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CARBOXYLIC ACIDS
• Since the carboxyl group is polar, carboxylic acids contain dipole-dipole forces, London forces and are able to hydrogen bond.
• Therefore carboxylic acids will have high melting and boiling points and will be soluble in water.
• Contain the carboxyl functional group
C
O
OH
NAMING CARBOXYLIC ACIDS
1. Identify the longest chain containing the carboxyl group, remove the “e” and add “oic acid”.
Examples
C
O
HO
methanoic acid
C
H3C
O
OH
ethanoic acid
H
Naming Carboxylic Acids
• Any substituents are numbered using the lowest sum.
• The carboxyl carbon is always C-1 on a chain, so no locator number is needed. Carboxylic acids rank over aldehydes, ketones, alcohols, alkenes and alkynes
Examples:O
OH
O
OH
COOH O
OH
propanoic acid
benzoic acid
2-ethylhexanoic acid pent-3-enoic acid
O OH
O
O OH
O
OH
5-oxo-2-propylhexanoic acid
2-(3-hydroxypropyl)hexanedioic acid
Multiple Carboxyl Groups
• When naming multiple carboxyl groups, the suffix –dioic acid is used for acids with a carboxyl group at each end of the parent chain.
• Note that the full alkyl name is used (the ‘e’ is not dropped)
Examples:
O O
HO OH
O OHO
OH
propanedioic acid
2-ethyl-5-methylhexanedioic acid
Ring StructuresKeep the “e” and add suffix “carboxylic acid”.
O
OH
O
OH
OOH
cyclohexanecarboxylic acid
cyclohexanedicarboxylic acid
Expanded Molecular FormulasCarboxyl group is represented by COOH
O
OH
HOOCCH2CH2CH2CH3
COMMON ORGANIC ACIDS
C
O
HO
formic acidmethanoic acid
(ant sting)
H
C
H3C
O
OH
acetic acidethanoic acid
(vinegar 3-4 % solution)
O
OH
butyric acidbutanoic acid(rancid butter)
HO
O
OH
lactic acid2-hydroxypropanoic acid
(causes muscle cramps due to O2 debt)
Making Carboxylic Acids: An Oxidation Reaction
aldehyde + water carboxylic acidKMnO4
H2Cr2O7
C C
O
ethanal
HH
H
H
+ H2OKMnO4
H2Cr2O7C C
O
HHO
H
H
ethanoic acid(acetic acid)
+ 2H+
What is an ester?
R
C
O
R'
O
• Made from an alcohol and a carboxylic acid.
Making an Ester
carboxylic acid + alcohol ester + waterH2SO4
C
O
OH
ethanoic acid(acetic acid)
+ + H2OCH
H
O
HC
H
H
H
C
O
C
H
H
H
C
H
H
H
O
methanol methylethanoate(methylacetate)
H2SO4/
H
NAMING• An ester has two parts – the part that comes from the alcohol
and the part that comes from the carboxylic acid
• Convert the suffix “(a)nol” ending of the alcohol to ‘yl’
• Convert the ‘oic acid’ ending of the carboxylic acid to “oate”
i.e. “alkyl oate”
• Note the space between the alkyl and oate names
CH2CH3
C
O
H3C
O
methyl propanoate
alcohol Carboxylic acid
Side Chains on the Alcohol Side• The carbon atoms that are attached to an oxygen atom
are assigned as C-1 (this means that you are numbering atoms from the middle of the molecule)
HH
C
H3
C 3
CO
C
O
H3
C
12
1-methylethyl ethanoate
(isopropyl ethanoate)
• If there is a side chain attached to the alcohol part, then the side chain names are attached to the ‘akyl’ part of the ester name
12
Side Chains on the Acid Side
• It there are side chains attached to the carboxylic acid part, then the side chain names are attached to the ‘oate’ part of the ester name
HH
C CC
OC
O
H3
HC
HC3
3 ethyl 2-methylpropanoate12
32
Side Chains Everywhere!
HH
C CC
OC
O
H3
HC
HC3
3
HC3
HC3
12
3
41
2
1-methylethyl 2-methylbutanoate
More Reactions of Esters
Hydrolysis (breaking down an ester)
ester + excess water alcohol + carboxylic acid
CO
HOethanoic acid(acetic acid)
++ H2O
H2SO4/
C H
H
O
H CH
HH
CO
CH
HH
CH
HH
O
methanolmethylethanoate(methylacetate)
H2SO4/
H
Waxes• Waxes are mixtures of esters having carbon
chains in the range of 16 to 34 carbons on each side of the ester linkage.
H3C(H2C)7
CO
(CH2)29CH3
O
Example
Beeswax
• Since the hydrocarbon chains are so long, waxes are very water repellant.
• Biological Importance: fruit, leaves, insects
Fats and Oils• Fats and oils are triesters of glycerol that contain at least one fatty acid.• Fatty acids are carboxylic acids that contain 14-18 carbons and having varying degrees of
unsaturation
H C C
H
C
OH
glycerol1,2,3-propanetriol
OH
HH
H
OH
stearic acid
CH3(CH2)15 C
O
OH
glycerol + 1 fatty acid --> monoglyceride + water
glycerol + 2 fatty acids --> diglyceride + water
glycerol + 3 fatty acids --> triglyceride + water
Salicylates
• Contain salicylic acid.• Most common is acetyl salicyclic acid “ASA”
(AKA aspirin) which is used for pain relief and as an antiseptic.
HO
O
HO
salicylic acid
O
OHO
acetyl salicylic acidASA
O
OH
Odours of Selected Esters• Esters occur naturally in many plants and
are responsible for the odours of fruits and flowers. Synthetic esters are often added as flavourings to processed foods, and as scents to cosmetics and perfumes.