alcoholsr-o-h classification ch 3, 1 o, 2 o, 3 o nomenclature: common names: “alkyl alcohol”...
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Alcohols R-O-H
Classification CH3, 1o, 2o, 3o
Nomenclature:
Common names: “alkyl alcohol”
IUPAC: parent = longest continuous carbon chain containing the –OH group.
alkane drop -e, add –ol
prefix locant for –OH (lower number for OH)
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CH3 CH3
CH3CHCH2CHCH3 CH3CCH3
OH OH4-methyl-2-pentanol tert-butyl alcohol
2-methyl-2-propanol 2o 3o
CH3
HO-CHCH2CH3 CH3CH2CH2-OH
sec-butyl alcohol n-propyl alcohol 2-butanol 1-propanol 2o 1o
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Physical properties of alcohols:
polar + hydrogen bonding
relatively higher mp/bp
water insoluble!
(except for alcohols of three carbons or less)
CH3CH2CH2CH2CH2CH2CH2CH2CH2CH2-OH
hydrophobic hydrophilic
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Oldest known organic synthesis:
“fermentation”
Sugar + yeast ethyl alcohol + CO2
Grape juice => “wine”
Barley => “beer”
Honey => “mead”
Rice => “sake”
~5-11% ethanol
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Distillation of fermented beverages to produce “distilled spirits” with a greater percentage of ethyl alcohol (bp 78.3 oC).
Ethyl alcohol forms a binary azeotrope with water:
95% ethanol + 5% water (bp 78.15oC)
Diluted with water => “vodka” 40% ethyl alcohol in water.
“proof”: when aqueous alcohol is placed on a sample of gunpowder and ignited, the gunpowder will burn at a minimum concentration of 50% alcohol. This is called “100-proof”.
(proof = 2 * alcohol percent)
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Add oil of juniper => gin
Add peat smoke => scotch
Age in a burned barrel => whiskey
Add peppermint => schnapps
Etc.
Ethyl alcohol is a poison. LD50 = ~10g/Kg orally in mice.
Nausea, vomiting, flushing, mental excitement or depression, drowsiness, impaired perception, loss of coordination, stupor, coma, death may occur. (intoxication)
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Alcohols, synthesis:
1.
2.
3.
4. Hydrolysis of alkyl halides (CH3 or 1o)
5.
6.
7.
8.
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NR NR NR some
NR NR NR 1o/2o
NR NR
NR NR NR
R-H R-X R-OH
Acids
Bases
Active metals
Oxidation
Reduction
Halogens
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Alcohols, reactions:
R-|-OH
1. With HX
2. With PX3
3. (later)
RO-|-H
4. As acids
5. Ester formation
6. Oxidation
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1. Reaction of alcohols with HX: (#1 synthesis of RX)
R-OH + HX R-X + H2O
a) HX: HI > HBr > HCl
b) ROH: 3o > 2o > CH3 > 1o
c) May be acid catalyzed
d) Rearrangements are possible except with most 1o alcohols.
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CH3CH2CH2CH2-OH + NaBr, H2SO4, heat CH3CH2CH2CH2-Br
n-butyl alcohol n-butyl bromide
1-butanol 1-bromobutane
CH3 CH3
CH3C-OH + HCl CH3C-Cl (room temperature) CH3 CH3
tert-butyl alcohol tert-butyl chloride
2-methyl-2-propanol 2-chloro-2-methylpropane
CH3CH2-OH + HI, H+, heat CH3CH2-I
ethyl alcohol ethyl iodide
ethanol iodoethane
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Mechanism?
CH3-OH and most 1o alcohols react with HX via SN2 mechanism
3o and 2o react with HX via SN1 mechanism
Both mechanisms include an additional, first step, protonation of the alcohol oxygen:
R-OH + H+ R-OH2+ “oxonium ion”
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Whenever an oxygen containing compound is placed into an acidic solution, the oxygen will be protonated, forming an oxonium ion.
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Mechanism for reaction of an alcohol with HX:
CH3OH or 1o alcohols:
1) R-OH + HX R-OH2 + X
2) X + R-OH2R-X + H2O
RDS
SN2
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Mechanism for reaction of an alcohol with HX:
2o or 3o alcohols:
SN1
1) R-OH + HX R-OH2 + X
2) R-OH2 R + H2ORDS
3) R + X R-X
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May be catalyzed by acid.
SN2 rate = k [ ROH2+ ] [ X- ]
SN1 rate = k [ ROH2+ ]
Acid protonates the -OH, converting it into a better leaving group (H2O), increasing the concentration of the oxonium ion, and increasing the rate of the reaction.
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Rearrangements are possible (except with most 1o alcohols):
CH3 CH3
CH3CHCHCH3 + HBr CH3CCH2CH3 OH Br
Br-
CH3 CH3 [1,2-H] CH3
CH3CHCHCH3 CH3CHCHCH3 CH3CCH2CH3
OH2+ + + 2o carbocation 3o carbocation
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CH3CH2CH2CH2CH2-OH + HBr, H+, heat
CH3CH2CH2CH2CH2-Br
1o alcohol:No rearrangement, SN2
In the reaction of most 1o alcohols with HX you don't haveto worry about the possibility of rearrangements. The mechanismis SN2 and does not involve carbocations.
1-pentanol
1-bromopentane
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Most 1o? If large steric requirement…
CH3 CH3
CH3CCH2-OH + HBr CH3CCH2CH3
CH3 Brneopentyl alcohol 2-bromo-2-methylbutane
CH3 CH3 CH3
CH3CCH2-OH2+ CH3CCH2+ CH3CCH2CH3
CH3 CH3 + 1o carbocation 3o carbocation
[1,2-CH3]
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2. With PX3
ROH + PX3 RX
a) PX3 = PCl3, PBr3, P + I2
b) No rearrangements
c) ROH: CH3 > 1o > 2o
CH3 CH3
CH3CCH2-OH + PBr3 CH3CCH2-Br CH3 CH3
neopentyl alcohol 2,2-dimethyl-1-bromopropane
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3. Dehydration
(later)
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4) As acids.
a) With active metals:
ROH + Na RONa + ½ H2
b) With bases:
ROH + NaOH NR!
CH4 < NH3 < ROH < H2O < HF
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CH3CH2OH + NaOH H2O + CH3CH2ONa
WA WB SA SB
CH3CH2OH + CH3MgBr CH4 + MgBr(OCH2CH3)
SA SB WA WB
CH3OH + NaNH2 NH3 + CH3ONa
SA SB WA WB
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5. Ester formation.
CH3CH2-OH + CH3CO2H, H+ CH3CO2CH2CH3 + H2O
CH3CH2-OH + CH3COCl CH3CO2CH2CH3 + HCl
CH3-OH + CH3SO2Cl CH3SO3CH3 + HCl
Esters are alkyl “salts” of acids.
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R COH
OR C
ONa
OR C
OR'
O
carboxylic acid sodium salt ester
R S
O
O
OH R S
O
O
OK R S
O
O
OR'
sulfonic acid potassium salt ester
HO P
O
OH
OH HO P
O
OH
OR HO P
O
OR
OR RO P
O
OR
OR
phosphoric acid monoester diester triester
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"Lasso" chemistry
R CO H
OR C
O R'
OH-O-R'
H+
+ + H2O
CH3CO
O H
+ H-O CHCH3
CH3 H+CH3C
O
O CHCH3
CH3 + H2O
acetic acid isopropyl alcohol isopropyl acetate
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R CCl
OR C
O R'
OH-O-R'
H+
+ + HCl
CH3CO
Cl
+ H-O CHCH3
CH3 H+CH3C
O
O CHCH3
CH3 + HCl
acetyl chloride isopropyl alcohol isopropyl acetate
acid chloride + alcohol --> ester
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R S
O
O
Cl
sulfonyl chloride
+ H-O-R R S
O
O
O-R + HCl
alcohol sulfonate ester
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oxidation states of carbon
- oxidation
CH4 CH3OH CH2O HCO2H CO2
-4 -2 0 +2 +4
reduction -
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6. Oxidation
Oxidizing agents: KMnO4, K2Cr2O7, CrO3, NaOCl, etc.
Primary alcohols:
CH3CH2CH2-OH + KMnO4, etc. CH3CH2CO2H
carboxylic acid
Secondary alcohols: OH O CH3CH2CHCH3 + K2Cr2O7, etc. CH3CH2CCH3
ketoneTeriary alcohols:
no reaction.
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Primary alcohols can also be oxidized to aldehydes:
CH3CH2CH2-OH + C5H5NHCrO3Cl CH3CH2CHO
pyridinium chlorochromate aldehyde
or
CH3CH2CH2-OH + K2Cr2O7, special conditions
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Alcohols, synthesis:
1.
2.
3.
4. Hydrolysis of alkyl halides (CH3 or 1o)
5.
6.
7.
8.
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Alcohols, reactions:
R-|-OH
1. With HX
2. With PX3
3. (later)
RO-|-H
4. As acids
5. Ester formation
6. Oxidation