In the reaction of an aldehyde with malononitrile (Knoevenagel Condensation), the conversion calculation must be based on which of the raw materials (aldehyde or malononitrile)?
In general, the conversion for every reaction is calculated based on the limiting reactant. The limiting reactant is the one which forms the smallest amount of the desired product. In the Knoevenagel reaction, the reactants are consumed 1 to 1. Thus, if you use less aldehyde than malononitrile conversion is calculated based on the aldehyde, if you use more aldehyde than malononitrile, it's based on malononitrile.
To calculate Knoevenagel Condensation conversion, you need to analyse the mixture by HPLC .
Dear Mahdie, I think that Patrick already provided the perfect answer to your interesting technical question. If you run the reaction in a molar ratio of 1:1 then you can calculate the conversion based on any of the starting materials. When e.g. the malononitrile is used in an access, then the calculation should be based on the aldehyde.
In this context you might be interesting in reading the following article in which a "green" version of the Knoevenagel condensation is reported:
The green Knoevenagel condensation: solvent-free condensation of benzaldehydes
Article The green Knoevenagel condensation: solvent-free condensatio...
This useful paper is freely available as public full text on RG.
Good luck with your research!