Acrolein condenses with acetaldehyde and amines to give methylpyridines. Overheated cooking oils emit acrolein and formaldehyde. Chlorine-free processes from propylene include the synthesis of glycerol from acrolein and propylene oxide. Examples of unsaturated carbonyls are acrolein (propenal), mesityl oxide, acrylic acid, and maleic acid. The glycerol route begins with pyrolysis to acrolein, which undergoes ammoxidation to give acrylonitrile. It is produced industrially by condensation of acrolein, ammonia, and formaldehyde. Dehydration of glycerol gives acrolein which condenses with the amine followed by a cyclization. An example is the production of acrylic acid from acrolein, propylene and propane. In alternative fashion, propylene can be oxidized to acrolein, which upon hydrogenation gives the alcohol. The main metabolic pathway for acrolein is the alkylation of glutathione. The degradation of glycerol by some strains of LAB can yield the compound acrolein. The carcinogen acrolein and its derivatives also contribute to the chronic inflammation present in COPD. Acrolein is prepared industrially by oxidation of propene. These two anticancer agents, "in vivo", may be converted to urotoxic metabolites, such as acrolein. Propane represents a promising but challenging feedstock for the synthesis of acrolein (and acrylic acid).