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An ester of a carboxylic acid.R stands for any group (typically hydrogen or organyl) and R ′ stands for any organyl group.. In chemistry, an ester is a compound derived from an acid (organic or inorganic) in which the hydrogen atom (H) of at least one acidic hydroxyl group (−OH) of that acid is replaced by an organyl group (R ′). [1]
Unlike acid-catalyzed ester hydrolysis, it is not an equilibrium reaction and proceeds to completion. Hydroxide ion attacks the carbonyl carbon to give a tetrahedral intermediate, which then expels an alkoxide ion. The resulting carboxylic acid quickly protonates the alkoxide ion to give a carboxylate ion and an alcohol. [1]
Mechanism for acid-catalyzed hydrolysis of an amide. Upon hydrolysis, an amide converts into a carboxylic acid and an amine or ammonia (which in the presence of acid are immediately converted to ammonium salts). One of the two oxygen groups on the carboxylic acid are derived from a water molecule and the amine (or ammonia) gains the hydrogen ion.
The hydroxide anion adds to the carbonyl group of the ester. The immediate product is called an orthoester. Saponification part I. Expulsion of the alkoxide generates a carboxylic acid: Saponification part II. The alkoxide ion is a strong base so the proton is transferred from the carboxylic acid to the alkoxide ion, creating an alcohol:
The OH group is the main site of reaction, as illustrated by the conversion of acetic acid to acetyl chloride. Other substitution derivatives include acetic anhydride; this anhydride is produced by loss of water from two molecules of acetic acid. Esters of acetic acid can likewise be formed via Fischer esterification, and amides can be
Alkenes can be made from alcohols by dehydration. This conversion, among others, is used in converting biomass to liquid fuels. [2] The conversion of ethanol to ethylene is a fundamental example: [3] [4] CH 3 CH 2 OH → H 2 C=CH 2 + H 2 O. The reaction is accelerated by acid catalysts such as sulfuric acid and certain zeolites.
In the presence of strong bases such as sodium hydroxide or strong acids such as hydrochloric acid or sulfuric acid it is hydrolyzed back into methanol and acetic acid, especially at elevated temperature. The conversion of methyl acetate back into its components, by an acid, is a first-order reaction with respect to the ester.
Acid–base extraction is a subclass of liquid–liquid extractions and involves the separation of chemical species from other acidic or basic compounds. [1] It is typically performed during the work-up step following a chemical synthesis to purify crude compounds [2] and results in the product being largely free of acidic or basic impurities.