Green Chemistry for the Classroom: Hydrothermal Synthesis of Organic Compounds

Hydrothermal synthesis (HTS) designates the use of hot liquid water as medium for chemical reactions. The technique is very well established for generating crystalline inorganic materials. Recently it was shown that HTS can also be used to prepare organic compounds, which are all bearing a high content in aromatics and heterocyclics. The technique is environmentally friendly for using solely water as medium, especially in comparison to conventional syntheses of such compounds. Here we present HTS of organic compounds in a fashion that allows for implementing it in the classroom. First, we show how HTS can be used as an example to introduce the timely concepts of green chemistry and sustainable syntheses. Second, we review organic cyclocondensation reactions including reaction equilibrium and enthalpic/entropic driving forces as well as real-life examples of cyclocondensation products, as HTS is especially amenable to cyclocondensations. Third, as liquid high-temperature water is well suited to review the temperature-dependence of certain physicochemical features, we provide interactive plots for exploring these data. Fourth, we develop a classroom friendly HTS of a simple organic colorant, that can be performed simple in kitchen pressure cookers. Fifth, at the hand of this classroom experiment we show how measures for the green-ness of a chemical synthesis, such as the Ecoscale are used.