Nitro group, lability

Polysiloxanes containing a-cyano and a- or ]]-fluorine substituents are. thermally labile at comparatively low temperatures and are not used in gas chromatography. Polysiloxane phases containing 3,3,3-trifluoropropyl groups are thermally Stable up to about 250-275 C and possess rather unique selectivity, particularly for electron-donor solutes, such as ketones and nitro groups. The electronegative trifluoropropyl... 

Cross-linked polystyrene can be directly nitrated with fuming nitric acid at low temperatures (-25 °C to 0°C) [189,203,374] polymers with up to one nitro group per arene result [203]. Partial nitration can be achieved with milder nitrating agents, such as acetyl nitrate [203]. Because direct nitrations are not compatible with most linkers (which are often acid- or oxidant-labile), nitro compounds are generally not prepared on supports but in solution, and are then linked to the support. 

All of the unsymmetrical TNT isomers react with nucleophilic reagents with selective replacement of the labile nitro group located in the position indicated in Table 12. The 23>6-isomer may react in this way, but the position of the reactive group has not been established with certainty, and early work even suggested that a mixt of compds is formed (Ref 1)... 

Direct nucleophilic displacement of the halogen in an aryl halide is difficult and hydrolysis to phenols requires high temperatures and pressures the method is therefore only suitable on the large scale. The presence of a nitro group in the ortho or para position, however, makes the halogen more labile since electron withdrawal by the nitro group in these positions stabilises the intermediate anion by electron delocalisation. p-Chloronitrobenzene, for example, is hydrolysed to p-nitrophenol when heated with 15 per cent sodium hydroxide solution at about 150 °C. 

A reaction worth noting in the context of nitro-group interactions with <-amino functions involves the rapid photolytic breakdown of 2,4-dinitrophenyl derivatives of a-amino acids. The lability of such derivatives in sunlight has long been known to protein chemists who... 

It will be recalled that not only halogen atoms, but also nitro and sulfo groups, can be replaced by phenyl- or arylamines. The lability of the nitro group, particularly in the anthraquinone nucleus, permits the preparation of some important intermediates which cannot be discussed here. Also, highly nitrated benzene derivatives give access to interesting condensation products. 

Remarks. Nitro-p-dichlorobenzene can be reduced to p-dicbloroaniline in tbe usual way with iron and a small amount of acid. Tbe chlorine ortbo to tbe nitro group is labile and can be replaced by various substituents, less easily, however, than the chlorine in 2,4-dinitrochlorobenzene, but more easity than that in o-nitrochloro-benzene. The replacement of the chlorine by hydrojyl by the action of aqueous sodium hydroxide is described in the following preparation. Reaction wiUi sodium methylate yields 4-chloro-2-nitroanisole, which is reduced to 4-chloro-2-am sidine (chloramsidine P, or fast red R base). With ammonia under pressure, 4-chloro-2-nitroaniline (fast red 3CL base) is formed. These bases are important starting materials for the preparation of azo dyes, especial pigment and lake coIots, as well as ice colors. 

The kinetics of substitution of bipy or phen into Co (467, 574), Ni (144), and Pt (697) complexes have been reported. Several studies of the hydrolysis of complexes of form [Co(III)(bipy)2XY] may be found. For both cis and trans isomers where X = Y = CY, hydrolysis is instantaneous (581), whereas for the cis isomer with X = acetate and Y = acetate or OH , reaction is very slow as a conjugate base mechanism cannot operate and the first-order reaction is therefore independent of [OH ] (124). One NO2 group in acid dependent and under acidic conditions is thought to proceed via protonation of one nitro group (289, 472). The interconversion of the cis and trans isomers, where X = N02 and Y = H2O, has an overall rate constant equal to + A [H+], implying reactions for both OH and... 

However, the problem was recently revived. It was recalled that Frisch, Silverman and Bogart [46] pointed out the lability ofo-nitro group in 4-amino-3-nitroveratrole. This compound in acid condition can be transformed into 4-... 

---