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Ethoxylation is a chemical process used in industry to create surfactants, which are compounds that reduce the surface tension of liquids. The process of ethoxylation involves adding ethylene oxide to an alcohol or phenol to produce products. Many products produced by ethoxylation have commercial applications, and some are used in biochemistry and medicine. While most surfactants can be widely used, others are hazardous to humans and the environment, and in some countries their use is restricted.
Compounds that are commonly ethoxylated include nonylphenol, amines, fatty acids and fatty alcohols. A catalyst such as potassium hydroxide must usually be added along with ethylene oxide to help speed the ethoxylation reaction. Some compounds, such as lactic acid and 12-hydroxystearic acid, can be ethoxylated without a catalyst.
In industrial plants, ethoxylation may involve a pre-treatment step where water is removed to prevent the formation of extraneous compounds and a post-treatment step where the catalyst is neutralized and removed. The various steps of the reaction may take place in different vessels, or in one large reactor. The design of the reaction depends on efficiency. Industrial chemists often directly monitor the ethoxylation process and make modifications to increase productivity.
The products of ethoxylation are known as ethoxylated materials, or surfactants. These are organic compounds that contain both hydrophilic (water-attractant) and hydrophobic (water-repellent) groups. Surfactants change the surface properties of liquids because their structure causes them to migrate to the liquid’s boundary interface. For example, in water, surfactants will migrate to the air-water boundary, but in an oil-water mixture, surfactants will migrate to the oil-water boundary. The term surfactant is a shortened version of the term surface active agent, reflecting this behavior.
Surfactants can be found in detergents, shampoos, paints, inks, pesticides, and numerous other commercial products. They are typically used as emulsifiers, causing otherwise unmixable liquids to mix, or as foaming agents and cleaners. Some surfactants have biochemical applications and are used to extract proteins from cells or make proteins soluble in solution.
A specific type of ethoxylation, known as PEGylation, is used in medicine to promote drug delivery in the body. In PEGylation, chains of polyethylene glycol are attached to a therapeutic protein or drug. This prevents the body’s immune system from recognizing and attacking the drug or protein, and also allows normally insoluble drugs to become soluble in water.
Some ethoxylated materials can be hazardous and are currently regulated by some government agencies. Nonylphenol ethoxylates (NPEs), which are used in pesticides, industrial detergents, and some household cleaning products, can reach groundwater and soil via the sewer system. NPEs have toxic effects on aquatic life, and additionally cause reproductive problems in animals. Concern about the possibility that NPEs may migrate through agricultural land into human food has led to their use being limited in several countries.