What is picric acid? why 2,4,6 tri-nitro phenol is called picric acid ?
2,4,6-tri-nitro phenol is generally known as picric acid. It is a very strong organic acid. 2,4,6-trinitro phenol contains three strong electron withdrawing
nitro group.
Hence , like other organic or inorganic acid, it easily ionizes and gives ‘H+’ ion. Besides this, it decomposing carbonates like another acid and the pKa value of 2,4,6-trinitro phenol is 0.38.
Hence , like other organic or inorganic acid, it easily ionizes and gives ‘H+’ ion. Besides this, it decomposing carbonates like another acid and the pKa value of 2,4,6-trinitro phenol is 0.38.
Consequently, 2,4,6-trinitro phenol is also called picric acid.
Preparation of picric acid :
There are different method
for preparation of picric acid. But picric acid is prepared commercially by
first sulphonating phenol and then
nitrating the product.
Another commercial method
for the preparation of picric acid by
the nitration of chloro benzene
are as follows,
Properties of picric acid.
Picric acid is a yellow crystalline solid with a bitter
taste. The melting point of picric acid is 122⁰C . it is a strong acid .
The pKa value is 0.38. It reacts with
carbonate to form a salt sodium picrate.
Picric acid also forms CT complex known as picrates , with aromatic hydrocarbons, amines and phenols.
Picric acid also forms CT complex known as picrates , with aromatic hydrocarbons, amines and phenols.
Why p-nitro phenol is stronger acid than m-nitro phenol ?
The strength of acid depends on the stability of the concern anion of that acid . The anion of both acid stabilized through
resonance.
But the resonating effect is more effective in p-nitro phenoxide ion than m-nitro phenoxide ion due to more number of resonating structure.
Hence, p-nitro phenoxide ion is more stable than the meta isomer.
Consequently, Why p-nitro phenol is stronger acid than m-nitro phenol.
But the resonating effect is more effective in p-nitro phenoxide ion than m-nitro phenoxide ion due to more number of resonating structure.
Hence, p-nitro phenoxide ion is more stable than the meta isomer.
Consequently, Why p-nitro phenol is stronger acid than m-nitro phenol.
Why ortho-nitro phenol is less acidic than para-nitro phenol ?
The strength of acid depends on the stability of the
conjugate base of that acid. The conjugate base of p-nitro phenol gets stabilized through resonance .
However, the resonance gets hindered in o-nitro phenoxide ion . Besides this, o-nitro phenol is less ionized due to formation of intra molecular H-bonding.
For the above reason , ortho-nitro phenol is less acidic than para-nitro phenol.
However, the resonance gets hindered in o-nitro phenoxide ion . Besides this, o-nitro phenol is less ionized due to formation of intra molecular H-bonding.
For the above reason , ortho-nitro phenol is less acidic than para-nitro phenol.
Summary :
What is picric acid ? Why 2,4,6 tri-nitro phenol is called picric acid ?
Why p-nitro phenol is stronger acid than m-nitro phenol ?
Why o-nitro phenol is less acidic than para isomer ?
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