Pharmaceutical Dissolution and Solubility Lecture Review

This set of vocabulary flashcards covers concepts of dissolution kinetics, solubility calculations, acid-base behavior, and partition coefficients as detailed in the lecture transcript.

Interfacial reaction

An instantaneous process where cavities in the solvent take up ions/molecules of solute that become solvated by the end of this process.

Diffusion through boundary layers

The limiting step of dissolution that defines the rate of dissolution; in this process, solvated solute ions/molecules travel away from the surface of the solute into the solution\u2019s bulk according to a concentration gradient.

Noyes-Whitney equation

An equation stating that the rate of dissolution of a spherical solid particle is directly proportional to the surface area of the particle ($A$) and the concentration difference across the boundary layers ($\Delta C$), and inversely proportional to the thickness of the boundary layers ($h$).

Stirring

An action that helps increase the dissolution rate by reducing the thickness of the boundary layers ($h$).

Particle size reduction

A technique that increases the dissolution rate by increasing the total surface area ($A$) of the solute particles.

Prop-1,2,3-triol

A compound with a molecular weight ($MR$) of $92.094\,g\,mol^{-1}$ and a density ($\rho$) of $1.26\,kg\,dm^{-3}$.

Salicylic acid

A compound with a molecular weight ($MR$) of $138.12\,g\,mol^{-1}$ and a density ($\rho$) of $1.44\,kg\,dm^{-3}$.

Strong acids

Acids that dissociate completely when added to water.

Weak acids

Acids that dissociate partially, where the proportion of dissociated and undissociated species depends on the acid\u2019s $pKa$ and the $pH$ of the solution.

Zwitterionic compound

A compound whose overall charge is affected by $pH$; the cationic form predominates at low $pH$ due to an abundance of $H^+$ and the anionic form predominates at high $pH$ due to low $[H^+]$.

Log P (Partitioning coefficient)

A measure of a compound\u2019s preference for a hydrophilic solvent and a hydrophobic solvent, calculated by the ratio of the solubility values of the compound in both these solvents.

Log D (Distribution coefficient)

A measurement that considers the effect of $pH$ on a compound depending on its $pKa$ and assumes that the ionised fraction is unable to partition to the hydrophobic phase.

Lactic acid

A compound with a $log\,P$ of $-0.7$ and a $pKa$ of $3.86$.

Triethanolamine

An alkali compound with a $log\,P$ of $-1.0$ and a $pKa$ of $7.76$.

Benzoic acid

A compound with a $pKa$ of $4.19$ and a $log\,P$ of $1.87$, with a solubility in water of $0.29\,g.L^{-1}$ and in chloroform of $15.0\,g.L^{-1}$.

Methylparaben

A compound with a $pKa$ of $8.4$ and a molecular weight ($MR$) of $152.15\,g\,mol^{-1}$.

Hydration

A specific term for solvation when the process occurs in an aqueous solution.

Saturated solution

A solution that contains a solute at its limit of solubility.