Patent GB-811504-A (GB)
Title: Improvements in and relating to nuclear carboxylation
IPC: C07C51/15
Filed: 1955-08-08
Abstract: A process for the nuclear carboxylation of an aromatic hydroxy compound comprises reacting an esterified phenolic compound having at least one hydrolysable acylated hydroxyl group joined directly to an aromatic nucleus with carbon dioxide and potassium carbonate.  The reaction product is hydrolysed to form an hydroxy aromatic carboxylic acid.  Only a minor proportion of the carbonate employed need be potassium carbonate and mixtures thereof, e.g. with sodium or lithium carbonate may be employed. Carbon dioxide gas may be introduced into the reaction system or may be generated in situ from the carbonate. Ordinary or elevated temperatures and pressures may be used and the reaction may be carried out in the presence of solvents, e.g. benzene, toluene, xylene, hexane, petroleum ethers and other non-polar solvents. The reaction product is hydrolysed with water alone, aqueous acid, e.g. hydrochloric acid or alkali, e.g. sodium hydioxide. The preferred acylated starting materials may be represented by the formula <FORM:0811504/IV (b)/1> wherein the group <FORM:0811504/IV (b)/2> represents an acylated hydroxyl group R, preferably being an alkyl group of 1-4 carbon atoms, <PICT:0811504/IV (b)/1> represents an aromatic nucleus of one or more carbocyclic rings, Z represents hydrogen or an hydroxyl, alkoxy, alkyl, aralkyl, aryl or amino group and x and y are either 0 or 1.  Starting materials mentioned include phenyl acylates of the formula <FORM:0811504/IV (b)/3> wherein Z and <FORM:0811504/IV (b)/4> have the meanings given above such as acetates, propionates and butyrates of phenol, cresols and m-aminophenol; phenyl diacylates of the general formula <FORM:0811504/IV (b)/5> wherein Z and <FORM:0811504/IV (b)/6> have the meanings given above such as hydroquinone diacetate, toluhydroquinone diacetate and the corresponding dibutyrates; partial esters of the general formula <FORM:0811504/IV (b)/7> wherein <FORM:0811504/IV (b)/8> has the meaning given above such as the mono-acetate, propionate and butyrate of hydroquinone and toluhydroquinone monoacetate, acyl esters of b -naphthol or substituted naphthols and esters of polyhydroxy compounds such as trihydroxy benzene, 5-amino-1-naphthoic acid or an ester of 2-hydroxydiphenylene oxide.  In examples: 2:5-dihydroxy and gentisic acids are obtained by heating hydroquinone diacetate with anhydrous potassium carbonate, benzene and carbon dioxide and hydrolysing the products (1-3); in a similar process ferrous sulphide is also present (4); gentisic acid only is obtained in a process similar to (1) (5); salicylic, p-hydroxybenzoic and 4-hydroxy isophthalic acid is obtained from the products resulting from the heating of phenyl acetate, potassium carbonate and benzene under pressure (6), gentisic acid is obtained from hydroquinone dibutyrate in a process similar to (1) (7); gentisic and 2:5-dihydroxy benzoic acids are obtained in a process similar to (1) in which carbon dioxide is added in solid form and no solvent is employed (8); salicylic and p-hydroxybenzoic acid are obtained using phenyl acetate in a process similar to (8), (9); in a similar process benzene and solid carbon dioxide are included in the reaction mixture (10); salicylic and 4-hydroxyphthalic acids are obtained in a similar process (11); salicylic and p-hydroxybenzoic acids are obtained by a process similar to (10), (12); salicylic and p-hydroxybenzoic acids are obtained by heating phenyl acetate with potassium carbonate and xylene under reflux (13); salicylic, p-hydroxy-benzoic and 4-hydroxyisophthalic acids are obtained by heating phenyl acetate with a mixture of potassium carbonate, sodium carbonate and solid carbon dioxide (14); 3- and 4-tertiary butyl 2:5-dihydroxybenzoic acids are obtained from the products obtained by heating hydroquinone diacetate with potassium carbonate under pressure with carbon dioxide (15) and (16); 2-hydroxy-5-methyl benzoic acid is similarly obtained using p-cresol acetate as starting material (17); m-aminophenol carboxylates are obtained by heating m-aminophenol diacetate with potassium carbonate and carbon dioxide in an autoclave (18); 2-hydroxy-5-methoxy benzoic acid is similarly obtained from hydroquinone monomethyl ether acetate (19); 1:4-naphthohydroquinone monomethyl ether acetate is monocarboxylated similarly (20) and carboxylated derivatives of toluhydroquinone (21) and hydroxyhydroquinone are similarly obtained.