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In chemistry, initiation is a chemical reaction that triggers one or more secondary reactions. Initiation creates a reactive centre on a molecule which produces a chain reaction . [ 1 ] The reactive centre generated by initiation is usually a radical , but can also be cations or anions . [ 2 ]
In the simplest example oxygen can be used as it exists naturally in its triplet state (i.e. it is a diradical). This is referred to as air inhibition and is a diffusion-controlled reaction with rates typically in the order of 10 7 –10 9 mol −1 s −1 , [ 3 ] the resulting peroxy radicals (ROO•) are less reactive towards polymerisation.
For example, di-tert-butyl peroxide (t-Bu OOt-Bu) gives two t-butoxy radicals (t-BuO•) and the radicals become methyl radicals (CH 3 •) with the loss of acetone. Benzoyl peroxide (( Ph C)OO) 2 ) generates benzoyloxyl radicals (PhCOO•), each of which loses carbon dioxide to be converted into a phenyl radical (Ph•).
Initiation steps are classified according to the way that energy is provided: thermal initiation, high energy initiation, and chemical initiation, etc. Thermal initiation uses molecular thermal motion to dissociate a molecule and form active centers. High energy initiation refers to the generation of chain carriers by radiation.
The chemical decomposition of triacetone triperoxide (TATP) may be an example of an entropic explosion. [1] It is not a thermochemically highly favored event because little energy is generated in chemical bond formation in reaction products, but rather involves an entropy burst, which is the result of formation of one ozone and three acetone ...
Chemical reactions involving thermal runaway are also called thermal explosions in chemical engineering, or runaway reactions in organic chemistry.It is a process by which an exothermic reaction goes out of control: the reaction rate increases due to an increase in temperature, causing a further increase in temperature and hence a further rapid increase in the reaction rate.
Initiation (formation of active particles or chain carriers, often free radicals, in either a thermal or a photochemical step) Propagation (may comprise several elementary steps in a cycle, where the active particle through reaction forms another active particle which continues the reaction chain by entering the next elementary step).
In organosulfur chemistry, the thiol-ene reaction (also alkene hydrothiolation) is an organic reaction between a thiol (R−SH) and an alkene (R 2 C=CR 2) to form a thioether (R−S−R'). This reaction was first reported in 1905, [ 1 ] but it gained prominence in the late 1990s and early 2000s for its feasibility and wide range of applications.