04-01-2013, 11:40 AM
Oxidizing Agents
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The principle problem in oxidation reactions are
1) Induction of the desired reaction
2) satisfactory control of extent of reaction
For oxidation we required an oxidizing medium. So first we must understand the behavior of different oxidizing agents.
So that we can select an oxidizing agent which full fill our requirements(above two condition)
Permanganates
Solid salts of per manganic acid ( HMnO2) are powerful oxidizing agents.
E.g. Calcium per manganate induces rapid oxidation of ethanol that inflammation may occur.
Aqueous solutions of permanganate also possess powerful oxidizing properties like KMnO4.
Potassium salt is avauilable in the form of stable crystals.
It functions as an oxidizing agent of different strength in Alkaline , neutral, and acid solution.
Dichromates
Oxidation with dicharomates usualy occur in the pressence of sulfuric acid.
Although the dichromate exert an oxidizing tendency in the absence of acid, but oxidation reaction are ossur much more quickly in the presence of acid.
Such reactions reacts to give oxygen as follows
K2Cr2O7 + 4H2SO4 K2SO4 + Cr2(SO4)3 +4H2O +3O
2moles of chromic acid(H2CrO4) ( 1 mole of dichromate ) giving three atoms of oxygen.
Sodium salt is cheaper and much more soluble in water, and consequently more often used.
Chromic acid solution
chromic anhydride, CrO3 , dissolved in glacial acetic acid, used as oxidizing agent.
2 moles of anhydride yields 3 atoms of oxygen.
2CrO3 Cr2O3 + 3O
Chromic acid and chromates have numerous applications in organic chemistry.
In the manufacture of perfumes they may be used to oxidized anethole to anisic aldehyde, isosafrol to piperonel etc.
They are also used in the preparation of methyl blue and other dyestuffs.
Fuming Sulfuric acid (Oleum)
Fuming sulfuric acid (H2S2O7) in the presence of mercury salts is a powerful oxidizing agent.
Fuming sulfuric acid attained importance as an oxidizing agent for the introduction of hydroxyl groups in anthraquinone derivatives.
At low temp fuming acid may be used to convert alizarin and other hydroxy derivatives of anthraquinone to tri-hydroxy or upto hexa-hydroxy derivatives.
ozone
Ozone is another powerful oxidizing agent.
Use of ozone for oxidation of oleic acid to azelic acid + pelargonic acids reached commercial applicability in a million dollar plant.
Ozone costs may range about 8-10 cents per pound under favorable, and 50 cents if conditions are not favorable.
Ozone is being promoted for use in the conversion of tertiary amines to amines oxides.
Ozone is also used for the oxidation of lower molecular paraffinic hydrocarbons at room temperature.
Kinetics of oxidation reactions
Main emphasis in oxidation is to control the oxidation. because oxidation is highly exothermic
During oxidation water and CO2 both are formed but must be is less amounts.
Appropriate oxidizing agent is required.
Equilibrium is favorable
Control of extent of oxidation
[attachment=46427]
The principle problem in oxidation reactions are
1) Induction of the desired reaction
2) satisfactory control of extent of reaction
For oxidation we required an oxidizing medium. So first we must understand the behavior of different oxidizing agents.
So that we can select an oxidizing agent which full fill our requirements(above two condition)
Permanganates
Solid salts of per manganic acid ( HMnO2) are powerful oxidizing agents.
E.g. Calcium per manganate induces rapid oxidation of ethanol that inflammation may occur.
Aqueous solutions of permanganate also possess powerful oxidizing properties like KMnO4.
Potassium salt is avauilable in the form of stable crystals.
It functions as an oxidizing agent of different strength in Alkaline , neutral, and acid solution.
Dichromates
Oxidation with dicharomates usualy occur in the pressence of sulfuric acid.
Although the dichromate exert an oxidizing tendency in the absence of acid, but oxidation reaction are ossur much more quickly in the presence of acid.
Such reactions reacts to give oxygen as follows
K2Cr2O7 + 4H2SO4 K2SO4 + Cr2(SO4)3 +4H2O +3O
2moles of chromic acid(H2CrO4) ( 1 mole of dichromate ) giving three atoms of oxygen.
Sodium salt is cheaper and much more soluble in water, and consequently more often used.
Chromic acid solution
chromic anhydride, CrO3 , dissolved in glacial acetic acid, used as oxidizing agent.
2 moles of anhydride yields 3 atoms of oxygen.
2CrO3 Cr2O3 + 3O
Chromic acid and chromates have numerous applications in organic chemistry.
In the manufacture of perfumes they may be used to oxidized anethole to anisic aldehyde, isosafrol to piperonel etc.
They are also used in the preparation of methyl blue and other dyestuffs.
Fuming Sulfuric acid (Oleum)
Fuming sulfuric acid (H2S2O7) in the presence of mercury salts is a powerful oxidizing agent.
Fuming sulfuric acid attained importance as an oxidizing agent for the introduction of hydroxyl groups in anthraquinone derivatives.
At low temp fuming acid may be used to convert alizarin and other hydroxy derivatives of anthraquinone to tri-hydroxy or upto hexa-hydroxy derivatives.
ozone
Ozone is another powerful oxidizing agent.
Use of ozone for oxidation of oleic acid to azelic acid + pelargonic acids reached commercial applicability in a million dollar plant.
Ozone costs may range about 8-10 cents per pound under favorable, and 50 cents if conditions are not favorable.
Ozone is being promoted for use in the conversion of tertiary amines to amines oxides.
Ozone is also used for the oxidation of lower molecular paraffinic hydrocarbons at room temperature.
Kinetics of oxidation reactions
Main emphasis in oxidation is to control the oxidation. because oxidation is highly exothermic
During oxidation water and CO2 both are formed but must be is less amounts.
Appropriate oxidizing agent is required.
Equilibrium is favorable
Control of extent of oxidation