GB511393A - Improvements in carboxylation of alkali metal salts of phenols - Google Patents

Abstract

511,393. Hydroxy carboxylic acids. CALCO CHEMICAL CO., Inc. July 12, 1938, No. 20654. Convention date, July 31, 1937. [Class 2 (iii)] Alkali metal salts of phenols or naphthols, particularly #-naphthol, are carboxylated by the action of carbon dioxide on a substantially - anhydrous solution ; thereof in a solvent having as the major component pyridine, compounds containing condensed pyridine rings or their homologues. Examples of suitable solvents are pyridine, the picolines, lutidines, and collidines, quinoline, quinaldine, lepidine, isoquinoline or mixtures of such compounds obtained from the acid soluble coal tar fraction. Phenols mentioned are phenol, cresols, chlorphenols, naphthols, hydroxyanthracenes, '5, 6, 7, 8-tetrahydro-2-naphthol, p-benzylphenol, hydroxycarbazoles and hydroxybenzocarcazoles. The prepared alkali metal salt may be directly dissolved in the solvent, or the phenol may be dissolved in the solvent and'alkali added, water formed being removed with excess alkali as a layer which separates on warming below the alkali phenolate solution, or by the use of lime or calcium carbide as dehydrating agents, or by distillation with or without a portion of the solvent. Wet 'solvent may be re-dried by refluxing over quick lime. In the case of phenols prepared by alkali fusion of sulphonic acids, the ground salt may be extracted with the solvent, alkali phenolate being dissolved and inorganic salts left. The dry phenolate solutions are reacted with carbon dioxide at ordinary or slightly elated temperatures, and the sodium' salts of the hydroxycarboxylic acids precipitate. When the reaction is effected at raised temperature, the pressure must be increased to increase the solubility of the carbon dioxide in the solvent. In the case of sodium betanaphthalate, two isomeric acids are formed, the salt of the 2-1 isomer being formed at lower temperatures and the more valuable 2-3 isomer at higher temperatures, e.g. 230-270‹C. Preferably in this case carbon dioxide is introduced at 230- 270‹C, the pressure being raised slowly and not too high to avoid formation of the 2-1 acid which tends to form a naphthoxanthene and tarry by products. Some pure betanaphthol is preferably present in the starting solution. Iron apparatus is not suitable. Nickel and its alloys are suitable materials. Examples describe the preparation of (1) sodium 1-hydroxy-2- naphthoate from sodium alpha-naphtholate in pyridine ; (2) the sodium salt of 5, 6, 7, 8 tetrahydro-2-hydroxy-3 naphthoic acid from the corresponding phenolate in pyridine ; (3) the sodium salt of 2-hydroxy-3 naphthoic acid from sodium #-naphtholate in pyridine or quinoline or an acid soluble coal tar oil of boiling point 250-260‹C ; (4) the potassium salt of 2-hydroxy- 1 naphthoic acid from potassium #-naphtholate in pyridine. Specifications 384,619 and 483,795 are referred to.