Chapter 17 Aldehydes and Ketones Part 3- Chemistry free study material by TEACHING CARE online tuition and coaching classes

 

 

• Manufacture : Acetone is manufactured by following methods:
  • By air-oxidation of isopropyl alcohol : The air oxidation occurs at 500 ^o C .

 

 

o

2CH3 CHOHCH3 + O2  ¾¾⁵⁰⁰¾¾^C ® 2CH3 COCH3

• 2H 2 O

 

Isopropyl alcohol                                                     Acetone

 

• By dehydrogenation of isopropyl alcohol : The vapours of isopropyl alcohol are passed over heated copper at 300 ^o C .

CH 3 CHOHCH3  ¾¾^C¾^u ® CH 3 COCH 3  + H 2

300^o C

 

• From propene

• Wacker’s process : The mixture of propene and air under pressure is passed through palladium chloride and cupric chloride solution when acetone is

CH3 CH = CH 2 + PdCl 2 + H 2 O ¾¾® CH3 COCH3 + Pd + 2HCl Pd + 2CuCl2 ¾¾® PdCl 2 + 2CuCl

4CuCl + 4 HCl + O2 ¾¾® 4CuCl2 + 2H 2 O

• Propene is absorbed in concentrated sulphuric acid and the resulting product is boiled with water when isopropyl alcohol is Isopropyl alcohol on dehydrogenation yields acetone.

CH3 CH  = CH 2  + H 2 SO4  ¾¾® CH3 CH(HSO4 )CH3  ¾¾^H2¾^O ® CH3 CH(OH)CH3  ¾¾^C¾^u ® CH3 COCH3

 

Isopropyl alcohol

300^o C

Acetone

 

 

• From ethyl alcohol : By passing a mixture of ethyl alcohol vapour and steam over a catalyst, zinc chromite at 500^o C , acetone is The yield is about 80%.

2C2 H5OH + H2O ¾¾^Zn(C¾^rO¾2¾⁾2  ® CH3COCH3  + CO2  + 4 H2

• From acetylene : By passing a mixture of acetylene and steam over a catalyst, magnesium or zinc vanadate at 420^o C , acetone is

2CH º CH + 3H2O ¾¾® CH3COCH3 + CO2 + 2H2

• From pyroligneous acid : Pyroligneous acid containing acetic acid, acetone and methyl alcohol is distilled in copper vessel and the vapours are passed through hot milk of lime. Acetic acid combines to form nonvolatile calcium The unabsorbed vapours of methanol and acetone are condensed and fractionally

distilled. Acetone distills at 56^o C .

The acetone thus obtained is purified with the help of sodium bisulphite as described in laboratory preparation.

• Physical properties : (i) It is a colourless liquid with characteristic pleasant
• It is inflammable It boils at 56^o C .
• It is highly miscible with water, alcohol and

 

 

 

(4)  Chemical properties

Reduction H₂, Ni¸Pd

or LiAlH4 Amalgamated Zn + conc. HCl   NaHSO3   HCN   CH3MgI Ether   NH2OH   NH2NH2     C6H5NHNH2   H2NNHCONH2   PCl5   Cl2   I2 +NaOH       Conc. H2SO4

CH₃CHOHCH₃

Isopropyl alcohol

CH3 CH2 CH3

Propane

 

(CH₃ )₂ C(OH)SO₃ Na

CaOCl2 (Bleaching powder) heat K2Cr2O7 + H2SO4     CHCl3   Ba(OH)2   HNO2   NH3   Mg–Hg + H2O   Schiff’s reagent   Tollen’s reagent   Fehling’s solution

Acetone sodium bisulphite derivative

 

OH

 

(CH3 )2 C   CN

CHCl3

 

Acetone cyanohydrin

(CH ) COH

CH COCH

Chloroform

 

3 3

Tertiary butyl alcohol

3              3

(Acetone)

CH₃COOH + CO₂ + H₂O

 

 

 

(CH₃)₂ C = NOH

Acetoxime

(CH

₃ )2 C(OH)CCl3

Chloretone

 

CH₃COCH₃

(Acetone)

 

(CH3 )2 C = NNH2

Acetone hydrazone

(CH3  )2   C(OH)CH2COCH3

Diacetone alcohol

 

 

(CH  ) C = NNHC H

CH COCH = NOH

 

 

3 2                   6    5                                                                                  3

 

Acetone phenyl hydrazone

(Oximino acetone)

 

(CH₃ )₂ C = NNHCONH₂

Acetone semicarbazone

(CH

₃ )2 C(NH 2 )CH2COCH3

 

Diacetone amine

 

Cl

(CH3 )2 C    Cl

OH     OH

|          |

 

Isopropylidene chloride

CH COCCl

(CH3 )2  C

— C

Pinacol

(CH3 )2

 

^{3             3}                                                                                             No reaction

 

Trichloro acetone

 

CHI3

Iodoform

CH₃

C

No reaction No reaction

 

CH

 

C

CH

CH₃

CH

 

CH₃

 

Mesitylene

(1, 3, 5-trimethyl benzene

If acetone would be in excess in ketal condensation or catalyst

(ZnCl ₂ / dry HCl)

is used then three moles of

 

acetone undergoes condensation polymerisation and form a compound called ‘Phorone’.

CH                                                                                                                CH

3                                                                                                                      3

|                                                                                                                      |

 

CH₃ – C = O       H

CH

H

CH₃ – C = CH

C = O

 

 

CH                                                C = O

¾¾ZnC¾l2  ®

CH3 – C

|

= CH

 

3                                                                      dry. HCl

|

CH3

 

CH₃ – C = O       H

CH

H

 

Molecular mass of phorone = 3 mole of acetone – 2 mole of

H 2 O

 

 

 

Mesityl oxide (CH 3 )2 C(OH)CH 2 COCH3

Note : ® If two moles of acetone are used then

Reformatsky reaction: This reaction involves the treatment of aldehyde and ketone with a bromo acid ester in presence of metallic zinc to form b -hydroxy ester, which can be easily dehydrated into a, b -unsaturated ester.

 

 

(a)

BrCH

₂COOC2 H 5

• Zn ¾¾^Ben¾^ze¾^ne ® Br –

Å

Zn– CH

₂COOC2 H 5

 

 

(b) Addition to carbonyl group

Organo zinc compound

 

 

 

CH                           Zn+ Br

CH3

CH3

 

3                         |

C = O +

¾¾® CH

|

C

• – CH CH COOC H

¾¾^HO¾^{H / H}¾+  ® CH   –       –  CH

 

CH2COOC2 H 5

3      |              2        2

2    5

ë

é- Zn

û

Br ù

3     C                 2

|           |

 

CH3

OZnÅBr

ê            OH ú

OH  COOC2H5

 

|

b -hydroxyesters

CH3

|

 

¾¾® CH ₃ – C –

|

CH 2  – COOC2 H 5

 

OH

(5)  Uses

• As a solvent for cellulose acetate, cellulose nitrate, celluloid, lacquers, resins,
• For storing
• In the manufacture of cordite – a smoke less powder
• In the preparation of chloroform, iodoform, sulphonal and
• As a nailpolish
• In the preparation of an artificial scent (ionone), plexiglass (unbreakable glass) and synthetic

(6)  Tests

• Legal’s test : When a few drops of freshly prepared sodium nitroprusside and sodium hydroxide solution are added to an aqueous solution of acetone, a wine colour is obtained which changes to yellow on
• Indigo test : A small amount of orthonitrobenzaldehyde is added to about 2 ml. of acetone and it is diluted with KOH solution and A blue colour of indigotin is produced.
• Iodoform test : Acetone gives iodoform test with iodine and sodium hydroxide or iodine and ammonium

Comparison between Acetaldehyde and Acetone

 

Reaction	Acetaldehyde	Acetone
Similarty
1. Reduction with H2 and	Forms ethyl alcohol	Forms isopropyl alcohol
Ni or LiAlH4	CH 3 CHO + H 2  ¾¾Ni ® CH 3 CH 2 OH	CH 3 COCH3 + H 2 ¾¾® CH 3 CHOHCH 3
2.                     Clemmensen’s	Forms ethane	Forms propane
reduction (Zn/Hg and conc. HCl)	CH3 CHO + 4 H ¾¾® CH3 CH3 + H 2 O	CH3 COCH3 + 4H ¾¾® CH3 CH 2 CH3 + H 2 O
3. Addition of HCN	Forms acetaldehyde cyanohydrin	Forms acetone cyanohydrin

 

 

 

 

 

4. Addition of NaHSO₃

White crystalline derivative

White crystalline derivative

 

 

 

 

5. Grignard reagent followed by hydrolysis

 

 

6. With hydroxylamine

(NH₂OH)

7. With hydrazine

(NH2 NH2 )

8. With phenyl hydrazine

(C6 H5 NHNH2 )

 

 

9. With semicarbazide

(H₂ NNHCONH₂)

 

10. With PCl₅

Forms isopropyl alcohol

 CH3CHO + CH3 MgI ¾¾®(CH3 )2 CH – OMgI

¾¾^H2¾^O ® CH 3 CHOHCH3

Forms acetaldoxime

 CH 3 CHO + H 2 NOH ¾¾® CH 3 CH = NOH

Forms acetaldehyde hydrazone

CH 3 CHO + H 2 NNH 2 ¾¾® CH 3 CH = NNH 2

Forms acetaldehyde phenylhydrazone

 CH3 CHO + H 2 NNHC6 H5 ¾¾®

 

Forms acetaldehyde semicarbazone

 CH 3 CHO + H 2 NNHCONH 2 ¾¾®

 CH₃CH  = NNHCONH ₂

Forms ethylidene chloride

Forms tertiary butyl alcohol

(CH3 )2 CO + CH3 MgI ¾¾®(CH3 )3 COMgI

¾¾^H2¾^O ®(CH 3 )3 COH

Forms acetoxime

(CH3 )2 CO + H 2 NOH   ¾¾®(CH3 )2 C = NOH

Forms acetone hydrazone

(CH3 )2 CO + H 2 NNH 2  ¾¾®(CH3 )2 C = NNH 2

Forms acetone phenyl hydrazone

(CH 3 )2 CO + H 2 NNHC6 H5 ¾¾®

(CH 3 )2 C = NNHC6 H5

Forms acetone semicarbazone

(CH 3 )2 CO + H 2 NNHCONH 2 ¾¾®

(CH ₃ )₂ C = NNHCONH ₂

Forms isopropylidene chloride

 

 

 

• With chlorine Forms chloral Forms trichloro acetone

12. With alcohols Forms acetal                                                               Forms ketal

 

 

 

13. With SeO2

Forms glyoxal

CH3CHO + SeO2 ¾¾® CHOCHO + Se + H2O

Forms methyl glyoxal

(CH3 )2 CO + SeO2 ¾¾® CH3 COCHO + Se + H2O

 

 

 

14. Iodoform reaction

(I₂ + NaOH)

Forms iodoform

Forms iodoform

 

15. Bleaching powder Forms chloroform                                                      Forms chloroform

 

16. Aldol condensation with mild alkali

Forms aldol

2CH3CHO ¾¾® CH3CHOHCH2CHO

Forms diacetone alcohol

2CH3COCH3  ¾¾®(CH3 )2 C(OH)CH2COCH3

 

17. Polymerisation Undergoes polymerisation                                     Does not undergo polymerisation but gives

condensation reaction

 

18. With NH₃

Forms acetaldehyde ammonia                            Forms diacetone ammonia

 

 

 

 

Aromatic aldehydes are of two types :

The compounds in which – CHO group is attached directly to an aromatic ring, e.g., benzaldehyde, C6 H5CHO .

 

Those in which aldehyde (-CHO) group is attached to side chain, e.g., phenyl acetaldehyde, They closely resemble with aliphatic aldehydes.

C6 H5CH2CHO  .

 

Aromatic ketones are compounds in which a carbonyl group ( > C = O) is attached to either two aryl groups or one aryl group and one alkyl group. Examples are :

 

CHO

COCH3

COC6 H5

OH

CHO

 

 

 

Benzaldehyde Acetophenone

(Methyl phenyl ketone)

Benzophenone (Diphenyl ketone)

Salicylaldehyde

 

 

 

 

Benzaldehyde, C6H5CHO or

CHO

 

 

Benzaldehyde is the simplest aromatic aldehyde. It occurs in bitter almonds in the form of its glucoside,

 

amygdalin

and HCN

(C20 H27O11 N). When amygdalin is boiled with dilute acids, it hydrolyses into benzaldehyde, glucose

 

CN

|

C6 H5CHOC12 H21O10 + 2H2O ¾¾® C6 H5CHO+ 2C6 H12O6 + HCN

 

Amygdalin

Benzaldehyde

Glucose

 

Benzaldehyde is also known as oil of bitter almonds.

(1)  Method of preparation

• Laboratory method : It is conveniently prepared by boiling benzyl chloride with copper nitrate or lead nitrate solution in a current of carbon

2C6 H5 CH2Cl+ Cu(NO3 )2  ¾¾^he¾^at ® 2C6 H5 CHO+ CuCl2  + 2HNO2                  [2HNO2  ¾¾® NO + NO2  + H2O]

 

Benzyl chloride

or

Pb(NO3)2

CO2

Benzaldehyde

 

• Rosenmund reaction : C6 H5COCl + H2  ¾¾^{Pd /}¾^BaS¾^O¾4  ® C6 H5CHO + HCl
• By dry distillation of a mixture of calcium benzoate and calcium formate

O

||

 

C6 H5

CH

CH    ¾¾^he¾^at ® 2C6 H5 CHO+ 2CaCO3

 

C6 H5

||                              Benzaldehyde

O                            (Major product)

 

• By oxidation of benzyl alcohol : This involves the treatment of benzyl alcohol with dil. potassium dichromate or chromic anhydride in acetic anhydride or with copper catalyst at 350^o C .

HNO3

or acidic

 

 

 

 

Benzyl alcohol

CH2OH ¾¾^[¾^O] ®

CHO

Benzaldehyde

 

This method is used for commercial production of benzaldehyde.

 

• By hydrolysis of benzal chloride :

CHCl2

¾¾NaO¾H  ®

Ca(OH)₂

OH

CH      OH

¾¾(- H¾2¾O) ®

 

CHO

 

Benzyal Chloride

 

 

This is also an industrial method.

• By oxidation of Toluene

CH3

+ O2  ¾¾^V2O¾5  ®

350^o C

Intermediate (unstable)

 

 

 

 

 

CHO

• H 2 O

Benzaldehyde

 

 

 

Commercially the oxidation of toluene is done with air and diluted with nitrogen (to prevent complete

 

oxidation) at 500^o C

in the presence of oxides of

Mn, Mo

or Zr as catalyst.

 

Partial oxidation of toluene with manganese dioxide and dilute sulphuric acid at benzaldehyde.

35^o C , also forms

 

C H CH

¾¾^CrO¾3  ® C  H  CH(OCOCH  )

¾¾^H + ¾^{/ H}2¾^O ® C  H  CHO + 2CH  COOH

 

6   5

Toluene

3 (CH 3 CO)2 O

6    5                            3 2

Benzylidene acetate

6    5                          3

 

• Etard‘s reaction : C6 H5CH3 + 2CrO2Cl2  ¾¾® C6 H5CH3 2CrO2Cl2  ¾¾^H¾2O ® C6 H5CHO

Brown addition product                           Benzaldehyde

• Gattermann-koch aldehyde synthesis : Benzene is converted into benzaldehyde by passing a mixture of carbon monoxide and HCl gas under high pressure into the ether solution of benzene in presence of anhydrous aluminium chloride and cuprous

 

 

• CO + HCl ¾¾^AlC¾^l3 ®

CHO

• HCl

 

 

Benzene                                                Benzaldehyde

 

 

• Gattermann reaction

 

HC º N + HCl + AlCl

 

¾¾®

^Å = NH + AlCl ^– ;

 

C H H+

 

+                                                                                +

= NH ¾¾® C H CH =

 

₃         H C

4          6    5         HC

6    5             NH2

 

Benzene

 

+

C H CH =

+ H O + AlCl ^– ¾¾® C H CHO + NH

+ AlCl

+ HCl

 

6     5             NH2          2

4                  6    5

3               3

CHO

 

Thus,

+ HCN + HCl + H 2 O ¾¾^AlC¾^l3  ®

+ NH4 Cl

 

• Stephen’s reaction : Benzaldehyde is obtained by partial reduction of phenyl cyanide with stannous chloride and passing dry HCl gas in ether solution followed by hydrolysis of the aldimine stannic chloride with

C6 H5C º N ¾¾^HC¾^{l / S}¾^nC¾^l2  ®[C6 H5 CH  = NH]2 H2SnCl6  ¾¾^H2¾^O ® 2C6 H5CHO

 

Phenyl cyanide

Ether

aldimine complex

 

 

• By ozonolysis of styrene

O

 

C6 H5 CH  = CH2  ¾¾^O¾3  ® C6 H5  – CH

Vinyl benzene

 

CH2  ¾¾^H2¾^O ® C6 H5 CHO + HCHO + H2O2

 

O       O

O                                                                       O                       Br

||                                                                       ||

 

• Grignard reaction

HCOC2 H5 + BrMgC6 H5 ¾¾® C6 H5 C – H+ Mg

 

Ethyl formate

Benzaldehyde

OC2 H5

 

Other reagents like carbon monoxide or HCN can also be used.

 

 

 

 

• From Diazonium salt

 

N = N – Cl + HCH = NOH ¾¾®

Formaldoxime

 

CH = NOH + HCl + N₂

Benzaldoxime

 

 

(2)  Physical properties

Benzaldehyde

 

• Benzaldehyde is a colourless oily Its boiling point is 179^o C .
• It has smell of bitter
• It is sparingly soluble in water but highly soluble in organic
• It is steam
• It is heavier than water (sp. 1.0504 at 15^o C ).
• It is poisonous in

(3)  Chemical properties

• Addition reaction: The carbonyl group is polar as oxygen is more electronegative than carbon,

d +         d –

C = O

 

Thus, The positive part of the polar reagent always goes to the carbonyl oxygen and negative part goes to carbonyl carbon.

 

HCN

OH                                     OH

C  H  CH             ¾¾^H¾+  ® C  H  CH

 

6   5                        H2O            6  5

CN

COOH

 

 

 

 

CHO

NaHSO₃

Benzaldehyde cyanohydrin

 

OH

C6 H5CH

SO3 Na

Benzaldehyde sodium bisulphite

(White solid)

OMgI

Mandelic acid

 

 

 

 

 

 

 

 

OH

 

CH MgI

C H CH

¾¾^H¾+  ® C  H  CH

 

3

(Benzaldehyde)

6    5

CH3

H2O             6   5

CH3

 

1- Phenyl -1- ethanol

(2o alcohol)

 

 

2[H]

LiAlH₄

C6 H5CH2OH

Benzyl alcohol

 

 

However on reduction with sodium amalgam and water, it gives hydrobenzoin,

C6 H5 CH  = O + 2H + O = HCC6 H5  ¾¾^Na–¾^H¾^g ® C6 H5 CH– CH – C6 H5

 

H2O

|          |

OH  OH

 

Hydrobenzoin

 

 

 

• Reactions involving replacement of carbonyl oxygen

 

H₂NNH₂

C H CH = NNH  + H O

 

6    5                    2        2

 

 

 

CHO

H₂N.NHC₆H₅

 

H₂NOH

Benzaldehyde hydrazone

 

C6 H5CH = N.NHC6 H5 + H2O

Benzaldehyde phenyl hydrazone

 

C H CH = NOH + H O

 

6    5                            2

Benzaldoxime

 

 

(Benzaldehyde)

H₂N.NHCONH₂

C H CH = NNHCONH + H O

 

6    5                                2        2

Benzaldehyde semicarbazone

 

H₂NC₆H₅ PCl₅

 

2CH₃OH

C6 H5CH = NC6 H5  + H2O

Benzylidine aniline (Schiff’ s base)

 

C6 H5 CHCl2  + POCl3

Benzal chloride

 

OCH3

|

 

 

HCl

C6 H5 CH

|

OCH3

• H2O

 

Methyl acetal of benzaldehyde

 

• Oxidation : Benzaldehyde is readily oxidised to benzoic acid even on exposure to

C6 H5 CHO ¾¾^[¾^O] ® C6 H5 COOH

 

Acidified

K₂Cr₂O₇ , alkaline

KMnO4

and dilute

HNO3

can be used as oxidising agents for oxidation.

 

• Reducing properties : Benzaldehyde is a weak reducing It reduces ammonical silver nitrate solution (Tollen’s reagent) to give silver mirror but does not reduce Fehling’s solution.

C6 H5 CHO+ Ag 2 O ¾¾® 2Ag + C6 H5 COOH

Benzaldehyde                                                   Benzoic acid

• Clemmensen’s reduction : With amalgamated zinc and HCl, benzaldehyde is reduced to toluene.

C6 H5 CHO + 4 H ¾¾^Zn–¾^H¾^g ® C6 H5 CH3  + H 2 O

HCl

• Schiff’s reaction: It restores pink colour to Schiff’s reagent (aqueous solution of p-rosaniline hydrochloride decolourised by passing sulphur dioxide).
• Tischenko reaction : On heating benzaldehyde with aluminium alkoxide (ethoxide) and a little of

 

anhydrous

AlCl₃ or

ZnCl₂ , it undergoes an intermolecular oxidation and reduction (like aliphatic aldehydes) to

 

form acid and alcohol respectively as such and react to produce benzyl benzoate (an ester).

2C6 H5 CHO ¾¾^Al(O¾^C2¾^H5¾⁾3  ® C6 H5 CH2 OOCC6 H5

Benzaldehyde                                         Benzyl benzoate (ester)

• Reactions in which benzaldehyde differs from aliphatic aldehydes

• With fehling’s solution : No reaction
• Action of chlorine : Benzoyl chloride is formed when chlorine is passed through benzaldehyde at its boiling point in absence of halogen This is because in benzaldehyde there is no a -hydrogen atom present which could be replaced by chlorine.

 

C6 H5

CHO + Cl₂

¾¾¹⁷⁰¾o¾^C ® C

6

D

H₅COCl + HCl

 

 

 

 

• Reaction with ammonia

C6 H5 CH O + H 2 N H

 

 

• O HCC₆ H₅ ¾¾®

 

C6 H5 CH = N

 

 

CHC6 H5 + 3H 2 O

 

C6 H5 CH O + H 2 N  H

C6 H5 CH = N

Hydrobenzamide

 

 

• Cannizzaro‘s reaction : 2C6 H5 CHO ¾¾^KO¾^H ® C6 H5 CH2 OH+ C6 H5 COOK

 

 

The possible Mechanism is

Benzaldehyde

Benzyl alcohol

Potassium benzoate

 

 

First step is the reversible addition of hydroxide ion to carbonyl group.

H

 

C6 H5

• C = O + OH ^– (Fast)   C H

6

5

|

H

|

• C – O^–

|

OH

 

Second step is the transfer of hydride ion directly to the another aldehyde molecule, the latter is thus reduced to alkoxide ion and the former (ion I) is oxidised to an acid.

 

 

 

H                           H

|                            |            –

H

Hydride                     |           –

 

C6 H5 C  = O + C6 H5 C  – O   ¾¾¾¾®  C6 H5 C – O

• C6 H5 C = O

 

|                   ion transfer

OH                 (slow)

|

H

Alkoxide ion

|

OH

acid

 

 

(H⁺ exchange)         –H⁺

 

 

+ H ⁺

H

|

C6 H5 – C – OH+ C6 H5 – C  = O

 

|

H

Benzyl alcohol

|

O–

Benzoate ion

 

Third Step is exchange of protons to give most stable pair alcohol and acid anion.

So one molecule of aldehyde acts as hydride donar and the other acts as hydride acceptor. In other words, Cannizzaro’s reaction is an example of self reduction and oxidation.

Note : ® Two different aldehydes each having no a -hydrogen atom, exhibit crossed Cannizzaro’s reaction when heated in alkaline solution.

 

C6 H5CHO+

HCHO

¾¾^NaO¾^H ® C6 H5CH2OH+ HCOONa

 

Benzaldehyde

Formaldehyde

heat

Benzyl alcohol

Sod. formate

 

Aldehyde  which  do  not  have  a –  hydrogen  ( C6 H5 – CHO, CCl3CHO,(CH3 )3 C – CHO, CH2O

undergoes Cannizzaro’s reaction.

etc.

 

 

 

 

 

Intramolecular cannizzaro reaction

 

¾¾NaO¾H¾/ 10¾0 o¾C  ®

H + / H 2 O

CH₂

OH

 

COOH

COOH

 

 

OH

CH₂

 

• Benzoin Condensation

 

H          O

|           ||

– C   +  C –

||            |

O          H

¾¾Alc.¾KC¾N  ®

H         O

|          ||

– C   – C –

|

OH

( b – hydroxy ketone)

 

Two molecules of benzaldehyde                                                            Benzoin

Benzoin can also be reduced to a number of product i.e.,

 

 

[H]

Na–Hg/C₂H₅OH

C6 H5

• CHOH – CHOH – C₆H₅

Hydrobenzoin

 

 

 

OH  O

|      ||

[H]

OH    H

|        |

 

– H O

 

C6 H5 – C –  C– C6 H5

|

H

Benzoin

Zn–Hg/HCl

 

 

H₂

H₂/Raney Ni

C6 H5 – CH – CH– C6 H5  ¾¾¾2¾® C6 H5CH  = CHC6 H5

Stilbene

 

 

 

 

C6 H5 – CH2 – CH2 – C6 H5 + 2H2O

Dibenzyl

 

Benzoin can be readily oxidised to a diketone, i.e, benzil.

C6 H5  – CH – C– C6 H5 + [O] ¾¾^CuS¾^O¾4  ® C6 H5  – C– C– C6 H5

 

|          ||

OH     O

Pyridine

H2O

||   ||

O  O

 

Benzoin

 

• Perkin’s reaction

Benzil

 

 

C6 H5 CH O+ H2 CHCOOCOCH3  ¾¾^CH¾3CO¾^ON¾^a ® C6 H5 CH  = CHCOOCOCH3

 

Benzaldehyde

Acetic anhydride

 

CHO CHO

– H2O

¾¾^H2¾^O ® C6 H5 CH  = CHCOOH+ CH3COOH

 

 

CH3

H C– CO

CHO CH|O

2

 

CH3

Cinnamic acid

Acetic acid

 

C6 H5

CH = O +

O ¾¾CH¾3CH¾2CO¾ON¾a ® C6

|

H5 CH = C

• COOH + CH

₃CH

₂COONa

 

 

 

Mechanism

CH3  – CH2CO

Propionic anhydride

a -Methyl cinnamic acid

 

 

 

CH3

CO.O.COCH₃

• CH3



COO–

CH₂CO.O.COCH₃

• CH

₃COOH

 

 

 

 

 

C6 H5 – C                                                                      C

–H₂O

O   O OH || +  C H  – | | –  CH CO.O.COCH H+   C H  –      – | H CH2CO.O.COCH3                 6     5 | H 2                            3           6     5      C | H

CH₂CO.O.COCH₃

 

 

 

CH3COOH + C6 H5CH  = CHCOOH ¬¾^hyr¾^oly¾^sis¾ C6 H5CH  = CHCO.O.COCH3

 

 

• Claisen condensation [Claisen-schmidt reaction]

Cinnamic acid

(H2O)

 

CH3                                                           CH3

 

C6 H5

CHO +

|

H2C

• CHO

¾¾NaO¾H ® C6

|

H5 CH = C

• CHO + H₂O

 

Propionaldehyde

(Dil.)

a -Methyl cinnamic aldehyde

 

C6 H5 CHO + H2CHCOCH3  ¾¾^NaO¾^H(¾^D¾^il.) ® C6 H5 CH = CHCOCH3 + H2O

 

Acetone

• Knoevenagel reaction

COOH

C6 H5CH = O + H2 C

Benzylidene acetone

 

 

 

¾¾^Pyri¾^di¾^ne ® C6 H5CH  = CHCOOH+ CO2 + H2O

 

COOH                   D

Cinnamic acid

 

 

Malonic acid

• Reaction with aniline : Benzaldehyde reacts with aniline and forms Schiff’s base

C6 H5CH  = O + H2 NC6 H5 ¾¾^War¾^m ® C6 H5CH  = NC6 H5

 

Aniline

(- H 2 O)

Benzylidene aniline (Schiff’s base)

 

Reaction with Dimethylaniline

CH

N(CH3 )2

 

+

 

N(CH3 )2

 

 

¾¾Con¾c. H¾2SO¾4  ®

(- H2O)

N(CH3 )2

 

 

N(CH3 )2

 

Dimethyl aniline

Tetramethyl diamino triphenyl methane (Malachite green)

 

• Reaction with Ammonia : Benzaldehyde reacts with ammonia to form hydrobenzamide aldehyde other than

 

CH2 O

give aldehyde ammonia while CH2 O

forms urotropine.

 

C6 H5  – CHO + H2 NH ¾¾O=C¾H -¾C6 H¾5  ® C6 H5  – CH  = N

CH – C  H

 

C6 H5 – CHO

H2 NH

C6 H5 – CH = N                        ^{6   5}

Hydrobenzamide

 

• Reformatsky reaction

 

C₆ H₅CH = O+ Zn +

a

Br C H 2 COOC2 H5

¾¾® C6

H5 CHCH

₂COOC2 H5

¾¾^H2¾^O ® C6 H5

• CH – CH 2 COOC2 H5

 

Benzaldehyde

Bromo ethylacetate

|

OZnBr

|

OH

b -hydroxy ester

 

 

 

 

• Reaction of benzene ring

 

 

 

 

 

CHO

HNO₃(conc.) H₂SO₄ (conc.)

 

 

H₂SO₄

fuming

CHO

 

NO₂

m-Nitrobenzaldehyde

 

 

CHO

 

SO₃H

 

Benzaldehyde

m-Benzaldehyde Sulphonic acid

 

 

 

 

 

 

• Uses : Benzaldehyde is used,
  • In perfumery
  • In manufacture of dyes

Cl₂ FeCl₃

CHO

 

Cl

m-Chlorobenzaldehyde

 

• In manufacture of benzoic acid, cinnamic acid, cinnamaldehyde, Schiff’s base,

 

• Tests : (i) Benzaldehyde forms a white precipitate with

NaHSO₃ solution.

 

• Benzaldehyde forms a yellow precipitate with 2 : 4 dinitrophenyl
• Benzaldehyde gives pink colour with Schiff’s
• Benzaldehyde forms black precipitate or silver mirror with Tollen’s

 

• Benzaldehyde on treatment with alkaline benzoic acid on

KMnO4

and subsequent acidification gives a white precipitate of

 

Acetophenone, C₆H₅COCH₃, Acetyl Benzene

(1)  Method of preparation

• Friedel-Craft’s reaction : Acetyl chloride reacts with benzene in presence of anhydrous aluminium chloride to form

C6 H5 H + Cl COCH3 ¾¾^AlC¾^l3  ® C6 H5COCH3 + HCl

 

Benzene

Acetyl chloride

Acetophenone

 

• By distillation of a mixture of calcium benzoate and calcium

O

 

C6 H5 COO

Ca + Ca

||

O CCH3

O

D

||

¾¾® 2C6 H5 CCH3 + 2CaCO3

 

C6 H5 COO

Calcium benzoate

OCCH3

||

O

Calcium acetate

Acetophenone

 

• By methylation of benzaldehyde with

C6 H5CHO + CH2 N2 ¾¾® C6 H5COCH3 + N2

• By treating benzoyl chloride with dimethyl

 

 

 

2C6 H5COCl + (CH3 )2 Cd ¾¾® 2C6 H5COCH3 + CdCl2

• By Grignard reagent

 

• CH C º N + C H

MgBr ¾¾® CH C

= NMgBr

H₂O

 

3                     6    5

3 |

C6 H5

C6 H5COCH3 + NH3 + Mg(OH)Br

O                                     O

 

• C6 H5

MgBr +

||

H5C2OCCH 3

Ethyl acetate

¾¾®

||

C6 H5  CCH3

• Mg

Br OC2 H5

 

• Commercial preparation : Ethylbenzene is oxidised with air at 126^o C

catalyst manganese acetate.

under pressure in presence of a

 

CH2CH3

• O2 ¾¾Cata¾ly¾st ®

126^o C pressure

COCH3

• H2O

 

 

 

• Physical properties : It is a colourless crystalline compound with melting point

202^o C

and boiling point

 

20^o C . It has characteristic pleasant odour. It is slightly soluble in water. Chemically, It is similar to acetone.

 

• Chemical properties :

 

 

 

 

HCN

C6 H5

OH

|

• C – CH3

|

CN

 

Acetophenone cyanohydrine

 

CH3

 

|

C6 H5 – C

=  NOH ¾¾Rea¾rran¾gem¾e¾nt ® C6 H5

NHCOCH₃

 

 

C₆H₅COCH₃

(Acetophenone)

Acetophenone oxime or (Methylphenyl ketoxime)

 

 

 

C H CH CH

H2SO4

Acetanilide

 

6    5      2       3

Ethyl benzene

 

C6 H5 CH OH

|

CH3

Methyl phenyl carbinol (2o alcohol)

 

C  H  COCOOH ¾¾^[¾^O] ® C  H  COOH

Cold KMnO                     ^{6   5                                    6   5}

4                   Phenyl glyoxylic acid                      Benzoic acid

 

 

Oxidation

C6 H5COCHO

Phenyl glyoxal

 

 

 

 

 

 

 

C₆H₅COCH₃

C6 H5CCl2CH3

2, 2-Dichloroethylbenzene

 

 

C6 H5COCH2Cl

 

 

It is relatively harmless but powerful lachrymator or tear gas and is used

 

(Acetophenone)

Phenacyl chloride

(Used as a tear gas)

 

C H COONa + CHI

by police to disperse mobs.

 

6   5

 

 

CH3

|

3

Iodoform

 

O

||

 

C6 H5 – C = CH – C– C6 H5

Dypnone (It is used as hypnotic)

 

NO2C6 H4 COCH3

m– Nitroacetophenone

 

HSO3C6 H4 COCH3

Acetophenone

m-sulphonic acid

 

 

• Uses : It is used in perfumery and as a sleep producing

Quinones

Quinones are unsaturated cyclic diketones. Two quinones of benzene are possible (m-benzoquinone is not possible as it is not possible to construct such formula by maintaining tetravalency of carbon).

Note that quinones are non-aromatic conjugated cyclic diketones. Since they are highly conjugated they are highly coloured substances.

p-Benzoquinone, being the most important, is commonly known as quinone. It is prepared by the oxidation of hydroquinone or aniline.

 

 

 

 

O                             O                                     OH O

;

O

¾¾FeC¾l3  ®

NH₂

;

O

¾¾^MN¾^O¾2 ®

H2SO4

 

 

o – Benzoquinone

O

p-Benzoquinone

OQuHinol

O

p – Benzoquinone

 

Aniline

O

p – Benzoquinone

 

[Laboratory method]

 

 

a, b-Unsaturated carbonyl compounds

a, b-Unsaturated carbonyl compounds. As the name represents these compounds contain unsaturation between

O

|       |     ||

a-and b-carbon atoms with respect to carbonyl group, i.e., – C = C– C– . Such molecules are quite stable due to

the presence of conjugated system of double bond. Such molecules give properties of the double bond, carbonyl group and some additional properties due to the interaction of the two groups. Due to electron withdrawing nature

 

of the

• C = O

group, the reactivity of

C = C

towards electrophilic reagents decreases as compared to an isolated

 

double bond. On the other hand, C = C

simple alkenes.

group undergoes nucleophilic addition reactions which are uncommon for

 

Two important addition reactions of a, b-unsaturated carbonyl compounds are Michael reaction and Diels-Alder reaction.

Michael reaction:  C6 H5CH = CHCOC6 H5 + CH2(COOC2 H5 )2 ¾¾^Pipe¾^ridi¾^ne ® C6 H5 CH.CH2.COC6 H5

 

 

 

Diel’s-Alder reaction

CH CH

Benzal acetophenone

 

 

 

 

CH2

CH.CHO

+

CH2

 

 

 

¾¾¹⁰⁰¾o¾^C ®

 

 

 

CHO

 

1, 2, 3, 6 – Tetrahydrobenzaldehyde

|

CH(COOC2H5)2

 

CH2

1,3 butadiene

 

Acrolein