Acrylonitrile

Structure and basic properties

Acrylonitrile is an organic compound with the formula and the structure . It is a colorless, volatile liquid although commercial samples can be yellow due to impurities. It has a pungent odor of garlic or onions. Its molecular structure consists of a vinyl group () linked to a nitrile (). It is an important monomer for the manufacture of useful plastics such as polyacrylonitrile. It is reactive and toxic at low doses.

Production

Acrylonitrile was first synthesized by the French chemist Charles Moureu in 1893.

• See especially pp. 187–189 ("Nitrile acrylique ou cyanure de vinyle (Propène-nitrile)").
• Acrylonitrile is produced by catalytic ammoxidation of propylene, also known as the SOHIO process. In 2002, world production capacity was estimated at 5 million tonnes per year, rising to about 6 million tonnes by 2017. Acetonitrile and hydrogen cyanide are significant byproducts that are recovered for sale. :

In the SOHIO process, propylene, ammonia, and air (oxidizer) are passed through a fluidized bed reactor containing the catalyst at 400–510 °C and 50–200 kPag. The reactants pass through the reactor only once, before being quenched in aqueous sulfuric acid. Excess propylene, carbon monoxide, carbon dioxide, and dinitrogen that do not dissolve are vented directly to the atmosphere, or are incinerated. The aqueous solution consists of acrylonitrile, acetonitrile, hydrocyanic acid, and ammonium sulfate (from excess ammonia). A recovery column removes bulk water, and acrylonitrile and acetonitrile are separated by distillation. One of the first useful catalysts was bismuth phosphomolybdate () supported on silica. Further improvements have since been made.

Alternative routes

Various green chemistry routes to acrylonitrile are being explored from renewable feedstocks, such as lignocellulosic biomass, glycerol (from biodiesel production), or glutamic acid (which can itself be produced from renewable feedstocks). The lignocellulosic route involves fermentation of the biomass to propionic acid and 3-hydroxypropionic acid, which are then converted to acrylonitrile by dehydration and ammoxidation. The glutamic acid route employs oxidative decarboxylation to 3-cyanopropanoic acid, followed by a decarbonylation-elimination to acrylonitrile. Of these, the glycerol route is broadly considered to be the most viable, although none of these green methods are commercially competitive.

Uses

Acrylonitrile is used principally as a monomer to prepare polyacrylonitrile, a homopolymer, or several important copolymers, such as styrene-acrylonitrile (SAN), acrylonitrile butadiene styrene (ABS), acrylonitrile styrene acrylate (ASA), and other synthetic rubbers such as acrylonitrile butadiene (NBR). Hydrodimerization of acrylonitrile affords adiponitrile, used in the synthesis of certain nylons: : Acrylonitrile is also a precursor in the manufacture of acrylamide and acrylic acid.

Synthesis of chemicals

Hydrogenation of acrylonitrile is one route to propionitrile. Hydrolysis with sulfuric acid gives acrylamide sulfate, . This salt can be converted to acrylamide with treatment with base or to methyl acrylate by treatment with methanol.

The reaction of acrylonitrile with protic nucleophiles is a common route to a variety of specialty chemicals. The process is called cyanoethylation: : Typical protic nucleophiles are alcohols, thiols, and especially amines. When hydrogen cyanide is used the product is succinonitrile.

Acrylonitrile and derivatives, such as 2-chloroacrylonitrile, are dienophiles in Diels–Alder reactions.

Health effects

Acrylonitrile is toxic with LD50 = 81 mg/kg (rats). It undergoes explosive polymerization. The burning material releases fumes of hydrogen cyanide and oxides of nitrogen. It is classified as a Class 1 carcinogen (carcinogenic) by the International Agency for Research on Cancer (IARC), and workers exposed to high levels of airborne acrylonitrile are diagnosed more frequently with lung cancer than the rest of the population. Acrylonitrile is one of seven toxicants in cigarette smoke that are most associated with respiratory tract carcinogenesis. The mechanism of action of acrylonitrile appears to involve oxidative stress and oxidative DNA damage. Acrylonitrile increases cancer in high dose tests in male and female rats and mice and induces apoptosis in human umbilical cord mesenchymal stem cells.

It evaporates quickly at room temperature (20 °C) to reach dangerous concentrations; skin irritation, respiratory irritation, and eye irritation are the immediate effects of this exposure. Pathways of exposure for humans include emissions, auto exhaust, and cigarette smoke that can expose the human subject directly if they inhale or smoke. Routes of exposure include inhalation, oral, and to a certain extent dermal uptake (tested with volunteer humans and in rat studies). Repeated exposure causes skin sensitization and may cause central nervous system and liver damage.

There are two main excretion processes of acrylonitrile. The primary method is excretion in urine when acrylonitrile is metabolized by being directly conjugated to glutathione. The other method is when acrylonitrile is enzymatically converted into 2-cyanoethylene oxide which will produce cyanide end products that ultimately form thiocyanate, which is excreted via urine. Exposure can thus be detected via blood draws and urine sampling.

In July 2024, the International Agency for Research on Cancer upgraded acrylonitrile's classification from 'possibly carcinogenic' to carcinogenic for humans. The Agency found sufficient evidence linking it to lung cancer.

Use in plastic bottles

In June 1974 Coca-Cola introduced the acrylonitrile/styrene 32oz Easy‐Goer plastic bottle, offering energy savings during manufacture, increased durability, and weight savings over glass. In March 1977 after a suit filed by the Natural Resources Defense Council the FDA rescinded approval of acrylonitrile bottles citing adverse effects on test animals. Monsanto, Coca-Cola's bottle manufacturer refuted the decision, stating "repeated tests have demonstrated that there is no detectable migration of acrylonitrile into the bottle's content." After several appeals in court by September 1977 the FDA finalized their ban.

Incidents

A large amount of acrylonitrile (approximately 6500 tons) leaked from an industrial polymer plant owned by Aksa Akrilik after the violent 17th August 1999 earthquake in Turkey. Over 5000 people were affected and the exposed animals had died. The leak was only noticed by the company 8 hours after the incident. Healthcare workers did not know about the health effects of acrylonitrile and tried to treat the victims with painkillers and IV fluids. One lawyer, Ayşe Akdemir, sued the company with 44 families as the plaintiffs. An increase in cancer cases in the area was confirmed by the Turkish Medical Association, as the cancer rate in the affected area has increased by 80%, from 1999 to April 2002. In 2003, the owner of Aksa Akrilik died from lung cancer related to acrylonitrile exposure. As of 2001, this is the largest known acrylonitrile leak.

Occurrence

Acrylonitrile is not naturally formed on Earth. It has been detected at the sub-ppm level at industrial sites. It persists in the air for up to a week. It decomposes by reacting with oxygen and hydroxyl radical to form formyl cyanide and formaldehyde. Acrylonitrile is harmful to aquatic life. Acrylonitrile has been detected in the atmosphere of Titan, a moon of Saturn. Computer simulations suggest that on Titan conditions exist such that the compound could form structures similar to cell membranes and vesicles on Earth, called azotosomes.

References

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