Glycol ethers are used extensively as solvents because they tend to be quite soluble in both water and organic liquids. General uses include inks and dyes, enamels, paints and as cleaning agents in the dry-cleaning and glass-cleaning industries. The semiconductor industry also uses these compounds extensively as solvents and cleaning agents.
The ethylene glycol ethers are used widely as solvents for resins, lacquers, paints, varnishes, dyes and inks, as well as components of painting pastes, cleaning compounds, liquid soaps, cosmetics and hydraulic fluids. Propylene and butylene glycol ethers are valuable as dispersing agents and as solvents for lacquers, paints, resins, dyes, oils and greases.
Ethylene glycol monoethyl ether is a solvent in the lacquer, printing, metal and chemical industries. It is also used for dyeing and printing in the textile industry and as a leather-finishing agent, an anti-icing additive for aviation fuels, and a component of varnish removers and cleansing solutions. Diethylene glycol monomethyl ether and ethylene glycol monobutyl ether acetate function in industry as high-boiling solvents. Diethylene glycol monomethyl ether is used for non-grain-raising wood stains, for brushing lacquers with mild odours, for stamp pad inks and for leather finishing. In the paint industry, it is a coalescing agent for latex paint; and in the textile industry, it is used for printing, textile soaps and dye pastes, as well as for setting the twist and conditioning yarns and cloth.
The solvents diethylene glycol monomethyl ether, diethylene glycol monoethyl ether and diethylene glycol mono-n-butyl ether serve as diluents in hydraulic brake fluids. 2-Phenoxyethanol is a fixative for perfumes, cosmetics and soaps, a textile dye carrier and a solvent for cleaners, inks, germicides and pharmaceuticals. 2-Methoxyethanol is also a perfume fixative. It is used in the manufacture of photographic film, as a jet fuel anti-icing additive, as a solvent for resins used in the electronics industry, and as a leather-dyeing agent. 2-Methoxyethanol and propylene glycol methyl ether are useful for solvent-sealing of cellophane. Ethylene glycol mono-n-butyl ether is a solvent for protective coatings and for metal cleaners. It is used in the textile industry to prevent spotting in printing or dyeing.
Generally speaking, the acute effects of glycol ethers are limited to the central nervous system and are similar to acute solvent toxicity. These effects include dizziness, headache, confusion, fatigue, disorientation, slurred speech and (if severe enough) respiratory depression and loss of consciousness. The effects of long-term exposure include skin irritation, anaemia and bone marrow supression, encephalopathy and reproductive toxicity. 2-Methoxyethanol and 2-ethoxyethanol (and their acetates) are most toxic. Because of their relatively low volatility, exposure most often occurs as a result of skin contact with liquids, or inhalation of vapours in closed spaces.
Most of the ethylene glycol ethers are more volatile than the parent compound and, consequently, less easily controlled with respect to vapour exposure. All of the ethers are more toxic than ethylene glycol and exhibit a similar symptomatological complex.
Ethylene glycol monomethyl ether (methyl cellosolve; Dowanol EM; 2-methoxyethanol). The oral LD50 for ethylene glycol monomethyl ether in rats is associated with delayed deaths involving lung oedema, slight liver injury, and extensive kidney damage. Renal failure is the probable cause of death in response to repeated oral exposures. This glycol ether is moderately irritating to the eye, producing acute pain, inflammation of the membranes, and corneal clouding which persists for several hours. Although ethylene glycol monomethyl ether is not appreciably irritating to skin, it can be absorbed in toxic amounts. Experience with human exposure to ethylene glycol monomethyl ether has indicated that it can result in the appearance of immature leucocytes, monocytic anaemia, and neurological and behavioural changes. Studies have also shown that inhalation exposure in humans can lead to forgetfullness, personality changes, weakness, lethargy and headaches. In animals, inhalation of higher concentrations can result in testicular degeneration, damage to the spleen, and blood in the urine. Animal studies have shown anaemia, thymus and marrow damage at 300 ppm. At 50 ppm during pregnancy in animals, major foetal abnormalities were reported. The most important health effect seems to be the effect on the human reproductive system, with diminished spermatogenesis. Thus, it is evident that the monomethyl ether of ethylene glycol is a moderate toxic compound and that repeated skin contact or inhalation of vapour must be prevented.
Ethylene glycol monoethyl ether (cellosolve solvent; Dowanol EE; 2-ethoxyethanol). Ethylene glycol monoethyl ether is less toxic than the methyl ether (above). The most significant toxic action is on the blood, and neurological symptoms are not expected. In other respects it is similar in toxic action to ethylene glycol monomethyl ether. Excessive exposure can result in moderate irritation to the respiratory system, lung oedema, central nervous system depression and marked glomerulitis. In animal studies, foetotoxicity and teratogenicity were seen at levels above 160 ppm, and behavioural changes in offspring were obvious after maternal exposure at 100 ppm.
Other ethylene glycol ethers. Mention of ethylene glycol monobutyl ether is also in order because of its extensive use in industry. In rats, deaths in response to single oral exposures are attributable to narcosis, whereas delayed deaths result from lung congestion and renal failure. Direct contact of the eye with this ether produces intense pain, marked conjunctival irritation and corneal clouding, which may persist for several days. As with monomethyl ether, skin contact does not cause much skin irritation, but toxic amounts can be absorbed. Inhalation studies have shown that rats can tolerate 30 7-hour exposures to 54 ppm, but some injury occurs at a concentration of 100 ppm. At higher concentrations, rats exhibited haemorrhaging in the lungs, congestion of the viscera, liver damage, haemoglobinuria and marked erythrocyte fragility. Foetotoxicity has been seen in rats exposed to 100 ppm, but not at 50 ppm. Enhanced erythrocyte fragility was evident at all exposure concentrations above 50 ppm of ethylene glycol monobutyl ether vapours. Humans appear to be somewhat less susceptible than laboratory animals because of apparent resistance to its haemolytic action. While headache and eye and nasal irritation was seen in humans above 100 ppm, red blood cell damage was not found.
Both the isopropyl and n-propyl ethers of ethylene glycol present particular hazards. These glycol ethers have low single-dose oral LD50 values and they cause severe kidney and liver damage. Bloody urine is an early sign of severe kidney damage. Death usually occurs within a few days. Eye contact results in rapid conjunctival irritation and partial corneal opacity in the rabbit, with recovery requiring about 1 week. Like most other ethylene glycol ethers, the propyl derivatives are only mildly irritating to the skin but can be absorbed in toxic amounts. Furthermore, they are highly toxic via inhalation. Fortunately, ethylene glycol monoisopropyl ether is not a prominent commercial compound.
Diethylene glycol ethers. The ethers of diethylene glycol are lower in toxicity than the ethers of ethylene glycol, but they have similar characteristics.
Polyethylene glycols. Triethylene, tetraethylene, and the higher polyethylene glycols appear to be innocuous compounds of low vapour pressure.
Propylene glycol ethers. Propylene glycol monomethyl ether is relatively low in toxicity. In rats, the single oral dose LD50 caused death by generalized central nervous system depression, probably respiratory arrest. Repeated oral doses (3 g/kg) over a 35-day period induced in rats only mild histopathological changes in the liver and kidneys. Eye contact resulted in only a mild transitory irritation. It is not appreciably irritating to the skin, but confinement of large amounts of the ether to rabbit skin causes central nervous system depression. The vapour does not present a substantial health hazard if inhaled. Deep narcosis appears to be the cause of death in animals subjected to severe inhalation exposures. This ether is irritating to the eyes and upper respiratory tract of humans at concentrations that are not hazardous to health; hence it does have some warning properties.
Di- and tripropylene glycol ethers exhibit toxicological properties similar to the monopropylene derivatives, but present essentially no hazard with respect to vapour inhalation or skin contact.
Polybutylene glycols. Those that have been examined can cause kidney damage in excessive doses, but they are not injurious to the eyes or skin and are not absorbed in toxic amounts.
Acetic esters, diesters, ether esters. These derivatives of the common glycols are of particular importance since they are employed as solvents for plastics and resins in diverse products. Many explosives contain ester of ethylene glycol as a freezing-point depressant. With respect to toxicity, the glycol ether fatty acid esters are considerably more irritating to mucous membranes than the parent compounds discussed previously. However, the fatty acid esters have toxicity properties essentially identical to the parent materials once the former are absorbed, because the esters are saponified in biological environments to yield fatty acid and the corresponding glycol or glycol ether.
Safety and Health Measures
Measures used to control and limit the exposure to glycol ethers are essentially the same as those used to control solvent exposure as discussed elsewhere in this Encyclopaedia. Substitution of one material for another less toxic one, if possible, is always a good starting point. Adequate ventilation systems that can effectively minimize the concentration of material in the breathing zone is important. Where explosive and fire hazards are in issue, care must be taken to avoid open flames or sparks and to store materials in “explosion safe” containers. Personal protective equipment, such as respirators, gloves and clothing, while important, should not be relied upon exclusively. Protective eyewear should always be worn if splash exposure is a risk. When using ethylene glycol monomethyl ether, workers should wear chemical safety goggles, and adequate ventilation is necessary. Eye protection is also recommended whenever the possibility of such contact exists with ethylene glycol monobutyl ether. Inhalation of its vapours and skin contact should be avoided. Particularly when working with 2-methoxyethanol or 2-ethoxyethanol, all skin contact should be strictly avoided.
Glycol ethers tables
Table 1 - Chemical information.
Table 2 - Health hazards.
Table 3 - Physical and chemical hazards.
Table 4 - Physical and chemical properties.