Chapter 21 Carboxylic Acids and their derivatives Part 4- Chemistry free study material by TEACHING CARE online tuition and coaching classes

Chapter 21 Carboxylic Acids and their derivatives Part 4- Chemistry free study material by TEACHING CARE online tuition and coaching classes

File name : Chapter-21-Carboxylic-acids-and-their-derivatives-Part-4.pdf

 

 

 

The compounds which are obtained by replacing the

  • OH

of the carboxylic group by other atoms or groups

 

such as

X , – NH  , – OR and O CR

2

||

O

are known as acid derivatives.

 

  • RC

||

O

group is common to all the derivatives and is known as acyl group and these derivatives are termed

 

as acyl compound.

  • The important derivatives are given below :

 

Reactivity

Acyl derivatives are characterised by nucleophilic substitution reactions.

 

 

R

C = O : + : Nu– L               ..

Nu                       Nu

R              ..          |

CO.. : ® R –  C

L

= O+ : L

 

 

O

||

(L = X, NH2,OCR or OR)

Intermediate

 

The relative reactivities of various acyl compounds have been found to be in the following order:

O            O

R                               ||       ||                 O                         O

C = O > R CO CR > R C                  > R C

X                                                                               OR                     NH2

Out of acid halides, the acid chlorides are more important ones.

The overall order of reactivity can be accounted for in terms of the following three factors:

(i) Basicity of the leaving group (ii) Resonance effects and (iii) Inductive effects.

 

 

 

  • Basicity of the leaving group : Weaker bases are good leaving Hence, the acyl derivatives with

 

weaker bases as leaving groups are more reactive. Chloride ion is the weakest base while – NH2

base. Thus, acyl chlorides are most reactive and amides are least reactive.

is the strongest

 

  • Resonance effect : The leaving group in each case has an atom with lone pair of electrons adjacent to the carbonyl The compound exists, therefore, as a resonance hybrid.

O

||

 

RC

..¬¾® RC L

 

This makes the molecule more stable. The greater the stabilization, the smaller is the reactivity of the acyl compound. However, acyl chlorides are least affected by resonance. Due to lower stabilization, the acid chlorides are more

 

reactive as the loss of

they are less reactive.

  • Cl

is easier. Greater stabilization is achieved by resonance in esters and amides and thus,

 

  • Inductive effect : Higher the –I effect, more reactive is the acyl Inductive effect of oxygen in ester is greater than nitrogen in amide, hence ester is more reactive than an amide.

Acyl Halides

 

 

RC

O where R may be alkyl or aryl group.

Cl

 

Nomenclature: The common names as well as IUPAC names of the acid halides are derived by replacing ic acid by yl halide.

 

Acyl chlorideCommon nameIUPAC name
 HCOClFormyl chlorideMethanoyl chloride
 CH3COClAcetyl chlorideEthanoyl chloride
 CH3CH2COClPropionyl chloridePropanoyl chloride
 C6 H5COClBenzoyl chlorideBenzoyl chloride

 

 

(1)  Methods of Preparation

  • From carboxylic acid :

RCOOH + PCl5 ® RCOCl + POCl3  + HCl

3RCOOH + PCl3 ® 3RCOCl + HPO3

 

  • Industrial method : By distilling anhydrous sodium acetate

3CH3 COONa + PCl3  ¾¾he¾at ® 3CH3 COCl + Na3 PO3

2CH3 COONa+ POCl3  ¾¾he¾at ® 2CH3 COCl+ NaPO3  + NaCl

Sodium acetate                                                Acetyl chloride

(CH3COO)2 Ca+ SO2Cl2 ¾¾he¾at ® 2CH3COCl+ CaSO4

 

Calcium acetate

Sulphuryl chloride

Acetyl chloride

 

  • With thionyl chloride : RCOOH + SOCl2 ® RCOCl + SO2 + HCl

 

This is the best method because SO2

and HCl are gases and easily escape leaving behind acyl chloride.

 

 

 

  • Physical properties : The lower acyl chloride are mobile, colourless liquid while the higher members are coloured

Acyl chloride have very pungent, irritating order and are strong lachrymators (tears gases) The fume in air due to the formation of hydrochloric acid by hydrolysis.

They are readily soluble in most of the organic solvent. Acyl chloride don’t form intermolecular hydrogen bonding. Therefore, their boiling points are lower than those of their parent acids.

(3)  Chemical properties

 

 

O

C

R – || – Cl+ : Nu – ® R

O

|

C  Cl ® R

|

Nu

O

||

C + Cl

|

Nu

 

Cl + H + ® HCl

  • Hydrolysis : CH3 COCl+ HOH  ® CH3COOH+ HCl

Acetyl chloride                                 Acetic acid

C6 H5 COCl+ H2O ® C6 H5 COOH+ H2O

Benzoyl chloride                            Benzoic acid

  • Reaction with alcohols (alcoholysis)

CH3COCl + CH3CH2OH ® CH3COOCH2CH3 + HCl

Ethyl acetate

 

C6 H5COCl+ C2 H5OH ¾¾aq N¾aO¾H¾or ® C6 H5COOC2 H5 + HCl

 

Benzoyl chloride

Ethyl alcohol

Pyridine

Ethyl benzoate

 

This reaction is called Schotten Baumann reaction.

  • Reaction with salts of carboxylic acid

O            O

 

CH COCl + CH

COO– Na +  ¾¾Pyri¾di¾ne ®

||             ||

  • O – – CH

 

3               3                            CH3 C              C            3

Acetic anhydride

 

  • Reaction with benzene (acylation) : This reaction is called friedel craft

COCH3

 

 

  • CH3COCl

¾¾Anh¾yd.¾AlC¾l3  ®

  • HCl

 

 

 

Acetyl chloride

Acetophenone

COC6H5

 

 

 

  • C6 H5 COCl

¾¾Anh¾yd.¾AlC¾l3  ®

  • HCl

 

 

 

Benzoyl chloride

 

  • Reaction with ammonia or amines :

Benzophenone

 

CH3 COCl+ 2NH3  ® CH3 CONH2 + NH4 Cl

 

Acetyl chloride                                    Acetamide

C6 H5COCl + 2NH3 ® C6 H5CONH2 + NH4Cl

Benzamide

 

 

 

However, acyl chlorides react with amines to form substituted amides.

O

||

CH3 COCl + HNC2 H5  ® CH3 CNH C2 H5

N-Ethyl acetamide

 

CH3 COCl + (C2 H5 )2 NH  ® CH3 CON(C2 H5 )2  + HCl

N, N-Diethyl acetamide

 

 

  • Reduction :

CH3COCl ¾¾LiA¾lH4 ¾or ®

NaBH4

CH3CH2OH

Ethanol (Primary alcohol)

 

CH3 COCl + H2  ¾¾Pd /¾BaS¾O¾4  ® CH3 CHO + HCl

 

This reaction is called Rosenmund reaction.

  • Reaction with organocadmium compounds (formation of ketones)

2CH3 COCl + (CH3 )2 Cd ® 2CH3 COCH3 + CdCl2

 

Dimethyl Cadmium

Acetone

 

2C6 H5 COCl + (CH3 )2 Cd ® 2C6 H5 COCH3 + CdCl2

Acetophenone

  • Reaction with diazomethane

O                                                                  O                                                                    O

 

||

CH   –     – Cl + 2CH

+

–     º N ® CH

||      –

–    –

+

–     º N ¾¾HO ®

||

OH

 

3   C                         2      N

3   C   CH     N

CH3 CH2 C

 

Diazomethane

Diazoacetone

(- N2 )

 

  • Reaction with water :
  • Reaction with chlorine :

CH3 COCl ¾¾AgN¾O/ HO ® CH3 COOH + AgCl + HNO3

CH3 COCl + Cl2  ¾¾Red¾P ® ClCH2  – COCl + HCl

Mono-a -chloroacetyl chloride

 

  • Reaction with Grignard reagent

 

CH3 CO

CH3

® CH

3COCH3

  • Mg I

Cl

 

Methyl magnesium iodide                             Acetone

 

  • Reaction with KCN : CH3COCl + KCN  ® CH3COCN  ¾¾HO ® CH3COCOOH

 

 

  • Reaction with Salicylic acid

Acetyl cyanide

Pyruvic acid

 

 

 

OH       + ClOCCH ®

OOCCH3

 

 

 

Salicylic acid

COOH

3             COOH

Acetyl salicylic acid (Aspirin)

+ HCl

 

 

  • Reaction with ether : CH3 COCl + C2 H5 OC2 H5 ¾¾ZnC¾l2  ® CH3 COOC2 H5 +  C2 H5 Cl

 

Diethyl ether

anhy.

Ethyl acetate

Ethyl chloride

 

  • Reaction with sodium peroxide (Peroxide formation)

 

O

||               +        –         – +

O                    O

||                     ||

 

3

2CH3 – CCl+ Na OONa ® CH3 CO O CCH

  • 2NaCl

 

Acetyl chloride                                                  Acetyl peroxide

 

 

 

  • Reaction with hydroxylamine and hydrazine

CH3 COCl + H2 NOH ® CH3 CONHOH+ HCl

 

Hydroxyl amine

Acetyl hydroxylamine (hydroxamic acid)

 

CH3 COCl + H2 NNH2  ® CH3CONHNH2 + HCl

 

 

(4)  Uses

Hydrazine

Acetyl hydrazine

 

  • As an acetylating
  • In the estimation and determination of number of hydroxyl and amino
  • In the preparation of acetaldehyde, acetic anhydride, acetamide, acetanilide, aspirin, acetophenone

Acid Amides

 

RC

O NH 2

where, R = –CH3

, – CH

2CH3

, – C6 H5

 

Nomenclature

  • In common system, –c., acid is replaced by amide.
  • In IUPAC system, e of parent hydrocarbon is replaced by

 

Acyl amidesCommon nameIUPAC name
 HCONH2

 CH3CONH2

 C2 H5CONH2

 C6 H5CONH2

Formamide Acetamide Propionamide

Benzamide

Methanamide Ethanamide Propanamide

Benzamide

 

  • The hydrogen atom of the acid may also be replaced by alkyl

 

CH3CONHCH3

N-Methyl ethanamide (N-Methyl acetamide)

 

Therefore, the acid amides are classified:

CH3CONHC2 H5

N- Ethyl ethanamide (N- Ethyl acetamide)

 

O

||

R CNH2

1o Amide

Similarly

O

||

CH3CNHCH3

N-Methylethanamide (N-Methyl acetamide)

O

||

R CNHR¢

2o Amide

 

 

 

CONHCH3

O

||

RCNR

3o Amide

 

 

NHCOCH3

 

 

 

NHCOC6 H5

 

 

 

N-Methylbenzamide

N-Phenylethanamide (Acetanilide)

N-Phenyl benzamide (Benzanilide)

 

O      CH3

||      |

O      CH3

||      |

 

H3CN   –  CH3

CH3CN  –  CH3

 

N-N-Dimethyl methanamide (N,N-Dimethyl formamide, DMF)

N,N-Dimethyl ethanamide

(N,N-Dimethyl acetamide, DMA)

 

 

 

 

(1)  Methods of preparation

  • Ammonolysis of acid derivatives

CH3 COCl + 2NH3  ® CH3 CONH2 + NH4 Cl

Acetamide

 

(CH3CO)2 O + 2NH3  ® CH3CONH2 + CH3COONH4

Acetamide                 Amm. acetate

 

C6 H5 COCl+ NH3  ® C6 H5 CONH2 + HCl

Benzoyl chloride                              Benzamide

  • From ammonium salts of carboxylic acids (Laboratory Method)

CH3COONH4  ¾¾He¾at ® CH3CONH2 + H2O

Acetamide

Note : ® Ammonium acetate is always heated in presence of glacial acetic acid to avoid the side product ( CH3COOH).

  • By partial hydrolysis of alkyl cyanide : CH3C º N ¾¾Con¾ H¾Cl ® CH3CONH2

 

 

  • By heating carboxylic acid and urea

H2O / OH

Acetamide

 

H2 NCNH2  + RCOH ¾¾he¾at ® RCNH2 + CO2  + NH3

 

||                            ||

O                           O

 

(2)  Physical properties

||

O

Amide

 

  • Physical state : Formamide is a liquid while all other amides are
  • Boiling points : Amides have high boiling points than the corresponding

Acetic Acid                        Acetamide

b.p. 391 K                                        b.p. 494 K

Benzoic acid                      Benzamide

b.p. 522 K                                        b.p. 563 K

The higher boiling points of amides is because of intermolecular hydrogen bonding

H     R                              H    R                              H    R

|      |                                 |      |                                 |      |

……….H N C = O………H N C = O……… H N C = O

  • Solubility : The lower members of amide family are soluble in water due to the formation of hydrogen bonds with

(3)  Chemical properties

 

  • Hydrolysis :

CH3CONH2  + H2O ¾¾Slow¾ly ® CH3COOH + NH3 CH3CONH2 + H2O + HCl ¾¾Rap¾id¾ly ® CH3COOH + NH4Cl CH3CONH2  + NaOH ¾¾Far¾mor¾e ra¾pid¾ly ® CH3COONa + NH3

 

 

 

 

  • Amphoteric nature (Salt formation)

It shows feebly acidic as well as basic nature.

 

CH3CONH2 + HCl(conc.) ®

CH3CONH2.HCl

Acetamide hydrochloride

(only stable in aqueous solution)

 

2CH3CONH2 +

Acetamide

HgO

Mercuric Oxide

® (CH3CONH)2 Hg + H2O

Mercuric acetamide

 

CH  CONH   + Na ¾¾Eth¾er ® CH  CONHNa+ 1 H

2

3               2                                       3                                 2

Sodium acetamide

 

  • Reduction :

CH3CONH2 + 4[H] ¾¾LiA¾lH¾4  ® CH3CH2 NH2 + H2O

 

Acetamide                                                 Ethylamine

 

C6 H5CONH2 + 4[H] ¾¾Na /¾C2H¾5O¾H ® C6 H5CH2 NH2 + H2O

Benzamide                                                          Benzylamine

 

  • Dehydration: CH3CONH2 ¾¾P2O¾5  ® CH3C º N + H2O

 

Acetamide

heat

Methyl cyanide

 

 

C6 H5CONH2  ¾¾P2O¾5  ® C6 H5C º N + H2O

 

Benzamide

heat

Phenyl cyanide

 

 

C6 H5 CONH2  ¾¾SOC¾l2  ® C6 H5C º N

Phenyl cyanide

  • Reaction with nitrous acid

CH3CONH2  + HONO ¾¾NaN¾O/ H¾Cl ® CH3COOH+ N2  + H2O

Acetic acid

 

C6 H5 CONH2  + HONO ¾¾NaN¾O/ H¾Cl ® C6 H5COOH+ N2  + H2O

Benzoic acid

 

  • Hofmann bromamide reaction or Hofmann degradation : This is an important reaction for reducing a carbon atom from a compound, e., CONH2 is changed to – NH2 group.

 

CH3CONH2

¾¾B¾r2  ®    CH3 NH2

 

Acetamide

NaOH or KOH Methyl amine (p-)

 

This reaction occurs is three steps:

O

||

CH3  – CNH2  + Br2  + KOH ® CH3CONHBr+ KBr + H2O

Acetobromamide

 

O

||

CH3CNHBr2 + KOH ®

CH3 NCO + KBr + H2O

Methyl isocyanate

 

CH3 NCO + 2KOH ® CH3 NH2 + K2CO3

Methyl amine

CH3CONH2 + Br2 + 4 KOH ® CH3 NH2 + 2KBr + K2CO3 + 2H2O

 

 

O       ..                      O   ..

 

C

Mechanism:

||

R CNH2

  • Br2

¾¾KO¾H ® R – || – NBr + KBr + H  O

2

|

H

N – Bromamide

 

..
..

O                                     é      O                 ù-

||                         KOH            ê      ||                   ú     +

 

RCNBr ¾¾¾® êRCN..- Brú  K

  • H2O

 

H

|                               êë

úû

Unstable salt

 

é      O

ê       ||      ..

ù         é

ú      +      ê

O           ù

..

||            ú

é      O           ù

ê
..

;           ||            ú

 

Rearrangement

 

êR CN Brú   K

® êR CN :ú + KBr

êRCN :ú ¾¾¾¾¾¾® O = C = NR

 

ê

ë            ..     úû

ëê               úû

Unstable (acyl nitrene)

ëê               úû

Acetyl nitrene

(Intramolecular)

Isocyanate

 

RN  = C = O ¾¾2KO¾H ® RNH2  + K2CO3

 

COOH

 

CONH2

 

2KOD/Br2 D

N3 (–HOD)

D

 

COND2

 

2KOH/Br2.D

 

 

 

ND2 + K2CO3 + HOD

NH2 + 2HOD + K2CO3

 

 

 

Note : ® In this reaction a number of intermediates have been isolated; N-bromamides,

RCONHBr;

salts of

 

these bromamides [RCONBr ] K +

; Isocyanates, RNCO.

 

  • Nitrene rearranges to form
  • Action with alcohol : CH3CONH2 + CH3OH ¾¾H¾Cl ® CH3COOCH3 + NH4 Cl

 

 

(viii)  Reaction with grignard reagent

70o C

methyl acetate

 

OMgBr

 

CH3

  • Mg Br + CH3
  • CONH2

® CH4

  • CH3
  • CONHMgBr ¾¾CHMg¾Br ® CH3

|

  • C

|

CH3

NH MgBr

 

 

 

é

ê

H O / H +

OH                                 é

ù
ú

|               – NH             ê

O              ù

||                ú

 

¾¾2 ¾¾®êCH3  – C

NH2 ú¾¾¾3  ®êCH3  – CCH3 ú

 

Hydrolysis     ê

ê

ë

|                  ú

CH3             ú

Unstable            û

ëê       Acetone           úû

 

 

 

(4)  Uses

  • In organic The compounds like methyl cyanide, Methylamine and ethylamine can be prepared.
  • In leather tanning and paper
  • As a wetting agent and as soldering

Amides such as dimethyl formamide (DMF), dimethyl acetamide (DMA) are used as solvents for organic and inorganic compounds.

Esters, R C OR

||

O

These are the most important class of acid derivatives and are widely distributed in nature in plants, fruits and flowers.

Nomenclature : In common names and IUPAC system, change the suffix ic acid by ate.

 

 

HCOOCH3 CH3COOCH3 CH3COOC2 H5 CH3COOC6 H5

Methyl formate                                 Methyl methanoate

Methyl acetate                                 Methyl ethanoate

Ethyl acetate                                     Ethyl ethanoate

Phenyl acetate                                  Phenyl ethanoate

 

 

 

 

The name of some aromatic esters are given below :

 

COOCH3

COOC2 H5

COOCH5

OCOCH3

 

 

 

 

 

 

 

Methyl benzoate

 

 

Ethyl benzoate

 

 

Br

Ethyl 4 – bromobenzoate

CH3

3-Methylphenyl ethanoate

 

(1)  Methods of preparation

  • From carboxylic acid [Esterification] : Laboratory

 

O

R                                     ¢ H

||                                   +

  • OH + H OR

O

||

R –    – OR¢+ H O

 

C                                              C                     2

Ester

 

CH3COOH+

Acetic acid

CH2 N2

Diazomethane

¾¾Eth¾er ® CH3COOCH3 + N2

Methyl acetate

 

C6 H5COOH+

Benzoic acid

CH2 N2

Diazomethane

¾¾Eth¾er ® C6 H5COOCH3 + N2

Methyl benzoate

 

  • With diazomethane is the best
  • From acid chloride or acid anhydrides

CH3 CO                    OC2 H5 ® CH3 COOC2 H5 + HCl

 

Acetyl chloride

Ethyl alcohol

Ethyl acetate

 

CH3CO

O + CH CH  OH ® CH  COOCH CH

  • CH COOH

 

CH3CO

3        2                       3

2        3            3

Ethyl acetate

 

Acetic anhydride

C6 H5 CO

Ethyl alcohol

OC2 H5 ® C6 H5 COOC2 H5 + HCl

 

Benzoyl chloride

Ethyl alcohol

Ethyl benzoate

 

 

 

 

  • From alkyl halide :

C2 H5 Br + CH3COOAg ® CH3COOC2 H5 + AgBr

 

Ethyl bromide

Silver acetate

Ethyl acetate

 

  • From ether :

CH3  – OCH3 + CO ¾¾B¾F3  ® CH3COOCH3

 

Methoxy methane

350 K

Methyl acetate

 

  • From Tischenko reaction : CH3 – CH + O = CCH3  ¾¾Al(O¾CH)3  ® CH3  – COC2 H5

||                        |                                                           ||

O                      H                                                          O

(2)  Physical properties

  • Physical state and smell : Esters are colourless liquids (or solids) with characteristic fruity Flavours of some of the esters are listed below :

 

EsterFlavourEsterFlavour
Amyl acetate

Benzyl acetate Amyl butyrate

Banana

Jasmine Apricot

Isobutyl formate

Ethyl butyrate Octyl acetate

Raspberry

Pineapple Orange

  • Solubility : They are sparingly soluble in water but readily soluble in organic solvents such as alcohol, ether
  • Boiling points : Their boiling points are lower than the corresponding acids because of the absence of hydrogen i.e., ethyl acetate = 77.5oC.

(3)  Chemical properties

  • Hydrolysis : CH3 COOC2 H5 + H2O acid CH3 COOH  + C2 H5 OH

 

Ethyl acetate

Acetic acid

Ethyl alcohol

 

CH3 COOC2 H5 + NaOH               CH3 COONa + C2 H5 OH

 

Ethyl acetate

Sod. acetate

Ethyl alcohol

 

Hydrolysis of ester by alkalies (NaOH) is known as saponification and leads to the formation of soaps

Mechanism : It follows three steps :

 

Step I : The nucleophile,

O

||

OH

ion from the alkali attacks the carboxyl carbon to form an intermediate.

O

|

 

CH3 – C

|

+  OH ® CH3 – C OC2 H5

|

 

OC2H5                                  OH

Step II : The intermediate, then loses a molecule of ethoxide ion to form acetic acid as:

 

 

CH3 – C

O

  • OC2 H5 ® CH3 – C

O

  • OC2H5

 

OH                                                   OH

Step III : Ethoxide ion abstracts the acidic proton from acetic acid to form acetate ion.

 

 

CH3 – C

O                                                      O

+OC2 H5 ® CH3 – C

OH                                                     O

+ C2 H5OH

 

Resonance stabilized

 

Note : ® This reaction is irreversible because a resonance stabilized carboxylate (acetate) ion is formed.

®The acid hydrolysis of esters is reversible.

 

 

 

 

  • Reaction with ammonia (ammonolysis) :

CH3CO

Ethyl acetate

 

NH2  ® CH3CONH2 + C2 H5OH

Acetamide

 

 

  • Reduction : CH3COOC2 H5  + 4[H] ¾¾LiA¾lH¾4  ® 2C2 H5OH

or Na / C2H5OH

 

 

COOCH5

 

  • 4 H

¾¾LiA¾lH¾4  ®

CH2OH

 

  • C H OH

 

or Na / C2 H5 OH                                                                      2  5

 

 

 

Ethyl benzoate

 

  • Reduction in presence of

Na / C2 H5OH

Benzyl alcohol

 

is known as Bouveault Blanc reduction.

 

  • The catalytic hydrogenation of ester is not easy and requires high temperature and The catalyst most commonly used is a mixture of oxides known as copper chromate (CuO.CuCr2O4 ) .

O

 

||

R –    – OR¢ + 2H

¾¾CuO¾.Cu¾Cr ¾O¾® RCH  OH + R¢OH

 

C                        2                     2  4                           2

525 K, 200 – 300atm

 

  • Reaction with PCl5 or SOCl2

CH3COOC2 H5  + PCl5  ® CH3COCl + C2 H5Cl + POCl3

CH3COOC2 H5 + SOCl2 ® CH3COCl+ C2 H5Cl + SO2

Acetyl chloride         Ethyl chloride

 

C6 H5COOC2 H5 + PCl5  ® C6 H5COCl+ POCl3  + C2 H5Cl

Ethyl benzoate                                  Benzoyl chloride

 

  • Reaction with alcohols : On refluxing ester undergoes exchange of alcohols

 

 

R C

O

OR¢

  • R¢OH H
+

(Excess)

RC

O

OR¢

  • R¢OH

 

CH3 COOC2 H5 + CH3 OH ® CH3 COOCH3 + C2 H5 OH

Ethyl acetate                                              Methyl acetate

 

 

  • This reaction is known as alcoholysis or trans
    • Reaction with Grignard reagents

O

||

 

 

é

êCH

 

OMgBr        ù

|                      ú             

 

|
û

CH3  – COC2 H5 + CH3 MgBr ® ê         3 – C OC2 H5 ú

 

 

 

 

3o alcohol : CH

 

O

|

–     – CH

Ethyl acetate

 

 

 

¬ ¾H+  ¾ CH

 

OMgBr

|

–    – CH

ê

ë

 

¬¾CH¾3 M¾g¾Br ¾ CH

CH3               ú

O

||

–    – CH

C2H5OMgBr

 

3   C

|

CH3

3       H2O

3      C            3

|

CH3

3      C            3

 

 

 

 

 

  • Claisen condensation

O                                                                                                              O

 

||

CH   –     –

  • CH COOC H

¾¾C2 H¾5O¾- N¾a+  ® CH

||

  • CH COOC H
  • C H OH

 

3     C                                          2               2   5

3     C            2

2    5        2    5

 

Ethyl acetate (2 molecules)

 

  • Reaction with hydroxyl amine

O                                                                               O

||                                                                                ||

Ethyl acetoacetate (b -ketoester)

 

CH3  – COC2 H5 + H  HNOH  ¾¾ba¾se ® CH3  – CNHOH+ C2 H5 OH

 

Ethyl acetate

Hydroxyl amine

Hydroxamic acid

 

 

  • Reaction with hydrazine : CH3COOC2 H5 + H2 NNH2 ® CH3CONHNH2 + C2 H5 OH

Hydrazine                  Acid hydrazide

  • Halogenation : CH3COOC2 H5  + Br2 ¾¾Red¾P ® CH2 BrCOOC2 H5 + HBr

a -Bromoethyl acetate

  • Reaction with HI: CH3COOC2 H5 + HI ® CH3COOH+ C2 H5 OH

 

 

(4)  Uses

  • As a solvent for oils, fats, cellulose, resins
  • In making artificial flavours and
  • In the preparation of ethyl

(5)  General Tests

  • It has sweet
  • It is neutral towards

Acetic acid

Ethyl alcohol

 

  • A pink colour is developed when one or two drops of phenolphthalein are added to dilute sodium hydroxide The pink colour is discharged when shaken or warmed with ethyl acetate.
  • Ethyl acetate on hydrolysis with caustic soda solution forms two compounds, sodium acetate and ethyl

CH3COOC2 H5  + NaOH  ® CH3COONa + C2 H5 OH

 

 

 

Acid Anhydride

CH3CO    O

3         2

or    (CH CO) O

 

CH3CO

 

 

  • Method of preparation
    • From carboxylic acid

O                                O                                           O            O

 

||

R –    –

||                                            ||             ||

O                      Quartz tube

–    – R ¾¾¾¾¾® R –   – O –    – R+ H  O

 

C                                 C                                           C             C                2

 

Porcelain chips 1073 K

Acid anhydride

O            O

 

C H CO

OOCC H

¾¾P O¾® C  H

||             ||

  • O – – C H
  • H O

 

6     5                                          6     5

4 10

6     5     C             C        6     5         2

 

heat

Benzoic anhydride

 

 

 

 

 

  • From carboxylic acid salt and acyl chloride [Laboratory method]

CH3 COONa + CH3COCl ¾¾Py ® CH3COOCOCH3 + NaCl

Acetic anhydride

 

C6 H5 COONa + C6 H5 COCl ¾¾Py ® C6 H5COOCOC6 H5 + NaCl

Benzoic anhydride

 

  • From acetylene

CH                                       HgSO

CH3

 

 

 

Distill

 

CH3 CO

 

|||

CH

+ 2CH3COOH ¾¾  ¾4  ® |

CH(OOCCH3 )2

¾¾¾® CH3CHO +

heat

O

CH3 CO

 

Acetic anhydride

 

  • From acetaldehyde : CH3 CHO + O2 ¾¾Cob¾¾alt ® 2CH3  – COOH ® (CH3 CO)2 O + H2O

acetate                       ||

O

(2)  Physical properties

  • Physical state : Lower aliphatic anhydrides are colourless liquids with sharp irritating The higher members of the family as well as the aromatic acid anhydrides are solids in nature.
  • Solubility : They are generally insoluble in water but are soluble in the organic solvents such as ether, acetone, alcohol,
  • Boiling points : The boiling points of acid anhydrides are higher than those of carboxylic acids because of the greater molecular

(3)  Chemical Properties

O            O

||             ||

 

  • Hydrolysis :

CH3  – CO CCH3 + H2O ® 2CH3 COOH

 

Acetic anhydride                                             Acetic acid

  • Action with ammonia : (CH3 CO)2 O + 2NH3 ® CH3 CONH2 + CH3 COONH4

Acetamide                 Amm. acetate

  • Acetylation : Acetic anhydride react with compound having active

(CH3 CO)2 O + C2 H5 OH ® CH3 COOC2 H5 + CH3 COOH

Ethyl alcohol                 Ethyl acetate

(CH3 CO)2 O + HNC2 H5  ® CH3 CONHC2 H5 + CH3 COOH

Ethyl amine                   N -Ethyl acetamide

(CH3 CO)2 O + HN(C2 H5 )2  ® CH3 CON(C2 H5 )2 + CH3 COOH

Diethylamine              N, N -Diethyl acetamide

(CH3 CO)2 O + HNC6 H5  ® CH3 CONHC6 H5 + CH3 COOH

 

 

 

(CH

 

3CO)2 O +

Aniline

Salicylic acid

OH COOH

Acetanilide

 

 

¾¾®

 

Acetyl salicylic acid (Aspirin)

OOCCH3 + CH COOH

 

3COOH

 

 

 

  • Action of dry HCl : (CH3 CO)2 O + HCl ® CH3 COCl + CH3 COOH
  • Reaction with chlorine : (CH3 CO)2 O + Cl2 ® CH3 COCl + CH2ClCOOH

 

Acetyl chloride

Monochloroacetic acid

 

  • Reaction with PCl5 : (CH3 CO)2 O + PCl5 ® 2CH3 COCl + POCl3
  • Friedel crafts reaction : (CH3 CO)2 O + C6 H6 ¾¾AlC¾l3  ® C6 H5 COCH3 + CH3 COOH

Benzene                          Acetophenone

  • Reaction with acetaldehyde : (CH3 CO)2 O + CH3 CHO ® CH3 CH(OOCCH3 )2

 

 

  • Reduction : (CH3 CO)2 O ¾¾LiA¾lH¾4 ® CH3 CH2OH

Acetaldehyde

Ethylidene acetate

 

Ether

Ethyl alcohol

 

  • Action with ether : CH3 CO O.COCH3 + C2 H5 – O C2 H5 ® 2CH3 COOC2 H5

 

 

(xi)  Action with N O

: CH

COOCOCH

+ N O

Diethyl ether

 

 

® CH

  • CO N

Ethyl acetate

 

O

 

2    5             3

3          2   5

3     ||                      O

O

 

  • Uses : Acetic anhydride is used
  • as an acetylating
  • For the detection and estimation of hydroxyl and amino
  • in the manufacture of cellulose acetate, aspirin, phenacetin, acetamide, acetophenone,

 

 

Urea or Carbamide

O = C

NH2

NH2

 

Urea may be considered as diamide of an unstable and dibasic carbonic acid from which both the hydroxyl

 

groups have been replaced by – NH2

OH

groups.

NH 2

NH 2

 

O = C

¾¾O¾H ® O = C

  • NH2

OH

¾¾O¾H ® O = C

  • NH2

OH

NH 2

 

Carbonic acid

Carbamic acid, (Monoamide)

Urea, diamide of carbonic acid or carbamide

 

  • Urine in 1773 by Roulle and hence the name urea was
  • It was the first organic compound synthesised in the laboratory from inorganic material (by heating a mixture of ammonium sulphate and potassium cyanate) by Wohler in
  • This preparation gave a death blow to Vital force theory.
  • It is the final decomposition product of protein’s metabolism in man and mammals and is excreted along with
  • Adults excrete about 30 grams of urea per day in the

(1)  Method of preparation

 

  • From urine : Urine is treated with nitric acid where crystals of urea nitrate obtained.

CO(NH2 )2 .HNO3

are

 

 

2CO(NH 2 )2 .HNO3 + BaCO3 ® 2CO(NH 2 )2 + Ba(NO3 )2  + H 2 O + CO2

Urea nitrate                                                    Urea

 

  • Laboratory preparation

 

  • Wohler synthesis :

2KCNO   +

Potassium cyanate

(NH4 )2 SO4   ®

Ammonium sulphate

2NH4 CNO  + K2SO4

Ammonium cyanate

 

NH4 CNO

¾¾Isom¾eric¾ch¾an¾ge ® NH2CONH2

 

Ammonium cyanate

On heating

Urea

 

  • The solid residue is extracted with alcohol and the extract evaporated when the crystals of urea are obtained. It can be recrystalised from
  • From phosgene or alkyl carbonate

 

O = C

Cl+ 2NH Cl     3

® O = C

NH2 + 2HCl NH2

 

Carbonyl chloride (Phosgene)

Urea

 

O = C        OC2 H5 + 2NH

® O = C

NH2 + 2C  H  OH

 

OC2 H5                  3

Ethyl carbonate

  • Industrial method

Urea

NH2            2    5

 

  • By partial hydrolysis of calcium cyanide

CaC2 + N2  ¾¾he¾at ® CaCN2 + C

 

Calcium Carbide

Calcium cyanamide

 

The cyanamide is treated with dilute sulphuric acid at of urea. CaCN2  ¾¾H2S¾O¾4  ® H2 NCN ¾¾HO ® H2 NCONH2

40o C

where partial hydrolysis occurs with the formation

 

CaSO4

Cyanamide

(H2O2 )

(Urea)

 

2          2             2       4                             2               2                  4

or       CaCN   + H  O + H  SO   ¾¾40o¾C ® NH  CONH   + CaSO

  • From carbon dioxide and ammonia

 

CO2

  • 2NH3

¾¾150¾- 20¾0o¾C ® NH

2COONH4

¾¾hea¾t (14¾0o¾C) ® NH

  • H2O

2CONH2

 

Ammonium carbamate                                              Urea

  • Physical properties : Urea is a colourless, odourless crystalline It melts at 132o C . It is very soluble in water, less soluble in alcohol but insoluble in ether, chloroform.

Crystal structure: In solid urea, both nitrogen atoms are identical.

 

HN

1.37 Å     C

||

O

NH2

¬¾®

+

HN

C

|

O

NH2

¬¾®

HN

C

|

O

+

NH2

 

 

This indicates that C N bond in urea has some double bond character.

(3)  Chemical Properties

  • Basic nature (Salt formation): It behaves as a weak monoacid base (Kb= 5 ´ 10-14 ) . It forms strong acid.

NH2CONH2  + HNO3 (conc.) ® NH2CONH2.HNO3

Urea nitrate

 

2NH2CONH2   +  H2C2O4    ® (NH2CONH2 )2 H2C2O4

Oxalic acid                           Urea oxalate

 

 

 

Due to resonance stabilization of cation, the negatively charged oxygen atom is capable of coordination with one proton.

 

H2 N

 

C

||

  • OH

NH2

 

¬¾®

+

H2  N

C

|

OH

NH2

 

¬¾®

H2 N

C

|

OH

+

NH2

 

 

Note : ® An aqueous solution of urea is neutral.

OH                                           OH

 

  • Hydrolysis : O = C

¾¾Aq.¾alka¾li¾or ® O C

acid

OH

  • 2NH3

OH  Ammonia

 

Urea

Carbonic acid

¯

CO2+H2O

 

NH2CONH2 + 2NaOH ® 2NH3 + Na2CO3

An enzyme, urease, present in soyabean and soil also brings hydrolysis .

 

NH2CONH2  + 2H2O ®

(NH4 )2 CO3

Ammonium carbonate

® 2NH3 + CO2 + H2O

 

  • Action of heat :

NH2CO

HNCONH2  ¾¾he¾at ® NH2CONHCONH2 + NH 3

 

(Two molecules of urea)                                                         Biuret

Urea is identified by the test known as biuret test. The biuret residue is dissolved in water and made alkaline with a few drops of NaOH. When a drop of copper sulphate solution is added to the alkaline solution of biuret, a violet colouration is produced.

when heated rapidly at 170o C , polymerisation takes place:

 

NH 2 CONH 2  ¾¾he¾at ® NH 3  + HOCN(HN  = C = O)

Cyanic acid

 

 

 

3HOCN ¾¾Poly¾me¾risat¾i¾on ®(HOCN)3 or (H 3 N 3 C3 O3 ) or

 

 

 

O = C

H

C

C = O

 

H      N                N H

C

O

 

  • Reaction with nitrous acid

Cyanuric acid

 

O  N  OH

 

H2  NCON  H2 + 2HNO2 ¾¾NaN¾O+ H¾Cl ®

H2CO3

+ 2N2 + 2H2O

 

HO   N  O

Carbonic acid

¯

H2O+CO2

 

  • Reaction with alkaline hypohalides

NaOH + Br2 ® NaOBr + HBr

NH2CONH2 + 3NaBrO ® N2 + 2H2O + CO2 + 3NaBr

 

 

 

  • Reaction with acetyl chloride or acetic anhydrides

NH2CONH2 + CH3COCl ® NH2CONHCOCH3 + HCl

Acetyl chloride                   Acetyl urea (Ureide)

NH 2 CONH 2  + (CH3 CO)2 O ® NH 2 CONHCOCH3 + CH3 COOH

 

 

2
2
  • Reaction with hydrazine

Acetyl urea

Acetic acid

 

NH2CONH2

  • H2 N.NH2

¾¾100¾o¾C ® NH  CONH.NH

  • NH3

 

Urea

Hydrazine

Semicarbazide

 

 

  • Reaction with ethanol : H2 NCO NH2  + H OC2 H5  ¾¾he¾at ® H2 NCOOC2 H5 + NH3

 

 

 

  • Reaction with chlorine water :

 

O = C

Ethanol

 

NH 2

  • 2Cl2 ® O = C

NH 2

Urethane

 

NHCl

  • 2HCl

NHCl

 

Urea                                   Dichloro urea

 

  • Dehydration :

NH2CONH2 + SOCl2 ® H2 N C º N + SO2 + 2HCl + H2O

 

  • Reaction with fuming sulphuric acid

NH2CONH2 + H2SO4  + SO3  ® 2NH2SO3 H+ CO2

sulphamic acid

 

Oleum

  • Formation of cyclic ureides

O

||

 

O

||

NH C

 

O = C

+

NH

Urea

CH2  ¾¾PC¾l3  ® O = C

C

||

O

NH C

||

O

CH2  + 2C2 H5OH

 

 

 

O = C

Diethyl malonate

 

 

 

+

 

¾¾PC¾l3  ® O = C

Barbituric acid (Malonyl urea)

 

NH C = O

 

 

  • 2C2 H5OH

 

NH H

Urea

C2 H5O CO

Diethyl oxalate

NH C = O

Parabanic acid (Oxalyl urea)

 

  • Reaction with formaldehyde

 

 

O = C

NH H

C2 H 5 O – CO

+

CH ® O = C

NH CO

CH

 

NH H

HO  C

CH3

NH CH 3

4 -Methyl urecil

 

CH2  = O + NH2CONH2 ¾¾H¾Cl ® CH2 (OH)NHCONH2  ¾¾CH¾2 =¾O ®

Formaldehyde                                         Monomethylol urea

 

 

 

 

 

 

 

(4)  Uses

CH 2 (OH)NHCONH(OH)CH 2

Dimethylol urea

¾¾he¾at  ®

Resin

(Urea-Formaldehyde)

 

  • Mainly as a nitrogen It has 46.4% nitrogen.
  • In the manufacture of formaldehyde-urea plastic and
  • As animal
  • For making barbiturates and other
  • As a stabilizer for nitrocellulose

(5)   General Tests

  • When heated with sodium hydroxide, ammonia is
  • When heated gently, it forms biuret which gives violet colouration with sodium hydroxide and a drop of copper sulphate
  • Its aqueous solution with concentrated nitric acid gives a white

 

  • On adding sodium nitrite solution and HCl (i.e., gives effervescence due to carbon dioxide.

 

HNO2 ) to urea solution, nitrogen gas is evolved and

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