18.7 Salts of Carboxylic Acids Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Carboxylic Acids are Deprotonated by Strong Bases Equilibrium lies far to the right; K is ca For low molecular weight acids, sodium and potassium carboxylate salts are soluble in water. stronger acid weaker acid RCOH + HO – RCO – + H2OH2O OO

Unbranched carboxylic acids with carbons give carboxylate salts that form micelles in water. Micelles O ONa sodium stearate (sodium octadecanoate) CH 3 (CH 2 ) 16 CO O Na + –

Micelles O ONa polar nonpolar

Micelles O ONa polar nonpolar Sodium stearate has a polar end (the carboxylate end) and a nonpolar "tail“. The polar end is hydrophilic ("water-loving”). The nonpolar tail is hydrophobic ("water-hating”). In water, many stearate ions cluster together to form spherical aggregates; carboxylate ions are on the outside and nonpolar tails on the inside.

Figure 18.5: A micelle

Micelles The interior of the micelle is nonpolar and has the capacity to dissolve nonpolar substances. Soaps clean because they form micelles, which are dispersed in water. Grease (not ordinarily soluble in water) dissolves in the interior of the micelle and is washed away with the dispersed micelle.

18.8 Dicarboxylic Acids

Dicarboxylic Acids One carboxyl group acts as an electron- withdrawing group toward the other; effect decreases with increasing separation. Oxalic acid Malonic acid Heptanedioic acid COH O HOC O pKapKa HOCCH 2 COH OO HOC(CH 2 ) 5 COH OO

18.9 Carbonic Acid

Carbonic Acid HOCOH O CO 2 + H2OH2O HOCO – O H+H %0.3% overall K for these two steps = 4.3 x CO 2 is major species present in a solution of "carbonic acid" in acidic media.

Carbonic Acid HOCO – O – OCO – O H+H+ + K a = 5.6 x Second ionization constant:

18.10 Sources of Carboxylic Acids

side-chain oxidation of alkylbenzenes (Section 11.12) oxidation of primary alcohols (Section 15.9) oxidation of aldehydes (Section 17.15) Synthesis of Carboxylic Acids: Review

18.11 Synthesis of Carboxylic Acids by the Carboxylation of Grignard Reagents

Carboxylation of Grignard Reagents RX Mg diethyl ether RMgX CO2CO2 H3O+H3O+ RCOMgX O RCOH O converts an alkyl (or aryl) halide to a carboxylic acid having one more carbon atom than the starting halide

R MgX C O –– diethyl ether O MgX + – R C O O H3O+H3O+ R C OHOH O Carboxylation of Grignard Reagents

Example: Alkyl Halide CH 3 CHCH 2 CH 3 (76-86%) 1. Mg, diethyl ether 2. CO 2 3. H 3 O + CH 3 CHCH 2 CH 3 ClCO 2 H

Example: Aryl Halide (82%) 1. Mg, diethyl ether 2. CO 2 3. H 3 O + CH 3 CO2HCO2H Br CH 3

18.12 Synthesis of Carboxylic Acids by the Preparation and Hydrolysis of Nitriles

Preparation and Hydrolysis of Nitriles RX RCOHRCOH O The reactions convert an alkyl halide to a carboxylic acid having one more carbon atom than the starting halide A limitation is that the halide must be reactive toward substitution by S N 2 mechanism. – C N RCRC N SN2SN2 H3O+H3O+ heat + NH 4 +

Example NaCN DMSO (92%) CH 2 ClCH 2 CN (77%) H2OH2O H 2 SO 4 heat CH 2 COH O

Example: Dicarboxylic Acid BrCH 2 CH 2 CH 2 Br NaCN H2OH2O (77-86%)NCCH 2 CH 2 CH 2 CN H 2 O, HCl heat (83-85%) HOCCH 2 CH 2 CH 2 COH OO

via Cyanohydrin 1. NaCN 2. H + CH 3 CCH 2 CH 2 CH 3 O OH CN (60% from 2-pentanone) H2OH2O HCl, heat CH 3 CCH 2 CH 2 CH 3 OH CO2HCO2H