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: RCOOH + SOCl 2 PCl 3 PCl 5 RCOCl
Acid chlorides, reactions: 1. Conversion into acids and derivatives: a) hydrolysis b) ammonolysis c) alcoholysis 2. Friedel-Crafts acylation 3. Coupling with lithium dialkylcopper 4. 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 Na. OH 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: 1) 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.
Amides, reactions. 2) Conversion to nitriles.
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Esters, syntheses: 1) From acids RCO 2 H + R’OH, H+ RCO 2 R’ + H 2 O 2) From acid chlorides and anhydrides RCOCl + R’OH RCO 2 R’ + HCl 3) From esters (transesterification) RCO 2 R’ + R”OH, H+ RCO 2 R’ + R”ONa RCO 2 R” + R’OH RCO 2 R” + 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 Le. Chatelier’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: 1) Conversion into acids and derivatives a) hydrolysis b) ammonolysis c) alcoholysis 2) Reaction with Grignard reagents 3) 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 a) catalytic b) chemical
Spectroscopy: Infrared: RCO 2 R 1740 strong absorbance ~ 1700 cm-1 for C=O Ar. CO 2 R 1715 -1730 RCO 2 Ar 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 bend
Ethyl acetate CH 3 CO 2 CH 3 b c a Note which hydrogens are upfield. c b a
Methyl propionate CH 3 CH 2 CO 2 CH 3 a b c Note which hydrogens are upfield. c b a
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