84559-79-5Relevant academic research and scientific papers
Photoreaction mechanisms of 2-bromophenols studied by low-temperature matrix-isolation infrared spectroscopy and density-functional-theory calculation
Akai, Nobuyuki,Kudoh, Satoshi,Takayanagi, Masao,Nakata, Munetaka
, p. 591 - 597 (2002)
Photoreaction mechanisms of 2-bromo, 2-bromo-4-chloro and 2,4-dibromophenols in low-temperature argon matrices have been investigated by Fourier transform infrared spectroscopy. Density-functional-theory calculations are performed to assign the observed i
Catalysis of the Debromination of 4-Alkyl-4-bromo-2,5-cyclohexadienones in Aqueous Solution by α-Cyclodextrin
Tee, Oswald S.,Bennett, Janice M.
, p. 3226 - 3230 (2007/10/02)
α-Cyclodextrin (CD) has little or no effect on the rates of enolization of transient 4-bromo-2,5-cyclohexadienones (2), formed during the aqueous bromination of alkylphenols.In contrast, saturation kinetics and large catalytic effect are observed for the debromination of the title dienones (4), formed by ipso bromine attack on 4-alkylphenols (alkyl = Me, Et, i-Pr, n-pr, t-Bu, 3,4-diMe).With the exception of the n-propyl case, the extent of the catalysis kc/ku = 23-78) and the dissociation constant of the CD.dienone complexes (Kd = 2.32-4.83 mM) show surprisingly little variation for the different alkyl groups.The simplest interpretation of the results is that the CD-catalyzed debromination reaction involves attack by free bromide ion on the CD.dienone complex.However, the kinetically equivalent pathway, the reaction between the free dienone 4 and the CD complex of bromide ion, is much more consistent with the low sensitivity of the catalysis to the length and size of the different alkyl groups.For this mechanism the rate enhancements are much larger (2400-4600) and almost constant.They imply that Br- in its CD complex is a stronger nucleophile than bromide ion that is completely solvated by water.The preferred mechanism is the microscopic reverse of that postulated for the CD-catalyzed bromination of phenols.The common transition state for the ipso bromination of 5 (R=Me) and the debromination of 4 (R=Me) is strongly bound by CD (Kd ca. 4.5 1E-5 M).
Observation of Transient Cyclohexadienones during the Aqueous Bromination of Phenols
Tee, Oswald S.,Iyengar, N. Rani
, p. 455 - 459 (2007/10/02)
Transient 4-bromo-2,5-cyclohexadienone intermediates have been observed during the aqueous bromination of phenol and several methylated derivatives.They enolize to the corresponding p-bromophenols by both acid-catalyzed and water-catalyzed pathways in the pH range 0-6.Studies carried out in buffers also indicate both general acid catalysis (α ca 0.0) and general base catalysis (β=0.54).The latter is ascribed to simple rate-limiting proton abstraction, but the former is not so easily rationalized.The very low α is attributed to a termolecular transition state (water, substrate, and general acid) in which the dienone becomes more anion-like than cation like.This seemingly anomalous behaviour can be explained by the very large enol/keto ratio (ca. 1011) for phenol.
