Why is salicylic acid more acidic than aspirin?
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Why is salicylic acid more acidic than aspirin?
Salicylic acid forms intra hydrogen bonding so it is not capable of forming hydrogen bonds with water, whereas the aspirin contains a carboxylic group free to form hydrogen bond with water so becomes more soluble.
What is the pKa value of salicylic acid?
2.97
Salicylic acid
| Names | |
|---|---|
| Acidity (pKa) | 2.97 (25 °C) 13.82 (20 °C) |
| UV-vis (λmax) | 210 nm, 234 nm, 303 nm (4 mg/dL in ethanol) |
| Magnetic susceptibility (χ) | −72.23·10−6 cm3/mol |
| Refractive index (nD) | 1.565 (20 °C) |
What makes a pKa lower?
Resonance – If a molecule has electrons that are spread over more than one bond (if a molecule has resonance), it will have a lower pKa compared to a molecule that does not. Atom Size – As the atom size increases down a column on the periodic table, the acidity increases.
Why salicylic acid is acidic?
When salicylic acid deprotonates (losing the proton from the carboxyl group) it forms a hydrogen bond with between the oxygen in the carboxylate anion and the hydrogen in the alcohol group.
Why is aspirin less irritating than salicylic acid?
Salicylic acid contains a phenol group, and phenols are known to be irritating. The Bayer Company replaced the phenol group with an ester group. This esterified compound (acetylsalicylic acid, also known as aspirin) was shown to be much less irritating than salicylic acid.
What is the pH of salicylic acid?
Salicylic acid at close to neutral pH (mostly in its neutralized form as salicylate, pH 6.50) exerted a corneodesmolytic activity as good as that of salicylic acid in an acidic vehicle (pH 3.12) after only two days of application.
When does pH equal pKa?
This means that when the pH is equal to the pKa there are equal amounts of protonated and deprotonated forms of the acid. For example, if the pKa of the acid is 4.75, at a pH of 4.75 that acid will exist as 50\% protonated and 50\% deprotonated.
What is relation between pH and pKa?
The lower the pH, the higher the concentration of hydrogen ions [H+]. The lower the pKa, the stronger the acid and the greater its ability to donate protons. pH depends on the concentration of the solution. This is important because it means a weak acid could actually have a lower pH than a diluted strong acid.
Why is salicylate a stronger acid than salicylic acid?
This would make salicylate the weaker conjugate base, and therefore salicylic acid is the stronger acid. Apparently this effect is stronger than the effect of pi electron donation. Salicylic acid quickly loses H+ to form a Hydrogen bond stabilized salicylate ion.
What is the difference between salicylate and aspirin?
Salicylic acid has ortho -OH, while aspirin has ortho -OCOCH3. -OH is more pi-electron-donating than -OCOCH3. This raises the free energy of the carboxylate ion (by negative-negative charge repulsion) in salicylate more than in acetylsalicylate.
Why is benzoic acid less acidic than salicylic acid?
Benzoic acid is less acidic than salicylic acid because of? Structurally, the only difference between salicylic acid and benzoic acid is the presence of the hydroxy (-OH) group ortho to the carboxyl group. The more acidic molecule is the one with a more stable conjugate base.
What is the role of OH group in salicylic acid?
However, in the salicylic acid,the -OH acts as an electron-withdrawing group, removing part of the negative charge from the benzene ring and stabilizing the ion. In salicylic acid the hydrogen atom in OH group have a tendency to form hydrogen bonding with oxygen atom in the COO – group thus leaving the H+ ion freely available.