Thermal analysis of fusion and decomposition processes was carried out on organosulphur and organoselenium compounds in order
to establish thermal stability criteria. Degradation and fusion temperatures of 20 biological active compounds, synthesized
by our research group were determined using thermogravimetry (TG) and differential scanning calorimetry (DSC). Analysis of
the thermal data indicated that: (a) in general, sulphur compounds are more stable than selenium compounds; (b) the pyridine
ring diminished stability of sulphur and selenium compounds much more than the carbocyclic aromatic rings did (6a > 9a; 2b > 3b);
(c) selenomethyl derivatives are more stable than selenoethyl and selenoisopropyl compounds; (d) a chlorine atom on selenocompounds
has surprising effects.