Editing Hydrocarbon (section)

==Reactions==
Saturated hydrocarbons are notable for their inertness. Unsaturated hydrocarbons (alkanes, alkenes and aromatic compounds) react more readily, by means of substitution, addition, polymerization. At higher temperatures they undergo dehydrogenation, oxidation and combustion.<ref name=Ullmann/>

===Saturated hydrocarbons===
====Cracking====
{{Main|Cracking (chemistry)}}
{{Further information|Steam reforming}}
The cracking of saturated hydrocarbons is the main industrial route to [[alkene]]s and [[alkyne]].  These reactions require [[heterogeneous catalyst]]s and temperatures >500 °C.
===Oxidation===
Widely practice conversions of hydrocarbons involves their reaction with oxygen.  In the presence of excess oxygen, hydrocarbons combust.  With, however, careful conditions, which have been optimized for many years, partial oxidation results.  Useful compounds can obtained in this way: [[maleic acid]] from [[butane]], [[terephthalic acid]] from [[xylene]]s, [[acetone]] together with [[phenol]] from [[cumene]] (isopropylbenzene), and [[cyclohexanone]] from [[cyclohexane]].  The process, which is called [[autoxidation]], begins with the formation of [[hydroperoxide]]s (ROOH).<ref>{{March6th|page=967}} </ref>

====Combustion====
{{Main|Combustion}}
Combustion of hydrocarbons is currently the main source of the world's energy for [[electric power|electric power generation]], heating (such as home heating), and transportation.<ref>{{Cite web|title=Generating Electricity|url=https://electricity.ca/learn/electricity-today/generating-electricity/|access-date=2021-12-05|website=Canadian Electricity Association|language=en-US}}</ref><ref>{{Cite journal|last1=Zou|first1=Caineng|last2=Zhao|first2=Qun|last3=Zhang|first3=Guosheng|last4=Xiong|first4=Bo|date=2016-01-01|title=Energy revolution: From a fossil energy era to a new energy era|journal=Natural Gas Industry B|language=en|volume=3|issue=1|pages=1–11|doi=10.1016/j.ngib.2016.02.001|issn=2352-8540|doi-access=free|bibcode=2016NGIB....3....1Z }}</ref> Often this energy is used directly as heat such as in home heaters, which use either [[petroleum]] or [[natural gas]]. The hydrocarbon is burnt and the heat is used to heat water, which is then circulated. A similar principle is used to create [[electrical energy]] in [[Power Plants|power plants]].  Both saturated and unsaturated hydrocarbons undergo this process.

Common properties of hydrocarbons are the facts that they produce steam, [[carbon dioxide]] and heat during [[combustion]] and that [[oxygen]] is required for combustion to take place. The simplest hydrocarbon, [[methane]], burns as follows:
:<chem>\underset{methane}{CH4} + 2O2 -> CO2 + 2H2O</chem>

In inadequate supply of air, [[carbon black]] and [[Water vapor|water vapour]] are formed:
:<chem>\underset{methane}{CH4} + O2 -> C + 2H2O</chem>

And finally, for any [[linear alkane]] of n carbon atoms,
:<math chem="">\ce{C}_n \ce{H}_{2n+2} + \left({{3n+1}\over 2}\right)\ce{O2->} n\ce{CO2} + (n+1)\ce{H2O}</math>

Partial oxidation characterizes the reactions of alkenes and oxygen. This process is the basis of [[rancidification]] and [[drying oil|paint drying]].

[[Benzene]] burns with [[soot]]y flame when heated in air:
:<chem>\underset{benzene}{C6H6} + {15\over 2}O2 -> 6CO2 {+} 3H2O</chem>

====Halogenation====
{{Main|Free-radical halogenation}}
Saturated hydrocarbons react with [[chlorine]] and [[fluorine]]. In the case of chlorination, one of the chlorine atoms replaces a hydrogen atom.  The reactions proceed via  [[free-radical pathway]]s, in which the halogen first dissociates into a two neutral radical atoms ([[Homolysis (chemistry)|homolytic fission]]).
:CH{{sub|4}} + Cl{{sub|2}} → CH{{sub|3}}Cl + HCl
:CH{{sub|3}}Cl + Cl{{sub|2}} → CH{{sub|2}}Cl{{sub|2}} + HCl
all the way to CCl{{sub|4}} ([[carbon tetrachloride]])

:C{{sub|2}}H{{sub|6}} + Cl{{sub|2}} → C{{sub|2}}H{{sub|5}}Cl + HCl
:C{{sub|2}}H{{sub|4}}Cl{{sub|2}} + Cl{{sub|2}} → C{{sub|2}}H{{sub|3}}Cl{{sub|3}} + HCl
all the way to C{{sub|2}}Cl{{sub|6}} ([[hexachloroethane]])

===Unsaturated hydrocarbons===
====Substitution====
{{Main|Substitution reaction}}
Aromatic compounds, almost uniquely for hydrocarbons, undergo substitution reactions. The chemical process practiced on the largest scale is the reaction of benzene and [[ethene]] to give [[ethylbenzene]]:
:{{chem2|C6H6 + C2H4 -> C6H5CH2CH3}}
The resulting ethylbenzene is dehydrogenated to [[styrene]] and then polymerized to manufacture [[polystyrene]], a common [[thermoplastic]] material.

====Addition====
{{Main|Addition reaction}}
{{Main|Hydrogenation}}
{{Main|Polyolefin}}
{{Further information|Addition polymer}}

Addition reactions apply to alkenes and alkynes.  It is because they add reagents that they are called unsaturated. In this reaction a variety of reagents add "across" the pi-bond(s).  Chlorine, hydrogen chloride, [[water]], and [[hydrogen]] are illustrative reagents.  

Polymerization is a form of addition. [[Alkenes]] and some alkynes also undergo [[polymerization]] by opening of the multiple bonds to produce [[polyethylene]], [[polybutylene]], and [[polystyrene]]. The alkyne [[acetylene]] polymerizes to produce [[polyacetylene]]. Oligomers (chains of a few monomers) may be produced, for example in the [[Shell higher olefin process]], where [[Alpha-olefin|α-olefin]]s are extended to make longer α-olefins by adding ethylene repeatedly.

===Metathesis===
Some  hydrocarbons undergo ''metathesis'', in which substituents attached by C–C bonds are exchanged between molecules. For a single C–C bond it is [[alkane metathesis]], for a double C–C bond it is [[Olefin metathesis|alkene metathesis]] (olefin metathesis), and for a triple C–C bond it is [[alkyne metathesis]].