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Chemical Reactions of Alkanes

Home Chemical Reactions of Alkanes

Alkanes are saturated hydrocarbons. They contain only strong C-C and C-H sigma bonds. Hence,alkanes are quit less reactive and are knon as! "araffins #"arum-little affinis-reactivity or

affinity$. Alkanes are generally in toards acids, bases, o%idi&ing and reducing agents. Alkane

being saturated com"ounds can undergo only substitution reactions. Thus, the ty"ical reactionsof alkanes a' substitution reactions.

(m"ortant reactions of alkanes are as follos)

HALOGENATION

Halogenation involves the re"lacement of one or more atoms of alkane by corres"onding number

of halogen atom

Chlorination can be carried out by treatment of ith chlorine, either in the "resence of diffused

sunlight ultraviolet light or at high tem"erature #*+-++ $. e%am"le, hen methane is

chlorinated, e get mi%ture of different substitution "roducts.

/romination, though similar to chlorination, occurs k ra"idly.

(odination is e%tremely slo and is reversible in natural luorination of alkanes takes "lace ith

almost violence to "roduce fluorinated com"ounds. (t also involve ru"ture of some C-C bonds incase of higher alkanes. reaction can be made less violent by dilution of fluorine nitrogen.

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SULPHONATION

Alkanes containing si% or more carbon atoms on heating ith fuming tetrao%osul"hate #0($ acid

for several hours yield the corres"onding sul"honic acids.

OXIDATION

Alkanes on burning in air or o%ygen get com"letely o%idised to carbon #(0$ o%ide and ater ith

the evolution of large amount of heat.

CH12 343C432 3H34 2 Heat

C1H'52 ' 6 3 437 1C432 *H34 2Heat

8ue to evolution of large amount of heat, during combustion, alkanes are used as fuels.

The general chemical equation for combustion of alkanes may be ritten as)

(n the "resence of insufficient su""ly of o%ygen, alkanes on combustion "roduce carbon #(T$o%ide, hich is highly "oisonous. Carbon #(T$ o%ide combines ith haemoglobin in the blood to

form carbo%y haemoglobin and makes it unfit for carrying o%ygen. As a result, the "erson may

die due to suffocation.

ISOERISATION

(n this "rocess, n-alkanes on heating ith anhydrous aluminium chloride and hydrogen chloride

get converted into branched chain alkanes.

CRAC!ING OR PH"ROL"SIS

(t is a "rocess of decom"osing higher hydrocarbons into loer hydrocarbons ith lo boiling

"oints by strong heating. The "rocess involves the cleavage of carbon-carbon and carbon-

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hydrogen bonds and results in the formation of loer hydrocarbons and is believed to be a free

radical reaction.

The ty"es of hydrocarbons formed de"end u"on the conditions em"loyed for cracking. ore%am"le,

4il gas or "etrol gas is "re"ared by "yrolysis of kerosene oil or "etrol. 9imilarly, gasoline can be

"re"ared by "yrolysis of kerosene oil or fuel oil. or e%am"le, dodecane, a constituent of

kerosene oil, on heating to :+ in the "resence of "latinum, "alladium or nickel, gives ami%ture of he"tane and "entene.

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