| 摘要 |
The invention comprises 3-hydroxy-2-imino-1(2H)-pyridine sulphonic acid. It may be obtained, together with 2-amino-3-pyridinol, by reacting furfurol in an aqueous medium with chlorine or a compound yielding chlorine under the reaction conditions, e.g. NaOCl, the molar proportion of the two components being 1:1-1.5, reacting the reaction mixture with sulphamic acid or a salt thereof at a pH above 0.5 at a temperature within a range limited by the crystallization point of the reaction mixture and the boiling-point thereof, either isolating the precipitated 3-hydroxy-2-imino-1(2H)-pyridine sulphonic acid monohydrate and, if desired, hydrolysing it into 2-amino-3-pyridinol, or hydrolysing the precipitated monohydrate without previous isolation from the reaction mixture into 2-amino-3-pyridinol. The chlorination reaction is preferably effected at a pH below 6 and at below 40 DEG C. in the presence of a chlorination catalyst, e.g. NaBr, KBr or a molybdenum salt and the subsequent reaction with sulphamic acid is preferably effected at between 0 DEG and 10 DEG C. The 2-amino-3-pyridinol is obtained in the form of its sulphuric acid salt by heating or storing the sulphonic acid monohydrate or the reaction mixture containing it and the free base may be liberated from the salt by the addition of an acid binding agent, e.g. concentrated NaOH solution followed by filtration, or it may be isolated by making the aqueous reaction mixture weakly alkaline and then extracting, e.g. with ether. The desired pH value in each reaction stage of the main process may be attained by adding compounds having a basic or acidic reaction as appropriate. |
