Download - Elementary analysis
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Elementary analysis
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Mass spectrometer
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n-hexane
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MS
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Alcohols, ethers, thiols
• Sweet• Hydrogen bonding• Hydrophilic• Hydrophobic• Oxidation
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12.1 Alcohols: Structure and Physical Properties
• An organic compound containing a hydroxyl group attached to an alkyl group
• Alcohols have the general formula R-OH
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Physical Properties
• R-O-H has a structure similar to that of water• Hydroxyl group is very polar• Hydrogen bonds can form readily
12.1
Str
uctu
re a
nd P
hysi
cal P
rope
rties
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Trends in Alcohol Boiling Points
CH3CH2OH
CH3O CH3
CH3CH2CH3 bp -42 oC
bp -23 oC
bp +78.5 oC
12.1
Str
uctu
re a
nd P
hysi
cal P
rope
rties
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Solubility
• Low molecular weight alcohols (up to 5-6 carbons) are soluble in water– Very polar – Hydrogen bond with the water molecule
• CH3CH2OH very soluble
• CH3OCH3 barely soluble
• CH3CH2CH2CH2OH, 7 g per 100 mL
– HOCH2CH2CH2CH2OH is very soluble (two OH groups)
12.1
Str
uctu
re a
nd P
hysi
cal P
rope
rties
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Use of alcohols
• Which alcohols do we know?
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12.3
Med
ical
ly Im
port
ant A
lcoh
ols
• Very viscous, thick• Has a sweet taste• Non-toxic• Highly water soluble• Used in:
• Cosmetics• Pharmaceuticals• Lubricants
• Obtained as a by-product of fat hydrolysis
1,2,3-Propanetriol
OH CH2CH CH2OHOH
glycerol(in fats,a moisturizer)
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Sorbitol
OH
OH
OH
OH
OH
HO
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1,2-ethanediol
HO
OH
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Naming of alcohols
• Find longest chain in which the OH group is included
• -ol• Lowest possible number• Diols, triols etc.
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12.4 Classification of Alcohols
• Alcohols, depending on the number of alkyl groups attached to the carbinol carbon, are classified as:– Primary– Secondary – Tertiary
• Carbinol carbon is the carbon bearing the hydroxyl group
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Structures of Different Alcohol Categories12
.4 C
lass
ifica
tion
of A
lcoh
ols
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12.5 Reactions Involving AlcoholsPreparation of Alcohols• Hydration
– Addition of water to the carbon-carbon double bond of an alkene produces an alcohol
– A type of addition reaction called hydration– Requires a trace of acid as a catalyst
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• Hydrogenation– Addition of hydrogen to the carbon-oxygen double
bond of an aldehyde or ketone produces an alcohol– A type of addition reaction– Also considered a reduction reaction– Requires Pt, Pd, or Ni as a catalyst
Preparation of Alcohols12
.5 R
eacti
ons
Invo
lvin
g Al
coho
ls
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Dehydration of Alcohols• Alcohols dehydrate with heat in the presence of strong
acid to produce alkenes• Dehydration is a type of elimination reaction
– A molecule loses atoms or ions from its structure– Here –OH and –H are removed / eliminate from adjacent carbon
atoms to produce an alkene and water– A reversal of the hydration reaction that forms alcohols
12.5
Rea
ction
s In
volv
ing
Alco
hols
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Zaitsev’s Rule• Some alcohol dehydration reactions produce a
mixture of products• Zaitsev’s rule states that in an elimination
reaction the alkene with the greatest number of alkyl groups on the double bonded carbon is the major product of the reaction
CH3
OH
CH3
major product:more substitutedalkene
warmH2SO4 orH3PO4
12.5
Rea
ction
s In
volv
ing
Alco
hols
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Oxidation Reaction of Primary Alcohols
• Primary alcohols usually oxidize to carboxylic acids
• With some care (using CrO3 as the reagent) an aldehyde may be obtained
12.5
Rea
ction
s In
volv
ing
Alco
hols
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Oxidation Reaction of Secondary Alcohols
• Secondary alcohols oxidize to ketones – This reaction is also an elimination of 2H
• The usual oxidizing agent is a Cr(VI) species• Tertiary alcohols do not oxidize as there is no
H on the carbonyl carbon to remove
12.5
Rea
ction
s In
volv
ing
Alco
hols
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12.6 Oxidation and Reduction in Living Systems
• Oxidation– loss of electrons
• Reduction– gain of electrons
• These changes are easily detected in inorganic systems with formation of charged ions
• In organic systems it is often difficult to determine whether oxidation or reduction has taken place as there might be no change in charge
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Organic Oxidation and Reduction• In organic systems changes may be tracked:
– Oxidation• gain of oxygen• loss of hydrogen
– Reduction• loss of oxygen• gain of hydrogen
R CH
HH
R CH
OHH
R CH
O R COH
O
12.6
Oxi
datio
n an
d Re
ducti
on in
Liv
ing
Syst
ems
More oxidized form
More reduced formAlkane Alcohol Aldehyde Acid
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Biological Oxidation-Reduction • Oxidoreductases catalyze biological
redox reactions • Coenzymes (organic molecules) are
required to donate or accept hydrogen• NAD+ is a common coenzyme
O CCOO
-
HCH2COO
-
H OCCOO
-
CH2COO
-
+ NAD+
Malatedehydrogenase
+ NADH + H+
12.6
Oxi
datio
n an
d Re
ducti
on in
Liv
ing
Syst
ems
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•
Oxidation of ethanol
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12.7 Phenol• Phenols are compounds in which the hydroxyl group is
attached to a benzene ring– Polar compounds due to the hydroxyl group– Simpler phenols are somewhat water soluble– Components of flavorings and fragrances
• Phenols have the formula Ar-OH– Ar must be an aromatic ring (e.g., Benzene)
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Phenol Derivatives
• Widely used in healthcare as: – Germicides– Antiseptics – Disinfectants
12.7
Phe
nols
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Green tea
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Phenol Reactivity
• Phenols are acidic, but not as acidic as carboxylic acids
• They react with NaOH to give salt and water
OH+NaOH
ONa
+H2O
12.7
Phe
nols
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12.8 Ethers• Ethers have the formula R-O-R
– R can be aliphatic or aromatic• Ethers are slightly polar due to the polar C=O
bond• Do not hydrogen bond to one another as there
are no –OH groups
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Ether Physical Properties
• Ethers have much lower boiling points than alcohols due to the lack of hydrogen bonding
12.8
Eth
ers
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Common Names of Ethers• Common names for ethers consist of the names
of the two groups attached to the O listed in alphabetical order (or size) and followed by ‘ether’
• Each of the three parts is a separate word• Name:
CH3 CH O
CH3
CH3
CH3CH2O
Isopropyl methyl ether Ethyl phenyl ether
12.8
Eth
ers
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IUPAC Nomenclature of Ethers• The IUPAC names for ethers are based on the
alkane name of the longest chain attached to the oxygen
• The shorter chain is named as an alkoxy substituent– Alkane with the -ane replaced by -oxy– e.g., CH3CH2O = ethoxy
CH3CH2CH2CH2CH2-O-CH3
1-methoxypentane
12.8
Eth
ers
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Reactivity of Ethers• Chemically, ethers are moderately inert
– Do not normally react with reducing agents or bases– Extremely volatile– Highly flammable = easily oxidized in air
• Symmetrical ethers may be prepared by dehydrating two alcohol molecules– Requires heat and acid catalyst
CH3 CH2O CH2 CH3
CH3 CH2OH CH3CH2OH
H+ (H3PO4) warm
12.8
Eth
ers
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Medical Uses of Ethers• Ethers are often used as anesthetics• Accumulate in the lipid material of nerve cells
interfering with nerve impulse transmission• Today halogenated ethers are used routinely as
general anesthetics– Less flammable– Safer to store and to work with
CH3 CH2O CH2 CH3
Diethyl ether - First successfulgeneral anesthetic
CH3O C C HF
F
Cl
Cl
Penthrane
12.8
Eth
ers
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12.9 Thiols• Thiols have the formula R-SH• Similar in structure to alcohols with S replacing O• Disulfides have the formula R-S-S-R
– R may be aliphatic or aromatic• Name is based on longest alkane chain with the
suffix –thiol position indicated by number
CH2 CH2CH3 CHSH
CH3
3-methyl-1-butanethiol
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Thiols and Scent• Thiols, as many other sulfur-containing
compounds can have nauseating aromas– Defensive spray of North American striped skunk– Onions and garlic
• Compare with pleasant scents below
12.9
Thi
ols
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Naming Thiols
• Write the IUPAC name for the thiols shown
12.9
Thi
ols
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Disulfide Formation
The thiol-disulfide redox pair controls a critical factor in protein structure called a disulfide bridge
– Two cysteine molecules (amino acids) can undergo oxidation to form cystine
– Forms a new bond called a disulfide bond
12.9
Thi
ols
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Disulfide Formation and Insulin Structure12
.9 T
hiol
s
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Reaction Schematic
Ketone
Alcohol
Aldehyde
NO REACTION DehydrationIf primary
If tertiary
If secondary
+ H+ and heat
Alkene
Hydration Carbonyl
Reduction
Oxidation
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Summary of Reactions1. Preparation of Alcohols
a. Hydration of Alkenesb. Reduction of Aldehyde or Ketone
2. Reactions of Alcoholsa. Dehydration b. Oxidation
i. Primary alcohol to aldehydeii. Secondary alcohol to ketoneiii. Tertiary alcohol does not react
3. Dehydration Synthesis of an Ether
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NinhydrinO
O
O