Acetic acid (ethanoic acid in the IUPAC system; as figure 10.16 indicates) is by far the most important carboxylic acid. Lt is manufactured industrially by oxidizing acetaldehyde (figure 10.18), a raw material obtained by oxidizing ethanol or hydrating acetylene. Acetic acid is also formed in vinegar, as Acetobacter bacteria oxidize ethanol. Vinegar, which contains about 5 percent acetic acid in water, has been used for centuries to flavor foods. But glacial acetic acid (100 percent acetic acid) is toxic (LD50=3.5 g/kg). The first person to synthesize acetic acid directly from chemical elements was Adolph Kolbe (German, 1818-84) in 1845. Acetic acid is used in the manufacture of cellulose acetate, vinyl acetate, drugs, insecticides, photographic chemicals, and food additives.