Acrolein

Not to be confused with Propanol, Acyloin, or Propanal.

Acrolein

Names
IUPAC name Prop-2-enal
Other names Acraldehyde Acrylic aldehyde Allyl Aldehyde Ethylene Aldehyde Acrylaldehyde
Identifiers
CAS Number	107-02-8 Y
ChEBI	CHEBI:15368 Y
ChEMBL	ChEMBL721 Y
ChemSpider	7559 Y
IUPHAR/BPS	2418
Jmol 3D model	Interactive image Interactive image
KEGG	C01471 Y
PubChem	7847
UNII	7864XYD3JJ Y
InChI InChI=1S/C3H4O/c1-2-3-4/h2-3H,1H2 Y Key: HGINCPLSRVDWNT-UHFFFAOYSA-N Y InChI=1/C3H4O/c1-2-3-4/h2-3H,1H2 Key: HGINCPLSRVDWNT-UHFFFAOYAQ
SMILES O=CC=C C=CC=O
Properties
Chemical formula	C3H4O
Molar mass	56.06 g·mol−1
Appearance	Colorless to yellow liquid. Colorless gas in smoke.
Odor	irritating
Density	0.839 g/mL
Melting point	−88 °C (−126 °F; 185 K)
Boiling point	53 °C (127 °F; 326 K)
Solubility in water	Appreciable (> 10%)
Vapor pressure	210 mmHg
Vapor pressure	{{{value}}}
Related compounds
Related alkenals	Crotonaldehyde cis-3-Hexenal (E,E)-2,4-Decadienal
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Y verify (what is YN ?)
Infobox references

Acrolein (systematic name: propenal) is the simplest unsaturated aldehyde. It is a colourless liquid with a piercing, disagreeable, acrid smell. The smell of burnt fat (as when cooking oil is heated to its smoke point) is caused by glycerol in the burning fat breaking down into acrolein. It is produced industrially from propylene and mainly used as a biocide and a building block to other chemical compounds, such as the amino acid methionine.

Production

Acrolein is prepared industrially by oxidation of propene. The process uses air as the source of oxygen and requires metal oxides as heterogeneous catalysts:

CH₂CHCH₃ + O₂ → CH₂CHCHO + H₂O

About 500,000 tons of acrolein are produced in this way annually in North America, Europe, and Japan. Additionally, all acrylic acid is produced via the transient formation of acrolein. The main challenge is in fact the competing over oxidation to this acid. Propane represents a promising but challenging feedstock for the synthesis of acrolein (and acrylic acid).

When glycerol (also called glycerin) is heated to 280 °C, it decomposes into acrolein:

(CH₂OH)₂CHOH → CH₂=CHCHO + 2 H₂O

This route is attractive when glycerol is cogenerated in the production of biodiesel from fatty acids. The dehydration of glycerol has been demonstrated but has not proven competitive with the route from petrochemicals.

Niche or laboratory methods

The original industrial route to acrolein, developed by Degussa, involves condensation of formaldehyde and acetaldehyde:

HCHO + CH₃CHO → CH₂=CHCHO + H₂O

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

Reactions

Acrolein is a relatively electrophilic compound and a reactive one, hence its high toxicity. It is a good Michael acceptor, hence its useful reaction with thiols. It forms acetals readily, a prominent one being the spirocycle derived from pentaerythritol, 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 lyral, norbornene-2-carboxaldehyde, and myrac aldehyde.

Uses

Biocide

Acrolein is mainly used as a contact herbicide to control submersed and floating weeds, as well as algae, in irrigation canals. It is used at a level of 10 ppm in irrigation and recirculating waters. In the oil and gas industry, it is used as a biocide in drilling waters, as well as a scavenger for hydrogen sulfide and mercaptans.

Chemical precursor

A number of useful compounds are made from acrolein, exploiting its bifunctionality. The amino acid methionine is produced by addition of methanethiol followed by the Strecker synthesis. Acrolein condenses with acetaldehyde and amines to give methylpyridines. It is also thought to be an intermediate in the Skraup synthesis of quinolines, but is rarely used as such due to its instability.

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. Over time, it will polymerize with itself to form a clear, yellow solid. In water, it will form a hard, porous plastic.

Acrolein is sometimes used as a fixative in preparation of biological specimens for electron microscopy.

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 of glutathione. The WHO suggests a "tolerable oral acrolein intake" of 7.5 μg/day per kilogram of body weight. Although acrolein occurs in French fries, the levels are only a few micrograms per kilogram. In response to occupational exposures to acrolein, the US Occupational Safety and Health Administration has set a permissible exposure limit at 0.1 ppm (0.25 mg/m³) at an eight-hour time-weighted average.

Cigarette smoke

Connections exist between acrolein gas in the smoke from tobacco cigarettes and the risk of lung cancer. In terms of the "noncarcinogenic health quotient" for components in cigarette smoke, acrolein dominates, contributing 40 times more than the next component, hydrogen cyanide. E-cigarettes, used normally, generate "negligible" levels of acrolein.

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.

Analytical methods

The "acrolein test" is for the presence of glycerin or fats. 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 (KHSO
₄), the glycerol portion of the molecule is dehydrated to form the unsaturated aldehyde, acrolein (CH₂=CH–CHO), which has the odor peculiar to burnt cooking grease. More modern methods exist.

In the US, EPA method 603 is designed to measure acrolein in industrial and municipal wastewater streams.