You're welcome again, and sorry for the confusion! I looked up the solubilities and melting points of the three isomers of hydroxybenzoic acid for comparison. In 3- and 4-hydroxybenzoic acid, intramolecular hydrogen bonding will not occur (because the two –OH groups are too far apart) and as a result they hydrogen bond more strongly with each other in the solid state (intermolecular hydrogen bonding instead of intramolecular), causing their melting points to be higher than that of 2-hydroxybenzoic acid (salicylic acid).
The water solubility of 4-hydroxybenzoic acid is also much higher than the solubility of 2-hydroxybenzoic acid, again because the two –OH groups in 4-hydroxybenzoic acid, being too far apart to hydrogen bond with each other, hydrogen bond to water molecules instead, increasing the solubility.
Sometimes it makes sense!
Steve
Compound Melting Point Water Solubility
2-hydroxybenzoic acid 159°C 1 g / 460 mL
(salicylic acid)
3-hydroxybenzoic acid 201-204°C (could not find)
4-hydroxybenzoic acid 214-217°C 1 g / 125 mL
Free Forum Hosting
Important Announcement
Prev Message
