Nitro groups compounds

Anthraquinone can be brominated, chlorinated directly to the tetrachloro (I, 4, 5, 8-) stage, nitrated easily in the 1-position, but gives the 1,5-and 1,8-dinitro-derivalives on prolonged nitration the nitro groups in these compounds are easily displaced by neutral solutions of alkali sulphites yielding the corresponding sulphonic acids. Sulphonation with 20-30 % oleum gives the 2- 2,6- and 2,7-derivatives in the presence of Hg the 1- 1,5- and 1,8- derivatives are formed. 

Some nitro-compounds are themselves coloured and can be used as dyestuffs, e.g. picric acid. In this case the nitro-group can be considered to be the chromophore. For aliphatic nitro-compounds see nitroparaffins. 

Nitro compounds, when hquid, have characteristic odours, are insoluble in water, highly refractive and with a density greater than unity. Many are crystalline sohds. Most nitro compounds are slightly coloured, generally yellow the intensity of the colour increases with the number of nitro groups. The following reactions will assist in their detection. 

A number of selected aromatic nitro compounds are collected in Table IV,16A, It will be noted that a few nitro aromatic esters have been included in the Table. These are given here because the nitro group may be the first functional group to be identified aromatic nitro esters should be treated as other esters and hydrolysed for final identification. 

It is convenient to include under Aromatic Amines the preparation of m-nitroaniline as an example of the selective reduction of one group in a polynitro compound. When wt-dinitrobenzene is allowed to react with sodium polysulphide (or ammonium sulphide) solution, only one of the nitro groups is reduced and m-nitroanUine results. Some sulphur separates, but the main reaction is represented by ... 

Investigations of the solubilities of aromatic compounds in concentrated and aqueous sulphuric acids showed the activity coefficients of nitrocompounds to behave unusually when the nitro-compound was dissolved in acid much more dilute than required to effect protonation. This behaviour is thought to arise from changes in the hydrogenbonding of the nitro group with the solvent. 

Allylic nitro compounds form rr-allylpalladium complexes by displacement of the nitro group and react with nucleophiles, and allylation with the tertiary nitro compound 202 takes place at the more substituted side without rearrangement to give 203[8,9,128]. 

Formic acid is a good reducing agent in the presence of Pd on carbon as a catalyst. Aromatic nitro compounds are reduced to aniline with formic acid[100]. Selective reduction of one nitro group in 2,4-dinitrotoluene (112) with triethylammonium formate is possible[101]. o-Nitroacetophenone (113) is first reduced to o-aminoacetophenone, then to o-ethylaniline when an excess of formate is used[102]. Ammonium and potassium formate are also used for the reduction of aliphatic and aromatic nitro compounds. Pd on carbon is a good catalyst[103,104]. NaBH4 is also used for the Pd-catalyzed reduction of nitro compounds 105]. However, the ,/)-unsaturated nitroalkene 114 is partially reduced to the oxime 115 with ammonium formate[106]... 

Esters of 2-thiazole carboxylic acids (75) (383) are also prepared from ethyl monothiooxamate (74) (Scheme 34), and several compounds of this type with hydrogen, alkyl, or aryl groups in the 4- or 5-position (201, 209, 210, 242, 294) or a nitro group in the 5-position (674) have been reported. 

A large number of variously 2-, 4-, and 5-substituted thiazoles with alkyl, aryl, hydroxy, methylthio, mercapto, halo, and nitro groups have been analyzed by thin-layer chromatography on silica and alumina by the Stahl s technique (167, 170, 172). Among the many systems recommended for the elution of these compounds are the following ... 

Nitro groups are readily reduced to primary amines by a variety of methods Cat alytic hydrogenation over platinum palladium or nickel is often used as is reduction by iron or tin m hydrochloric acid The ease with which nitro groups are reduced is especially useful m the preparation of arylamines where the sequence ArH ArN02 ArNH2 IS the standard route to these compounds... 

Reduction of aryl nitro compounds (Sec tion 22 9) The standard method for the preparation of an arylamine is by nitra tion of an aromatic ring followed by reduction of the nitro group Typical re ducing agents include iron or tin in hydro chloric acid or catalytic hydro genation... 

Controlled-potential coulometry also can be applied to the quantitative analysis of organic compounds, although the number of applications is significantly less than that for inorganic analytes. One example is the six-electron reduction of a nitro group, -NO2, to a primary amine, -NH2, at a mercury electrode. Solutions of picric acid, for instance, can be analyzed by reducing to triaminophenol. 

In the examples, a nitro group is substituted for a hydrogen atom, and water is a by-product. Nitro groups may, however, be substituted for other atoms or groups of atoms. In Victor Meyer reactions which use silver nitrite, the nitro group replaces a hahde atom, eg, I or Br. In a modification of this method, sodium nitrite dissolved in dimethyl formamide or other suitable solvent is used instead of silver nitrite (1). Nitro compounds can also be produced by addition reactions, eg, the reaction of nitric acid or nitrogen dioxide with unsaturated compounds such as olefins or acetylenes. 

Nitro alcohols form salts upon mild treatment with alkahes. Acidification causes separation of the nitro group as N2O from the parent compound, and results in the formation of carbonyl alcohols, ie, hydroxy aldehydes, from primary nitro alcohols and ketols from secondary nitro alcohols. 

Analytical and Test Methods. o-Nitrotoluene can be analyzed for purity and isomer content by infrared spectroscopy with an accuracy of about 1%. -Nitrotoluene content can be estimated by the decomposition of the isomeric toluene diazonium chlorides because the ortho and meta isomers decompose more readily than the para isomer. A colorimetric method for determining the content of the various isomers is based on the color which forms when the mononitrotoluenes are dissolved in sulfuric acid (45). From the absorption of the sulfuric acid solution at 436 and 305 nm, the ortho and para isomer content can be deterrnined, and the meta isomer can be obtained by difference. However, this and other colorimetric methods are subject to possible interferences from other aromatic nitro compounds. A titrimetric method, based on the reduction of the nitro group with titanium(III) sulfate or chloride, can be used to determine mononitrotoluenes (32). Chromatographic methods, eg, gas chromatography or high pressure Hquid chromatography, are well suited for the deterrnination of mononitrotoluenes as well as its individual isomers. Freezing points are used commonly as indicators of purity of the various isomers. 

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