Acrolein

Acrolein (systematic name: propenal) is the simplest unsaturated aldehyde. It is produced widely but is most often immediately reacted with other products due to its instability and toxicity. It has a piercing, disagreeable, acrid smell, smell of burning fat, which is caused by glycerine in fat decomposing.

Synthesis
Acrolein is prepared industrially by oxidation of propene. Efforts are under way to use propane as feedstock for the synthesis; however, this is more difficult. Several million tons of acrolein are produced each year.

When glycerol is heated to 280 °C, it decomposes into acrolein. Acrolein may also be produced on lab scale by the reaction of potassium bisulfate on glycerol (glycerine).

Uses
Acrolein is used in the preparation of polyester resin, polyurethane, propylene glycol, acrylic acid, acrylonitrile, and glycerol. Acrolein tends to polymerize when left at room temperature, leaving a gummy yellowish residue with a putrid odor. 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 is sometimes used as a fixative in preparation of biological specimens for electron microscopy. It is also used as a contact herbicide to control submersed and floating weeds, as well as algae, in irrigation canals.

Health risks
Acrolein is a severe pulmonary irritant and lachrymatory agent. It was used as a chemical weapon during World War I. It is, however, not outlawed by the Chemical Weapons Convention. Dermal exposure of acrolein to the eyes (0.3ppm in air) can cause severe irritation. Acrolein is not a suspected human carcinogen; no studies have been conducted on the carcinogenic effects of acrolein on humans, but studies on rats have shown an increase in cancerous tumors from ingestion. In October 2006, researchers found connections between acrolein in the smoke from tobacco cigarettes and the risk of lung cancer. Furthermore, acrolein is a possible metabolite of cyclophosphamide, a cytotoxic chemotherapy agent, and results in hemorrhagic cystitis. N-acetylcysteine or mesna are used to counteract the acrolein.

Due to its ability to damage myelin nerve sheaths, acrolein may be a factor in the development of multiple sclerosis. The antihypertensive drug hydralazine, a known scavenger of acrolein, was found to reduce myelin damage and significantly improve behavioral outcomes in a mouse model of multiple sclerosis (experimental autoimmune encephalomyelitis).

EPA method 603 is designed to measure acrolein in industrial and municipal wastewater streams.

Acrolein test
Acrolein test is a test 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, the glycerol portion of the molecule is dehydrated to form the unsaturated aldehyde, acrolein (CH2=CH–CHO), which has the peculiar odor of burnt grease.