Regiospecificity of branching in simple esters


Nascent Technologies Corporation, Lawrenceville Ga, USA


Cosmetic esters have become a more and more important raw material in the formulation of products in the personal care market. There has been a growing need to evaluate this class of materials to replace oils that are not natural, sustainable or biodegradable. The use of an ester must always have the pleasing aesthetics which is critical to consumer acceptance. In a previous article, liquid esters were presented in which the alcohol used in the synthesis was propoxylated before esterification, by reaction with fatty acids (1). This approach while effective, requires an acceptance of an ester containing a portion of the molecule derived from propylene oxide. This article will evaluate the effect of another approach that is free on this raw material and based upon higher molecular weight branched alcohols.

There are two significant ways to improve the liquidity of esters. The first is introduction of double bonds into the molecule, and the second the introduction of branching.  The introduction of  double bonds into the molecule can result in a decreased OSI (Oxidative Stability Index) (2) which indicates oxidative instability and rancidity. This article will deal with the critical question, where should one place branching in an ester for best cosmetic performance? By performance is meant that the ester will be clear, light color and not develop odor or precipitate over time.


The Guerbet (3) reaction provides not only branching but longer alkyl branching which is quite effective in providing liquidity at high molecular weight. Not only is the molecule highly branched, but it produces a primary alcohol, making reaction to form the ester with fatty acids easier.