Acetic anhydride is a chemical compound with the formula (CH3COO)2. It is an organic compound composed of two acetyl functional groups linked together by an oxygen atom. It is a colorless liquid with a pungent, vinegar-like odor and is highly reactive, producing acetate esters when reacted with alcohols. Acetic anhydride is used in the production of cellulose acetate for films and fibers, as a dehydrating agent in the synthesis of other organic compounds, and as a reagent in organic chemical reactions.
Structure and properties
Acetic anhydride, also known as ethanoic anhydride, has the molecular formula (CH3CO)2O and is a colorless, highly reactive liquid with a strong, pungent odor. It is a highly reactive chemical used as a reagent in organic synthesis.
In terms of structure, acetic anhydride consists of two acetyl (CH3COO-) groups joined by an oxygen atom (-O-). The molecule has a planar geometry and is polar, with the oxygen atom having a negative charge and the carbon atom having a partial positive charge.
The properties of acetic anhydride include its high reactivity, low boiling point, and strong odor. It is a strong irritant to the skin, eyes, and respiratory system, and is also highly flammable. It readily reacts with water to produce acetic acid and is also a strong dehydrating agent, capable of removing water from other organic compounds.
Acetic anhydride is used in a variety of industrial and laboratory applications, including:
- Synthesis of esters: Acetic anhydride is used as a reagent in the production of esters, which are compounds commonly used as solvents and flavors.
- Cellulose acetate production: Acetic anhydride is used in the production of cellulose acetate, a cellulose derivative used to make items such as photographic film, plastics, and textiles.
- Pharmaceutical production: Acetic anhydride is used as a starting material in the production of several types of drugs, including aspirin, and acetaminophen.
- Analysis of organic compounds: Acetic anhydride is used as a reagent in the analysis of organic compounds, such as amino acids, by techniques such as thin-layer chromatography.
- Pesticide production: Acetic anhydride is used in the production of certain types of pesticides, including carbamate pesticides.
The reaction of starch with acetic anhydride
The reaction of starch with acetic anhydride is called esterification. During this reaction, the hydroxyl groups on the starch molecule react with the acetic anhydride to form ester bonds, resulting in the formation of an acetylated starch product. The reaction is typically performed in the presence of an acid catalyst, such as sulfuric acid, which helps to speed up the reaction and increase the yield of the desired acetylated starch product. This reaction can be used to modify the properties of the starch, such as its solubility, viscosity, and thermal stability, making it useful in a variety of industrial applications.
Acetic anhydride is used as a reagent in esterification reactions. In esterification, an alcohol reacts with a carboxylic acid to form an ester and a molecule of water. In this case, acetic anhydride acts as a source of the carboxylic acid moiety and reacts with the hydroxyl groups on the starch molecule to form an ester bond and produce a molecule of acetic acid. This reaction results in the formation of a modified starch known as an acetylated starch.