Transcript Alcohols, ethers and thiols

ALCOHOLS, ETHERS AND
THIOLS
MATERIAL ADAPTED FROM: INTRODUCTION TO GENERAL,
O R G A N I C A N D B I O C H E M I S T R Y 7 TH E D .
BY: HEIN, BEST, PATTISON, ARENA
FUNCTIONAL GROUPS
• Alcohols –OH group
• Phenol- OH group off of an aromatic ring
• Ethers- R-O-R, where R is an alkyl group or aromatic ring
• Aldehydes-
*terminal H
• Ketones-
*no terminal H
MORE FUNCTIONAL GROUPS
• Thiols- R-SH
*thio means sulfur!
• Ester- R-COO-R
• Carboxylic acid- R-COOH
• Amines- R-NH2, R2NH, or R3N
• Amides- R-CON-R
CONNECTION BETWEEN ALCOHOLS,
ETHERS, THIOLS AND PHENOLS
• All of these groups are derived from the structure of
water, with a few substitutions.
• Alcohols- remove one H from water and add an alkyl
group
• Thiols- replace the O in an alcohol with an S
• Ethers- remove both H atoms from water and add two
alkyl groups in their place
• Phenols- replace the alkyl group from alcohols with an
aromatic ring
• *Functional groups are important because they
determine the “function” and properties of the molecule
ALCOHOLS
• Classified as primary, secondary and tertiary,
depending on whether the carbon attached to the
OH group is connected to 1, 2 or 3 other carbon
atoms.
• Polyhydroxy alcohols or polyols- molecules that
have more than 1 –OH group per molecule
PRACTICE
• For the following, determine if they are primary,
secondary or tertiary alcohols:
• 1) CH3OH
• 2) CH3CH(OH)CH3
• 3)CH3CH(CH3)CH2OH
• 4) CH3C(CH3)2OH
IUPAC NAMING OF ALCOHOLS
• 1) Select the longest continuous chain of carbon
atoms containing the hydroxyl (OH) group.
• 2) Number the carbons so that the lowest number
carbon is closest to the –OH group.
• 3) Name the parent alcohol by replacing the –e at
the end of the alkane name with an –ol.
• Designate the position of the –OH group by placing
the hyphenated carbon number in front of the
parent alcohol name.
• 4) Name each side chain or branch alphabetically,
and use numbers to designate its position off the
main chain.
PRACTICE NAMING AND DRAWING
ALCOHOLS
• 1)
• 2)
• 3)
• 4)3,3-dimethyl-2hexanol
• 5) 2-ethyl-1pentanol
• 6) 2-bromo-4-ethyl3-heptanol
COMMON NAMES
• Alcohols have a lot
of common names
so it is important to
recognize these for
safety in lab.
• Examples:
• 1) isopropyl alcohol
• 2) n-butyl alcohol
• 3) sec-butyl alcohol
• 4) tert-butyl alcohol
PHYSICAL PROPERTIES OF ALCOHOLS
• High boiling points
compared to their
alkanes
• Example:
Methane -162°C
Methanol 65°C
• Boiling points of alcohols
increases with the
increasing number of
carbon atoms.
• What part of their
structure accounts for
their high boiling points?
• Most are soluble in water.
Solubility becomes
lessened as the carbon
chain lengthens. WHY?
• Predict the effect of
dihydroxy alcohols on
solubility in water.
ACIDIC/BASIC PROPERTIES OF
ALIPHATIC ALCOHOLS
• Similar to water…
which is
amphiprotic or
amphoteric, which
means it can act as
an acid OR base in
solution.
• In strong acids, it will
accept a proton
and become an
oxonium ion.
• Small alcohols, like
methanol and
ethanol, have same
acid strength as
water. Larger acids
are weaker.
REACTION WITH ALKALI METALS
• Just like water, alcohols react with group 1 metals to
form an anion and hydrogen gas.
• Example:
2 CH3CH2OH + 2 Na  2 Na+ + -OCH2CH3 + H2(g)
• The resulting anion is called an alkoxide ion (RO-)
and is a stronger base than hydroxide! These are
used in industry when a strong base is required.
• Primary>secondary>tertiary alcohols as far as
reaction with sodium and potassium. As molar mass
of alcohol increases, the reactivity decreases.
OXIDATION OF ALCOHOLS
• Carbon atoms exist in progressively higher stages of
oxidation in different functional groups:
Alkanes  Alcohols  aldehydes and ketones 
carboxylic acids  carbon dioxide
• Converting alcohols to aldehydes, ketones and
carboxylic acids allows scientists to make plastics,
antibiotics, fertilizers, etc.
• Common oxidizing agents: oxygen from the air,
KMnO4 in basic solution, K2Cr2O7 in acidic solution.
OXIDATION OF ALCOHOLS
Source:
http://dwb4.unl.edu/Chem/CHEM869E/CHEM869ELinks/www.siue.edu
/~rdixon/classes/chem120b99/lectures/chpt-14/chpt-14.html
PRACTICE
• 1) Determine the products when the following react
with potassium dichromate and concentrated
sulfuric acid:
• A) 1-propanol
• B) 2-propanol
• C) cyclohexanol
DEHYDRATION OF ALCOHOLS
2 types:
1) Intramolecular dehydration of alcohols forms alkenes
Sulfuric acid is used as well as heating up the reaction
Water is removed from a single alcohol molecule
Secondary and tertiary alcohols yield alkenes
If there are two neighboring carbons that have
hydrogens that may leave with the OH group, follow
Saytzeff’s rule.
• Saytzeff’s rule: If there is a choice of positions for the
carbon-carbon double bond, the preferred location is
the one that gives the more highly substituted alkene.
• Example: 2-butanol  2-butene + 1-butene
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DEHYDRATION OF ALCOHOLS
• 2) Intermolecular dehydration of alcohols forms
ethers
• Two alcohol molecules come together, eliminate
water and form an ether…(called a condensation
reaction)
• ONLY works for primary alcohols!!!!
• Depends on temperature and number of reactant
molecules…lower temps and higher concentration
of alcohol yield ethers.
ESTERIFICATION
• Alcohols can react with carboxylic acids to form
esters and water.
• Important reaction…discussed more in later
chapter.
Photo Source:http://chempaths.chemeddl.org/services/chempaths/?q=book/
General%20Chemistry%20Textbook/1352/properties-organic-compounds-andother-covalent-substances&title=CoreChem:Esters
HYDROXYL GROUP IMPORTANCE
• The –OH group is a gateway to many organic
reaction AND biochemical reactions as well.
• Example: Fats are degraded from alkanes to
alkenes…then hydrated to form an alcohol.
• Then, the alcohol is oxidized to form a ketone. This
process is necessary to use energy from fats.
• 10% of infants that die of SIDS cannot degrade fats.
It is hypothesized that this lack of ability to use fat for
energy may be a leading cause of SIDS.
MAKING ALCOHOLS
• Generally, the reverse of the reactions that we have
discussed so far are the ones used to make alcohols.
• 1) Hydrolysis of esters
• 2) Alkaline hydrolysis of an alkyl halide (primary and
secondary alcohols only)
• 3) Catalytic reduction of aldehydes and ketones to
make primary and secondary alcohols.
• These starting materials are expensive, so specific methods are
devised for specific alcohols.
METHANOL
• Used to be made by heating wood in a non-oxygen
atmosphere…called destructive distillation.
• Early 1920s, began catalytic hydrogenation of
carbon monoxide…
• CO + 2 H2  CH3OH
• Requires catalysts, high temp and high pressure
• Can be made from coal as well, significant as a
non-petroleum source
• Is useful in conversion to manufacture of other
chemicals, polymers, etc.
ETHANOL
• Aka: grain alcohol, ethyl alcohol, spirit
• Earliest and most widely known alcohol
• Prepared by fermentation of starch and sugar (for
drinking)
• Pure ethanol is hygroscopic (water seeking), reaches
equilibrium at 95.6% ethanol.
• For industrial uses, it is made by acid-catalyzed addition of
water to ethylene.
• Uses: intermediate in manufacture of acetaldehyde,
acetic acid, ethyl acetate and diethyl ether
• Ethanol for industrial use is usually denatured by adding
small amounts of methanol and other chemicals that are
hard to remove and cannot be consumed.
ISOPROPYL ALCOHOL (2PROPANOL)
• Synthesized from propene and water, catalyzed by
acid…2 propanol, not 1-propanol, is produced
because of Markovnikov’s rule.
• Low-cost alcohol, used in production of acetone
• Principle component in rubbing alcohol
• Also used as an industrial solvent
ETHYLENE GLYCOL (1,2-ETHANEDIOL)
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Simplest alcohol containing 2 –OH groups
Prepared from ethylene, derived from petroleum
Common uses:
Preparation of synthetic fibers such as Dacron and
Mylar
Major ingredient in “permanent” antifreeze for
vehicles
As a solvent in paint and plastics industries
In the formulation of printing ink and ballpoint pen
ink
EXTREMELY TOXIC IF INGESTED!!!!!
GLYCEROL (1,2,3-PROPANETRIOL)
• Also known as glycerine
• Syrupy liquid with a super sweet taste, about 0.6 times as
sweet as cane sugar.
• It’s a by-product of processing animal and vegetable
fats to make soap and other products.
• Made commercially from propene
• Uses:
• Raw material in manufacture of polymers and explosives
• An emollient in cosmetics
• Humectant in tobacco products
• Sweetener
PHENOLS
• Naming:
• Most are named as derivatives of the parent
compound, much like aromatics
• Para, Meta and Ortho apply here too
• Examples:
A FEW COMMON PHENOLS
Vanillin
PROPERTIES OF PHENOLS
• In its pure state, phenol is a colorless, crystalline solid
with a melting point at 41°C and a characteristic
odor.
• Highly poisonous…can cause nausea, vomiting and
death from respiratory collapse.
• Weak acid…
• Widely used as an antiseptic and disinfectant…one
of the first used in hospitals as a disinfectant.
MAKING PHENOLS
• Benzene and propene are mixed in the presence of
acid to form cumene.
• Cumene is then oxidized to form cumene
hydroperoxide, which is then treated with dilute
acid to form phenol and acetone.
ETHERS
• IUPAC rules for naming ethers:
• 1) Select the longest carbon chain and label it with
the name of the corresponding alkane.
• 2) Change the –yl ending of the other hydrocarbon
group to –oxy to obtain the alkoxy group name.
• Examples: CH3O- methoxy
• CH3CH2O- ethoxy
• Phenyl phenoxy
• 3) Combine the two names from step 1 and 2,
giving the alkoxy name and its position on the
longest carbon chain first, to form the ether name.
PRACTICE
• 1)
• 4) ethoxyethane
• 5) 2-methyl-2-propoxy-2methylpropane
• 2)
• 6) ethoxybenzene
• 3)
STRUCTURES AND PROPERTIES OF
ETHERS
• Ether molecules have a
bent shape, much like
that of water.
• More polar than alkanes,
but less polar than
alcohols, since no H is
attached to the O.
• Can hydrogen bond with
water molecules and
acids, which accounts for
its solubility in these
substances.
• Ethers are very good
solvents for organic
compounds. Both polar
and nonpolar substances
can dissolve in ethers.
• Little chemical reactivity,
but they have a great
value as solvents.
• Use can be dangerous
because of their volatility
and creation of explosive
vapors with air.
• Oxygen slowly reacts with
ethers to form unstable
peroxides.
PREPARATION OF ETHERS
• Intermolecular
dehydration of
alcohols- (we already
did this!)
• Williamson synthesisalkyl halides can
react with sodium
alkoxides
• The alkyl halide can
be primary or methyl
but NOT secondary or
tertiary.
• The alkoxide can be
methyl, primary,
secondary, or tertiary.
• Write equations for the
preparation of:
• A) 1-propoxybutane
B) Methyl phenyl ether
C) Benzyl ethyl ether
THIOLS