Patent GB-483795-A (GB)
Title: Carboxylation of alkali metal salts of phenols
Inventor: LECHER HANS Z
IPC: C07C51/15
Filed: 1937-08-23
Abstract: The carboxylation of alkali metal salts of phenols is effected by the action of carbon dioxide on a substantially anhydrous solution of the alkali metal phenolate in a heterocyclic compound having a six-membered ring with two oxygen atoms therein and free from groups capable of reacting with the reactants or reaction products. Suitable solvents are those containing the ring systems of 1 : 4- and 1 : 3-dioxane, 1 : 4- and 1 : 3-dioxene and 1 : 4-dioxine, e.g. dioxane, m-dioxane, 1 : 4-dioxene, 2-methyl-m-dioxane, 2 : 5-dimethyl-p-dioxane, 2 : 3-diphenyl-p-dioxane, 2 : 3-diethoxydioxane, saligenin methylene ether, pyrocatechol ethylene ether, di-o-phenylene dioxide, glyoxal bis-ethylene acetal and glyoxal bis-o-phenylene acetal. The process is applicable to the treatment of the alkali metal salts of phenol, o-cresol, p-chlorophenol, a - and b -naphthol, a - and b -anthrol, ar.-tetrahydro-a - and b -naphthol, o- and p-benzylphenol, hydroxycarbazoles and hydroxynaphthocarbazoles. In the case of b -naphthol, 2 : 1-hydroxynaphthoic acid is formed at low temperatures and the 2 : 3-isomer at high temperatures, and in order to obtain a good yield of the latter, carbon dioxide should be introduced only after the reaction solution has been heated to 230-270 DEG  C.  The phenolate solutions may be prepared by dissolving the phenolate in the solvent, or by leaching out with the solvent the product of alkali fusion of a sulphonic acid, or by reacting the free phenol in the presence of the solvent with sodium or sodamide, or with caustic alkali with removal of the water formed, e.g. by distilling it off with or without a portion of the solvent or by the use of dehydrating agents, e.g. caustic alkali, calcium oxide, barium oxide or calcium carbide.  In examples: (1) a -naphthol is dissolved in dioxane and treated with sodium hydroxide, and the solution is dehydrated and then saturated with carbon dioxide, producing the sodium salt of 1 : 2-hydroxynaphthoic acid, from which the free acid is liberated with sulphuric acid; (2) b -naphthol is similarly treated, the carboxylation being effected at 50-60 DEG  C. to yield 2 : 1-hydroxynaphthoic acid; (3) sodium naphthalene b -sulphonate is subjected to soda fusion, the product is extracted with dioxane and the solution treated as in (2); (4) a solution of sodium b -naphtholate in dioxane is heated in an autoclave, preferably made of or lined with nickel, to 250 DEG  C., and carbon dioxide is then passed in; alternatively the carboxylation is effected first at 50-60 DEG  C. and then at 240-260 DEG  C., producing a mixture of the sodium salts of 2 : 1- and 2 : 3-hydroxynaphthoic acids; (5) b -naphthol is dissolved in dioxane and treated with potassium and sodium hydroxides and the solution is dehydrated with calcium carbide and treated as in (4); (6) b -naphthol is dissolved in dioxane in an autoclave, caustic soda is added, wet dioxane is distilled off and replaced by dry, the solution is then heated to 250 DEG  C. and carbon dioxide is passed in; (7) in the process of (6), sufficient sodium hydroxide is used to convert only a part of the b -naphthol into its sodium salt; (8) b -naphthol is dissolved in m-dioxane and treated with sodium hydroxide, and the dehydrated solution is treated with carbon dioxide at 85 DEG  C.; (9) b -naphthol is melted with a mixture of stereoisomeric naphthodioxanes prepared by reacting 2 : 3-dichloro-1 : 4-dioxane with ethylene glycol, sodium hydroxide is added, and the solution is dehydrated by distillation and treated with carbon dioxide at 120-130 DEG  C.; (10) b -naphthol is dissolved in benzo-1 : 4-dioxene, sodium hydroxide is added, and the solution is dehydrated by distillation and treated with carbon dioxide at 80 DEG  C.; (11) p-benzylphenol is treated with sodium hydroxide dioxane as in (6), and the solution is treated with carbon dioxide at 150 DEG C. in an autoclave to yield 2-hydroxy-5-benzylbenzoic acid; (12) ar.-tetrahydro-b -naphthol is treated with caustic soda in dioxane as in (6), and the solution is treated with carbon dioxide at 165 DEG C. in an autoclave to produce 5 : 6 : 7 : 8-tetrahydro:2 : 3-hydroxynaphthoic acid; (13) b -anthrol is treated with sodium hydroxide in dioxane as in (6), and the solution is treated with carbon dioxide at 80 DEG  C., yielding 2-hydroxy-1-anthroic acid.