Alkanes reacting with halogens

Alkanes react with halogens, such as chlorine and bromine, to form halogenoalkanes. 

Alkanes are fuels they burn in air if ignited. Complete combustion gives carbon dioxide and water less complete combustion gives carbon monoxide or other less oxidized forms of carbon. Alkanes react with halogens (chlorine or bromine) in a reaction initiated by heat or light. One or more hydrogens can be replaced by halogens. This substitution reaction occurs by a free-radical chain mechanism. 

In the presence of light or heat, alkanes react with halogens to form alkyl halides. Haiogenation is a radical substitution reaction, because a halogen atom X replaces a hydrogen via a mechanism that involves radical intermediates. 

Higher alkanes react with halogens by the same kind of chain mechanism as those that we have just seen. Ethane, for example, reacts with chlorine to produce chloroethane (ethyl chloride). The mechanism is as follows ... 

Alkanes react with halogens (except iodine) by a radical chain mechanism to give haloalkanes. The mechanism consists of initiation to create a halogen atom, two propagation steps, and various termination steps. 

Alkanes also react with halogens to form substitution products. 

Halogenation reactions of alkanes provide good examples of radical processes, and may also be used to illustrate the steps constituting a radical chain reaction. Alkanes react with chlorine in the presence of light to give alkyl chlorides, e.g. for cyclohexane the product is cyclohexyl chloride. 

You should know halogenation of an atkene for die MCAT. Notice that alkanes will not react with halogens without light or heat but alkenes will. Alkynes behave just like alkenes when exposed to halogens. 

Alkanes can react with halogens (F2, CI2, Br2,12) to form alkyl halides. For example, methane reacts with chlorine (CI2) to form chloromethane (methyl chloride), dichloromethane (methylene chloride), trichloromethane (chloroform), and tetra-chloromethane (carbon tetrachloride). 

The double bond in alkenes has important consequences for their chemical properties. Alkenes are much more reactive than alkanes. For example, alkenes react with halogens in the absence of light, but alkanes do not. 

The nnsaturated hydrocarbons include the alkenes, which contain one double bond per molecule, and the alkynes, which contain one triple bond per molecnle. Their systematic names begin as the names of the corresponding alkanes do, bnt they end with -ene or -yne, respectively. The location of the multiple bond may have to be specified in the name by including the address of the mnltiple-bonded carbon atom that is closer to the end of the chain. The alkenes and alkynes are more active than the alkanes for example, they react with halogens to form halogenated hydrocarbons under mnch less severe... 

Fluorinated ethenes react with halogenated alkanes by an electrophilic alkylation reaction in the presence of antimony(V) fluoride or hydrogen fluoride/antimony(V) fluoride. For example, the reaction of 1,1,1-trifluoroethane with tetrafluoroethene in the presence of antimony(V) fluoride yields 1.1,1,2,2,3,3-heptafluorobutane (8) in good yield. ... 

Owing to the presence of the double bond, the alkenes are said to be unsaturated and are more reactive than the alkanes. The alkenes may react with hydrogen gas in the presence of a catalyst to produce the corresponding alkane. They may react with halogens or hydrogen hahdes at low temperatures to form compounds containing only single bonds. 

Alkanes react with molecular halogens to produce alkyl halides by a subsdtudon reaction called radical halogenadon. 

Alkanes react with a halogen in ultraviolet light to produce an allg l halide, R—X. Halogenation is a general term for the substitution of a halogen atom for a hydrogen atom. 

Alkanes react with chlorine (CI2) or bromine (Br2> to form alkyl chlorides or alkyl bromides. These halogenation reactions take place only at high temperatures or in the presence of light. (Irradiation with light is symbolized by hv.)... 

Halogenation and combustion (burning) are the oidy reactions that alkanes undergo (without the assistance of a metal catalyst). In a combustion reaction, alkanes react with oxygen at high temperatures to form carbon dioxide and water. 

In contrast to the free radical substitution observed when halogens react with alkanes halogens normally react with alkenes by electrophilic addition... 

Strong oxidizers and strong acids are incompatible with nikanolamines. Reactions, generating temperature and/or pressure increases, may occur with halogenated organic compounds. Alkan olamines are corrosive to copper and brass and may react. Contact with aluminum by alkan olamines, particularly when wet or at elevated temperatures (60°C), should be avoided. 

Halogenated and halogenoalkyl substituted imines react with diazo alkanes under very mild conditions and preferentially yield aziridines [5, 146 147] Diazonium betaines have been considered as intermediates of these reactions [148,... 

Alkanes are sometimes referred to as paraffins, a word derived from the Latin parum affinis, meaning "little affinity." This term aptly describes their behavior, for alkanes show little chemical affinity for other substances and are chemically inert to most laboratory reagents. They are also relatively inert biologically and are not often involved in the chemistry of living organisms. Alkanes do, however, react with oxygen, halogens, and a few- other substances under appropriate conditions. 

This allylic bromination with NBS is analogous to the alkane halogenation reaction discussed in the previous section and occurs by a radical chain reaction pathway. As in alkane halogenation, Br- radical abstracts an allylic hydrogen atom of the alkene, thereby forming an allylic radical plus HBr. This allylic radical then reacts with Br2 to yield the product and a Br- radical, which cycles back... 

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