Alkanes [Paraffines]
"Alkanes are saturated hydrocarbon containing only carbon-carbon single bond in their molecules."
Alkanes are less reactive so known as paraffins; because under normal conditions alkanes do not react with acids, bases, oxidising agents and reducing agent.
General formula : CnH2n+2
Examples are CH4, C2H6, C3H8,
General Methods of preparation
(i) By catalytic hydrogenation of alkynes and alkenes (Sabatie and sanderen's reaction)
![2449_catalytic hydrogenation.png](https://www.expertsmind.com/../CMSImages/2449_catalytic hydrogenation.png)
- Methane is not created by this process
(ii) Birch reduction :
![2443_birch reduction.png](https://www.expertsmind.com/../CMSImages/2443_birch reduction.png)
(iii) From alkyl halide
(a) By reduction : ![2493_alkyl halide.png](https://www.expertsmind.com/../CMSImages/2493_alkyl halide.png)
(b) With hydrogen in existence of pt/pd : ![2061_alkyl halide1.png](https://www.expertsmind.com/../CMSImages/2061_alkyl halide1.png)
(c) With HI in existence of Red phosphorus :
(iv) By Zn-Cu couple :
![2115_zn cu couple.png](https://www.expertsmind.com/../CMSImages/2115_zn cu couple.png)
(v) Wurtz reaction :
![2094_Wurtz reaction.png](https://www.expertsmind.com/../CMSImages/2094_Wurtz reaction.png)
- R-Br or RI preferred in this reaction. The total result in that reaction is the formation of even no. of carbon atoms in molecules.
(vi) Frankland's reaction :
![1907_frankland.png](https://www.expertsmind.com/../CMSImages/1907_frankland.png)
(vii) Corey-house synthesis
![1524_corey house.png](https://www.expertsmind.com/../CMSImages/1524_corey house.png)
- Reaction is suitable for odd number of Alkanes.
(viii) From Grignard reagent
(a) By action of acidic 'H' :
![1788_grignard reagent.png](https://www.expertsmind.com/../CMSImages/1788_grignard reagent.png)
(b) By reaction with alkyl halide :
![504_grignard reagent1.png](https://www.expertsmind.com/../CMSImages/504_grignard reagent1.png)
(ix) From carboxylic acids
(a) Laboratory method [Decarboxylation reaction or Duma reaction]
![695_duma reaction.png](https://www.expertsmind.com/../CMSImages/695_duma reaction.png)
- NaOH and CaO is in the ratio of 3 : 1. (Sodalime)
(b) Kolbe's synthesis :
![2219_kolbe synthesis.png](https://www.expertsmind.com/../CMSImages/2219_kolbe synthesis.png)
At anode [Oxidation] :
![2352_kolbe synthesis1.png](https://www.expertsmind.com/../CMSImages/2352_kolbe synthesis1.png)
At cathode [Reduction] :
- Both free radical and ionic process are required in this reaction.
(c) Reduction of carboxylic acid :
![366_kolbe synthesis3.png](https://www.expertsmind.com/../CMSImages/366_kolbe synthesis3.png)
(x) By reduction of alcohols, ketones, acid derivatives or aldehyde
![234_reduction.png](https://www.expertsmind.com/../CMSImages/234_reduction.png)
q Aldehyde and ketones when reduced with conc. HCl and amalgamated zinc also yield alkanes.
Clemmenson reduction :
![425_clemmenson reduction.png](https://www.expertsmind.com/../CMSImages/425_clemmenson reduction.png)
![47_clemmenson reduction1.png](https://www.expertsmind.com/../CMSImages/47_clemmenson reduction1.png)
- Ketones and aldehydes (>C = O) may be converted to hydrocarbon in presence of excess of hydrazine and sodium alkoxide on heating.
Wolff-kishner reduction :
![1258_wollf kishner.png](https://www.expertsmind.com/../CMSImages/1258_wollf kishner.png)
(xi) Hydroboration of alkenes
(a) On treatment with acetic acid
![374_hydroboration.png](https://www.expertsmind.com/../CMSImages/374_hydroboration.png)
(b) Coupling of alkyl boranes by incomes of silver nitrate
![1615_hydroboration1.png](https://www.expertsmind.com/CMSImages/1615_hydroboration1.png)
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