The Dissociation Constants of the Chlorophenyl and Phenetyl Boric Acids<sup>1</sup>

Branch, Gerald E. K.; Yabroff, David L.; Bettman, Bernard

doi:10.1021/ja01319a053

Cited by 51 publications

(19 citation statements)

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“…It should be pointed out here that the beneficial effect of an excess or high concentration of base is not related to the formation of phenyl boronate. From the pK a of phenyl boronic acid (8.86), [24] one can calculate that in all the experiments in Figure 2, > 97 % of phenyl boronic acid is present as (water-soluble) sodium phenyl boronate Na[B(Ph)(OH) 3 ]. [25] The effect of an increasing volume of the water phase was also investigated for three other reactions: the reaction of 4- (Figure 3).…”

Section: Precatalystmentioning

confidence: 99%

Suzuki Coupling Reactions in Neat Water as the Solvent: Where in the Biphasic Reaction Mixture Do the Catalytic Reaction Steps Occur?

Röhlich

Wirth

Köhler

2012

Chemistry A European J

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Many reports on water-compatible palladium catalysts have appeared in the recent literature. For hydrophobic substrates, mixtures with pure water are biphasic, and it is widely not regarded that the elusive locality of the catalytic process (in water, the organic layer, or at the phase boundary) has an important impact on the mechanism and efficiency of the reaction. In the present work, for the first time systematic variation of reaction parameters has been performed for Suzuki coupling experiments with chloro- and bromoarenes in pure water. The investigations are not only aimed at the factors influencing the catalytic activity, but also at the effects that may occur particularly in water/organic biphasic media, and on the question as to in which of the two liquid phases the reaction takes place. These investigations have revealed that dilution of the base (in the aqueous layer) and the Pd species (in the organic layer) are detrimental to the reaction, and that phase-transfer processes play a major role in the overall mechanism. A series of experiments with variation of parameters like precatalyst hydrophilicity, organic and water phase volume, additives, stirring rate, base concentration, and so forth, indicate that for the systems under study the reaction occurs in the organic layer. The water phase needs to be present to dissolve and provide polar reactants, and re-absorb side products. The results encourage to pay more regard to the question of phase locality of coupling reactions in water in general.

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Section: Precatalystmentioning

confidence: 99%

Suzuki Coupling Reactions in Neat Water as the Solvent: Where in the Biphasic Reaction Mixture Do the Catalytic Reaction Steps Occur?

Röhlich

Wirth

Köhler

2012

Chemistry A European J

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“…Experimentally, the structural integrity of boronate esters depends on the solvent and the pH of the surrounding medium. It is commonly accepted that the optimal pH for the interaction of a given diol and a boronic acid is above the pK a of the boronic acid (e.g., phenylboronic acid has a pK a of 8.70 in water at 25 8C), [23,[26][27][28] as demonstrated for the diols in Table 1. In the presence of phenylboronic acid, a fluorescent ARS-boronate anion complex is generated with the equilibrium constant of K tetr and the formation of the trigonal planar boronate ester proceeds with K trig , whereas the difference between these two constants (K tetr > K trig ) can be up to about five orders in magnitude.…”

Section: Constructing Responsive Macromolecules and Assemblies On Bormentioning

confidence: 99%

“…[20] The first equilibrium between the boronic acid and ARS can be directly measured by fluorescence spectroscopy, whereas the second equilibrium between the boronic acid and, for example, a carbohydrate perturbs the first equilibrium, resulting in an impact on the emission intensity of the boronic acid/ ARS complexation. It is commonly accepted that the optimal pH for the interaction of a given diol and a boronic acid is above the pK a of the boronic acid (e.g., phenylboronic acid has a pK a of 8.70 in water at 25 8C), [23,[26][27][28] as demonstrated for the diols in Table 1. Nonetheless, the boronic acid/ARS system represents an exception since optimal binding is found at pH 7.…”

Section: Constructing Responsive Macromolecules and Assemblies On Bormentioning

confidence: 99%

Reversible Click Reactions with Boronic Acids to Build Supramolecular Architectures in Water

Arzt

Seidler

et al. 2014

Chemistry An Asian Journal

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The interaction of boronic acids with various bifunctional reagents offers great potential for the preparation of responsive supramolecular architectures. Boronic acids react with 1,2-diols yielding cyclic boronate esters that are stable at pH>7.4 but can be hydrolyzed at pH<5.0. The phenylboronic acid (PBA)-salicylhydroxamic acid (SHA) system offers ultra-fast reaction kinetics and high binding affinities. This Focus Review summarizes the current advances in exploiting the bioorthogonal interaction of boronic acids to build pH-responsive supramolecular architectures in water.

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“…It should be pointed out here that the beneficial effect of an excess or high concentration of base is not related to the formation of phenylboronate. From the pK a of phenylboronic acid (8.86), [32] one can calculate that in the experiments with 1.5 equivalents of NaOH, > 97% of phenylboronic acid are present as (the water-soluble salt) sodium phenylboronate Na[B(Ph)(OH) 3 ]. [33] The results, that is, the positive effect of an excess of base, can be explained when we consider the reaction equation Eq.…”

Section: Effect Of Excess Base On the Activity Of Pd/mo X Catalysts Fmentioning

confidence: 99%

Suzuki Coupling Reactions in Pure Water Catalyzed by Supported Palladium – Relevance of the Surface Polarity of the Support

2011

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Heterogeneous (supported) palladium catalysts like palladium on carbon and a variety of metal oxides have been shown to be highly active for Suzuki coupling reactions in neat water under mild reaction conditions (T = 65 8C). It has been demonstrated for the first time that hydrophobic effects of the catalyst surface play an important role for the catalyst activity in water. Catalysts possessing hydrophobic surfaces (e.g., palladium on carbon) show higher activity for Suzuki coupling reactions in water than their hydrophilic counterparts (palladium on metal oxides). Tuning of the surface polarity of metal oxide supports (by silylation) results in higher activity under these conditions. Stronger alkaline conditions (three-fold excess of base) compensate the effect of hydrophobic supports and result in high activity of the catalysts also with hydrophilic supports. The addition of tetrabutylammonium bromide to generate, activate and stabilize the catalytic species (dissolved palladium complexes) is necessary for the conversion of more demanding substrates. The reaction is considered to be homogeneous taking place near the catalyst surface inside a droplet or layer of the reactant.

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The Dissociation Constants of the Chlorophenyl and Phenetyl Boric Acids¹

Cited by 51 publications

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Suzuki Coupling Reactions in Neat Water as the Solvent: Where in the Biphasic Reaction Mixture Do the Catalytic Reaction Steps Occur?

Suzuki Coupling Reactions in Neat Water as the Solvent: Where in the Biphasic Reaction Mixture Do the Catalytic Reaction Steps Occur?

Reversible Click Reactions with Boronic Acids to Build Supramolecular Architectures in Water

Suzuki Coupling Reactions in Pure Water Catalyzed by Supported Palladium – Relevance of the Surface Polarity of the Support

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The Dissociation Constants of the Chlorophenyl and Phenetyl Boric Acids1

Cited by 51 publications

References 0 publications

Suzuki Coupling Reactions in Neat Water as the Solvent: Where in the Biphasic Reaction Mixture Do the Catalytic Reaction Steps Occur?

Suzuki Coupling Reactions in Neat Water as the Solvent: Where in the Biphasic Reaction Mixture Do the Catalytic Reaction Steps Occur?

Reversible Click Reactions with Boronic Acids to Build Supramolecular Architectures in Water

Suzuki Coupling Reactions in Pure Water Catalyzed by Supported Palladium – Relevance of the Surface Polarity of the Support

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The Dissociation Constants of the Chlorophenyl and Phenetyl Boric Acids¹