Electrolytic Production of Aminoguanidine Bicarbonate' T. Duraiswamy Balakrishnan, K. Shrivara Udupa, G. Srinivasan Subramanian, and H. Venkatakrishna Udupa Central Electrochemical Research Institute, Karaikudi-3, S . Rly, Madras, India
The paper gives some preliminary details of the studies made on the electrolytic reduction of nitroguanidine to aminoguanidine using the rotating cathode technique which hus simplified the design of large scale cells. The reduction proceeds with high efficiency (85%) even at high current density conditions (up to 20 A/dm2). Lead, amalgamated lead, and zinc are suitable materials for the cathode, and the results are reproducible on a zinc surface. The catholyte is similar to that used by Sugino and Yamashita and i s a 3070 aqueous solution of ammonium sulfate. The reduction proceeds via nitrosoguanidine, and it is necessary to keep the temperature below 18' C to get good yields of aminoguanidine. The estimation of aminoguanidine and its isolation as a bicarbonate are also briefly enumerated.
A m i n o g u a n i d i n e and its salts are largely used for synthesis of a variety of products, the most important being 1,2,4aminotriazole which is largely used as a weedicide in cotton plantations. T h e demand for aminotriazole in India is estimated t o be of the order of 200-300 tons/year and there is no established production of aminoguanidine in the country. T h e object of this investigation is to work out a suitable electrochemical method for the synthesis of aminoguanidine bicarbonate. T h e chemistry of aminoguanidine has been reviewed by Lieber and Smith (1939) and more recently by Kurzer and Godfrey (1962). Aminoguanidine is synthesized in three ways: b y reduction of nitroguanidine; b y hydrazinolysis (replacement of other groups b y hydrazine) ; and by hydrazinatioh (addition of hydrazine). Among the three methods, the reduction of nitroguanidine is the most suitable because of the economy and the ease of preparation of the starting material, namely nitroguanidine. The other two methods are of greater importance in the preparation of substituted aminoguanidine. The chemical method of reduction of nitroguanidine, carried out b y the use of zinc with ammonium chloride, has been dealt with in detail in organic syntheses (Shriner e t al., 1947). Under the best of conditions, i t is not possible to get more than 63-64y0 of the material yield. T h e electrochemical methods of reducing nitroguanidine have also been studied in detail by a number of workers and the references to previous work in this field are given b y Fichter (1942). T h e usual conditions employed are the use of dilute sulfuric acid as catholyte and various metals like tin (Spreter and Briner, 1949) or mercury as cathodes (Pathy, 1965; Shreve and Carter, 1944). Yamashita and Sugino (1957) have appreciated the importance of p H of the catholyte in this reduction and have shown that the reduction proceeds via the nitroso stage, the formation of nitrosoguanidine being favored a t p H 8 to 9. Accordingly, they have reduced nitroguanidine in a n ammonium sulfate bath and have established good yields of aminoguanidine under these conditions. iicareful appraisal of these conditions reveals t h a t yields as high as 80 to 90% of aminoguanidine are obtained only 1 Address correspondence to S. Gopal, Central Electrochemical Research Institute, Karaikudi 3, Madras, India.
after passing 1 times t,he theoretical current so that the overall current efficiencies are only of the order of 50-55yoo. Moreover, the current densities employed by them are also of the low order, less than 5 A/dm2. The advantages of the rot'at,ing cathode technique in electrochemical reductions have been well established b y studies carried out in these laboratories, and the suitability of such a technique for the reduction of nitroguanidiiie to aminoguanidine was investigat'ed. The technique has made the design of large scale cells possible, and based on t'he dat'a obtained, high amperage (300 X) cells were designed and worked successfully. Experimental
Chemicals. T h e ammonium sulfate used was
