Acrolein (systematic name: propenal) is the simplest unsaturated aldehyde. It is a colorless liquid with a foul and acrid aroma. The smell of burnt fat (as when

cooking oil Cooking oil (also known as edible oil) is a plant or animal liquid fat used in frying, baking, and other types of cooking. Oil allows higher cooking temperatures than water, making cooking faster and more flavorful, while likewise distributing h ...

is heated to its smoke point) is caused by

glycerol Glycerol () is a simple triol compound. It is a colorless, odorless, sweet-tasting, viscous liquid. The glycerol backbone is found in lipids known as glycerides. It is also widely used as a sweetener in the food industry and as a humectant in pha ...

in the burning fat breaking down into acrolein. It is produced industrially from

propene Propylene, also known as propene, is an unsaturated organic compound with the chemical formula . It has one double bond, and is the second simplest member of the alkene class of hydrocarbons. It is a colorless gas with a faint petroleum-like od ...

and mainly used as a

biocide A biocide is defined in the European legislation as a chemical substance or microorganism intended to destroy, deter, render harmless, or exert a controlling effect on any harmful organism. The US Environmental Protection Agency (EPA) uses a sli ...

and a building block to other chemical compounds, such as the

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although over 500 amino acids exist in nature, by far the most important are the 22 α-amino acids incorporated into proteins. Only these 22 a ...

methionine Methionine (symbol Met or M) () is an essential amino acid in humans. As the precursor of other non-essential amino acids such as cysteine and taurine, versatile compounds such as SAM-e, and the important antioxidant glutathione, methionine play ...

History

Acrolein was first named and characterized as an aldehyde by the Swedish chemist

Jöns Jacob Berzelius Baron Jöns Jacob Berzelius (; 20 August 1779 – 7 August 1848) was a Swedish chemist. Berzelius is considered, along with Robert Boyle, John Dalton, and Antoine Lavoisier, to be one of the founders of modern chemistry. Berzelius became a memb ...

in 1839. He had been working with it as a thermal degradation product of

, a material used in the manufacture of soap. The name is a contraction of 'acrid' (referring to its pungent smell) and 'oleum' (referring to its oil-like consistency). In the 20th century, acrolein became an important intermediate for the industrial production of

acrylic acid Acrylic acid (IUPAC: prop-2-enoic acid) is an organic compound with the formula CH2=CHCOOH. It is the simplest unsaturated carboxylic acid, consisting of a vinyl group connected directly to a carboxylic acid terminus. This colorless liquid has ...

and acrylic plastics.

Production

Acrolein is prepared industrially by oxidation of

. The process uses air as the source of oxygen and requires

metal oxide An oxide () is a chemical compound containing at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion (anion bearing a net charge of −2) of oxygen, an O2− ion with oxygen in the oxidation state o ...

s as heterogeneous catalysts: : About 500,000 tons of acrolein are produced in this way annually in North America, Europe, and Japan. Additionally, all

is produced via the transient formation of acrolein.

Propane Propane () is a three-carbon chain alkane with the molecular formula . It is a gas at standard temperature and pressure, but becomes liquid when compressed for transportation and storage. A by-product of natural gas processing and petroleum ref ...

represents a promising but challenging feedstock for the synthesis of acrolein (and acrylic acid).The main challenge is in fact the overoxidation to this acid. When

(also called glycerin) is heated to 280 °C, it decomposes into acrolein : This route is attractive when glycerol is co-generated in the production of biodiesel from vegetable oils or animal fats. The dehydration of glycerol has been demonstrated but has not proven competitive with the route from

petrochemical Petrochemicals (sometimes abbreviated as petchems) are the chemical products obtained from petroleum by refining. Some chemical compounds made from petroleum are also obtained from other fossil fuels, such as coal or natural gas, or renewable s ...

Niche or laboratory methods

The original industrial route to acrolein, developed by Degussa, involves aldol condensation of

formaldehyde Formaldehyde ( , ) (systematic name methanal) is an organic compound with the chemical formula and structure , more precisely . The compound is a pungent, colourless gas that polymerises spontaneously into paraformaldehyde. It is stored as ...

and

acetaldehyde Acetaldehyde (IUPAC systematic name ethanal) is an organic compound, organic chemical compound with the chemical formula, formula , sometimes abbreviated as . It is a colorless liquid or gas, boiling near room temperature. It is one of the most ...

: : Acrolein may also be produced on lab scale by the action of potassium bisulfate on glycerol (glycerine). :

Reactions

Acrolein is a relatively

electrophilic In chemistry, an electrophile is a chemical species that forms bonds with nucleophiles by accepting an electron pair. Because electrophiles accept electrons, they are Lewis acids. Most electrophiles are positively charged, have an atom that carr ...

compound and a reactive one, hence its high toxicity. It is a good Michael acceptor, hence its useful reaction with thiols. It forms

acetal In organic chemistry, an acetal is a functional group with the connectivity . Here, the R groups can be organic fragments (a carbon atom, with arbitrary other atoms attached to that) or hydrogen, while the R' groups must be organic fragments n ...

s readily, a prominent one being the spirocycle derived from

pentaerythritol Pentaerythritol is an organic compound with the formula C(CH2OH)4. The molecular structure can be described as a neopentane with one hydrogen atom in each methyl group replaced by a hydroxyl (–OH) group. It is therefore a polyol, specifically a ...

, diallylidene pentaerythritol. Acrolein participates in many Diels-Alder reactions, even with itself. Via Diels-Alder reactions, it is a precursor to some commercial fragrances, including myrac aldehyde ("lyral") and norbornene-2-carboxaldehyde. The monomer 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexane carboxylate is also produced from acrolein via the intermediacy of tetrahydrobenzaldehyde.

Uses

Military uses

Acrolein was used in warfare due to its irritant and blistering properties. The French used the chemical in their hand grenades and artillery shells during

World War I World War I or the First World War (28 July 1914 – 11 November 1918), also known as the Great War, was a World war, global conflict between two coalitions: the Allies of World War I, Allies (or Entente) and the Central Powers. Fighting to ...

under the name "Papite".

Biocide

Acrolein is mainly used as a contact herbicide to control submersed and floating weeds, as well as algae, in

irrigation canal Canals or artificial waterways are waterways or engineered channels built for drainage management (e.g. flood control and irrigation) or for conveyancing water transport vehicles (e.g. water taxi). They carry free, calm surface f ...

s. It is used at a level of 10 ppm in irrigation and recirculating waters. In the

oil and gas industry The petroleum industry, also known as the oil industry, includes the global processes of exploration, extraction, refining, transportation (often by oil tankers and pipelines), and marketing of petroleum products. The largest volume products ...

, it is used as a

in drilling waters, as well as a scavenger for

hydrogen sulfide Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is toxic, corrosive, and flammable. Trace amounts in ambient atmosphere have a characteristic foul odor of rotten eggs. Swedish chemist ...

and mercaptans.

Chemical precursor

A number of useful compounds are made from acrolein, exploiting its bifunctionality. The amino acid

is produced by addition of

methanethiol Methanethiol (also known as methyl mercaptan) is an organosulfur compound with the chemical formula . It is a colorless gas with a distinctive putrid smell. In small amounts, it is pervasive in nature and found in certain foods, such as some n ...

followed by the Strecker synthesis. Acrolein condenses with acetaldehyde and amines to give methylpyridines. It is also an intermediate in the Skraup synthesis of

quinoline Quinoline is a heterocyclic aromatic organic compound with the chemical formula C9H7N. It is a colorless hygroscopic liquid with a strong odor. Aged samples, especially if exposed to light, become yellow and later brown. Quinoline is only sl ...

s. Acrolein will polymerize in the presence of oxygen and in water at concentrations above 22%. The color and texture of the polymer depends on the conditions. The polymer is a clear, yellow solid. In water, it will form a hard, porous plastic. Acrolein has been used as a fixative in preparation of biological specimens for

electron microscopy An electron microscope is a microscope that uses a beam of electrons as a source of illumination. It uses electron optics that are analogous to the glass lenses of an optical light microscope to control the electron beam, for instance focusing i ...

Health risks

Acrolein is toxic and is a strong irritant for the skin, eyes, and nasal passages. The main metabolic pathway for acrolein is the

alkylation Alkylation is a chemical reaction that entails transfer of an alkyl group. The alkyl group may be transferred as an alkyl carbocation, a free radical, a carbanion, or a carbene (or their equivalents). Alkylating agents are reagents for effecting al ...

glutathione Glutathione (GSH, ) is an organic compound with the chemical formula . It is an antioxidant in plants, animals, fungi, and some bacteria and archaea. Glutathione is capable of preventing damage to important cellular components caused by sources ...

. The

WHO The World Health Organization (WHO) is a specialized agency of the United Nations which coordinates responses to international public health issues and emergencies. It is headquartered in Geneva, Switzerland, and has 6 regional offices and 15 ...

suggests a "tolerable oral acrolein intake" of 7.5 μg per day per kg of body weight. Although acrolein occurs in

French fries French fries, or simply fries, also known as chips, and finger chips (Indian English), are '' batonnet'' or '' julienne''-cut deep-fried potatoes of disputed origin. They are prepared by cutting potatoes into even strips, drying them, and f ...

(and other fried foods), the levels are only a few μg per kg. In response to occupational exposures to acrolein, the US

Occupational Safety and Health Administration The Occupational Safety and Health Administration (OSHA; ) is a regulatory agency of the United States Department of Labor that originally had federal visitorial powers to inspect and examine workplaces. The United States Congress established ...

has set a

permissible exposure limit The permissible exposure limit (PEL or OSHA PEL) is a legal limit in the United States for exposure of an employee to a chemical substance or physical agents such as high level noise. Permissible exposure limits were established by the Occupational ...

at 0.1 ppm (0.25 mg/m³) at an eight-hour time-weighted average.CDC - NIOSH Pocket Guide to Chemical Hazards
/ref> Acrolein acts in an immunosuppressive manner and may promote regulatory cells, thereby preventing the generation of allergies on the one hand, but also increasing the risk of cancer. Acrolein was identified as one of the chemicals involved in the 2019 Kim Kim River toxic pollution incident.

Cigarette smoke

Connections exist between acrolein gas in the smoke from tobacco cigarettes and the risk of

lung cancer Lung cancer, also known as lung carcinoma, is a malignant tumor that begins in the lung. Lung cancer is caused by genetic damage to the DNA of cells in the airways, often caused by cigarette smoking or inhaling damaging chemicals. Damaged ...

. Acrolein is one of seven

toxicant A toxicant is any toxic substance, whether artificial or naturally occurring. By contrast, a toxin is a poison produced naturally by an organism (e.g. plant, animal, insect, bacterium). The different types of toxicants can be found in the air, so ...

s in

cigarette A cigarette is a narrow cylinder containing a combustible material, typically tobacco, that is rolled into Rolling paper, thin paper for smoking. The cigarette is ignited at one end, causing it to smolder; the resulting smoke is orally inhale ...

smoke that are most associated with

respiratory tract The respiratory tract is the subdivision of the respiratory system involved with the process of conducting air to the alveoli for the purposes of gas exchange in mammals. The respiratory tract is lined with respiratory epithelium as respirato ...

carcinogenesis Carcinogenesis, also called oncogenesis or tumorigenesis, is the formation of a cancer, whereby normal cell (biology), cells are malignant transformation, transformed into cancer cells. The process is characterized by changes at the cellular, G ...

. The mechanism of action of acrolein appears to involve induction of increased

reactive oxygen species In chemistry and biology, reactive oxygen species (ROS) are highly Reactivity (chemistry), reactive chemicals formed from diatomic oxygen (), water, and hydrogen peroxide. Some prominent ROS are hydroperoxide (H2O2), superoxide (O2−), hydroxyl ...

and DNA damage related to

oxidative stress Oxidative stress reflects an imbalance between the systemic manifestation of reactive oxygen species and a biological system's ability to readily detoxify the reactive intermediates or to repair the resulting damage. Disturbances in the normal ...

. In terms of the "noncarcinogenic health quotient" for components in cigarette smoke, acrolein dominates, contributing 40 times more than the next component,

hydrogen cyanide Hydrogen cyanide (formerly known as prussic acid) is a chemical compound with the chemical formula, formula HCN and structural formula . It is a highly toxic and flammable liquid that boiling, boils slightly above room temperature, at . HCN is ...

. The acrolein content in cigarette smoke depends on the type of cigarette and added

glycerin Glycerol () is a simple triol compound. It is a colorless, odorless, sweet-tasting, viscous liquid. The glycerol backbone is found in lipids known as glycerides. It is also widely used as a sweetener in the food industry and as a humectant in pha ...

, making up to 220 μg acrolein per cigarette. Importantly, while the concentration of the constituents in mainstream smoke can be reduced by filters, this has no significant effect on the composition of the side-stream smoke where acrolein usually resides, and which is inhaled by

passive smoking Passive smoking is the inhalation of tobacco smoke, called passive smoke, secondhand smoke (SHS) or environmental tobacco smoke (ETS), by individuals other than the active Tobacco smoking, smoker. It occurs when tobacco smoke diffuses into the ...

. E-cigarettes, used normally, only generate "negligible" levels of acrolein (less than 10 μg "per puff").

Chemotherapy metabolite

Cyclophosphamide and ifosfamide treatment results in the production of acrolein. Acrolein produced during cyclophosphamide treatment collects in the urinary bladder and if untreated can cause hemorrhagic cystitis.

Endogenous production

Acrolein is a component of reuterin. Reuterin can be produced by gut microbes when glycerol is present. Microbe-produced reuterin is a potential resource of acrolein.

Analytical methods

The "acrolein test" is for the presence of

fat In nutrition science, nutrition, biology, and chemistry, fat usually means any ester of fatty acids, or a mixture of such chemical compound, compounds, most commonly those that occur in living beings or in food. The term often refers specif ...

s. A sample is heated with potassium bisulfate, and acrolein is released if the test is positive. When a fat is heated strongly in the presence of a dehydrating agent such as potassium bisulfate (), the glycerol portion of the molecule is dehydrated to form the unsaturated

aldehyde In organic chemistry, an aldehyde () (lat. ''al''cohol ''dehyd''rogenatum, dehydrogenated alcohol) is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred ...

, acrolein (CH₂=CH–CHO), which has the odor peculiar to burnt cooking grease. More modern methods exist. In the US, EPA methods 603 and 624.1 are designed to measure acrolein in industrial and municipal

wastewater Wastewater (or waste water) is water generated after the use of freshwater, raw water, drinking water or saline water in a variety of deliberate applications or processes. Another definition of wastewater is "Used water from any combination of do ...

streams.Method 624.1 — Purgables by GC-MS>
/ref>

References

{{Authority control Alkenals IARC Group 2A carcinogens Lachrymatory agents Pulmonary agents Foul-smelling chemicals hi:एक्रोलिन