The bromination of salicylate anions. Evidence for the participation of the ortho carboxylate group

Tee, Oswald S.; Iyengar, N. Rani

doi:10.1021/jo00223a011

Cited by 10 publications

(8 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…that the reverse reaction, bromine attack ipso to the alkyl group of the p-alkylphenol (4), is catalyzed by general bases (reaction [2] Complementary to these conclusions, we also found that debromination of the ipso-dienone 5 by bromide ion is strongly catalyzed by the internal carboxyl group (reaction [3]) (36, 6, 9). '…”

supporting

confidence: 73%

“…For comparative purposes, we also studied the rates of bromination of anisole (methoxybenzene) and of 2-pyridone, which also show second-order kinetics in their reactions with bromine (14, 15). Depending on the pH of the medium, phenols react with bromine either as such or by way of their anions (3,4,11,12); the same is true of 2-pyridone (15). Therefore, in order to maximise our chances of observing general base catalysis, 3~h e practical reasons for using high concentrations of bromide ion have been given previously (13).…”

Section: Resultsmentioning

confidence: 99%

“…The attack of molecular bromine on simple phenoxide ions is diffusioncontrolled (3,4,11,12), and so the reaction of Br2 with the phenoxide ion within the encounter complex {Br2 .Ph-0-1 must be much faster than diffusional separation of the two reactants ( -1 0 '~ s-I) (18). Thus, one can imagine that proton transfer within the encounter complex {Br2 .Ph-0H.A-} [8] {Br2 .Ph-0H.A-} --t {Br2 .Ph-0-.HA) --t {Br -.BrCh=O.HA} leads to a highly reactive ternary complex {Br2 .Ph-0-.…”

Section: Discussionmentioning

confidence: 99%

“…Several recent studies in this laboratory have been concerned with the mechanism of bromination of phenol derivatives in I aqueous solution (3)(4)(5)(6)(7)(8)(9). Some of these studies dealt mainly with electrophilic bromine attack (3,4), while others were devoted to the enolization or debromination of transient bromocyclohexadienones (5-9).…”

mentioning

confidence: 99%

“…Some of these studies dealt mainly with electrophilic bromine attack (3,4), while others were devoted to the enolization or debromination of transient bromocyclohexadienones (5-9). Three studles, in particular, suggested that bromine attack may be catalyzed by general bases.…”

mentioning

confidence: 99%

See 4 more Smart Citations

Kinetics and mechanism of the bromination of phenols in aqueous solution. Evidence of general base catalysis of bromine attack

Tee¹,

Iyengar²

1990

Can. J. Chem.

Self Cite

View full text Add to dashboard Cite

This paper is dedicated to Professor Ross Stewart ot1 tlze occasion of his 65th birthda!.OSWALD S. TEE and N. RANI IYENGAR. Can. J. Chem. 68, 1769 (1990).The reactions of bromine with phenol, 4-bromophenol, and 4-methylphenol (p-cresol) in aqueous solution are catalyzed by carboxylate anions, confirming the suggestions of earlier work. The results are consistent with deprotonation of the phenol hydroxyl group by a general base occurring at more or less the same time as electrophilic attack by molecular bromine. 1769 (1990) Les rCactions du brome avec le phenol, le 4-bromophCno1 et le 4-mCthylphCno1 (p-cresol), en solution aqueuse, sont catalyskes par les anions carboxylates; cette observation confirme les suggestions faites anter~eurement. Les resultats sont en accord avec un mCcanisme impliquant une dCprotonation du groupement hydroxyle du phCnol par une base gCnCrale qui se produirait pratiquement en m&me temps que I'attaque Clectrophile par le brome moleculaire. On d~scute des origines possible de la catalyse basique gCnCrale. Si I'on combine les rCsultats actuels avec ceux obtenus antkrieurement, on peut suggerer qu'une I cyclohexadi&none protone'e n'est pas un intermediaire nCcessaire dans la bromation du phCnol; cet intermidiaire peut &tre evite par la formation et par l'enolisation de l'intermediaire cyclohexadi6none par une catalyse gCnCrale.Mots cle's : bromation, phenol, mkcanisme, catalyse, cinktique.[Traduit par la revue]The importance of acid-base catalysis for a large number of reactions occurring in aqueous solution is firmly established (1). Many reactions which are sluggish or non-existent in other media are facilitated by the ease of proton transfers in water, 1 thereby allowing highly unfavorable intermediates to be stabil-I ized or avoided (1,2). As reported herein, such may be the case I with phenol bromination in aqueous solution. ISeveral recent studies in this laboratory have been concerned with the mechanism of bromination of phenol derivatives in I aqueous solution (3-9). Some of these studies dealt mainly with electrophilic bromine attack (3, 4), while others were devoted to the enolization or debromination of transient bromocyclohexadienones (5-9). Three studles, in particular, suggested that bromine attack may be catalyzed by general bases.Firstly, we found that salicylate (o-hydroxybenzoate) anions (1) have an enhanced reactivity towards bromine and a reduced selectivity (less negative p+), when compared to analogous, monosubstituted phenols (36). As a result, we argued that the attack of bromine on 'salicylate anions is intramolecularly catalyzed by their ortho carboxylate groups (reaction [l]). Complementary to these conclusions, we also found that debromination of the ipso-dienone 5 by bromide ion is strongly catalyzed by the internal carboxyl group (reaction [3]) (36, 6,9).'Since three, quite distinct studies strongly suggested that the attack of bromine on phenols is catalyzed by general bases, we have looked for buffer catalysis in the aqueous bromination of phenol and tw...

show abstract

supporting

confidence: 73%

Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

See 3 more Smart Citations

Kinetics and mechanism of the bromination of phenols in aqueous solution. Evidence of general base catalysis of bromine attack

Tee¹,

Iyengar²

1990

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