Willgerodt-Kindler Reaction of Benzaldehydes: A Comparative Study for a Sustainable Synthesis of Secondary Thiobenzamides
The synthesis of thiobenzamides from benzaldehydes, elemental
sulfur and cyclic secondary amines was carried out by
Willgerodt-Kindler reaction following three different protocols,
avoiding the harsh conditions usually reported in the literature.
Protocol A was solventless, protocol B was in acetonitrile, while
protocol C was electrochemical in acetonitrile (using electrogenerated
acetonitrile anion). For all protocols the temperature
was 60 8C. In all cases, a stoichiometric amount of reagents was
used, with waste lessening with respect to literature syntheses.
Good to high yields were obtained by chemical or electrochemical
methods, neat or in acetonitrile. Advantages and
limits of these sustainable syntheses are highlighted. A
mechamism hypothesis is reported for the reaction induced by
electrogenerated acetonitrile anion.