Acetylpropionyl, or 2,3-propanedione, in an organic compound with properties similar to Diacetyl in terms of flavoring.
Acetylpropionyl has been replacing Diacetyl in the food industry when the latter got bad press for its link to bronchiolitis obliterans, a rare and serious disease of the lungs.
This flavor is also used in the elaboration of receipes of e-liquids.
Acetylpropionyl is authorized as a flavoring substance in the European food industry but its use has become controversial in e-liquids upon the publication of a study by Farsalinos et al. (2014) revealing possible irreversible damages upon inhalation.