Nitration Of Phenolic Compounds Research Articles

Nitration of Phenolic Compounds with Magnesium nitrate and acetic acid

Nitration of aromatic compounds is an indispensible reaction for organic chemists. Various metal nitrates are being used now-a-days as an eco-friendly nitrating agent instead of harsh strong acids, namely, nitric and sulfuric acids. A mixture of calcium nitrate and acetic acid, as well as a mixture of magnesium nitrate and alumina sulfuric acid, are reported to be used as nitrating agent. Inferring from these ideas, a mixture of magnesium nitrate and acetic acid (glacial or about 80% aqueous) is introduced for the first time as a fairly efficient nitrating agent for phenolic compounds successfully.

Formation of 2-nitrophenol from salicylaldehyde as a suitable test for low peroxynitrite fluxes

There has been some dispute regarding reaction products formed at physiological peroxynitrite fluxes in the nanomolar range with phenolic molecules, when used to predict the behavior of protein-bound aromatic amino acids like tyrosine. Previous data showed that at nanomolar fluxes of peroxynitrite, nitration of these phenolic compounds was outcompeted by dimerization (e.g. biphenols or dityrosine). Using 3-morpholino sydnonimine (Sin-1), we created low fluxes of peroxynitrite in our reaction set-up to demonstrate that salicylaldehyde displays unique features in the detection of physiological fluxes of peroxynitrite, yielding detectable nitration but only minor dimerization products.By means of HPLC analysis and detection at 380nm we could identify the expected nitration products 3- and 5-nitrosalicylaldehyde, but also novel nitrated products. Using mass spectrometry, we also identified 2-nitrophenol and a not fully characterized nitrated dimerization product. The formation of 2-nitrophenol could proceed either by primary generation of a phenoxy radical, followed by addition of the NO2-radical to the various resonance structures, or by addition of the peroxynitrite anion to the polarized carbonyl group with subsequent fragmentation of the adduct (as seen with carbon dioxide). Interestingly, we observed almost no 3- and 5-nitrosalicylic acid products and only minor dimerization reaction.Our results disagree with the previous general assumption that nitration of low molecular weight phenolic compounds is always outcompeted by dimerization at nanomolar peroxynitrite fluxes and highlight unique features of salicylaldehyde as a probe for physiological concentrations of peroxynitrite.

ChemInform Abstract: Nitration of Phenolic Compounds and Oxidation of Hydroquinones Using Tetrabutylammonium Chromate and Dichromate under Aprotic Conditions.

AbstractEfficient and selective mononitration of structurally different phenolic compounds is achieved using NaNO2 in the presence of the title ammonium chromates under non‐acidic and aprotic conditions.

Nitration of Phenolic Compounds by Antimony Nitrate

Antimony nitrate is new compound to be an efficient nitration reagent in the nitration of phenolic compounds with high yields. This producer works efficiently on most of the examples, as a grinding nitration reaction, proceed very fast (∼1 min) and thermogenic.

Highly Efficient Nitration of Phenolic Compounds using Some Nitrates and Oxalic Acid under Solvent-Free Conditions

Nitrophenols can be obtained by direct nitration of phenols with some nitrates and oxalic acid at room temperature in moderate to high yields under solvent-free conditions. A small amount of water proved to be important in the initial period of the reaction.

Nitration of phenolic compounds and oxidation of hydroquinones using tetrabutylammonium chromate and dichromate under aprotic conditions

In this work, we have reported a mild, efficient and selective method for the mononitration of phenolic compounds using sodium nitrite in the presence of tetrabutylammonium dichromate (TBAD) and oxidation of hydroquinones to quinones with TBAD in CH2Cl2. Using this method, high yields of nitrophenols and quinones were obtained under neutral aprotic conditions. Tetrabutylammonium chromate (TBAC) can also be used as oxidant at same conditions. A mild and efficient mononitration of phenolic compounds was performed under neutral aprotic conditions using sodium nitrite in the presence of tetrabutylammonium dichromate (TBAD) and tetrabutylammonium chromate (TBAC). Also, hydroquinones were easily oxidized to quinones with TBAD and TBAC.

Nitration of phenolic compounds by metal salts impregnated Yb-Mo-montmorillonite KSF

Nitration of phenolic compounds by metal salts impregnated Yb-Mo-montmorillonite KSF

Nitration of Phenolic Compounds by Metal‐Modified Montmorillonite KSF.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Nitration of phenolic compounds by metal-modified montmorillonite KSF

The nitration of phenolic compounds with 60% nitric acid (1.2 equiv) has been carried out in the presence of metal-modified montmorillonite KSF, prepared from different metals (V, Mo, W; Sc, La, Yb, Eu, In, Bi, Ti, Zr, Hf) and KSF or nitric acid treated HKSF, as catalysts. These catalysts showed good stabilities and high catalytic activities in nitration process. In addition, these catalysts can be recovered easily and reused for many times in nitration. This process is an eco-safer and environment-benign way for clean synthesis of nitrated phenolic compounds.

Formation of reactive nitrogen species at biologic heme centers: a potential mechanism of nitric oxide-dependent toxicity.

The peroxidase-catalyzed nitration of tyrosine derivatives by nitrite and hydrogen peroxide has been studied in detail using the enzymes lactoperoxidase (LPO) from bovine milk and horseradish peroxidase (HRP). The results indicate the existence of two competing pathways, in which the nitrating species is either nitrogen dioxide or peroxynitrite. The first pathway involves one-electron oxidation of nitrite by the classical peroxidase intermediates compound I and compound II, whereas in the second pathway peroxynitrite is generated by reaction between enzyme-bound nitrite and hydrogen peroxide. The two mechanisms can be simultaneously operative, and their relative importance depends on the reagent concentrations. With HRP the peroxynitrite pathway contributes significantly only at relatively high nitrite concentrations, but for LPO this represents the main pathway even at relatively low (pathophysiological) nitrite concentrations and explains the high efficiency of the enzyme in the nitration. Myoglobin and hemoglobin are also active in the nitration of phenolic compounds, albeit with lower efficiency compared with peroxidases. In the case of myoglobin, endogenous nitration of the protein has been shown to occur in the absence of substrate. The main nitration site is the heme, but a small fraction of nitrated Tyr146 residue has been identified upon proteolytic digestion and high-performance liquid chromatography/mass spectrometry analysis of the peptide fragments. Preliminary investigation of the nitration of tryptophan derivatives by the peroxidase/nitrite/hydrogen peroxide systems shows that a complex pattern of isomeric nitration products is produced, and this pattern varies with nitrite concentration. Comparative experiments using chemical nitrating agents indicate that at low nitrite concentrations, the enzymatic nitration produces a regioisomeric mixture of nitrotryptophanyl derivatives resembling that obtained using nitrogen dioxide, whereas at high nitrite concentrations the product pattern resembles that obtained using peroxynitrite.

The mechanism of the nitration of donor-activated benzenes with nitric and nitrous acid as studied by 15N CIDNP

15N CIDNP effects observed during nitration of phenolic compounds with nitric and nitrous acid are comparable showing that nitrous acid is not only a catalyst during nitration with nitric acid but also a reactive intermediate. The 15N CIDNP effects are generated in radical pairs formed during encounters of NO 2 and arene radical cations or aroxyl radicals. The mechanism given is valid for arenes more reactive than toluene.

Peroxynitrite oxidises catechols to o-quinones

Nitration of phenolic compounds is a well-established mechanism on interaction with peroxynitrite. However, while nitration is the predominant reaction for monophenolic hydroxycinnamates, this does not take place with the catechol-containing hydroxycinnamate, caffeic acid. The aim of the present study was to investigate the mechanism of the chemical interaction of caffeic acid with peroxynitrite and to characterise the products formed. A novel compound was detected and characterised as the o-quinone of caffeic acid based on its reaction with nucleophilic thiol compounds, glutathione and l-cysteine. The same novel product was identified following the oxidation of caffeic acid in alkaline solutions confirming the identity of this species as a caffeic acid oxidation product.

Nitrosation by Peroxynitrite: Use of Phenol as a Probe

Nitrosation is an important pathway in the metabolism of nitric oxide, producingS-nitrosothiols that may be critical signal transduction species. The reaction of peroxynitrite with aromatic compounds in the pH range of 5 to 8 has long been known to produce hydroxylated and nitrated products. However, we here present evidence that peroxynitrite also can promote the nitrosation of nucleophiles. We chose phenol as a substrate because the nitrosation reaction was first recognized during a study of the CO2-modulation of the patterns of hydroxylation and nitration of phenol by peroxynitrite (Lemercieret al., Arch. Biochem. Biophys.345, 160–170, 1997). 4-Nitrosophenol, the principal nitrosation product, is detected at pH 7.0, along with 2- and 4-nitrophenols; 4-nitrosophenol becomes the dominant product at pH ≥ 8.0. The yield of 4-nitrosophenol continues to increase even after pH 11.1, 1.2 units above the pKaof phenol, suggesting that the phenolate ion, and not phenol, is involved in the reaction. Hydrogen peroxide is not formed as a by-product. The nitrosation reaction is zero-order in phenol and first-order in peroxynitrite, suggesting the phenolate ion reacts with an activated nitrosating species derived from peroxynitrite, and not with peroxynitrite itself. Under optimal conditions, the yields of 4-nitrosophenol are comparable to those of 2- and 4-nitrophenols, indicating that the nitrosation reaction is as significant as the nitration of phenolic compounds by peroxynitrite. Low concentrations of CO2facilitate the nitrosation reaction, but excess CO2dramatically reduces the yield of 4-nitrosophenol. The dual effects of CO2can be rationalized if ONOO−reacts with the peroxynitrite anion–CO2adduct (ONOOCO−2) or secondary intermediates derived from it, including the nitrocarbonate anion (O2NOCO−2), the carbonate radical (CO•−3), and•NO2. The product resulting from these reactions can be envisioned as an activated intermediate XNO (where X is OONO2, NO2, or CO−3) that could transfer a nitrosyl cation (NO+) to the phenolate ion. An alternative mechanism for the nitrosation of phenol involves the one-electron oxidation of the phenolate ion by CO•−3to give the phenoxyl radical and the oxidation of ONOO−by CO•−3to give a nitrosyldioxyl radical (ONOO•), which decomposes to give•NO and O2; the•NO then reacts with the phenoxyl radical giving nitrosophenol. Both mechanisms are consistent with the high yields of NO−2and O2during the alkaline decomposition of peroxynitrite and the potent inhibitory effect of N−3on the nitrosation of phenol by peroxynitrite and peroxynitrite/CO2adducts. The biological significance of the peroxynitrite-mediated nitrosations is discussed.