Why is salicylic acid (2_hydroxy benzoic acid) stronger than 2_methoxy benzoic acid?

Question

Answer

Acid is strong when its anion is stable after giving H+ ion to solution . here we can see orthohydroxybenzote ion is more stable by H bonding between o- and H  SO It is a better acid than orthomethoxy benzoic acid

Answer

Because methoxy benzene provides negative charge in ring by +m effect (MESOMERIC EFFECT) because of which it becomes less acidic

Answer

Introduction:
Salicylic acid (2-hydroxy benzoic acid) and 2-methoxy benzoic acid are both derivatives of benzoic acid. Salicylic acid is known to be stronger than 2-methoxy benzoic acid due to several factors related to its chemical structure and properties.

1. Difference in Functional Groups:
Salicylic acid contains a hydroxyl group (-OH) attached to the benzene ring, while 2-methoxy benzoic acid contains a methoxy group (-OCH3) in place of the hydroxyl group. The presence of the hydroxyl group in salicylic acid plays a significant role in its stronger acidic nature compared to the methoxy group in 2-methoxy benzoic acid.

2. Effect of Electron-Withdrawing Groups:
The hydroxyl group in salicylic acid is an electron-donating group, which increases the electron density on the oxygen atom. This electron-donating effect stabilizes the negative charge on the oxygen atom when the acid dissociates, making it easier for salicylic acid to donate a proton and act as an acid. On the other hand, the methoxy group in 2-methoxy benzoic acid is an electron-withdrawing group, which decreases the electron density on the oxygen atom. Consequently, the negative charge on the oxygen atom is less stabilized, making it harder for 2-methoxy benzoic acid to donate a proton.

3. Resonance Effects:
The presence of the hydroxyl group in salicylic acid allows for resonance stabilization of the resulting carboxylate ion. The lone pair of electrons on the oxygen atom can delocalize into the benzene ring, spreading the negative charge and providing additional stability to the ion. In contrast, the methoxy group in 2-methoxy benzoic acid does not participate in resonance, leading to a less stable carboxylate ion.

4. Strength of Acidic Conjugate Base:
When salicylic acid donates a proton, it forms a salicylate ion, which is a more stable conjugate base compared to the methoxy benzoate ion formed from 2-methoxy benzoic acid. The stronger stability of the salicylate ion contributes to the overall stronger acidic nature of salicylic acid.

Conclusion:
In conclusion, salicylic acid is stronger than 2-methoxy benzoic acid due to the presence of a hydroxyl group, its electron-donating effect, resonance stabilization, and the formation of a more stable conjugate base. These factors collectively contribute to the increased acidity of salicylic acid compared to 2-methoxy benzoic acid.

Answer

The strongest  acid is one which easily donate h+ ion or make stable carbonation so in hydroxy benzene carbocation stable by mesomeric effect where as in methyl hydroxy stable by inductive effect

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