What Is Diacetyl?
Diacetyl is a yellow-green liquid known for its strong, characteristic odor. Its chemical formula is C4H6O2, with a molecular weight of 86.09, and its CAS number is 431-03-8. It comprises two acetyl groups linked to a carbonyl group’s carbon. The IUPAC name for diacetyl is 2,3-butanedione.
Present naturally in alcoholic beverages, diacetyl is also added to various foods as a flavoring agent, imparting a buttery flavor due to its butter-like aroma when diluted.
Uses of Diacetyl
Diacetyl finds extensive use in the food industry, particularly as a flavoring agent in margarine, butter and cheese-flavored snack foods, wine, and vinegar. It’s also employed as a liquid flavoring in e-cigarettes. During the brewing process of beer and other alcoholic beverages, diacetyl is naturally produced by microorganisms. The brewing process is controlled to manage diacetyl levels, as excessive amounts can negatively impact the beverage’s aroma.
Properties of Diacetyl
Diacetyl boasts a melting point of -2°C, a boiling point of 88°C, and a density of 0.99 g/mL. It is flammable, with a flash point of 6°C and a spontaneous combustion point of 365°C. Its explosive vapor-air mixtures and solubility in water (20 g/100 mL) make it notable, along with its miscibility in most organic solvents. Diacetyl is also a natural fermentation byproduct, formed through thiamine pyrophosphate-mediated condensation of pyruvate and acetyl CoA in some bacteria.
Structure of Diacetyl
Diacetyl and other vicinal diketones are distinguished by the long carbon-carbon bond between the two carbonyl centers, measuring 1.54 Å compared to 1.45 Å in 1,3-butadiene. This bond elongation results from the repulsive forces between the polarized carbonyl carbon centers.
Other Information on Diacetyl
1. Diacetyl Production Method
Diacetyl is primarily produced by dehydrogenating 2,3-butanediol, with acetoin serving as an intermediate. An alternative method involves hydrolyzing methyl ethyl ketone with sodium nitrite and hydrochloric acid.
2. Regulatory Information
Although not designated under specific environmental or poisonous substance control laws, diacetyl is classified as a flammable liquid, and a hazardous and noxious substance, requiring careful handling.
3. Handling and Storage Precautions
Handling and storage precautions include keeping the container tightly closed in a cool, dry, and well-ventilated area, away from heat and ignition sources. It’s important to wear appropriate protective gear and to take special precautions due to the risk of irreversible obstructive pulmonary disease upon exposure.