Monosubstituted anilines para substituents

In this review, attention is focused primarily on the oxidation mechanisms under the given conditions, which is the essential topic of interest for organic chemists. Reaction pathways will be outlined if they seem to be well established. However, even small differences in medium properties used by different researchers can lead to serious variations as will be shown in some examples. Anodic oxidation of unsubstituted aniline is discussed in Section II and electrode reactions of /V-substifilled and C-substituted anilines in Sections III and IV, respectively. In the last case, the oxidation of reactants with monosubstituted ring is presented first (para-substituents separately from the effects of ortho- and mefa-substituents), and next the oxidation of di- and trisubstituted anilines. In each part the processes in dipolar aprotic solvents, in particular in acetonitrile (ACN) and /V. /V-dimethylformamide (DMF), are compared with those proceeding in aqueous solutions, chiefly in commonly used acidic media. 

The introduction of substituents in the positions meta and para to the amino group of aniline leads to marked changes in the piT value which reveal clearly the two effects (inductive and mesomeric) which are operative in the molecules concerned. The effects of ortho substituents are more complicated and therefore they will be discussed separately. The pJfa values for a range of monosubstituted anilines are shown in Table 9. 

Monosubstitution of the free amine may be achieved by using a less reactive electrophile. Thus aniline and o-toluidine may be mono-iodinated (Expt 6.60) by treatment with iodine (in the presence of sodium hydrogen carbonate or calcium carbonate to remove the liberated hydrogen iodide), the substituent entering the position para to the amino group. Direct iodination can also be effected by using the more powerfully electrophilic reagent, iodine monochloride... 

The nomenclature of benzene derivatives is described in Sec. 4.6. Common names and structures to be memorized include those of toluene, styrene, phenol, aniline, and xylene. Monosubstituted benzenes are named as benzene derivatives (bromobenzene, nitrobenzene, and so on). Disubstituted benzenes are named as ortho- (1,2-), meta- (1,3-), or para- (1,4-), depending on the relative positions of the substituents on the ring. Two important groups are phenyl (C6H5-) and benzyl (C6H5CH2-). 

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