304. The kinetics and mechanisms of aromatic halogen substitution. Part VI. Some observations relating to substitution meta- to principally ortho–para-directing substituents; and to steric inhibition of tautomeric electron release from the acetamido-group

Abstract

The rates of chlorination, by molecular chlorine in acetic acid, of 4-acetamidodiphenyl, 1 : 4-diacetamidobenzene, and 2 : 6-dimethylacetanilide are compared with the corresponding rates of chlorination of 2-methylacetanilide, 4-methylacetanilide, N-methylacetanilide, m-xylene, and benzene. The phenyl and the acetamido-group only slightly deactivate for meta-chlorination. The proportion of 6-chloro-derivative formed in the chlorination of 2-methylacetanilide has been determined by isotopic dilution as 20.0%; that of the 4-chloro-derivative in the chlorination of 2 : 6-dimethylacetanilide is 2.6% ; and that of 3-chloro-derivative in the chlorination of 4-acetamidodiphenyl is 90%. These values, together with the rate-ratios, allow the effect of steric inhibition of tautomeric electron release from the acetamido-group in these compounds to be estimated.

Reactivity of the Polyamide Membrane Monomer with Free Chlorine: Role of Bromide

“…20 In one previous study, various model compounds representing the polyamide monomer (e.g., acetanilide or BA; eq 10) and an N-substituted version of this monomer (e.g., N-CH 3 -acetanilide or N-CH 3 -BA; eq 11) were directly exposed to Br 2 . 22,34 Direct ring bromination occurred for all these compounds and did so preferentially at the para position (eqs 10 and 11). 22,34 The results for N-CH 3 -BA were in agreement with our previous results with this compound, which underwent ring chlorination when exposed to Cl 2 (formed via eq 3).…”

The Conformation of Some Disubstituted Anilides

“…In the case of 2, 6-dimethylacetanilide this leads to the steric inhibition of resonance between the aromatic ring and the amide group thus diminishing the influence of the amide on the orientation of aromatic substitution. 1,2 Consequently the electrophilic aromatic substitution of 2,6-dimethylacetanilide occurs predominantly at the C-3 position under the influence of the methyl groups rather than at C-4 para to the acylamino group. The original suggestion 3 for the influence of the methyl groups on the rotation of the acylamino group was based on dipole moment measurements.…”

Oxidative Iodination of Aromatic Amides Using Sodium Perborate or Hydrogen Peroxide with Sodium Tungstate†

“…The substitution pattern was clear from the 1 H NMR spectrum which showed two aromatic doublets (d H 6.80 and 7.67, J 8.1 Hz). The abnormal aromatic substitution of 2,6-dimethylacetanilide has been noted previously 12 and rationalized 13 in terms of the steric inhibition of resonance. The dierence between the bromination and iodination may re¯ect a dierence in mechanism.…”