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Syntheses of Soaps and DetergentsAbstract

Soap is produced by the saponification (hydrolysis) of a triglyceride (fat or oil). In this process the triglyceride is reacted with a strong base such as sodium hydroxide to produce glycerol and fatty acid salts. On the other hand, a synthetic detergent can be prepared by reacting dodecyl alcohol with sulfuric acid. Soaps and detergents are similar in their general structure and properties, but different in composition and specific properties. The emulsifying ability of detergents are great in hard and soft water while soaps are only best with soft water. A detergent does not form precipitates with metal ions while a soap does. Thus, these properties identify the best uses of soaps and detergents.

Introduction: A soap is a salt of a compound

known as a fatty acid. A soap molecule consists of a long hydrocarbon chain (composed of carbons and hydrogens) with a carboxylic acid group on one end which is ionic bonded to a metal ion, usually a sodium or potassium. The hydrocarbon end is nonpolar and is soluble in nonpolar substances (such as fats and oils), and the ionic end (the salt of a carboxylic acid) is soluble in water.

Glycerol is a by-product of saponification which is useful as an anti-freeze, as a tobacco-moistening agent, and in the manufacture of nitroglycerine and dynamite. Acrolein test is used to detect the presence of glycerol by heating the sample with potassium bisulfate

Detergents are structurally similar to soaps, but differ in the water-soluble portion.

The cleaning action of both soaps and detergents results from their ability to emulsify or disperse water-insoluble materials and hold them in suspension in water. When a soap or detergent is added to water that contains oil or other water-insoluble materials, the soap or

detergent molecules surround the oil droplets. The oil or grease is dissolved in the alkyl groups of the soap molecules, while the ionic end allows the oil-soap complex to dissolve in water. As a result, the oil droplets are dispersed throughout the water and can be rinsed away.

Experimental: Soaps are prepared by the

alkaline hydrolysis of fats and oils. This process is known as saponification.

Filtration of the soap through a cheesecloth is done for the extraction and test for glycerol.

For the extraction of glycerol, the filtrate was neutralized and evaporated to a small volume or syrupy consistency. Then, the residue is extracted with 10mL of 95% ethanol and evaporated in a water bath. The residue contains the glycerol.

To test the glycerol, a pinch of powdered potassium bisulfate is added to the residue and heated strongly. The odor is observed.

The synthetic detergent, a sodium alkyl sulfate called sodium dodecylsulfate, can be prepared by

2reacting dodecyl alcohol with sulfuric acid.

The emulsifying ability and behavior in hard water of soaps and detergents are tested by the addition of cooking oil to test tubes of soaps

and detergents with calcium chloride and magnesium chloride each. The emulsifying ability of soap or detergent are observed by the amount of suds formed.

Results and Discussion:

SOAP DETERGENTColor and Appearance White Solid Bar; Clear Liquid Colored Viscous LiquidSolubility in 1% CaCl2 Formation of precipitate No precipitateSolubility in 1% MgCl2 Formation of precipitate No precipitateEmulsifying Ability in Hard Water with CaCl2 and MgCl2

Light suds Heavy suds

Figure 1 Properties of soaps and detergents

The sodium and potassium salts of most carboxylic acids are water soluble. However, the calcium, magnesium, and iron salts are not. Thus, when soaps are placed in hard water that contains such ions, an insoluble, curdy solid forms. The calcium, magnesium, and iron forms of most detergents are more soluble in water than the corresponding soap compounds. Consequently, detergents function almost as well in hard water as they do in soft water.

Soaps, will react with metal ions in the water and can form insoluble precipitates. The precipitates can be seen in the soapy water and are referred to as “soap scum”. This soap scum can form deposits on clothes causing them to be gray or yellow in color. To eliminate the metal ions in water, washing aids such as washing soda (sodium carbonate) and borax (sodium tetraborate) were added to the wash water. These compounds would precipitate the metal ions, eliminating most of the soap scum. With the discovery of synthetic detergents, much of the need for washing aids was reduced. A detergent works similar to a soap, but does not form precipitates with metal ions, reducing the discoloration of clothes due to the precipitated soap.

Modern laundry detergents are mixtures of detergent, water softeners,optical brighteners, stain removers, and enzymes.

As for the test of glycerol, acrolein is released after heating the residue containing the glycerol with potassium bisulfate. Acrolein has a pungent, irritating odor. Acrolein was also called acraldehyde, and its systematic name is propenal.References:David, K.A. (2000). The chemistry of soaps and detergents.

http://www.chymist.com/Soap%20and%20detergent.pdfJenkin. Food Science.

http://www.chemistry-react.org/go/default/Faq/Faq_23913.html