W-Nitrophenol

The catalysed nitration of phenol gives chiefly 0- and />-nitrophenol, (< 0-1% of w-nitrophenol is formed), with small quantities of dinitrated compound and condensed products. The ortho para ratio is very dependent on the conditions of reaction and the concentration of nitrous acid. Thus, in aqueous solution containing sulphuric acid (i 75 mol 1 ) and nitric acid (0-5 mol 1 ), the proportion of oriha-substitution decreases from 73 % to 9 % as the concentration of nitrous acid is varied from o-i mol l i. However, when acetic acid is the solvent the proportion of ortAo-substitution changes from 44 % to 74 % on the introduction of dinitrogen tetroxide (4-5 mol 1 ). 

After the w-nitrophenol is distilled the flask should be allowed to cool before air is admitted. Otherwise the residue may decompose with explosive violence. 

For phenols, the number of chlorines replaced depends in part on the acidity of the phenol. Under mild conditions, phenol or w-nitrophenol displaces only one chlorine from TiCl4, whereas >-chlorophenol, o-nitrophenol, >-nitrophenol, picric acid, or 2-naphthol gives (ArO)0TiCl2. If the mixtures are heated sufficiently, eg, in refluxing phenol, all four chlorines can be displaced (49—52). 

Problem 19.11 Assign numbers from 1 for LEAST to 4 for MOST to indicate the relative acid strengths in the following groups (a) phenol, m-chlorophenol, w-nitrophenol, m-cresol (b) phenol, benzoic acid, p-nitrophenol, carbonic acid (c) phenol, p-chlorophenol, p-nitrophenol, p-cresol (d) phenol, o-nitrophenol, w-nitrophenol, p-nitrophenol (e) phenol, /z-chlorophenol, 2,4,6-trichlorophenol, 2,4-dichlorophenol (f) phenol, benzyl alcohol, benzenesulfonic acid, benzoic acid. 

MS absent(M+) 286(VS, loss of COo and nitrophenyl radical) 242(W, loss of 2CO2 and nitrophenyl radical) 139(W, nitrophenol) 104(s, loss of 2CO2 and 2 nitrophenyl radicals). 

Of the methods for the preparation of this substance two would seem best suited for laboratory use In the first place, one can start with w-nitraniline, diazo-tize this, and decompose the diazo compound by boiling with dilute acid, forming w-nitrophenol, but as the yield is not very good and the nitrophenol must subsequently be reduced to the ammo compound, the method is scarcely suited for the preparation of considerable amounts of this material. On the other hand, the method involving the direct replacement of one of the hydroxyl groups of resorcinol, w-C6H4(OH)2 by ammonia, was found to be very satisfactory. 

For example, the time-averaged conformation of the inclusion complex between a-cyclodextrin and w-nitrophenol was determined by this method as shown in Fig. 

Pyridinecarbonitrile 1,3-Dinitrobenzene Bromobenzene Chlorobenzene o-Chlorophenol w-Chlorophenol / -Chlorophenol Benzenesulfonyl chloride 4-Chlorobenzenethiol Fluorobenzene lodobenzene A -Sulfinylaniline Nitrobenzene o-Nitrophenol w-Nitrophenol / -Nitrophenol Benzene w-Bromoaniline o-Chloroaniline w-Chloroaniline o-Nitroaniline... 

Fig. 8-6 Log /f - ApiC plot for ideal case, imidazole (pX = 6.95, donors glucose, phenol, HP207, p-nitrophenol, acetic acid) and acetylacetonate (pX = 9.5, donors H2O, glycerine, mannose, glucose, trimethylphenol, phenol, o-chlorophenol, w-nitrophenol, p-nitrophenol, dimedone, acetic acid, benzoic acid, chloraoetic acid, (Data from Eigen and Kruse [12],...

---