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CHEM2213 Topic 10b.docx

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Department
Chemistry
Course
Chemistry 1027A/B
Professor
Mark Workentin
Semester
Fall

Description
Topic 10b Derivatives Of Carboxylic Acids What Some Derivatives Of Carboxylic Acids, & How Are They Named?  Acid Halide: derivative of carboxylic acid in which –OH is replaced by a halogen  Carboxylic Anhydride: compound in which two acyl groups are bonded to an O  The functional group of a phosphoric anhydride is two phosphoryl groups bonded to an O atom  Carboxylic Ester: acyl group bonded to –OR or –OAr o Lactone: cyclic ester  Phosphoric acid has three –OH groups and forms mono-, di-, and triphosphoric esters  Amide: acyl group bonded to a trivalent N atom o Lactam: cyclic amide What Are The Characteristic Reactions Of Carboxylic Acid Derivatives?  Addition of a nucleophile to the carbonyl C to form a tetrahedral carbonyl addition intermediate  Intermediate collapses to expel leaving group and regenerates the carbonyl group  Nucleophilic Acyl Substiution: reaction in which a nucleophile bonded to a carbonyl C is replaced by another nucleophile o The weaker the base, the better the leaving group is o Amide < ester < anhydride < acid halide What Is Hydrolysis?  Chemical process whereby a bond in a molecule is broken by its reaction with water  Water molecule is also typically split into H and OH  Acid chlorides react very rapidly with water to form carboxylic acids and HCl  Acid anhydrides are generally less reactive than acid chlorides, react readily with water to form two molecules of carboxylic acid  Esters are hydrolyzed very slowly but hydrolysis becomes more rapid when esters are refluxed in aqueous acid / base o Role of acid catalyst is to protonate the carbonyl O, thereby increasing electrophilic character of the carbonyl C toward attack by water to form a tetrahedral carbonyl addition intermediate o An internal proton transfer to the alkoxy group makes that group a good leaving group and allows collapse of intermediate to give a carboxylic acid and alcohol o Saponification: hydrolysis of an ester in aqueous NaOH / KOH to an alcohol and salt of a carboxylic acid o Acid is required in only catalytic amounts, base is required in equimolar amounts because it is a reactant o Acid is reversible, base is irreversible because a carboxylic acid anion is not attacked by ROH  Amides require considerably more vigorous conditions for hydrolysis in both acid and base than do esters o Undergo hydrolysis in hot aqueous acid to give a carboxylic acid and ammonia o In aqueous base, products
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