Acid anhydrides are chemical compounds that look like, and sometimes are, the product resulting from dehydration of an acid. Most commonly, they form the acid when mixed with water. In organic chemistry, the acids involved are often carboxylic acids; for such cases, please see carboxylic anhydride. A chemical compound is a chemical substance formed from two or more elements, with a fixed ratio determining the composition. ... An acid (often represented by the generic formula HA) is traditionally considered any chemical compound that, when dissolved in water, gives a solution with a pH of less than 7. ... Organic chemistry is a specific discipline within the subject of chemistry. ... Structure of a carboxylic acid The 3D structure of the carboxyl group A space-filling model of the carboxyl group Carboxylic acids are organic acids characterized by the presence of a carboxyl group, which has the formula -(C=O)-OH, usually written as -COOH. In general, the salts and anions... Acid anhydrides have the general formula (RCO)2O, and appear to be the dehydration product of two carboxylic acid molecules. ...
Classically, simple anhydrides arise via the following reaction:
2 XOH → X2O + H2O
In principle, such a conversion could describe all known oxides and hydroxides. In practice those of greatest interest have both a stable acid and a stable anhydride.
For a typical mineral acid with formula HxEOy, the fully dehydrated compound has formula EOy-x/2 or E2O2*y-x.
Glacial acetic acid boils at 118°C, and has a density of 1.049 g/mL at 25°C. It is flammable with a flash point of 39°C. Through hydrogen-bonding interactions, acetic acid is miscible (mixable) in all proportions with water, ethyl alcohol, and diethyl ether.
Acetic anhydride is a clear, colorless, mobile (free-flowing) liquid with a sharp odor similar to that of acetic acid.
Acetic anhydride melts at 73°C, boils at 139°C, and has a density of 1.080 g/mL at 15°C. It is flammable with a flash point of 54°C. This compound is readily combustible and represents a fire hazard.
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