Carboxylic Acids SANTOSH CHEMISTRY DEPT

Carboxylic acids: R-COOH, R-CO 2 H, Common names: HCO 2 Hformic acid CH 3 CO 2 Hacetic acid CH 3 CH 2 CO 2 Hpropionic acid CH 3 CH 2 CH 2 CO 2 Hbutyric acid CH 3 CH 2 CH 2 CH 2 CO 2 Hvaleric acid

C—C—C—C—C=O δ γ β αused 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 HCOOHmethanoic acid CH 3 CO 2 Hethanoic acid CH 3 CH 2 CO 2 Hpropanoic acid CH 3 CH 3 CHCOOH2-methylpropanoic acid Br CH 3 CH 2 CHCO 2 H2-bromobutanoic acid

Dicarboxylic acids HOOC-COOHoxalic acid HO 2 C-CH 2 -CO 2 Hmalonic acid HO 2 C-CH 2 CH 2 -CO 2 H succinic acid HO 2 C-CH 2 CH 2 CH 2 -CO 2 Hglutaric acid HOOC-(CH 2 ) 4 -COOHadipic acid HOOC-(CH 2 ) 5 -COOHpimelic acid

salts of carboxylic acids: name of cation + name of acid: drop –ic acid, add –ate CH 3 CO 2 Nasodium acetate or sodium ethanoate CH 3 CH 2 CH 2 CO 2 NH 4 ammonium butyrate ammonium butanoate (CH 3 CH 2 COO) 2 Mg 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 RCO 2 H + NaOH  RCO 2 - Na + + H 2 O stronger stronger weaker weaker acid base base acid Two molecules of a carboxylic acid can hydrogen bond together.

RCO 2 HRCO 2 - covalentionic water insolublewater 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.

1.oxidation of 1 o alcohols: CH 3 CH 2 CH 2 CH 2 -OH + CrO 3  CH 3 CH 2 CH 2 CO 2 H n-butyl alcohol butyric acid 1-butanol butanoic acid CH 3 CH 3 CH 3 CHCH 2 -OH + KMnO 4  CH 3 CHCOOH isobutyl alcohol isobutyric acid 2-methyl-1-propanol` 2-methylpropanoic acid General Methods of preparation of Carboxylic Acids:

2.Oxidation of alkylbenzenes: note: aromatic acids only!

( R-Li ) 3. Carbonation of Grignard Reagents:

Hydrolysis of Nitriles DMSO H 2 SO 4 H2OH2O heat SN2SN2

or CO 2 CrO 3 H 2 SO 4 KMnO 4 H 2 SO 4 KMnO 4 NaCN acetone DIBAL or Rosenmund KMnO 4 Li or Mg H2OH2O H2OH2O H 2 SO 4 H2OH2O or KMnO 4 SYNTHESIS OF CARBOXYLIC ACIDS KMnO 4 ( benzene = R sidechain = R’ ) SOCl 2

Carboxylate Ion Formation pK a   5 carboxylate ioncarboxylic acid

+ +.. : : H 2 SO 4.. : + Protonation and Deprotonation of a Carboxylic Acid.. : NaOH.. : - equivalent structures due to resonance

Electron-withdrawing Groups: – strengthen acids – weaken bases Electron-releasing Groups: – weaken acids – strengthen bases

Substituents with Electron-Withdrawing Resonance ( - R ) Effects -R substituents strengthen acids and weaken bases X Y

+R substituents weaken acids and strengthen bases Substituents with Electron-Releasing Resonance ( + R ) Effects hydroxy mercapto methyl amino fluoro bromo alkoxy acyloxy dialkylamino alkyl chloro iodo Y..

Substituents with Electron-Withdrawing ( - I ) Inductive Effects ( - I ) Inductive Effects -I substituents strengthen acids and weaken bases carboxyl alkoxycarbonyl acyl hydroxyl mercapto amino chloro nitro cyano sulfonic acid alkoxy dialkylamino trimethylammonium fluoro bromo iodo X

Substituents with Electron-Releasing Inductive ( + I ) Effects +I substituents weaken acids and strengthen bases methyl alkyl oxide carboxylate R

increasing acidity

Benzoic Acid: pK a = 4.19 ortho meta para ortho meta para

Benzoic Acid: pK a =

1.as acids 2.conversion into functional derivatives a)  acid chlorides b)  esters c)  amides 3.reduction 4.alpha-halogenation 5.EAS Chemical Properties of Carboxylic Acids:

a)with active metals RCO 2 H + Na  RCO 2 - Na + + H 2 (g) b)with bases RCO 2 H + NaOH  RCO 2 - Na + + H 2 O c)relative acid strength? CH 4 < NH 3 < HC  CH < ROH < HOH < H 2 CO 3 < RCO 2 H < HF d)quantitative HA + H 2 O  H 3 O + + A - ionization in water Ka = [H 3 O + ] [A - ] / [HA] 1) Salt formation:

2) Formation of acid chlorides:

“direct” esterification: H + RCOOH + R´OH  RCO 2 R´ + H 2 O -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 + PCl 3  RCOCl + R´OH  RCO 2 R´ -convert the acid into the acid chloride first; not reversible 3) Formation of esters:

“indirect” only. RCOOH + SOCl 2  RCOCl + NH 3  RCONH 2 amide Directly reacting ammonia with a carboxylic acid results in an ammonium salt: RCOOH + NH 3  RCOO - NH 4 + acid base 4) Formation of amides:

RCO 2 H + LiAlH 4 ; then H +  RCH 2 OH 1 o alcohol Carboxylic acids resist catalytic reduction under normal conditions. RCOOH + H 2, Ni  No Reaction (NR) 5) Reduction:

RCH 2 COOH + X 2, P  RCHCOOH + HX X α-haloacid X 2 = Cl 2, Br 2 6) Halogenation of alkyl groups(Hell-Volhard-Zelinsky reaction): 6) Halogenation of alkyl groups (Hell-Volhard-Zelinsky reaction):

(-COOH is deactivating and meta- directing) 5) Aromatic Substitution: