Patent GB-392290-A (GB)
Title: Process for eliminating sulphonic acid groups from anthraquinone-ª-sulphonic acids
IPC: C09B1/20
Filed: 1932-02-03
Abstract: Sulphonic acid groups are eliminated from anthraquinone-b -sulphonic acids containing as homonuclear substituents hydroxy, amino-, alkylamino- or arylamino groups and which may also contain heteronuclear substituents, by treating in aqueous alkali solution in the absence of air and at a temperature about 0 DEG  C. with about one molecular proportion of hydrosulphite for each sulphonic acid group to be eliminated, or a corresponding proportion of another suitable reducing agent, and subsequently heating; the sulphonic groups are eliminated with intermediate formation of leuco-derivatives.  Suitable reducing agents are those which are capable of reducing anthraquinones to leuco-compounds at about 0 DEG C.; zinc dust, aluminium bronze, or metal or metal alloys of like action are specified.  In examples (1) 1-oxy-4-aminoanthraquinone-2-sulphonate is treated in aqueous alkali with about 1 molecular proportion of sodium hydrosulphite at -5 DEG C. until all the parent material is reduced, when the solution is warmed to 40 DEG  C. to give 1 - oxy - 4 - aminoanthraquinone; the hydrosulphite may be replaced by aluminium bronze.  The reaction is similar when 1-amino-4-oxy-anthraquinone-2-sulphonic acid is used: (2) similar treatment to (1) but employing only room temperatures instead of 40 DEG  C. for the final heating converts 1 - amino - 4 - phenylaminoanthraquinone-2.5-disulphonate to 1-amino-4-phenylaminoanthraquinone-5-sulphonate, 1,4-dioxyanthraquinone-2-sulphonate to quinizarin, 1,5 - diamino - 4,8 - dioxyanthraquinone-3,7-disulphonate to 1,5-diamino-4,8-dioxyanthraquinone - 3 - sulphonate, 1,8 - diamino-4,5-dioxyanthraquinone - 3,6 - disulphonate to diaminochrysazin (2 mols. reducing agent): (3) similar treatment of 1-amino-4-phenylaminoanthraquinone-2-sulphonate with final heating to 50-60 DEG  C. yields 1-amino-4-phenylaminoanthraquinone; if the hydrosulphite is added at room temperatures with immediate heating to 50 DEG  C. amino groups are probably eliminated also; the hydrosulphite may be replaced by zinc dust: (4) a mixture of 1,5 - diamino - 4,8 - dioxyanthraquinone - 3,7 - disulphonate and 1,8 - diamino - 4,5 - dioxyanthraquinone-3,6-disulphonate is treated in aqueous alkali with about one molecular proportion of zinc dust at -5 to 0 DEG  C., and then heated to 50 DEG  C. whereby one sulphonic acid group is eliminated; by similar treatment of 1,5 - diamino - 4,8 - dioxyanthraquinone - 3,7 - disulphonic acid in two stages p-diaminoanthrarufin and its monosulphonic acid are derived. Specifications 17206/99, [Class 2, Acids and salts, Organic &c.], 274,558, and 274,966, [both in Class 2 (iii), Dyes &c.], also are referred to.  1-Amino-4-phenylanthraquinone - 2.5 - disulphonic acid is prepared by brominating 1-aminoanthraquinone-5-sulphonic acid to give the 2.4-dibromo derivative, condensing this derivative with aniline and then replacing the 2-bromo atom by a sulphonic acid group by treatment with sodium sulphite.  The Specification as open to inspection under Sect. 91 includes also a reference to the use of hydrogen in the presence of a nickel catalyst for reduction purposes but this subject-matter does not appear in the Specification as accepted.