Nitrophenol hydrogenation

Fig. 7.12. Host-guest interaction observed in the a-CyD complex with p-nitrophenol. Hydrogen atoms of the phenylene ring are in van der Waals contact with hydrogen atoms of C-5H methine groups (dashed lines) and are...

Fig. 32. Structure of the 1 2 dibenzo[24]crown-8 complex with sodium o-nitrophenolate. Hydrogens...

Aluminum chloride/o-nitrophenol/hydrogen chloride Modified DObner-Miller synthesis... 

Greater electronic frequency shifts are observed when intramolecular charge transfer occurs upon excitation in push-pull compounds such as 4-nitroaniline and 4-nitrophenol. For example, in cyclohexane, free 4-nitrophenol absorbs at 285 nm and 4-nitrophenol hydrogen bonded to triethylamine at 307 nm. The shift amounts to 2515 cm (30 kJ mol ). 

The induction period could result from a more complex behavior than reduction, which can in principle be done ex situ. Appearance of the induction period in the case of nitrophenol hydrogenation over Au nanoparticles (Fig. 9.38) was ascribed to the surface restructuring induced by the adsorbed substrate. A rearrangement of the surface atoms seems to be necessary to create catalyticaUy active sites as, for example, comers or edges on the surface. 

Aminophenols are either made by reduction of nitrophenols or by substitution. Reduction is accompHshed with iron or hydrogen in the presence of a catalyst. Catalytic reduction is the method of choice for the production of 2- and 4-aminophenol (see Amines BY reduction). Electrolytic reduction is also under industrial consideration and substitution reactions provide the major source of 3-aminophenol. 

Production is by the acetylation of 4-aminophenol. This can be achieved with acetic acid and acetic anhydride at 80°C (191), with acetic acid anhydride in pyridine at 100°C (192), with acetyl chloride and pyridine in toluene at 60°C (193), or by the action of ketene in alcohoHc suspension. 4-Hydroxyacetanihde also may be synthesized directiy from 4-nitrophenol The available reduction—acetylation systems include tin with acetic acid, hydrogenation over Pd—C in acetic anhydride, and hydrogenation over platinum in acetic acid (194,195). Other routes include rearrangement of 4-hydroxyacetophenone hydrazone with sodium nitrite in sulfuric acid and the electrolytic hydroxylation of acetanilide [103-84-4] (196). 

Some ortho-substituted phenols, such as o-nitrophenol, have significantly lower-boiling points than those of the rneta and para isomers. This is because the intramolecular hydrogen bond that forms between the hydroxyl group and the substituent partially compensates for the energy required to go from the liquid state to the vapor. 

Later, Taft and his coworkers examined the H-bonding donor ability of the amino protons in 4-nitroaniline and 4-nitrophenol as the hydrogen bond donors. They also tried... 

Hydrogenation reactions, particularly for the manufacture of fine chemicals, prevail in the research of three-phase processes. Examples are hydrogenation of citral (selectivity > 80% [86-88]) and 2-butyne-l,4-diol (conversion > 80% and selectivity > 97% [89]). Eor Pt/ACE the yield to n-sorbitol in hydrogenation of D-glucose exceeded 99.5% [90]. Water denitrification via hydrogenation of nitrites and nitrates was extensively studied using fiber-based catalysts [91-95]. An attempt to use fiber-structured catalysts for wet air oxidation of organics (4-nitrophenol as a model compound) in water was successful. TOC removal up to 90% was achieved [96]. 

Hydrogenations of substituted 2-nitrophenols and nitrobenzenesulphonic acid double bond Ciba-Geigy Buser and Urwyler (1993)... 

Schrader prepared the ester (38) in 60% yield by reaction of sodium p-nitrophenate with diethyl chlorophosphate, using xylene as solvent for the reaction. He made it, but in lower yields, from p-nitrophenol and diethyl chlorophosphate, using, respectively, pyridine and sodium cyanide as acceptors for hydrogen chloride. Schrader also prepared it in 96% yield by nitrating diethyl phenyl phosphate at 0° C. or below. Under the conditions he used, Schrader claims that the nitro group is directed to the para position. No yield is given for the diethyl phenyl phosphate, which he presumably made from sodium phenate and diethyl chlorophosphate. Diethyl chlorophosphate may be prepared in high yield (30) from diethyl phosphite and chlorine. 

Goi A, Trapido M (2002) Hydrogen peroxide photolysis, Fenton reagent and photo-Fenton for the degradation of nitrophenols a comparative study. Chemosphere 46 913-922... 

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