Chapter 2 Cont

Chapter 2 (cont.)  FATS -

Natural substances called lipids.

-

A group of organic compounds that make up the structure of cells found in plant and animal tissues. They are water-insoluble compounds.

-

Fats and oils are chemically very similar, but differ in their physical states.

-

Fats found in animals are solid at room temperature but for plant fats, they are in liquid state at room temperature and thus, called as oils.

-

Fats and oils are mixtures of different esters derived from a variety of long-chain carboxylic acids called fatty acids with the alcohol propane-1,2,3-triol or glycerol.

-

Fatty acids are long straight-chain carboxylic acids containing between 12 to 18 carbon atoms per molecule.

-

A molecule of glycerol may combine with one, two or three fatty acids to form a monoester, diester or triester. A molecule of water is eliminated when a fatty acid joins to the glycerol molecule and the resulting bond formed is called an ester link (-COO-)

-

Could you state why do we need oils and fats????

-

The length of the carbon chain can differ, ranging from 12 to 18 carbon atoms and may be saturated or unsaturated.

-

If the fatty acid has only 1 double bond = monosaturated, >1 double bond = polysaturated.

-

Converting unsaturated fats to saturated?? -Catalytic hydrogenation -Bubbling hydrogen gas through hot liquid oil in the presence of fine particles of nickel catalyst. -Temperature = 200oC -Pressure = 4 atm -The higher the double bonds get hydrogenated, the relative molecular mass of the oil molecule increases. Intermolecular forces become stronger and more energy needed to overcome them

-

Extraction process of palm oil….

-

1) sterilizer 2) stripper 3) digestor 6) purififcation 7) vacuum drying

4) pressing

5) clarification

 NATURAL RUBBER -

A polymer is a large, long chain molecule formed by joining together thousands of small monomer molecules.

-

2 groups : a) natural b) synthetics

-

Proteins

-

The building blocks = amino acids

-

Amino acids are joined together by a condensation polymerization

-

Carbohydrates

-

The building block monomer = glucose

-

C6H12O6

-

2 types of complex carbohydrates polymers : a) starch b) cellulose

 NATURAL RUBBER -

The monomer = isoprene = 2-methylbuta-1,3-diene

-

An addition polymerization joins thousands of isoprene units together to form (polyisoprene) or natural rubber.

-

Coagulation process of latex

-

The milky fluid = latex

-

Consists of an aqueous suspension of colloidal rubber particles.

-

Each rubber particle is made of rubber polymers covered by a layer of protein membrane.

-

‘-‘ charges are found on the surface of the membrane, making each rubber particle negatively charged. the negatively charged rubber particles repel each other, preventing themselves from combining and coagulating

-

Acid such as methanoic acid (formic acid) are added to make the latex coagulate.

-

Hydrogen ions from the acid neutralize the negative charges on the surface of the membrane. A neutral rubber particle is formed.

-

When these neutral particles collide each other, their outer membrane layers break up and the rubber polymers are set free.

-

The rubber polymers start to coagulate by combining together to form large lumps of rubber polymers which then precipitate out of the latex solution.

-

Latex can still coagulate if acids are not added, normally if left overnight.

-

Bacteria from the air slowly attack the protein on the membrane to produce lactic acid. Ionization of the lactic acid produces the hydrogen ions. The H ions neutralize the negative charges to form neutral rubber particles, allowing coagulation to occur.

-

Alkalis such as ammonia solution are added to latex to prevent coagulation.

-

The hydroxide ions from alkali neutralize H ions produced by lactic acid as a result of bacterial attack on protein.

-

Because there are no H ions to neutralize the negative charges on the rubber particles, they remain negatively charged and hence cannot combine and coagulate.

 Properties of Natural Rubber -

elastic

-

unstable to heat

-

unstable to oxidation = the presence of double bond makes it susceptible to oxidation.

-

insoluble in water

 Vulcanisation of Rubber -

a manufacturing process to convert raw rubber into a tough useful product.

-

1-3% sulphur by weight is added to raw rubber and the mixture is carefully heated.

-

Sulphur atoms form cross-links between adjacent chains of rubber polymer at the carbon-carbon double bonds.

-

The number of sulphur atoms in the cross-links is usually one to four.