Functional Derivatives of Carboxylic Acids

Nomenclature: the functional derivatives’ names are derived from the common or IUPAC names of the corresponding carboxylic acids. Acid chlorides: change –ic acid to –yl chloride Anhydrides: change acid to anhydride

Amides: change –ic acid (common name) to –amide -oic acid (IUPAC) to –amide Esters: change –ic acid to –ate preceded by the name of the alcohol group

Nucleophilic acyl substitution:

Mechanism: Nucleophilic Acyl Substitution 1) 2)

Mechanism: nucleophilic acyl substitution, acid catalyzed 1) 2) 3)

nucleophilic acyl substitution vs nucleophilic addition to carbonyl aldehydes & ketones – nucleophilic addition functional deriv. of carboxylic acids – nucleophilic acyl substitution

Acid Chlorides Syntheses: SOCl2 RCOOH + PCl3  RCOCl PCl5

Acid chlorides, reactions: Conversion into acids and derivatives: a) hydrolysis b) ammonolysis c) alcoholysis Friedel-Crafts acylation Coupling with lithium dialkylcopper Reduction

acid chlorides: conversion into acids and other derivatives

Schotten-Baumann technique – aromatic acid chlorides are less reactive than aliphatic acid chlorides. In order to speed up the reactions of aromatic acid chlorides, bases such as NaOH or pyridine are often added to the reaction mixture.

acid chlorides: Friedel-Crafts acylation

acid chlorides: coupling with lithium dialkylcopper

acid chlorides: reduction to aldehydes

Anhydrides, syntheses: Buy the ones you want! Anhydrides, reactions: Conversion into carboxylic acids and derivatives. a) hydrolysis b) ammonolysis c) alcoholysis 2) Friedel-Crafts acylation

2) anhydrides, Friedel-Crafts acylation.

Amides, synthesis: Indirectly via acid chlorides.

Amides, reactions. 1) Hydrolysis.

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Esters, syntheses: From acids RCO2H + R’OH, H+ RCO2R’ + H2O From acid chlorides and anhydrides RCOCl + R’OH RCO2R’ + HCl From esters (transesterification) RCO2R’ + R”OH, H+ RCO2R” + R’OH RCO2R’ + R”ONa RCO2R” + R’ONa

Esters often have “fruity” or “floral” odors: isopentyl acetate banana oil n-pentyl butyrate apricot isopentyl isovalerate apple ethyl butyrate peach ethyl heptanoate cognac ethyl nonate flower bouquet ethyl laurate tuberose methyl butyrate pineapple octyl acetate orange

“Direct” esterification is reversible and requires use of LeChatelier’s principle to shift the equilibrium towards the products. “Indirect” is non-reversible.

In transesterification, an ester is made from another ester by exchanging the alcohol function.

Esters, reactions: Conversion into acids and derivatives a) hydrolysis b) ammonolysis c) alcoholysis Reaction with Grignard reagents Reduction a) catalytic b) chemical 4) Claisen condensation

Tracer studies confirm that the mechanism is nucleophilic acyl substitution:

Esters, reaction with Grignard reagents

Esters, reduction catalytic chemical

Spectroscopy: Infrared: strong absorbance ~ 1700 cm-1 for C=O RCO2R 1740 ArCO2R 1715-1730 RCO2Ar 1770 Esters also show a strong C—O stretch at 1050-1300 Amides show N—H stretch at 3050 –3550 and N—H bend in the 1600-1640 region. Nmr: NB in esters the protons on the alcohol side of the functional group resonate at lower field than the ones on the acid side. RCOO—C—H 3.7 – 4.1 ppm H—C—COOR 2 – 2.2 ppm

methyl propionate C=O C--O

butyramide C=O N—H N—H bend

Ethyl acetate CH3CO2CH2CH3 b c a Note which hydrogens are upfield. c b a

Methyl propionate CH3CH2CO2CH3 a b c Note which hydrogens are upfield. c b a