Chapter 18 Carboxylic Acids and their derivatives Part 1- Chemistry free study material by TEACHING CARE online tuition and coaching classes

Chapter 18 Carboxylic Acids and their derivatives Part 1- Chemistry free study material by TEACHING CARE online tuition and coaching classes

File name : Chapter-18-Carboxylic-Acids-and-their-derivatives-Part-1.pdf

 

 

Carboxylic Acids

æ               ö

Carboxylic acids are the compounds containing the carboxyl functional group ç – C– OH ÷
ç
÷

ç    ||             ÷

è   O             ø

The carboxyl group is made up of carbonyl ( C = O) and hydroxyl (–OH) group.

(1)  Classification

  • Carboxylic acids are classified as monocarboxylic acids, dicarboxylic acids, tricarboxylic acids depending on the number of – COOH groups present in the molecule.

CH2COOH

|

 

CH 3 COOH

C H 2COOH

|

CH2COOH

C HCOOH

|

CH2COOH

 

monocarboxylic acid     Dicarboxylic acid       Tricarboxylic acid

  • Monocarboxylic acids of aliphatic series are commonly known as fatty acids such as palmitic acid (C15 H 31 COOH) and stearic acid (C17 H 35 COOH) .

 

  • The general formula for monocarboxylic acids is carbon

Cn H 2n+1 COOH  or Cn H 2n O2 . Where n = number of

 

  • The carboxylic acids may be aliphatic or aromatic depending upon whether – COOH group is attached to aliphatic alkyl chain or aryl group

Aliphatic acids

 

 

HCOOH

Formic acid

 

 

Aromatic acids

 

COOH

 

 

 

Benzoic acid

CH 3 COOH

Acetic acid

 

 

 

 

COOH

 

 

NO2

m-Nitrobenzoic acid

CH3CH COOH

|

CH3

Isobutyric acid

 

 

 

COOH

CH3

 

 

 

o-Toluic acid

 

 

 

(2)  Structure :

  • The name carboxyl is derived from carbonyl hydroxyl groups are directly linked to each

C = O

and hydroxyl (– OH) because both carbonyl and

 

  • The carboxylic carbon atom and two oxygen atom in carboxylic acid are sp2

 

 

 

 

 

 

 

1.23 Å

O

R – C

1.36 Å ® |

H

|

R C OH

|

 

1.43Å

Pure p-orbital

 

RC = O

|

1.20Å

 

O H                                        H                                                                            R

Delocalized p-electron cloud

  • The shorter bond (c o) and longer bond (c = o) of carboxylic acid than alcohol and ketone is due to delocalization of p
  • Nomenclature : The monocarboxylic acids are named according to following
    • Common or trivial names : The names of lower members are derived from the Latin or Greek word that indicates the source of the particular The common names have ending –ic acid.

 

FormulaSourceCommon name
 HCOOHRed ant (Latin, ant = Formica)Formic acid
 CH3 COOHVinegar (Latin; vinegar = Acetum)Acetic acid
 C2 H5 COOHProton-pion (Greek; Proton = first, Pion = Fat)Propionic acid
 C3 H7 COOHButter (Latin ; Butter = Butyrum)Butyric acid
 C4 H9 COOHRoot of valerian plantValeric acid
  • Derived system : Monocarboxylic acids may be named as alkyl derivatives of acetic

 

CH3CH 2COOH

Methyl acetic acid

CH3C H COOH

|

CH3

Dimethyl acetic acid

 

  • IUPAC system : Acids are named as alkanoic acids (Alkane – e + oic acid). The name is derived by replacing ‘e’ of the corresponding alkane by –oic

HCOOH                                      Methanoic acid (Methane – e + oic acid)

 

CH3COOH

Ethanoic acid (Ethane – e + oic acid)

 

In case of substituted acids,

 

 

 

 

 

5               4            3           2          1

Br

4             3|           2           1

 

C H3 – C H C H C H 2 COOH;         C H3 – C HC H COOH;

 

|

CH3

|

CH3

|

CH3

 

3,4-Dimethylpentanoic acid

(4)  Isomerism

3-Bromo- 2- methyl butanoic acid

CH3

|

 

(i)  Chain isomerism :

CH3  – CH2 – CH 2 – CH 2 – COOH  ;

Pentanoic acid

CH3CH 2C H COOH

2-methyl butanoic acid

 

(ii)  Position isomerism :

CH3C H CH2COOH

|

CH3

3- methyl butanoic acid

;   CH3CH 2C H COOH

|

CH3

2-methyl butanoic acid

 

(iii)  Functional isomerism :

 

  • Optical isomerism

C2H5

|

CH3CH 2COOH               ;

Propanoic acid

 

 

C2H5

|

CH3 COOCH3

Methyl acetate

;    HCOOC2    H5

Ethyl formate

 

CH3  – CC3 H7

|

COOH

C3 H7  – CCH3

|

COOH

 

2-Ethyl-2Methyl Pentanoic Acid

(1)  By oxidation of alcohols, aldehydes and ketones

RCH 2 OH ¾¾[O¾} ® RCHO ¾¾[¾O] ®  RCOOH

 

alcohol

K2Cr2O7

K2Cr2O7

Carboxylic acid

 

RCHO ¾¾[¾O] ® RCOOH

Aldehyde

Ketones and secondary alcohols form acid with fewer carbon atoms.

2
2 7

R       CHOH ¾¾[O¾} ®             R       C = O ¾¾K C¾r O¾® RCOOH + R¢COOH

 

R¢CH2

Sec. Alcohol

Ketones

H2SO4

 

Note : ® Aldehyde can be oxidized to carboxylic acid with mild oxidising agents such as ammonical silver

2

nitrate solution [Ag 2O or Ag(NH3 )+ OH ]

 

  • Methanoic acid can not be prepared by oxidation
  • Ketones can be oxidized under drastic conditions using strong oxidising agent like

K2Cr2O7 .

 

  • Methyl ketones can also be converted to carboxylic acid through the haloform reaction.

RCCH3  + 3I 2  + 3NaOH ¾¾D ® RCOH + CHI 3  + 3NaI + 3H 2 O

||                                                    H2O                     ||

O                                                                       O

(2)  By Hydrolysis of nitriles, ester, anhydrides and acid chloride

(i)  Hydrolysis of nitriles

 

RC º N + HOH ¾¾H¾Cl ®éRC

OH ù ¾¾Rea¾rran¾gem¾e¾nt ® R – C              O

¾¾HO ® RCOOH + NH  Cl

 

ë

or NaOH  ê

NH ú

NH2

HCl                                                          4

 

û
  • Hydrolysis of Esters : RCOOR‘+ HOH ¾¾H¾Cl ® RCOOH+ ROH

 

Ester

OH

Acid

Alcohol

 

 

 

 

 

(iii)  Hydrolysis of Anhydrides :

O

||

CH3 – C

 

O + HOH ¾¾H+ ¾/ OH¾-  ® 2CH  COOH

 

CH3

  • C

||

O

Ethanoic anhydride

3

Ethanoic acid

 

(iv)  Hydrolysis of acid chloride and nitro alkane

RCCl + HOH ¾¾H+ ¾/ OH¾-  ® RCOOH + HCl

||

O

RCH 2  – NO2  ¾¾85%¾HSO¾4  ® RCOOH

       X

 

 

 

é              OHù                             O

 

 

ê
ú
  • Hydrolysis of Trihalogen : R C X + 3NaOH ® êR C

OHú ¾¾- H¾2O  ® RC

OH + 3NaX

 

X

(3)  From Grignard Reagent

C

O

ëê               OHúû

 

O = C = O +

dd +

RMgX

¾¾Dry¾eth¾er ® R – || – OMgX ¾¾H+ ¾/ HO ® RCOOH + Mg(OH)X

 

Carbon dioxide Grignard reagent

(R = CH3 ,C2 H5 ,(CH3 )2 CH-,(CH3 )3 C

 

(4)  From Alkene or Hydro-carboxy-addition (koch reaction)

When a mixture of alkene, carbon monoxide and steam is heated under pressure at 350°C in presence of phosphoric acid (H3 PO4 ) monocarboxylic acid is formed.

CH 2  = CH 2  + CO + H 2 O ¾¾H3 P¾O¾4  ® CH 3 CH 2 COOH

500-1000atm

&350°C

 

Mechanism :

 

 

H            Å

 

H                                         H                                       H

+

|                                           |                                         |

 

OH

|

C= O

|

 

(i)

C = C

+ H + ®

C C

(ii)

CC– ¾¾Cº¾O ®

CC

¾¾HO ® – CC

 

|                                             |       |

|       |              –H Å                     |       |

 

 

 

(5)          Special Methods

Carbocation

C=O

Å

Acyl cation

Carboxylic acid

 

  • Carboxylation of sodium alkoxide : RONa + CO ® RCOONa ¾¾H¾Cl ® RCOOH

 

Sod. alkoxide

Sod. salt

Acid

 

 

(ii)  Action of heat on dicarboxylic acid :

RCH       COOH ¾¾CO¾2  ® RCH

COOH

 

COOH

Substituted malonic acid

heat

2

Monocarboxylic acid

 

 

(iii)  From Acetoacetic ester :

CH3 CO

CHRCO

OC2 H5  ¾¾Hyd¾roly¾¾sis ®

CH3COOH

 

OH H

(iv)  Oxidation of alkene and alkyne

OH  H

  • RCH COOH + C H OH

2                        2    5

 

 

 

RCH  = CHR¢ ¾¾[¾O] ® RCOOH + R¢COOH

 

Alkene

Hot alkalne

KMnO4

 

RC º CR¢ ¾¾(i)O¾3  ® RCOOH + R¢COOH

 

Alkyne

(ii)H2O

 

(v)  The Arndt-Eistert Synthesis :

RCCl    + CH 2 N 2  ® RCCHN 2  ¾¾HO ® RCH 2  – COOH

 

||                                                  ||

O                                                 O

Ag2O

 

(vi)  From acid amides :

RCONH 2 + H 2 O ¾¾Ac¾id ® RCOOH+ NH 3

 

Amide

or Alkali

Acid

 

RCONH 2 +

Amide

HNO2

Nitrous acid

® RCOOH + N 2 + H 2O

 

 

Important physical properties of carboxylic acids are described below :

  • Physical state : The first three members (upto 3 carbon atoms) are colourless, pungent smelling The next six members are oily liquids having unpleasant smell. The higher members are colourless and odourless waxy solids.
  • Solubility : The lower members of the aliphatic carboxylic acid family (upto C4) are highly soluble in The solubility decreases with the increase in the size of the alkyl group. All carboxylic acids are soluble in alcohol, ether and benzene etc.

Note : ® The solubility of lower members of carboxylic acids is due to the formation of hydrogen bonds between the – COOH group and water molecules.

  • Acetic acid exists in the solution in dimer form due to intermolecular hydrogen The observed molecular mass of acetic acid is 120 instead of 60.

(3)  Melting point

  • The melting points of carboxylic acids donot vary smoothly from one member to
  • The melting point of the acids having even number of carbon atoms are higher than those containing an odd number immediately above and below

 

5 0

 

3 0

 

1 0

 

–1 0

 

–3 0

 

 

–5 0

1

3            5            7            9            11

No. of C-atoms/molecule

 

  • The acids with even number of carbon atoms have the – COOH group and the terminal – CH3 group on the opposite side of the carbon
  • In the case of odd numbers, the two groups lie on the same side of the

 

 

 

 

 

 

CH3

CH2

CH2

COOH

 

CH3

CH2

CH2

CH2

 

COOH

 

the two terminal groups lie on the opposite sides of the chain

the two terminal groups lie on the same side of the chain

 

When the terminal groups lie on the opposite sides the molecules fit into each other more closely. More effective packing of the molecule in the lattice. Therefore, results into higher melting point.

  • Boiling point : Boiling point of carboxylic acids increase regularly with increase of molecular mass. Boiling points of carboxylic acids are higher than those of alcohols of same molecular mass. This is due to intermolecular hydrogen bonding between two acid

 

 

 

CH3 – C

Hydrogen bonding

 

O        H – O

O – H                O

 

 

C – CH3

 

 

Hydrogen bonding Acetic acid dimer

Among organic compounds, carboxylic acid are the most acidic and ionize in aqueous solution. It is expressed in term of dissociation constant (Ka)

 

R COOH+ H 2O

Carboxylic acid

RCOO  +

Carboxylate ion

H3O+

Hydronium ion

 

 

K    = [RCOO ][H3O+ ]

a             [RCOOH]

 

Note : ® Greater the value of Ka or lesser the value of

  • Acidic nature ( Ka ) a 1/molecular weight

pKa

stronger is the acid, i.e.

pKa = – log Ka

 

HCOOH

  • CH3COOH > C2 H5COOH

 

Ka Value

17.7 ´ 10-5

1.75 ´ 10-5

1.3 ´ 10-5

 

  • The formic acid is strongest of all fatty acids.
  • Acetic acid is less weak acid than sulphuric acid due to less degree of

(1)  Cause of Acidic Nature

  • A molecule of carboxylic acid can be represented as a resonance hybrid of the following

..                ..

..

O:                O:

||                                     |        Å

RC  O..- H « R –  C   = O..- H

  • (II)
  • Due to electron deficiency on oxygen atom of the hydroxyl group (Structure II), their is a displacement of electron pair O–H bond toward the oxygen This facilitate the release of hydrogen as proton (H+).

 

 

 

O– Å                                 é               O                             O–                                                                              ù

 

R C    

O ¬ H « êR C

O– « R C

º R C

O

1.27 A°ú

ê

1.27 A°ú

 

ëê                               Resonance hybrid                                                úû

  • The resulting carboxylate ion also stabilized by resonance (As negative charge is dispersed on both the oxygen atom). This enhance the stability of carboxylate anion and make it weaker

(2)  Effect of substituent on acidic nature

  • An electron withdrawing substituent (– I effect) stabilizes the anion by dispersing the negative charge and therefore increases the

 

 

G ¬ C

Où

O

ú

û

G ® C

Où

O

ú

û

 

  • (II)
  • An electron releasing substituent (+ I effect) stabilizes negative charge on the anion resulting in the decrease of stability and thus decreased the acidity of

Electron with drawing nature of halogen : F > Cl > Br > I

Thus, the acidic strength decreases in the order :

FCH 2 COOH > ClCH2 COOH > BrCH 2 COOH > ICH 2 COOH

similarly : CCl3 COOH  > CHCl2 COOH  > CH 2 ClCOOH  > CH3 COOH

  • Inductive effect is stronger at a-position than b-position similarly at b-position it is more stronger than at g -position

Example: CH3  – CH2  – C HCOOH > CH3  – C H CH2  – COOH > C H 2 – CH 2  – CH 2  – COOH

|                                              |                                              |

Cl                                           Cl                                           Cl

 

  • Relative acid strength in organic and inorganic acids

RCOOH > HOH > ROH > HC º CH > NH 3 > RH

 

 

(1)  Reaction involving removal of proton from –OH group

  • Action with blue litmus : All carboxylic acids turn blue litmus

 

(ii)  Reaction with metals :

 

 

  • Action with alkalies :

2CH3 COOH + 2Na ® 2CH3 COONa+ H 2

Sodium acetate

2CH3 COOH + Zn ® (CH3 COO)2 Zn + H 2

Zinc acetate

CH3 COOH+ NaOH  ® CH3 COONa+ H 2 O

 

Acetic acid

(iv)  Action with carbonates and bicarbonates

Sodium acetate

 

2CH3 COOH + Na2 CO3  ® 2CH3 COONa+ CO2  + H 2 O

Sod. acetate

CH3 COOH + NaHCO3  ® CH3 COONa+ CO2  + H 2 O

Sod. acetate

Note : ® Reaction of carboxylic acid with aqueous sodium carbonates solution produces bricks effervescence. However most phenols do not produce effervescence. Therefore, this reaction may be used to distinguish between carboxylic acids and phenols.

 

 

 

(2)  Reaction involving replacement of –OH group

 

(i)  Formation of acid chloride :

CH3 COOH+ PCl5   ® 3CH3 COCl+ POCl3  + HCl

 

Acetic acid                              Acetyl chloride

3CH3 COOH+ PCl3  ® 3CH3 COCl+ HPO3

Acetic acid                                Acetyl chloride

CH3 COOH+ SOCl2  ® CH3 COCl+ SO2  + HCl

 

Acetic acid

 

(ii)  Formation of esters (Esterification)

Acetyl chloride

 

CH3 CO

Acetic acid

OC2 H5

OH + H

Ethyl alcohol

  Conc.H2SO4

D

CH3 COOC2 H5 + H 2 O

Ethyl acetate (Fruity smelling)

 

  • The reaction is shifted to the right by using excess of alcohol or removal of water by
  • The reactivity of alcohol towards

tert-alcohol < sec-alcohol < pri-alcohol < methyl alcohol

  • The acidic strength of carboxylic plays only a minor

R3 CCOOH < R2 CHCOOH < RCH 2 COOH < CH3 COOH < HCOOH

Mechanism of Esterification : The mechanism of esterification involves the following steps :

Step I : A proton from the protonic acid attacks the carbonyl oxygen of acetic acid.

 

CH   C         O

+     H+      CH   C

O+H               

CH   C

  • OH

 

3         OH

Acetic acid

3          OH

Protonated acetic acid

3           OH

 

Step II : The electron rich oxygen atom of the ethyl alcohol attaches itself at positively charged carbon atom.

H                                              OH H

OH                          |                                                 |       |

 

CH3 – C

+      : O -& C2 H5

CH3 – COC2 H5

 

OH                         ··                                                                         |       +

Ethyl alcohol                                OH

 

Step III : From the resulting intermediate, a proton shifts to OH group as :

..

: OH H                                                           OH2

 

C

|

CH   –      –

|

C H

 Proton transfer   CH

|

–     – OC  H

 

2
5
3

O                                                             C             2     5

3

|         +                                                                                             |

OH                                                                  OH

Step IV : The intermediate obtained in Step III loses a water molecule to form a carbocation.

 

 

CH3 – COCH5

|

OH

+

CH3 – COC2 H5  + H 2 O

|

OH

Carbocation

 

Step V : The carbocation loses a proton to form an ester.

 

 

CH3

+

  • COC2 H5

|

H+

CH3

  • COC2 H5

||

O

Ethyl acetate

 

 

 

Note : ® The OH

group for making H2O comes from acid.

 

  • The mechanism is supported by labelling of Isotopic oxygen as :

 

O

||

CH   –     – OH +

18             H+

O

||     18

CH   –     –

  • H O

 

3   C                 CH3 CH 2 O H                                   3      C   OCH5            2

When methanol is taken in place of ethanol. then reaction is called trans esterification.

 

(iv)  Formation of amides :

CH3 COOH+ NH 3  ¾¾he¾at ® CH3 COONH4  ¾¾D ® CH3 CONH 2 + H 2 O

 

Acetic acid

Amm. acetate

Acetamide

 

(v)  Formation of acid anhydrides :

CH3COO H                      CH  CO

Heat              3

+          ¾¾¾®

O + H 2 O

 

CH3CO OH

Acetic acid

P2O5

CH3 CO

Acetic anhydride

 

(vi)  Reaction with organo-metallic reagents :

RCH2 MgBr + RCOOH ¾¾eth¾er ® RCH3 + RCOOMgBr

Alkane

 

  • Reaction involving carbonyl (>C = O) group : Reduction :

RCOH ¾¾LiA¾lH¾4  ® RCH 2  – OH

||

O

 

Carboxylic acid are difficult to reduce either by catalytic hydrogenation or

(4)          Reaction involving attack of carboxylic group (– COOH)

O

Na C2 H 5 OH

 

||

C
  • Decarboxylation : R – – OH ¾¾(C¾O¾2 ) ® RH

When anhydrous alkali salt of fatty acid is heated with sodalime then :

RCOONa+ NaOH ¾¾Ca¾O ® RH+ Na 2 CO3

 

Sodium salt

heat

Alkane

 

Note : (Exception) q When sodium formate is heated with sodalime H2 is evolved.

HCOONa + NaOH ¾¾Ca¾O ® H 2  + Na 2 CO3

  • Heating of calcium salts : (RCOO)2 Ca ¾¾he¾at ® RCOR+ CaCO3

 

Sodium salt

Ketone

 

  • Electrolysis : (Kolbe’s synthesis) : RCOONa  

RCOO + Na +

 

At anode

2RCOO ® R R + 2CO2 + 2e

 

At cathode

2Na +  + 2e  ® 2Na ¾¾2H¾2¾O ® 2NaOH + H 2

 

2CH 3 COOK+ 2H 2 O ¾¾Elec¾trol¾y¾sis ® CH 3  – CH 3 + 2CO2  + 2KOH + H 2

Potassium acetate                                                            Ethane

(iv)  Formation of Alkyl halide (Hunsdiecker’s reaction) :

 

CH 3 COOAg+ Br2  ¾¾he¾at ®

CH 3 Br

  • AgBr + CO2

 

Silver acetate

CCl4

Methyl bromide

 

Mechanism : Two step process –

C

O                                                       O

 

Step – I :

||

R COAg + Br2

O

¾¾CC¾l4  ® R – || – OBr + AgBr

O

 

||                                           ||      . .

 

Step II : (ii)

R COBr + Br2 ® R CO+ Br

 

 

 

.
.

O

||

R CO ® R+ CO2

. .

R+ Br ® R Br

Note : ® In Hunsdiecker reaction, one carbon atom less alkyl halide is formed from acid salt.

 

  • Formation of amines (schmidt reaction) :

RCOOH+

Acid

N 3 H

Hydrazoic acid

¾¾H2S¾O(con¾¾c.) ® RNH 2 + CO2  + N 2

Primary amine

 

In schmidt reaction, one carbon less product is formed.

Mechanism :

 

O

||             H +

OH

||

  • HN

OH

|                     – H O

O

||              – N

O

||      +

 

R C

|

OH

¾ ¾® RC

|

OH

¾¾¾3  ®

R COH

+

¾¾¾2

® R C

|

¾¾¾2  ® RCNH

+

 

H N N º N

NH N º N

H +

¾¾¾® RN  = C = O ¾¾HO ® RNH2  + CO2

 

(vi)  Complete reduction :

CH3 COOH+ 6HI ¾¾P ® CH3 CH3 + 2H 2 O + 3I 2

 

Acetic acid                                       Ethane

In the above reaction, the – COOH group is reduced to a CH3 group.

(5)  Reaction involving hydrogen of a-carbon

Halogenation

(i)  In presence of U.V. light

H                                                         Cl

– |                                        U.V .D                 |

C COOH + Cl2 ¾¾¾® – CCOOH + HCl

|                                                           |

a -chloro acid

(ii)  In presence of Red P and diffused light [Hell Volhard-zelinsky reaction]

Carboxylic acid having an a-hydrogen react with Cl2 or Br2 in the presence of a small amount of red phosphorus to give chloro acetic acid. The reaction is known as Hell Volhard-zelinsky reaction.

CH3 COOH ¾¾Cl2 ¾,red ¾P4  ® ClCH2 COOH ¾¾Cl2 ¾,red¾P4  ® Cl2 CHCOOH ¾¾Cl, red ¾P4  ® Cl3 CCOOH

 

Acetic acid

Mechanism :

HCl

Chloro acetic acid

HCl

Dichloro acetic acid

HCl

Trichloro acetic acid

 

Step – I :

R CH2C

O

O H

¾¾P+B¾r2  ® RCH2 – C

(PBr3 )

O    enolisation  R – CH C          OH Br                      Br

 

 

CH
..

..                           Br

 

Step – II :

R CH = C

O H + BrBr ¾¾H¾Br ® R –  |           – C        O

Br

 

 

 

Step – III :

 

R C HC

|

Br

Br

 

O + RCHC

Br                2

O ® R CH C OH |

Br

 

O                                   O

OH + R CH2C          Br

Acid bromide (IV)

 

Second molecule of acid

a -bromocarboxylic acid

 

 

 

Formic Acid or Methanoic acid (HCOOH)

Formic acid is the first member of monocarboxylic acids series. It occurs in the sting of bees, wasps, red ants, stinging nettles. and fruits. In traces it is present in perspiration, urine, blood and in caterpillar’s.

  • Methods of preparation : The following methods can be used for its preparation
(i)  Oxidation of methyl alcohol or formaldehyde :

 

 

CH OH + 1 O

3              2   2

¾¾Pt ® HCHO + H 2 O

 

 

 

HCHO + 1 O

2   2

® HCOOH

 

 

CH 3 OH + O2 ® HCOOH + H 2O

Formic acid

 

  • Hydrolysis of hydrocyanic acid : Formic acid is formed by the hydrolysis of HCN with acids or

HCN + 2H 2 O ¾¾H¾Cl ® HCOOH + NH 3 ;  HCN + H 2 O ¾¾NaO¾H ® HCOONa + NH 3

  • Laboratory preparation : Formic acid is conveniently prepared in the laboratory by heating glycerol

with oxalic acid at 100-120°C. In actual practice, glycerol is first heated at 105 o C and then hydrated oxalic acid is

added and the temperature is raised to 110°C. Glycerol monoxalate is first formed which decomposes into glycerol monoformate and carbon dioxide. When the evolution of carbon dioxide ceases, more of oxalic acid is added. The monoformate gets hydrolysed to formic acid regenerating glycerol which reacts with fresh oxalic acid. Thus, a small quantity of glycerol is sufficient to convert large quantities of oxalic acid into formic acid.

 

CH2OH HO OCCOOH

CH2OOC COO  H

CH2OOCH

CH2OH

 

|                        Oxalic acid

H  O              |

CO             |

(COOH) 2H O                                            |

 

CHOH

¾¾¾2¾®  CHOH

¾¾¾2  ® CHOH

¾¾¾¾2   ¾2¾® HCOOH+ CHOH

 

|

CH2OH

Glycerol

|

CH2OH

Glycerol monoxalate

110°C

|

CH2OH

Glycerol monoformate

Formic acid

|

CH2OH

Glycerol

 

The following procedure is applied for obtaining anhydrous formic acid.

2HCOOH + PbCO3 ® (HCOO)2 Pb+ CO2 + H 2 O ;  (HCOO)2 Pb + H 2 S ® Pbs+ 2HCOOH

 

Lead formate

ppt.

Formic acid

 

  • Industrial preparation : Formic acid is prepared on industrial scale by heating sodium hydroxide with carbon monoxide at 210°C under a pressure of about 10

CO + NaOH ® HCOONa

Sodium formate

Sodium formate thus formed is distilled with sodium hydrogen sulphate, when anhydrous formic acid distils over.

HCOONa + NaHSO4 ® HCOOH + Na 2 SO4

(2)  Physical properties

  • It is a colourless pungent smelling
  • It melts at 4°C and boils at 100.5°C.
  • It is miscible with water, alcohol and It forms azeotropic mixture with water.
  • It is strongly corrosive and cause blisterson

 

 

 

  • It exists in aqueous solution as a dimer involving hydrogen bonding.

Hydrogen bonding

 

 

H C

O  H O O H     O

C H

Hydrogen bonding

 

  • Chemical properties : Formic acid is the strongest acid among all the members of the homologous

series. It exhibits some characteristics which are not shown by other members. This unique nature is due to the fact that it contains both aldehyde group and carboxyl group.

 

 

HC

O

O               ||

HC

OH Aldehyde

OH H

O

||

COH

Carboxyl

 

Formic acid

group

group

 

(i)  Acidic properties
  • It is a monobasic Its dissociation constant value is 18 × 10–5 at 25°C. It’s acidic properties are due to its ionisation in aqueous solution.

 

HCOOH

Formic acid

HCOO + H +

Formate ion

 

  • It reacts with carbonates and bicarbonates evolving carbon dioxide. HCOOH +   NaHCO3   ®   HCOONa + H2+ CO2   ­ 2HCOOH + Na2CO3 ® 2HCOONa + H2O + CO2 ­
  • It reacts with alkalies to form corresponding The salts of formic acid are termed as formates. Most of

the formates are soluble in water but lead and silver formates are insoluble.

HCOOH + NaOH ® HCOONa + H2O

HCOOH + NH4 OH ® HCOONH4 + H2O

Amm. formate

  • Highly electropositive metals evolve hydrogen when react with formic 2HCOOH + 2Na ® 2HCOONa + H 2
  • It combines with alcohols to form It is not necessary to use a mineral acid as to catalyse the reaction since the formic acid itself acts as a catalyst.

HCOOH + CH3 OH HCOOCH3 + H2O

Methyl formate

  • It reacts with PCl5 or SOCl2 to give formyl chloride which is not a stable It decomposes at once into hydrogen chloride and carbon monoxide.

 

HCOOH + PCl5 ®

HCOCl

Formyl chloride

  • POCl3 + HCl

 

HCOCl ® HCl + CO

  • Action of heat : When heated above 160°C, it decomposes to give carbon dioxide and

HCOOH ® CO2 + H2

(iii)  Action of heat on formates
  • When sodium formate is heated to 360°C. It decomposes to form sodium oxalate and

COONa

 

2HCOONa ® |

COONa

Sodium oxalate

  • H 2

 

 

 

  • It does not form a hydrogen when sodium formate is heated with sodalime or its aqueous solution is

HCOONa + NaOH ¾¾Ca¾O ® Na2CO3  + H2

  • Formaldehyde is formed when dry calcium formate is

(HCOO)2 Ca ® HCHO + CaCO3

formaldehyde

(iv)  Reducing properties
  • Like aldehyde formic acid behaves as reducing agents, it is oxidised to an unstable acid, carbonic acid, which decompose into CO2 and H2O

O

||

H  COOH ¾¾[O¾] ® HOCOH ® CO2  + H2O

Carbonic acid

  • It decolourises acidified KMno4.

 

2KMnO4  + 3H 2 SO4

[HCOOH + O

®   K 2 SO4  + 2MnSO4  + 3H 2 O + 5[O]

®  CO2 + H 2O] ´ 5

 

 

2KMnO4 + 3H 2 SO4  + 5HCOOH ® K 2 SO4  + 2MnSO4  + 5CO2  + 8H 2 O

  • It reduces mercuric chloride to mercurous chloride to mercury black

HCOOH + 2HgCl2 ® Hg2Cl2 + CO2 + 2HCl HCOOH + Hg 2 Cl2 ® CO2 + 2HCl + 2Hg

  • It reduces ammonical silver nitrate (Tollen reagents)

HCOOH + Ag 2O ¾¾he¾at ® 2Ag + CO2  + H2O

Silver mirror

  • It reduces fehling solution give red precipitate of Cu2O

HCOOH + 2CuO ® Cu2O + CO2 + H2O

(Red ppt.)

  • Uses : Formic acid is
    • In the laboratory for preparation of carbon
    • In the preservation of
    • In textile dyeing and
    • In leather
    • As coagulating agent for rubber
    • As an antiseptic and in the treatment of
    • In the manufacture of plastics, water proofing
    • In electroplating to give proper deposit of
    • In the preparation of nickel formate which is used as a catalyst in the hydrogenation of
    • As a reducing
    • In the manufacture of oxalic

(5)  Tests of Formic Acid

  • It turns blue litmus
  • Its aqueous solution gives effervescences with sodium

 

 

 

  • Its neutral solution gives red precipitate with Fehling’s
  • Its neutral solution with Tollen’s reagent gives silver mirror or black
  • It gives white precipitate with mercuric chloride which changes to

HgCl2 ® Hg2Cl2 ® Hg

White ppt.            Grey

Acetic Acid (Ethanoic Acid) (CH3COOH)

Acetic acid is the oldest known fatty acid. It is the chief constituent of vinegar and hence its name (Latin acetum = vinegar)

(1)  Preparation

 

(i)  By oxidation of acetaldehyde (Laboratory-preparation) :

CH3 CHO ¾¾Nacro7  ® CH3 COOH

H2So4 (O)

 

(ii)  By hydrolysis of methyl cyanide with acid :

CH3 CN + 2H2O ¾¾H¾Cl ® CH3 COOH + NH3

 

O                                            æ           O            ö

 

(iii)   By Grignard reagent : CH

MgBr + CO

® CH

||

  • OMgBr

H 2O H +

ç            ||             ÷

CH   –    – OH

 

3                          2                3      C

¾¾¾¾®ç    3      C             ÷

ç                        ÷

è                        ø

 

(iv)  By hydrolysis of acetyl chloride, acetic anhydride or acetamide and ester
  • CH3COOC2 H5 + H2O ¾¾H2S¾O4 (¾con¾) ® CH3COOH + C2 H5OH Ester
  • CH3COCl + H2O ¾¾dil.H¾Cl ® CH3COOH + HCl

acetylchloride

2
  • (CH3CO) O + H2O ¾¾dil.H¾Cl ® 2CH3COOH
(v)  Manufacture of acetic acid
  • From ethyl alcohol (Quick vinegar process) : Vinegar is 6-10% aqueous solution of acetic acid. It is obtained by fermentation of liquors containing 12 to 15% ethyl alcohol. Fermentation is done by Bacterium Mycoderma aceti in presence of air at 30-35°C. The process is termed acetous fermentation.

CH3 CH2OH+ O2  ¾¾Myc¾ode¾rma¾ac¾eti ® CH3 COOH+ H2O

 

Ethyl alcohol

Bacteria

Acetic acid

 

It is a slow process and takes about 8 to 10 days for completion. In this process, the following precautions are necessary:

  • The concentration of the ethyl alcohol should not be more than 15%, otherwise the bacteria becomes
  • The supply of air should be With less air the oxidation takes place only upto acetaldehyde stage while with excess of air, the acid is oxidised to CO2 and water.
  • The flow of alcohol is so regulated that temperature does not exceed 35°C which is the optimum temperature for bacterial

Acetic acid can be obtained from vinegar with the help of lime. The calcium acetate crystallised from the solution is distilled with concentrated sulphuric acid when pure acetic acid distils over.

  • From acetylene : Acetylene is first converted into acetaldehyde by passing through 40% sulphuric acid at 60°C in presence of 1% HgSO4 (catalyst).

CH  º CH+ H2O ¾¾H2S¾O4 ¾(d¾il.) ® CH3 CHO

 

Acetylene

HgSO4

Acetaldehyde

 

The acetaldehyde is oxidised to acetic acid by passing a mixture of acetaldehyde vapour and air over manganous acetate at 70°C.

2CH3 CHO + O2  ¾¾Man¾gan¾ous¾ace¾ta¾te ® 2CH3 COOH

70°C

 

 

Note : ® Acetylene required for this purpose is obtained by action of water on calcium carbide.

CaC2 + 2H2O ® Ca(OH)2  + C2 H2

The yield is very good and the strength of acid prepared is 97%. The method is also quite cheap.

  • By the action of CO on methyl alcohol : Methyl alcohol and carbon monoxide react together under a pressure of 30 atmospheres and 200°C in presence of a catalyst cobalt octacarbonyl, Co2(CO)8 to form acetic

CH3 OH + CO ¾¾Co(CO¾)8  ® CH3 COOH

 

Methyl alcohol

(2)  Physical properties

30atm200°C

Acetic acid

 

  • At ordinary temperature, acetic acid is a colourless, corrosive liquid with a sharp pungent odour of It has a sour taste.
  • Below 5°C, it solidifies as an icy mass, hence it is named glacial acetic acid.
  • It boils at 118° The high boiling point of acetic acid in comparison to alkanes, alkyl halides or alcohols of nearly same molecular masses is due to more stronger hydrogen bonding between acid molecules. This also explains dimer formation of acetic acid in vapour state.
  • It is miscible with water, alcohol and ether in all
  • It is good solvent for phosphorus, sulphur, iodine and many organic
  • Chemical properties : Acetic acid is a typical member of fatty acids. It shows all the general characteristics of monocarboxylic

Reaction chart of Acetic acid

 

NaOH

 

NaHCO3

 

C2H5OH

H2SO4

PCl3 or PCl5

or SOCl2

P2 O5

heat

(i) NH3

(ii) heat

LiAlH4

 

NaOH+CaO

heat

(i) CaCO3

(ii) heat

(i) CaCO3

(ii) (HCOO)2 Ca, heat

N3H

Conc. H2SO4

(i) KOH

(ii) Electrolysis

Cl2 red P

 

Na                         CH3COONa

Sodium acetate

CH3COONa

CH COONa+H O+CO ­

3                       2                     2

 

CH COOC H

3             2     5

 

 

 

 

 

CH COOH

Ethyl acetate

CH3COCl

Acetyl chloride

(CH3CO)2O

Acetic anhydride

CH CONH

 

3

Acetic acid

3              2

Acetamide

 

CH3CH2OH

Ethyl alcohol

CH4

Methane

CH COCH

 

 

 

 

 

 

 

  • Uses : It is used,

 

 

 

 

 

 

 

 

heat

3             3

Acetone

CH3CHO

Acetaldehyde

CH3NH2

Methyl amine

CH3–CH3

Ethane

CH2ClCOOH

Chloroacetic acid

 

 

 

 

 

 

 

Cl2 P

 

 

 

 

CHCl2COOH

Dichloro acetic acid

 

 

 

 

 

 

 

Cl2 P

 

 

 

 

CCl3COOH

Trichloro acetic acid

 

  • As a solvent and a laboratory

 

 

 

  • As vinegar for table purpose and for manufacturing
  • In coagulation of rubber
  • For making various organic compounds such as acetone, acetic anhydride, acetyl chloride, acetamide and
  • For making various useful metallic acetates, such as:
  • Basic copper acetate which is used for making green
  • Al, Fe and Cr acetates which are used as mordants in
  • Lead tetra-acetate which is a good oxidising
  • Basic lead acetate which is used in the manufacture of white
  • Aluminium acetate which is used in the manufacture of water-proof
  • Alkali acetates which are used as

(5)  Tests

  • Its aqueous solution turns blue litmus
  • Its aqueous solution gives effervescences with sodium
  • The neutral solution of the acetic acid gives a wine red colour with neutral ferric chloride
  • When heated with ethyl alcohol in presence of a small amount of concentrated sulphuric acid, it forms ethyl acetate which has fruity
  • Acetic acid does not show reducing properties like formic acid, e., it does not reduce Tollen’s reagent, Fehling’s solution and mercuric chloride.

Comparison of Formic Acid and Acetic Acid

 

PropertyFormic acidAcetic acid
1. Acidic nature,

(i)    With electro- positive metals

 

(ii)      With bases

 

(iii)                                      With

carbonates      and bicarbonates

 

 

2.  Ester formation

 

 

 

 

 

3.  Reaction with PCl5

 

 

4.  Heating of ammonium salt

 

Forms salts, Hydrogen is evolved.

HCOOH + Na ® HCOONa + 1 H 2

2

Forms salts.

 HCOOH + NaOH ® HCOONa + H 2O

Forms salts. Carbon dioxide is evolved.

 HCOOH + NaHCO3 ® HCOONa + H 2 O + CO2

 

 

Forms esters when treated with alcohols.

 HCOOH + C2 HOH ® HCOOC2 H5 + H 2 O

 

 

 

Forms formyl chloride which decomposes into CO and HCl.

 HCOOH + PCl5 ® HCOCl(HCl + CO) + POCl3 + HCl

 

Forms formamide.

 HCOONH4 ® HCONH 2 + H 2O

 

Forms salts. Hydrogen is evolved.

CH3 COOH + Na ® CH3 COONa + 1 H 2

2

Forms salts.

 CH3 COOH + NaOH  ® CH3 COONa + H 2O

Forms salts. Carbon dioxide is evolved.

 CH3COOH + NaHCO3 ®

 

 CH 3COONa + H 2O + CO2

Forms      esters     when     treated     with alcohols.

 CH 3 COOH + C2 H5 OH ¾¾H2S¾O(co¾n¾c.) ®

 

 CH 3 COOC2 H5 + H 2 O

Forms acetyl chloride which is a stable compound.

 CH 3COOH + PCl5 ®

 CH 3 COCl + POCl3 + HCl

Forms acetamide.

 CH 3 COONH4  ® CH 3 CONH 2  + H 2 O

 

 

 

 

  1. Heating alone it decomposes into CO2 and H2

 HCOOH ® CO2 + H 2

Unaffected

 

  1. Heating with H2SO4

Decomposed into CO and H2O

Unaffected

 

 

 

  1. Reaction with Cl2 in presence of red P

8 Action of heat on salts,

Unaffected                                                              Forms mono, di or trichloro acetic acids.

 

  • Calcium salt Forms

(HCOO)2 Ca ® HCHO + CaCO3

Forms acetone.

(CH  COO) Ca ® CH  COCH  + CaCO

 

3            2                    3              3                  3

  • Sodium salt Forms sodium                                             Unaffected.

 

 

 

 

  • Sodium salt with soda-lime

Forms sodium carbonate and H2.

 HCOONa + NaOH ¾¾Ca¾O ® Na2 CO3  + H 2

Forms sodium carbonate and methane.

 CH 3 COONa + NaOH ¾¾Ca¾O ®

 

 

 

 

  1. Electrolysis of sodium or potassium salt
  2. On heating with P2O5
  3. Reducing

 CH 4  + Na2 CO3

It evolves hydrogen.                                                It forms ethane.

 

 

Unaffected                                                              Forms acetic anhydride.

2CH 3 COOH ¾¾P2O¾5  ®(CH 3 CO)2 O + H 2 O

 

nature,

  • Tollen’s reagent
  • Fehling’s solution
  • Mercuric chloride

Gives silver mirror or black precipitate.

 HCOOH + Ag 2 O ® 2Ag + CO2 + H 2 O

 

Gives red precipitate

 HCOOH + 2CuO ® Cu2 O + CO2  + H 2 O

Forms a white ppt. which changes to greyish black.

 HgCl 2 ® Hg 2Cl 2 ® 2Hg

Unaffected.

 

 

Unaffected. Unaffected.

 

  • Acidified KMnO4
  • Acid (neutral solution) + NaHSO3 +

Sodium nitroprusside.

Decolourises                                                            Unaffected.

 

Greenish blue colour.                                              Unaffected.

 

  • Acid (neutral solution) + neutral ferric

Red colour which changes to brown ppt. on heating.

Wine red colour.

 

 

 

Interconversions

  • Ascent of series : Conversion of formic acid into acetic

 

HCOOH ¾¾Ca(¾OH¾)2 ®(HCOO)2 Ca ¾¾he¾at ®

HCHO

¾¾CH¾3 M¾gB¾r ® CH 3 CH 2 OMgBr ¾¾HO ® CH 3 CH 2 OH

 

Formic acid

Calcium formate

Formaldehyde

Addition product

H +                  Ethyl alcohol

 

¾¾[¾O] ® CH 3 CHO ¾¾[¾O] ® CH 3 COOH

 

 

HCHO

¾¾H2  ¾Ni ®  CH3OH

Acetaldehyde

 

¾¾H¾I ® CH3 I ¾¾KC¾N(A¾l¾c.) ® CH3CN ¾¾HO ® CH3COOH

Acetic acid

 

Formaldehyde

Methyl alcohol

Methyl iodide

Methyl           H +

cyanide

Acetic acid

 

Arndt-Eistert homologation : This is a convenient method of converting an acid, RCOOH to RCH2COOH.

RCOOH ¾¾SO¾CL¾2 ® RCOCl ¾¾CH¾2 N¾2 ® RCOCHN 2  ¾¾EtO¾H ® RCH 2 COOC2 H5  ¾¾Hyd¾rol¾y¾sis ® RCH 2 COOH

Ag2O

  • Descent of series : Conversion of acetic acid into formic

 

¾¾NH ® CH 3 NH 2  ¾¾NaN¾OH¾Cl ®  CH 3 OH

¾¾[¾O] ®

HCHO

¾¾[¾O] ® HCOOH

 

H2SO4

Methyl amine

Methyl alcohol

Formaldehyde

Formic acid

 

CH 3 COOH ¾¾NH¾3  ® CH 3 COONH 4  ¾¾he¾at ® CH 3 CONH 2  ¾¾BrKO¾¾H ® CH 3 NH 2

 

Acetic acid

Amm. acetate

Acetamide

Methyl amine

 

 

 

¾¾NaO¾H ® CH3COONa ¾¾Sod¾alim¾e ® CH4

¾¾C¾l2 ® CH3Cl ¾¾AgO¾H ®  CH3OH

¾¾[¾O] ®

HCHO

¾¾[¾O] ® HCOOH

 

Sodium acetate

heat

Methane      hv

Methyl chloride

Methyl alcohol Na2Cr2O7 + H2SO4 Formaldehyde

Formic acid

 

 

 

(CH3CO)2O

Acetic anhydride

Conversion of Acetic acid into other organic compound

 

 

 

CH3CH3

Cl2 hv

CH3CH2Cl

Ethyl chloride

AgOH           CH3CH2OH

Ethyl alcohol

[O]     CH3CHO

Acetaldehyde

 

Ethane

 

 

CH3CH2NH2

Ethyl amine

 

CH CH CH NH

 

[H]     CH CH CN         H2O

 

CH3CH2COOH

 

3       2       2       2

LiAlH                  3       2

H+                      Propionic acid

 

Sodalime

n-Propyl amine

Cl

4

AgOH

[O]

[O]

NaOH

 

2

CH4

hv               CH3 Cl

CH3OH

Methyl alcohol

HCHO

Formaldehyde

HCOOH

Formic acid

 

Methane

Methyl chloride

COOH

|

COOH

Oxalic acid

 

CH3COONa

Sodium acetate

H2SO4

COONa

|

COONa

Sodium oxalate

 

heat

HCOONa

Sodium formate

 

 

 

CH3COOH

Ca(OH)2  (CH COO) Ca

heat CH COCH

H2/Ni   CH CHOHCH

Alc.KOH CH CH= CH

 

3            2                          3             3                   3                    3                       3                  2

 

Calcium acetate

Acetone

 

I2 + NaOH

CHI3

Iodoform

 

CH3CONH2

Acetamide

Isopropyl alcohol

 

 

 

HC CH

acetylene

 

Br2/KOH            CH3NH2

Methyl amine

Propene 500°C Cl2

ClCH2CH= CH2

Allyl chloride

 

 

 

 

 

 

CH3COCl

Acetyl chloride

NH3

 

C2H5OH

CH3CN

heat

Methyl cyanide

 

CH3COOC2H5

Ethyl acetate

[H]

LiAlH4

CH3CH2NH2

Ethyl amine

 

 

Rosenmund’s reduction

 

CH3CHO

Acetaldehyde

HCN           CH CH          OH

3

CN

H2O H+

CH3CHOHCOOH

Lactic acid

 

Cyanohydrin

The acids containing two carboxylic groups are called dicarboxylic acids.

The saturated dicarboxylic acid are represented by the general formula Cn H 2n (COOH)2 where n = 0, 1, 2, 3 etc.

HO C– (CH 2 )n COH  or HOOC(CH 2 )n COOH

||                       ||

O                       O

According to IUPAC system, the suffix-dioic acid is added to the name of parent alkane, i.e. Alkane dioxic acid.

 

FormulaCommon nameIUPAC name
HOOCCOOHOxalic acidEthanedioic acid
HOOCCH2COOHMalonic acid1-3 Propanedioic
  acid
HOOCCH2CH2Succinic acid1,4-Butanedioic acid

 

 

 

COOH  
HOOC(CH2)3COOHGlutaric acid1,5-Pentanedioic acid
HOOC(CH2)4 COOHAdipic acid1,6-Hexanedioic acid

 

Oxalic Acid or Ethanedioic Acid

COOH

 

|

COOH

or      (COOH)2

or     (C2 H 2 O4 )

 

Oxalic acid is first member of dicarboxylic series.

It occurs as potassium hydrogen oxalate in the wood sorel, rhubarb and other plants of oxalis group and as calcium oxalate in plants of rumex family.

It is found in the form of calcium oxalate in stony deposits in kidneys and bladdar in human body. Oxalic acid present in tomatoes.

(1)  Methods of Preparation

(i)  By oxidation of ethylene glycol with acidified potassium dichromate

CH2OH+ 4[O] ¾¾K  C¾r O¾® COOH + 2H   O

|                          2    2  7          |                 2

 

CH2OH

Glycol

H2SO4

COOH

 

 

(ii)  By hydrolysis of cyanogen with conc. hydrochloric acid :

CN

2

| + 4 H CN

O ¾¾2(H¾C¾l) ® COOH+ 2NH   Cl COOH

 

(iii)
|
4
By heating sodium or potassium in a current of carbon dioxide at 360°C

 

 

2Na + 2CO

¾¾he¾at ®

COONa

 

2                |

COONa

Sodium oxalate

 

(iv)  Laboratory preparation :

C12 H

22 O11

+ 18[O] ¾¾HN¾O¾3  ®

COOH

6 |          + 5H 2O

 

Sucrose

V2O5

COOH

Oxalic acid

 

(v)  Industrial method :

2HCOONa ¾¾360¾°¾C ® COONa + H

 

|
2

Sod. formate

COONa

Sod. oxalate

 

Sodium formate is obtained by passing carbon monoxide over fine powdered of sodium hydroxide.

CO + NaOH ¾¾200¾°¾C ® HCOONa

8-10atm

The sodium oxalate thus formed is dissolved in water and calcium hydroxide is added. The precipitate of calcium oxalate is formed which is separated by filtration. It is decomposed with calculated quantity of dilute sulphuric acid.

 

COONa

|

COONa

  • Ca(OH)2 ®

COO

|

COO

Calcium oxalate

Ca + 2NaOH

 

COO

|

COO

COOH

Ca + H 2SO4 (dil.) ® |            +

COOH

Oxalic acid (soluble)

CaSO4

Calcium sulphate (insoluble)

 

 

 

(2)  Physical Properties

  • It is a colourless crystalline It consists of two molecules of water as water of crystallisation.
  • The hydrated form has the melting point 101.5°C while the anhydrous form melts at 190°C.
  • It is soluble in water and alcohol but insoluble in
  • It is poisonous in It affects the central nervous system.

(3)  Chemical Properties

  • Action of heat : It becomes

(COOH)2 2H2O ¾¾100¾10¾5°¾C ®(COOH)2 + 2H2O

 

Hydrated oxalic acid

Anhydrous oxalic acid

 

  • At 200°C, (COOH)2 + HCOOH+ CO2

Formic acid

On further heating, formic acid also decomposes.

HCOOH ® CO2 + H 2

  • Heating with H2SO4

 

COOH

|

COOH

¾¾H2S¾O¾4  ® CO + CO2  + H 2 O

(conc.)

 

(ii)  Acidic nature

Salt formation

COOH

 

 

 

KOH

 

 

COOK

 

 

 

 

 

KOH

 

 

COOK

 

|          +

COOH

Oxalic acid

®     |

COOK

Acid pot. oxalate

¾¾¾® |

COOK

Pot. oxalate

 

COOH

|

COOH

  • 2NaHCO3 ®

COONa

|

COONa

Sod. oxalate

+ 2CO2 + 2H 2O

 

COOH

|

COOH

COONa

  • Na 2 CO3 ® |

COONa

  • H 2 O + CO2

 

(iii)  Esterification

COOH

 

 

 

C H OH

COOCH5

 

 

 

C H OH

COOC2 H5

 

|

COOH

¾¾2 ¾5   ¾® |

COOH

Ethyl hydrogen oxalate

¾¾2 ¾5   ¾®  |

COOC2 H5

Ethyl oxalate

 

 

 

 

(iv)  Reaction with PCl5 :

COOH

|

COOH

COCl

+ 2PCl5 ® |

COCl

Oxalyl chloride

  • 2POCl3 + 2HCl

 

 

 

(v)  Reaction with ammonia

 

 

COOH

COONH4

NH             COONH4

 

|

COOH

  • NH3 ®

|

COOH

Acid ammonium oxalate

¾¾¾3  ® |

COONH4

Amm. oxalate

 

H2O heat                    – 2H2O heat

 

 

CONH2

|

COOH

Oxamic acid

CONH2

|

CONH2

Oxamide

 

  • Oxidation : When oxalic acid is warmed with acidified

KMnO4 .

 

2KMnO4 + 3H 2 SO4  ® K 2 SO4  + 2MnSO4  + 3H 2 O + 5[O]

 

éCOOH

ê|

ëCOOH

+ [O] ® 2CO   + H  Où ´ 5

2              ú2

û

 

2KMnO4

Pot. permanganate (Purple)

COOH

+ 3H2SO4 + 5 |

COOH

Oxalic acid

® K2SO4 + 2MnSO4 + 10CO2 + 8H2O

Colourless

 

Note : ® Oxalic acid decolourises the acidic

(vii)  Reaction with ethylene glycol

KMnO4 solution.

 

 

 

 

O=                                         CH2

|

O=                                         CH2

 

 

heat

H2O

O=C

| O=C

O

CH2

| CH2

O

 

Oxalic acid               Ethylene glycol

 

  • Reduction : COOH+ 4 H ¾¾Z¾n ® CH2OH + H  O

Ethylene oxalate

 

|

COOH

H2SO4

|                2

COOH

Glycolic acid

 

It can also be reduced electrolytically using lead cathode into glycolic acid and glyoxalic acid.

 

 

COOH

2 |

CH2OH

¾¾Elec¾tro¾lytic¾red¾uct¾io¾n ®  |             +

COOH

|

  • 2H2O

 

COOH

 

6[H]

 

COOH

Glycolic acid

 

CHO

Glyoxalic acid

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