Editing Alkane (section)

==Chemical properties==
Alkanes are only weakly reactive with most chemical compounds. They only reacts with the strongest of electrophilic reagents by virtue of their strong C–H bonds (~100 kcal/mol) and C–C bonds (~90 kcal/mol).  They are also relatively unreactive toward free radicals. This inertness is the source of the term ''paraffins'' (with the meaning here of "lacking affinity"). In [[crude oil]] the alkane molecules have remained chemically unchanged for millions of years.

===Acid-base behavior===
The [[acid dissociation constant]] (p''K''<sub>a</sub>) values of all alkanes are estimated to range from 50 to 70, depending on the extrapolation method, hence they are extremely weak acids that are practically inert to bases (see: [[carbon acid]]s). They are also extremely weak bases, undergoing no observable protonation in pure [[sulfuric acid]] (''H''<sub>0</sub> ~ −12), although [[superacid]]s that are at least millions of times stronger have been known to protonate them to give hypercoordinate alkanium ions (see: [[Methanium|methanium ion]]). Thus, a mixture of [[antimony pentafluoride]] (SbF<sub>5</sub>) and [[fluorosulfonic acid]] (HSO<sub>3</sub>F), called [[magic acid]], can protonate alkanes.<ref>{{cite journal | author-link = George A. Olah |first1=G.A. |last1=Olah |last2=Schlosberg |first2=R.H. | title = Chemistry in Super Acids. I. Hydrogen Exchange and Polycondensation of Methane and Alkanes in FSO<sub>3</sub>H–SbF<sub>5</sub> ("Magic Acid") Solution. Protonation of Alkanes and the Intermediacy of CH<sub>5</sub><sup>+</sup> and Related Hydrocarbon Ions. The High Chemical Reactivity of "Paraffins" in Ionic Solution Reactions | journal = Journal of the American Chemical Society | year = 1968 | volume = 90 | pages = 2726–7 | doi = 10.1021/ja01012a066 | issue = 10 }}</ref>

===Reactions with oxygen (combustion reaction)===
All alkanes react with [[oxygen]] in a [[combustion]] reaction, although they become increasingly difficult to ignite as the number of carbon atoms increases. The general equation for complete combustion is:
:C<sub>''n''</sub>H<sub>2''n''+2</sub> + ({{sfrac|3|2}}''n''&nbsp;+&nbsp;{{sfrac|2}})&nbsp;O<sub>2</sub> → (''n''&nbsp;+&nbsp;1)&nbsp;H<sub>2</sub>O + ''n''&nbsp;CO<sub>2</sub>
:or C<sub>''n''</sub>H<sub>2''n''+2</sub> + ({{sfrac|3''n'' + 1|2}})&nbsp;O<sub>2</sub> → (''n''&nbsp;+&nbsp;1)&nbsp;H<sub>2</sub>O + ''n''&nbsp;CO<sub>2</sub>

In the absence of sufficient oxygen, [[carbon monoxide]] or even [[soot]] can be formed, as shown below:

:C<sub>''n''</sub>H<sub>2''n''+2</sub> + (''n''&nbsp;+&nbsp;{{sfrac|2}})&nbsp;[[oxygen|O<sub>2</sub>]] → (''n''&nbsp;+&nbsp;1)&nbsp;H<sub>2</sub>O + ''n''&nbsp;[[carbon monoxide|CO]]

:C<sub>''n''</sub>H<sub>2''n''+2</sub> + ({{sfrac|2}}''n''&nbsp;+&nbsp;{{sfrac|2}})&nbsp;[[oxygen|O<sub>2</sub>]] → (''n''&nbsp;+&nbsp;1)&nbsp;H<sub>2</sub>O + ''n''&nbsp;[[carbon|C]]

For example, [[methane]]:
:2&nbsp;CH<sub>4</sub> + 3&nbsp;O<sub>2</sub> → 4&nbsp;H<sub>2</sub>O + 2&nbsp;CO
:CH<sub>4</sub> + O<sub>2</sub> → 2&nbsp;H<sub>2</sub>O + C

See the [[Standard enthalpy change of formation (data table)#Alkanes|alkane heat of formation table]] for detailed data.
The [[standard enthalpy change of combustion]], Δ<sub>c</sub>''H''<sup>⊖</sup>, for alkanes increases by about 650&nbsp;kJ/mol per CH<sub>2</sub> group. Branched-chain alkanes have lower values of Δ<sub>c</sub>''H''<sup>⊖</sup> than straight-chain alkanes of the same number of carbon atoms, and so can be seen to be somewhat more stable.

===Biodegradation===
Some organisms are capable of metalbolizing alkanes.<ref>{{Cite journal|doi=10.3389/fmicb.2013.00058 |doi-access=free |title=Structural insights into diversity and n-alkane biodegradation mechanisms of alkane hydroxylases |date=2013 |last1=Ji |first1=Yurui |last2=Mao |first2=Guannan |last3=Wang |first3=Yingying |last4=Bartlam |first4=Mark |journal=Frontiers in Microbiology |volume=4 |page=58 |pmid=23519435 |pmc=3604635 }}</ref><ref>{{Cite journal| doi=10.1264/jsme2.ME14090| issn=1342-6311| volume=30| issue=1| pages=70–75| last1=Dashti| first1=Narjes| last2=Ali| first2=Nedaa| last3=Eliyas| first3=Mohamed| last4=Khanafer| first4=Majida| last5=Sorkhoh| first5=Naser A.| last6=Radwan| first6=Samir S.| title=Most Hydrocarbonoclastic Bacteria in the Total Environment are Diazotrophic, which Highlights Their Value in the Bioremediation of Hydrocarbon Contaminants| journal=Microbes and Environments| date=March 2015| pmid=25740314| pmc=4356466}}</ref>  The [[methane monooxygenase]]s convert methane to [[methanol]].  For higher alkanes, [[cytochrome P450]] convert alkanes to alcohols, which are then susceptible to degradation.

=== Free radical reactions ===
[[Free radical]]s, molecules with unpaired electrons, play a large role in most reactions of alkanes.  [[Free radical halogenation]] reactions occur with halogens, leading to the production of [[haloalkanes]]. The hydrogen atoms of the alkane are progressively replaced by halogen atoms.  The reaction of alkanes and fluorine is highly [[exothermic reaction|exothermic]] and can lead to an explosion.<ref>{{Ullmann |doi=10.1002/14356007.a11_349 |chapter=Fluorine Compounds, Organic  |last1=Siegemund |first1=Günter |last2=Schwertfeger |first2=Werner |last3=Feiring |first3=Andrew |last4=Smart |first4=Bruce |last5=Behr |first5=Fred |last6=Vogel |first6=Herward |last7=McKusick |first7=Blaine  }}</ref> These reactions are an important industrial route to halogenated hydrocarbons. There are three steps:
* '''Initiation''' the halogen radicals form by [[homolysis (chemistry)|homolysis]]. Usually, energy in the form of heat or light is required.
* '''Chain reaction''' or '''Propagation''' then takes place—the halogen radical abstracts a hydrogen from the alkane to give an alkyl radical. This reacts further.
* '''Chain termination''' where the radicals recombine.
Experiments have shown that all halogenation produces a mixture of all possible isomers, indicating that all hydrogen atoms are susceptible to reaction. The mixture produced, however, is not statistical: Secondary and tertiary hydrogen atoms are preferentially replaced due to the greater stability of secondary and tertiary free-radicals. An example can be seen in the monobromination of propane:<ref name = m&b/>
[[Image:Monobromination of propane.png|500px|center|Monobromination of [[propane]]]]

In the [[Reed reaction]], [[sulfur dioxide]] and [[chlorine]] convert hydrocarbons to [[Sulfonic acid|sulfonyl chlorides]] under the influence of [[photochemistry|light]].

Under some conditions, alkanes will undergo [[Nitration]].

===C-H activation===
Certain transition metal complexes promote non-radical reactions with alkanes, resulting in so [[carbon-hydrogen bond activation|C–H bond activation]] reactions.<ref>{{cite journal |doi=10.1021/acs.chemrev.3c00207 |title=Transition-Metal-Catalyzed Silylation and Borylation of C–H Bonds for the Synthesis and Functionalization of Complex Molecules |date=2023 |last1=Yu |first1=Isaac F. |last2=Wilson |first2=Jake W. |last3=Hartwig |first3=John F. |journal=Chemical Reviews |volume=123 |issue=19 |pages=11619–63 |pmid=37751601 |s2cid=263150991 }}</ref>

=== Cracking ===
{{Main|Cracking (chemistry)}}
Cracking breaks larger molecules into smaller ones. This reaction requires heat and catalysts. The thermal cracking process follows a [[homolysis (chemistry)|homolytic]] mechanism with formation of [[Radical (chemistry)|free radicals]]. The catalytic cracking process involves the presence of [[acid]] [[catalyst]]s (usually solid acids such as [[silica-alumina]] and [[zeolite]]s), which promote a [[heterolytic cleavage|heterolytic]] (asymmetric) breakage of bonds yielding pairs of ions of opposite charges, usually a [[carbocation]]. Carbon-localized free radicals and cations are both highly unstable and undergo processes of chain rearrangement, C–C scission in position [[beta scission|beta]] (i.e., cracking) and [[Intramolecular reaction|intra-]] and [[intermolecular]] hydrogen transfer or [[hydride]] transfer. In both types of processes, the corresponding [[reactive intermediate]]s (radicals, ions) are permanently regenerated, and thus they proceed by a self-propagating chain mechanism. The chain of reactions is eventually terminated by radical or ion recombination.{{Citation needed|date=January 2021}}

=== Isomerization and reformation ===
Dragan and his colleague were the first to report about isomerization in alkanes.<ref name="Asinger, Friedrich 1967">{{cite book |last= Asinger |first=Friedrich | title = Paraffins; Chemistry and Technology | url = https://archive.org/details/paraffinschemist0000asin | url-access = registration | publisher = Pergamon Press | date = 1967 |oclc=556032}}</ref> Isomerization and reformation are processes in which straight-chain alkanes are heated in the presence of a [[platinum]] catalyst. In isomerization, the alkanes become branched-chain isomers. In other words, it does not lose any carbons or hydrogens, keeping the same molecular weight.<ref name="Asinger, Friedrich 1967"/> In reformation, the alkanes become [[cycloalkane]]s or [[aromatic hydrocarbon]]s, giving off hydrogen as a by-product. Both of these processes raise the [[octane number]] of the substance. Butane is the most common alkane that is put under the process of isomerization, as it makes many branched alkanes with high octane numbers.<ref name="Asinger, Friedrich 1967"/>

===Other reactions===
In [[steam reforming]], alkanes react with [[steam]] in the presence of a [[nickel]] [[catalyst]] to give [[hydrogen]] and carbon monoxide.