SAM Organic Chemistry Esters and Triglycerides

8/7/2019 SAM Organic Chemistry Esters and Triglycerides

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SUBTOPIC: ESTERS

Functional group

O

R-C-O-R

1) Name of functional group:

2) Name of family:

3) Uses:

a. Short chain esters

i. food flavouring compounds

ii. perfumes

b. long chain estersi. animal fats

ii. vegetable oils

Nomenclature1) Identify parent chain, which is the longest continuous carbon chain containing ester fg

2) No need to designate the position of ester fg bc it always assume position no 1.

3) Replace the suffix ane with oate

a. Eg:

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Physical properties

Solubility in water

1) The possible hydrogen bonds btw esters and water is not very extensive

2) Alkyl group hinders water molecules from coming close3) Therefore form hydrogen bond at a distance (weak hydrogen bond)

4) Esters are sparingly soluble in water compared to carboxylic acids and alcohols.5) Water solubility decreases with increasing molecular mass

Boiling points/melting points

1) Bp of esters are lower than bp of alcohols and carboxylic acid

2) Esters are polar cpds but they cannot form strong hydrogen bonds to each other

3) Diagram:

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Physical state

- Lower esters may be volatile

-Higher esters are less volatile

Chemical properties

Formation of esters1) The name of chemical reaction is ESTERIFICATION

2) The type of reaction is condensation reaction

3) Esters can be prepared from carboxylic acids and alcohols

4) 3 stages are involved in the preparation of an ester

a. esterification (using reflux apparatus)

i. A carboxylic acid and an alcohol are placed in the round bottom flask with anti-bumpings .

ii. Concentrated sulfuric acid is added as a catalyst to speed up the rate of reaction

iii. Then they are heated under reflux for half an hour

iv. Diagram:

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Hydrolysis of ester

1) Acidic hydrolysis

a. Ester can be hydrolysed into carboxylic acid and alcohol in the presence of acid

b. Acid such as sulfuric acid, is used as catalyst to speed up the rate of reaction

c. Acid is used in trace amountd. Equation:

2) Alkaline hydrolysis

a. Ester can be hydrolysed into carboxylate ion and alcohol in the presence of alkali

b. The common alkalis used are NaOH and KOH

c. Equation:

d. Carboxylic acid is formed from carboxylate ion by adding dilute strong acid such as HCl

e. Equation

f. Alkaline hydrolysis is used in soap-making

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SUBTOPIC: TRIGLYCERIDES

1) Lipids a family of cpds, which are non-polar in nature and insoluble in water

2) Lipids can be classified into 3 classes

a. Triglyceridesb. Waxes

c. Steroids

3) Triglycerides are naturally occurring esters

4) General structure of a triglyceride molecule

Examples:

5) A triglyceride is derived from 1,2,3-propantriol and various carboxylic acids

6) Carboxylic acids have long hydrocarbon chain with even no of carbon atoms ( C12-C22) and haveno branches are known as fatty acids.

7) Triglycerides can be divided into fats and oils

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Chemical properties

1) Formation of a triglyceride

Example:

2) Hydrolysis

a. Acid hydrolysis

Example:

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b. Alkaline hydrolysis

Example:

3) Hydrogenationa. A process to convert oils into solid fats in the presence of high temperature, pressure and

Nickel catalyst

b. Addition reaction using hydrogen gas

c. Used in the making of margarine

d. In hydrogenation reaction, some or all multiple covalent bonds are converted into singlebonds

4) Determination of the degree of unsaturation in fats/oils

a. Addition reaction using bromine solution

b. The degree of unsaturation is quoted in Iodine Number

c. Iodine No = the amount of Iodine exactly reacted with 100g fats or oils

d. Use volumetric analysis (titration) to measure the degree of unsaturation

e. The endpoint is reached when there is a permanent colour change from colourless to

orange brown

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f. The more bromine solution added, the greater the no of multiple bonds present in fats or

oils

g. Calculations:

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SAM Organic Chemistry Esters and Triglycerides

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