Studies of hydrazinium salts

Abstract

The present investigation aims at synthesis, characterization, reactivity, thermal properties and applications of some of the hydrazinium salts. In the introductory Chapter, a literature survey on the chemistry of hydrazine and its derivatives is presented. The scope and the objective of the present investigation are highlighted. Chapter II is devoted to the analytical procedures and instrumental methods employed in the present study. The instrumental methods used are magnetic susceptibility measurements, differential thermal analysis (DTA), thermogravimetry (TG), differential scanning calorimetry (DSC), X?ray powder diffraction and infrared, nuclear magnetic resonance and Mössbauer spectroscopy and mass spectrometry. In Chapter III, synthesis, characterization and thermal properties of some hydrazinium salts such as acetate, metavanadate, thiocyanate, sulfamate, picrate, sulfite, sulfate and phosphates have been discussed. The hydrazinium salts have been prepared by the reaction of hydrazine hydrate with the corresponding ammonium salts. The thermal decomposition studies show that all the hydrazinium salts except hydrazinium acetate decompose exothermically. Hydrazinium thiocyanate melts and rearranges at 80°C to thiosemicarbazide. Hydrazinium metavanadate is probably the first hydrazinium salt reported containing an oxyacid of a metal ion. Chapter IV: Hydrazinium bisulfate, N?H?HSO?, has been prepared and its physico?chemical and thermal properties have been studied and compared with those of hydrazonium sulfate, N?H?SO?, and dihydrazinium sulfate, (N?H?)?SO?. Hydrazinium bisulfate decomposes to a mixture of ammonium sulfate and ammonium bisulfate, whereas hydrazonium sulfate and dihydrazinium sulfate decompose to ammonium bisulfate. From the vacuum DTA experiments, it appears that all the three hydrazine sulfates decompose to ammonium sulfate initially. Activation energies for their decomposition have been determined to differentiate the decomposition path. Chapter IV, Appendix: Hydrazonium sulfate, N?H?SO?, exists in orthorhombic and monoclinic modifications at room temperature. The orthorhombic form of N?H?SO? is reported to undergo a phase transition at 208°C. During the course of our study on N?H?SO? by DSC, it has been observed that this phase transition is sluggish and partially reversible. Further, this phase transition temperature decreases with increase of particle size. This unusual dependence of phase transition temperature on particle size has been explained by extending the melting?point theory of Reiss and Wilson to solid?state phase transformation. From the DSC studies of N?H?SO?, it appears that it is the strain energy and not the surface energy which controls the phase transformation. The enthalpy of the phase transformation is determined to be 0.867 kcal·mol?¹. Chapter V deals with the reactivity of hydrazinium thiocyanate, N?H?SCN, and hydrazinium hydrazinocarboxylate. Reaction of N?H?SCN with bivalent metal ions such as Mn, Fe, Co, Ni, Zn, Cd and Mg results in the formation of the complex [M(N?H?)?(NCS)?], whereas Cu(NCS)? is formed with Cu(II) salts. This reaction of N?H?SCN with Cu(II) salts has been used for the quantitative estimation of copper. The complexes of the type [M(N?H?)?(NCS)?] have been characterized by chemical analysis, X?ray powder diffraction, magnetic susceptibility and infrared and Mössbauer spectroscopy. The thermal decomposition of [M(N?H?)?(NCS)?] (where M = Mn, Fe, Co, Ni, Zn, Cd and Mg) has been studied in air and nitrogen atmosphere. The thermal decomposition of the complexes in nitrogen leads to the formation of the corresponding metal sulfides through M(NCS)? (M = Mn or Zn) or M(SCN)(CN) (M = Mg, Cd, Fe, Co or Ni) intermediate. The thermal stability of these complexes follows the Irving–Williams order: Mn < Fe < Co < Ni > Zn > Cd. Hydrazinium hydrazinocarboxylate has been accidentally found to react with acetonitrile at ambient conditions to form 4?amino?3,5?dimethyl?1,2,4?triazole and 3,6?dimethyl?1,2,4,5?tetrazine. The probable reaction mechanism has been proposed. Chapter VI: Monohydrazinium phosphate, N?H?H?PO? (MHP), and dihydrazinium phosphate, (N?H?)?HPO? (DHP), have been investigated as flame retardants. When a piece of cellulose paper treated with 2% hydrazinium phosphate was ignited, it carbonized without flame. The flame?retardant property of MHP and DHP on cellulose has been investigated using TG, DTA and mass spectrometry. From DTA and TG experiments it appears that the phosphate present in the hydrazinium phosphates acts in the condensed phase to minimize the depolymerization of cellulose and stimulate dehydration with the formation of more char. Both DTA and TG results are supported by the mass?spectrometric analysis of gaseous products of pyrolysis of treated and untreated cellulose. The flame?retardant property of DHP has been compared with those of diammonium phosphate, (NH?)?HPO? (DAP), and phosphoric acid, H?PO? (PA). The results of the investigations indicate that MHP, DHP and PA are equally good in retarding the flame.