Comparatively Speaking: Fatty Alcohols vs. Fatty Acids vs. Esters

By: Anthony J. O'Lenick Jr., Siltech LLC

Posted: July 6, 2010

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Oxo alcohols and iso-alcohols are alpha-olefin based and are approximately 50% branched at the second carbon position. Oxo alcohols are about 50% linear. Iso-alcohols are 100% multiple methyl branched.

Melting points or pour points are much lower for branched/Guerbet alcohols than for their linear counterparts of the same number of c-chains. Linear unsaturated alcohols are liquid; however, they suffer from poor heat stability due to unsaturation. The saturated Guerbet alcohols or branched iso alcohols offer fluidity and also thermal stability and oxidation stability. These differentiating physico-chemical properties of branched chain alcohols make them immensely important in the synthesis and derivatization into cosmetics and personal care emollients.

Fatty Acids
Fatty acids are organic acids comprised of carbon chains with a carboxyl group at the end. Saturated fatty acids have all carbons with a full quota of hydrogens. There is a single bond between adjacent carbon atoms. Unsaturated fatty acids have one or more carbon-carbon double bond in the molecule. Chemically, these double bonds will take up hydrogen, a process termed hydrogenation, that yields saturated fatty acids. Table 2 gives common names, IUPAC names, chemical structures and abbreviation designating presence or absence of unsaturation for fatty acid.

Saturated and unsaturated fatty acids are different in their form, as unsaturated fatty acids have one or more alkenyl functional group along the chain. Each alkene substitutes a single bonded CH2-CH2 segment of the chain with a double bonded CH2=CH2 segment, thus a carbon double-bonded to another carbon. Unsaturated fatty acids such as oleic acid can show two of their distinct forms (isomers), i.e. cis and trans forms. The cis form has adjacent carbons on the same side of the double bond. The trans form has adjacent carbons bound to the opposite side of the double bond. The trans form is more rigid than the cis form. Oleic acid has one double bond whereas linoleic acid has two double bonds and liolenic acid has three double bonds.

Fatty acids react just like any other carboxylic acid, meaning they can undergo esterification and acid-base reactions. Reduction of fatty acids gives corresponding fatty alcohols. Unsaturated fatty acids undergo addition reactions, with the most prominent being hydrogenation. Such hydrogenation is used to convert vegetable oils into margarines. Partial hydrogenation of unsaturated fatty acids gives isomers mainly converting cis form to trans form.