Nitration of dinitrophenol

This is the most modem industrial method for the preparation of picric acid from chlorobenzene via chlorodinitrobenzene (for preparation of dinitrophcnol from chlorodinitrobenzene, see p. 484). The nitration of dinitrophenol to picric acid is carried out by conventional methods, using nitrating mixtures containing some 0-5% of water. 

The following three grades of purity of picric acid are specified in the U S S R, standard, OST 3515 (Table 118). 

General appearance Colour crystalline powder free from foreign matter light yellow  

Picric acid should be transported in wooden cases or barrels with thick walls 1.5 cm. 

Nitration grade phenol should be completely soluble in water, giving a clear solution. Not more than 0.1% of non-volatile residue left after the evaporation of phenol, when heated on a steam bath, is permissible. 

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VII. Preparation. There are two industrial methods of manufg PA 1) nitration of Phenol 2) nitration of dinitrophenol prepd by hydrolysis of chloro dinitrobenzene... 

Nitration of dinitrophenol. This is a multistage process. First chlorobenzene is nitrated to chlorodinitrobenzene as shown schematically below ... 

The explosive power of picric acid is somewhat superior to that of -> TNT, both as regards the strength and the detonation velocity. Picric acid is prepared by dissolving phenol in sulfuric acid and subsequent nitration of the resulting phenoldisulfonic acid with nitric acid or by further nitration of dinitrophenol (prepared from dinitrochlorobenzene). The crude product is purified by washing in water. 

Picric acid (Figure 3.9) is made by dissolving phenol in sulfuric acid, then nitrating with nitric acid. Another route is from nitration of dinitrophenol, which is made from dinitrochlorobenzene. Picric acid was used extensively in World War I as a bomb and grenade filler both by itself and in mixtures with other explosives. Its major drawback (besides its toxicity) is that it reacts with metals... 

Principles of manufacture Nitration of phenol Nitration of dinitrophenol Methods based on phenol nitration Raw materials... 

The nitration of anisole in 40% aq. nitric acid in the presence of some nitrous acid yielded 2,4-dinitrophenol as the main product. In more concentrated solutions of nitric acid 0- and />-nitroanisoles were the main products, less than o-1 % of the weta-isomer being formed. " The isomeric ratios for nitration imder a variety of conditions are given later ( 5.3.4). 

An ipso attack on the fluorine carbon position of 4-fIuorophenol at -40 °C affords 4-fluoro-4-nitrocyclohexa-2 5-dienone in addtion to 2-nitrophenol The cyclodienone slowly isomenzes to the 2-nitrophenol Although ipso nitration on 4-fluorophenyl acetate furnishes the same cyclodienone the major by-product is 4 fluoro-2,6-dinitrophenol [25] Under similar conditions, 4-fluoroanisole pnmar ily yields the 2-nitro isomer and 6% of the cyclodienone The isolated 2 nitro isomer IS postulated to form by attack of the nitromum ion ipso to the fluorine with concomitant capture of the incipient carbocation by acetic acid Loss of the elements of methyl acetate follows The nitrodienone, being the keto tautomer of the nitrophenol, aromatizes to the isolated product [26] (equation 20) Intramolecular capture of the intermediate carbocation occurs in nitration of 2-(4-fluorophenoxy)-2-methyIpropanoic acid at low temperature to give the spiro products 3 3-di-methyl-8 fluoro 8 nitro-1,4 dioxaspiro[4 5]deca 6,9 dien 2 one and the 10-nitro isomer [2d] (equation 21)... 

Dinitrophenol. Yel needles from w or thick crysts from ale mp 144—5° d 1.681 at 20°. Can be prepd by the nitration of m-nitrophenol, with 2,5- and 3,4-Dinitrophenols being formed simultaneously. Very easily sol in eth and hot ale... 

Mor alpha-) Dinitrophenol- Yel orthorhombic crysts from w, leaflets from ale mp 112—14° bp (decomp) d 1.683g/cc at 24°, 1.4829 at 72.5/4°. Sublimes when carefully heated volatile with steam. Can be prepd by the nitration of phenol, but this method is not considered commercially practicable because of partial decompn of the phenolic ring. A better method is by hydrolysis under pressure of 2,4-dinitrochloro-benzene, which in turn can be obtained by nitrating chlorobenzene. Other methods are given in Ref 1... 

Trinitr ophenol (jS-Trinjtrophenoi). White needles from dil ale, mp 96°. Can be prepd by the nitration of 3,4-Dinitrophenol or by other methods. Very sol in ale,eth and benz, sol in hot w, diff sol in cold w. It is an expl forms metallic salts such as those of K and Ba... 

Phenol ethers, like the parent phenols, are reactive substrates. Phenol ethers like anisole and phenetole are readily nitrated to their picryl ethers, 2,4,6-trinitroanisole and 2,4,6-trinitrophenetole respectively, on treatment with mixed acid composed of concentrated nitric and sulfuric acids at 0 °C. Such reactions are vigorous, prone to oxidative side-reactions, and pose a considerable safety risk. The direct nitration of 2,4-dinitrophenol ethers, obtained from the reaction of 2,4-dinitrochlorobenzene with alkoxides, provides a more practical route to picryl ethers on an industrial scale. ... 

The nitration of 2-amino-4,6-dinitrotoluene (63) with a mixtnre of nitric acid in sulfuric and acetic acids yields 2-diazo-3-methyl-4,6-dinitrophenol (65) in 75 % yield without isolation of the intermediate nitramine (64)." ... 

The nitration of both 4-methyl- and 4-chloro-2,6-dinitrotoluenes (66 and 67) with mixed acid in acetic acid at subambient temperature allows the isolation of the nitramines, (68) and (69), respectively. Thermolysis of (68) and (69) in refluxing methylene chloride yields the corresponding diazophenols, (70) and (71), respectively. Scilly and co-workers isolated 2-diazo-4,6-dinitrophenol (DINOL) (53) from the thermolysis of fV,2,3,5-tetranitroaniline (73) in ethyl acetate at 60 °C. 

The best process for the production of dinitrophenol is probably the autoclaving of dinitrochlorobenzene with aqueous caustic soda. The product is obtained on acidification and is used as such, or is nitrated to picricacid for the commercial production of that material by the so-called synthetic process. 

Figure 17.1 (a) Proposed pathway for the nitration of 2-nitrophenol to 2,4-dinitrophenol. (b) Corresponding pathway for the nitration of 4-nitrophenol. The reaction schemes are based on the experimental data of reference [51]. 

Laurent [8] was the first to obtain dinitrophenol by nitrating phenol. Investigations that followed revealed that Laurent s dinitrophenol was not a chemical individual, but a mixture of the 2,4- and 2,6-isomers. Kiimer [ 17] obtained pure 2,4-dinitrophenol by the nitration of p- nitrophenol and Armstrong [ 18] prepared... 

Oxidation of nitrosophenols. This method is applied when fewer nitro groups are to be introduced on the ring than those obtained by way of nitration. It is also applied when a pure product, free from its isomers, is to be prepared, e.g. p- nitro-phenol from phenol. Direct nitration of phenol yields a mixture of the o- and p- isomers, dinitrophenol being readily formed as a by-product. Similarly dinitroresorcinol may be obtained by oxidation of dinitrosoresorcinol (p. 537). 

After 60-75 min, when nitration has come to an end, water should be added to bring the temperature down to 70°C and to reduce the solubility of dinitrophenol in the spent acid. 

It is used as a spray in towers for the recovery of the nitrogen oxides evolving during the nitration of phenol to dinitrophenol. As a result of this operation the HN03 content in the acid rises to 19-20%. 

The spent acid from the nitration of phenol by the methods described contains several by-products, among them 2,4-dinitrophenol-6-sulphonic acid in the proportions of 22 parts per 100 parts of phenol used for the process, which corresponds to a 8% loss of the phenol, and oxalic acid in the proportion of 5-6 parts per 100 parts of phenol. These are the principal by-products that lower the yield of picric acid. 

Store, of chlorobenzene Nitration of Hydrolysis to dinitrophenol, Trinitration ( Washing... 

Absence of nitro derivatives was also observed upon irradiation of nitro-phenols and nitrate. Also in this case, the electron-withdrawing character of the nitro group can account for the inhibition of nitration [109]. The difficulty to nitrate nitrophenols to dinitrophenols is widely recognised [125] and also constitutes a problem in environmental chemistry, since field data seem, in contrast, to indicate that the nitration of 2-nitrophenol to 2,4-dinitrophenol in the atmospheric aqueous phase (e.g. cloud water) is an important process [126]. In fact, aqueous-phase nitration might be a relevant sink for 2-nitrophenol and possibly the main source of the dinitro compound, which is a powerful phytotoxic agent [127,128]. In the presence of nitrate under irradiation the main transformation intermediates of nitrophenols are the hydroxyl derivatives, while other compounds may derive from the direct photolysis of the substrates (catechol and 2-nitrosophenol from 2-nitrophenol hydroquinone, benzoquinone, hydroxybenzoquinone and 4-nitrosophenol from 4-nitrophenol) [109]. 

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