Editing Alkene (section)

==== Oxidation ====
Alkenes react with [[Peroxy acid|percarboxylic acids]] and even hydrogen peroxide to yield [[epoxide]]s:
:{{chem2|RCH\dCH2  +  RCO3H  ->  RCHOCH2 + RCO2H}}

For ethylene, the [[epoxidation]] is conducted on a very large scale industrially using oxygen in the presence of silver-based catalysts:
:{{chem2|C2H4 + 1/2 O2  ->  C2H4O}}

Alkenes react with ozone, leading to the scission of the double bond.  The process is called [[ozonolysis]].  Often the reaction procedure includes a mild reductant, such as dimethylsulfide ({{chem2|SMe2}}):
:{{chem2|RCH\dCHR'  +  O3  +  SMe2  -> RCHO  +  R'CHO  +  O\dSMe2}}
:{{chem2|R2C\dCHR'  +  O3  ->  R2CHO  +  R'CHO  +  O\dSMe2}}

When treated with a hot concentrated, acidified solution of {{chem2|[[potassium permanganate|KMnO4]]}}, alkenes are cleaved to form [[ketone]]s and/or [[carboxylic acid]]s.  The stoichiometry of the reaction is sensitive to conditions. This reaction and the ozonolysis can be used to determine the position of a double bond in an unknown alkene.

The oxidation can be stopped at the [[vicinal (chemistry)|vicinal]] [[diol]] rather than full cleavage of the alkene by using [[osmium tetroxide]] or other oxidants:
:<chem>R'CH=CR2 + 1/2 O2  + H2O  -> R'CH(OH)-C(OH)R2</chem>
This reaction is called [[dihydroxylation]].

In the presence of an appropriate [[photosensitiser]], such as [[methylene blue]] and light, alkenes can undergo reaction with reactive oxygen species generated by the photosensitiser, such as [[hydroxyl radical]]s, [[singlet oxygen]] or [[superoxide]] ion. Reactions of the excited sensitizer can involve electron or hydrogen transfer, usually with a reducing substrate (Type I reaction) or interaction with oxygen (Type II reaction).<ref>{{cite journal |last1=Baptista |first1=Maurício S. |last2=Cadet |first2=Jean |last3=Mascio |first3=Paolo Di |last4=Ghogare |first4=Ashwini A. |last5=Greer |first5=Alexander |last6=Hamblin |first6=Michael R. |last7=Lorente |first7=Carolina |last8=Nunez |first8=Silvia Cristina |last9=Ribeiro |first9=Martha Simões |last10=Thomas |first10=Andrés H. |last11=Vignoni |first11=Mariana |last12=Yoshimura |first12=Tania Mateus |title=Type I and Type II Photosensitized Oxidation Reactions: Guidelines and Mechanistic Pathways |journal=Photochemistry and Photobiology |date=2017 |volume=93 |issue=4 |pages=912–9 |doi=10.1111/php.12716|pmid=28084040 |pmc=5500392 |doi-access=free }}</ref> These various alternative processes and reactions can be controlled by choice of specific reaction conditions, leading to a wide range of products. A common example is the [4+2]-[[cycloaddition]] of singlet oxygen with a [[diene]] such as [[cyclopentadiene]] to yield an [[endoperoxide]]: