Chemistry:Glycol ethers

Short description: Class of chemical compounds

Ethylene glycol monomethyl ether, a glycol ether

Glycol ethers are a class of chemical compounds consisting of alkyl ethers that are based on glycols such as ethylene glycol or propylene glycol. They are commonly used as solvents in paints and cleaners. They have good solvent properties while having higher boiling points than the lower-molecular-weight ethers and alcohols.

History

The name "Cellosolve" was registered in 1924 as a United States trademark by Carbide & Carbon Chemicals Corporation (a division of Union Carbide Corporation) for "Solvents for Gums, Resins, Cellulose Esters, and the Like". "Ethyl Cellosolve" or simply "Cellosolve" consists mainly of ethylene glycol monoethyl ether and was introduced as a lower-cost solvent alternative to ethyl lactate. "Butyl Cellosolve" (ethylene glycol monobutyl ether) was introduced in 1928, and "Methyl Cellosolve" (ethylene glycol monomethyl ether) in 1929.

Types

Glycol ethers are designated "E-series" or "P-series" for those made from ethylene oxide or propylene oxide, respectively. Typically, E-series glycol ethers are found in pharmaceuticals, sunscreens, cosmetics, inks, dyes and water-based paints, while P-series glycol ethers are used in degreasers, cleaners, aerosol paints and adhesives. Both E- and P-series glycol ethers can be used as intermediates that undergo further chemical reactions, producing glycol diethers and glycol ether acetates. P-series glycol ethers are marketed as having lower toxicity than the E-series.

Health Impacts

Most glycol ethers are water-soluble, biodegradable and only a few are considered toxic.

In the early 1990's, studies found higher than expected rates of miscarriages among women who worked in semiconductor plants, which was traced back to ethylene glycol ethers (EGEs) used in the photoresist substances that coat semiconductors.

One study suggests that occupational exposure to glycol ethers is related to low motile sperm count, a finding disputed by the chemical industry.

Subclasses of Glycol Ethers

Glycol ether solvents

• Ethylene glycol monomethyl ether (2-methoxyethanol, CH₃OCH₂CH₂OH)
• Ethylene glycol monoethyl ether (2-ethoxyethanol, CH₃CH₂OCH₂CH₂OH)
• Ethylene glycol monopropyl ether (2-propoxyethanol, CH₃CH₂CH₂OCH₂CH₂OH)
• Ethylene glycol monoisopropyl ether (2-isopropoxyethanol, (CH₃)₂CHOCH₂CH₂OH)
• Ethylene glycol monobutyl ether (2-butoxyethanol, CH₃CH₂CH₂CH₂OCH₂CH₂OH), a widely used solvent in paintings and surface coatings, cleaning products and inks
• Ethylene glycol monophenyl ether (2-phenoxyethanol, C₆H₅OCH₂CH₂OH)
• Ethylene glycol monobenzyl ether (2-benzyloxyethanol, C₆H₅CH₂OCH₂CH₂OH)
• Propylene glycol methyl ether, (1-methoxy-2-propanol, CH₃OCH₂CH(OH)CH₃)
• Diethylene glycol monomethyl ether (2-(2-methoxyethoxy)ethanol, methyl carbitol, CH₃OCH₂CH₂OCH₂CH₂OH)
• Diethylene glycol monoethyl ether (2-(2-ethoxyethoxy)ethanol, carbitol cellosolve, CH₃CH₂OCH₂CH₂OCH₂CH₂OH)
• Diethylene glycol mono-n-butyl ether (2-(2-butoxyethoxy)ethanol, butyl carbitol, CH₃CH₂CH₂CH₂OCH₂CH₂OCH₂CH₂OH)
• Dipropyleneglycol methyl ether
• C12-15 pareth-12 a polyethylene glycol ether used as an emulsifier in cosmetics

Dialkyl ethers

• Ethylene glycol dimethyl ether (dimethoxyethane, CH₃OCH₂CH₂OCH₃), a higher boiling alternative to diethyl ether and THF, also used as a solvent for polysaccharides, a reagent in organometallic chemistry and in some electrolytes of lithium batteries
• Ethylene glycol diethyl ether (diethoxyethane, CH₃CH₂OCH₂CH₂OCH₂CH₃)
• Ethylene glycol dibutyl ether (dibutoxyethane, CH₃CH₂CH₂CH₂OCH₂CH₂OCH₂CH₂CH₂CH₃)

Esters

• Ethylene glycol methyl ether acetate (2-methoxyethyl acetate, CH₃OCH₂CH₂OCOCH₃)
• Ethylene glycol monoethyl ether acetate (2-ethoxyethyl acetate, CH₃CH₂OCH₂CH₂OCOCH₃)
• Ethylene glycol monobutyl ether acetate (2-butoxyethyl acetate, CH₃CH₂CH₂CH₂OCH₂CH₂OCOCH₃)
• Propylene glycol methyl ether acetate (1-methoxy-2-propanol acetate)