Evolved gas analysis of dichlorobis(thiourea)zinc(II) by coupled TG-FTIR and TG/DTA-MS techniques

Identification and monitoring of gaseous species released during thermal decomposition of the title compound 1, Zn(tu)₂Cl₂, (tu=thiourea, (NH₂)₂C=S) have been carried out in flowing air atmosphere up to 800°C by both online coupled TG-EGA-FTIR and simultaneous TG/DTA-EGA-MS. The first gaseous products of 1, between 200 and 240°C, are carbon disulfide (CS2) and ammonia (NH₃). At 240°C, an exothermic oxidation of CS₂ vapors occurs resulting in a sudden release of sulphur dioxide (SO₂) and carbonyl sulphide (COS). An intense evolution of hydrogen cyanide (HCN) and beginning of the evolution of cyanamide (H₂NCN) and isothiocyanic acid (HNCS) are also observed just above 240°C. Probably because of condensation and/or polymerization of cyanamide vapors on the windows and mirrors of the FTIR gas cell optics, some strange baseline shape changes are also occurring above 330°C. Above 500°C the oxidation process of organic residues appears to accelerate which is indicated by the increasing concentration of CO₂, while above 600°C zinc sulfide starts to oxidize resulting in the evolution of SO₂. All species identified by FTIR gas cell were also confirmed by mass spectrometry, except for HNCS. This revised version was published online in July 2006 with corrections to the Cover Date.