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Although slower reacting than acid chlorides, anhydrides react with water to form carboxylic acids, with alcohols to form esters, and with amines to form amides. Anhydrides can also be reduced to 1 o alcohols by hydride reduction.
Acid Anhydrides react with water to form carboxylic acids. General Reaction. Example 1: Mechanism. 1) Nucleophilic Attack by the water molcule. 2) Deprotonation by pyridine. 3) Leaving group removal. 4) Protonation of the carboxylate. Acid Anhydrides react with alcohols to form esters. Reactions of anhydrides use Pyridine as a solvent. Example 1:
This page looks at the reactions of acid anhydrides with water, alcohols and phenols (including the manufacture of aspirin). These reactions are all considered together because their chemistry is so similar. There is also a great similarity between acid anhydrides and acyl chlorides (acid chlorides) as far as these reactions are concerned.
To form an acid anhydride, a water molecule is lost in a condensation reaction between two carboxylic acids. This is why acid anhydrides are called anhydride – lack of water.
Reactions of Acid Anhydrides. The chemistry of acid anhydrides is similar to that of acid chlorides, although anhydrides react more slowly. Thus, acid anhydrides react with water to form acids, with alcohols to form esters, with amines to form amides, and with LiAlH 4 to form primary alcohols.
Acid anhydrides react with alcohols to produce esters as shown in the reaction below. The reactions of anhydrides frequently use pyridine as a solvent. A carboxylic acid is also produced, but is not considered a synthetic product.
The reactions (of both acyl chlorides and acid anhydrides) involve things like water, alcohols and phenols, or ammonia and amines. All of these particular cases contain a very electronegative element with an active lone pair of electrons - either oxygen or nitrogen.
