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  Fats-Oils and Amino Acids, Chemistry tutorial

Introduction:

Fats and oil are the naturally occurring alkanoates made from the trihydric alkanol, propane - 1, 2, 3- triol (generally termed as glycerol) and long chain alkanoic acids (generally termed as fatty acids) having C12 to C24 carbon atoms. A trihydric alkanol is one having three hydroxyl groups (-OH) in the molecule; therefore during esterification, each and every molecule of the trihydric alkanol reacts by three molecules of fatty acids to give the fats and oils as shown:

1286_Esterification process-Fats and oils.jpg

Fig: Esterification process-Fats and oils

This esterification method takes place naturally in plants and animals to give fats and oils that are usually termed to as the lipids. Fats are solids, at room temperature, generally of animal origin whereas oils are liquids, at room temperature, mostly of plant origin. The fatty acids generally found in lipids can be categorized into saturated fatty acids (that is, have no double bond in their hydrocarbon chain) and unsaturated fatty acids (that is, have one or more double bond in their hydrocarbon chain). Illustrations of such fatty acids are illustrated below:

Table:

Common Name

Source

Formula

IUPAC

Palmitic acid

Oil Palm

CH3(CH2)14COOH

Hexadecanoic acid

Stearic acid

Tallow (animal fat)

CH3(CH2)16COOH

Octadecanoic acid

Oleic acid

Olive or Peanut oil

CH3(CH2)7CH=CH(CH2)7COOH

Octadec-9-enoic acid

Linoleic acid

Vegetable oil

CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH

Octadeca-9,12-dienoic acid

Amino acids are the substituted alkanoic acids in which the hydrogen atom(s) in the alkyl groups have been substituted via amino group (-NH2 group).

For example:

2112_Amino acids substituted alkanoic acids.jpg

Fig: Amino acids substituted alkanoic acids

Amino acids are the vital substituted alkanoic acids for they are the components parts of proteins that take place broadly in all plants and animals.

Sources of Fats and Oils:

Fats and oils are broadly distributed in nature. They are mainly employed by man for cooking, as source of energy and for the manufacture of soap. Animal fats and oils are generally obtained by treating the animal tissues with hot water. This breaks down the cell walls and allows the molten fats or oil to increase the surface of water. Tallow is obtained in this manner from beef or mutton (consider the sauce obtained whenever meat is boiled in water); pure lard from pigs. Vegetable oils are generally obtained via pressing the plant to squeeze out the oil or both extractions by organic solvents.

The table illustrates a few common fats and oils and their natural sources.

 

Fats or Oils

Natural Source

Groundnut Oil

Groundnut

Palm Oil

Oil Palm

Coconut Oil

Coconut tree

Cotton seed oil

Cotton

Castor Oil

Castor seed

Palm kernel Oil

Oil Palm

Soya bean Oil

Soya tree

Tallow fat

Sheep and Cow

Coca butter

Cocoa

Sunflower Oil

Sunflower

Lard fat

Pigs

Wool grease

Sheep

Hardening of Oils:

The vegetable oils can be modified to fats through catalytic hydrogenation (that is, addition of hydrogen to the double bond present in the hydrocarbon chain of the oil). Margarine (example: Blue Band) is made up through this process. The oils, generally from plants like oil palm, groundnut and soya-bean are heated to around 180oC in the presence of finely divided nickel, as catalyst, and hydrogen gas is bubbled in at 2 to 5 atmosphere. The hydrogen is added across the double bonds present in the unsaturated hydrocarbon chains of the oil. The product is a fat, which is then mixed by vitamins, salt, milk and other additives to prepare margarine.

Soap Manufacture: Saponification

We are familiar that saponification is the alkaline hydrolysis of alkanoates. Fats and oils that are alkanoates of fatty acids can be hydrolyzed by caustic alkali to give propane - 1, 2, 3-triol and the corresponding sodium and potassium salts of the component fatty acid. Such salts are the major constituents of soap. Sodium chloride is employed to take out (salt out) the soap from the mother liquor, which is denser than the soap. After washing the soap free of surplus alkali, different additives (like dyes and perfumes) are then added to give the varieties of soaps. The nature of the staring oil to find out the kind of soap obtained.

549_Soap Manufacture-Saponification.jpg

Fig: Soap Manufacture-Saponification

Detergents:

These are the substances that encompass the capability to clean an object like soaps. Detergents are generally categorized into two main types - soapy detergents and soapless detergents. The soapy detergents example: soaps are the sodium or potassium salts of fatty acids prepared by the saponification of fats and oils.

Soapless detergents are the alkyl benzene sulphonates, generally abbreviated as ABS.

A soapless detergent molecule is:

109_Soapless detergent molecule.jpg

Fig: soapless detergent molecule

Similar to soap, soapless detergents are sodium salts of sulphonic acid to which an aromatic - alkyl chain is linked. Soapless detergents are the more favored clearing agents nowadays than the soapy detergents.

They are available as solids or liquids and the raw materials for their manufacture are petrochemicals obtained from refining crude oil.

Soapless detergents are more preferred due to:

1) They don't form scum by hard water and thus retain their cleansing properties irrespective of the kind of water employed.

2) They are neutral in water, while soapy decagons at slightly alkaline in water and thereat not stable fix washing acid-sensitive fabrics.

3) They include broader applicants, in terms of removing different kinds of stains, than soapy detergent.

Uses of Fats and Oils:

1) As foodstuffs: Most of the fats are consumed as food; altogether with carbohydrates, they give source of energy for animals.

2) In making soaps, the fats and oils generally used for making soaps are tallow, coconut on, bleached palm oil, soya bean oil and olive oil.

3) In making candles, whenever tallow is hydrolyzed under pressure it provides products employed in making the candles.

4) In making glycerol, glycerol is the by-product acquired in the manufacture of soap. It is mainly employed in the manufacture of creams and medicine.

5) In making paints: linseed oil is employed for making the oil paints.

6) In making margarines: margarines are made up by hardening oils and is a good replacement for butter.

Tests for Fats and Oils:

a) Paper test: A drop of oil or melted fat on a piece of paper makes a translucent (that is, allow light to pass via) grease spot.

b) Sudan III test: To a mixture of oil and water add 4 to 5 drops of sudan III stain, a red stain confirms fats and oils.

Amino Acids:

Amino acids are the derivatives of alkanoic acids in which the hydrogen of the alkyl dual is substituted through the amino group (-NH2). Each amino acid includes two functional groups: the carboxyl group (-COOH) and the amino group (-NH2). It thus consists of a general structure as follows.

1831_Amino acids.jpg

Fig: Amino Acids

Amino acids are the fundamental structural units of proteins. All the amino acids obtained through hydrolysis of animal and plant proteins encompass the amino group linked to the carbon adjacent the carboxyl group. They are known as α - amino adds mid twenty (20) of such amino acids have been isolated in the nature. All the proteins found in living organisms are combinations of such amino acids.

In the aqueous solution, amino acids are neutral to litmus, however they can act as an acid, on account of the -COOH group, or as a base, on account of the -NH2 group. Amino acids can thus react by acids or bases to form the salts.

Let us now consider the given reactions:

NH2CH2COOH + HCl → Cl- + NH3CH2COOH

NH2CH2COOH + NaOH → NH2CH2COO-Na+ + H2O

In neutral solution, the amino acids exist as the dipolar ions (zwitterion) and this polar structure accounts for their high melting point (example: amino-ethanoic acid melts at 235oC) solubility in water and insolubility in the organic solvent.

1108_Amino acid as dipolar ions.jpg

Fig: Amino acid as dipolar ions

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