GB794885A - Process for the production of aromatic hydroxy aldehydes - Google Patents

Abstract

Aromatic hydroxy aldehydes are made by reacting at elevated temperature an aromatic hydroxy compound containing on the nucleus carrying the hydroxy group a total of one or two free ortho- or para-positions with hexamethylene tetramine and formaldehyde in the presence of a concentrated mineral acid and an aliphatic carboxylic acid of not more than 5 carbon atoms or an anhydride thereof. In modifications, paraformaldehyde may replace formaldehyde, and a mixture of (a) ammonia or a salt of ammonia with a weak acid and (b) formaldehyde or paraformaldehyde may be used instead of hexamethylene tetramine. Aliphatic carboxylic acids specified are acetic, propionic, butyric and valeric acids, and mineral acids mentioned are sulphuric and hydrochloric. The aromatic hydroxy compounds may be phenols and naphthols and may contain substituents such as methyl and carboxylic groups or halogen atoms. The reaction may be conducted at 90-120 DEG C. by mixing the aromatic hydroxy compound with hexamethylene tetramine and paraformaldehyde in glacial acetic acid with addition of concentrated mineral acid or by addition of acetic acid to a melt of the reactants. Examples describe (1) the preparation of 3 : 5-dichloro-, 3 : 5-dimethyl-, 5-methyl-, 3-methyl-5-chloro-, and 3-chloro - 5 - methyl - 2 - hydroxy - benzaldehydes, 2 - hydroxy - 1 - naphthaldehyde, 2 : 6-dihydroxynaphthalene - 1 : 5 - dialdehyde, 2 : 3-dihydroxynaphthalene - 1 : 4 - dialdehyde, and 2 - hydroxy - 3 - carboxy - 1 - naphthaldehyde; (2) the use of aqueous or gaseous ammonia and paraformaldehyde, and of ammonium carbonate or acetate and paraformaldehyde in place of hexamethylene tetramine is illustrated.