Carboxylic acids:R-COOH, R-CO2H, Common names: HCO2H CH3CO2H CH3CH2CO2H CH3CH2CH2CO2H formic acid L. formica ant

acetic acid L. acetum vinegar propionic acid G. first salt butyric acid L. butyrum butter L. valerans

CH3CH2CH2CH2CO2H valeric acid

Carboxylic acids, common names: CH3(CH2)4CO2H CH3(CH2)5CO2H CH3(CH2)6CO2H CH3(CH2)7CO2H CH3(CH2)8CO2H CH3(CH2)9CO2H CH3(CH2)10 CO2H caproic acid --caprylic acid --capric acid --lauric acid oil of lauryl L. caper goat

5 4 3 2 1 CCCCC=O used in common names

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 CH3CO2H methanoic acid ethanoic acid propanoic acid

CH3CH2CO2H CH3 CH3CHCOOH

2-methylpropanoic acid

Br CH3CH2CHCO2H 2-bromobutanoic acid

dicarboxylic acids: HOOC-COOH HO2C-CH2-CO2H HO2C-CH2CH2-CO2H HO2C-CH2CH2CH2-CO2H HOOC-(CH2)4-COOH HOOC-(CH2)5-COOH oxalic acid malonic acid succinic acid glutaric acid adipic acid pimelic acid

Oh, my! Such good apple pie!

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+ + H2Ostronger acid stronger base weaker base weaker acid

RCO2H covalent water insoluble

RCO2ionic 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 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 RCOOH

1.oxidation of 1o alcohols:

CH3CH2CH2CH2-OH +n-butyl alcohol 1-butanol

CrO3 CH3CH2CH2CO2Hbutyric acid butanoic acid

CH3 CH3CHCH2-OH +isobutyl alcohol 2-methyl-1-propanol`

KMnO4

CH3 CH3CHCOOH

isobutyric acid 2-methylpropanoic acid

2.oxidation of arenes:

note: aromatic acids only!

3.carbonation of Grignard reagent: R-X Mg RMgX CO2 RCO2MgX H+ RCOOH

Increases the carbon chain by one carbon.Mg CH3CH2CH2-Br n-propyl bromide CO2 H+

CH3CH2CH2MgBr butyric acid

CH3CH2CH2COOH

4.Hydrolysis of a nitrile: 5. H2O, H+ R-C N R-CO2H heat H2O, OHR-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!

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+ + Aionization in water

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

Ka for carboxylic acids 10-5 Why are carboxylic acids more acidic than alcohols? ROH + H2O H3O+ + RORCOOH + H2O H3O+ + RCOOGo = -2.303 R T log Keq The position of the equilibrium is determined by the free energy change, Go. Go= H - TS Go H Ka is inversely related to H, the potential energy difference between the acid and its conjugate base. The smaller the H, the larger the Ka and the stronger the acid.

H

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

Resonance stabilization of the carboxylate ion decreases the H, 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 ClCH2COOH Cl2CHCOOH Cl3CCOOH 1.75 x 10-5 136 x 10-5 5,530 x 10-5 23,200 x 10-5

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

Electron donating groups will destabilize the anion, increase the H, 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 p-hydroxybenzoic acid p-methoxybenzoic acid p-toluic acid benzoic acid p-chlorobenzoic acid p-nitrobenzoic acid 1.4 x 10-5 2.6 x 10-5 3.3 x 10-5

4.2 x 10-5 6.3 x 10-5 10.3 x 10-5 36 x 10-5

2.Conversion into functional derivatives: b) acid chlorides

b) esters direct esterification: H+ RCOOH + ROH 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 + ROH RCO2R -convert the acid into the acid chloride first; not reversible

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

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

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

4.Alpha-halogenation: (Hell-Volhard-Zelinsky reaction) RCH2COOH + X2, P RCHCOOH + HX X -haloacid X2 = Cl2, Br2

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

spectroscopy: IR: -COOH OH stretch 2500 3000 cm-1 (b) C=O stretch nmr: -COOH 10.5 12 ppm 1680 1725 (s)

p-toluic acid

-COOH stretch

C=O

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