This research work gives the description of how the saponification value of some selected natural oil can be determined. A definite amount of each sample of oil was reflexed in a given volume of standard ethanolic potassium hydroxide solution for 45 minutes. On completing the saponification reaction, the ethanolic KOH was titrated against a standard HCL solution.
From the obtained result, palm kernel oil had the highest saponification value and would therefore be the best natural oil for soap – making. The value obtained for palm oil was below expectation. This might be due to lack of proper purification during its preparation.
TABLE OF CONTENT
Table of content
Types of oil
Occurrence and extraction
General physical characteristics
General chemical characteristics
Analysis of fats and oils
Fats as food
Uses of oils and fats
Aim of the project
Results and Calculations
Saponification is a routine laboratory and industrial reaction of particular interest as most soaps are being manufacture by the saponification of animal fats.
Saponification is an alkaline – catalysed chemical reaction in which an ester splits to form an alcohol and a salt of carboxylic acid. The term arose from the alkaline hydrolysis of fat to yield soaps, hence soaps are potassium or sodium salts of long chain carboxylic acid. (William, 1976).
Saponification is made effected by boiling the ester in an aqueous alkali (KOH or NaOH) solution. The free carboxylic acid can be recovered by neutralizing the mixture via mineral acid.
R – C – OR1 + Na+ OH-+ H2O R – C – O – Na+ + R1 - OH
ester Alkali carboxylate Alcohol
the insoluble carboxylic acid in solution, can be separated from the solution. The glycerol or other alcohol is separated from the water by distillation. (Fernandez, 1980).
Types of oil
Naturally, there are four types of oily substances
1) Natural oils and fats: the commonly called oils and fats are the ester of glycerol, known as glyceries and are with higher fatty acids. they are the glycerides of stearic, palmittic and oleic acids. The acid usually have normal chain and even number of carbon atoms. In butter fat, a few ester if acids with odd number of carbon atoms and with branched chains are also present. Glyceride are contained in chaulmoogra oil with cyclic structures.
2) Mineral oils: these are the mixture of various hydrocarbon, occurring inderneathe the earth surface. Some important ones are petrol, gas oil, paraffin oil and petroleum which we obtain kerosene. They generally possess unpleasant odour.
3) Essential Oils: They are liquids, possessed with pleasant smell and they occur in plants. e.g. kiltus oil, rose oil, lemon oil, olive oil, turpentine etc. The main constituents are the turpenes with the groups of aldehyde, ketone, alcohol, esters etc.
4) Waxes: These are examples of simple lipids. They are esters of higher fatty acids with monohydric alcohol of high molecular weight.
They are insoluble in water and difficult to hydrolyse; these properties explain their value as protective layer on leaves, stems, fruits, on fur of animal and the integument of insects (Cutidle). They differ from paraffin wax which is a mixture of alkanes, they dissolve readily in benzene, carbon disulphide and light petroleum.
The major difference between oils and fats is that oils are liquids at ordinary temperature, as fats are solids at ordinary temperature. The incorporation into glycerides of low molecular weight fatty acids and high molecular weight acid, containing unsaturated groupings, result in fats with low melting point, hence the incorporation of saturated, high molecular weight fatty acids produce triglycerides which are semi – solids or solids at room temperature. Examples of fats are oleic acid (C27H31COOH), Linolenic (C18H29COOH) acid while fats can be exemplified as; (C11H23COOH) lauric acid, (C13H27COOH) myristic acid etc.
The system for naming is based upon the constituents of the fatty acid e.g. glycerol tristerene contains three stearic acids and Oleodiesterene contains one oleic acid and 2 stearic acids.
In stearic and palmittic acids, the glyceride of unsaturated oleic acid is a liquid (TEWARI, 1980). Usually, the same glyceride may contain more than one acid residue. Such a glycerode is a ‘mixed glyceride’. These are present in naturally occurring oils and fats. Examples are Oleo – palmito – stearic, palmito distearin which are in lard, the fat obtained from pig.
Oleo palmito – stearin Palmito – distearin.
Occurrence and Extraction
Oils and fats are mainly found in seeds of plant while they are present under the skin in tissues and muscles of animals.
Extraction: The following processes are generally used for extracting fats and oils from the parent materials. (TWEARI, 1980).
i. Pressing: In this, vegetable fats and oils – containing seeds are crushed by rollers and pressed in hydraulic press or continuous expellers. The oil separates leaving behind the ‘oil cake’ which is used as cattle feed. The produced pressed cake is heated and further pressed to give second grade oil which contains undesirable components and a strong odour.
ii. Rendering: This is the usual process for extracting animal fats. The animal tissues are chapped off and boiled with water or steam. The fats melt and float on the surface whence it is withdrawn.
iii. Solvent Extraction: This usually follows the pressing process. The hot – press cake is crushed and extracted with organic solvents such as carbon tetrachloride, benzene, petroleum ether etc to obtain the remaining oil.
Refining: The fat or crude oil undergoes treatment with a little alkali to neutralize free acid and for coagulation of any colloidal impurities present. Warming follows at 70 – 80OC with animal charcoal or plaster of paris. This is called bleaching. Half an hour later, the decolorized oil is filtered, superheated steam will then be passed through it. The oil is quickly cooled and withdrawn.
General Physical Characteristics
Oils and fats are colourless liquids or solids, lighter than water and immiscible with it, but due to impurities, they may yellow or brown. They are freely soluble in organic solvents such as benzene, petroleum, ethyl ether e.t.c. they are non-volatile but decompose on strongly heating which produces irritating odour of acrolein. Their agitation with water in the presence of soap results in emulsions. Instead of soap, gelatin or ther emulsifiers may be used.
Animal fats contain cholesterol, an unsaturated alcohol, likewise vegetable fats contain phylosterol (TEWARI 1967).
General Chemical Characteristics
1. Drying: certain oils, containing glycerides of unsaturated acids with two or three double bonds such as linolenic (3 double bonds) and linoleic acids (2 double bonds), have the properly of slow absorption of oxygen from air and polymerizing to form a hard transparent coating which are used in making paints and oil cloth. This is known as drying and the oils are drying oils.
Drying takes place much more readily, as compared to glycerides containing non-conjugated double bondsif the acid contains conjugated system of double bonds e.g eleostearic acid present in tung oil.
2. Rancidification: this is another property (chemical) which explains its nature on long storage. When it is in contact with air and moisture, oils and fats undergo slow decomposition and develop unpleasant smell. This process is called rancidification. Rancidification is believed to take place with the accompany of the following chemical changes.
a) Enzymatic Hydrolysis: hydrolysis of lower fats and oils take place producing bad smelling lower fatty acids when there are actions of micro-organism and enzyme.
b) Aerial oxidation of unsaturated acid is produced during hydrolysis, forming aldehydes and ketones with unpleasant odour.
c) Oxidation of saturated acids produced as a result of hydrolysis, followed by decarboxylation forming ketones possessing unpleasant flavour (Jane, 1979) .
3. Hydrolysis: dilute acids hydrolse fats and oils into glycerol and fatty acids. Hydrolysis may also be brought about by alkalis or superheated steam or enzymes e.g lipase.
CH2O C R1 CH2 OH
CHO C R2 + 3H2O H+ OH- CH2 OH + 3RCOOH
lipase (fatty acid)
CH2O C R3 CH2 OH
The hydrolysis of oils and fats by alkalis is known as saponification, the result being formation of soaps and glycerol.
4. Hydrogenation: Fats contains less of unsaturated glycerides than oils and so are solid or semi solids at ordinary temperature. Under pressure, if hydrogen is passed through them in the presence of suitable catalyst, usually finely divided nickel or Roney Nickel, the unsaturated glycerides are converted into saturated glycerides and the oil attain a solid or semi – solict form. It can then be known as vegetable ghee or margarine.
CHO.CO.C17H33 3H2 CHO.CO.C17H35
Ni/175 – 190OC
Olein (m.p = 17OC) sterim (m.p = 71OC)
Hydrogenation is mentioned in improvement of colour, odour, taste. Hydrogenated oils are used as ‘vegetable’ or ‘vanaspat ghee’ and also for the manufacture of margarine, candles and soaps.
In some developed countries, large quantities of ‘vanaspat ghee’ are prepared from cotton seed. ‘Vanaspat ghee’ with melting point below 73OC is dutable for human consumption, as it is easily assimilated in the digestive system, but those with melting point 37O and above are unfit for use as they remain unmelted in the stomach and cause a number of intestinal disorders.