PURPOSE: To obtain a salicylic acid derivative by dissolving a 2,4-dialkylphenol and an alkali metal hydroxide in a lower alcohol, reacting, distilling out the lower alcohol and generated water to obtain an anhydrous alkali metal salt of the dialkylphenol and reacting CO2 with the resultant salt.
CONSTITUTION: A 2,4-dialkylphenol and NaOH, etc., (solid or aqueous solution) are dissolved in a lower alcohol (e.g. 1-4C alkanol) in an amount of 0.2-3wt. times to the dialkylphenol at 50-60°C and reacted, heated, then a mixture of distilled lower alcohol and water is removed to obtain an anhydrous alkali metal salt of the 2,4-dialkylphenol. Process of the distilling out is gradually performed in normal pressure for 2-5hr and further at 100-130°C inner temperature in reduced pressure. Next, CO2 is blown into the resultant anhydrous salt and reacted in a pressure from reduced pressure to near atmospheric pressure with keeping at 130-150°C to afford a 3,5-dialkylsalicyclic acid. Said compound is useful as color developer for pressure-sensitive recording paper.