Flash vacuum pyrolysis (FVP) is a technique in

organic synthesis Organic synthesis is a branch of chemical synthesis concerned with the construction of organic compounds. Organic compounds are molecules consisting of combinations of covalently-linked hydrogen, carbon, oxygen, and nitrogen atoms. Within the gen ...

. It entails heating a precursor molecule intensely and briefly. Two key parameters are the temperature and duration (or residence time), which are adjusted to optimize yield, conversion, and avoidance of intractable products. Often the experiment entails volatilizing a precursor, which is drawn through a "hot zone" followed by rapid condensation. The apparatus typically is conducted under dynamic vacuum. The hot zone must impart heat to the gaseous molecules, so it is generally packed with solids to induce gas-solid collisions. The packing material is generally chemically inert, such as quartz. The precursor (i) volatilizes with gentle heating and under vacuum, (ii) the precursor fragments or rearranges in the hot zone, and finally (iii) the products are collected by rapid cooling. Rapid post-reaction cooling and the dilution inherent in gases both suppress bimolecular degradation pathways.

Examples

The technique is applied to conversions that proceed via unimolecular pathways. 2-Acetoxy dioxane, when heated at 425 °C converts to the highly reactive dioxene, via loss of

acetic acid Acetic acid , systematically named ethanoic acid , is an acidic, colourless liquid and organic compound with the chemical formula (also written as , , or ). Vinegar is at least 4% acetic acid by volume, making acetic acid the main compone ...

. 2-Furonitrile has been prepared by flash-dehydration of 2-furoic acid amide or oxime over

molecular sieve A molecular sieve is a material with pores of uniform size comparable to that of individual molecules, linking the interior of the solid to its exterior. These materials embody the molecular sieve effect, in which molecules larger than the pore ...

s. The strained ring benzocyclobutenone has been prepared by FVP from a simple benzoyl chloride precursor. BenzoCyclobutanoneFVP

References

{{Reflist Pyrolysis Organic reactions Chemical processes