Guerbet alcohols are the beta branched primary alcohols, which are the condensation products of alcohols. This chemistry has made possible the synthesis of regiospecific, beta-branched hydrophobe which introduces high-purity branching into the molecule. The chemistry has resulted in the preparation of many materials that find applications in metal lubrication, plastic mold release, paper processing, and personal care products.
The reaction involves the following steps:
* Oxidation of alcohols to aldehydes
* Aldol condensation after proton extraction
* Dehydration of the aldol product
* Hydogenation of the allylic aldehyde
The reaction is catalyzed in presence of hydrogen transfer catalyst. These include nickel, lead salts, oxides of copper, lead, zinc, chromium, molybdenum, tungsten, manganese and some palladium compounds. At low temperatures of 130-140°C, oxidation process is the rate limiting step. At somewhat higher temperatures 160-180°C, the rate limiting step is the aldol condensation .At higher temperatures, other degradative reactions occur and can become dominant. Cannizaro reaction is the major side reaction described.
Most commonly used raw materials for the preparation of Guerbet alcohols are alcohols of natural origin which are primary, with even numbered, straight carbon chains. Oxo alcohols can also be used, but the reaction rate and conversions are reduced.
Guerbet alcohols are branched, essentially saturated and of high molecular weight, exhibit the following properties Have low irritation potential Are liquid to low temperatures Are low in volatility Are reactive and can be used to make many derivatives Are good lubricants Exhibit very good oxidative stability at elevated temperatures Have excellent color initially and at elevated temperatures Exhibit improved stability over unsaturated products in many applications.
They are prepared by the oxidation of Guerbet alcohols to produce primary carboxylic acids. Oxidative alkali fusion with alkali metal salts dehydrogenates the alcohol and gives excellent yields of carboxylic acids.
Guerbet alcohols as well as acids melt at lower temperatures than linear alcohols containing the same number of carbon atoms. Compared to Guerbet alcohols with the same number of alcohols corresponding Guerbet acids melt at higher temperature.
One of the desired effects of introducing Guerbet branching into ester molecules is to extend their liquidity to very low temperatures. With the availability of Guerbet acids and alcohols, branching can be introduced into the alcohol, acid or both.
It is observed that products with the lowest titer carry Guerbet branching in both the acid and the alcohol part of the molecule. The next lowest titer point is obtained when the Guerbet branch is in the acid moiety. Branching in the alcohol part results in the highest titer value. Products derived from linear acids and linear alcohols differ substantially from those derived from linear acids and Guerbet alcohols. Specifically, the former are rock hard solids while the latter are liquids with a snowy precipitate. Introduction of Gurbet branching in to the ester molecule do not alter the solubility of the resulting ester.
GUERBET SULFATES AND ETHER SULFATES
Sulfates and ether sulfates are typical anionic surfactants. One of the salient properties of surfactant is the Kraft point which is a measure of water solubility. It is defined as the temperature in °C at which a 1% dispersion becomes clear under gradual heat. The Kraft point of sulfates rises with increasing molecular weight of the hydrophobe or with the addition of propylene oxide to the hydrophobe. The Kraft point decreases with the addition of ethylene oxide. The Kraft point provides another illustration of the differences between the linear and Gurbet based sulfates.
The location of the branch within the hydrophobe has a major effect upon functional properties of anionic surfactants, such as their HLB and emulsifying power. Guerbet based surfactants promote their micellization in the oil phase because of its twin tail structure which require less cosurfactant to make micro emulsions. Guerbet ether sulfates are very efficient emulsifiers for oil and emulsify three to five times more oil than the sulfates made from linear hydrophobes.