SYNTHESIS OF SOAPJeuz Koz Geluz

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Nicolas Leblanc invented a method of making alkali soda from salt that became one of the most important chemical processes of the nineteenth century.

SOAP SYNTHESIS

The preparation of soap through a chemical reaction is known as saponification.

Historically, soaps were made by boiling the fat of an animal in a solution containing potash. Today this process is known to be the reaction of fatty acids with a strong base such as sodium hydroxide or potassium hydroxide. The hydrolysis of the fat or oil results in the formation of glycerol and soap.

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METHODOLOGYHeat a water bath about two thirds

with water t o boiling

Dissolve 2.5 g of Sodium Hydroxide and 20 ml. of Ethyl Alcohol in 5 ml distilled water

Add the solution to 5g. of hydrogenated

shortening.

Heat the mixture in water bath

Stir to prevent spattering.

Dilute soap

Add to brine solution

Stir the mixture

Collect the precipitate

Wash the soap twice

Dissolve 2g soap in 10 ml.

cold water

Water bath and stir the remaining

soap and cool

TEST FOR THE SOAP

Physical Properties •Determination of the melting point•Color, texture, appearance and odor

Chemical test •Test the ph of the soap solution

To 10 ml proportion of the soap•Add 1 ml 0.1 % calcium chloride•Shake vigorously•Repeat procedures for dilute magnesium chloride and ferric chloride solution

TEST FOR THE SOAP

To 50 ml of the soap solution•Add dilute hydrochloric acids to Congo Red•Cool mixture in Ice.•Collect precipitate•Wash with 20 ml. cold water

Test Solubility •Add 2ml of Methylene Chloride

Test with mineral oil •Add 4 drops in soap solution•Add 4 drops 10 ml. water

SAFETY PRECAUTIONS

Sodium hydroxide is a highly corrosive base. Contact with skin will

cause irritation and burning. Place excess in appropriate labeled waste

container in hood after use.

Ethanol is flammable and also toxic. Prolonged exposure to vapors can cause headaches. Place excess in

appropriate labeled waste container in hood after use.

The filtrate from this experiment should be disposed in appropriate

labeled waste container in hood after use.

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Theoretical Yield 5.28 g.

Actual Yield

Percent Yield

Calculations:C51H9806 + 3NaOH C3H8O3 + Na3C48H93O6

Fat: 5 gramsNaOH: 2.5 gramsMW of fat: 806g/molMW of NaOH: 40g/molMW of Glycerol: 92g/molMW of soap: 278g/mol

Fat: 5gfat x 1molfat x 3molsoap = 0.019molsoap 806 g fat 1molfat

NaOH:2.5gNaOH x 1molNaOH x 3molsoap =

40gNaOH 3molNaOH0.062molsoap

Theoretical Yield 0.019molsoap x 278gsoap = 5.28gsoap

1molsoap

Percent Yield%yield = Xg x 100 = X 5.28g

RESULTS

Appearance Solid mass

Color White

Odor Odorless

Texture Powdery

Melting Point 78C-88C

Ph (litmus paper)

Basic

Calcium Chloride

Cloudy solution

MagnesiumChloride

White solution

Ferric Chloride

Yellow solution

Solubility Soluble

Mineral Oil Miscible

Mineral oil and water

Immiscible

Physical Properties Chemical Properties

SOAP

SOAP

Most soaps are soluble sodium or potassium salts of carboxylic acids.

The most common commercial soap is sodium stearate, Na[C17H35CO2].

It dissolves in water, forming the sodium and stearate ions.  Even though most of the stearate ion is a hydrocarbon chain, it dissolves in water because of the carboxylate group.

The carboxylate end is called hydrophilic (water-loving), and the hydrocarbon tail is called hydrophobic (water-fearing).  

SOAP

The salt of the fatty acid

LIPIDS

Lipids are one of the four major classes of biomolecules (along with carbohydrates,proteins and nucleic ands).

They store energy in the body for use when food is not readily available.

They are integral for cell membranes to separate compartments within the cell, and can act as chemical messengers in the endocrine system and throughout the body.

FATTY ACIDS

Fatty acids are straight-chain monocarboxylic acids.

The most common fatty acids range in size from 10-20 carbons and most often have an even number of carbon atoms including the carboxyl group carbon.

The carbon-carbon bonds in saturated fatty acids are all single bonds, while unsaturated fatty acids have one or more carbon-carbon double bonds in their chains.

FATTY ACIDS

Fatty acids are seldom found as free molecules in nature but are most often a part of a larger molecule called a triglyceride.

Triglycerides consist of a three-membered carbon chain (glycerol backbone) with a fatty acid bonded to each of the three carbon atoms in the glycerol backbone.

The bond between the fatty acid and the glycerol backbone is referred to as an ester linkage.

In the saponification process, the ester linkage is broken to form glycerol and soap.

TRIACYLGLCEROLS

Triacylglycerols in fats and oils have no ionic charges, and are nonpolar and hydrophobic. Triacylglycerols are the form of lipid energy storage in the body, and they also provide thermal insulation and protective padding.

TAGs can be hydrolyzed into their component fatty acids and alcohols – that is, they are broken down by the addition of a water molecule. In the body, enzymes known as hydrolases carry out this hydrolysis. This reaction can also be carried out in the laboratory by a process called saponification – where the hydrolysis is carried out in the presence of a strong base (such as NaOH or KOH).

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Soap is made by treating fats with a strong solution of lye (NaOH). The ester functional groups are hydrolyzed releasing its alcohol portion as glycerol and the acid portions as the a mixture of the sodium salts of the fatty acid. The glycerol is water soluble and is separated from the fatty acid salts. These are nearly insoluble in water, and are washed and compressed into a cake -- soap.

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The mechanism of this reaction, which is called saponification) can be illustrated more easily on a simple ester than a fat. It follows the normal pattern for a carboxylic acid derivative and the first step is analogous to base-catalyzed hydration of aldehydes -- attack of the nucleophile hydroxide ion at the carbonyl carbon atom. This is followed by the usual departure of the leaving group (in this case, the OR'- of the ester). Since the OR'- is more basic than RCOO-, the last step is a neutralization reaction.

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To finish up, we need to look at how soaps work and how that relates to their structures. Soaps are "bridge" molecules. Their long hydrocarbon chains are very much like oils, so they mix well with oils. In fact, we can say that the chains of soap dissolve in oils. At the same time, their ionic heads are polar enough to dissolve in water. If we imagine a small globule of oily material which has dissolved a bunch of soap molecules, we can see that the polar ionic heads will stick out (insoluble in oil) at the surface. These polar bumps on the surface attract water molecules, so that the oily glob is coated with water molecules that are held there by the ions. The glob is now ready to be washed away in water. Since much of the dirt we hope to get rid of is held in place by oily films, removing the oils removes the dirt.

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The structural requirements for a soap (or more generally, for a detergent) are a long hydrocarbon tail (12 or more carbons) and a polar (often ionic) head. In synthetic detergents, the hydrocarbon tail is usually formed by linking several ethylene molecules together and attaching this to a benzene ring. The polar part is derived by covalently bonding the sulfur of a sulfate ion to the benzene ring.

GUIDE QUESTIONS

What is the reaction involved in the synthesis of soap?

Saponification Salting Out

GUIDE QUESTIONS

Write the reaction pathway and mechanism for the synthesis of soap.

GUIDE QUESTIONS Why was the dilute solution poured in a solution of

sodium chloride in water? The process of pouring a diluted solution in a

solution of sodium chloride in water is known as “salting-out”. The salt increases the density of the solution. The addition of sodium chloride or some other electrolyte to a solution of a monelectrolyte reduces the solubility of the latter; thus, soap is removed from the water, glycerol and unreacted NaOH. The NaCl solution provides Na+ and Cl- ions that bind to the polar water molecules, and help separate the water from the soap. The soap is forced out of solution or precipitated by the addition of a NaCl solution. So, the final product will be the sodium salt of the fatty acid.

GUIDE QUESTIONS

Explain the result obtained when the dilute soap solution is treated with calcium chloride, magnesium chloride and ferric chloride solutions.

Soap is normally made from sodium or potassium salts which are soluble in water. When the carboxylate anions from these salts combine with certain ions such as calcium, magnesium, and iron ions that are found in hard water, soap molecules will form an insoluble precipitate known as a soap scum.

GUIDE QUESTIONS How does the soap function as an emulsifying agent

for oil In water? Draw a picture of an oil droplet and several soap molecules to illustrate your answer.

When grease or oil, with non-polar hydrocarbons, are mixed with a soap- water solution, the soap molecules work as a bridge between polar water molecules and non-polar oil molecules. Since soap molecules have both properties of non-polar and polar molecules the soap can act as an emulsifier. An emulsifier is capable of dispersing one liquid into another immiscible liquid. This means that while oil, which attracts dirt, doesn't naturally mix with water, soap can suspend oil/dirt in such a way that it can be removed. The soap will form micelles and trap the fats within the micelle. Since the micelle is soluble in water, it can easily be washed away.

EMULSIFICATION

APPLICATION

Suppose that you wanted to emulsify a water-insoluble compound in water. Would soap be a reasonable choice for the emulsifying agent if the water were slightly acidic? Why? If it would not be a good choice, draw the structure of an organic molecule that might be more suitable.

Soap is sensitive to acidic solutions. If you put a soap into an acidic solution (pH < 4.5), the carboxylate group will be protonated:

The protonation of oleate ion to form oleic acid can occur at pH below 4.5. This forms an uncharged, insoluble molecule, which is not surface-active. The protonated soap molecule does not have a charged head, so it is no longer soluble in water. The soap molecules precipitate out forming a cloudy mixture, which, like hard water, leads to the formation of a scum. Soaps are not suitable for use in acidic conditions.

Although soaps are excellent cleansers, they do have disadvantages. As salts of weak acids, they are converted by mineral acids into free fatty acids which do not have any cleaning ability:

CH3(CH2)16CO2-Na+

+ HCl ----> CH3(CH2)16CO2H + Na+ + Cl-

These fatty acids are less soluble than the sodium or potassium salts and form a precipitate or soap scum. Because of this, soaps are ineffective in acidic water.

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