Nitrophenols

Nitrophenols are less important as intermediates than chlorophenols. Nitrophenols can be obtained by nitration of phenol or, preferably, by nucleophilic substitution of the corresponding chloronitrobenzenes (see Chapter 5.8.1) with alkali solution. Nitration of phenol yields an o-/p-mixture consisting of around 55% o-nitrophenol and 45% p-nitrophenol separation of the isomers is possible by steam distillation. 

Methyl parathion, a broad-spectrum insecticide, is produced by the reaction of sodium p-nitrophenolate and 0,0-dimethyl thiophosphoryl chloride. 

The diethyl derivative also serves as an insecticide total world production of these phosphoric acid esters is estimated to be around 20,000 tpa. 

Nitration of phenol in sulfuric acid produces 2,4,6-trinitrophenol (picric add). Picric acid is used predominantly as an intermediate in the production of picramic acid, a raw material for dyestuffs picric acid has lost its earlier importance as an explosive. 

Iutennefliate phases of the reriuetinn can l e separate 1 flit ease of o- and jemfropheno), if eoncent rated s t nli n aniline hydrochloride is used as electrolyte , oh. t. Compi Ciited condensation products are obtained. It seem that mlrosophenols primtirily formed react in the form of quinon oximes with aniline. 

Kohde has investigated the influence of methyl groups in f he iimidfegroiips in alkaline reduction. 

Ihuwiylcnediamine is pro Sneed in alkeiup -uhifhuc nanU he t K eef d (Kibsn 

The nitrotoluidines when reduced electrolylieally in acid and alkaline solution Indiave like the nitnuiilines. The position of the nnhyl group must, of course, lie bona in mind. 

Iii this m.se the hydroxyl group occupies the o-position in resjieet to tie original ntiro-group. 

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As with the phenols, but in contrast to the pyridines, for the methyl-substituted anilines there is a relationship between AH and AS, This is shown in Fig. 2, a plot of T AS against AH, It is seen that there is some compensation oi AH by TAS. This effect Laidler 248 ascribes mainly to solvent and steric factors. 

The introduction of a methyl group into the para position of aniline causes a decrease in both A H and d. S. A possible explanation of this is in terms of solvent effect. The — CHg group will tend to reduce the positive charge on the —group andthere will, therefore, be less electrorestriction of water and a consequent increase in enthalpy and entropy of the cationic form, BH+. For the para 

In contrast, for m-toluidine, there is an increase in both AH and A S (the opposite of the effect observed for m-cresol) as compared with the values for aniline. Now it is likely that there is some steric interference between the —NHg and w-CHg groups and this will cause a lowering of the entropy of the cationic form, BH+. In the neutral form this will not occur and there will be a consequent 

With a methyl group in the orthothe effect of an increased entropy of the cationic form, will be much more 

It is significant that, in agreement with these ideas, these effects are not found in the pyridines, where steric effects are not to be expected. For the pyridines, the JS values are practically constant for the mononieth i derivatives, since the inductive effect lea ires d jS unaffected, except in so far as it causes alteration in electrorestriction of solvent molecules. 

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Prepared by reduction of 4-nitrophenol or 4-nitrosophenoi. Can be diazotized and used as a first component in azo-dyes. Chief outlet is for sulphur dyes in which it is fused with sodium polysulphides. L/sed as a photographic developer. 

Bright yellow needles m.p. 45 C, b.p. 2 4°C. Prepared together with 4-nitrophenol by careful nitration of phenol. Sodium sulphide reduces it to 2-aminophenol which is used in dyestuffs and photographic processes. 

Ditrophenol, -nitropbenol, C H NOj. Colourless needles m.p. 114 C. Prepared as 2-nitrophenol. Reduction with iron and hydrochloric acid gives 4-aminophenol. 

Naphthalene, oxalic acid (hydrated), cinnamic acid, acetamide, benzamide, m-dinitrobenzene,/>-nitrophenol, toluene p-sulphon-... 

Students should carry out the purification by steam distillation of (a) crude nitrobenzene or chlorobenzene, or of (b) crude naphthalene, o-nitrophenol (p. 170) or />-tolunitrile (p. 194) as examples of solid compounds which may also be purified in this way. When the distillation is complete, disconnect the tubing (Fig. 15) between C and D before removing the flame from under D, otherwise the contents of C will be sucked back into D as the latter cools. 

If phenol is treated even with dilute nitric acid at room temperature, nitration readily occurs with the simultaneous formation of the yellow o-nitro-phenol and the white /> nitrophenol. These compounds can be readily... 

For the latter purpose, dissolve the crystals in hot ethanol, and then add water drop by drop to the well-stirred solution until a line emulsion just appears then add more ethanol, also drop by drop, until the emulsion just redissolves. ow allow the solution to cool spontaneousK if the emulsion reappears, add a few drops of ethanol from time to time in order to keep the solution clear. Finally the o-nitrophenol separates in crystals, and the well-stirred mixture may now be cooled in ieewvater until crystallisation is complete. Filter, drain and diy either in an atmospheric desiccator, or by pressing between drying-paper. 

The o-nitrophenol is obtained as bright yellow crystals, m.p. 46°, possessing an odour which resembles both that of phenol and of nitrobenzene. 

The preparation can be shortened by omitting this stage and extracting the black residue by boiling it first with the water already present in the flask. In this case the yield of p-nitrophenol is increased somewhat, but the product is usually verv dark in colour. 

Sodium carbonate solution [cf. Section 5, p. 330). Note that phenols (except those containing acidic groups, e.., nitrophenols) give no reaction with sodium carbonate solution. 

The Reaction has the following limitations (i) a compound that can liberate nitrous acid in acid solution is required (e.g., a metallic nitrite or a nitroso-amine, p. 204). (2) Nitrophenols and />-substituted phenols do not give the test. (3) Among the dihydroxyphenols. only resorcinol gives a satisfactory positive test. 

Note. Some substituted phenols, particularly nitrophenols, are sufficiently acidic to liberate CO, from Na,CO,. Nitrophenols, however, all give yellow or red solutions with NajCOj. 

Some nitrophenols give colorations with ferric chloride. 

Give acetyl derivatives, but that from o-nitrophenol is not so readily obtained. 

Nitrophenol gives similarly a bright yellow coloration with NaOH solution. 

Reaction with sodium carbonate. Boil about 0 5 g. of 0- and of />-nitrophenol in turn with Na2C03 solution, using the method described in Section 5, p. 336, and note the evolution of CO2. 

Reduction to aminophenol. Reduce about 0 5 g. of o-nitrophenol with cone. HCl and tin as described on p. 385. After a few minutes the yellow molten o-nitrophenol disappears completely, the solution becoming homogeneous and colourless due to the formation of 0-aminophenol (which is soluble in HCl). Cool and add 30% aqueous NaOH solution note that a white precipitate is first formed and then redissolvcs in an excess of NaOH, and that the solution does not develop an orange coloration, indicating that the nitro-group has been reduced. 

Nitrophenol is reduced similarly and the product does not give a yellow coloration with alkali. 

Ferric chloride coloration. Add FeCl, solution to a few crystals (or to an aqueous solution) of /> nitrophenol a violet-red coloration is produced. o-Nitrophenol does not give a coloration. 

Acetylation. Heat i g. of />-nitrophenol with 5 ml. of an acetic acid-acetic anhydride mixture under reflux for 15 minutes. Pour into water the solid acetate separates. Filter, wash with water and re-crystallise from ethanol m.p. 77 5°. This treatment usually leaves o-nitrophenol unchanged. The addition, however, of about 0 5 ml. of cone. H2SO4 to the acetylating mixture gives the o-derivative, m.p. 40°. 

A) Benzoyl Derivative. Since acetylation and benzoylation do not always proceed smoothly with nitrophenols, it is best to reduce them to the aminophenol as in (3) above. Add an excess of 20% aqueous sodium hydroxide to the reaction mixture after reduction, cool and then add a small excess of benzoyl chloride, and shake in the usual way. The dibenzoyl derivative wiU separate. Filter, wash with water and recrystalUse. (M.ps., p. 551.)... 

Yellow. Quinones, m- and p-nitroaniline, o-nitrophenol, and many other nitrO"Compounds. [Note that some nitro-compounds often appear yellow (e.g. m-dinitrobenzene and 3, 5 -dinitro-benzoic acid), but are colourless when absolutely pure.] Iodoform. 

Monohydric alcohols, aldehydes (including chloral hydrate), ketones, cinnamic acid, amines (2-naphthylaminc is odourless), nitrophenols (resemble both phenol and nitro-compound),... 

COj liberated. All acids esters which hydrolyse easily, e.g., methyl oxalate (p. 357) salts of amines nitrophenols. 

In practice superheated steam is generally employed for substances with a low vapour pressure (< 5-1 mm.) at 100°. Thus in the recovery of the products of nitration or aromatic compounds, the ortho derivative e.g., o-nitrophenol) can be removed by ordinary steam distillation the... 

A brief account of aromatic substitution may be usefully given here as it will assist the student in predicting the orientation of disubstituted benzene derivatives produced in the different substitution reactions. For the nitration of nitrobenzene the substance must be heated with a mixture of fuming nitric acid and concentrated sulphuric acid the product is largely ni-dinitrobenzene (about 90 per cent.), accompanied by a little o-dinitrobenzene (about 5 per cent.) which is eliminated in the recrystallisation process. On the other hand phenol can be easily nitrated with dilute nitric acid to yield a mixture of ortho and para nitrophenols. It may be said, therefore, that orientation is meta with the... 

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