Before you can learn about aldehydes and ketones, you must first know something about the nomenclature of carboxylic acids since many of the names of aldehydes

and ketones are derived from the names of the corresponding carboxylic acids.

R-COOH, R-CO2H,

Common names:

HCO2H formic acid L. formica ant

CH3CO2H acetic acid L. acetum vinegar

CH3CH2CO2H propionic acid G. “first salt”

CH3CH2CH2CO2H butyric acid L. butyrum butter

CH3CH2CH2CH2CO2H valeric acid L. valerans

Carboxylic acids, common names CH3(CH2)4CO2H caproic acid L. caper

goat

CH3(CH2)5CO2H ---

CH3(CH2)6CO2H caprylic acid

CH3(CH2)7CO2H ---

CH3(CH2)8CO2H capric acid

CH3(CH2)9CO2H ---

CH3(CH2)10CO2H lauric acid oil of lauryl

5 4 3 2 1 C—C—C—C—C=O δ γ β α used in common names

IUPAC nomenclature for carboxylic acids: parent chain = longest, continuous carbon chain that contains

the carboxyl group alkane, drop –e, add –oic acid

HCOOH methanoic acid

CH3CO2H ethanoic acid

CH3CH2CO2H propanoic acid

CH3

CH3CHCOOH 2-methylpropanoic acid

Br

CH3CH2CHCO2H 2-bromobutanoic acid

dicarboxylic acids :

HOOC-COOH oxalic acid

HO2C-CH2-CO2H malonic acid

HO2C-CH2CH2-CO2H succinic acid

HO2C-CH2CH2CH2-CO2H glutaric acid

HOOC-(CH2)4-COOH adipic acid

HOOC-(CH2)5-COOH pimelic acid

salts of carboxylic acids: name of cation + name of acid: drop –ic acid, add –ate

CH3CO2Na sodium acetate or sodium ethanoate

CH3CH2CH2CO2NH4 ammonium butyrate

ammonium butanoate

(CH3CH2COO)2Mg magnesium propionate

magnesium propanoate

physical properties: polar + hydrogen bond relatively high mp/bp

water insoluble

exceptions: four carbons or less

acidic turn blue litmus red

soluble in 5% NaOH

RCO2H + NaOH → RCO2-Na+ + H2O

stronger stronger weaker weaker

acid base base acid

RCO2H RCO2- covalent ionic water insoluble water soluble

Carboxylic acids are insoluble in water, but soluble in 5%

NaOH.

Identification. Separation of carboxylic acids from basic/neutral organic

compounds. The carboxylic acid can be extracted with aq. NaOH

and then regenerated by the addition of strong acid.

Carboxylic acids, syntheses: 1. oxidation of primary alcohols

RCH2OH + K2Cr2O7 RCOOH

2. oxidation of arenes

ArR + KMnO4, heat ArCOOH

3. carbonation of Grignard reagents

RMgX + CO2 RCO2MgX + H+ RCOOH

4. hydrolysis of nitriles

RCN + H2O, H+, heat RCOOH

oxidation of 1o alcohols:

CH3CH2CH2CH2-OH + CrO3 CH3CH2CH2CO2H n-butyl alcohol butyric acid 1-butanol butanoic acid

CH3 CH3 CH3CHCH2-OH + KMnO4 CH3CHCOOH isobutyl alcohol isobutyric acid 2-methyl-1-propanol` 2-

methylpropanoic acid

oxidation of arenes:

note: aromatic acids only!

carbonation of Grignard reagent:

R-X RMgX RCO2MgX RCOOH

Increases the carbon chain by one carbon.

Mg CO2 H+

CH3CH2CH2-Br CH3CH2CH2MgBr CH3CH2CH2COOH

n-propyl bromide butyric acid

Hydrolysis of a nitrile:

H2O, H+ R-C N R-CO2H heat

H2O, OH- R-C N R-CO2- + H+ R-CO2H heat

R-X + NaCN → R-CN + H+, H2O, heat → RCOOH 1o alkyl halide

Adds one more carbon to the chain. R-X must be 1o or CH3!

carboxylic acids, reactions: as acids

conversion into functional derivatives

a) acid chlorides

b) esters

c) amides

reduction

alpha-halogenation

EAS

as acids: with active metals RCO2H + Na RCO2-Na+ + H2(g) with bases RCO2H + NaOH RCO2-Na+ + H2O relative acid strength? CH4 < NH3 < HC CH < ROH < HOH < H2CO3 < RCO2H <

HF quantitative HA + H2O H3O+ + A- ionization in

water Ka = [H3O+] [A-] / [HA]

Ka for carboxylic acids ~ 10-5

Why are carboxylic acids more acidic than alcohols? ROH + H2O ↔ H3O+ + RO- RCOOH + H2O ↔ H3O+ + RCOO- ΔGo = -2.303 R T log Keq The position of the equilibrium is determined by the free

energy change, ΔGo. ΔGo = ΔH - TΔS ΔGo ~ ΔH Ka is inversely related to ΔH, the

potential energy difference between the acid and its conjugate base. The smaller the ΔH, the larger the Ka and the stronger the acid.

The smaller the ΔH, the more the equilibrium lies to the right, giving a larger Ka ( a stronger acid ).

Resonance stabilization of the carboxylate ion decreases the ΔH, shifts the ionization in water to the right, increases the Ka, and results in carboxylic acids being stronger acids.

Effect of substituent groups on acid strength?

CH3COOH 1.75 x 10-5

ClCH2COOH 136 x 10-5

Cl2CHCOOH 5,530 x 10-5

Cl3CCOOH 23,200 x 10-5

-Cl is electron withdrawing and delocalizes the negative charge on the carboxylate ion, lowering the PE, decreasing the ΔH, shifting the ionization to the right and increasing acid strength.

Effect of substituent groups on acid strength of benzoic acids?

Electron withdrawing groups will stabilize the anion, decrease the ΔH, shift the ionization to the right, increasing the Ka, increasing acid strength.

Electron donating groups will destabilize the anion, increase the ΔH, shift the ionization in water to the left, decreasing the Ka, decreasing acid strength.

-NH2, -NHR, -NR2 -OH -OR electron donating -NHCOCH3 -C6H5 -R -H -X -CHO, -COR -SO3H -COOH, -COOR electron withdrawing -CN -NR3+ -NO2

Relative acid strength?

Ka

p-aminobenzoic acid 1.4 x 10-5

p-hydroxybenzoic acid 2.6 x 10-5

p-methoxybenzoic acid 3.3 x 10-5

p-toluic acid 4.2 x 10-5

benzoic acid 6.3 x 10-5

p-chlorobenzoic acid 10.3 x 10-5

p-nitrobenzoic acid 36 x 10-5

Conversion into functional derivatives:

acid chlorides

esters

“direct” esterification: H+ RCOOH + R´OH ↔ RCO2R´ + H2O -reversible and often does not favor the ester -use an excess of the alcohol or acid to shift equilibrium -or remove the products to shift equilibrium to completion

“indirect” esterification: RCOOH + PCl3 →RCOCl + R´OH RCO2R´ -convert the acid into the acid chloride first; not reversible

amides “indirect” only! RCOOH + SOCl2 RCOCl + NH3 RCONH2 amide

Directly reacting ammonia with a carboxylic acid results in an ammonium salt:

RCOOH + NH3 → RCOO-NH4+ acid base

Reduction : RCO2H + LiAlH4; then H+ → RCH2OH 1o alcohol

Carboxylic acids resist catalytic reduction under normal conditions. RCOOH + H2, Ni →NR

Alpha-halogenation Alpha-halogenation: (Hell-Volhard-Zelinsky reaction)

RCH2COOH + X2, P → RCHCOOH + HX

X

α-haloacid

X2 = Cl2, Br2

EAS: (-COOH is deactivating and meta- directing)

spectroscopy: spectroscopy:

IR: -COOH O—H stretch 2500 – 3000 cm-1 (b)

C=O stretch 1680 – 1725 (s)

nmr: -COOH 10.5 – 12 ppm

Carboxylic acids, syntheses:

oxidation of primary alcohols

RCH2OH + K2Cr2O7 → RCOOH

2. oxidation of arenes

ArR + KMnO4, heat → ArCOOH

3. carbonation of Grignard reagents

RMgX + CO2 → RCO2MgX + H+ → RCOOH

4. hydrolysis of nitriles

RCN + H2O, H+, heat → RCOOH

carboxylic acids, reactions:

as acids

conversion into functional derivatives

a) acid chlorides

b) esters

c) amides

reduction

alpha-halogenation

EAS