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

 

(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 = CH – CH₂OH –

(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

 

CH₂ – CH – CH₂

|           |          |

[O]

HNO

CH₂ – CH – COOH

3

|          |

^{Zn dust}     CH₂ – CH – 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

SO3 Na

¾¾NaO¾H  ®

Fuse

C6 H

₅ONa

¾¾^H+ ¾^{/ H}2¾^O ® 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   ¾¾^HN¾^O¾3  ® C  H  NO

¾¾^{Sn /}¾^H¾^Cl ® C  H  NH

¾¾^NaN¾^O¾2  ®

C H N Cl

¾¾^H2¾^O ® C  H  OH

 

6  6 H  SO  , 45^o 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

 

C6 H5 Br  + Mg ¾¾^Eth¾^er ®

C6 H5 MgBr

¾¾^O¾2  ®C6 H5OMgBr ¾¾^H¾2O ® C6 H5OH

 

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.

C6 H5 OH + NaOH  ® C6 H5 ONa + H 2 O ¾¾^CO¾2 , H¾2¾^O ® C6 H5 OH + Na2 CO3

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  ®

250^o C

C6 H

₅Cl + H

₂O ;

C6 H

₅Cl + H

O ¾¾⁴²⁵¾o¾^C ® 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).

 

C6 H

Cl  + 2NaOH ¾¾³⁰⁰¾o¾^C ® C

5

6

High pressure

H₅ONa + NaCl + H₂O

 

Chlorobenzene

sodium phenoxide on treatment with mineral acid yields phenol.

2C6 H5 ONa + H2 SO4 ® 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.

2C6 H6  + O2  ¾¾^V2O¾5  ® 2C6 H5 OH

315^o 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

C6 H5OH

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

C6 H5 OH + HOCH3  ¾¾^D,T¾^hO¾2  ® C6 H5  – O – CH3

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

 

C6 H5 OH + (CH3 CO)2 O ¾¾^NaO¾^H ® C6 H5 OOCCH3 + CH3 COOH ;

 

Acetic anhydride

O

||

Phenyl acetate (ester)

O

||

 

C6 H5OH + Cl C– C6 H5  ¾¾^NaO¾^H ® C6 H5  – O – C– C6 H5 + 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.

 

C6 H5 OH + NH 3  ¾¾^ZnC¾^l2  ® C6 H5 NH 2 + H 2 O

 

300^o 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 H5 OAlCl2  + 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

¾¾^H2S¾^O¾4  ® o – and p – C6 H4

/ 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⁺

C – O–

||                H⁺

COOH

 

+ C = O

||

O

C – O

||

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 ¾¾^AlC¾^l3  ® 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 (C₆H_11,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

¾¾^NaN¾^O¾2  ®  Red colour

Excess of water

¾¾^NaO¾^H ®  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

 

 

Property	Phenol (C6H5OH)	Alcohol (C2H5OH)
Odour	Typical phenolic odour	Pleasant alcoholic odour
Nature, reaction with alkali	Acidic,         dissolves        in       sodium	Neutral, no reaction with alkalies.
	hydroxide            forming            sodium
	phenoxide.
Reaction with neutral FeCl3	Gives  violet   colouration   due   to	No reaction.
	formation of complex compound.
Reaction with halogen acids	No reaction with halogen acids.	Forms ethyl halides.
Oxidation	Pink     or     brown  colour      due   to	Undergoes        oxidation        to       give
	formation         of         quinone         and	acetaldehyde and acetic acid.
	phenoquinone.
Reaction with HCHO	Forms polymer (bakelite).	No reaction.
Liebermann’s nitroso reaction	Positive.	Does not show.
Coupling with benzene diazonium	Forms azo dye.	Does not form any dye.
chloride
Reaction with PCl5	Mainly forms triphenyl phosphate.	Forms ethyl chloride
Iodoform test	Does 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

C6 H5 NO2  ¾¾Soli¾d KO¾¾H ® C6 H4

 

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

¾¾^B¾^r2  ®

 

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

Na 2 CO3

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

O H 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