GB555981A - A process of obtaining ª‡-and ª‰-methylnaphthalene and fractions enriched in either of these compounds - Google Patents

Abstract

555,981. Alpha and beta methylnaphthalene. COULSON, E. A. Feb. 19, 1942, No. 2223. [Class 2 (iii)] Alpha-methylnaphthalene is separated from a mixture of α- and #-methyl naphthalene or a mixture containing the two isomers such as tar oil by a process which comprises sulphonating the mixture to produce the monosulphonic acids of oc- and #-methylnaphthalene and selectively hydrolysing the mixture to desulphonate the greater part of the α-isomer, which is finally recovered. The selective hydrolysis is preferably carried out by heat, and the product recovered by steam distillation. After the separation of the α-isomer, further hydrolysis results in the isolation of the #-isomer. This may be still further purified by sulphonation followed by fractional crystallization from dilute sulphuric .acid. The preferred temperature for the hydrolysis of the α-isomer is at or below 124‹C., and for the #-isomer from 124‹- 150‹C. In examples, (1) A neutral tar fraction boiling between 232‹-240‹C. is treated with 98 per cent. sulphuric acid in the presence of silver sulphate at a temperature below 30‹C. The reaction mixture is poured on crushed ice and the aqueous layer separated from the unsulphonated oil. The aqueous layer is heated to boiling and steam passed through. The α- methyl naphthalene is thus distilled off. The residue is heated to 145‹-150‹C. and again steam-distilled to give a product predominating in #-methyl naphthalene. (2) The fraction rich in #-methyl naphthalene obtained in example (1) is again sulphonated as in example (1) and the product fractionally crystallized and finally desulphonated to give pure #-methyl naphthalene.