As the formulator becomes more interested in the sustainability of the ingredients used in formulations, the source of the raw materials used to manufacture those ingredients becomes important, and following the ingredient back to its source is the only way to evaluate its sustainability. There are three common sources of alcohols used to make cosmetic raw materials: natural alcohols, oxo alcohols and Ziegler alcohols. Table 1 illustrates the source and processes used to make these alcohols and a list of common alcohols and their carbon atoms is shown in Table 2. In addition, a list of derivatives that can be made from alcohols is shown in Figure 1.
Natural fatty alcohols are made by the reduction of methyl esters with high pressure hydrogen. The process has been known for almost 70 years and has undergone extensive fine tuning by key producers. The catalyst used for the reaction determines the products that are prepared. For instance, if copper chromite is used as a catalyst with an unsaturated methyl ester, hydrogenation of any C=C unsaturation also occurs, resulting in a saturated species alcohol. However, if a group-specific catalyst like aluminum oxide is used, the unsaturation is not affected, resulting in an unsaturated alcohol. This is the route used to make oleyl alcohol.
Ziegler alcohols are made by the oxidation of trialkyl aluminum alkoxylates, chain growth and subsequent hydrolysis. Continental Oil Co., Ethyl Corp. and Condea developed this technology in the mid-1960s. Since ethylene is the material used in the chain growth portion of the reaction, the molecules (unlike oxo alcohols) are linear. Due to their lack of branching, Ziegler alcohols are more like natural alcohols than oxo alcohols.
Oxo alcohols are prepared by the reaction of alpha olefin with hydrogen and carbon monoxide using a catalyst, commonly a cobalt compound. The reaction occurs in two parts; first is the preparation of the aldehyde, and second is the reduction of the aldehyde to the alcohol. It should be noted that two different aldehyde compounds, one linear and the other with a methyl branch, form in the first part of the reaction. Both then rearrange into alcohols.
In general, Ziegler alcohols are most like natural alcohols structurally and can be easily confused with their natural counterparts when made into derivatives. Also, because of their branching, oxo alcohols have a different INCI name.