Urethane (or ethyl carbamate) is an organic compound. The urethane formula is C3H7NO2, and it has a molecular weight of 89.09 g/mol. It is an ester of carbamic acid, and its melting and boiling point are 46 to 50 °C and 182 to 185 °C, respectively.
Ethyl carbamate is a colorless crystal or white powder with almost no odor. It is used in the production of pesticides and fungicides, and it was formerly used as a therapeutic or anesthetic agent.
Urethane may also refer to polyurethane (PU), which is an organic polymer composed of units joined by carbamate linkages. Polyurethanes are extensively used in buildings, refrigerators, upholstery, coatings and adhesives.
Synthesis of Urethane
The synthesis of urethane can be accomplished by the reaction of ammonia and ethyl chloroformate, in which the ammonia attacks the acid chloride functional group to form an amide.
The industrial production of urethane usually involves the heating of urea and ethyl alcohol. This process is more popular because it is cost-effective, and the end product, ammonia, can be easily recycled for the synthesis of urea or used further in the manufacture of other chemicals such as plastics, explosives, textiles, pesticides and dyes.
Polyurethanes, on the other hand, are synthesized by the reaction of isocyanate (organic compounds containing two or more isocyanate groups -N=C=O) with polyol (compounds with two or more hydroxyl groups -OH) in the presence of a catalyst or ultraviolet light.
This polymerization reaction produces polymer with the urethane linkage (-NH-C(=O)-O-). A tertiary amine, such as 1,4-diazabicyclo[2.2.2]octane (DABCO), can act as catalyst, and the reaction mechanism is as follows:
Urethane Toxicity and Environmental Impact
Ingestion of urethane is toxic. Both inhalation and skin absorption are harmful. Acute exposure to urethane may result in symptoms such as nausea, vomiting, diarrhea, coma, gastroenteric hemorrhages and kidney and liver injury. Chronic exposure may even lead to neurological disorders because of urethane toxicity.
Studies with rodents have shown that oral and inhalation of urethane is correlated with the increased incidence of lung cancer, although no such information is available for humans due to ethical considerations. However, in 2007, the International Agency for Research on Cancer (IARC) classified urethane into Group 2B, possibly carcinogenic to humans.
Urethane is also present in many fermented food products and alcoholic beverages including soy sauce, kimchi and breads, along with wine and sake. Due to the potential health hazard of this compound, measures have been taken to mitigate its cumulative and long-term effects on humans.
The thermal decomposition of polyurethane will generate carbon monoxide, nitrogen oxide, isocyanates, hydrogen cyanide and other toxic substances. In landfills, biodegradation of polyurethane is dependent on its structure. It can be achieved by incorporating labile and hydrolysable moieties into the polymer, for example, the ester bonds in poly(ester-urethanes) are hydrolysable and thus prone to microbial degradation.
Uses of Urethane
Urethane has been used as a antineoplastic agent for its therapeutics purposes. Prior to World War II, urethane was also extensively used in the treatment of multiple myeloma. However, these applications ended when it was discovered to be carcinogenic.
This compound is still frequently used today as an anesthetic in animal experiments, or as a solubilizer and cosolvent for pesticides and fumigants. It is also an intermediate for many pharmaceuticals products.
Polyurethanes have wide applications in material science. Rigid polyurethane foams can provide insulation for buildings and refrigerator appliances, making them useful for sustainability and energy conservation. Flexible polyurethane foams, on the contrary, are used as filling material for upholstery and mattresses.
Polyurethanes can be made light yet highly abrasion-resistant, which is excellent for shoe soles and automobile wheels. Some polyurethanes are durable, corrosion- and weather-resistant, making them suitable as coatings for vehicles, cables, walls or bridges. The binding qualities of polyurethane also make it useful as adhesive for a variety of materials such as wood, rubber, cardboard or glass.