1973 Volume 46 Issue 12 Pages 3795-3799
In order to develop fireproof materials, an attempt was made to prepare guanidium condensed phosphates ((H5CN3)n·Hn+2PnO3n+1, n=1–10) by means of a reaction between dicyandiamide (H4C2N4) and ammonium dihydrogen phosphate (NH4H2PO4) in an autoclave; then the conditions of the synthesis were investigated, and the components of the product were also identified. In the synthesis of gaunidium salt by means of a reaction between dicyandiamide and ammonium salt, generally only ammonium salts of strong acid have been used; also, high yields of guanidium salt could not be obtained with the (NH4)2H2PO4 used previously. In the present study, a mixture of 1 mol of H4C2N4 and 2 mol of NH4H2PO4 was heated in an autoclave at 130–300°C; 70–80% of the dicyandiamide was then converted into guanidium salt under the most suitable conditions. The majority of the product is soluble in water (the insoluble part is less than 3.5% at 150–220°C), and the solution is almost neutral. The components of the soluble part were 25–26% N and 20–24% P, the mole ratio of N to P being 2.8–2.5; this ratio decreased with an increase in the reaction temperature. On the other hand, the phosphates in the product consist of ortho-, pyro-, tri-, and middlepoly phosphates (n=4–10). The guanidium condensed phosphates thus obtained can be utilized as useful flame retarders for paper and wood, as guanidium orthophosphate can be.
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