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

R COH

O

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 1C—C—C—C—C=Oδ γ β α used in common names

CH3CH2CH2CHCOOH

BrCH3CHCH2COOH

CH3

bromovaleric acid -methylbutyric acid

isovaleric acid

COOH

COOH COOH COOH

CH3

CH3CH3

benzoic acid

o-toluic acid m-toluic acid p-toluic acid

special 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

BrCH3CH2CHCO2H 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

Oh, my! Such good apple pie!

CO2H

CO2H

CO2H

CO2H

CO2H

CO2Hphthalic acid isophthalic acid

terephthalic acid

CCOOHH

CCOOHH

CCOOHH

CHHOOC

maleic acid fumaric 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

HOC

OH

O

NaOC

ONa

O

HOC

ONa

O

carbonic acid sodium bicarbonatesodium hydrogen carbonate

sodium carbonate

NaHCO3

Na2CO3

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 ionicwater insoluble water soluble

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

1. Identification.

2. 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

1. 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 acid2-methyl-1-propanol` 2-methylpropanoic acid

2. oxidation of arenes:

CH3

CH3

H3C

CH2CH3

KMnO4, heat

KMnO4, heat

KMnO4, heat

COOH

COOH

HOOC

COOH

toluene benzoic acid

p-xylene terephthalic acid

ethylbenzene benzoic acid

+ CO2

note: aromatic acids only!

3. carbonation of Grignard reagent:

R-X RMgX RCO2MgX RCOOH

Increases the carbon chain by one carbon.

Mg CO2 H+

CH3CH2CH2-Br CH3CH2CH2MgBr CH3CH2CH2COOHn-propyl bromide butyric acid

Mg CO2 H+

C

O

O

RMgX + R CO

O-+ +MgX

H+

R CO

OH

CH3

Br

Mg

CH3

MgBr

CO2 H+

CH3

COOH

p-toluic acid

CH3

Br2, hvCH2Br

MgCH2MgBr

CO2

H+

CH2 COOH

phenylacetic acid

4. Hydrolysis of a nitrile:

H2O, H+

R-CN R-CO2H heat

H2O, OH-

R-CN R-CO2- + H+ R-CO2H

heat

R-X + NaCN R-CN + H+, H2O, heat RCOOH1o alkyl halide

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

CH3

Br2, hvCH2Br

NaCN

CH2 CN

H2O, H+, heat

CH2 COOH

CH3CH2CH2CH2CH2CH2-BrKCN

CH3CH2CH2CH2CH2CH2-CN

H2O, H+, heat

CH3CH2CH2CH2CH2CH2-COOH

1-bromohexane

heptanoic acid

toluene

phenylacetic acid

CO2H

CH2OH

CH3

Br

C N

MgBr

KMnO4, heat

KMnO4

MgCO2; then H+

H2O, H+, heat

carboxylic acids, reactions:

1. as acids

2. conversion into functional derivatives

a) acid chlorides

b) esters

c) amides

3. reduction

4. alpha-halogenation

5. EAS

as acids:

a) with active metals

RCO2H + Na RCO2-Na+ + H2(g)

b) with bases

RCO2H + NaOH RCO2-Na+ + H2O

c) relative acid strength?

CH4 < NH3 < HCCH < ROH < HOH < H2CO3 < RCO2H < HF

d) 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.

HA + H2O

H3O+ + A-po

tent

ial e

nerg

y

ionization

ΔH

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

R CO-

OR C

O-

O

R CO

O

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.

COO-

G

COO-

G

-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

2. Conversion into functional derivatives:

)a acid chlorides

R COH

O SOCl2

or PCl3orPCl5

R CCl

O

CO2H + SOCl2 COCl

CH3CH2CH2 CO

OH

PCl3CH3CH2CH2 C

O

Cl

)b 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

C CO

O

CH3

+ H2O

SOCl2

CCH3OH

O

OH+ CH3OH

O

Cl

H+

)c 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

OH

O

3-Methylbutanoic acid

PCl3

Cl

O NH3

NH2

O

CO

OH

PCl3C

O

ClC

O

NH2

NH3

NH3

amide

CO

O NH4

ammonium salt

3. Reduction:

RCO2H + LiAlH4; then H+ RCH2OH

1o alcohol

Carboxylic acids resist catalytic reduction under normal conditions.

RCOOH + H2, Ni NR

CH3CH2CH2CH2CH2CH2CH2COOH

Octanoic acid(Caprylic acid)

LiAlH4 H+

CH3CH2CH2CH2CH2CH2CH2CH2OH

1-Octanol

CH2 CO

OH

H2, PtNR

LiAlH4

H+

CH2CH2OH

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

RCH2COOH + X2, P RCHCOOH + HX X α-haloacid X2 = Cl2, Br2

COOH

Br2,PNR (no alpha H)

CH3CH2CH2CH2COOH + Br2,P CH3CH2CH2CHCOOH

Brpentanoic acid2-bromopentanoic acid

RCH2COOH + Br2,P RCHCOOH + HBr

Br

NH2OH

RCHCOOH RCHCOOH

RCH=CHCOOHRCH2CHCOOH

Br

aminoacid

NaOH;then H+

NH3

KOH(alc)

then H+

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

CO2H

CO2H

NO2

CO2H

SO3H

CO2H

Br

NR

HNO3,H2SO4

H2SO4,SO3

Br2,Fe

CH3Cl,AlCl3

benzoic acid

spectroscopy:

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

C=O stretch 1680 – 1725 (s)

nmr: -COOH 10.5 – 12 ppm

p-toluic acid

-COO—H stretch C=O

COOH

CH3 a

b

c

c b a

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

carboxylic acids, reactions:

1. as acids

2. conversion into functional derivatives

a) acid chlorides

b) esters

c) amides

3. reduction

4. alpha-halogenation

5. EAS