4-Hydroxybenzoates

Dissolve 10 g. of salicylic acid (o-hydroxybenzoic acid) in 7 ml. of dry pyridine contained in a too ml. conical flask. Then without delay (since this solution if allowed to stand tends to become a semi-solid mass) run in 7 5 ml. (8 3 g.) of acetyl chloride, adding about i ml. of the chloride at a time, and shaking the mixture continuously during the addition. The heat of the reaction causes the temperature of the mixture to rise rapidly ... 

It is of interest to record that />-hydroxybenzoic acid may be prepared by the thermal rearrangement of potassium salicylate at 230° ... 

This may be determined roughly by treating a small test portion with 3-4 ml. of hot water and acidifying with concentrated hydrochloric acid the absence of a precipitate in the warm solution indicates the essential completeness of the reaction. Salicylic acid is sparingly soluble and p-hydroxybenzoic acid is relatively soluble under these conditions. 

Interpretation of spectra. The infrared spectrum of m-hydroxybenzoic acid (solid ground in Nujol) is shown in Fig. A, 7, 1. The more important bands may be interpreted as follows. 

One of the hydroxybenzoic acids is known by the common name salicylic acid Its methyl ester methyl salicylate occurs in oil of wintergreen Methyl salicylate boils over 50°C lower than either of the other two methyl hydroxybenzoates What is the structure of methyl salicylate Why is its boiling point so much lower than that of either of its regioisomers ... 

The Kolbe-Schmitt reaction is an equilibrium process governed by thermodynamic control The position of equilibrium favors formation of the weaker base (salicylate ion) at the expense of the stronger one (phenoxide ion) Thermodynamic control is also responsible for the pronounced bias toward ortho over para substitution Salicylate anion IS a weaker base than p hydroxybenzoate and predominates at equilibrium... 

Salicylate anion is a weaker base than p hydroxybenzoate because it is stabilized by intramolecular hydrogen bonding... 

Treatment of p hydroxybenzoic acid with aqueous bromine leads to the evolution of carbon dioxide and the formation of 2 4 6 tnbromophenol Explain... 

Methyl salicylate is the methyl ester of o hydroxybenzoic acid Intramolecular (rather than mtermolecular) hydrogen bonding is responsible for its relatively low boiling point... 

Kolbe-Schmitt reaction (Section 24 10) The high pressure re action of the sodium salt of a phenol with carbon dioxide to give an o hydroxybenzoic acid The Kolbe-Schmitt reac tion IS used to prepare salicylic acid in the synthesis of as pinn... 

Salicylic acid 2-Hydroxybenzoic acid LeSCN2+ at pH 3 is reddish-brown Typical uses Pe(III) titrated with EDTA to colorless iron-EDTA complex... 

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