Environmental Science 456

Environmental Chemistry

Soaps and Detergents

 

I.         Introduction

A.      Soaps

Original cleaning products produced from the hydrolysis of naturally occurring plant and animal fats having limited effectiveness.

B.      Detergents

Cleaning products derived from synthetic organic chemicals that have a broad range of function and effectiveness to clean.

C.      Soaps and detergents represent one of the largest market segments of chemicals that are produced. In US, annual consumption is about 10 billion pounds each year (40 pounds per person).

D.      Uses of soaps and detergents

1.       Personal care products

·         Bar soaps

·         Shampoos

·         Cosmetics

2.       Household cleaners

·         Laundry detergents

·         Dishwashing

·         Car cleaning

·         Bathroom cleaners

3.       Industrial

·         Computer chip

·         Oil recovery

·         Paper manufacturing

·         Metal finishing

·         Textiles

II.       Surfactants

A.      Surface active agents

1.       Organic molecules that contain both polar and nonpolar regions. The nonpolar tails are hydrocarbon chains (C10 to C20)

 

 

 

 

 

 

2.       They are active at the interface between water and either air, solids, or nonpolar liquids by modifying these surfaces.

3.       Surfactants lower the surface tension between water and air, solids. Water would prefer to interact only with itself and does not want to interact with air or solids. Surfactants allow water to interact more intimately with air or solids.  This occurs where the hydrophilic heads orient themselves towards the water molecules whereas the hydrophobic tails point towards the air, oil, or solid phase

B.      Micelles

1.       Where the concentration of surfactants begins to reach its solubility limit (the highest concentration that the surfactant remains soluble), clusters of 50-100 surfactant molecules clump together in such a way that the hydrophobic tails all point inward. These clusters are called micelles

2.       Micelles can form a number of different shapes such as spheres and sheets.

3.       The inside portion of the micelle is like a drop of oil floating in water. The nonpolar, inside portion of the micelle can solubilize a small droplet of oil or grease. This represents one way that surfactants clean – they solubilize normally water insoluble substances like grease and oil.

4.       Critical Micelle Concentration (CMC) is achieved at the lowest surfactant concentration at which the surface tension is minimized. CMCs range from 0.1 to 10 millimole per liter  (if surfactant had a molecular weight of 300 g/mole, then 1 mM would be equivalent to 0.3 g surfactant per liter).

C.      Types of surfactants

1.       Anionic surfactants – negatively charged head

·         Fatty acids

 

 

 

 

 

·         Linear alkylbenzene sulfonates

 

 

 

 


 

 

·         Alcohol sulfates

 

 

 

 

·         Alcohol ether sulfates

 

 

 


 

2.       Cationic surfactants – positively charged head

·         Quarternary ammonium chloride (dimethy-tetradecylbenzyl-ammonium chloride

 

 

 

 

 

 


 

 

3.       Nonionic surfactants – uncharged head with high polarity

·         Alcohol ethoxylates

 

 

 

 

 

·         Alkylaryl ethoxylates

 

 

 

 

 

 

·         Alkyl glucosides

4.   Amphoteric surfactant – contains both negatively and positively charged region Quarternary ammonium chlorides

·         Sulfobetaine

 

 

 

 

 

 

 

 

 

 

 

 

III.      Synthesis

A.      Soaps

1.       Hydrolysis of fatty esters


 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

2.       Neutralization of fatty acids

 

 

 

 

 

 

 

 

B.      Alkylbenzene sulfonates

1.       Dehydrogenation of C10-C15 paraffins

2.       Alkylation of benzene

·         positional isomers - according to where benzene is inserted on the chain

·         homologs – different chain hydrocarbon chain lengths

3.       Sulfonation of alklybenzene

4.       Neutralization of alkylbenzene sulfonate

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


 

 

 

 

 

 

 

 

 

 

 

C.      Alcohol sulfates

1.       Long chain fatty alcohols can be prepared by hydrolyzing olefins or reducing fatty acids

2.       These fatty acids can be sulfonated with SO3 and then neutralized with NaOH.

D.      Alcohol ethoxylates

1.       Fatty alcohols are reacted with n units of ethylene oxide that form various polymeric couplings of (CH2O) where n varies from 4 to 15.

2.       Results in very complex mixtures of different isomers, homologs, and number of ethylene oxide units

IV.    Detergents

A.      Components

1.       Surfactants – usually a mixture of anionic and nonionic surfactants because the former is better at removing “soil” from clothing and the latter removes sebum, oil and grease.

2.       Builder – polyphosphates or zeolite water softeners

3.       Enzymes – protease, lipase, cellulase

4.       Bleaching agents – perborate or percarbonates

5.       Carboxymethylcellulose –

6.       Optical brighteners

7.       Dyes

8.       Perfumes

B.      Laundry performance

The surfactants allow the wash water to wet the fabric and “soil”. The removal of dirt and stains is increased up by heat and agitation

C.      Builders

1.       Water contains hardness ions (Ca2+ and Mg2+) that interfere with washing performance by reacting with fatty acids and bicarbonates in the wash water to form soap scum.  Gives clothes a dingy appearance.

2.       Builders are added to detergents to soften the water by sequestering hardness ions.  They also promote cleaning by maintaining a high, alkaline pH. They sequester hardness ions by maintaining them in solution so they cannot form precipatates with bicarbonates or fatty acids.

3.       Most cost-effective builders are sodium tripolyphosphates.  These materials have recently been removed from US detergents because they contribute to increasing the phosphate levels of fresh bodies of water.  Increasing phosphorus leads to eutrophication of these bodies of water.

4.       Synthetic zeolites (aluminosilicate cages) have replaced phosphate builders.  These materials are environmentally innocuous since they are synthetic clays.

D.      Enzymes

1.       Protease - solubilize protein stains (grass, blood)

2.       Lipase - solubilize sebum (facial and body oils)

3.       Cellulase – dissolve damaged cotton fibers

E.      Non-chlorine bleaches

Solid materials that safely “bleach” fabrics using sodium perborates or sodium percarbonates.  These materials generate active oxygen similarly to hydrogen peroxide.  The active oxygen bleaches like chlorine bleach., but is less harsh and less effective.

F.      Optical brighteners

Highly conjugated organic molecules that have a chromophore that adsorb UV light and reflect Visible light making your clothes look whiter, bluer, and brighter than they really are.

V.      Toxicity

A.      Soaps and detergents (except quaternary ammonium chlorides) have very low oral toxicity to mammals (LD50 > 1 g/kg). Some are used in food products as emulsifiers.

1.       They are readily metabolized.

2.       Low Kow, so they are not bioaccumulated.

B.      They have significantly higher levels of toxicity to aquatic organisms and have LC50 values in the mg per liter (1000 times more toxic to aquatic organisms).  Toxicities increase as HLB decreases that can occur because the hydrocarbon chain length increases or the ethylene oxide chain decreases.

VI.    Biodegradation

A.      Alkylbenzene sulfonate (ABS) was manufactured prior to LAS. It persisted in the environment and was observed as foam in rivers and lakes during the 1950s and early 1960s.

1.       Olefins were prepared by polymerinzing propylene rather than by dehydrogenation of paraffins.

2.       This process produced branched hydrocarbon chains attached to the benzene ring.

3.       These branched chains contained secondary (2o) and tertiary (3o) carbon atoms that were resistant to biodegradation because bacteria lacked the enzymes that could oxidized anything but primary carbons. Very few naturally occurring secondary and tertiary carbon atoms.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


 

B.      Linear alkylbenzene sulfonate is biodegraded rapidly in warm aerobic environments by b-oxidation. They do not persist, bioaccumulate or bioconcentrate.

1.       Oxidation of one of the terminal carbon atoms in the hydrocarbon chain followed by removal of two carbon fragments (acetyl groups) until the hydrocarbon chain was short. 

2.       Next, the ring would open up and undergo further degradation.

3.       Eventually, LAS would be converted to CO2 and water. This process was proved to occur over a period of days to weeks.

C.      Other popular surfactants (AEO, AES, AS) were found to be rapidly biodegradable if the hydrocarbon chain is linear.