Ethoxylation

Ethoxylation is a chemical reaction in which ethylene oxide adds to a substrate. It is the most widely practiced alkoxylation, which involves the addition of epoxides to substrates. Ethoxylation is a chemical reaction in which ethylene oxide adds to a substrate. It is the most widely practiced alkoxylation, which involves the addition of epoxides to substrates. In the usual application, alcohols and phenols are converted into R(OC2H4)nOH where n ranges from 1 to 10. Such compounds are called alcohol ethoxylates. Alcohol ethoxlates are often converted to related species called ethoxysulfates. Alcohol ethoxylates and ethoxysulfates are surfactants, used widely in cosmetic and other commercial products. The process is of great industrial significance with more than 2,000,000 metric tons of various ethoxylates produced worldwide in 1994. The process was developed at the Ludwigshafen laboratories of I.G. Farben by Conrad Schöller and Max Wittwer during the 1930s. Industrial ethoxylation is primarily performed upon fatty alcohols in order to generate fatty alcohol ethoxylates (FAE's), which are a common form of nonionic surfactant (e.g. octaethylene glycol monododecyl ether. Such alcohols may be obtained by the hydrogenation of fatty acids from seed oils, or via hydroformylation in the Shell higher olefin process. The reaction proceeds by blowing ethylene oxide through the alcohol at 180 °C and under 1-2 bar of pressure, with potassium hydroxide (KOH) serving as a catalyst. The process is highly exothermic (ΔH -92000 J/mol of ethylene oxide reacted) and requires careful control to avoid a potentially disastrous thermal runaway. The starting materials are usually primary alcohols as they react ~10-30x faster than do secondary alcohols.Typically 5-10 units of ethylene oxide are added to each alcohol, however ethoxylated alcohols can be more prone to ethoxylation than the starting alcohol, making the reaction difficult to control and leading to the formation of a product with varying repeat unit length (the value of n in the equation above). Better control can be afforded by the use of more sophisticated catalysts, which can be used to generate narrow-range ethoxylates. Ethoxylated alcohols are considered to be a high production volume (HPV) chemical by the US EPA. Ethoxylation is sometimes combined with propoxylation, the analogous reaction using propylene oxide as the monomer. Both reactions are normally performed in the same reactor and may be run simultaneously to give a random polymer, or in alternation to obtain block copolymers such as poloxamers. Propylene oxide is more hydrophobic than ethylene oxide and its inclusion at low levels can significantly affect the properties of the surfactant. In particular ethoxylated fatty alcohols which have been 'capped' with ~1 propylene oxide unit are extensively marketed as low-foaming surfactants. Ethoxylated fatty alcohols are often converted to the corresponding organosulfates, which can be easily deprotonated to give anionic surfactants such as sodium laureth sulfate. Being salts, ethoxysulfates exhibit good water solubility (high HLB value). The conversion is achieved by treating ethoxylated alcohols with sulfur trioxide. Laboratory scale synthesis may be performed using chlorosulfuric acid: The resulting sulfate esters are neutralized to give the salt: Small volumes are neutralized with alkanolamines such as triethanolamine (TEA). In 2006, 382,500 metric tons of alcohol ethoxysulfates (AES) were consumed in North America.(subscription required)