Phenoxides, reactions with nitroaromatics

The range of nueleophiles whieh have been observed to partieipate in nueleophilie aromatie substitution is similar to that for S[, 2 reactions and includes alkoxides, phenoxides, sulftdes, fluoride ion, and amines. Substitutions by earbanions are somewhat less common. This may be because there are frequently complications resulting from eleetron-transfer proeesses with nitroaromatics. Solvent effects on nucleophilic aromatic substitutions are similar to those discussed for S 2 reactions. Dipolar... 

A variety of other C-bonded phenoxide complexes of nitroaromatics have since been reported in most cases, the oxygen-bonded adduct is not observed. For example, in the reaction of TNB with 1-napthoxide, only the 1 1 and 2 1 C-bonded adducts 9 and 10 were formed (28) ... 

It is reported that an industrial explosion was initiated by charging potassium hydroxide in place of potassium carbonate to the chloro-nitro compound in the sulfoxide [1], Dry potassium carbonate is a useful base for nucleophilic displacement of chlorine in such systems, reaction being controlled by addition of the nucleophile. The carbonate is not soluble in DMSO and possesses no significant nucleophilic activity itself. Hydroxides have, to create phenoxide salts as the first product. These are better nucleophiles than their progenitor, and also base-destabilised nitro compounds. Result heat and probable loss of control. As it nears its boiling point DMSO also becomes susceptible to exothermic breakdown, initially to methanethiol and formaldehyde. Methanethiolate is an even better nucleophile than a phenoxide and also a fairly proficient reducer of nitro-groups, while formaldehyde condenses with phenols under base catalysis in a reaction which has itself caused many an industrial runaway and explosion. There is thus a choice of routes to disaster. Industrial scale nucleophilic substitution on chloro-nitroaromatics has previously demonstrated considerable hazard in presence of water or hydroxide, even in solvents not themselves prone to exothermic decomposition [2],... 

This study reports on the reactions of ambident nucleophiles with electron-deficient nitroaromatic and heteroaromatic substrates anionic complex formation or nucleophilic substitution result. Ambident behavior is observed in the case of phenoxide ion (O versus C attack) and aniline (N versus C attack). O or N attack is generally kinetically preferred, but C attack gives rise to stable thermodynamic control. Normal electrophiles such as 1,3,5-trinitrobenzene or picryl chloride are contrasted with superelectrophiles such as 4,6-dinitrobenzofuroxan or 4,6-dinitro-2-(2,4,6-trinitrophenyl)benzotriazole 1-oxide (PiDNBT), which give rise to exceptionally stable a complexes. Further interesting information was derived from the presence in PiDNBT of two electrophilic centers (C-7 and C-l ) susceptible to attack by the ambident nucleophilic reagent. The superelectrophiles are found to exhibit lesser selectivity toward different nucleophilic centers of ambident nucleophiles compared with normal electrophiles. 

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