition under the conditions shown in Table 1 (only 0.01 mol % catalyst) gave 2-octanone in only 35 % yield (TOF ¼ 3500 h À1 , entry 1), while th...

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