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Acetaldehyde (ethanal), CH3CHO [75-07-0], was observed in 1774 by Scheele during reaction of black manganese dioxide and sulfuric acid with alcohol. Its constitution was explained in 1835 by Liebig who prepared pure acetaldehyde by oxidation of ethanol with chromic acid and designated this product “aldehyde,” a contraction of the term “alcohol dehydrogenatus.”
Acetaldehyde is a mobile, low-boiling, highly flammable liquid with a pungent odor. Because of its high chemical reactivity, acetaldehyde is an important intermediate in the production of acetic acid, acetic anhydride, ethyl acetate, peracetic acid, butanol, 2-ethylhexanol, pentaerythritol, chlorinated acetaldehydes (chloral), glyoxal, alkyl amines, pyridines, and other chemicals. The first commercial application was the production of acetone via acetic acid between 1914 and 1918 in Germany (Wacker-Chemie and Hoechst) and in Canada (Shawinigan).
Occurrence. Acetaldehyde is an intermediate in the metabolism of plant and animal organisms, in which it can be detected in small amounts. Larger amounts of acetaldehyde interfere with biological processes. As an intermediate in alcoholic fermentation processes it is present in small amounts in all alcoholic beverages, such as beer, wine, and spirits. Acetaldehyde also has been detected in plant juices and essential oils, roasted coffee, and tobacco smoke.
Commercial production processes include dehydrogenation or oxidation of ethanol, addition of water to acetylene, partial oxidation of hydrocarbons, and direct oxidation of ethylene. In the 1970s, the world capacity of this last process, the Wacker-Hoechst direct oxidation, increased to over 2×106 t/a. However, the importance of acetaldehyde as an organic intermediate is now steadily decreasing, because new processes for some acetaldehyde derivatives have been developed, such as the oxo process for butanol and 2-ethylhexanol and the Monsanto process for acetic acid. In the future, new processes for acetic anhydride (Halcon, Eastman, Hoechst), for vinyl acetate (Halcon), and for alkyl amines (from ethanol) will diminish the use of acetaldehyde as a starting material.
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