Tyler Durden: I make and sell soap. "The yardstick of civilisation" (Fight Club)

Fight Club

Durden: To make soap, first we render fat. The salt balance has to be just right…so the best fat comes from humans.

Narrator: Wait what is this place?
Durden: A liposuction clinic. Pay dirt! Richest, creamiest fat in the world. Fat of the land!

Durden: As the fat renders, the tallows float to the surface. Like in boy scout's. Once the tallow hardens, you skim off a layer of glycerine.

 

U.K. CERTIFICATE: 18

RUNTIME: 139 mins

VIDEO CLIP: Click here

SYNOPSIS: In order to make the best soap, Tyler Durden (Brad Pitt) and the narrator (Edward Norton) venture into a liposuction clinic, to steal human fat. Once they have obtained the fat Durden explains the process of soap-making.

Saponification

Saponification is the base catalysed hydrolysis of an ester whereby an alcohol and salt of the acid is formed. The process involves the reaction of a metallic alkali (base), such as NaOH or KOH with that of a fat or oil to form soap.

CH2-OOC-R-CH-OOC-R-CH2-OOC-R + 3NaOH

CH2-OH-CH-OH-CH2-OH (glycerol) + 3R-CO2-Na (soap)
[Where R = (CH2)14CH3]

Vegetable oils and animal fats are fatty esters in the form of triglycerides. The added base cleaves the ester bond releasing a fatty acid and glycerol. The soap is then salted out by precipitating it with saturated sodium chloride (NaCl). 


Saponification of a lipid with potassium hydroxide  

Base Catalysed Hydrolysis of an Ester

Step 1: The hydroxide anion (from NaOH or KOH) is an effective enough nucleophile to attack the carbonyl group of the ester, generating a tetrahedral intermediate A. This process is reversible because pHaH values are similar (-OH: pHaH 14; -OR: pHaH 16). However, as -OH has a lower pHaH it is a more effective leaving group, which means the equilibrium is slightly over to the right.
Step 2: The -O lone pair on the tetrahedral intermediate expels the relatively weak leaving groups, to regenerate the carbonyl group forming either carboxylic acid (Step 2b: expels -OR) or the starting materials (Step 2a: expels -OH).
Step 3: -OR immediately deprotonates the acid yielding an alcohol and an anion which is soluble in water.
Step 4: Protonation of the anion yields the carboxylic acid which is insoluble and precipitates from the reaction mixture.

Saponification of an ester [R = CH3]

Click on the picture above to interact
with the 3D model of the
Stearic Acid structure

Click on the picture above to interact
with the 3D model of the
Glycerol structure

The movable image below shows what happens when 1 stearic acid triglyceride molecule and 3 sodium hydroxide (lye) molecules come together to form 3 soap molecules and 1 glycerol molecule.

Fight Club

Durden: Now, ancient people found their clothes got cleaner if they washed them at a certain spot in the river. You know why? Human sacrifices were once made on the hills above this river. Bodies burnt. Water speeded through the wood ashes to create lye.

[Holds up a bottle]
Durden: This is lye. The crucial ingredient. Once it  mixed with the melted body fat, a white soapy discharge crept into the river. May I see your hand, please?

[Tyler licks his lips, takes the Narrator's hand and kisses the back of it]
Narrator: What is this?
Tyler Durden: This...[pours the lye on the narrator's hand]... is chemical burn. It will hurt more than any burn and it will leave a scar.

Narrator: I’m getting water!
Durden: You can use water and make it worse or…use vinegar to neutralise the burn.

 

U.K. CERTIFICATE: 18

RUNTIME: 139 mins

SYNOPSIS: Durden demonstrates the caustic/corrosive properties of lye (NaOH) by placing the powder on the back of the narrator's wet hand.

Lye

History: Historically, soap was prepared by mixing animal fats with lye. As lye is a caustic base, this was a dangerous process, which resulted in serious chemical burns or blindness. Before lye was produced on a commercial scale, it was made at home for soap making from the ashes of a wood fire. [Click here for the method of traditional soap making]

Description: Lye is a form of sodium hydroxide (NaOH - 'soda' lye) or potassium hydroxide (KOH - 'potash' lye). Hard soap is formed using NaOH, whereas soft soap is formed when KOH is used. Lye is a main ingredient in the soap making process. Although NaOH is now most commonly used for this procedure, KOH was traditionally used, as it was easier to get hold of.

Confusion: Both NaOH and KOH are commonly called "lye" in United States, which may cause some confusion for us in the United Kingdom. However, the most commercially available lye is NaOH.

Saponification in Corpses: If certain soils (burial grounds) are highly alkaline, this will result in the formation of adipocere in a corpse due to the conversion of fat and other soft tissue. The alkaline source acts on the corpse’s fat by hydrolysing it, converting into a sort of soap, and thus ‘soap mummies’ are born.

 

Caustic Base

Caustic means "burning" and caustic soda takes its name from the dangerous skin burns that it can cause.

Precautions: Gloves and eye protection should be worn when handling NaOH, since there is a high risk of causing chemical burns, permanent injury or scarring, and even blindness. Vinegar (ethanoic acid) is a mild organic acid that will neutralize lye, a strong base to yield the corresponding salt and water:

NaOH(aq) + CH3COOH(aq) CH3COO-Na+(aq) + H2O(l)


Corrosive warning symbol

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