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ORGANIC CHEMISTRY II
2. ALCOHOLS ETHERS AND PHENOLS ALCOHOLS : Alcohols are the organic compounds with OH group as the functional group.
They are monoalkyl derivatives of water. Based on the number of OH groups alcohols are classified as
1) Monohydric 2) Dihydric 3) Trihydric 4) Polyhydric Monohydric alcohols one OH group Eg: CH3 OH , C2H5 OH Dihydric alcohols two OH groups (glycols)
OH|
2CH
OH|
2CH ethylene glycol
CH2 CH(OH)2 ethyledene glycol
OH|
2CH
OH|
CH3CH propylene glycol
CH3 CH2 CH (OH)2 n propyledene glycol
3CH
OH
OH
|
|C3CH isopropyledene glycol
Based on the carbon to which OH group is attached alcohols are of 3 types. 1) primary alcohols 2) Secondary alcohols of 3) Tertiary alcohols Primary alcohols: CH3 CH2 OH CH3 CH2 CH2 OH OH2CH
3CH|CH3CH
OH2CH3CH
3CH
|
|C3CH
(Ethyl alcohol) (Propylalcohol) (Iso butyl alcohol) (neo-pentyl alcohol) Secondary alcohols : Tertiary alcohols :
3CH
OH|CH3CH 3CH
OH|CH2CH3CH OH
3CH
3CH
|
|C3CH OH
3CH
3CH
|
|C5H2C
(Isopropyl alcohol) (sec butylalcohol) (tertiary butyl alcohol) (tertiary amyl alcohol)
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Isomerism in alcohols :
They exhibit chain, position, functional isomerism. For saturated monohydric alcohols CnH2n+2O (or) Cn H2n+1OH C2H6O functional isomers are
H3C CH2 OH (ethyl alcohol) H3C O CH3 (dimethyl ether)
C2H6O2 positional isomers are CH3 CH (OH)2 ( ethyledene glycol)
OH|
2CH
OH|
2CH ( ethyleneglycol )
C3H8O CH3 CH2 CH2 OH ( n propyl alcohol)
3CHOH|CH3CH (isopropyl alcohol)
CH3 O - C2H5 (methyl ethyl ether) C4H10O a) CH3 CH2 CH2 CH2 OH (n butyl alcohol)
b) 3CHOH|CH2CH3CH (sec butyl alcohol)
c) OH2CH
3CH|CH3CH (isobutyl alcohol)
CH3 CH2 O CH2 CH3 (diethyl ether) CH3 O CH2 CH2 CH3 (methyl propyl ether)
d) OH3CH
3CH
|
|C3CH (tertiary butyl alcohol)
3CH
3CH|CHO3CH (isopropyl methyl ether )
a, b position ; a, c chain a, dposition and chain b, c position and chain b, d chain c, d position
If tetrahedral carbon is bonded to four different atoms or different groups of atoms it is called asymmetric carbon.
Organic compound containing one or more asymmetric carbons will exhibit optical isomerism. Certain alcohols having asymmetric carbon will exhibit optical isomerism.
CH3 OH CH3 CH2 OH CH3 CH2 CH2 OH
OH
3CH|CH3CH
Doesnt show optical isomerism
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3CH2CH
OH|CH3CH
COOH
OH|CH3CH
Ethyl alcohol : Grain alcohol or spirit of wines ( C2H5OH)
Preparation : By the hydrolysis of ethyl halide : (industrial method) Ethyl halide on hydrolysis with aqueous sodium hydroxide or potassium hydroxide gives ethyl alcohol.
NaXOHCHCHNaOHXHC 2352 ++ ; X = Cl, Br, I In the place of NaOH or KOH, AgOH can be used.
By the hydrolysis of ester : Hydrolysis of ethyl acetate with aqueous alkali gives ethyl alcohol. ( ) OHHCCOOKCHKOHHCOOCCH 523aq523 ++
By the hydration of Ethylene :(industrial method ) Ethylene on reaction with conc. sulphuric acid at 7580C gives ethylalcohol.
423422 HSOCHCHHSOHCHCH += 4223423 SOHOHCHCHOHHHSOCHCH ++
By the reduction of Acetaldehdye (CH3CHO) : Acetaldehyde on reduction with Hydrogen and Nickel or Lithium aluminum hydride gives ethyl alcohol.
OHCHCHHCHOCH 23LiAlH
orNi/H23
4
2 + From Grignard reagent and formaldehyde: Methyl magnesium halide on reaction with
formaldehyde followed by hydrolysis gives ethyl alcohol.
( )BrOHMgOHCHCHOMgBrCHCHMgBrCHOCH 23OHH2332 + += ++ Formaldehyde+any grignard reagent primary alcohol
Fermentation of molasses : The breaking of complex organic molecule into smaller ones in the presence of enzymes is called fermentation. In any fermentation process the by product is CO2. Molasses is a dark, brown coloured liquor left after the crystallization of sugar. Molasses still contain about 40% sugar. It is diluted to 10% sugar and yeast cells are added. PH is maintained at 4 by adding dilute H2SO4. Temperature is maintained between 300C and 400C. Ammonium Sulphate or Ammonium phosphate is added to yeast cells which acts as food for yeast.
Yeast cells produce invertase and zymase enzyme In presence of invertase enzyme sucrose (sugar) is hydrolysed to glucose and fructose
( ) ( )Fructose 6126ecosGlu 6126Invertase
2sucrose
112212 OHCOHCOHOHC + + Glucose or fructose is then converted into alcohol in presence of zymase enzyme.
252zymase
6126 CO2OHHC2OHC + The alcohol obtained above is 6 10% pure which is called as wash or wort.
Wash is further concentrated to the 95.6% by fractional distillation. 95.6% alcohol is called rectified spirit. 95.6 % alcohol and 4.4% water will form constant boiling mixture [azeotropic mixture] therefore it cant be further concentrated to 100% alcohol by normal distillation methods. Quicklime (CaO) or magnesium ethoxide [Mg(OC2H5)2] can be used to convert 95.6% into 100%
Exhibits optical isomerism
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alcohol which is called absolute alcohol or absolute spirit. Anhydrous CaCl2 is laboratory desiccant but CaCl2 should not used for drying alcohol as if forms
an addition compound with it. That addition compound is CaCl2.3C2H5OH. Fermentation of starch :
Starch is present in wheat, maize, potato etc. The source of starch is crushed and treated with steam and the product is called Mash. The product is added to germinated Barley seeds which is called malt.
Malt contains diastase enzyme. In presence of diastase enzyme starch is hydrolyzed to give maltose
( )( ) ( )maltose 112212
diastase2
starchn5106 OHnCOnHOHC2 +
Yeast cells are added to produce maltase and zymase enzymes. In presence of maltase, maltose, converts into glucose which then converts into ethyl alcohol in the presence of zymase enzyme.
( )ecosglu 6126maltose
2112212 OHC2OHOHC +
+ 252zymase6126 CO2OHHC2OHC The ethyl alcohol obtained is 6 10%. It is further concentrated to 100% alcohol as listed above. Physical properties : 1) It is a colourless liquid with characteristic smell. 2) It has burning taste 3) It forms hydrogen bonds with water and also with it itself therefore it exists as associated
liquid, soluble in water and boiling point is very high (78.1 0C). 4) Its dissolution in H2O is exothermic and there is slight contraction in volume. 5) Non ideal solution.
Chemical reactions: The reactions of alcohols involve either cleavage of O H bond or C OH bond. Reactivity of alcohols involved in cleavage of O H
HOR Primary alcohol>secondary alcohol>tertiary alcohol Reactivity of alcohols which involve cleavage of COH
HOR Primary alcohol=>>> primary alcohol>secondary alcohol>tertiary alcohol 2) with grignard reagent : Ethyl alcohol on reaction with Grignard reagent forms alkane.
OMgBrHCCHMgBrCHOHHC 524352 ++
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3) with acetic acid (esterification) : Ethyl alcohol on reaction with carboxylic acid gives ester. This reaction is catalysed by mineral acid.
OHHHCOOCCHCOOHCHOHHC 523352 ++ This reaction is called Fischer esterification
4) With acetyl chloride and acetic anhydride : With acetyl chloride and acetic anhydride also ethyl alcohol gives ester.
HClHCOOCCHCOClCHOHHC 523352 ++ ( ) 52332352 HCOOCCHCOOHCHOCOCHOHHC ++ 5) With hydrogen halides : Ethyl alcohol on reaction with hydrogen halides in the presence of anhydrous ZnCl2 gives ethyl halide.
OHClHCHClOHHC 252ZnCl
hydrousan52
2
+ + OHBrHCHBrOHHC 25252 ++
6) With phosphorous halides : Ethyl alcohol on reaction with phosphorus halides gives ethyl halides.
3 3352352 POHClHC3PClOHHC ++ 3352352 POHBrHC3PBrOHHC3 ++
3352352 POHIHC3PIOHHC3 ++ HClPOClClHCPClOHHC 352552 +++
8) With SOCl2 : Thionyl chloride reacts with ethyl alcohol to give ethyl chloride. HClSOClHCSOClOHHC 252252 +++
9) Dehydration : Ethyl alcohol on dehydration gives different products at different temperatures.
OHHSOHCOHHC 2452C110
SOH.con52 0
42 +
(ethylhydrogen sulphate) OHHCOHCOHHC2 25252
C140
SOH.conc52 0
42 +
(diethyl ether) OHHCOHHC 242
C170
SOH.conc52 0
42 +
(ethylene) In presence of excess of H2SO4 product is C2H4 with excess of alcohol the product is diethyl ether.
Instead of conc. H2SO4, Alumina can be used. OHHCOHCOHHC2 25252
C250
OAl.conc52 0
32 +
OHHCOHHC 242C350
OAl.conc52 0
32 +
10) Reduction : Ethyl alcohl is reduced to ethane by HI / red P. OHIHCHI2OHHC 2262
Pred52 ++ +
11) Dehydrogenation (oxidation): a) Ethyl alcohol in the presence of copper at 300C gives acetaldehyde.
23C300,Cu
23 HCHOCHOHCHCH0 +
(acetaldehyde)
H3O+
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b) On oxidation with acidified potassium permanganate (KMnO4) or potassium dichromate (K2Cr2O7) ethyl alcohol forms acetic acid. [ ]
aldehyde.pri3
OCrK
orKMnO23 CHOCHOOHCHCH
722
4 + [ ] COOHCH3O 12) with Chlorine : Chlorine oxidises ethyl alcohol to chloral.
HCl3CHOCClCl3OHCHCHchloral3223 ++
13) with bleaching powder : Ethyl alcohol and bleaching powder mixture on distillation gives chloroform. ( ) HClCaHCOOCHClOHCaOClOHHC 232252 ++++ 14) Iodoform reaction : Yellows crystals of CHI3 will be formed when ethylalcohol is treated
with I2 solution and potassium hydroxide. OH5HCOOKKI5CHIKOH6I4OHHC 23252 +++++
Alcohols containing
OH|
CH3CH or Aldehydes or ketones containing O||C3CH will react with
iodine and alkali to give iodoform which is yellow crystalline solid. ETHERS : [R O R1 alkoxy alkanes] ether is the dialkyl derivative of water
RORHOH
ether is the anhydride of alcohol. Naming of ethers IUPAC Common name
CH3 O CH3 Methoxy methane Dimethyl ether CH3 O C2H5 methoxy ethane ethyl methyl ether C2H5 O C2H5 Ethoxy ethane Diethyl ether CH3 O CH2 CH2 CH3 1 methoxy propane Methyl n propy ether
3
3
CH
CH3 CHOCH 2 methoxy propane Methyl isopropyl ether
32
CH|
52 CHCHCHOHC
3
2 ethoxy butane Ethyl secondary butyl ether
Ethers are classified into two types based on the nature of alkyl groups. 1) Symmetrical ethers (or) simple ethers are
R = R R O R CH3 O CH3 C2H5 O C2H5 2) unsymmetrical ethers (or) mixed ethers :
R R R O R CH3 O C2H5 C2H5 O CH2 CH2 CH3
Isomerism shown by ethers: Ethers will exhibit metamerism, functional isomerism and chain isomerism.
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33 CHOCH OHHC 52
5252 HCOHC
3223 CHCHCHOCH 3CH
3CH|CHO3CH
General molecular formula of ether CnH2n+2O Diethyl ether (sulphuric ether) : Preparation : 1) Dehydration :
a) By the dehydration of ethyl alcohol in the presence of conc. H2SO4 at 1400C. OHHCOHCOHHC2 25252
C140
SOH.conc52 0
42 + b) By the dehydration of ethyl alcohol in presence of anhydrous alumina at 2500C.
OHHCOHCOHHC2 25252C250
OAl52 0
32 + 2) From ethyl chloride : By the reaction of ethyl chloride with dry silver oxide.
AgCl2HCOHCOAgClHC2 5252252 ++ 3) Williamsons synthesis : Alkyl halides react with sodium alkoxides to produce ethers.
This method is suitable for the preparation of both simple and mixed ethers. NaClHCOHCHNaOCClHC 52525252 ++
Physical properties : 1) It is a colourless liquid with pleasant smell. 2) It does not form hydrogen bonds and will not exist as associated liquid. Therefore it is highly
volatile, low boiling point 307.50C and it is slightly miscible with water. 3) It is inflammable. 4) Its vapours cause unconsciousness. 5) It forms explosive mixture with air [ether +O2 etherperoxide]
In ether O is sp3 hybridised, shape is angular. Bond angle is 1100 due to the repulsions between bond pair and because of bulky nature of alkyl
groups. It is slightly polar and its 0.
Chemical reactions: Ethers are chemically inert because O is flanked in between two bulky alkyl groups.
Therefore ethers are not easily oxidisable and they will not decolourise permanganate or dichromate. 1) - halogenation : The - hydrogens present in ether are substituted by halogen atoms.
+ dark23223 Cl2CHCHOCHCH HCl2CHCl
HCOClCHCH 3||3
1
+ (, 1 dichloro diethyl ether)
O
C2HC2H1100
Functional isomers
Metamers
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+ sunlight23223 Cl2CHCHOCHCH 3CHCl
Cl
|
|CO
Cl
Cl
|
|CCH3 (, 1 1 tetrachloro diethyl ether)
In dark the two - hydrogens are substituted by two chlorines on reaction with chlorine. 2) with air : Diethyl ether when exposed to air forms a mixture due to the formation of diethyl
peroxide.
52) (explosive5225252HCOOHCO
21HCOHC + (or) 5252 HCHC
O
O It is
freed from peroxide by treating with ferrous sulphate. 3) with dil.H2SO4 : Diethyl ether is hydrolysed to ethyl alcohol in presence of sulphuric acid
OHHC2OHHHCOHC 52SOH.dil
5252 42 + 4) with cold and conc. mineral acids.
Ether reacts with cold and conc. mineral acids like HCl, H2SO4, HNO3 etc. to form oxonium salts. Formation of these oxonium salts with the mineral acids is the indication of its basic nature.
( ) ( ) +
+ ClOHHCHClOHC 252252 (diethyl oxonium chloride)
( ) ( )[ ] 24225242252 SOOHHCSOHOHC + + (diethyl oxonium sulphate ) 5) with HI: With cold HI, one C O bond is cleaved and the products are ethyl alcohol and ethyl
iodide. IHCOHHCHIHCOHC 52525252 ++ With hot and excess of HI , both C O bonds are cleaved and two moles of C2H5 I are formed
OHIHC2HI2HCOHC 2525252 ++ In case of mixed ethers I of HI is added to smaller alkyl group.
HHCOCH 523 + I CH3 I + C2H5 OH Ziesels method is useful to detect and estimate the number of methoxy groups present in the given
ether. The reaction of ether with HI forms the basis for Ziesels method.
6) with PCl5 : with PCl5 diethyl ether gives ethylchloride
35255252 POClClHC2PClHCOHC ++ 7) Dehydation : on dehydration in the presence of alumina diethyl ether gives ethylene.
OHHC2HCOHC 242C360
COAl.an5252 0
32 +
8) with CO: In the presence of BF3 at 150C and 500 atm pressure diethyl ether reacts with CO
and forms ethyl propionate (Ester)
5252atm500
C150,BF5252 HCOOCHCCOHCOHC
03 + (ethyl propionate)
9) Reduction : Diethyl ether reduces to ethane on reduction with Na/liq.NH3.
OHHCHCH2HCOHC 5262NH.liq/Na
52523 + +
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ELECTROPHILIC SUBSTITUTION.
1) HALOGENATION:
2) NITRATION:
3) FRIEDEL-CRAFTS REACTION:
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USES : ETHER IS USED IN/AS 1. a solvent for oils, fats, waxes, plastics etc. 2. the extraction of organic compounds from aqueous solutions. 3. an inert medium for various reactions (ex.Wurtz reaction) and preparation of RMgX 4. an anaesthesia in surgery without causing any damage to heart or lungs. (Recently,
HALOTHANE is widely used for this purpose since it is harmless and quick in action CF3CHClBr. ) (IUPAC name : 2-Bromo-2- chloro-1,1,1-trifluroethane)
5. NATALITE(mixture of Alcohol and Ether), a substitute for petrol 6. Refrigerant along with dry ice (solid CO2 ) which produces a temperature around -110C i) Enthrane 2 2( )CHFCl CF O CHF and isoflurane ( 3 2 )CFCHCl O CHF are used as
anesthetics in place of diethyl ether as the later one has slow effect. ii) Substituted anisols are used as flavourings and in perfumes due to their pleasant odour. Eg :
1.ANITHOLE is a constituent of anise seed.
2.EQUGINOL is present in cloves.
3.VANILLIN is present in oil of vanilla been
4.THYMOL is present in thyme and mint are used as flavourings and in perfumes.
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Identification of primary , secondary , tertiary alcohols
Test Primary alcohol Secondary alcohol Tertiary alcohol 1) Lucas test : No reaction Reacts with in Reacts within The alcohol is (No turbidity) 5 minutes to 30 seconds to give treated with Lucas give turbidity turbidity reagent 2) Victor Meyers : Red colouration Blue colouration No colour is produced test : The alcohol is observed is observed 3R COH is treated with red 2RCH OH 2R CHOH 2I red P + phosphorous and 2 /I red P 2I red P + 3R CI and the product 2RCH I 2R CHI 2AgNO is treated with 2AgNO 2AgNO 3 2R CNO and then 2 2RCH NO 2 2R CHNO 2 &HNO alkali with nitrous acid 2HNO 2HNO No reaction.
2 2 4( )NaNO H SO+ and finally made (Nitrolic acid) (pseudo nitrol) alkaline alkali alkali red colouration blue colouration 3) Catalytic Aldehyde, H2 is Ketone, H2 is produced Dehydration takes place dehydrogenation produced 2R COH giving alkene and H2O with copper at 0300 c 2RCH OH 2 2R CO H+ 3 3( )CH COH
2RCHO H+ 33 2 21
CH
CH C CH H O = +
4) Oxidation ( )2ORCH OH ( )2 OR CHOH 3R C OH (O)
with acidified RCHO 2R CO Ketone + acid ( )O
4KMnO ( )O ( )O Mixture of acids RCOOH Mixture of ketone contains lesser same number alcohol and no. of carbons than . of carbon atoms ketone contain alcohol. Acid contain still in alcohol, same no. of lesser no. of carbons than aldehyde and acid carbons but that of ketone. acids contains lesser no. of carbons
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MECHANISM OF DEHYDRATION : It takes place in three steps : i) 3 3 2 4CH CH OH H SO +
|
. .
3 2 3CH CH O H OSO HH
+ + ii) Formation of carbonation. It is the slowest step or rate determining step.
|
. .
3 2CH CH O HH
+ . .3 2 2 :CH C H H O+ +
iii) Elimination of proton to get alkene
Since the rate determining step is the formation of carbocation, the rate of dehydration is directly
proportional to the formation of carbocation. Since the stability of carbocation is 0 0 03 2 1> > , the order of dehydration of alcohols is ( ) ( )3 3 3 23 2CH COH CH CHOH CH CH OH> > Dehydration of alcohol requires 95% 2 4H SO at
0 02 4170 , 2H SO C alcohol requires 75% 2 4H SO at
1000, where 03 as alcohol requires 5% 2 4H SO at 050 C .
The dehydration of 1o alcohol goes by 2E mech nism, but that of 2o and 3o alcohols go by 1E
mechanism. When more than one product is formed, the major product is according to Zaitsevs rule. It states
that hydrogen is removed from carbon that is bonded to the least number of hydrogen atoms.( -elimination)
Eg. Dehydration of 2-butanol predominantly gives 2-butene.
2 43 2 3ConcH SOCH CH CHOH CH
3 3 3 2 2CH CH CH CH CH CH CH CH = + = 2-butene(major) 1-butene (minor) FORMATION OF ADDTION COMPOUNDS : Ethyl alcohol reacts with anhydrous metal salts
to form addition compounds (that is alcohol of crystallisation) a) 2 5 2 2 5 2.3 , .6 ,C H OH CaCl C H OH MgCl 2 5 4.3C H OH CuSO USES OF SOME IMPROTANT COMPOUNDS (Methanol and ethanol) METHANOL 1. Methanol a colourless liquid with b.pt 067 C .is used as solvent, paints, varnishes, shellac etc., 2. Used in the manfacture of HCHO, perfumes and dyes. 3. Used in the preparation of methylated spirt, a mixture of recatified spirit (95.6% ethyl alcohol +
4.4%water) and methyl alcohol making ethyl alcohol unfit for drinking . 4. Two types of methylated spirits: a) mineralised spirit = 90% rectified spirit + 9% methyl alcohol + 1% pyridine
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b) Surgical spirit = 95% rectified spirit + 5% MeOH 5. In denaturation of ethyl alcohol copper sulphate is added to give colour and pyridine is added to
make it a foul smelling liquid. Because of denaturation alcohol becomes unfit for drinking. USES OF ETHYL ALCOHOL 1. As a solvent for pharmaceutical preparations, paints, perfumes, varnishes, gums etc., 2. In alcoholic bevarages. 3. As reaction medium, extractant and crystallsing 4. A source for the preparation of acetaldehyde, chloral, chloroform, iodoform, acetic acid ether etc. 5. A preservative for biological specimens, an antifreeze for automobile radiotors, a fuel in spirit
lamps, stoves, a petrol substitute known as power alcohol. PERPARATION OF WINE Grapes are the source of sugar and yeast. Sugar increases in ripe grapes and yeast grows on the outer skin. On crushing the grapes, sugar
and enzyme come in contact and fermentation starts in anaerobic conditions. If air is present it oxidises alcohol to acids
PHENOL NAMING OF PHENOLS
Molecule Common name IUPAC name
Phenol Phenol
O-cresol 2-methyl phenol
m-cresol 3-methyl phenol
p-cresol 4-methyl phenol
Catechol Benzene-1,2-diol
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Resorcinol Benzene-1,3-diol
Hydroquinone (or)quinol Benzene-1,4-diol
2,6-dimethyl phenol METHODS OF PREPARATION OF PHENOL : 1) Phenol was first isolated from coaltar. 2) From haloarenes
+ NaOH 350 & 320o C atm HCl
3) From diazonium salt :
0 52o CNaNO HCl + + 2 ,H O warm 2N HCl+ +
4) From benzene sulphonic acid :
2 4 3. ,conc H SO SO molten NaOH HCl + NaCl 5) From cumene : Phenol is manufactured from cumene (isopropyl benzene)
2 ( )O oxidation with air 2/H H O+ 3 3CH COCH+ cumene hydroperoxide
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ACIDITY OF PHENOLS : The reactions of phenol with metals as well as NaOH indicate it is relatively more acidic than alcohols and also water. This is explained on the basis of the structure of phenol. The hydroxyl group in phenol is directly attached to 2sp carbon of benzene ring. The 2sp carbon attached to O being more electronegative than 3sp carbon of alcohols, it decreases the electron density on oxygen. Because of this oxygen develops still more electron seeking character and releases proton by taking the shared pair of electrons with it. The acidic nature of phenol can also be explained .On the basis of resonance stabilization of phonoxide ion. Electron withdrawing groups of phenol increase the acidic nature. Electron releasing group of phenol decrease the acidity of phenols. Acidic strength increases with the decrease of the aKP values. The order of the strength of phenols is as follows
> > > >
> > > =
PHYSICAL AND CHEMICAL PROPERTIES OF PHENOLS PHYSICAL : 1) Phenol has higher boiling point than the arenes or haloarenes or ethers of same molecular weight. It is due to the formation of intermolecular hydrogen bond. 2) Phenols are relatively more soluble in water due to their ability to form hydrogen bonding with water. 3) As the hydrocarbon part increases in size and mass, the solubility decreases. CHEMICAL PROPERTIES : 1) Acidic nature of phenol : Alcohols and phenols react with active metals like Na, K, Al etc to liberate hydrogen gas. 22 2 2ROH Na RONa H+ + 6 5 6 5 22 2C H OH Na C H ONa H+ + Phenols also react with aqueous NaOH solution to produce the salt sodium phenoxide and water. 6 5 6 5 2C H OH NaOH C H ONa H O+ + The acidic nature of alcohols is due to the polar nature of O-H group. Electron releasing groups like alkyl groups increase the electron density on oxygen and decrease the polarity of O-H bond. This decreases the acidic strength. The order of acidic strength is 2 2 2 3H O RCH OH R CHOH R COH> > >
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Even through the electron releasing groups like 3 2 5,CH C H etc decrease the acidic strength of phenol, Phenol does not liberate 2CO with 2 3Na CO or 3NaHCO because phenol is weaker acidic than carbonic acid and carboxylic acids. ESTERIFICATION OF PHENOL : Phenols react with carboxylic acids and their derivatives like acid chlorides and anhydrides to form esters. This reaction (benzoylation ) is called Schotten-Baumann reaction. 6 5C H OH RCOOH+ 6 5 2C H O CO R H O + 6 5 6 5
pyridineC H OH RCOCl C H O CO R HCl+ + Salicylic acid on acetylation gives acetyl salicylic acid known as Aspirin.
3 2( )CH CO O+ 2 4.conc H SO
Electrophilic aromatic substitution reactions of phenol In phenol, -OH group is ring activating and ortho and para directing as these positions get more
electron density through resonance structures. a) NITRATION :
3.dil HNO + O-nitrophenol is steam volatile due to intramolecular hydrogen bond. P-nitrophenol is less volatile due intermolecular hydrogen bond. Phenol when treated with conc. 3HNO gives 2,4,6-trinitrophenol known as picric acid
3.conc HNO Now a days picric acid is prepared by treating phenol with conc. 2 4H SO and then with conc. 3HNO .
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2 4.conc H SO 3.conc HNO b) HALOGENATION :
2 2 0oBr in CS at C +
Here no Lewis acids like are required because highly activating effect of -OH group polarises bromine quickly. Phenol reacts with bromine water and gives 2,4,6-tribromo phenol (white precipitate)
202 0 53H O
CBr +
c) REIMER-TIEMANN REACTION : Phenol when treated with chloroform in the presence of NaOH give salicylaldehyde. Mechanism : i)
3 2 3 2:CHCl OH H O CCl CCl Cl
+ + + Dichloro carbene ( 2: )CCl is the attacking electrophile in this reaction :
ii) + 2:CCl NaOH
d) KOLBES REACTION :
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NaOH 2) & )i CO ii H + e) ACTION OF ZINC DUST : Phenol on heating with zinc dust produces benzene. f) OXIDATION : Phenol oxidation with chromic acid 2 2 7 2 4( )Na Cr O H SO+ produces benzoquinone, which is a conjugate diketone.
2 4
chromic acidH CrO
g) FRIES REARRANGEMENT :
33 2( )
anhydrous AlClCH CO O+
3Re
AlClarrangement +
USES OF PHENOL : 1) It is raw material for the manufacture of important dyes, drugs, pharmaceuticals, polymers and
several other compounds. 2) It is strong antiseptic. 2,4-dichloro-3,5 dimethyl phenol is used as powerful antiseptic under
the name Dettol. 3) It is used as a preservative for ink. 4) It is used in the manufacture of drugs like Aspirin, Salol etc. 5) It is used for causterising wounds caused by the bite of mad dogs. Tests of Phenol : i) Aqueous solution of phenol gives violet colour with a drop a 3FeCl . ii) Aqueous phenol gives white precipitate with bromine water.
iii) Phenol gives blue colour with ammonia and sodium hypochlorite.
