Azobis (isobutyronitrile)

Structural formula
General
Surname	Azobis (isobutyronitrile)
other names	2,2 '- [( E ) -1,2-diazenediyl] bis (2-methylpropanenitrile) ( IUPAC ) 2,2′-azobis (2-methylpropionitrile) Azoisobutyronitrile AIBN
Molecular formula	C 8 H 12 N 4
Brief description	colorless odorless solid
External identifiers / databases
CAS number 78-67-1 34241-39-9 [( E ) -isomer] 156473-35-7 [( Z ) -isomer] EC number 201-132-3 ECHA InfoCard 100.001.030 PubChem 6547 ChemSpider 6299 Wikidata Q423679
properties
Molar mass	164.21 g mol −1
Physical state	firmly
density	1.11 g cm −3
Melting point	102-104 ° C 50 ° C (decomposition)
solubility	very heavy in water (0.35 g l −1 at 25 ° C) soluble in organic solvents and vinyl monomers
safety instructions
GHS hazard labeling from  Regulation (EC) No. 1272/2008 (CLP) , expanded if necessary danger H and P phrases H: 242-302-332-412 P: 210-280-273
Toxicological data	100 mg kg −1 ( LD 50 ,  rat ,  oral )
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

AIBN is the short name of the chemical compound azobis (isobutyronitrile) , which belongs to the substance classes of azo compounds and nitriles . It is used in organic chemistry as an initiator for the radical chain reaction in the manufacture of plastics .

Appearance and properties

AIBN is made from acetone cyanohydrin and hydrazine ; the 1,2-bis (2-methylpropionitrilo-2-yl) hydrazine formed by condensation is then oxidized to AIBN (for example by chlorine ). Because of the toxicity of the decomposition product tetramethylsuccinic acid dinitrile , it is no longer used in industrial plants. AIBN is a colorless to gray, odorless, water-insoluble powder, which can be dissolved in organic solvents and vinyl monomers. Depending on the method of presentation, a fine crystalline, white solid is also formed.

AIBN decomposes into two isobutyronitrile radicals from a temperature of more than 25 ° C , releasing molecular nitrogen . The formation of nitrogen provides the necessary driving force for the decay reaction. This disintegration can already occur through impact or friction.

Due to its degradability, commercially available AIBN often contains impurities and must be purified before use. The cleaning is mostly carried out by recrystallization , whereby, because of the increase in decomposition at higher temperatures, care must be taken not to overheat when dissolving. If the procedure is rapid, recrystallization can be carried out from methanol (solubility 6.1 g per 100 g solvent) at a maximum of 45 ~ 50 ° C. If the AIBN is only exposed to this temperature for a few minutes, only small amounts of decomposition products are formed, which remain dissolved in the methanol during subsequent crystallization.

When using AIBN as an initiator for free-radical polymerizations or for other free-radical reactions, the temperature-dependent half-life is of great importance. The temperature is usually chosen so that the AIBN does not disintegrate too quickly. If the decay was too rapid, the radical concentration in the reaction mixture would increase, and with it the probability that radicals would recombine with themselves instead of initiating the (chain) reaction that is actually desired. The half-life in the thermal decomposition of AIBN is about 10 h at 65 ° C, but can vary somewhat with the choice of solvent for the reaction.

Individual evidence

1. ↑ ^{a b c d e f g h i} Entry on 2,2′-dimethyl-2,2′-azodipropiononitrile in the GESTIS substance database of the IFA , accessed on January 10, 2017(JavaScript required) .
2. ↑ ^{a b c} Entry on Azobis (isobutyronitrile). In: Römpp Online . Georg Thieme Verlag, accessed on April 13, 2014.
3. ↑ Entry on 2,2′-dimethyl-2,2′-azodipropiononitrile in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on February 1, 2016. Manufacturers or distributors can expand the harmonized classification and labeling .
4. ↑ ^{a b} Azo Initiators from Otsuka Chemicals , accessed January 29, 2018.