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Position of Equilibrium in Acid-Base Reactions

Position of Equilibrium in Acid-Base Reactions

In any solution, the value of pKa indicates whether an acid is completely dissociated or not. A negative pKa corresponds to a stronger acid, whereas a positive pKa corresponds to a weaker acid. Consider the reaction between ammonia and an ethoxide ion. In this reaction, ethanol with a pKa of 15.9 is a stronger acid than ammonia with a pKa of 38. Recall that the strong acid forms a weak conjugate base, and a weak acid forms a strong conjugate base. Hence, the ethoxide ion is a weak base.

Weak Acid Solutions

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Few compounds act as strong acids. A far greater number of compounds behave as weak acids and only partially react with water, leaving a large majority of dissolved molecules in their original form and generating a relatively small amount of hydronium ions. Weak acids are commonly encountered in nature, being the substances partly responsible for the tangy taste of citrus fruits, the stinging sensation of insect bites, and the unpleasant smells associated with body odor. A familiar example of a...

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Being able to calculate equilibrium concentrations is essential to many areas of science and technology—for example, in the formulation and dosing of pharmaceutical products. After a drug is ingested or injected, it is typically involved in several chemical equilibria that affect its ultimate concentration in the body system of interest. Knowledge of the quantitative aspects of these equilibria is required to compute a dosage amount that will solicit the desired therapeutic effect.
A more...

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In addition to the oxymercuration–demercuration method, which converts the alkenes to alcohols with Markovnikov orientation, a complementary hydroboration-oxidation method yields the anti-Markovnikov product. The hydroboration reaction, discovered in 1959 by H.C. Brown, involves the addition of a B–H bond of borane to an alkene giving an organoborane intermediate. The oxidation of this intermediate with basic hydrogen peroxide forms an alcohol.

Regioselectivity and Stereochemistry of Hydroboration

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A significant aspect of hydroboration–oxidation is the regio- and stereochemical outcome of the reaction.
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn stereochemistry.

Weak Base Solutions

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Some compounds produce hydroxide ions when dissolved by chemically reacting with water molecules. In all cases, these compounds react only partially and so are classified as weak bases. These types of compounds are also abundant in nature and important commodities in various technologies. For example, global production of the weak base ammonia is typically well over 100 metric tons annually, being widely used as an agricultural fertilizer, a raw material for chemical synthesis of other...

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Updated: Jan 15, 2026

Synthesis of a Borylated Ibuprofen Derivative Through Suzuki Cross-Coupling and Alkene Boracarboxylation Reactions

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The Boroxine-Boronic Acid Equilibrium.

Chen Li¹, Lia Sotorrios², Patrick J Boaler¹

¹University of Edinburgh, Joseph Black Building, David Brewster Road, Edinburgh EH9 3FJ, U.K.

Journal of the American Chemical Society

|October 13, 2025

Summary

This summary is machine-generated.

The study reveals a three-step mechanism for boroxine-boronic acid interconversion, identifying key intermediates and the catalytic role of water. This clarifies their chemical behavior and applications.

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Last Updated: Jan 15, 2026

Synthesis of a Borylated Ibuprofen Derivative Through Suzuki Cross-Coupling and Alkene Boracarboxylation Reactions

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Optimization of Radiochemical Reactions using Droplet Arrays

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Published on: February 12, 2021

Area of Science:

Organic Chemistry
Physical Chemistry
Chemical Kinetics

Background:

Boroxine-boronic acid equilibrium is crucial for their properties and applications.
The mechanism and kinetics of this interconversion are not well understood.

Purpose of the Study:

To elucidate the detailed mechanism and kinetics of arylboronic acid-arylboroxine interconversion.
To investigate the role of solvent properties and water in the hydrolytic sequence.

Main Methods:

¹H/¹⁹F NMR and UV-vis spectroscopy, including titrations and stopped-flow kinetics.
Magnetization transfer, kinetic isotope effects, numerical simulations, and DFT calculations.
Explicit solvation approaches were used in DFT calculations.

Main Results:

Identified two acyclic anhydride intermediates in a three-step interconversion process.
Water acts as both a reagent and catalyst; solvent hydrogen-bond acceptor properties influence equilibrium.
Discovered competing equilibria and direct associative transfer pathways.

Conclusions:

The findings clarify the complex hydrolytic mechanism of boroxines and boronic acids.
Provides a tool for estimating equilibrium speciation and has implications for diverse applications.
Highlights the importance of solvent effects and alternative reaction pathways.