Orton rearrangement

What is Orton rearrangement?

The Orton rearrangement, also known as the N-chloro acyl anilide rearrangement, was first reported by Bender in 1886 and subsequently explored by Armstrong in 1890. Orton et al. extensively studied this reaction starting in 1899, which involves the conversion of an N-chloro acyl anilide to an N-acyl p-chloroanilide in the presence of an acid like HCl.

Orton rearrangement - general reaction scheme - N-chloro acyl anilide rearrangement,
Orton rearrangement

R = alkyl, aryl (see list of acronyms)

The Orton rearrangement is believed to occur through a multistep process, with the liberation of chlorine and subsequent irreversible electrophilic substitution being the primary steps. Although hypochlorous acid has been suggested as an intermediate in the chlorination of the aromatic ring, this mechanism was abandoned by Orton. It is now known that the Orton rearrangement is promoted by both proton (H) and chloride.

Orton rearrangement (nitro variant) - general reaction scheme
Orton rearrangement (nitro variant)

R = H, alkyl (see list of acronyms)

The reaction rate of the Orton rearrangement is influenced by various factors, including the solvent composition and substrate. For instance, in acetic acid, no hydrogen chloride HCl is detected, and tertiary acyl anilides such as N-methyl benzanilide and N-phenyl benzanilide do not form chlorination products. The rearrangement yield and the ortho/para ratio of isomers increase with increasing solvent viscosity.

Moreover, the Orton rearrangement can be triggered by a Lewis acid, such as AgBF4, and light, such as irradiation from a mercury-vapor lamp even in the solid state. Additionally, when N-nitro-anilides are treated with a strong acid, the nitro group rearranges in a similar fashion to the migration of chlorine. The ortho-nitroanilides are formed when the para position of the aniline moiety is occupied by an electron-donating group, whereas the rearrangement is relatively suppressed when the para position is occupied by an electron-withdrawing group such as a nitro, cyano, or sulfonyl group.

Interestingly, in the presence of HNO3, H2SO4, HCl, or HClO4, N-nitro-2,4-dichloroaniline is converted to 2-nitro-4,6-dichloroaniline, whereas 2,4-dichlorobenzenediazonium bromide is obtained quantitatively in the presence of HBr.

References

  • Bender, G., Ber., 1886, 19, 2272
  • Armstrong, H. E., J. Chem. Soc., Trans., 1900, 77, 1047
  • Chattaway, F. D. and Orton, K. J. P., J. Chem. Soc., 1899, 75, 1046
  • Chattaway, F. D.; Orton, K. J. P. and Hurtley, W. H., J. Chem. Soc., Trans., 1900, 77, 800
  • Chattaway, F. D. and Orton, K. J. P., J. Chem. Soc., Trans., 1900, 77, 797
  • Chattaway, F. D. and Orton, K. J. P., J. Chem. Soc., Trans., 1900, 77, 787
  • Chattaway, F. D. and Orton, K. J. P., J. Chem. Soc., Trans., 1900, 77, 134
  • Chattaway, F. D. and Orton, K. J. P., J. Chem. Soc., Trans., 1901, 79, 816
  • Orton, K. J. P., Proc. Chem. Soc., 1902, 18, 200
  • Orton, K. J. P. and Smith, A. E., J. Chem. Soc., 1905, 87, 389
  • Orton, K. J. P. and Smith, A. E., Proc. Chem. Soc., 1905, 21, 91
  • Kipping, F. S.; Orton, K. J. P.; Ruhemann, S.; Lapworth, A. and Hewitt, J. T., Brit. Assoc. Rep., 1905, 103
  • Reed, W. W. and Orton, K. J. P., J. Chem. Soc., Trans., 1907, 91, 1543
  • Smith, A. E. and Orton, K. J. P., Proc. Chem. Soc., 1907, 23, 14
  • Orton, K. J. P. and Pearson, C., J. Chem. Soc., Trans., 1908, 93, 725
  • Smith, A. E. and Orton, K. J. P., Proc. Chem. Soc., 1908, 24, 27
  • Kipping, F. S.; Orton, K. J. P.; Rhemann, S.; Lapworth, A. and Hewitt, J. T., Chem. News & J. Ind. Sci., 1908, 96, 85
  • Orton, K. J. P. and Jones,W. J., J. Chem. Soc., Trans., 1909, 95, 1456
  • Orton, K. J. P. and Jones, W. J., Proc. Chem. Soc., 1909, 25, 196
  • Jones, W. J. and Orton, K. J. P., J. Chem. Soc., Trans., 1909, 95, 1056
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