Alcohol and Phenol
Alcohol and Phenol
Alcohol and Phenol
DR. MOHD BAKRI BAKAR DEPARTMENT OF CHEMISTRY FACULTY OF SCIENCE UNIVERSITI TEKNOLOGI MALAYSIA C18-208 bakri@kimia.fs.utm.my
BIO-FUEL?
Petronas Methanol Labuan The plant currently produces 660,000 tonnes of methanol per year, using some 55 million standard cubic feet of gas per day as feedstock
Phenolic resin
Structure of Alcohols
Classification of Alcohols
v Primary ROH: Carbon with OH is bonded to one other carbon.
v Secondary ROH: Carbon with OH is bonded to two other carbons. v Tertiary ROH: Carbon with OH is bonded to three other carbons. v Aromatic alcohol or phenol: -OH is bonded to a benzene ring.
IUPAC Nomenclature/Names
v Find the longest carbon chain containing the carbon with the -OH group. Drop the -e from the alkane name, add -ol. Number the chain, starting from the end closest to the -OH group. Number and name all substituents.
v v
OH CH3 CH CH2CH3
2-butanol
2-methyl-1-propanol
OH
CH3
Unsaturated Alcohols
v Priority goes to the hydroxyl group; assign that carbon the lowest number. v Use alkene or alkyne name.
OH CH2 CHCH2CHCH3
4-penten-2-ol (pent-4-ene-2-ol)
Hydroxy Substituent
v v When -OH is part of a higher priority class of compound, it is named as hydroxy. Example:
OH CH2CH2CH2COOH
4-hydroxybutanoic acid
Common Names
v Alcohol can be named as alkyl alcohol. v Useful only for small alkyl groups. v Examples:
OH CH CH2CH3
isobutyl alcohol
sec-butyl alcohol
Naming Diols
v Two numbers are needed to locate the two -OH groups. v Use -diol as suffix instead of -ol.
HO
1,6-hexanediol
OH
Glycols
v v 1, 2 diols (vicinal diols) are called glycols. Common names for glycols use the name of the alkene from which they were made.
CH2CH2 OH OH
1,2-ethanediol ethylene glycol
CH2CH2CH3 OH OH
1,2-propanediol propylene glycol
Naming Phenols
v v -OH group is assumed to be on carbon 1. For common names of disubstituted phenols, use ortho- for 1,2; meta- for 1,3; and para- for 1,4. Methyl phenols are cresols.
OH
OH H3C
Cl
3-chlorophenol meta-chlorophenol
4-methylphenol para-cresol
Physical Properties
v
v Unusually high boiling points due to hydrogen bonding between molecules. Small alcohols are miscible in water, but solubility decreases as the size of the alkyl group increases; why??? alkyl group is hydrophobic.
i) B.p. increases as the number of C atoms increases. Reason: larger surface area of alkyl group, creates more Van der Waals forces, thus requires more energy to boil off. ii) B.p. decreases as branching increases. Reason: smaller surface area, smaller van de waals forces.
Boiling Points
Intermolecular forces involved: a) hydrogen bonding b) dipole-dipole attractions In increasing order: Propane < dimethyl ether < ethanol
Solubility in Water
CH3O
+ H O H
H
v pKa range: 15.5-18.0 (pKa water = 15.7) v Not strong enough to react with weak bases (NaHCO3) v Acidity decreases as alkyl group increases. - simple alcohol= negatively charged oxygen atoms accessible for solvation - bulky group bonded to OH = ability of water molecules to solvate the alkoxides ion decreases
Formation of Alkoxide Ions v React methanol and ethanol with sodium metal
O H + pKa = 10 OH
v Phenoxide ion is more stable; delocalization of the ve charge via resonance around the benzene ring make it stable; hence increase the acidity
SYNTHESIS OF ALCOHOLS
Synthesis (Review)
v Nucleophilic substitution on an alkyl halide, RX v Hydration of alkenes, (-C=C-) water in acid solution (H2O, H+) oxymercuration - demercuration hydroboration - oxidation
Hydration of alkenes
Water in Acid Solution, H2O/H+
v Oxymercuration-Demercuration Markovnikov product formed Anti addition of H-OH No rearrangements v Hydroboration-Oxidation Anti-Markovnikov product formed Syn addition of H-OH
Oxymercuration - demercuration
v Reagent is mercury(II) acetate which dissociates slightly to form +Hg(OAc) in H2O. v +Hg(OAc) is the electrophile, will be attacked by the pi bond.
v The intermediate is a cyclic mercurinium ion, a three-membered ring with a positive charge. v Water approaches the mercurinium ion from the side opposite the ring (anti addition). v Water adds to the more substituted carbon to form the Markovnikov product.
Sodium borohydride (NaBH4), a reducing agent, replaces the mercury with hydrogen.
Hydroboration - Oxidation
v Borane, BH3, adds a hydrogen to the most substituted carbon in the double bond. v The alkylborane is then oxidized to the alcohol which is the anti-Mark product.
Hydroboration - Oxidation
Glycols (Review)
v Syn hydroxylation of alkenes q osmium tetroxide, hydrogen peroxide q cold, dilute, basic potassium permanganate (BAEYER TEST)- for alkene
O C H H
H C
O H H3O
+
H C
O H H
H C
O H H
Comparison of Reducing Agents v LiAlH4 is stronger. v LiAlH4 reduces more stable compounds which are resistant to reduction.
Catalytic Hydrogenation
v Add H2 with Raney nickel catalyst. v Also reduces any C=C bonds.
OH NaBH4
O H2, Raney Ni
OH
Organometallic Reagents
v v v
Carbon is bonded to a metal (Mg or Li). Carbon is nucleophilic (partially negative). It will attack a partially positive carbon: a) C - X b) C = O v A new carbon-carbon bond forms.
Grignard Reagents
v v v v Formula R-Mg-X (reacts like R:- +MgX) Stabilized by anhydrous ether Iodides most reactive May be formed from any halide a. b. c. d. e. primary secondary tertiary vinyl aryl
Br + Mg ether
MgBr
Cl CH3CHCH2CH3 + Mg ether
MgCl CH3CHCH2CH3
CH3C CH2 Br + Mg
ether
Organolithium Reagents
v v v Formula R-Li (reacts like R:- +Li) Can be produced from alkyl, vinyl, or aryl halides, just like Grignard reagents. Ether not necessary, wide variety of solvents can be used.
Synthesis of 1 Alcohols 1
v Grignard + formaldehyde yields a primary alcohol with one additional carbon.
H C H MgBr
H C O H CH3
H C O H MgBr
H C O H H
HOH
Synthesis of 2 Alcohols
v Grignard + aldehyde yields a secondary alcohol.
H C H MgBr
H3C C O H CH3
CH3 C O H MgBr
CH3 C O H H
HOH
Synthesis of 3 Alcohols
v Grignard + ketone yields a tertiary alcohol.
H C H MgBr
CH3 C O H CH3
HOH
O CH3CH2CCH2CH3 + C6H5MgBr
O CH2CH2
MgBr
HOH O H CH2CH2
Reactions of Alcohols
Dehydration of Alcohols
v Reversible reaction v Use concentrated sulfuric (H2SO4) or phosphoric acid (H3PO4) v Protonation of OH converts it to a good leaving group, HOH v Formed carbocation as intermediate v Protic solvent removes adjacent H+
Mechanism
Types of Alcohols
H R C OH H 1
O
R' R C OH H
R' R C OH R"
2O
3O
Saytzeff Rule
In elimination reactions, the most substituted alkene which is the most stable alkene, is usually the major product.
Types of Carbocations
H R C H 1O
R' R C H R' R C R"
2O
Increasing stability
3O
R' R C R"
3O
CH3 CH3CHCH2
H O H +
1,2-Methyl Shift
CH3H H3C C C CH3 H
+
CH3OH
CH3H C C + CH3
CH3
CH3
Ring Expansion
H CH2OH H
+
CH2
O H +
CH2
+
H
CH2 H +
Keep in Mind!
Whenever a reaction leads to the formation of a carbocation (or radical), CHECK its structure for the possibility of rearrangement.
Oxidation of 2 Alcohols 2
v 2 alcohol becomes a ketone v Reagent is; sodium dichromate Na2Cr2O7/H2SO4 v Color change: orange to greenish-blue
OH CH3CHCH2CH3
Na2Cr2O7 / H2SO 4
O CH3CCH2CH3
orange
Greenish-blue
Oxidation of 1 Alcohols 1
v 1 alcohol to aldehyde to carboxylic acid v Difficult to stop at aldehyde v Use pyridinium chlorochromate (PCC) to limit the oxidation. v PCC can also be used to oxidize 2 alcohols to ketones.
OH CH3CH2CH2CH2
N H CrO3Cl
O CH3CH2CH2CH
Reduction of Alcohols
v Dehydrate with conc. H2SO4, then add H2 v Tosylate, then reduce with LiAlH4
OH CH3CHCH3 alcohol
OH CH3CHCH3 alcohol
H2SO4
CH2
CHCH3
H2 Pt
alkene
OTs CH3CHCH3 tosylate LiAlH4
CH3CH2CH3 alkane
TsCl
CH3CH2CH3 alkane
H C O O Cl S O
N O C H O S O
C O O S O
CH3
p-toluenesulfonyl chloride TsCl, tosyl chloride
CH3
R O H
H3O
H R O H
Br
Br
Limitations of HX Reactions
v HI does not react v Poor yields of 1 and 2 chlorides v May get alkene instead of alkyl halide v Carbocation intermediate may rearrange.
Dehydration Reactions
v Conc. H2SO4 produces alkene v Carbocation intermediate v Saytzeff product v Bimolecular dehydration produces ether v Low temp, 140C and below, favors ether v High temp, 180C and above, favors alkene
Dehydration Mechanisms
H OH CH3CHCH3 alcohol
H2O CH2 CHCH3
H2SO4
OH CH3CHCH3
CH3CHCH3
CH3OH
H3O
CH3
OH2
CH3
O CH3 H
CH3OH
H2O
CH3OCH3
=>
Dehydration Mechanisms
Fischer Esterification
v Acid + Alcohol yields Ester + Water v Sulfuric acid is a catalyst. v Each step is reversible.
O CH3COCH2CH3
ii)
O C6H5CCl
O C6H5COCH2CH3
Alkoxide Ions
v ROH + Na (or NaH) yields sodium alkoxide v RO- + 1 alkyl halide yields ether (Williamson ether synthesis)
Synthesis of phenols
1) Alkali fusion of sodium benzenesulfonate (1890)
SO 3H
NaOH
350o C
(fusion) HCl
ONa+
NaCl
OH
CH3CH H2SO4
CH2
H3O+ OH
+
CH3 C CH3 O
Cl
2 NaOH
150 atm
HCl
OH
1. Reduction by catalytic hydrogenation at 300C 2. Electrophilic Aromatic Substitution (o, p-director) (with bromin water obtain 2,4,6-tribromophenol) 3. Reaction to the hydroxyl groups a) formation of phenoxide ions b) esterification of phenol phenol + NaOH.+ acyl chloride phenol + acids/H+,heat c) formation of ether phenol + alkyl halide
Reactions of Phenols
Reduction of phenols
OH Ni + 3 H2 high temperature
Oxidations of phenols different from alcohol
OH
OH H2CrO4
Kuinon
O
Formation of salts
OH
ONa
NaOH
H2O
(insoluble in water)
OH
Na
very reactive
O O CH3C
CH3
+
Cl
NaCl
Formation of ether
ONa
+
O CH3CH2 Cl
CH2 CH3
+
NaCl
Both alcohols and phenols contain OH group, and will therefore exhibit a certain degree of acidic properties.
OH
H2O
H3O+
pKa = 16.0
alkoxide ion
OH
H2O
O
Phenoxide ion
H3O+
pKa = 10.0
From pKa values, phenol is more acidic than alcohol. Why?. The answer lies on the degree of stability of the ions formed. Try doing delocalisation of the negative electron on the alkoxide and phenoxide ions.
negative charge on phenoxide ion can be delocalised, thus increasing its stability.
OH OH
Hydration of 3-phenyl-1-butene in dilute H2SO4 is not good method to prepare 3phenyl-2-butanol, Because 2-phenyl-2-butanol is obtained, why?
OH H2O, H+
CH3
Hg(OAc)2 NaBH4
BH3.THF H2O2
H2, Raney Ni
NaBH4
Show how you would synthesis the following alcohols by adding an appropriate grignard reagent to formaldehyde?
a)
OH
b) OH
c)
CH2OH
Show how you would synthesise each alcohol by adding appropriate Grignard reagent to a ketone
a) 1-Methylcyclohexanol b) Ph3COH
Give the grignard reagent and carbonyl compound that can be used to prepare following alcohols:
CH3CH2CH2OH
OH
OH CH3CH2C-CH3 Ph
Write the mechanism for reaction of HBr with i) butanol ii) t-butyl alcohol
HCl
PBr3
SOCl2
OH
Provide the reagents for following reaction that shows a way to indirectly isomerize alcohols
OH OH
PCC
H2SO4
OH H2CrO4 PBr3
i) Na ii) CH3CH2CH2Br
http://www.chemguide.co.uk/
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