Chapter 13 Hydroxy Compounds (Alcohals, Phenols) and Ethers Part 2 – Chemistry free study material by TEACHING CARE online tuition and coaching classes

Chapter 13 Hydroxy Compounds (Alcohals, Phenols) and Ethers Part 2 – Chemistry free study material by TEACHING CARE online tuition and coaching classes

File name : Chapter-13-Hydroxy-Compounds-Alcohals-Phenols-and-Ethers-Part-2.pdf

 

(4)  Uses

  • As antifreeze in automobile
  • In the preparation of good quality of soap-hand lotions shaving creams and tooth
  • As a lubricant in
  • As a
  • As a sweetening agent in confectionary, beverages and medicines being non toxic in
  • In manufacture of explosives such as

(5)  Analytical tests of glycerol

 

  • Acrolein test : When glycerol is heated with

KHSO4

a very offensive smell is produced due to formation

 

of acrolein. Its aqueous solution restores the colour of schiff’s reagent and reduces Fehling solution and Tollen’s reagent.

  • Dunstan’s test : A drop of phenophthalein is added approximately 5 ml of borax solution. The pink colour appears on adding 2-3 drops of glycerol, pink colour disappears. The pink colour appears on heating and disappears on cooling
  • Preparation (Allyl alcohol)

 

  • From allyl halide :

CH2  = CH CH2 Br + H2O ® CH2  = CH CH2OH + HBr

Allyl alcohol

 

CH2OH

CH2OOC

CH2

 

|                   HOOC

-2H  O             |

|        Heat          ||

 

  • By heating glycerol with oxalic acid :

CH OH +

|   ¾¾¾2¾® CH OOC  ¾¾¾® CH

 

 

 

(2)  Physical properties

  • It is colourless, pungent smelling

|

CH2OH

HOOC

|

CH2OH

-2CO2

|

CH2OH

Allyl alcohol

 

  • It is soluble in water, alcohol and ether in all

 

(3)

Pt

 

Br2

 

 

HBr

 

 

HOCl

 

Alk. KMnO4

(O + H2O)

 

Na

CH3COOH
 

 

HCl

 

 

Oxidation

 

 

 

Br2

 

Chemical properties        H2

CH CH CH OH

 

3          2          2

1-propanol

CH Br CHBrCH OH

2                                         2

2, 3-dibromopropanol-1

CH2BrCH2 CH2OH

3-Bromopropanol-1

CH2OHCHClCH2OH

Glycerol b-monochlorohydrin

 

CH2

OH CHOH CH2OH

Glycerol

 

CH2 = CHCH2OH

(Allyl alcohol)

CH2 = CH CH2ONa

 

CH = CH CH OOCCH

2                                    2                         3

Allyl acetate

CH2 = CH CH2Cl

Allyl chloride

COOH

 

|             +

COOH

(CH OH)

Oxalic acid

HCOOH

Formic acid

 

CH2CH CH2

|           |          |

[O]

HNO

CH2CH COOH

3

|          |

Zn dust     CH2CH COOH

 

Br       Br        OH

Br        Br

3

Acrylic acid

 

 

 

It was discovered by Runge in the middle oil fraction of coal-tar distillation and named it ‘carbolic acid’ (carbo

= coal, oleum = oil) or phenol containing 5% water is liquid at room temperature and is termed as carbolic acid. It is also present in traces in human urine.

(1)  Preparation

  • From benzene sulphonic acid : Sodium salt of benzene sulphonic acid is fused with sodium hydroxide (NaOH) when sodium phenoxide is formed. Sodium phenoxide on treatment with dilute acid or carbon dioxide yields The start can be made with benzene.

 

C6 H6

¾¾H2S¾O4¾(f um¾in¾g) ®

C6 H5

SO3 H

¾¾NaO¾H  ®

C6 H5

SONa

¾¾NaO¾H  ®

Fuse

CH

5ONa

¾¾H+ ¾/ HO ® C

or CO2 / H2O             6

H5 OH

 

Benzene

Benzene sulphonic acid

Sodium benzene sulphonate

Sodium phenoxide

Phenol

 

This is one of the laboratory methods for the preparation of phenol. Similarly methyl phenols (cresols) can

 

be prepared.

SO3H

OK                                  OH

 

Solid KOH

Fuse

H+/H2O

 

CH3

p-Toluene sulphonic acid

CH3

CH3

p-Cresol

 

  • From benzene diazonium chloride : When benzene diazonium chloride solution is warmed, phenol is formed with evolution of nitrogen. The phenol from solution is recovered by steam distillation. In this case also, benzene can be taken as the starting This is also a laboratory method.

 

C  H   ¾¾HN¾O¾3  ® C  H  NO

¾¾Sn /¾H¾Cl ® C  H  NH

¾¾NaN¾O¾2  ®

C H N Cl

¾¾HO ® C  H  OH

 

6  6 H  SO  , 45o C     6  5           2

6  5        2

HCl, 0 – 5 o C

6  5  2

Warm        6  5

 

Benzene  2           4

Nitrobenzene

NH2

Aniline

N2Cl

Benzene diazonium chloride

OH

Phenol

 

CH3

m-Toluidine

HNO2

 

CH3

m-Toluene

diazonium chloride

HO2

 

 

 

m-Cresol

 

CH3

 

Note : ® Diazonium salts are obtained from aniline and its derivatives by a process called diazotisation.

  • From Grignard reagent : Chlorobenzene or bromobenzene is first converted into phenyl magnesium halide in presence of dry ether. The Grignard reagent on reaction with oxygen and subsequent hydrolysis by a mineral acid, yields

 

CHBr  + Mg ¾¾Eth¾er ®

C6 H5 MgBr

¾¾O¾2  ®CH5OMgBr ¾¾H¾2O ® CH5OH

 

Bromobenzene

Phenyl magnesium bromide

H +                   Phenol

 

  • From salicylic acid : When salicylic acid or its sodium salt is distilled with soda lime, decarboxylation occurs and phenol is

 

OH

 

 

Salicylic acid

COOH

+ 2NaOH       CaO

OH

 

 

Phenol

+ Na2CO3 + H2O

 

  • Middle oil of coal tar distillation : Middle oil of coal-tar distillation has naphthalene and phenolic Phenolic compounds are isolated in following steps.

 

Step I : Middle oil is washed with

H2SO4 . It dissolves basic impurities like pyridine (base).

 

 

Step II : Excessive cooling separates naphthalene (a low melting solid)

Step III : Filtrate of step II is treated with aqueous NaOH when phenols dissolve as phenoxides. Carbon dioxide is then blown through the solution to liberate phenols.

CHOH + NaOH  ® CHONa + HO ¾¾CO¾2 , H¾2¾O ® CHOH + NaCO3

Step IV : Crude phenol (of step III) is subjected to fractional distillation.

 

 

Crude phenols

180°C

Para

 

o, m, p-cresols

xylols (hydroxy xylenes)

 

  • Raschig’s process : Chlorobenzene is formed by the interaction of benzene, hydrogen chloride and air at 250°C in presence of catalyst cupric chloride and Ferric chloride it is hydrolysed by superheated steam at 425°C to form phenol and HCl. This is one of the latest methods for the synthesis of phenol. HCl may be again used to convert more of benzene into chlorobenzene.

 

C6 H6

+ HCl + 1 O

2    2

¾¾CuC¾l2 /¾FeC¾l3  ®

250o C

CH

5Cl + H

2O ;

CH

5Cl + H

O ¾¾425¾o¾C ® C

H5OH  + HCl

 

Benzene

Chlorobenzene

Chlorobenzene

steam

Phenol

 

2
6
  • Dow process : This process involves alkaline hydrolysis of chlorobenzene. Large quantities of phenol are formed by heating chlorobenzene with a 10% solution of caustic soda or sodium carbonate at 300°C under a very high pressure (200 atm).

 

CH

Cl  + 2NaOH ¾¾300¾o¾C ® C

5
6

High pressure

H5ONa + NaCl + H2O

 

Chlorobenzene

sodium phenoxide on treatment with mineral acid yields phenol.

2C6 H5 ONa + HSO4 ® 2C6 H5 OH + Na2 SO4

  • Oxidation of benzene : This is the latest method for the manufacture of The mixture of benzene and air is passed over vanadium pentaoxide at 315°C. Benzene is directly oxidised to phenol.

2CH6  + O2  ¾¾V2O¾5  ® 2CHOH

315o C

  • Oxidation of isopropyl benzene [Cumene] : Cumene is oxidised with oxygen or air into cumene hydroperoxide in presence of a This is decomposed by dilute sulphuric acid into phenol and acetone.

 

 

+ CH CH CH Cl     AlCl3

H3C

CH3

CH

O – OH

|

C(CH )                   OH

 

3       2       2

 

O2

Catalyst

3 2

 

H2O/H+

+ (CH3)2CO

Acetone

 

+ CH CH = CH

     AlCl3

Cumene

Cumene

Phenol

 

3                     2                                                         hydroperoxide

 

(2)  Physical properties

  • Phenol is a colourless crystalline, deliquescent It attains pink colour on exposure to air and light.
  • They are capable of forming intermolecular H-bonding among themselves and with Thus, they have high b.p. and they are soluble in water.

H                                             H

 

d+                    d–

d+                  |

d+                     d–

d+                    |

 

H O——-H O——-H O——-H O——-

 

 

d+                    d–                                                                                                            d+                     d–

H O——-H O——-H O——-H O——-

d–                                                                                                                                        d–

 

d+                    d–

d+                    d–

(crossed intermolecular H-bonding between water and phenol molecules)

 

(intermolecular H-bonding among phenol molecules)

 

 

  • Due to intermolecular H– bonding and high dipole moment, m.p. and b.p. of phenol are much higher than that of hydrocarbon of comparable molecular

    • It has a peculiar characteristic smell and a strong corrosive action on
    • It is sparingly soluble in water but readily soluble in organic solvents such as alcohol, benzene and
    • It is poisonous in nature but acts as antiseptic and

(3)  Chemical properties

  • Acidic nature : Phenol is a weak The acidic nature of phenol is due to the formation of stable phenoxide ion in solution.

 

C6 H 5 OH + H 2 O

C6 H 5 O + H 3 O +

Phenoxide ion

 

The phenoxide ion is stable due to resonance.

O                                    O                                   O

 

..

 

The negative charge is spread throughout the benzene ring. This charge delocalisation is a stabilising factor in the phenoxide ion and increase acidity of phenol. [No resonance is possible in alkoxide ions (RO) derived from alcohols. The negative charge is localised on oxygen atom. Thus alcohols are not acidic].

Note : ® Phenols are much more acidic than alcohols but less so than carboxylic acids or even carbonic acid. This is indicated by the values of ionisation constants. The relative acidity follows the following order

 

Ka (approx.)

(10-5 )

  • (10-7 )
  • (10-10 )

> (10-14 ) > (10-18 )

 

RCOOH

Carboxylic acid

H2CO3

Carbonic acid

CH5OH

Phenol

HOH

Water

ROH

Alcohols

 

Effects of substituents on the acidity of phenols : Presence of electron attracting group, (e.g.,

  • NO2 ,

 

3

–X, NR+ , –CN, –CHO, –COOH) on the benzene ring increases the acidity of phenol as it enables the ring to draw

more electrons from the phenoxy oxygen and thus releasing easily the proton. Further, the particular effect is more when the substituent is present on o– or p-position than in m-position to the phenolic group.

The relative strengths of some phenols (as acids) are as follows :

p-Nitrophenol > o-Nitrophenol > m– Nitrophenol > Phenol

 

Presence of electron releasing group, (e.g.,

  • CH3 ,
  • C2 H5 , – OCH3 , – NR2 ) on the benzene ring decreases

 

the acidity of phenol as it strengthens the negative charge on phenoxy oxygen and thus proton release becomes difficult. Thus, cresols are less acidic than phenol.

However, m-methoxy and m-aminophenols are stronger acids than phenol because of –I effect and absence of

+R effect.

m-methoxy phenol > m-amino phenol > phenol > o-methoxy phenol > p-methoxy phenol

 

Greater the value of nature of phenols are,

Ka or lower the value of

pKa , stronger will be the acid. Some other examples of acidic

 

 

Chloro phenols : o– > m– > p– Cresols : m– > p– > o– Dihydric phenol : m– > p– > o

The acidic nature of phenol is observed in the following :

  • Phenol changes blue litmus to

 

  • Highly electropositive metals react with

2C6 H5 OH + 2Na ® 2C6 H5 ONa + H2

 

  • Phenol reacts with strong alkalies to form C6 H5 OH + NaOH ® C6 H5 ONa + H2O

However, phenol does not decompose sodium carbonate or sodium bicarbonate, i.e., CO2 is not evolved because phenol is weaker than carbonic acid.

  • Reactions of OH group
  • Reaction with FeCl3 : Phenol gives violet colouration with ferric chloride solution (neutral) due to the formation of a coloured iron complex, which is a characteristic to the existence of keto-enol tautomerism in phenols (predominantly enolic form).

 

OH

 

 

Enol

This is the test of phenol.

O

 

 

Keto

OH

 

;       6           + FeCl3 ® 3H+ + Fe O

 

3–

+ 3HCl

6

 

  • Ether formation : Phenol reacts with alkyl halides in alkali solution to form phenyl ethers (Williamson’s synthesis). The phenoxide ion is a nucleophile and will replace halogenation of alkyl

 

C6 H5 OH + NaOH ® C6 H5 ONa+ H2O ;

Sod. phenoxide

C6 H5 ONa + ClCH3

®      C6 H5 OCH3           +

Methyl phenyl ether (Anisole)

NaCl

 

C6 H5 OK + IC2 H5 ® C6 H5 – O C2 H5 + KI ;  C6 H5 ONa + Cl HC(CH3 )2  ® C6 H5 – O HC(CH3 )2

 

Ethoxy benzene (Phenetol)

Isopropyl chloride

Isopropyl phenyl ether

 

Ethers are also formed when vapours of phenol and an alcohol are heated over thoria (ThO2 ) or

CHOH + HOCH3  ¾¾D,T¾hO¾2  ® CH5  – OCH3

Methoxy benzene

Al2O3 .

 

  • Ester formation : Phenol reacts with acid chlorides (or acid anhydrides) in alkali solution to form phenylesters (Acylation). This reaction (Benzoylation) is called Schotten-Baumann

O

||

C6 H5 OH + NaOH ® C6 H5 ONa + H2O ;         C6 H5ONa  + Cl CCH3 ® C6 H5OOCCH3 + NaCl

 

Sodium phenoxide

Acetyl chloride

Phenyl acetate

 

CHOH + (CHCO)2 O ¾¾NaO¾H ® CHOOCCH3 + CHCOOH ;

 

Acetic anhydride

O

||

Phenyl acetate (ester)

O

||

 

CH5OH + Cl CCH5  ¾¾NaO¾H ® CH5  – OCCH5 + NaCl + H2O

Benzoyl chloride                                         Phenyl benzoate

 

The phenyl esters on treatment with anhydrous

AlCl3

undergoes Fries rearrangement to give o– and p

 

hydroxy ketones.

OOCCH3

Phenyl acetate

 

 

AlCl3 (anhydrous) heat

OH

COCH3

+

OH

 

 

 

COCH3

 

 

hydroxy acetophenone

 

 

 

  • Reaction with PCl5 : Phenol reacts with and mainly triphenyl phosphate is

PCl5

to form chlorobenzene. The yield of chlorobenzene is poor

 

C6 H5 OH + PCl5 ® C6 H5 Cl + POCl3  + HCl ;  3C6 H5 OH + POCl3  ® (C6 H5 )3 PO4  + 3HCl

  • Reaction with zinc dust : When phenol is distilled with zinc dust, benzene is

C6 H5OH + Zn ® C6 H6 + ZnO

  • Reaction with ammonia : Phenol reacts with ammonia in presence of anhydrous zinc chloride at 300°C or

 

(NH4 )2 SO3  / NH3

at 150°C to form aniline. This conversion of phenol into aniline is called Bucherer reaction.

 

CHOH + NH 3  ¾¾ZnC¾l2  ® CHNH 2 + HO

 

300o C

Aniline

 

  • Action of P2S5 : By heating phenol with phosphorus penta sulphide, thiophenols are

5C6 H5OH + P2S5 ® 5C6 H5 SH+ P2O5

Thiophenol

  • Reactions of benzene nucleus : The –OH group is ortho and para It activates the benzene nucleus.

 

  • Halogenation : Phenol reacts with bromine in carbon disulphide (or mixture of ortho and para

CHCl3 ) at low temperature to form

 

OH

 

+ Br2

 

 

(CS2)

OH

Br

+

o-Bromophenol

OH

 

;

 

Br

p-Bromophenol

OH                                               OH

Br                     Br

+ 3Br2

 

Br

2, 4, 6-Tribromophenol

 

+ 3HBr

 

Phenol forms a white precipitate with excess of bromine water yielding 2, 4, 6-tribromophenol.

 

  • Sulphonation : Phenol reacts with benzene sulphonic acids.

H 2 SO4

readily to form mixture of ortho and para hydroxy

 

OH

 

(H2SO4)

OH                                           OH

SO3H

+

 

 

o-Hydroxybenzene sulphonic acid

SO3H

p-Hydroxybenzene

sulphonic acid

 

At low temperature (25°C), the ortho-isomer is the major product, whereas at 100°C, it gives mainly the para– isomer.

  • Nitration : Phenol reacts with dilute nitric acid at 5-10°C to form ortho and para nitro phenols, but the yield is poor due to oxidation of phenolic The –OH group is activating group, hence nitration is possible with

 

dilute nitric acid.

OH                                 OH

 

HNO3(dil.) (5-10°C)

OH

NO2

+

 

 

o-Nitrophenol

NO2

p-Nitrophenol

 

 

It is believed that the mechanism of the above reaction involves the formation of o– and p– nitroso phenol with

 

nitrous acid,

HNO2 (NaNO2 + HCl) at 0-5°C, which gets oxidised to o– and p– nitrophenol with dilute nitric acid.

 

OH                                   OH

NO

+

HONO

(0-5°C)

OH

 

[O]

HNO3 (Dil.)

OH                                 OH

NO2

+

 

 

o-Nitrosophenol

NO

p-Nitrosophenol

Nitrophenol

 

However, when phenol is treated with concentrated

HNO3

in presence of concentrated

H 2SO4 ,  2,4,6-

 

trinitrophenol (Picric acid) is formed.

OH

 

HNO3 (conc.)

H2SO4(conc.)

O2N

NO2

 

 

 

NO2

2, 4, 6-Trinitrophenol

(picric acid)

To get better yield of picric acid, first sulphonation of phenol is made and then nitrated. Presence of group prevents oxidation of phenol.

 

  • SO3 H

 

  • Friedel-Craft’s reaction : Phenol when treated with methyl chloride in presence of anhydrous aluminium chloride, p-cresol is the main A very small amount of o-cresol is also formed.

 

OH

 

+ CH3Cl

 

 

AlCl3

OH

 

+

 

CH3

p-Cresol (major product)

OH

 

 

o-cresol

CH3

 

RX and

AlCl3

give poor yields because

AlCl3

coordinates with O. So Ring alkylation takes place as follows,

 

C6 H5 OH + AlCl3 ® C6 HOAlCl2  + HCl

Thus to carry out successful Friedel-Craft’s reaction with phenol it is necessary to use a large amount of The Ring alkylation takes place as follows :

AlCl3 .

 

 

C6 H5

ì CH

OH     ï+

í

3CH = CH 2

¾¾H2S¾O¾4  ® o – and pCH4

/ OH

 

ï(CH3 )2 CH OH

î

OH

or HF

 

OH

COCH3

\ CH(CH  )

3
2

OH

 

+ CH3COCl

Acetyl chloride

anhydrous AlCl3                                                   +

 

 

ortho

 

COCH3

 

hydroxy acetophenone

 

 

  • Kolbe-Schmidt reaction (Carbonation) : This involves the interaction of sodium phenoxide with carbon dioxide at 130-140°C under pressure of 6 atmospheres followed by acid hydrolysis, Salicylic acid (o-Hydroxy

 

benzoic acid) is formed.

 

 

ONa

 

 

OCOONa                      OH

OH

 

D

 

 

OH                                           Salol

COOC6H5

 

 

+ CO2

 

130-140°C

6 atm

 

Rearrangement

 

Sodium phenyl carbonate

COONa

 

Sodium salicylate

 

H+ H2O

 

 

 

 

Salicylic acid

COOH

 

CH3COCl

OCOCH3

COOH

 

Aspirin

OH

 

 

The probable mechanism is : C6 H 5 OH ® C6 H 5 O + H +

OH

CH3OH

 

 

OH

 

 

 

Winter green

COOCH3

 

H

–       –H+

CO

||                H+

COOH

 

+ C = O

||

O

CO

||

O

+H+                                                                         O

 

At higher temperature (250-300°C), p-isomer is obtained.

  • Reimer-Tiemann reaction : Phenol, on refluxing with chloroform and sodium hydroxide (aq.) followed by acid hydrolysis yields salicylaldehyde (o-hydroxy benzaldehyde) and a very small amount of p-hydroxy However, when carbon tetrachloride is used, salicylic acid (predominating product) is formed.

 

OH

CHCl2 OH

 

NaOH

ONa

 

CHO

 

ONa

 

H+ H2O

OH

 

CHO

Salicylaldehyde

 

OH

 

 

NaOH(aq.) 60°C

CCl3

NaOH

COONa

H+ H2O

 

Salicylic acid

COOH

 

The electrophile is dichloromethylene : CCl 2

generated from chloroform by the action of a base.

 

OH + CHCl3  ⇌

HOH+

: CCl3

® Cl +

: CCl2

 

Dichloro carbene

Reimer-Tiemann reaction involves electrophilic substitution on the highly reactive phenoxide ring.

 

C6 H5 OH ® C6 H5 O + H +                    O

Phenoxide

Attack of electrophile (: CCl 2 )

O

CHCl2

 

 

 

O

CHCl2

+ 2NaOH       Hydrolysis

O

CH(OH)2

 

H2O

O

CHO  ;

O

CHO

+ H+

OH

 

Salicylaldehyde

CHO

 

 

  • Gattermann’s reaction : Phenol, when treated with liquid hydrogen cyanide and hydrochloric acid gas in presence of anhydrous aluminium chloride yields mainly p-hydroxy benzaldehyde (Formylation).

HCl + HC º N ¾¾AlC¾l3  ® ClCH  = NH

OH                                                            OH                         OH

 

 

HCl

+ ClCH = NH      AlCl3

H2O

NH3

 

 

 

CH = NH

CHO

p-Hydroxy benzaldehyde

 

  • Mercuration : Phenol when heated with mercuric acetate undergoes mercuration to form o– and p-isomers.

 

OH

 

+ (CH3COO)2Hg

OH                                                OH

HgOCOCH3

+

 

 

 

o-Hydroxy phenyl mercuric acetate

HgOCOCH3

p-Hydroxy phenyl mercuric acetate

 

  • Hydrogenation : Phenol, when hydrogenated in presence of a nickel catalyst at about 150-200°C, forms

 

cyclohexanol.

OH                                                  OH

 

 

 

 

 

  • Miscellaneous reactions

 

 

Phenol (C6H5OH)

Ni

+ 3H2

150-200°C

 

 

Cyclohexanol (C6H11,OH) (used as a good solvent)

 

  • Coupling reactions : Phenol couples with benzene diazonium chloride in presence of an alkaline solution to form a red dye (p-hydroxy azobenzene).

 

 

N = NCl +

Benzene diazonium chloride                              Phenol

OH  NaOH                     N = N                              OH

HCl

p-Hydroxyazobenzene

 

Phenol couples with phthalic anhydride in presence of concentrated used as an indicator.

H 2 SO4

to form a dye, (phenolphthalein)

 

O

||

C OH

D

 

C OH

||

O

Phthalic acid

O                                                          O

||                                                           ||

C                                                           C

O
O

Conc. H2SO4

(–H2O)

C                                                           C

||Phthalic anhydride

 

 

 

 

 

 

OH                                   OH

Phenol (2 molecules)

OH                               OH

Phenolphthalein

 

 

  • Condensation with formaldehyde : Phenol condenses with formaldehyde (excess) in presence of sodium hydroxide or acid (H + ) for about a week to form a polymer known as bakelite (a resin).

 

OH                                         OH

OH                                                          OH                          OH

+

CH2OH                                                     CH                              CH                          CH

 

+ CH2O

NaOH

 

o-hydroxy benzyl alcohol

Condensation with

HCHO

continues give

 

CH2OH

2

 

 

CH2

2                               2

 

 

CH2

 

p-hydroxy benzyl alcohol

 

 

  • Liebermann’s nitroso reaction : When phenol is reacted with

 

NaNO2

 

Polymer Bakelite (a resin)

 

and concentrated

 

H 2SO4 , it gives a

 

deep green or blue colour which changes to red on dilution with water. When made alkaline with NaOH original green or blue colour is restored. This reaction is known as Liebermann’s nitroso reaction and is used as a test of phenol.

 

OH       HONO

NO                         OH

p-Nitrosophenol

O                        NOH

Quinoxim

 

 

 

OH
O                        N

H2SO4 H2O

O                        N                         OH  NaOH

H O

2

Sod. Salt of indophenol (blue)

 

Indo phenol (Red)

  • Oxidation : Phenol turns pink or red or brown on exposure to air and light due to slow The colour is probably due to the formation of quinone and phenoquinone.

 

 

C H OH  or

OH   O2 by air

O                        O    C6H5OH                                       OH – – – O                          O – – – HO

 

6  5                                                 or CrO3

OH p-benzoquinone   O

[O]

CrO2Cl2

 

+ H2O

Phenoquinone (pink)

 

 

Phenol

O

p-benzoquinone

 

But on oxidation with potassium persulphate in alkaline solution, phenol forms 1, 4-dihydroxy benzene (Quinol). This is known as Elbs persulphate oxidation.

OH                                       OH

 

 

 

 

 

Phenol

K2S2O8 in

alkaline solution

 

OH

Quinol

 

  • Uses : Phenol is extensively used in The important applications of phenol are :
    • As an antiseptic in soaps, lotions and A powerful antiseptic is “Dettol” which is a phenol derivative (2, 4-dichloro-3, 5-dimethyl phenol).
    • In the manufacture of azo dyes, phenolphthalein,
    • In the preparation of picric acid used as an explosive and for dyeing silk and
    • In the manufacture of cyclohexanol required for the production of nylon and used as a solvent for rubber and
    • As a preservative for

 

 

  • In the manufacture of phenol-formaldehyde plastics such as
  • In the manufacture of drugs like aspirin, salol, phenacetin,
  • For causterising wounds caused by the bite of mad
  • As a starting material for the manufacture of nylon and artificial
  • In the preparation of disinfectants, fungicides and
  • Tests of phenol : (i) Aqueous solution of phenol gives a violet colouration with a drop of ferric
  • Aqueous solution of phenol gives a white precipitate of 2, 4, 6-tribromophenol with bromine
  • Phenol gives Liebermann’s nitroso

 

Phenol in conc. sulphuric acid

¾¾NaN¾O¾2  ®  Red colour

Excess of water

¾¾NaO¾H ®  Blue colour

(Excess)

 

  • Phenol combines with phthalic anhydride in presence of H 2SO4

gives pink colour with alkali, and used as an indicator.

  • With ammonia and sodium hypochlorite, phenol gives blue

Difference between phenol and alcohol

to form phenolphthalein which

 

 

PropertyPhenol (C6H5OH)Alcohol (C2H5OH)
OdourTypical phenolic odourPleasant alcoholic odour
Nature, reaction with alkaliAcidic,         dissolves        in       sodiumNeutral, no reaction with alkalies.
 hydroxide            forming            sodium 
 phenoxide. 
Reaction with neutral FeCl3Gives  violet   colouration   due   toNo reaction.
 formation of complex compound. 
Reaction with halogen acidsNo reaction with halogen acids.Forms ethyl halides.
OxidationPink     or     brown  colour      due   toUndergoes        oxidation        to       give
 formation         of         quinone         andacetaldehyde and acetic acid.
 phenoquinone. 
Reaction with HCHOForms polymer (bakelite).No reaction.
Liebermann’s nitroso reactionPositive.Does not show.
Coupling with benzene diazoniumForms azo dye.Does not form any dye.
chloride  
Reaction with PCl5Mainly forms triphenyl phosphate.Forms ethyl chloride
Iodoform testDoes not show.Positive.

 

 

 

(1)  Preparation

NITROPHENOLS

 

  • Phenol easily undergoes Ortho and para nitrophenols are obtained by nitration of phenol with

 

dilute

HNO3 in cold. Ortho isomer is separated by steam distillation as it is steam volatile.

 

OH                                OH

 

Dil. HNO3

 

o-isomer (steam volatile)

NO2

+

OH

 

 

 

NO2

p-isomer

(non-volatile)

 

  • o– and p-forms are also obtained by treating chloro or bromo nitrobenzene with caustic alkali at 120°C.

 

 

 

 

C6 H4

Cl

 

NO2

¾¾NaO¾H ®

C6 H4

OH

 

NO2

 

o– and p-chloro nitrobenzene                                    o– and p-nitrophenol

  • When heated with solid potassium hydroxide, nitrobenzene produces a mixture of o– and p-nitrophenols.

OH

CHNO2  ¾¾Soli¾d KO¾¾H ® CH4

 

Nitrobenzene

heat

NO2

 

o– and p-nitrophenol

  • m-Nitrophenol is obtained from m-dinitrobenzene. One of the nitrogroup is converted into which is diazotised. The diazonium compound on boiling yields m-nitrophenol.

 

  • NH2

 

group

 

OH

 

 

 

NO

m-Dinitrobenzene

NH4HS

2
2

or Na2S

NaNO2/HCl

0-5°C

2

NO

m-Nitroaniline

NO

m-Nitrobenzene

diazonium chloride

H2O

2

NO

m-Nitrophenol

 

  • Properties : o-Nitrophenol is a yellow coloured crystalline compound, while m– and p-isomers are colourless crystalline compounds.

 

Isomer m.pt.(°C)

ortho

45

meta

97

para

114

 

the lowest melting point of o-isomer is due to intramolecular hydrogen bonding whereas meta and para

isomers possess intermolecular hydrogen bonding and thus, they have higher melting points.

They are stronger acids than phenol. The order is :

p-isomer > o-isomer > m-isomer > phenol

When reduced, they form corresponding aminophenols. o– and p-Nitrophenols react with bromine water to

form 2, 4, 6-tribromophenol by replacement of nitro group.           OH

 

 

/

C6 H4 \

OH

 

NO2

Br                      Br

¾¾B¾r2  ®

 

o– or p-isomer

Br

2,4,6 Tribromophenol

 

Picric acid (2, 4, 6-trinitrophenol)

 

  • Preparation : It is obtained when phenol is treated with is prepared on an industrial scale :
    • From chlorobenzene

HNO3 . However, the yield is very poor. It

 

Cl

Chlorobenzene

Cl

NO2

HNO3 H2SO4

 

NO2

 

 

Aq. Na2CO3

OH

 

 

 

NO2

NO2

 

 

HNO3 H2SO4

O2N                     NO2

 

 

NO2

 

2, 4-Dinitrochlorobenzene

Picric acid

(2, 4, 6-Trinitrophenol)

 

 

  • From phenol through disulphonic acid

 

OH

 

H2SO4

OH

SO3H

 

 

HNO3

O2N

NO2

 

 

 

Phenol

SO3H

Phenol disulphonic acid

NO2

Picric acid

 

  • It may be prepared in the laboratory by oxidation of s-trinitrobenzene (TNB) with potassium ferricyanide.

 

 

O2N

NO2

+ [O]

Ke3Fe(CN)6

O2N

NO2

 

 

 

NO2

NO2

Picric acid

 

  • Properties : It is a yellow crystalline solid, m.pt. 122°C. it is insoluble in cold water but soluble in hot water and in ether. It is bitter in taste. Due to the presence of three electronegative nitro groups, it is a stronger acid than phenol and its properties are comparable to the carboxylic acid. It neutralises alkalies and decomposes carbonates with evolution of carbon

Dry picric acid as well as its potassium or ammonium salts explode violently when detonated. It reacts with

 

PCl5

to form picryl chloride which on shaking with

NH 3

yields picramide.

 

 

 

O N                    NO

 

NO

    PCl         O N

H O

NO

 

PicrylNchOloride

NH           O N

NO

 

PicrNamOide

 

 

 

When distilled with a paste of bleaching powder, it gets decomposed and yields chloropicrin, one of the products and is thus employed for the manufacture of tear gas.

CCl3 NO2 , as

 

It forms yellow, orange or red coloured molecular compounds called picrates with aromatic hydrocarbons, amines and phenols which are used for characterisation of these compounds.

Note : ® Picrates are explosive in nature and explode violently when heated. These are prepared carefully.

  • Uses : It is used as a yellow dye for silk and wool, as an explosive and as an antiseptic in treatment of

Catechol (1, 2-Dihydroxy benzene)

(1)  Preparation

  • By fusion of chlorosubstituted phenolic acid with caustic or by hydrolysis of o-dichlorobenzene or o– chlorophenol with dilute NaOH solution at 200°C and in the presence of copper sulphate catalyst.

 

OH

Cl

NaOH

OH

 

 

Catechol

Cl

OH

+ CO2 + NaCl ;

 

Cl

NaOH

200°C, Cu2+

ONa

 

ONa

OH

OH

H+/H2O

 

COOH

 

 

  • By fusing alkali salt of o-phenol sulphonic acid with caustic alkali and then hydrolysing the product with

 

mineral acid.

OH

SO3K

+ 3KOH

OK                                        OH

OK                                        OH

2HCl

 

 

 

  • It may be conveniently prepared in the laboratory by treating salicylaldehyde with alkaline

H2O2  .

 

CHO

 

OH

Salicylaldehyde

+ H2O2 + NaOH

 

Catechol

OH

+ HCOONa + H2O

OH

 

  • Properties : It is a colourless crystalline solid, pt. 105°C. it is soluble in water. It is affected on exposure to air and light. It acts as a reducing agent as it reduces Tollen’s reagent in cold and Fehling’s solution on heating. With silver oxide it is oxidised to o-benzoquinone.

 

OH

OH

+ Ag2O

O

 

 

o-Benzoquinone

O + 2Ag + H O

 

2

It forms insoluble lead salt (white ppt.) when treated with lead acetate solution and gives green colour with

 

FeCl 3

which changes to red on adding

NaCO3

solution. It forms alizarin dye stuff when condensed with phthalic

 

anhydride in the presence of sulphuric acid.

 

 

OH

O

||

C                                   OH

O +

C

||

O

 

 

Con H2SO4

(–H2O)

O

OH

||

C                      OH

 

C

||

O

 

Phthalic anhydride                                                                          Alizarin

  • Uses : It finds use as photographic developer, in the manufacture of alizarin and adrenaline hormone and as an antioxidant (inhibitor in auto oxidation) for preserving

Resorcinol (1, 3-Dihydroxy benzene)

  • Preparation : It is prepared by alkali fusion of 1,3, benzene disulphonic acid (Industrial method).

 

SO3H

 

SO3H

 

NaOH

Fuse

ONa

 

ONa

OH

HCl

OH

 

 

  • Properties : It is a colourless crystalline solid, pt. 110°C. it is affected on exposure by air and light. It is

 

soluble in water, alcohol and ether. It shows tautomerism. Its aqueous solution gives violet colour with reduces Fehling’s solution and Tollen’s reagent on warming.

With bromine water, it gives a crystalline precipitate, 2, 4, 6-tribromoresorcinol.

FeCl3 . It

 

OH

 

+ 3Br2

OH

OH

Br                     Br

OH

Br

 

+ 3HBr

 

 

On nitration, it forms 2, 4, 6-trinitro-1, 3-dihydroxybenzene.

 

OH

 

HNO3 H2SO4

OH

O2N

OH

 

 

 

NO2

Styphnic acid

NO2 OH

 

It condenses with phthalic anhydride and forms fluorescein.

OH                                                                 OH

 

 

O                    H

O = C C = O +

H

Conc. H2SO4

OH
OH

 

–2H2O

O

O = C  C                    O

 

 

 

 

Phthalic anhydride

OH

Resorcinol

(2 moles)

Fluorescein OH

 

With nitrous acid, it forms 2, 4-dinitrosoresorcinol

 

OH                                      OH

NO

HNO2                                               

OH                                      OH

NO

O

NOH

 

O

NOH

 

Resorcinol behaves as a tautomeric compound. This is shown by the fact that it forms a dioxime and a bisulphite derivative.

OH                                    O

 

 

 

(3)  Uses

OH

Dienol form

O

Diketo form

 

  • It is used as antiseptic and for making
  • It is also used in the treatment of eczema. 2, 4, 6-trinitroresorcinol is used as an

Hydroquinone or quinol (1, 4-Dihydroxy benzene)

  • Preparation : It is formed by reduction of p-benzoquinone with sulphurous acid (H2SO3 = H2O + SO2 ).

 

 

O                        O + SO2 + 2H2O H2SO3 + H2O

HO

Quinol

OH + H2SO4

 

(p-Benzoquinone is obtained by oxidation of aniline)

NH2                         O                               OH

 

 

[O]

MnO2/H2SO4

Fe/H2O

[H]

 

 

O                               OH

Quinol

 

 

  • Properties : It is a colourless crystalline solid, pt. 170°C. it is soluble in water. It also shows

 

tautomerism. It gives blue colour with FeCl3

solution.

 

It acts as a powerful reducing agent as it is easily oxidised to p-benzoquinone. It reduces Tollen’s reagent and

 

Fehling’s solution.

HO                        OH

[O]

FeCl3

O                        O

p-Benzoquinone

 

Due to this property, it is used as photographic developer.

  • Uses : It is used as an antiseptic, developer in photography, in the preparation of quinhydrone electrode and as an

Trihydric Phenols : Three trihydroxy isomeric derivatives of benzene are Pyrogallol (1, 2, 3), hydroxy quinol (1, 2, 4) and phloroglucinol (1, 3, 5).

Pyrogallol is obtained by heating aqueous solution of gallic acid at 220°C.

 

 

 

 

HOOC

OH

OH

 

OH

Gallic acid

 

 

 

heat 220°C

OH

 

 

 

Pyrogallol

OH

+ CO2

OH

 

 

Phloroglucinol is obtained from trinitrotoluene (TNT) by following sequence of reactions.

 

 

O2N

CH3

NO2

 

 

KMnO4

[O]

O2N

COOH

NO2

 

 

Fe/HCl

[H]

H2N

COOH

NH2

 

 

H2O/H+

100°C

HO                      OH

+ CO2

 

+ 3NH4Cl

 

 

 

NO2

2, 4, 6-trinitro toluene

NO2

NH2

OH

Phloroglucinol

 

 

Hydroxyquinol is prepared by the alkaline fusion of hydroquinone in air.

 

OH

 

+ ½ O2

OH

OH

NaOH

Fuse

 

 

 

OH

Quinol

OH

Hydroxy Quinol

 

The three isomers are colourless crystalline compounds. All are soluble in water and their aqueous solutions give characteristic colour with FeCl3 . For example, Pyrogallol-red; Hydroxy quinol-greenish brown; Phloroglucinol- bluish violet. Alkaline solutions absorb oxygen rapidly from air.

Uses of pyrogallol

  • As a developer in
  • As a hair
  • In treatment of skin diseases like
  • For absorbing unreacted oxygen in gas

Tags: ,

Leave a Reply

Your email address will not be published. Required fields are marked *