Thermal hazards of the Vilsmeier-Haack reaction on N,N-dimethylaniline

From literature data and a preliminary calorimetric study it is clear that the Vilsmeier-Haack reaction poses specific thermal hazards as both the Vilsmeier-Haack intermediate (1) in N,N-dimethylformamide (2) and the reaction mixture with N,N-dimethylaniline (3) are thermally unstable and can generate high and fast temperature and pressures rises when heated. Therefore alternatives were investigated for their thermal hazards. The stability of Vilsmeier intermediates generated from a series of other formamides was investigated. In principle the Vilsmeier intermediate could be generated and converted in situ, thus avoiding large amounts of an unstable intermediate in the process vessel and yielding the same reaction mixture. This concept could also be applied to the other formamides studied, and this option was also included in the investigation.