Catalyst Free Single Step Specific Determination of Hydrazine in UH 25 blend and Determination of Propellant Grade UH 25 blend Using Thiophenes with Active Carbonyl Groups

Abstract

Hydrazine and its derivatives such as monomethyl hydrazine (MMH), unsymmetrical dimethyl hydrazine (UDMH), and UH25 (a blend of 75 % UDMH and 25 % hydrazine hydrate by w/w) namely hydrazines are used as fuels (in liquid form) for rocket stages and satellites. They are hypergolic and well‐known toxic compounds. Workplace atmospheres involving vapours / liquid forms of these hydrazines need to be routinely monitored and screened. Simple, economical, and rapid kinetic spectrophotometric techniques are developed to meet the requirements by using thiophene‐3‐carboxaldehyde and 3‐butenone (E)‐1,1,1‐trifluoro‐4‐(3‐thienyl) (CF3enone) and compared. Classical −CHO based technique is applied for UH25 blend (in aqueous medium) in the presence of an acid catalyst. CF3enone based technique is used to determine hydrazine (Hz) in UH25 (in organic medium) selectively at levels as low as 0.05 mM without any catalyst. Variables such as temperature and concentration are optimized to determine UH25 in the concentration range of 0.5 mM to 0.1 M for thiophene‐3‐carboxaldehyde and to determine Hz of UH25 blend in the concentration range of 0.1 mM to 0.6 mM for CF3enone. Minimum detectable limits are found for UH25 and Hz of UH25 blend in the respective studies. GC‐MS study is also carried out to meet the unequivocal identification requirement. Initial rate and fixed time methods are adopted as calibration procedures. Orders of the reactions are found in both studies. Both techniques are simple and rapid after the chemisorption process with derivatizing agents in which pre‐treatment, pre‐concentration, and extraction steps are not involved. Advantages of CF3enone based technique over aldehyde‐based classical technique are 1) requirement of the minimum concentration of derivatizing agent 2) no catalyst 3) selectivity and specificity towards hydrazine in UH25 blend 4) shortened analysis time 5) linear dynamic range at very low concentrations of UH25.