Please use this identifier to cite or link to this item:
Title: Chemistry of 4-alkylaryloxenium ion "precursors": Sound and fury signifying something?
Contributor(s): Novak, Michael (author); Brinster, Aaron M (author); Dickhoff, Jill N (author); Erb, Jeremy M (author); Jones, Matthew P (author); Leopold, Samuel H (author); Vollman, Andrew T (author); Wang, Yue-Ting (author); Glover, Stephen (author)orcid 
Publication Date: 2007
DOI: 10.1021/jo701853e
Handle Link:
Abstract: Quinol esters '2b', '2c', and '3b' and sulfonamide '4c' were investigated as possible precursors to 4-alkylaryloxenium ions, reactive intermediates that have not been previously detected. These compounds exhibit a variety of interesting reactions, but with one possible exception, they do not generate oxenium ions. The 4-isopropyl ester '2b' predominantly undergoes ordinary acid- and base-catalyzed ester hydrolysis. The 4-tert-butyl ester '2c' decomposes under both acidic and neutral conditions to generate tert-butanol and 1-acetyl-1,4-hydroquinone, '8', apparently by an S(N)1 mechanism. This is also a minor decomposition pathway for '2b', but the mechanism in that case is not likely to be S(N)1. Decomposition of '2c' in the presence of N₃⁻ leads to formation of the explosive 2,3,5,6-tetraazido-1,4-benzoquinone, '14', produced by N₃⁻-induced hydrolysis of '8', followed by a series of oxidations and nucleophilic additions by N₃⁻. No products suggestive of N₃⁻-trapping of an oxenium ion were detected. The 4-isopropyl dichloroacetic acid ester '3b' reacts with N₃⁻ to generate the two adducts 2-azido-4-isopropylphenol, '5b', and 3-azido- 4-isopropylphenol, '11b'. Although '5b' is the expected product of N₃⁻ trapping of the oxenium ion, kinetic analysis shows that it is produced by a kinetically bimolecular reaction of N₃⁻ with '3b'. No oxenium ion is involved. The sulfonamide '4c' predominantly undergoes a rearrangement reaction under acidic and neutral conditions, but a minor component of the reaction yields 4-tert-butylcresol, '17', and 2-azido-4- tert-butylphenol, '5c', in the presence of N₃⁻. These products may indicate that '4c' generates the oxenium ion '1c', but they are generated in very low yields (ca. 10%) so it is not possible to definitively conclude that '1c' has been produced. If '1c' has been generated, the N₃⁻-trapping data indicate that it is a very short-lived and reactive species in H₂O. Comparisons with similarly reactive nitrenium ions indicate that the lifetime of '1c' is ca. 20-200 ps if it is generated, so it must react by a preassociation process. Density functional theory calculations at the B3LYP/6-31G*//HF/6-31G* level coupled with kinetic correlations also indicate that the aqueous solution lifetimes of '1a-c' are in the picosecond range.
Publication Type: Journal Article
Source of Publication: Journal of Organic Chemistry, 72(26), p. 9954-9962
Publisher: American Chemical Society
Place of Publication: United States
ISSN: 0022-3263
Field of Research (FOR): 030505 Physical Organic Chemistry
Peer Reviewed: Yes
HERDC Category Description: C1 Refereed Article in a Scholarly Journal
Statistics to Oct 2018: Visitors: 267
Views: 278
Downloads: 0
Appears in Collections:Journal Article
School of Science and Technology

Files in This Item:
3 files
File Description SizeFormat 
Show full item record


checked on Nov 30, 2018

Page view(s)

checked on Jan 3, 2019
Google Media

Google ScholarTM







Items in Research UNE are protected by copyright, with all rights reserved, unless otherwise indicated.