3. Comparison of techniques

Choosing the right method for a solvent-free reaction is not always a straightforward task, as not all methods will be suitable for every type of reaction. An example of a reaction comparing the efficiency of different methods for nitrone synthesis in the absence of solvent is described below.

Nitrones are important intermediates in organic synthesis. Among the various methods used to prepare them, the condensation reaction between an aldehyde and a hydroxylamine substituted on the nitrogen atom, in the presence of a base, is the most widely exploited. The condensation reaction can be carried out at different temperatures (cold, ambient or reflux) and reaction times are variable (from a few hours to two days), depending on the substrates. Anhydrous conditions and an excess of aldehyde are always required to achieve good yields (60-95%), chromatographic purification...