Related Experiment Video
Updated: Jul 15, 2026

Optimization of the Ugi Reaction Using Parallel Synthesis and Automated Liquid Handling
Published on: November 11, 2008
Determination of the dissolution rate controlling process for isomeric amides in alkane solvents
Abstract:
The mechanisms that control the dissolution rates of chemical compounds in liquids have long been of interest to pharmaceutical scientists. Generally, control of the dissolution rate can be classified as being by interfacial reaction rate or by the rate of mass transport. Little work has been done in the area of sparingly soluble compounds dissolving in nonpolar organic solvents. In this study the dissolution of three isomers of methylacetanilide was investigated in three nonpolar organic solvents (hexane, heptane, and cyclohexane). The dissolution apparatus used a flat plate into which the nondisintegrating tablet could be placed so that dissolution occurred only from one face of the tablet. Agitation was provided by a four-bladed stirrer whose outer edge was 2 cm from the tablet surface. Dissolution data were collected only for concentrations less than 5% of the saturation solubility of the given compound in the given solvent. All dissolution profiles were linear. Dissolution rates were obtained from the slopes of these plots. Plots of In (dissolution rate) versus In (stirring speed) were also linear and yielded slopes that were close to the value of 0.50 predicted by the convective diffusion model employed.
Related Concept Videos
Carboxylic Acids to Methylesters: Alkylation using Diazomethane
Preparation of Amides
The DCC-promoted synthesis of amides begins with the protonation of DCC by carboxylic acid. The protonation makes it a better acceptor. Next, the addition of carboxylate to the protonated carbodiimide gives a reactive acylating agent.
Subsequently, the amine acts as a nucleophile that attacks the acylating agent to form a tetrahedral intermediate. In the...
Amides to Carboxylic Acids: Hydrolysis
Acid-catalyzed hydrolysis:
Hydrolysis of amides under acidic conditions yields carboxylic acids. Since the reaction occurs slowly, hydrolysis requires the conditions of heat.
The mechanism begins with the protonation of the carbonyl oxygen by the acid catalyst. The protonation makes the amide carbonyl carbon more...
Aldehydes and Ketones with Amines: Imine Formation Mechanism
Imines are formed under mildly acidic conditions. A pH of 4.5 is ideal for the reaction.
If the pH is low or the solution is too acidic, the reaction slows down in the...
Theories of Dissolution: Diffusion Layer Model
This process starts with a thin layer, saturated with the drug, forming at the interface between the solid and liquid. The solute then diffuses from this layer into the main solution. The Noyes-Whitney equation suggests that the rate of dissolution relies on the diffusion...
Theories of Dissolution: The Danckwerts' Model and Interfacial Barrier Model

