Nitrosobenzoic acids

Category 3. Intramolecular Rearrangement. Two examples are the rearrangement of the trimesityl compound (1) to the enol ether (2), " and irradiation of o-nitrobenzaldehydes (3) to give o-nitrosobenzoic acids (4)." ... 

Nitro compounds have also been reported to undergo photocyclizations. The intermediacy of an isoxazoline in the photorearrangement of o-nitro-benzaldehyde to o-nitrosobenzoic acid is now in doubt,318 but intramolecular hydrogen abstraction by an excited nitro group in nitrobenzene derivatives can result in the formation of heterocycles. 4-tm-Butyl-3-methoxy-2,6-dinitrotoluene (384) on irradiation in methanolic sodium hydroxide solution... 

The transfer of the oxygen from a nitro-group to a carbon atom in the orfAo-position may not seem very likely, but several similar reactions are known. Thus o-nitrotoluene is converted by alkali into anthranilic acid (Binz), o-nitrobenzaldehyde by sunlight into o-nitrosobenzoic acid (Ciamician) ... 

The photodecarboxylation of p-(nitrophenyl) glyoxylic acid 156, which was studied by time-resolved and steady-state methods at room temperature93, leads to p-nitrosobenzoic acid and carbon dioxide in good yields with = 0.28 in aqueous solution at pH 2-12 and excitation at 313, 280 or 254 nm (equation 76). An intermediate (Xmax = 350, r 2 xs) observed by nanosecond laser flash photolysis is assigned to the aci-form of the nitroketene... 

Since p-nitrosobenzoic acid has been shown to have a half-life of some 4 min in rat blood, this intermediate, once formed in the capillaries of the irradiated skin, may meet the requirement of sufficient stability to reach sensitive targets as the bone marrow while travelling through the blood141. The reactivity of p-nitrosobenzoic acid with thiols appears not to have been tested hitherto. From the known Hammett constant (ap = +0.4555) one may deduce that the compound will show a reactivity in between the reactivities of nitrosobenzene and p-nitrosoacetophenone. 

The photochemistry of 4-nitrobenzaldehyde has been reinvestigated In aqueous solution, 4-nitrosobenzoic acid is formed. A ketene has been proposed as intermediate... 

The photochemical rearrangement of o-nitrobenzaldehyde or its acetals to the corresponding o-nitrosobenzoic acid derivatives has been known for many years. A careful study of the mass spectra and metastable ions obtained from methyl o-nitrosobenzoate and o-nitrobenzaldehyde dimethyl-acetal has provided strong evidence that the electron impact induced fragmentation strongly parallels the photochemical rearrangement Eq. (71). 

On exposure to sunlight, under in vivo-related circumstances relevant to the eye under treatment, p-nitrobenzaldehyde, p-nitrobenzoic acid, and p-nitrosobenzoic acid were found (9) in chloramphenicol eye drops. The amount of p-nitrosobenzoic acid foimd, represented 45 mol% of the initial amount of chloramphenicol. Patients should be informed if photoprotective storage of these eye drops is necessary, and that the intense photon exposure of the eye after administration of chloramphenicol eye drops should be avoided. 

In the 366 A photolysis of nitrobenzene in isopropyl alcohol the quantum yield of disappearance of nitrobenzene is 1.14x 10 the observed products were explained by reactions of triplet state nitrobenzene with the solvent When ortho substituents are present, e.g. aldehyde groups, an intramolecular rearrangement takes place to yield o-nitrosobenzoic acid . The following intermediates have been suggested ... 

It is interesting that treatment of some aromatic nitro compounds with ammonium amalgam yields among other products nitrosobenzenes [76]. 2-Nitrobenzoic acid thus gives about 45% 2-nitrosobenzoic acid together with anthranilic acid (10%), and 2-nitro-toluene (5g) yields 0.6 azoxytoluene, 2g 2-nitrosotoluene, and 1.5 g o-toluidine on treatment with NH4(Hg). 

Irradiation of o-nitrobenzaldehyde in benzene gives o-nitrosobenzoic acid ((/) 0.5) in a process that occurs via a triplet state having a lifetime of 0.6 ns, and the transient enol (49). A mechanism is proposed and this is outlined in Scheme 9. The kinetics of the photo-oxidation of benzaldehyde have been studied in the liquid phase and the rate constants extracted found to be in close agreement with those obtained from the photodecomposition of PhC020H. ... 

The photorearrangement of o-nitrobenzaldehyde (127) to o-nitrosobenzoic acid (128) has been re-examined. the mechanism of this conversion remains uncertain, but a transient species has been detected and tentatively assigned the... 

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