Download 1-13 acids esters fats

Carboxylic Acids, Esters and Fats (1.6)
Carboxylic acids and esters are like aldehydes and ketones in that they contain the carbonyl functional group.
O
O
-OH
C
carbonyl
hydroxyl
O
C OH
carboxylic acid
R'
C O C R
ester
Carboxylic acids are the acids found in organic molecules, the carbon based compounds necessary for life.
The term “carboxylic” is derived from carbonyl and “hydroxyl”, the two structures which make an organic
acid.
None of the carboxylic acids are classified as strong acids. Remember a strong acid is an acid which fully
dissociates in an aqueous environment. This is not to say an organic acid is not able to cause harm.
Small concentrations of hydrogen ion given off by organic acids are potent enough to kill most microscopic
organisms and cause tissue irritation and/or damage to larger organisms. Acetic acid is the acid found in
vinegar, a pickle stored in its brine may not spoil and be edible for years partly because of the organic acid
from the vinegar kills the bacteria which will cause spoilage.
Carboxylic acids are found in citrus fruits, crab apples, rhubarb and other foods characterized by sour, tangy
taste. Carboxylic acids are also distinctive and tracking fogs can follow odours and specific combinations of
carboxylic acids from a person’s sweat or feet.
Physical Properties
These molecules are more polar than alcohols as they have a more polar region and they can also form
hydrogen bonds because of the oxygen bonded to the hydrogen. The Melting point and boiling points and
solubility are therefore much higher.
Like alcohols the solubility diminishes as the molecule gets larger. Thus, smaller molecules are very soluble, but
larger molecules are virtually insoluble.
These molecules are also organic acids and will test RED in a litmus test or be acidic.
This can be used as a test to determine that an unknown substance is indeed a carboxylic acid from other
types of organic molecules.
Naming carboxylic acids:
1.
count number of carbons in the longest carbon chain containing the –COOH group
2.
replace the –e with the suffix –oic acid
3.
compound containing multiple -COOH groups do not drop the –e but add a di- or tri- to the ending –
carboxylic acid or add a di- or tri- to the suffix –oic acid.
Structural Formula
Condensed Structural
Formula
IUPAC
Common Name
O
CH3
C OH
O
CH3
CH2
C OH
O
HO C CH2
O
C OH
CH3COOH
CH3CH2COOH
HOOCCH2COOH
ethanoic acid
acetic acid
propanoic acid
-
propandioic acid
malonic acid
Synthesis of Carboxylic acids
The oxidation of a primary alcohol will lead through an aldehyde to a carboxylic acid.
[O] signifies Oxidation in the presence of a catalyst.
This is a multi-step process from an alcohol as a starting molecule. NOTE- the alcohol must be a PRIMARY
alcohol to form an aldehyde and then a carboxylic acid.
Reactions:
Ionization:
The first definition of an acid is a proton donator. A carboxylic acid donates the hydrogen attached to the
oxygen fulfilling the definition of an acid.
O
O
H+
CH3 C O
CH3 C O H
This reaction has a double arrow. The reason is that organic acids are weak acids and form an equilibrium in
a solution. Only a small percentage of the acids give up their hydrogen. Once the equilibrium has been
reached the concentration of acid, hydrogen ion and anion remain constant. In the above case we have acetic
acid, acetate anion and hydrogen ion.
Acid/Base:
Just as you can neutralize an inorganic acid, organic acid can be neutralized. The same product is formed, a
salt and water. If sodium hydroxide is used to neutralize acetic acid the following reaction occurs.
O
O
H
H
O
NaOH
CH3 C O Na
CH3 C O H
ethanoic acid
sodium hydroxide
sodium ethanoate
water
Acid Anhydrides:
Two carboxylic acids can be combined to form an acid anhydrides. The term anhydride combines an- and hydride. The prefix an- means anti, in this form it is describing a loss. The loss is of water, which is where the
hydride portion comes to play. So, two carboxylic acids are :
O
CH3
C O H
O
H O C CH3
CH3
O
O
C O
C CH3
H2O
Sources and uses
The carboxylic acid function group can be found in all facets of nature. A few of the more common acids are:
 formic acid, a chemical defense for some ants,
 acetic acid, found in vinegar,
 propanoic acid, found in cheese,
 butanoic acid, from spoiled butter,
 citric acid, from citric fruits, lactic acid, from dairy products,
 palmitic acid, found in palm oil
 stearic acid, from beef fat.
ESTERS are compounds which are made by reacting an alcohol and an organic acid together.
O
+
RC
R'OH
H2SO4
OH
acid
O
+
RC
H2O
OR'
+
alcohol
ester
+
water
(H2O is made from the OH of the acid and the H of the alcohol. This reaction is easily reversible
Naming Esters

first name the alkyl or aryl group from the alcohol

the second part of the name is obtained by replacing the “-ic” of the acid name by the suffix “-ate”
E.g.(draw the reaction molecules)
Ethyl alcohol reacts with propanoic acid to produce ethyl propanoate.
Butyl methanoate is made from the condensation of methanoic acid and butanol.
#1,2 p. 50
Properties of Esters

esters are often sweet smelling.

used in candy making and perfumery

molecules are polar and thus soluble in H2O if the # of C’s is low

The most utilized ester is that found in soap. Soap pre-dates history.

The production is simple, boil a fat in wood ash. The fat is actually the carboxylic acid, hence the
name fatty acid. A fat like stearic acid, beef fat, would work very well for producing soap. A
component of wood ash is potassium hydroxide, which is a strong base. So, your average caveman
could easily produce soap by boiling some beef fat combined with ash from the campfire.

Other uses include dry cleaner fluids, pharmaceutical drugs, flavorings and scents. Methyl salicylate
can be found in wintergreen flavored mints
Reactions of Esters (p.51)
1. Esterification =
Acid + Alcohol  Ester + water
2. Hydrolysis =
Practice # 1 p. 53
Ester + Base  Acid + Alcohol + Base Cation
FATS
Fats and oils are very large ester molecules known as Lipids.
They are formed when a Glycerol is combined with three fatty acids through esterification.
Each hydroxyl form an ester linkage with a fatty acid and the whole molecule is called a triglyceride.
They can be the same (simple)or different (mixed) fatty acid combination on the glycerol.
Above we mentioned Soaps. Fatty acids in the presence of a strong base produce a sodium (or potassium) salt
and a glycerol.
Physical properties of fats and oils
Lipids with fatty acids that contain double bonds are referred to as
unsaturated and these molecules have far lower densities than
saturated lipids. The more doible bonds, the more unsaturated and the
lower density the lipid.
The resulting Boiling point and melting points are lower than saturated
lipids
Cis double bonds are kinks that produce liquids at room temperature
but trans double bonds significantly kink the chains and are able to
turn normal lipids to solids at room temperature.
This results in a trans-fat. Margarine should be an oil, but is not due to its trans- kinks
The problem is that these kinks cannot be metabolized because they are synthetic and not recognized by our
bodies. They result in a build up of fats in our body and vessels and can lead to significant health issues.
Homework:
1,2 p. 54
1-11 p. 55