Industry expert Tony O'Lenick explains that urethanes and amides differ in structure, in the raw materials used to make them, and in their function in cosmetic formulations.
A urethane is a compound conforming to the structure in Figure 1. Urethanes are made by the reaction of an alcohol and an isocyanate. An example can be found in US Patent 5,972,324, assigned to Zofchak et al, that teaches the reaction of monohydric alcohols, generally fatty alcohols, and a diisocyanate. The compounds are urethane-based emollients, solubilizers, clarifiers and emulsifiers. A specific example of a reaction is shown in Figure 2.
An amide is a compound conforming to the structure in Figure 3. Amides are made by the reaction of an acid, ester or triglyceride with an amine. Alkanolamides are used to shift the salt curve in shampoos, allowing for a higher viscosity with less salt and the modification of bubble structures. A specific example is of a reaction is MEA alkanolamide, shown in Figure 4.