Natural fatty alcohols are linear materials with an even number of carbon atoms. They have the following structure: CH3(CH2)nOH The physical properties of linear primary fatty alcohols are shown in Table 1.
Guerbet alcohols are a class of highly branched alcohols. They were first developed in the 1890s by Marcel Guerbet, who synthesized them. The reaction sequence, which bears his name, is related to the Aldol Reaction and occurs at high temperatures under catalytic conditions. The overall reaction is represented by Figure 1. Guerbet alcohols have significantly lower melting points than the linear alcohols with the same number of carbon atoms. The melting point of Guerbet alcohols vs. linear alcohols is shown in Figure 2. This makes them highly desirable in the personal care market.
Only two approaches are possible to obtain alcohols with a high molecular weight and liquidity:
The first is the introduction of unsaturation. Stearyl alcohol (C18 saturated) is a waxy solid at ambient conditions and oleyl alcohol (C18 with one double bond) is liquid. The problem with this approach is the degraditive process of rancidity attacks the unsaturation, producing color and odor.
The second approach is the introduction of branching. Methyl branched products are slightly more liquid than their linear counterparts. Longer branches, like those obtained by Guerbet technology, are liquid to far lower temperatures than either the linear of methyl branched products, making them outstanding candidates for use as emollient oils.
Due to their branching, Guerbet alcohols are high molecular weight, hence they:
1) have low irritation properties;
2) are branched and therefore liquid to extremely low temperatures;
3) have low volatility;
4) are primary alcohols and hence are reactive and can be used to make many derivatives;
5) are useful as superfatting agents; and
6) are good lubricants.
Also, Guerbet alcohols are essentially saturated, hence they:
1) exhibit good oxidative stability at elevated temperatures;
2) have excellent color initially and at elevated temperatures; and
3) exhibit improved stability over unsaturated products in many applications.
It is these properties that make Guerbet alcohols of interest both as compounds and raw materials to make derivatives.