In organic chemistry, 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 , where n ranges from 1 to 10. Such compounds are called alcohol ethoxylates. Alcohol ethoxylates 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.
Production
The process was developed at the Ludwigshafen laboratories of IG Farben by Conrad Schöller and during the 1930s.
Alcohol ethoxylates
Industrial ethoxylation is primarily performed upon alcohols. Lower alcohols react to give glycol ethers which are commonly used as solvents, while longer fatty alcohols are converted to fatty alcohol ethoxylates (FAE's), which are a common form of nonionic surfactant. The reaction typically 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 = -92 kJ/mol of ethylene oxide reacted) and requires careful control to avoid a potentially disastrous thermal runaway.
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/propoxylation
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. 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 2008, 381,000 metric tons of alcohol ethoxysulfates were consumed in North America. Lauryl Alcohol Ethoxylate Analysis with Gas Chromatography (GC)
For the analysis of Lauryl Alcohol Ethoxylate using Gas Chromatography (GC), the selection of a suitable GC column depends on the specific ethoxylation level and the volatility of the compound. In general, Lauryl Alcohol Ethoxylates are non-volatile or semi-volatile, so derivatization might be necessary before GC analysis.
Here are some column options for analysis after derivatization (acetylation):
1. Non-polar columns (like DB-1, HP-1, or RTX-1):
These are made of 100% dimethylpolysiloxane.
Suitable for analyzing relatively non-polar, derivatized alcohol ethoxylates.
Common dimensions: 30 m length, 0.25 mm ID, 0.25 μm film thickness.
2. Mid-polarity columns (like DB-5, HP-5, or RTX-5):
These are 5% phenyl, 95% dimethylpolysiloxane.
They offer slightly better separation of ethoxylates with varying chain lengths.
Common dimensions: 30 m length, 0.25 mm ID, 0.25 μm film thickness.
3. Polar columns (like DB-WAX or HP-FFAP):
These are polyethylene glycol (PEG) columns.
They are more suited for polar compounds, but Lauryl Alcohol Ethoxylates may still need derivatization.
The DB-5 or HP-5 column is often preferred for surfactants like ethoxylates due to its moderate polarity, providing good separation of ethoxylation products.
It's essential to consider the specific range of ethoxylation (number of ethylene oxide units) to optimize the method further. Additionally, derivatization can help in improving volatility and peak shape.
Other materials
Although alcohols are by far the major substrate for ethoxylation, many nucleophiles are reactive toward ethylene oxide. Primary amines will react to give di-chain materials such as polyethoxylated tallow amine. The reaction of ammonia produces important bulk chemicals such as ethanolamine, diethanolamine, and triethanolamine.
Applications of ethoxylated products
Alcohol ethoxylates (AE) and alcohol ethoxysulfates (AES) are surfactants found in products such as laundry detergents, surface cleaners, cosmetics, agricultural products, textiles, and paint.
Alcohol ethoxylates
As alcohol ethoxylate based surfactants are non-ionic they typically require longer ethoxylate chains than their sulfonated analogues in order to be water-soluble. Examples synthesized on an industrial scale include octyl phenol ethoxylate, polysorbate 80 and poloxamers.
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" (polyethylene oxide is synonymous with polyethylene glycol, abbreviated as PEG). Carbon chain length is 8-18 while the ethoxylated chain is usually 3 to 12 ethylene oxides long in home products. They feature both lipophilic tails, indicated by the alkyl group abbreviation, R, and relatively polar headgroups, represented by the formula .
Alcohol ethoxysulfates
AES found in consumer products generally are linear alcohols, which could be mixtures of entirely linear alkyl chains or of both linear and mono-branched alkyl chains. A high-volume example of these is sodium laureth sulfate a foaming agent in shampoos and liquid soaps, as well as industrial detergents.
Environmental and safety
Alcohol ethoxylates (AEs)
Human health
Alcohol ethoxylates are not observed to be mutagenic, carcinogenic, or skin sensitizers, nor cause reproductive or developmental effects. One byproduct of ethoxylation is 1,4-dioxane, a possible human carcinogen. Undiluted AEs can cause dermal or eye irritation. In aqueous solution, the level of irritation is dependent on the concentration. AEs are considered to have low to moderate toxicity for acute oral exposure, low acute dermal toxicity, and have mild irritation potential for skin and eyes at concentrations found in consumer products.
Aquatic and environmental aspects
AEs are usually released down the drain, where they may be adsorbed into solids and biodegrade through anaerobic processes, with ~28–58% degraded in the sewer. The remaining AEs are treated at waste water treatment plants and biodegraded via aerobic processes with less than 0.8% of AEs released in effluent. The removal of AES due to degradation via anaerobic processes is estimated to be between 75 and 87%.
In water
Flow-through laboratory tests in a terminal pool of AES with mollusks found the NOEC of a snail, Goniobasis and the Asian clam, Corbicula to be greater than 730 ug/L. Corbicula growth was measured to be affected at a concentration of 75 ug/L. The mayfly, genus Tricorythodes has a normalized density NOEC value of 190 ug/L.
Human safety
AES has not been found to be genotoxic, mutagenic, or carcinogenic.