Radical initiator

Radical initiator

In chemistry, radical initiators are substances that can produce radical species under mild conditions and promote radical polymerization reactions. These substances generally possess weak bonds—bonds that have small bond dissociation energies. Radical initiators are utilized in industrial processes such as polymer synthesis. Typical examples are halogen molecules, azo compounds, and organic peroxides.

*Like all diatomic molecules, halogens can generate two free radicals resulting from the homolysis of the bond, but halogens undergo the homolytic fission relatively easily. Chlorine, for example, gives two chlorine radicals (Cl•) by irradiation with ultraviolet light. This process is used for chlorination of alkanes.

*Azo compounds (R-N=N-R') can be the precursor of two carbon-centered radicals (R• and R'•) and nitrogen gas upon heating and/or by irradiation. For example, AIBN and ABCN yield isobutyronitrile and cyclohexanecarbonitrile radicals, respectively.

*Organic peroxides each have a peroxide bond (-O-O-), which is readily cleaved to give two oxygen-centered radicals. The oxyl radicals are rather unstable and believed to be transformed into relatively stable carbon-centered radicals. For example, di-"t"(tertiary)-butylperoxide ("t"BuOO"t"Bu) gives two "t"-butanoyl radicals ("t"BuO•) and the radicals become methyl radicals (CH3•) with the loss of acetone. Benzoyl peroxide ((PhCOO)2) generates benzoyloxyl radicals (PhCOO•), each of which loses carbon dioxide to be converted into a phenyl radical (Ph•). Methyl ethyl ketone peroxide is also common, and acetone peroxide is on rare occasions used as a radical initiator, too.

Radical initiators, especially azo compounds and organic peroxides, are inherently unstable. They must be kept in a cool place or refrigerated. Care should be taken with the handling of the compounds or an explosion may occur.

See also: Initiator


Wikimedia Foundation. 2010.

Игры ⚽ Поможем написать курсовую

Look at other dictionaries:

  • Radical-nucleophilic aromatic substitution — or SRN1 in organic chemistry is a type of substitution reaction in which a certain substituent on an aromatic compound is replaced by a nucleophile through an intermediary free radical species:The substituent X is a halide and nucleophiles can be …   Wikipedia

  • Radical polymerization — is a type of polymerization in which the reactive center of a polymer chain consists of a radical.The polymerization reaction is initiated by three classes of free radical initiators: * certain compounds that can be broken down in two radicals at …   Wikipedia

  • Initiator — An initiator can refer to:* Pyrotechnic initiator, a device containing a pyrotechnic composition used primarily to ignite other, more difficult to ignite materials * Radical initiator, chemical substances that can produce radical species under… …   Wikipedia

  • Radical substitution — In organic chemistry, a radical substitution reaction is a substitution reaction involving free radicals as a reactive intermediate. The reaction always involves at least two steps, and possibly a third. In the first step called initiation a free …   Wikipedia

  • Living free radical polymerization — is a type of living polymerization where the active polymer chain end is a free radical. Several methods exist. IUPAC recommends[1] to use the term reversible deactivation radical polymerization instead of living free radical polymerization .… …   Wikipedia

  • Cobalt mediated radical polymerization — Cobalt based catalysts, when used in radical polymerization, have several main advantages especially in slowing down the reaction rate, allowing for the synthesis of polymers with peculiar properties. As starting the reaction does need a real… …   Wikipedia

  • Free radical addition — is an addition reaction in organic chemistry involving free radicals [L.G. Wade s Organic Chemistry 5th Ed. (p 319) Mechanism supplements original.] . The addition may occur between a radical and a non radical, or between two radicals.The basic… …   Wikipedia

  • Free radical reaction — A free radical reaction is any chemical reaction involving free radicals. This reaction type is abundant in organic reactions. Two pioneering studies into free radical reactions have been the discovery of the triphenylmethyl radical by Moses… …   Wikipedia

  • Oxygen radical absorbance capacity — (ORAC) is a method of measuring antioxidant capacities in biological samples in vitro.[1][2] A wide variety of foods has been tested using this method, with certain spices, berries and legumes rated highly.[3] There exists no physiological proof… …   Wikipedia

  • Living Radical Polymerization — Die Controlled Free Radical Polymerization (CFRP) oder Living Free Radical Polymerization (LFRP) (kontrollierte freie radikalische Polymerisation bzw. lebende freie radikalische Polymerisation) ist ein Polymerisations Verfahren, bei dem durch… …   Deutsch Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”