Nitrophenol, Ortho

Certain groups attached to an aromatic ring can donate electrons into its delocalized molecular orbitals. Examples of these electron-donating substituents include —NH2 and —OH. Electrophilic substitution of benzene is much faster when an electron-donating substituent is present. For example, the nitration of phenol, C6H5OH, proceeds so quickly that it requires no catalyst. Moreover, when the products are analyzed, the only products are found to be 2-nitrophenol (ortho-nitrophenol, 37) and 4-nitrophenol (pnra-mtrophcnol, 38 . 

Samajdar et al. (2000) performed nitration of aromatic compounds by bismnth nitrate on catalysis with montmorillonite KSF. The reaction develops in THF suspension on steering dnring 10 min. Nitration of anisole proceeds strictly in the para position (91% yield after 10 min), bnt in case of phenol, the reaction occnrs to be nonregioselective and 3 1 mixture of para and ortho nitro prod-nets is formed with a common yield of 89%. Nitration of estrone (the steroid phenol) also leads to 1 1 mixtnre of para and ortho nitrophenolic steroids in 94% yield. 

Zeyer, J., and H. P. Kocher, Purification and characterization of bacterial nitrophenol oxygenase which convert ortho-nitrophenol to catechol and nitrite , J. Bacteriol., 170,1789-1794 (1988). 

Fig. 12-15.—The atomic arrangement in the ortho-nitrophenol molecule. The interatomic distances and bond angles are given their correct values it is seen that the C—II bond is directed toward an oxygen atom of the nitro group.

More detailed work on the intramolecular hydrogen bond of ortho-nitrophenols has recently been carried out by Chopineaux-Courtois and coworkers and by Abraham and... 

In solution, ortho-nitrophenol is capable of intramolecular hydrogen bonding, while the para isomer inter-molecular hydrogen bonding only. 

As you can see in the diagram, the intramolecular hydrogen bonding is most pronounced in ortho-nitrophenol because of the proximity of the -NO group to die hydroxyl group. 

Separation by steam distillation is sometimes possible, but it is more usual to employ this procedure after one component has been rendered non-volatile, e.g. conversion of an acidic or basic substance into a salt. In addition to salts, compounds containing more than one polar group are generally non-volatile in steam, thougih there are many exceptions to this statement. Thus, while ortho-nitrophenol vaporizes in steam, the meta and para isomers do not, the difference in behaviour being attributable to chelation in the ortho compound. 

Ortho -nitrophenol is less acidic than/jara-nitrophenol. This is because an ortho-nitro group can form a hydrogen bond to the alcohol H. 

Under these basic conditions, the product (orf/jo-nitrophenol) is deprotonated upon its formation (because the resulting resonance stabilized anion is more stable than hyiioxide). In order to return the proton and regenerate ortho-nitrophenol, we must introduce a proton source into the reaction flask after the reaction is complete (aqueous acidic work-up). The problem statement did not mention an acidic workup, so the product is the following salt (the conjugate base of orf/jo-nitrophenol) ... 

Although these generaliaations furnish a satisfactoi picture of the efiiect of alkali and add on most phenol-formaldehyde reactions, the structure of the phenols involved is sometimes of paramount importance and may result in defimte exceptions to general rules. Ortho-nitrophenol forms methylol derivatives under acidic conditions and beta naphthol gives a quantitative yield of methylene bis-beta-uaphthol in the presence of alkaline catalysts. 

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