Vanadium pentoxide, Vanadium compounds
Vanadium pentoxide is used in different, industrial processes as catalyst: In the contact process it serves for the oxidation of SO2 to SO3 with oxygen at 440°C. Besides it is used in the oxidation of ethanol to ethanale and in the production of phthalic anydride, polyamide, oxalic acid and further products.
Vanadium pentoxide melts at 690°C and decomposes at 1750°C. V3+ is a strong reducing agent, which sets hydrogen free with water. This shows that Vanadium pentoxide may only rarely be applicable as sole oxidizing agent. Of interest are its abilities to form polyoxides. In the following process the oxidation number of the vanadium remains constant for example, but the polarization of the peroxide group increases:
Aldehydes undergo oxidative transformation to the methyl esters in methanol as solvent upon treatment with catalytic amounts of vanadium pentoxide in combination with hydrogen peroxide. This method features mild reaction conditions, short reaction times, high efficiencies, cost-effectiveness, and facile isolation of the desired products.
R. Gopinath, B. Patel, Org. Lett., 2000, 2, 577-579.
Oxidation of alcohols to aldehydes and ketones were performed under atmospheric oxygen with a catalytic amount of V2O5 in toluene at 100°C. Secondary alcohols can be chemoselectively converted into ketones in the presence of primary hydroxy groups.
S. Velusamy, T. Punniyamurthy, Org. Lett., 2004, 6, 217-219.
Optimized selective aerobic oxidations in ionic liquids convert various activated primary alcohols into their corresponding acids or aldehydes in good to excellent yields. The newly developed catalytic systems could also be recycled and reused for three runs without any significant loss of catalytic activity.
N. Jiang, A. J. Ragauskas, J. Org. Chem., 2007, 72, 7030-7033.
A new catalytic system for the asymmetric epoxidation of allylic alcohols has been developed featuring high enantioselectivity for Z olefins, catalyst loading of less than 1 mol%, reaction temperatures of 0°C to room temperature over a shorter time, and simple workup procedures for small expoxy alcohols.
W. Zhang, A. Basak, Y. Kosugi, Y. Hoshino, H. Yamamoto, Angew. Chem. Int. Ed., 2005, 44, 4389-4391.
Chiral bishydroxamic acid ligands provided good yields and high enantioselectivities in the vanadium-catalyzed asymmetric epoxidation of homoallylic alcohols.
W. Zhang, H. Yamamoto, J. Am. Chem. Soc., 2007, 129, 286-287.
The combination of very high ee values with high yield, the consequence of an efficient initial asymmetric oxidation followed by an efficient kinetic resolution, makes the reported system very practical for the asymmetric oxidation of simple akyl aryl sulfides.
C. Drago, L. Caggiano, R. F. W. Jackson, Angew. Chem. Int. Ed., 2005, 44, 7221-7223.
The asymmetric oxidation of sulfides to chiral sulfoxides with hydrogen peroxide in good yield and high enantioselectivity has been catalyzed very effectively by a chiral vanadium-salan complex. The efficient kinetic resolution of racemic sulfoxides catalyzed by the vanadium-salan system is also described.
J. Sun, C. Zhu, Z. Dai, M. Xang, Y. Pan, H. Hu, J. Org. Chem., 2004, 69, 8500-8503.