Simple Preparation of Nitroso Benzenes and Nitro Benzenes by Oxidation of Anilines with H₂O₂Catalysed with Molybdenum Salts

Abstract

Nitroso arenes 2a-k are prepared in 53-80% yield from anilines 1a-k by oxidation with H 2 O 2 catalysed with MoO 3 /KOH, ammonium molybdate or other molybdenum salts. Further oxidation to nitro arenes 3a,d,j in 66-90% is also described.Classic methods for the preparation of aromatic nitroso compounds are oxidation of anilines with peracids, 1 particularly Caro acid, 2 peracetic acid, 1 perbenzoic acid, 3,4 trifluoroperacetic acid 5 or more recently molybdic peroxo-complexes. 6 Catalytic methods using H 2 O 2 or tertbutyl peroxide as oxidant and sodium tungstate, 7 oxomolybdate complexes, 8 phosphotungstate, 9-11 phosphomolybdate 10,11 or zirconate salts 12 were published later. Dimeric products such as azo-or azoxy-derivatives 9,13a as well as over-oxidation to the nitro compounds 7,10,11 were often observed as by-products or sometimes as main products. 6,14 Some methods for the direct oxidation of aromatic amines to nitro derivatives were described with peracids, 15 and more recently with dioxirane, 16 tert-butyl peroxide or H 2 O 2 as oxidants and metal peroxocomplexes (Mo, 17 W, 6,10,11 V, 17 Zr, 12 Re 18 ) or with chromium silicalit 13 as catalyst.We describe herein a simple oxidation method of anilines, resulting in the corresponding nitroso compounds using 30% H 2 O 2 and molybdenum trioxide or other molybdenum salts as catalyst without the formation of azo-or azoxy-derivatives. Further oxidation to nitro compounds was examined in some cases. Oxidation of Anilines to Nitroso ArenesOxidation of anilines 1a-k was carried out in a watermethanol solution in which the anilines were only slightly soluble but the resulting nitroso compounds 2a-g,j,k were insoluble and could be isolated by filtration (Scheme 1). Side-reactions such as formation of nitro derivatives and dimeric compounds such as azo-or azoxy-derivatives was also minimised. This method appeared to be better than the previous two-phase preparation. 4,8,9,11 A complete oxidation and a sufficient reaction rate required an excess of H 2 O 2 (4 equiv) and 0.1 mol of molybdic derivative per 1 mol of aniline, smaller proportions of oxidant or catalyst led to slower or incomplete reactions and favoured the formation of azo-azoxy-or coloured-compounds. Scheme 1 a) Dependence on the pH-Valuep-Chloroaniline 1a was used as the model compound and the standard catalyst was 10 mol% MoO 3 in the presence of KOH as the base, which was added in various quantities. Oxidation of p-chloroaniline is very dependent on MoO 3 /KOH molar ratio. The results are listed in Table 1, and summarised here.-With MoO 3 only without added base, the oxidation occurred cleanly, but the progress of the reaction was slow (15% reaction after 1 d).-With MoO 3 and 1-1.8 equiv KOH, the oxidation rate increased with the concentration of base, but coloured impurities were formed when 1.5-1.8 equiv of base (pH value 5-7) were added. The best condition for the oxidation to the nitroso compound was with 1-1.2 equiv KOH, then the oxidation occurred cleanly and gave good yields (86-94%) of the nitro...

Understanding the Broad Substrate Repertoire of Nitroreductase Based on Its Kinetic Mechanism

“…p-NBA was from Acros Organics. p-Nitrosobenzoic acid (p-NOBA) was produced as per the procedure of Defoin (29) …”

Selective hydrogenation of chloronitrobenzene to chloroaniline in supercritical carbon dioxide over Ni/TiO2: Significance of molecular interactions

“…A higher temperature of 90°C was also used for p-CNB and p-CNSB at CO 2 pressures < 4 MPa and < 6 MPa, respectively. For those measurements, p-CNB (Wako) was used as received; commercially unavailable p-CNSB and p-CPHA, two of the intermediates (Scheme 1), were synthesized by the oxidation of p-CAN (Wako) with H 2 O 2 catalyzed with ammonium molybdate [38], and by the reduction of p-CNB with zinc dust [39], respectively. The formation of these compounds was confirmed by FTIR and NMR (JEOL A200II) [38,40].…”

Preparation of Azobenzenealkanethiols for Self-Assembled Monolayers with Photoswitchable Properties

“…[40] The required nitrosobenzenes 7-15 could be obtained in good to very good yields by the oxidation of the respective anilines with hydrogen peroxide in the presence of a catalytic amount of ammonium molybdate tetrahydrate. [56] To remove side-products (in particular the nitro compound), chromatography on silica was performed. Owing to the high volatility of the nitrosobenzenes, it is highly advised to use pentane for this purification step.…”