Nitration of Alkanes with Nitric Acid by Vanadium‐Substituted Polyoxometalates

Abstract

The nitration of alkanes by using nitric acid as a nitrating agent in acetic acid was efficiently promoted by vanadium-substituted Keggin-type phosphomolybdates such as [H4PVMo11O40], [H5PV2Mo10O40], and [H6PV3Mo9O40] as catalyst precursors. A variety of alkanes including alkylbenzenes were nitrated to the corresponding nitroalkanes as major products in moderate yields with formation of oxygenated products under mild reaction conditions. The carbon--carbon bond cleavage reactions hardly proceeded. ESR, NMR, and IR spectroscopic data show that the vanadium-substituted polyoxometalate, for example, [H4PVMo11O40], decomposes to form free vanadium species and [PMo12O40](3-) Keggin anion. The reaction mechanism involving a radical-chain path is proposed. The polyoxometalates initially abstract the hydrogen of the alkane to form the alkyl radical and the reduced polyoxometalates. The reduced polyoxometalates subsequently react with nitric acid to produce the oxidized form and nitrogen dioxide. This step would be promoted mainly by the phosphomolybdates, [PMo12O40](n-), and the vanadium cations efficiently enhance the activity. The nitrogen dioxide promotes the further formation of nitrogen dioxide and an alkyl radical. The alkyl radical is trapped by nitrogen dioxide to form the corresponding nitroalkane.

Assembly of three new POM-based Ag(I) coordination polymers with antibacterial and photocatalytic properties

“…It is noteworthy that nitration happens to compound 2 during the hydrothermal condition, which is quite rare [38][39][40][41]. The Ag1 shows a four-coordinated "sunken square-planar" geometry, coordinated by two N atoms from two nitrified Hbiim-NO 2 ligands and two O atoms from two PW 12 anions.…”

Nitroalkanes as Key Compounds for the Synthesis of Amino Derivatives

“…Direct nitration is possible on alkenes and this process is particularly suited for nitroalkene synthesis [13], or for the preparation of -nitro ketones from the corresponding enol ethers [14]. Substitution of hydrogen atoms with the nitro group in alkanes is a more complicated process since it often lacks selectivity and therefore a mixture of regioisomers is often obtained [15]. Even when activated carbon-hydrogen bonds are available, formation of other byproducts in relevant amount is hardly avoidable using nitrating reagents [16].…”

Effects of vanadium(V)-substitution on the oxidative properties of α-Keggin-type heteropolyanion clusters—progress in DFT theoretical studies

“…of each isomer, along with the respective d-orbital contributions of vanadium to the LUMO (DCVL), as listed in Table 1 [14] . Most recently, we investigated other homogeneous and heterogeneous catalytic oxidative reactions, including benzene hydroxylation under air and CO [41] , oxidative dehydrogenation of isobutyric acid [40] , oxidation of methane [42] , and nitration of adamantine [43] with [PMo 12−n V n O 40 ] (n+3)− (n = 1-3) as catalysts or catalytic precursors using the same method as that described in section 5.1. The relationships between the DCVL of the active isomers with the TON values from the experimental data in the literature [40][41][42][43] are plotted in Figure 3.…”

“…Most recently, we investigated other homogeneous and heterogeneous catalytic oxidative reactions, including benzene hydroxylation under air and CO [41] , oxidative dehydrogenation of isobutyric acid [40] , oxidation of methane [42] , and nitration of adamantine [43] with [PMo 12−n V n O 40 ] (n+3)− (n = 1-3) as catalysts or catalytic precursors using the same method as that described in section 5.1. The relationships between the DCVL of the active isomers with the TON values from the experimental data in the literature [40][41][42][43] are plotted in Figure 3. As shown in Figure 3, similar near-linear correlations do exist in these four kinds of catalytic reactions, i.e., in terms of the catalytic power per single vanadium, the ability of the mono-V-substituted species α-PV 1 is the highest, with the catalytic oxidizing capacity of the vanadium also being the most powerful; the DCVL is 10.5%, and the relative abundance is 100%.…”