Mechanochemical Synthesis of Two Polymorphs of the Tetrathiafulvalene-Chloranil Charge Transfer Salt: An Experiment for Organic Chemistry

Mechanochemical syntheses avoid or considerably reduce the use of reaction solvents, thus providing green chemistry synthetic alternatives that are both environmentally friendly and economically advantageous. The increased solid-state reactivity generated by mechanical energy imparted to the reactants by grinding or milling can offer alternative synthetic routes, occasionally yielding products (structures or stoichiometries) not obtainable via solution chemistry. Additionally, small volumes of solvents added during grinding can control the polymorphic form of the products. An undergraduate organic chemistry experiment is described involving liquid-assisted grinding (LAG) synthesis of the green and black polymorphs of the tetrathiafulvalene-chloranil (TTF-CA) charge transfer salt and their solid state characterization using FT-IR and melting point analysis.