Chapter 4
B.sc 1st year Book
(Page 10)

FLUOROCARBONS

Fluorocarbons are obtained from hydrocarbons or other organic molecules by the replacement of one or more hydrogen atoms with fluorine atoms. These compounds have very valuable properties and wide industrial applications.

Preparation of Fluorocarbons:

Fluorocarbons/Preparation can be prepared by the following methods,
  1. By heating metal fluorides with alkyl halides: When metal fluorides like LiF, NaF, CsF, ZnF2, ZnF2, SbF3, etc. are heated with alkyl halides yields fluorocarbons.
fluocarbon. is obtained.
  1. By electrolyzing organic compounds in liquid HF: When an organic compound is electrolyzed in liquid HF in steel cells with Ni anodes and steel cathodes fluorocarbon is obtained.
C8His  in iliq. HF  Electrolysis C8 F11 Fluorocarbon 
  1. By direct fluorination of hydrocarbons:

fluorination of hydrocarbons

5. By fluorinating ketones with SF4;

Properties of Fluorocarbons:

(1) Fluorocarbons are highly stable compounds because the bond energy of the C−F bond(486kd) m0−1) is very high as compared to the bond energies of C−H(415 kJ mol−1) and C−C (332 kJ mol−1) bonds.

(2) They are stable towards hydrolysis, this is because carbon does not have d – orbitals which could permit the formation of the 5 -coordinated intermediate by nucleophilic attack of H2O molecule.

(3) Since, the fluorine atom has small in size the replacement of H atoms by Fathoms does not produce any appreciable strain in the molecule. Where日s the replacement of H atoms by other halogens causes appreciable strain in the resulting molecules because of larger differences in the sizes of H and halogen atoms. As a result, the fluoro compounds are more stable than the other halogen compounds.

(4) Fluorocarbons are not attacked by acids, alkalies and other chemicals. They are only attacked by hot metals such as molten sodium.

(5) The fluoro compounds are not very reactive because the fluorine atoms shield the carbon atoms very effectively thereby making them less vulnerable to attack by other reagents.

(6) In the fluoro compounds, the CF bond is more polar than C−H and C−Cl bonds. Fluorine is more electronegative than a carbon atom, therefore, it pulls the electronic charge of the bond pair of electrons in the C-F bond towards itself. Thus, the carbon atom in the C-F bond develops a partial positive charge (+δ) on it and is considered oxidized. The hydrogen atom, on the other hand, is less electronegative than carbon, hence, the electronic charge of the bond pair of electrons in the C−H bond is pulled towards the carbon atom. Thus, the carbon atom in the C-H bond develops a partial negative charge and is considered reduced. Due to this reason, hydrocarbons are readily oxidized when exposed to atmospheric oxygen, The fluorocarbons, on the other hand, are not oxidized at all.

Uses of Fluorocarbons :

(1) Fluorocarbons are best used as lubricants because of their very low coefficient of friction.
(2) Chlorofluorocarbons(CFC’s) such as CCl3 F1CCIF3CCl2 F2 are used as retrigerants.
(3) Certain perfluoro organics are used as ‘synthetic blood’ for small mammals. These perfluoro organics are non-toxic and have the same properties as natural blood, I.e, they have the capacity to dissolve, transport and release O2 by simple solubility.
(4) Chlorine, bromine, and iodine oxofluorides are used as good fluorinating and oxidizing agents and are of great industrial importance.
(5) CHCiF2 is used for preparing tetrafluoro ethylene which on polymerization converted into a well-known polymer known as ‘Teflon’.

Teflon

 

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