The behavior of 4-alkyl-4-bromo-2,5-cyclohexadienones formed during the aqueous bromination of p-alkylphenols

Tee, Oswald S.; Iyengar, N. Rani; Bennett, Janice M.

doi:10.1021/jo00363a034

Cited by 9 publications

(1 citation statement)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Kinetics were measured using an Aminco DW2a uv-vis spectrophotometer, with an Aminco-Morrow stopped-flow accessory, interfaced to a microcomputer (23). The observation chamber was kept at 25°C by water circulation from a thermostat.…”

Section: Methodsmentioning

confidence: 99%

Catalysis of the deprotonation of β-keto esters by cyclodextrins

Tee¹,

Iyengar²,

Takasaki³

1993

Can. J. Chem.

Self Cite

View full text Add to dashboard Cite

. Can. J. Chem. 71, 2139 (1993). The rates of deprotonation of several P-keto esters in basic aqueous solution are elevated by a -and P-cyclodextrin (a-and P-CD). In most cases saturation kinetics are observed that indicate fairly strong binding of the esters to the CDs (K, = 0.22-1 1 mM); catalytic ratios (k,/k,) are in the range 1.9-17. For esters of the form RCO-CH,COOEt with both a-and P-CD the values of Kd and k,/k, show little sensitivity to the acyl group, RCO (R = Me, Et, Pr, i-Pr), and for 2-carboethoxycyclopentanone, a cyclic analogue, these parameters are similar. In contrast, for R-COCH,CO-OR' (R = Me or Et; R' = Me, Et, allyl) there is a marked dependence of the parameters on the alkoxyl group, OR'. These results suggest that the P-keto esters studied bind to the CDs with their alkoxyl groups in the CD cavity and that the catalysis ensues from the complexes thus formed. Variations in two other kinetic parameters, k, = k,/K, (substrate selectivity) and KT, = k,/k, (apparent constant for dissociation of CD from the transition state) support this interpretation. Apparent second-order rate constants for the reaction of the esters with neutral CD (k, = k,/K,) are 1900-360 000 M-' s-I (at pH ; = lo), whereas for hydroxide ion attack on ethyl acetoacetate koH = 5500 M-' s-I. Assuming the pK,s of the CDs are 12.2 and 12.3, deprotonation of the esters by the CD anions has rate constants of lo5 to 5 x lo7 M-' s-'. Thus, binding of the P-keto esters in the CD cavities, adjacent to a basic oxyanion site, enhances the reactivity of the CD anions towards these weak carbon acids by at least 2-4 orders of magnitude.OSWALD S. TEE, N. RANI IYENGAR et BRYAN K. TAKASAKI. Can. J. Chem. 71, 2 139 (1993). U s vitesses de dkprotonation de plusieurs p-cktoesters en solutions aqueuses basiques sont augmentkes par la prksence d'a-ou de P-cyclodextrine (a-et P-CD). Dans la plupart des cas, on observe des cinktiques de saturation qui indiquent la prksence d'une forte liaison des esters sur les CD (K, = 0,022-1 1 mM); les rapports catalytiques (k,/k,) sont de l'ordre de 1,9 2 1 17. Pour des esters de la forme RCO-CH,COOEt avec des CD tant a que P, les valeurs de Kd et de k,/k, ne prksentent qu'une faible sensibilitk i la nature du groupe acyle, RCO (R = Me, Et, Pr, i-Pr); pour le 2-carbokthoxycyclopentanone, un analogue cyclique, ces paramktres sont semblables. Par ailleurs, pour les esters du type R-COCH,CO-OR' (R = Me ou Et; R' = Me, Et ou allyle), il existe une dkpendance marquke des paramktres sur la nature du groupe alcoxyle, OR'. Ces rksultats suggkrent que les p-cktoesters se lient par leurs groupes alcoxyles ?I la cavitk des CD et que la catalyse dkcoule de la formation de ces complexes. Les variations dans deux autres paramktres cinktiques, k, = k,/K, (sklectivitk du substrat) et KT, = k,/k, (constante apparente de la dissociation de la CD de l'ktat de transition) sont en accord avec cette interpretation. Les constantes apparentes de vitesse du deuxikme ordre pour la rkaction des esters avec de la CD neutre (k, = kc/Kd)...

show abstract

Section: Methodsmentioning

confidence: 99%

Catalysis of the deprotonation of β-keto esters by cyclodextrins

Tee¹,

Iyengar²,

Takasaki³

1993

Can. J. Chem.

Self Cite

View full text Add to dashboard Cite

show abstract

Formation of Carbon–Halogen Bonds (Cl,Br,I)

Sasson

2009

Patai's Chemistry of Functional Groups

View full text Add to dashboard Cite

Introduction Halogenation in Presence of Solid Supports or Catalysts Halogen Exchange and Transhalogenation Reactions Oxyhalogenations Cohalogenation and Mixed Halogenation Halogen–Halogen Reagents Carbon–Halogen Reagents Nitrogen–Halogen and Phosphorus–Halogen Reagents Oxygen–Halogen Reagents Sulfur–Halogen Reagents Silicon–Halogen Reagents Halogenation with Metal Halides and Halodemetallation Halogenation in Special Environments Carbon–Halogen Bond Formation by Extrusion of CO , CO 2 or SO 2 Ring Opening of Oxiranes

show abstract

Tautomeric Equilibria and Rearrangements Involving Phenols

Koblik¹

2009

Patai's Chemistry of Functional Groups

View full text Add to dashboard Cite

Introduction Tautomerism in Phenols Rearrangements of Phenols Rearrangements of O ‐Substituted Phenol Derivatives Rearrangements of Functionalized Arenes Rearrangements of Non‐Aromatic Carbocycles Rearrangements of Heterocyclic Compounds

show abstract

The behavior of 4-alkyl-4-bromo-2,5-cyclohexadienones formed during the aqueous bromination of p-alkylphenols

Cited by 9 publications

References 0 publications

Catalysis of the deprotonation of β-keto esters by cyclodextrins

Catalysis of the deprotonation of β-keto esters by cyclodextrins

Formation of Carbon–Halogen Bonds (Cl,Br,I)

Tautomeric Equilibria and Rearrangements Involving Phenols

Contact Info

Product

Resources

About