Structural, Spectral, Biological and Electrochemical Studies Of Some ...

that the condensation reaction is initiated at the beginning and later the
transamination surpasses the condensation in the presence of solvent. It is reported
that condensation of carbonyl compound with 4-methyl-4-phenyl-3­
thiosemicarbazide results in the formation of thiosemicarbazones and attack of the
thiocarbonyl group of it by an amine gives a tetrahedral intermediate. Loss of N­
methyl aniline from these intermediate results in reformation of the thiocarbonyl
group and completes the transamination process. It is also noticed that deactivated
amines decelerates transamination process and in such cases, the major product is the
non-transaminated one. Refluxing time also plays a major role in shaping the
product. Longer refluxing time produces a mixture of transaminated and non­
transaminated product and even dithiourea derivatives [10].
The percentage oftautomer in the mixture ofproduct depends on the mode of
preparation and basicity of the medium. The more polar the medium and higher the
pH of the product, more will be the percentage of thiol tautomer in the mixture.
However re-crystallization from the solvent increases the percentage of thione
tautomer. The appearance of the crystals depends on the nature of the solvent used
and method adopted for their crystallization. To certain extent the shades of the
product depends on the amine used up for transamination. Our attempts to effect the
transamination with pyridine, piperidine and pyrimidine in methanol remained
unsuccessful.
2.8 Characterization ofligands
The colours, melting points and partial elemental analyses of the ligands are listed in
Table 2.1. All N-N-S donor ligands are pleasant yellow non-hygroscopic crystalline
substances and O-N-S donors are pale yellow non-hygroscopic crystalline substances.
2.8.1 IR spectral characterization
The tentative assignments of the IR spectral bands to establish the structural identity
of the ligands are listed in Table 2.2
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