Thermally evolved gases from thiourea complexes of CuCl in airDetailed comparisons by TG-FTIR and TG/DTA-MS for compounds poor and rich in thiourea

Detailed identification and monitoring of gaseous species released during thermal decomposition of two thiourea (tu) complexes of CuCl, one of them, Cu(tu)Cl 1/2H2O (1) poor, while the other, Cu(tu)3Cl (2) rich in thiourea, have been carried out in flowing air atmosphere up to 800 °C by both coupled TG-EGA-FTIR and simultaneous TG/DTA-EGA-MS. The thermal decomposition of 1, prepared actually from CuCl, has shown evolution of similar gas mixture and dynamics by TG/DTA-MS, as had been measured with TG-FTIR and published earlier, except that no evolution of ammonia has been detected, at all. Probably, the intense co-evolution of acidic vapors (HCl and SO2) has prevented NH3 to reach the ionization chamber of the mass spectrometer. While in case of anhydrous 2, Cu(tu)3Cl rich in thiourea, between 180 and 240 °C, the main gaseous decomposition products are ammonia (NH3), carbon disulfide (CS2), and isothiocyanic acid (HNCS). At about 250 °C, gas-phase exothermic oxidation of CS2 and HNCS vapors occurs, resulting in a sudden release of sulfur dioxide (SO2), carbonyl sulfide (COS), and hydrogen cyanide (HCN). Also a definite evolution of cyanamide (H2NCN) is observed just above 250 °C. Between 350 and 500 °C, a more intense oxidation process of both organic condensed residues and copper(I) sulfides into copper(II)-oxo-sulfates appears, which is also indicated by intense evolution of CO2, SO2, and H2NCN (and/or HNCO). Above 700 °C, the oxo-sulfates start to decompose resulting in repeated evolution of SO2. All species identified by FTIR gas cell have been also confirmed by mass spectrometry. Evolution of HCl from Cu(tu)3Cl (2) has been detected by either of the two EGA methods.