Journal of the Chemical Society. Perkin transactions II p. 1793 - 1802 (1983)
Update date:2022-08-17
Topics:
Bloomfield, Colin
Moodie, Roy B.
Schofield, Kenneth
Good first order kinetics of solvolysis of the above-named diene in water and in 6.5-43.6percent H2SO4 at 25 deg C, and in water and in 15.2-58.8percent H2SO4 at 5 deg C have been observed.The yields of 4-chlorotoluene, 5-chloro-2-methylphenyl acetate, 5-chloro-2-methylphenol, 4-chloro-2-nitrotoluene, 4-chloro-3-nitrotoluene, and 4-methyl-2-nitrophenol produced in water and in 21.5-92.4percent H2SO4 at 25 deg C in the presence of sulphanilic acid or hydrazinium sulphate, and additionally of 2- and 4-nitroanisole when anisole was also added, have been measured.The solvolysis proceeds by an acid-catalysed elimination of nitrous acid (confirming a tentative conclusion in another case), which competes with AAC2 and AAL1 ester solvolyses.With increasing acidity the solvolyses become dominant, the AAL1 reaction increasingly so.The small yield of 4-chloro-3-nitrotoluene comes from a thermal reaction of the diene unrelated to the elimination and solvolyses.The AAL1 reaction generates the ipso-Wheland intermediate (WiMe) that is also formed in the nitration of 4-chlorotoluene.The intermediate reacts by return to 4-chlorotoluene and nitronium ion (which can be captured by anisole), by 1,2-and 1,4-nucleophilic capture by water (giving 5-chloro-2-methylphenol and 4-methyl-2-nitrophenol, respectively), and by 1,2-rearrangement to 4-chloro-2-nitrotoluene.The first of these reactions never accounts for more than about 12percent of the WiMe and competition between capture and rearrangement moves strongly in favour of the latter with increasing acidity.Re-examination of the nitration of 4-chlorotoluene has revealed products arising from 1,2- and 1,4-capture of WiMe, previously overlooked.An improved assessmentof positional reactivities shows 59percent of primary attack by nitronium ion to occur at C-Me in 63percent H2SO4.
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