ORGANIC CHEMISTRY CHM 207

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ORGANIC CHEMISTRY CHM 207
CHAPTER 6 HYDROXYL COMPOUNDS (ALCOHOLS AND
PHENOL)
NOR AKMALAZURA JANI
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SUBTOPICS

• Nomenclature of alcohols, phenols.
• Classification of alcohols.
• Physical properties of alcohols
• - Physical state
• - Boiling points
• - Solubility of alcohols in water
• Acidity of alcohols and phenols
• Reactions of alcohols
• - Reaction with sodium
• - Oxidation
• - Esterification
• - Halogenation and haloform reactions
• - Dehydration
• - Formation of ether (Williamson ether
  synthesis)

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• Reactions of phenols
• - Reaction with sodium
• - Esterification
• - Halogenation of the ring
• - Nitration of the ring
• Tests to distinguish classes of alcohols
• i) Lucas test ii) Oxidation
• Haloform test to identify methyl alcohol group
• - Iodoform
• - Bromoform
• Uses of alcohols and phenols.

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ALCOHOLS

• Alcohols Organic compounds containing hydroxyl
  (-OH) functional groups.

• Phenols Compounds with hydroxyl group bonded
  directly to an aromatic (benzene) ring.

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NOMENCLATURE OF ALCOHOLS
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IUPAC RULES

1. Select the longest continuous chain of carbon
   atoms containing the hydroxyl group.
2. Number the carbon atoms in this chain so that the
   one bonded to the OH group has the lowest
   possible number.
3. Form the parent alcohol name by replacing the
   final e of the corresponding alkane name by
   ol. When isomers are possible, locate the
   position of the OH by placing the number
   (hyphenated) of the carbon atom to which the OH
   is bonded immediately before the parent alcohol
   name.
4. Name each alkyl branch chain (or other group) and
   designate its position by number.

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This is the longest continuous chain that
contains an hydroxyl group.
Select this chain as the parent compound.
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4
3
2
1
This end of the chain is closest to the OH.
Begin numbering here.
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4
3
2
1
3-methyl-2-butanol
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This is the longest continuous chain that
contains an hydroxyl group.
Select this chain as the parent compound.
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4
3
5
2
1
This end of the chain is closest to the OH.
Begin numbering here.
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4
3
5
3
2
1
2
3-methyl-2-pentanol
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NOMENCLATURE OF CYCLIC ALCOHOLS

• Using the prefix cyclo-
• The hydroxyl group is assumed to be on C1.

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NOMENCLATURE OF ALCOHOLS CONTAINING TWO DIFFERENT
FUNCTIONAL GROUPS

• Alcohol containing double and triple bonds
• - use the ol suffix after the alkene or alkyne
  name.
• The alcohol functional group takes precedence
  over double and triple bonds, so the chain is
  numbered in order to give the lowest possible
  number to the carbon atom bonded to the hydroxyl
  group.
• The position of the OH group is given by putting
  its number before the ol suffix.
• Numbers for the multiple bonds were once given
  early in the name.

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EXAMPLE

• 1) Longest carbon chain that contains
  OH group
• - 5 carbon
• 2) Position of OH group
• - Carbon-2
• 3) Position of CC
• - Carbon-4
• COMPLETE NAME 4-penten-2-ol

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• Some consideration
• - OH functional group is named as a hydroxy
  substituent when it appears on a structure with a
  higher priority functional group such as acids,
  esters, aldehydes and ketones.
• - Examples

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• MAIN GROUPS
• Acids
• Esters
• Aldehydes
• Ketones
• Alcohols
• Amines
• Alkenes
• Alkynes
• Alkanes
• Ethers
• Halides

decreasing priority
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NOMENCLATURE OF DIOLS

• Alcohols with two OH groups are called diols or
  glycols.
• Naming of diols is like other alcohols except
  that the suffix diol is used and two numbers are
  needed to tell where the two hydroxyl groups are
  located.

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NOMENCLATURE OF PHENOLS

• The terms ortho (1,2-disubstituted), meta
  (1,3-disubstituted) and para (1,4-disubstituted)
  are often used in the common names.

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• Phenols may be monohydric, dihydric or trihydric
  according to the number of hydroxyl groups
  present in the benzene ring.

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CLASSIFICATION

• According to the type of carbinol carbon atom (C
  bonded to the OH group).

• Classes
• i) Primary alcohol
• - -OH group attached to a primary carbon
  atom
• ii) Secondary alcohol
• - -OH group attached to a secondary
  carbon atom
• iii) Tertiary alcohol
• - -OH group attached to a tertiary
  carbon atom

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• TYPE STRUCTURE
  EXAMPLES
• Primary (1)
• Secondary (2)
• Tertiary (3)

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Polyhydroxy Alcohols

• Alcohols that contain more than one OH group
  attached to different carbons are called
  polyhydroxy alcohols.
• Monohydroxy one OH group per molecule.
• Dihydroxy two OH groups per molecule.
• Trihydroxy three OH groups per molecule.

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PHYSICAL PROPERTIES

• PHYSICAL STATES OF ALCOHOLS
• - simple aliphatic alcohols and lower aromatic
  alcohols (such as phenylmethanol, C6H5CH2OH) ?
  liquids at room temperature.
• - highly branched alcohols and alcohols with
  twelve or more carbon atoms ? solids.

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• BOILING POINTS
• - The boiling points of alcohols are higher than
  those of alkanes and chloroalkanes of similar
  relative molecular mass.
• - For example
• C2H5OH CH3CH2CH3 CH3Cl
• Relative molecular mass
  46 44 50.5
• Boiling point 78C
  -42C -24C
• - Reason
• intermolecular hydrogen bonds exist between
  the OH
• groups in the alcohol molecules.

d
d-
d
d-
d-
d-
hydrogen bonding
hydrogen bonding
- Branched chain alcohols boils at a lower
temperature (more volatile) than the straight
chain alcohols with the same number of carbon
atoms.
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• SOLUBILITY OF ALCOHOLS IN WATER
• i) alcohols with short carbon chains (such as
  methanol, ethanol, and propanol) dissolve in
  water.
• - when alcohols dissolve in water, hydrogen
  bonds are formed between the OH group of the
  alcohol molecule and the OH group of the water
  molecule.
• ii) the solubility of alcohols in water
  decreases sharply with the increasing length of
  the carbon chain. Higher alcohols are insoluble
  in water.
• - alcohol contains a polar end (-OH group)
  called hydrophilic and a non-polar end (the
  alkyl group) called hydrophobic.
• - the water solubility decreases as the alkyl
  group becomes larger.

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• iii) alcohols with more than one hydroxyl group
  (polyhydroxy alcohols) are more soluble than
  monohydroxy alcohols with the same number of
  carbon atoms. This is because they can form more
  hydrogen bonds with water molecule.
• iv) branched hydrocarbon increases the solubility
  of alcohol in water.
• - reason branched hydrocarbon cause the
  hydrophobic region becomes compact.
• Phenol is unusually soluble (9.3) because of
  its compact shape and the particularly strong
  hydrogen bonds formed between phenolic OH groups
  and water molecules.

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ACIDITY OF ALCOHOLS AND PHENOLS

• Alcohol is weakly acidic.
• In aqueous solution, alcohol will donated its
  proton to water molecule to give an alkoxide ion
  (R-O-).

R-OH H2O R-O- H3O Ka 10-16 to 10-18
alkoxide ion
Example
CH3CH2-OH H2O CH3CH2-O- H3O

• The acid-dissociation constant, Ka, of an alcohol
  is defined by the equilibrium

Ka
R-OH H2O R-O- H3O
More smaller the pKa value, the alcohol is more
acidic
Ka H3O RO- ROH
pKa - log (Ka)
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Acidity OF PHENOLS

• Phenol is a stronger acid than alcohols and
  water.

R-OH H2O R-O- H3O Ka 10-16 to
10-18
alcohol
alkoxide ion
Ka 1.2 x 10-10
H2O H2O HO- H3O Ka 1.8 x 10-16
hydroxide ion
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• Phenol is more acidic than alcohols by
  considering the resonance effect.
• i) The alkoxide ion (RO-)
• - the negative charge is confined to the oxygen
  and is not spread over the alkyl group.
• - this makes the RO- ion less stable and more
  susceptible to attack by positive ions such as H
  ions.

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• ii) The phenoxide ion
• - one of the lone pairs of electrons on the
  oxygen atom is delocalised into the benzene ring.
• - the phenoxide ion is more stable than the
  alkoxide ion because the negative charge is not
  confined to the oxygen atom but delocalised into
  the benzene ring.
• - the phenoxide ion is resonance stabilised by
  the benzene ring and this decreases the tendency
  for the phenoxide ion to react with H3O.

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EFFECTS OF Acidity

• The acidity decreases as the substitution on the
  alkyl group increase.
• - Reason a more highly substituted alkyl group
  inhibits solvation of the alkoxide ion and drives
  the dissociation equilibrium to the left.
• - For example methanol is more acidic than
  t-butyl alcohol.
• The present of electron-withdrawing atoms
  enhances the acidity of alcohols.
• - Reason the electron withdrawing atom helps to
  stabilize the alkoxide ion.
• - For example 2-chloroethanol is more acidic
  than ethanol because the electron-withdrawing
  chlorine atom helps to stabilize the
  2-chloroethoxide ion.
• - alcohol with more than one electron
  withdrawing atoms are more acidic. For example,
  2,2,-dichloroethanol is more acidic than
  2-chloroethanol.
• - Example of electron-withdrawing atom/groups
  
• Halogen atoms and NO2.

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REACTIONS OF ALCOHOLS

• Reaction with sodium
• Oxidation
• Esterification
• Halogenation and haloform reactions
• Dehydration
• Formation of ether (Williamson ether synthesis)

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Reaction with sodium

• Alcohols reacts with Na at room temperature to
  form salts (sodium alkoxides) and hydrogen.

2R-O-H 2Na ? 2R-O- Na H2

• For example
• CH3CH2OH Na ? CH3CH2O-Na 1/2H2
• alcohol sodium ethoxide

• Reactivity of alcohols towards the reactions with
  sodium
• CH3 gt 1 gt 2 gt 3

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Oxidation
1 alcohol
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Examples
1 alcohol
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2 alcohol
3 alcohol
Example
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Esterification

• Esterification
• - the reaction between an alcohol and a
  carboxylic acid to form an ester and H2O.

H catalyst
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Esterification also occurs when alcohols react
with derivatives of carboxylic acids such as acid
chlorides
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Halogenation and haloform reactions

• 1) Hydrogen halides (HBr or HCl or HI)
• R-OH H-X ? R-X H2O
• Example
• C2H5-OH H-Br C2H5-Br H2O
• Reactivity of hydrogen halides decreases in order
  HI gt HBr gt HCl
• Reactivity of alcohols with hydrogen halides
• 3 gt 2 gt 1

H
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• 2) Phosphorus trihalides, PX3
• 3R-OH PX3 3R-X H3PO3
• (PX3 PCl3 or PBr3 or PI3)
• Example
• (CH3)2CHCH2-OH PBr3 ? (CH3)2CHCH2-Br
• isobutyl alcohol isobutyl bromide
• 3) Thionyl chloride (SOCl2)
• R-OH SOCl2 ? R-Cl SO2 HCl
• Example
• CH3(CH2)5CH2-OH SOCl2 ? CH3(CH2)5CH2-Cl SO2
  HCl
• 1-heptanol
  1-chloroheptane

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Dehydration

• Dehydration of alcohols will formed alkenes and
  the products will followed Saytzeff rules.

conc. H2SO4
R-CH2-CH2-OH
R-CHCH2 H2O

• Saytzeff rule
• - A reaction that produces an alkene would
  favour the formation of an alkene that has the
  greatest number of substituents attached to the
  CC group.

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• Reactivity of alcohols towards dehydration
• 3 gt 2 gt 1
• Reagents for dehydration
• i) Concentrated H2SO4

conc. H2SO4
CH3-CH2-OH
CH2CH2 H2O
ii) With phosphoric (v) acid
iii) Vapour phase dehydration of
alcohols CH3CH2OH CH2CH2 H2O
Al2O3
heat
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Formation of ether (Williamson ether synthesis)

• Involves the SN2 attack of an alkoxide ion on an
  unhindered primary alkyl halides.
• The alkoxide is made by adding Na, K or NaH to
  the alcohol.
• R-O- R-X ? R-O-R X-
• alkoxide
• (R must be primary)

• The alkyl halides (or tosylate) must be primary,
  so that a back-side attack is not hindered.
• If the alkyl halides is not primary, elimination
  usually occurs to form alkenes.

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REACTIONS OF PHENOLS

• Reaction with sodium
• Esterification
• Halogenation of the ring
• Nitration of the ring

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REACTION WITH SODIUM
REACTION WITH AQUEOUS SODIUM HYDROXIDE
ROH NaOH no reaction
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ESTERIFICATION
H
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HALOGENATION

• More reactive towards electrophilic substitution
  than benzene.
• ortho-para director.

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• Monobromophenols are obtained if the bromine is
  dissolved in a non-polar solvent such as CCl4.

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NITRATION

• Dilute nitric (v) acids reacts with phenol at
  room temperature to give a mixture of 2- and
  4-nitrophenols.

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• By using concentrated nitric (v) acid, the
  nitration of phenol yields 2,4,6-trinitrophenol
  (picric acid).
• Picric acid is a bright yellow crystalline solid.
  It is used in the dyeing industry and in
  manufacture of explosives.

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TESTS TO DISTINGUISH CLASSES OF ALCOHOLS

• Lucas Test
• - The alcohol is shaken with Lucas reagent (a
  solution of ZnCl2 in concentrated HCl).
• - Tertiary alcohol - Immediate cloudiness (due
  to the formation of alkyl chloride).
• - Secondary alcohol - Solution turns cloudy
  within about 5 minutes.
• - Primary alcohol - No cloudiness at room
  temperature.

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• 2) Oxidation of alcohols
• - only primary and secondary alcohols are
  oxidised by hot acidified KMnO4 or hot acidified
  K2Cr2O7 solution.
• - the alcohol is heated with KMnO4 or K2Cr2O7 in
  the presence of dilute H2SO4.
• - 1o or 2o alcohol
• ? the purple colour of KMnO4 solution
  disappears.
• ? the colour of the K2Cr2O7 solution changes
  from orange to green.
• - 3o alcohol do not react with KMnO4 or K2Cr2O7.

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HALOFORM TEST TO IDENTIFY METHYL ALCOHOL GROUP

• 1) Iodoform
• Ethanol and secondary alcohols containing the
  group methyl alcohol group which react with
  alkaline solutions of iodine to form
  triiodomethane (iodoform, CHI3).
• Triiodomethane a pale yellow solid with a
  characteristic smell.

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• The iodoform test can distinguish ethanol from
  methanol

positive iodoform test
negative iodoform test
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• The iodoform test can distinguish 2-propanol
  from 1-propanol

positive iodoform test
negative iodoform test
TERTIARY ALCOHOLS DO NOT GIVE POSITIVE IODOFORM
TEST
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2) BROMOFORM
reagent
sample
iodoform
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USES OF ALCOHOLS

• As solvents
• - examples the lower alcohols such as methanol,
  ethanol and propanol.
• - methanol is used as a solvent for varnish and
  paints.
• As fuels
• - biofuel (fuel derived from a biological
  source).
• - ethanol can be produced from sugars such as
  sucrose from sugar cane, through fermentation and
  distillation. It can be blended with petrol and
  used as fuel in motor vehicles.
• - methylated spirit is ethanol made undrinkable
  by the addition of a little methanol. It is used
  as a fuel in camping stoves.

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• In alcoholic drinks
• - ethanol is used for making wine, beer and etc.
• As intermediates
• - methanol can be oxidised to methanal (HCHO), a
  chemical feedstock (starting material) for the
  manufacture of thermosetting plastics such as
  bakelite.
• - methanol is used to make methyl methacrylate
  which is used in the manufacture of another
  plastic called perspex.
• In cosmetics
• - ethanol is used as solvent for fragrances in
  perfumes and after-shave lotions.
• - polyhydroxyl alcohols (for example, glycerol)
  are used in moisturising creams.

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USES OF PHENOLS

• Making plastics such as bakelite (phenol-methanal
  plastic).
• The synthesis of cyclohexanol and hexanedioic
  acid to make nylon 6,6.
• Making dyes.
• Making antiseptics such as 4-chloro-3,5-dimethylph
  enol which is active ingredient in Dettol.