Hydrazinium phosphates

From the thermal decomposition of mono- and dihydrazinium phosphates it appears that both salts decompose through the intermediate formation of N2H5HP2O6 leading to metaphosphoric acid. Further, their decomposition patterns follow the corresponding decomposition pattern of ammonium salts. However, hydrazinium phosphate salts are of interest as superior flame retardants because of the hydrophilic nature or hygroscopic property of the hydrazinium ion. This supports dehydration more efficiently and limits the production of hydrocarbon gases, thereby promoting flame retardancy (see Chapter 6, Section 6.2.4). 

Monohydrazinium phosphate (MHP) and dihydrazinium phosphate (DHP) have also been investigated as flame retardants of cellulose and compared with the corresponding ammonium phosphates [6,7]. The flame retardant property of hydrazinium phosphates is checked using a Whatman No. 40 filter paper with an ash content of 0.018% as the cellulose source. This filter paper is treated with hydrazinium phosphates by dipping it into aqueous solutions of selected concentrations of 2.5% and 10% to ensure that the desired weight of phosphate is retained on the sample. The samples are then dried in air and used in pyrolysis experiments. 

Molybdenum blue method. When arsenic, as arsenate, is treated with ammonium molybdate solution and the resulting heteropolymolybdoarsenate (arseno-molybdate) is reduced with hydrazinium sulphate or with tin(II) chloride, a blue soluble complex molybdenum blue is formed. The constitution is uncertain, but it is evident that the molybdenum is present in a lower oxidation state. The stable blue colour has a maximum absorption at about 840 nm and shows no appreciable change in 24 hours. Various techniques for carrying out the determination are available, but only one can be given here. Phosphate reacts in the same manner as arsenate (and with about the same sensitivity) and must be absent. 

A. Molybdenum blue method Discussion. Orthophosphate and molybdate ions condense in acidic solution to give molybdophosphoric acid (phosphomolybdic acid), which upon selective reduction (say, with hydrazinium sulphate) produces a blue colour, due to molybdenum blue of uncertain composition. The intensity of the blue colour is proportional to the amount of phosphate initially incorporated in the heteropoly acid. If the acidity at the time of reduction is 0.5M in sulphuric acid and hydrazinium sulphate is the reductant, the resulting blue complex exhibits maximum absorption at 820-830 nm. 

Jonsson, P.G. and Liminga, R. (1971) Hydrogen bond studies. Neutron diffraction study of hydrazinium dihydrogen phosphate N2H5H2PO4. Acta Chemica Scandinav-ica (Copenhagen, Denmark 1989), 25, 1729-1741. 

The product has been characterized by chemical analysis and IR spectra (z/n n at 960 cm ). Table 2.7 lists the type of bond and the peak position for mono- and dihydrazinium phosphates. The very similar N—N stretching frequency characteristic of N2H5 in both these salts indicates the presence of the same hydrazinium cation. 

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