Acrolein

• Propenal
• Acrylaldehyde
• Acrolein
• AQUALIN
• 2- propenal
• Prop-2 -enal

Colorless to yellow, mobile liquid with a pungent odor

Liquid

0.84 g · cm -3

-88 ° C

52 ° C.

295 hPa ( 20 ° C)

Well in water (270 g · l-1 at 20 ° C)

1.4017 (20 ° C)

Risk

Not classified as carcinogenic effect

Template: Infobox chemical / molecular formula search available

Acrolein [ akrolei ː n] ( also propenal, acrylaldehyde, 2- propenal, or prop-2- enal, or AQUALIN ) is a chemical, and assigned as the aldehyde of organic chemistry. It is a clear liquid, having the molecular formula C3H4O.

Production and representation

Acrolein (3) can be obtained ( aldol condensation ) by partial oxidation of propylene or by reaction of acetaldehyde (2) with formaldehyde (1):

In addition, acrolein is undesirable product of many oxidation reactions of various organic compounds. Glycerol reacted at temperatures from 200 ° C with dehydration to acrolein. On combustion of various organic substances (printer ink, vegetable oils, biodiesel, wax, tobacco, etc.. ) Arise Acroleindämpfe. Thus, the typical Acroleingeruch occurs immediately after the extinction of a candle.

Acrolein is also produced when overheating of vegetable and animal fats, for example when frying. This process is greatly facilitated by the presence of water and acids. In this case, the fat (triglyceride ) is first in its ingredients glycerol and fatty acids broken down ( hydrolysis ). The glycerol is then converted by dehydration to acrolein ( dehydrated ).

The industrial production of chemical industry is carried out as far as possible via the gas phase oxidation of propane or propene in the presence of suitable heterogeneous catalysts. This partial oxidation of the fixed contact ( synonymous with " heterogeneous catalyst " ) is carried out with air as the oxidizing agent at temperatures of about 330-360 ° C, wherein tube reactors are used in which the highly exothermic reaction is cooled using salt baths. There is only a relatively dilute mixture of propene with air ( mostly still in the presence of water vapor ) is used to prevent the formation of explosive mixtures. The achievable with modern catalysts yields are 80-85 % with respect to propene, as byproducts 4-8% acrylic acid and 4-6 % carbon monoxide and carbon dioxide in addition to unreacted propene. The problem is the quenching and isolation of acrolein before further use as raw material for the synthesis of methionine, glutaraldehyde or various fragrances. When isolating it comes to the polymerization of acrolein and other active secondary components ( in particular acrylic acid esters), forcing the shutdown of the plant.

Increasingly, an attempt is made to cease producing acrolein from propane or propene. Propane and propene are products of the petrochemical industry, thus based on natural gas or oil. These fossil fuels are becoming increasingly scarce in the future. Therefore, many companies are trying to win acrolein by dehydration of glycerol. This fall as a cheap by-product in the production of biodiesel from natural fats and oils.

Properties

The small size of acrolein, the aldehyde group and the double bond ensure a high reactivity of the molecule. In its pure form acrolein is hardly stable.

Due to the existing C = C double bond of acrolein can readily polymerize. Acrolein is also implemented by the addition of water to glycerol.

The aldehyde can bind to proteins. Therefore, acrolein, like formalin used in the electron microscopy for fixation. The advantage lies in the very short in comparison with other aldehydes reaction time.

Acrolein reacts with elemental bromine to give the corresponding 2,3- dibromo compound, which can be selectively dehydrohalogenated for 2- bromoacrolein with dimethyl sulfoxide.

Hazards

Acrolein is very toxic and in addition also a strong environmental toxin. There is a strong water and marine pollution and very harmful to fish.

After the MAK Commission of the DFG acrolein is carcinogenic (category 3B). This category includes substances that give cause for concern because of its demonstrated / possible carcinogenic effect.

Acrolein is very flammable and can form explosive mixtures in air.

It forms peroxides by autoxidation, which must be removed before use of acrolein.

Use

Acrolein as an intermediate in the industrial production of synthetic amino acid DL -methionine and its hydroxy analog DL-2- hydroxy-4- methylmercaptobutyric that have considerable economic importance as a mixed feed ingredient in animal feed.