Ethoxylation
Ethoxylation is an industrial process in which ethylene oxide is added to alcohols and phenols to give surfactants. The invention of the process is attributed to Schöller and Wittwer at I.G. Farben industrie.[1]
Method and scope
In industrial ethoxylation, an alcohol is treated with ethylene oxide and potassium hydroxide (KOH), which serves as a catalyst. The reactor is pressurised with nitrogen and heated to about 150 °C. Typically 5-10 units of ethylene oxide are added to each alcohol:
- ROH + n C2H4O → R(OC2H4)nOH
A distribution of products are obtained.
PEGylation
Ethoxylation is commonly practiced, albeit on a much smaller scale, in the biotechnology and pharmaceutical industries to increase water solubility and, in the case of pharmaceuticals, circulatory half-life of non-polar organic compounds. In this application, ethoxylation is known as "PEGylation," because poly(ethylene oxide) is also known as poly(ethylene glycol), abbreviated as PEG.
Applications of ethoxylated products
Ethoxylated alcohols and phenols are important nonionic surfactants. They feature both a lipophilic tails (R in the equation above) and a relatively polar head group ((OC2H4)nOH in the above example). The amount of ethylene oxide and the reaction time determine the degree of ethoxylation (the value of n in the equation above), which in turn determines the surfactant properties of the ethoxylated product. Traditionally the alcohols were obtained by hydrogenation of fatty acids, but currently most are "oxo alcohols," obtained via hydroformylation. In addition to alcohols, amines and phenols are commonly ethoxylated.
Ethoxylated fatty alcohols are often converted to the organosulfate. A well known example is sodium laureth sulfate, a foaming agent in shampoos and toothpastes, as well as an industrial detergent. The conversion typically uses sulfur trioxide or chlorosulfuric acid: R(OC2H4)nOH + SO3 → R(OC2H4)nOSO3H
Environmental and safety issues
Some ethoxylated materials have been controversial because of their widespread use and the toxicity to aquatic life of their degradation products, such as nonylphenol.[1]
References
- ^ a b Eduard Smulders, Wolfgang von Rybinski, Eric Sung, Wilfried Rähse, Josef Steber, Frederike Wiebel, Anette Nordskog “Laundry Detergents” in Ullmann's Encyclopedia of Industrial Chemistry 2007, Wiley-VCH, Weinheim. doi:10.1002/14356007.a08_315.pub2. Schöller and Wittwer are listed as inventors on US Patent #1970578, issued 1934, "Assistants for the Textile and Related Industries."