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Hydroxy compounds
Hydroxy compounds are those compounds in which the hydroxy group, – OH is directly linked with the aliphatic or aromatic carbon.
Monohydric alcohols
These are compound containing one hydroxyl group. Their general formula is C (^) nH 2 n 2 O (1) Preparation : (i) From alkyl halide C HBr KOH CHOH KBr Bromoethan^25 e (Aqueous)^2 Ethanol^5 C HBr AgOH CHOH AgBr Bromoethan^25 e Moistsilveroxide^2 Ethanol^5 1° alkyl halide gives good yield of alcohols. 2° alkyl halide gives mixture of alcohol and alkene. 3° alkyl halide gives alkenes due to dehydrohalogenation.
(^2) (Major pro-Methy lpropduct) ene
3 2
| (Aqueous)^3
3 3
| (^3) |
CH
KOH CH C CH
CH
Br
CH C CH
KBr HO
CH
OH
CH C CH 2 Tert.buty lalcohol(sideproduct)
3 3
| 3 |
(ii) F rom alkenes : (a) Hydration Direct process : Alcohol
| |
| Alkene 2 4 | OH H
C C dil HOHH SO^ C C
Indirect process : Ethene^2 2 Sulphuric^2 acid Ethy l^3 hy drogen 2 sulphate^2
CH CH HOSO OH CHCHOSOOH
Boil^2 CH^3 Ethanol CH^2 OH H^2 SO^4 H^ O In case of unsymmetrical alkenes
rule 2 Markownikoff''s (^3) Propene 2
CHCH CH HOSOOH
Propan- 2 - ol
Boil^3 |^3 2
(^3) | 3 2 CH OH
CH CH OSOOH
CH CH CH H^ O
(b) Oxymercuration-demercuration Oxy mercura tion (^2) Mercuricacetate 2 C C HO Hg ( OAc )
Alcohol
Demercuration | |
| |
| |
4 OH H
C C
HgOAc
C
OH
C NaBH ^
This reaction is very fast and produces the alcohol in high yield. The alcohol obtained corresponds to Markownikoff’s addition of water to alkene. (c) Hydroboration oxidation (HBO) : (Antimarkownikoff’s orientation)
2
| , |
| (^2) | 22 BH
C
H
C C H BH C H^ O OH
Alcohol
| |
| | H OH
C C
Diborane is an electron defficient molecule. It acts as an electrophile reacting with alkenes to form alkyl boranes R 3 B.
(^) H ^ O
CH C CH^2
3 3
| ^ ^2 ^4
3 2
| (^) HSO CH C CH H
Alcohol
3 |^3
|
CH
OH
C CH
Alcohol, Phenol and Ether
Chapter
^ ^2
Alky l bora ne 2
(^22) | | 2 RCH^ CH B H
CH
H
R CH CH H BH R CH
Dialkyl bo^2 rane 22 Trialkyl b^2 orane 23
( R CH CH ) BH RCH ^ CH ^2 ( RCHCH ) B
Carbocation are not the intermediate in HBO hence no rearrangement take place. (iii) By reduction of carbonyl compounds
Aldehyde (^24) Primaryalcohol^2 RCHO H LiAlH Pd RCH OH
Secondaryalcohol
Ketone^2 or / |
4 R
OH
RCO R H NaBHNi ^ Pt R CH
LiAlH 4 also reduces epoxides into alcohol : LiAlH CH CHOH O
CH (^) 2 CH 2 4 3 2
Hydride selectively attacks the less alkylated carbon of the epoxide.
3 3
| (^3) |
3 2
| 3 4
CH
OH
H CH C CH
CH
O
CH C CH LiAlHH (^) ^
(iv) By reduction of carboxylic acids and their derivatives
(ii) primaryalcohol^2
(i) Carboxylic acid 2
R COOH^4 RCH OH
HO LiAlH
Carboxylic RCOOH acid^ ^ RCOO Ester R Catalyst H ^^2 RCH^2 OH R OH Esters are also reduced to alcohols (Bouveault Blanc reaction)
(^3) Ethanol (^2) Methanol 3 / Methy l(Ester) acetate 3
|| 3 OCH^4 [ H^ ]^25 CHCHOH CHOH
O
CH C Na^ C HOH
Reduction with aluminium isopropoxide is known as Meerwein-Ponndorff verley reduction (MPV) reduction.
( ) (^2) Isopropy l (^32) alcohol MeC O ( CH ) CHOH AlOCHMe^2
C O CH Me CHOH CH 3
3 2 (v) By alkaline hydrolysis of ester
Sod.saltofacid Alcohol
|| || (aq ) ONa ROH
O
OR HONa R C
O
R C .
(vi) From primary amines
CH CHNH HONO NaNO / HCl Aminoethan^3 2 e 2
2
CH CHOH N 2 H 2 O Ethanol^3
It is not a good method of preparation of alcohols because number of by product are formed like alkyl chloride alkenes and ethers. (vii) From Grignard reagent (a) With oxygen : 2 R Mg X O Al O^2 R O Mg X (^223)
^2 HOH ^ 2 ROH 2 Mg ( X ) OH (b) With ethylene oxide :
O
R Mg X CH 2 CH 2
RCH (^) 2 CH 2 OMgX H^^2 O^ RCH 2 CH 2 OH Mg ( X ) OH (c) With carbonyl compounds :
OH
R
H
R C
OMgX
R
H
R C
H
O
R Mg X R C H^ O
| |
| |
| ||
2
If R = H, product will be 1°alcohol. If R = R, product will be 2°alcohol. If carbonyl compound is a ketone, product will be 3° alcohol. It is the best method for preparation of alcohol because we can prepare every type of alcohols. (viii) The oxo process : It is also called carbonylation or hydroformylation reaction. A mixture of alkene carbon monoxides and hydrogen. Under pressure and elevated temperature in the presence of catalyst forms aldehyde. Catalyst is cobalt carbonyl hydride [ CoH ( CO ) 4 ] product is a mixture of isomeric straight chain (major) and branched chain (minor) aldehydes. Aldehydes are reduced catalytically to the corresponding alcohols. 2 CH 3 CH CH 2 2 CO 2 H 2
(2) Physical properties of monohydric alcohols (i) Character : Alcohols are neutral substances. These have no effect on litmus paper. This is analytical test for alcohols.
B 2 H 6
CH 3 CH 3 CH^3 HO
H 3 O +
HO – CH 2
CH 2 OH
CH 2 CH 2
CH 3 OH
H 2 O
CH 3 – CH – CHO
CH 3
(Minor)
CH 3 – CH – CH 2 OH
CH 3
Isobutyl alcohol
H 2 Zn – Cu
CH 3 – CH 2 – CH 2 – CH 2 –
OH
n- Butyl alcohol
(^3) (Major) 2 2 CH CH CH CHO Zn^ H –^2 Cu
Acylation : Acetic anhy dride^3 Ethanol^2
|| || 3 CH H OCHCH
O O C
O CH C
OCHCH CHCOOH
O CH C 3 Ethy lethanoate 2 3
|| 3
(d) Reaction with grignard reagents : CH OH CHMgBr CH CH 3 OMgBr alcoholMethy l^3 Ethy l^2 br^ magnesiumomide^5 Ethane^26
(e) Reaction with ketene :
R O H CH 2 C O
(Ketoform)
(^3) || (enolform)
2 | O R
O
O R CH C
H O
CH C
(f) Reaction with isocyanic acid : O R OH
N C
O
R O H H N C H
|| |
(Urethane)aminoester
|| O R O
H NH C
(g) Reaction with ethylene oxide :
1, 2 - dialkoxy ethane
(^2 2) | 2 | 2 2 | 2 | 2 OR
CH OR
CH OR
CH OH
CH O
R O H CH CH ROHH (^) O^
(h) Reaction with diazomethane : (^2 2) (Ether) 3 2
R OH CHN R O CH N
(ii) Alkylation : ROH R 2 SO 4 ROR R HSO 4
(iii) Reaction involving cleavage of C OH
| |
| | with
removal or substitution of – OH group (a) Reaction with hydrogen halides : Alcohols give alkyl halide. The reactivity of HX is in the order of HI > HBr > HCl and the reactivity of ROH is in the order of benzyl > allyl > 3° > 2°> 1°. The reaction follows a nucleophilic substitution mechanism. Grove’s process ROH HX anhy drous ZnCl ^2 R X H 2 O
If alcohols react with HI and red phosphorus, alkane will be formed.
C (^) 2 H 5 OH 2 HI Redheat P C 2 H 6 I 2 H 2 O
Primary alcohols follow S N 2 mechanism.
R OH X X R OH 2 R X H 2 O 1 alcohol
Protonated^2
o
In secondary and tertiary alcohols, the S N 1 mechanism operates
R OH R^ ^ OH 2 R^ ^ X ^ R X
(b) Reaction with PCl 5 : ROH PX 5 RX POX 3 HX ; X = Cl (Analytical test for alcohols) (c) Reaction with PCl 3 :
Phosphorusacid 3 3 Phosphorustrichloride chlorideAlky l
(^3) Alcohol ROH PCl 3 3 RCl HPO
(d) Reaction with thionyl chloride [ SOCl 2 ] : ROH SOCl 2 Py ridine RCl SO 2 HCl (e) Reaction with ammonia :
Primaryamine
ROH NH 3 360 Al^2 O o C^3 RNH 2
Tertiaryamine 3 Secondaryamine 23 R^^2 NH Al 2 O 3 R^ N
ROH AlO
ROH ^
(f) Reaction with HNO 3 :
R OH HNO R O N OO H 2 O alkylnitrate
conc. 3
(g) Reaction with H 2 SO 4 [Dehydration of alcohol] : The elimination of water from a compound is known as dehydration. The order of ease dehydration is Tertiary
Secondary > primary alcohol. The products of dehydration of alcohols are depend upon the nature of dehydrating agents and temperature.
Alcohol leading to conjugated alkene are dehydrated to a greater extent than those of alcohols leading to nonconjugated alkene. Thus dehydration is in order
H +^ – H 2 O
CH 3 CH 2 OH H^2 ^ SO ^4
Conc. H 2 SO 4
H^110 ° 2 SO 4 140° C
17 0
CH 2 = CH 2
Ethylene C 2 H 5 HSO 4 Ethyl hydrogen sulphate C 2 H 5 O – C 2 H 5 Diethyl ether
3 3
3 3 3
3
| |
| |
| (^3) |
CHOH CH
CH CHCH
CH C C C CH^ H
OH
CH CH CH CH OH
CH CH CH CH (^2) | (^332) | 3
3
3
3
| (^3) |
3
3
|^3
| (^3) | 2 (^2 4) CH
CH
CH
CH C CH
CH
CH OH
CH C CH CH HHSOO
2 - alkene 3
3
3
(^3) |
3 3 3
| | 3 CH
CH C CH
CH C
CH CH CH C CH CH H ^
(iv) General reaction of alcohols (a) Reduction : R OH 2 HI R H H 2 O I 2 (b) Oxidation : Difference between 1°, 2° and 3° alcohols. 1° Carboxy licacid
| Aldehy de
(^2) | O OH
O R C H
RCH OH R C
2° R
O
R R C OH
R CH CrO ^ || Secondaryalcohol
| 3
Drastic conditions^ O RCOOH CO^2 H^2 O
3° (Lesserof carbonnumberatoms) Acetone
|^3 3 (Underconditionstrong)
4 []
Tert.(Tertiary )buty lalcohol
3
3
| (^3) |
CH CH C O
CH
CH
CH C OH O ^
O CHCOOH CO 2 H 2 O
of(Lesser carbon^ numberatoms)
(Underconditionstrong) Acetic^3 acid
^4 [ ]
3 ° alcohols are resistant to oxidation, but on taking stronger oxidising agent they form ketone. (c) Catalytic oxidation/dehydrogenation
1° 2 (AcetaldehEthanal y de)
| , (^5733)
(Pri.Ethanolalcohol)
| (^3) | O H
H OH CH C
H
H
CH C Cu ^ K
(Acetone)Propanone
3 2
| 3 , 573
3
(Sec.^2 - Propanolalcohol)
| (^3) |
CH CH C O H
CH OH H
CH C Cu^ K
3° HO
CH CH C CH
CH
CH
CH C OH Cu K 2 2 - Methy lprop(Alkene) ene
3 2
| 3 , 573
2 - Methy lprop(Tert. alcohol)an- 2 - ol
3
3
| 3 | ^
Important reagents used for oxidation of alcohols PCC [Pyridinium chloro chromate ( 6 5 3 )
CH NHCl CrO ] to oxidise 1° alcohols to aldehydes and 2° alcohols to ketones. PDC [Pyridinium di chromate ( C 5 H 5. NH )^22 ^ Cr 2 O 72 ] to oxidise 1° alcohols to aldehyde and 2° alcohol to ketones. H 2 CrO 4 (chromic acid) to oxidise 1° alcohol to carboxylic acid. CrO 3 (^) H 2 SO 4 / Acetone to oxidise 2° alcohol to ketones. Jones reagents (chromic acid in aqueous acetone solution) oxidise 1° alcohol to aldehyde and 2° alcohol to ketone without affecting ( C = C ) double bond. MnO 2 selectively oxidises the – OH group of allylic and benzylic 1° and 2° alcohols to give aldehyde and ketone respectively. N 2 O 4 in CHCl 3 oxidises primary and secondary benzyl alcohol. (d) Self condensation : Guerbet’s reaction CH OH R
R CH 2 CH 2 OH H CH | 2
higher alcohol^2
| 2 5 , 2 2 CH OH
R NaOC ^ H R CH CH CH (e) Reaction with cerric ammonium nitrate : CerricammoniumYellow colour nitrate ROH Red colour solution of complex. This is analytical test for alcohols. (f) Iodoform test : When a few drops of alcohol are warmed with iodine and NaOH yellow precipitate of iodoform with characteristic smell is obtained. Any alcohol consists CH 3 CHOH group give iodoform test. Since reaction takes place with alkali solution as one of the reagents hence alkyl halide like CH (^) 3 CH 2 Cl and R Cl
CH (^) 3 CH | will also give this test.
(4) Uses of monohydric alcohol : (i) Uses of ethanol : It is used (a) In alcoholic beverages, (b) As a solvent in paints, varnishes, oils, perfumes etc., (c) In the preparation of chemical like chloroform, ether etc., (d) As a fuel in spirit lamps, (e) As an antifreeze for automobile radiators, (f) In the scientific apparatus like spirit levels, (g) As power alcohol. (ii) Uses of methanol :
CH 2 CH CH CH 3
t
CH CH CH CH
More amoun^2
CH (^) 2 CH CH 2 CH 3
OH
CH CH CH CH
(^2) | 2 3
H +^ H – 2 HSO 2 O^4
These are compound containing two hydroxyl groups. These are dihydroxy derivatives of alkanes. Their general formula is C (^) n H 2 n 2 O 2. The simplest and most important dihydric alcohol is ethylene glycol. They are classified as , , ….. glycols, according to the relative position of two hydroxyl groups. is 1, 2 glycol, is 1, 3 glycol. (1) Preparation (i) From ethylene : (a) Through cold dilute alkaline solution of Bayer’s reagent
(b) With O 2 in presence of Ag :
Ethy lene^2 gly col
| 2 dil. Ethy lene^2 oxide
2 Cataly st, 200400 |^2 Ethy lene^2
| |^2 2
1 CH OH
CHOH O CH
CH O CH
CH HCl
HO Ag (^) C
(c) With HOCl followed by hydrolysis : (Industrial method)
Ethy lene chlorohy dr^2 in
| 2 2
| |^2 CH Cl
CHOH
HOCl CH
CH
2 Gly col^2
(^3) | (^2) NaCl CO CHOH
NaHCO CHOH
(ii) From 1, 2 dibromo ethane [Lab method]:
2 2
2 3 2 |^2 2
| 2 2 NaBr CO CHOH
CHOH
NaCO HO CHBr
CH Br
Gly col^2 diacetate^3
| 2 3 2 3 2
CHOOCCH
CHOOCCH
CHCOOK
CHBr
CHBr KBr
CHCOOH
CHCOONa CHOH
NaOH CHOH 3 2
(2) Physical properties (i) It is a colourless, syrupy liquid and sweet in taste. Its boiling point is 197° C. (ii) It is miscible in water and ethanol in all proportions but is insoluble in ether. (iii) It is toxic as methanol when taken orally. (iv) It is widely used as a solvent and as an antifreeze agent. (3) Chemical properties
– C = C –
(i) dil. KMnO (ii) dil. 4 OH –
– C = C –
OH OH
(Syn- hydroxylation)
RCO 2 OH H 2 O H +
OH
– C – C –
OH
(Anti- hydroxylation)
– C – C –
O
Na 50° C
CH 2 Cl | CH 2 OH
PCl 5^ CH |^2 Cl CH 2 Cl 1,2 Dichloroethane
CH 2 ONa | CH 2 OH
CH 2 ONa | CH 2 ONa Dialkoxide (Disodium glycollate)
N 160° a C
PCl 5
Chlorohydrin
Dioxalane formation provides a path of protecting a carbonyl group in reaction studied in basic medium in which acetals are not affected. The carbonyl compound may be regenerated by the addition of periodic acid to aqueous solution of the dioxalane or by acidic hydrolysis.
2
2 2
O CH
O CH
C
R
R
CHOH
CHOH
C O
R
R
HIO ^^4 R CO R 2 HCHO
Aldehyde is more reactive than ketone in dioxalane formation.
(4) Uses (i) Used as an antifreeze in car radiators. (ii) Used in the manufacture of dacron, dioxane etc. (iii) As a solvent and as a preservatives. (iv) As a cooling agent in aeroplanes. (v) As an explosives in the form of dinitrate.
Trihydric alcohols.
The only important trihydric alcohol is glycerol (propane-1, 2, 3-triol). It occurs as glycosides in almost all animal and vegetable oils and fats. (1) Preparation (i) From oils and fats
Fattyacids Gly cerol
2
2
| steam^2 | Oilorfat
2
2
| | 3 3 RCOOH
CHOH
CHOH
HO CHOH
CHOOCR
CHOOCR
CH OOCR
CHOH
CHOH
CHOH
NaOH
NaOH
NaOH
CHOOCR
CHOOCR
CHOOCR
2
2
| |
Hy droly sis
Oilorfat
2
2
| | ^ higher^3 Sodium RCOONa fattysaltacidsof
(ii) By fermentation of sugar C 6 (^) Glucose H 12 O 6 Na Yeast 2 SO 3 C Glycerol 3 H 8 O 3 CH Acetaldehy 3 CHO de CO 2 (iii) From propene [Modern method]
Ally lalcohol
2
2
| ||
(dil)
Ally lchloride
2
2
| 600 || propene
3
2
| ||
2
CH OH
CH
CH
CHCl
CH
CH
CH
CH
CH NaOH C
Cl o
Gly cerol
2
2
| |
aq.
2
2
| |
CH OH
CH OH
CH OH
CHOH
CH OH
HOCl CH Cl NaOH
(iv) From propenal : CH (^) 2 CHCHO cataly st H ^2 CH 2 CHCH 2 OH
(^2) Glycerol 2
H^^2 O 2 / O^ H HOCHCHOHCHOH
(2) Physical properties (i) It is a colourless, odourless, viscous and hygroscopic liquid. (ii) It has high boiling point i.e., 290° C. The high viscosity and high boiling point of glycerol are due to association through hydrogen bonding. (iii) It is soluble in water and ethyl alcohol but insoluble in ether. (iv) It is sweet in taste and non toxic in nature. (3) Chemical properties (i) Reaction with sodium
Disodiumgly cerolate
2
2
| temperaturRoome | Monosodiumgly cerol
2
2
| temperaturRoome |
2
2
| |
CH ONa
CHONa
CH OH
CHONa
CH OH
CH OH
CH OH
CH OH
CH OH Na^ Na
(ii) Reaction with PCl 5 , PBr 3 and PI 3
(a) POCl HCl
CHCl
CHCl
PCl CHCl
CHOH
CHOH
CH OH 3 3 3 3
(1, 2,Gly cery l t 3 - Trichloroprichlorideropane)
2
2
| (^5) |
2
2
| |
(b) 3 3 1,2, 3 - Tribromopropane
2
2
| (^3) |
2
2
| | HPO
CHBr
CHBr
PBr CHBr
CHOH
CHOH
CH OH
(c) 2 Ally liodide
2
2
|| | (Unstable)
2
2
| (^3) |
2
2
| | I
CH
CHI
CH
CHI
CHI
PI CHI
CHOH
CHOH
CH OH
(iii) Reaction with HCl or HBr
monochloro(34%)hy drin
2
2
| | monochloro(66%)hy drin
2
2
| |
110
2
2
| |
CH OH
CHOH
CHCl
CHCl
CHOH
CHOH
CHOH
CHOH
CH OH HClC o (^)
, - dichlorohy(44%) drin Gly cerol
2
2
| |
, - dichlorohy(56%) drin Gly cerol
2
2
| 110 |
Excessof
CH Cl
CHCl
CHOH
CHCl
CHOH
CHCl C
HCl o
(iv) Reaction with HI
O
CHO
+ CH 2 OH – CH 2 OH
O
C
O
H
O
CH | 2 – OH CH 2 – OH
O
H 3 C CH 3
O O
O
H 3 C CH 3
O
This part does not react due to steric hindrance
Unsaturated alcohols (Allyl alcohol)
(1) Preparation (i) From allyl halide (^2 222) Ally lalcohol 2 CH CH CH Br HO CH CH CHOH HBr
(ii) By heating glycerol with oxalic acid :
Ally lalcohol
2
2
|| 2 |
Heat
2
2
| | | |^2
2
2
| | (^2)
2
CH
CHOH
CH
CHOOC
CHOH
CHOOC
HOOC
HOOC
CHOH
CHOH
CH OH ^ H O CO
(2) Physical properties (a) It is colourless, pungent smelling liquid. (b) It is soluble in water, alcohol and ether in all proportion.
(3) Chemical properties
Phenol (Carbolic acid) , C 6 H 5 OH or Hydroxy benzene
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 (i) From benzene sulphonic acid C H H^ SO f CHSOH NaOH Benzene^6 sulphonic^53 acid
(uming) Benzene^6
2 4
or /^6 Phenol^5
/ Sodium 6 benzene^5 sulphonate^3 Fuse Sodium^6 phenoxide^522
C HSONa CHONa^2 CHOH CO HO NaOH ^ H H O
This is one of the laboratory methods for the preparation of phenol. Similarly methyl phenols (cresols) can be prepared.
(ii) From benzene diazonium chloride (^6) Aniline 5 2 / Benzene^6624 ,^45 Nitrobenze^65 ne^2
C H^3 CHNO SnHCl CHNH HSO C
HNO o
, (^05) Benzene 6 diazonium^52 chloride Warm^6 Phenol^5
(^2) C HNCl H 2 O CHOH HCl C
NaNO (^) o
Diazonium salts are obtained from aniline and its derivatives by a process called diazotisation. (iii) From Grignard reagent
Phenyl magnesium^65 bromide
Ether Bromobenze^6 5 ne
C HBr Mg CHMgBr
(^6 56) Phenol 5 (^2) C HOMgBr (^2) CHOH H
O HO
(iv) From salicylic acid :
(v) Middle oil of coal tar distillation : Middle oil of coal-tar distillation has naphthalene and phenolic compounds. Phenolic compounds are isolated in following steps. Step I : Middle oil is washed with H 2 SO 4. It dissolves basic impurities like pyridine (base). Step II : Ecessive cooling separates naphthalene (a low melting solid)
H 2 Pt CH^31 CH - propanol^2 CH^2 OH
CH 2 = CH – CH 2 OH –
(Allyl alcohol)
CH 2 Br – CHBrCH 2 OH 2, 3-dibromopropanol- 1
Br 2
CH 2 BrCH 2 CH 2 OH 3 - Bromopropanol- 1
HBr
CH 2 OHCHClCH 2 OH Glycerol -monochlorohydrin
HOCl
CH 2 OH – CHOH – CH 2 OH Glycerol
Alk. KMnO ( O + 4 H 2 O )
CH 2 = CH – CH 2 OOCCH 3
Allyl acetate
CH 3 COOH
CH 2 = CH – CH 2 Cl Allyl chloride
HCl
COOH | COOH Oxalic acid
HCOOH
Formic acid
Oxidati on +
Na (^) CH 2 = CH – CH 2 ONa
CH 2 – CH – CH 2
| | | Br Br OH
CH 2 – CH – COOH
| | Br Br Zn dust
( CH 3 OH ) CH 2 = CH – COOH Acrylic acid
HNO [ O ] 3
Br 2
SO 3 H
CH 3
p - Toluene sulphonic acid
OK
CH 3
OH
CH 3
p - Cresol
Solid KOH Fuse
H +/ H 2 O
OH
COOH
Salicylic acid
OH
Phenol
NH 2
CH 3
m - Toluidine
N 2 Cl
CH 3
m - Toluene diazonium chloride
H 2 O
OH
CH 3
m - Cresol
HNO 2 HCl
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. C (^) 6 H 5 OH NaOH C 6 H 5 ONa H 2 O CO^ 2 ,^ H ^2 O C 6 H 5 OH Na 2 CO 3 Step IV : Crude phenol (of step III) is subjected to fractional distillation.
(vi) Raschig’s process C H HCl O CuCl oFeCl (^) C CHCl H 2 O (^250) Chlorobenz^65 ene
/ Benzene^6
^1
C HCl HO o C CHOH HCl (^6) Phenol 5 425 Chlorobenz^65 ene steam^2 (vii) Dow process C HCl NaOH C CHONa NaCl HO o Chlorobenz^6 5 ene^2 High^300 pressure^ ^65 ^2 sodium phenoxide on treatment with mineral acid yields phenol. 2 C 6 (^) H 5 ONa H 2 SO 4 2 C 6 H 5 OH Na 2 SO 4 (viii) Oxidation of benzene C H O CHOH C
VO (^2 6 62315) o (^265) ^2 5 (ix) Oxidation of isopropyl benzene [Cumene]
(2) Physical properties (i) Phenol is a colourless crystalline, deliquescent solid. It attains pink colour on exposure to air and light. (ii) They are capable of forming intermolecular H - bonding among themselves and with water. Thus, they have high boiling points and they are soluble in water.
Due to intermolecular H - bonding and high dipole moment, melting points and boiling points of phenol are much higher than that of hydrocarbon of comparable molecular weights. (iii) It has a peculiar characteristic smell and a strong corrosive action on skin. (iv) It is sparingly soluble in water but readily soluble in organic solvents such as alcohol, benzene and ether. (v) It is poisonous in nature but acts as antiseptic and disinfectant. (3) Chemical properties (i) Acidic nature : Phenol is a weak acid. The acidic nature of phenol is due to the formation of stable phenoxide ion in solution. C (^) 6 H 5 OH H 2 O ⇌ C HO ^ H 3 O Phenoxide^65 ion The phenoxide ion is stable due to resonance.
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]. 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
Alcohols
18 Water
14 (^6) Phenol 5
10 Carbonic^2 acid^3
7 Carboxy licacid
(approx. ) ( 105 ) ( 10 ) ( 10 ) ( 10 ) ( 10 ) RCOOH HCO CHOH HOH ROH
Ka ^ ^
Effects of substituents on the acidity of phenols : Presence of electron attracting group, ( e.g. , NO 2 , –
Crude phenols
fraction distillati al on
180° C
211°- 235° C
o , m , p - cresols
xylols (hydroxy xylenes)
AlCl 3
AlCl 3
+ CH 3 CH = CH 2
CH
Cumene
H 3 C CH 3
O 2 Cataly st
O – OH
| C ( CH 3 ) 2
Cumene hydroperoxi de
H + 2 O / H
OH
Phenol
+ ( CH 3 ) 2 CO
Acetone
H – O ------- H – O ------- H – O ------- H –
O ------- +^ – +^ –
+^ –^ +^ –
(intermolecular H - bonding among phenol
H H
| | H – O ------- H – O ------- H – O ------- H – O -------
+^ –^ + – –
+ + –
(crossed intermolecular H - bonding between water and phenol molecules)
O
.. –
O –^ O
.. –
O
.. –
3 C (^) 6 H 5 OH POCl 3 ( C 6 H 5 ) 3 PO 4 3 HCl (e) Reaction with zinc dust : When phenol is distilled with zinc dust, benzene is obtained.
C (^) 6 H 5 OH Zn C 6 H 6 ZnO (f) Reaction with ammonia : Phenol reacts with ammonia in presence of anhydrous zinc chloride at 300° C or ( NH 4 ) 2 SO 3 / NH 3 at 150° C to form aniline. This conversion of phenol into aniline is called Bucherer reaction.
C HOH NH CH NH HO C
ZnCl (^6 53300) o (^6) Aniline 5 2 2 ^2
(g) Action of P 2 S 5 : By heating phenol with phosphorus penta sulphide, thiophenols are formed.
5 C 6 (^) H 5 OH P 2 S 5 5 C Thiophenol 6 H 5 SH P 2 O 5
(iii) Reactions of benzene nucleus : The – OH group is ortho and para directing. It activates the benzene nucleus. (a) Halogenation : Phenol reacts with bromine in carbon disulphide (or CHCl 3 ) at low temperature to form mixture of ortho and para bromophenol.
Phenol forms a white precipitate with excess of bromine water yielding 2, 4, 6-tribromophenol. (b) Sulphonation : Phenol reacts with conc. H 2 SO 4 readily^ to^ form^ mixture^ of^ ortho^ and^ para hydroxy benzene sulphonic acids.
At low temperature (25° C ), the ortho - isomer is the major product, whereas at 100° C , it gives mainly the para - isomer.
(c) 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 group. The – OH group is activating group, hence nitration is possible with dilute nitric acid.
It is believed that the mechanism of the above reaction involves the formation of o - and p - nitroso phenol with nitrous acid, HNO (^) 2 ( NaNO 2 HCl )at 0-5° C , which gets oxidised to o - and p - nitrophenol with dilute nitric acid.
However, when phenol is treated with concentrated HNO 3 in presence of concentrated H 2 SO 4 , 2,4,6-trinitrophenol (Picric acid) is formed.
To get better yield of picric acid, first sulphonation of phenol is made and then nitrated. Presence of SO (^) 3 H group prevents oxidation of phenol. (d) Friedel-Craft’s reaction : Phenol when treated with methyl chloride in presence of anhydrous aluminium chloride, p - cresol is the main product. A very small amount of o - cresol is also formed.
OH
( CS 2 )
OH
Br
o - Bromophenol
p - Bromophenol
OH
Br
OH OH
Br Br
Br 2, 4, 6- Tribromophenol
OH
( H 2 SO 4 )
OH
SO 3 H
o - Hydroxybenzene sulphonic acid
OH
SO 3 H
p - Hydroxybenzene sulphonic acid
OH
NO 2
p - Nitrophenol
OH OH
NO 2
o - Nitrophenol
HNO )(5- 3 (dil. + 10° C )
OH
NO
p - Nitrosopheno l
OH OH
NO
o - Nitrosophenol
(0 HONO -^ +
5° C )
[ O ] HNO 3 (Dil.)
Nitrophenol
OH
NO p - 2
OH
NO 2
o -
OH OH
NO 2
2, 4, 6- Trinitrophenol (picric acid)
O 2 N
NO 2
HNO 3 (conc.) H 2 SO 4 - (conc.)
OH
CH 3
p - Cresol (major product)
OH
AlCl 3 +
OH
CH 3
o - cresol (minor)
RX and (^) AlCl 3 give poor yields because AlCl 3 coordinates with O. So Ring alkylation takes place as follows, C (^) 6 H 5 OH AlCl 3 C 6 H 5 OAlCl 2 HCl Thus to carry out successful Friedel-Craft’s reaction with phenol it is necessary to use a large amount of (^) AlCl 3. The Ring alkylation takes place as follows :
32
(^653322) or 6 4 \ ( )
2 4 CH CH
OH C HOH CHCHCHCHCHOH HSOHF o p CH
(e) Kolbe-Schmidt reaction (Carbonation) :
(f) 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 benzaldehyde. However, when carbon tetrachloride is used, salicylic acid (predominating product) is formed.
(g) 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 N AlCl ^^3 ClCH NH
(h) Mercuration
(i) Hydrogenation
(iv) Miscellaneous reactions (a) Coupling reactions : Phenol couples with benzene diazonium chloride in presence of an alkaline solution to form a red dye (p-hydroxy azobenzene).
ONa
+ CO 2 130 140°- 6 C
atm
OCOONa
Sodium phenyl carbonate
Rearrangem ent
OH
COONa
Sodium salicylate
OH
COOH
Salicylic acid
H + H 2 O
CH 3 OH
CH 3 COCl
OH
COOC 6 H 5
Salol OCOCH 3 COOH
Aspiri O^ n H COOCH 3
Oil of winter green
OH
CH = NH
OH OH
CHO
p - Hydroxy benzaldehyd e
H 2 O
- ClCH = NH (^) – NH 3 AlCl 3 HCl
( CH 3 COO ) 2 Hg
OH OH
HgOCOCH 3 p - Hydroxy phenyl mercuric acetate
OH
HgOCOCH 3
o - Hydroxy phenyl mercuric acetate
OH
Phenol ( C 6 H 5 OH )
OH
Cyclohexanol ( C 6 H 11, OH ) (used as a good solvent)
N = NCl + Benzene diazonium chloride Phenol
OH NaO H – HCl
N = N OH
p - Hydroxyazobenzene
OH
anhydrous AlCl 3 +
OH
COCH 3
OH
COCH 3
- CH 3 COCl Acetyl chloride
hydroxy acetophenone
orth o Para
ONa
CHO
H + H 2 O
OH
CHO
Salicylaldehy de
OH
OH
CHCl 2
NaOH CHCl 3 NaOH (aq. )
(i) As an antiseptic in soaps, lotions and ointments. A powerful antiseptic is “Dettol” which is a phenol derivative (2, 4-dichloro-3, 5-dimethyl phenol). (ii) In the manufacture of azo dyes, phenolphthalein, etc. (iii) In the preparation of picric acid used as an explosive and for dyeing silk and wool. (iv) In the manufacture of cyclohexanol required for the production of nylon and used as a solvent for rubber and lacquers. (v) As a preservative for ink. (vi) In the manufacture of phenol-formaldehyde plastics such as bakelite. (vii) In the manufacture of drugs like aspirin, salol, phenacetin, etc. (viii) For causterising wounds caused by the bite of mad dogs. (ix) As a starting material for the manufacture of nylon and artificial tannins. (x) In the preparation of disinfectants, fungicides and bactericides. (5) Tests of phenol
(i) Aqueous solution of phenol gives a violet colouration with a drop of ferric chloride. (ii) Aqueous solution of phenol gives a white precipitate of 2, 4, 6 - tribromophenol with bromine water. (iii) Phenol gives Liebermann’s nitroso reaction. Phenol in conc. sulphuric acid Excessof water NaNO ^2 Red
colour
(Excess)
NaOH Blue colour
(iv) Phenol combines with phthalic anhydride in presence of conc. H 2 SO 4 to form phenolphthalein which gives pink colour with alkali, and used as an indicator. (v) With ammonia and sodium hypochlorite, phenol gives blue colour.
Table : 26.2 Difference between phenol and alcohol Property Phenol ( C 6 H 5 OH ) Alcohol ( C 2 H 5 OH ) Odour Typical phenolic odour Pleasant alcoholic odour Nature, reaction with alkali Acidic, dissolves in sodium hydroxide forming sodium phenoxide.
Neutral, no reaction with alkalies.
Reaction with neutral FeCl 3 Gives violet colouration due to formation of complex compound.
No reaction.
Reaction with halogen acids No reaction with halogen acids. Forms ethyl halides. Oxidation Pink or brown colour due to formation of quinone and phenoquinone.
Undergoes oxidation to give acetaldehyde and acetic acid.
Reaction with HCHO Forms polymer (bakelite). No reaction. Liebermann’s nitroso reaction Positive. Does not show. Coupling with benzene diazonium chloride
Forms azo dye. Does not form any dye.
Reaction with PCl 5 Mainly forms triphenyl phosphate. Forms ethyl chloride Iodoform test Does not show. Positive.
Derivatives of phenol
NITROPHENOLS
(1) Preparation (ii)
120 6 4
- and -chloronitrobenze^2 ne
6 4 o p
C
NaOH
o p NO
OH CH NO
Cl C H (^)
(iii)
Nitrobenze^65 ne^2 Solidheat^64 o p
KOH NO
OH C HNO CH
OH OH
NO 2
o - isomer (steam volatile)
Dil. HNO 3
OH
NO 2
p - isomer (non-volatile)
(iv)
(2) Properties : o - Nitrophenol is a yellow coloured crystalline compound, while m - and p - isomers are colourless crystalline compounds.
m.pt.(C) 45 97 114
Isomer ortho meta para 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.
Picric acid (2, 4, 6-trinitrophenol) (1) Preparation : It is obtained when phenol is treated with conc. (^) HNO 3. However, the yield is very poor. It is prepared on an industrial scale : (i) From chlorobenzene
(ii) From phenol through disulphonic acid
(iii)
(2) Properties : It is a yellow crystalline solid, melting points 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 dioxide. Dry picric acid as well as its potassium or ammonium salts explode violently when detonated. It reacts with PCl 5 to form picryl chloride which on shaking with NH 3 yields picramide.
When distilled with a paste of bleaching powder, it gets decomposed and yields chloropicrin, CCl 3 NO 2 , as one of the products and is thus employed for the manufacture of tear gas. 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. Picrates are explosive in nature and explode violently when heated. These are prepared carefully.
NH 4 HS or NO 2^ Na^2 S m - Dinitrobenzen e
NO 2
m - Nitroaniline^ NO^2
NH 2
NaNO 2 / HCl 0 - 5° C
NO 2
m - Nitrobenzene diazonium chloride
N 2 Cl
H 2 O NO 2 m - Nitrophenol
OH
OH
Br Br
Br
^2
(^6 4) \
/ (^) Br
o p
NO
OH CH
2,4,6 Tribromophenol
Cl
HNO 3 H 2 SO 4 Chlorobenze ne 2, 4- Dinitrochlorobenzene
Cl NO 2
NO 2
Aq. Na 2 CO 3
OH
NO 2
Picric acid (2, 4, 6- Trinitrophenol)
O 2 N
NO 2
OH
NO 2
NO 2
HNO 3 H 2 SO 4
OH
NO 2
Picric acid
O 2 N
NO 2
H 2 SO 4
OH
Phenol Phenol disulphonic acid
OH
SO 3 H
SO 3 H
HNO 3
Picric acid
OH
O 2 N NO 2
NO 2
Ke 3 Fe ( CN ) 6
O 2 N NO 2
NO 2
+ [ O ]
TNB
OH
O 2 N NO 2
NO 2
PCl 5 H 2 O
NH 3
Picryl chloride
Cl O 2 N NO 2
NO 2
Picramide
NH 2
O 2 N NO 2
NO 2
Resorcinol behaves as a tautomeric compound. This is shown by the fact that it forms a dioxime and a bisulphite derivative.
(3) Uses (i) It is used as antiseptic and for making dyes. (ii) It is also used in the treatment of eczema. 2, 4, 6-trinitroresorcinol is used as an explosive. Hydroquinone or quinol (1, 4 - Dihydroxy benzene) (1) Preparation : It is formed by reduction of p - benzoquinone with sulphurous acid ( H (^) 2 SO 3 H 2 O SO 2 )^.
( p - Benzoquinone is obtained by oxidation of aniline)
(2) Properties : It is a colourless crystalline solid, melting points 170° C. it is soluble in water. It also shows tautomerism. It gives blue colour with FeCl 3 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.
Due to this property, it is used as photographic developer. (3) Uses : It is used as an antiseptic, developer in photography, in the preparation of quinhydrone electrode and as an antioxidant.
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.
Phloroglucinol is obtained from trinitrotoluene (TNT) by following sequence of reactions.
Hydroxyquinol is prepared by the alkaline fusion of hydroquinone in air.
The three isomers are colourless crystalline compounds. All are soluble in water and their aqueous solutions give characteristic colour with FeCl 3 (Red, brown or bluish violet). Alkaline solutions absorb oxygen rapidly from air.
Uses of pyrogallol (i) As a developer in photography. (ii) As a hair dye. (iii) In treatment of skin diseases like eczema. (iv) For absorbing unreacted oxygen in gas analysis.
Ether
OH
OH
Dienol form
O
O
Diketo form
O
Quinol
O + SO 2 +2 H 2 O HO OH + H 2 SO 4
H 2 SO 3 + H 2 O
[ O MnO 2 ]/ H 2 SO 4
O
O
Fe / H 2 [ OH ]
OH
OH
Quino l
OH
OH
HOOC (^) Gallic OH acid
hea 220° t C
OH
OH
Pyrogallol^ OH
+ CO 2
NaOH Fus e
OH
OH
Quinol
+ ½ O 2
OH
OH
Hydroxy Quinol
OH
KMnO 4 [ O ]
CH 3
NO 2
NO 2
O 2 N
2, 4, 6-trinitro toluene
COOH
NO 2
NO 2
O 2 N
Fe / HCl [ H ]
COOH
NH 2
NH 2
H 2 N
H 2 O / H + 100° C
OH
HO OH
Phlorogluci nol
NH 2
Aniline
HO OH O^ O
p - Benzoquinone
[ O ] FeCl 3 Quinol
Ethers are anhydride of alcohols, they may be obtained by elimination of a water molecule from two alcohol molecules. R OH HO R R Ether O R H 2 O General formula is C (^) nH 2 n 2 O General methods of preparation of ethers (1) From alkyl halides (i) Williamson’s synthesis It is a nucleophilic substitution reaction and proceed through S N 2 mechanism.
RONa R X ROR NaX C HONa CH I CHOCH NaI Sodium^25 ethoxide^3 Ethy l 3 methy l^2 ether^5 C HONa CHBr CHOCH NaBr Sodium^25 ethoxide Ethy l brom^25 ide^2 Ethoxy etha^52 ne 5 (a) Order of reactivity of primary halide is CH (^) 3 X CH 3 CH 2 X CH 3 CH 2 CH 2 X. (b) Tendency of alkyl halide to undergo elimination is 3 o^ 2 o 1 o. (c) For better yield alkyl halide should be primary and alkoxide should be secondary or tertiary.
Ethy l tert.buty lether
3
3
3
| (^25) |
tert.Sodium buty lsaltalcoholof
3
3
3
| Ethy l brom^25 ide |
CH
CH
CH O C CH
CH
CH
C HBr NaO C CH
(d) Secondary and tertiary alkyl halides readily undergo (^) E 2 elimination in the presence of a strong base to form alkenes.
3
3
| (^3) |
3
3
| (^3) | 2 5
CH
CH
CH C Cl
CH
CH
CH C Cl C^ H ONa ^ ,
3
2
2 5
| (^3) ||
3
2
2 5
| (^3) |
CH
CH
CH C CHOH
CH
CH H
CH C CHO
Aryl halide and sodium alkoxide cannot be used for preparing phenolic ethers because aryl halide are less reactive toward nucleophilic substitution reaction than alkyl halides. (ii) By heating alkyl halide with dry silver oxide 2 RX Ag 2 O heat R O R 2 AgX , 2 C HBr AgO CHOCH 2 AgBr (^2) Diethyl (^5) ether 2 5 2 heat Ethyl brom^2 5 ide
(2) From alcohols (i) By dehydration of alcohols (a) With conc. H 2 SO 4 at 140° C
ROH HOR ROR HO C
HSO 140^ o^ Ether^2
(conc.) 2 moleculesofalcohol
^2 4 .
In this reaction alcohol must be present in excess. This reaction is mainly applicable for the dehydration of primary alcohols. Secondary and tertiary alcohols form alkenes mainly. When this reaction is carried out between different alcohols then there is a mixture of different ethers is obtained. (b) With Al 2 O 3 at 250° C : ROH R O R HO C
AlO 250^ o^^2 2 ^2 ^3 (ii) By the action of diazomethane on alcohols : This reaction is in presence of catalyst, boron trifluoride or (^) HBF 4. ROH CH 2 N 2 BF ^3^^ R O CH 3 N 2 (a) This method is very useful for preparing mixed ethers. (b) In higher cases, there can be 1, 2-hydride or 1, 2 - methyl shift to form more stable carbonium ion. (3) Alkoxy mercuration-demercuration alkene (^) Mercuric trifluoro acetate^32 C C R OH Hg [ OOCCF ]
Ether
| |
| | 3
| |
| |
4 OR H
C C
HgOOCCF
C
OR
C NaBH ^
This is the best method for the preparation of t- ethers. (4) Reaction of lower halogenated ether with grignard reagent 2 Higherether 2 Halogenateether d reagantGrignard
ROCH (^) 2 X XMgR ROCH R MgX
(i) Higher members can be prepared by the action of grignard reagent on lower halogenated ethers. (ii) Ether form soluble coordinated complexes with grignard reagent. Physical properties (1) Physical state : Methoxy methane and methoxy ethane are gases while other members are volatile liquid with pleasant smell. (2) Dipole moment (D.M.) : Bond angle of ether is due to sp^3 hybridisation of oxygen atom. Since C – O bond is a polar bond, hence ether possess a net dipole moment, even if they are symmetrical. dipole moment of dimethyl ether is 1.3 D and dipole moment of di ethyl ether is 1.18 D. The larger bond angle may be because of greater repulsive interaction between bulkier alkyl groups as compared to smaller H-atoms in water.
