Esters,Fats and Oils Flashcards
Condensation
-In a condensation reactions small molecules join together to form a bigger molecules by the elimination of water
-Esters are formed by the reaction of carboxylic acid and an alcohol
What is the catalyst for producing esters
concentrated sulfuric acid also increases yield of esters and absorbs water produced
What is the purpose of cold water in test tube in condensation
acts as a condenser when the reaction mixture is being heated. Vapours which would otherwise escape, condense back to liquid and drip back into the mixture
Purpose of sodium carbonate in condensation
to neutralise the sulphuric acid
Uses of esters
flavorings
perfumes
solvents- some of the smaller esters are quite volatile and used as solvents in adhesives
Hydrolysis of esters
-In hydrolysis reactions larger molecules are broken down into smaller molecules by water
-An alkali is often used to catalyse the reaction and the mixture heated under reflux. (the process of boiling a liquid so that any vapour is liquefied and returned to the reacting mixture)
If sodium hydroxide is used, a sodium salt of the acid is formed. If this is reacted with a strong acid (eg. Hydrochloric acid) the acid can be
displaced from the salt
Fats and Oils
Fats and oils are naturally occurring esters of the alcohol glycerol and long chain carboxylic acids. (known as fatty acids)
Name of alcohol
glycerol is a tryhydric alcohol, propane-1,2,3-triol
Ratio to produce fats and oils
Fats and Oils are formed by combination of 3 moles of fatty acids to 1 mole of glycerol - a triglyceride. There are 3 ester linkages in the one molecule
Classification of fatty acids
-If the number of hydrogens is = or less than double the number of carbons Cn H<2n = unsaturated
-If the number of hydrogens is more than double the number of carbons Cn H>2n = saturated
Melting and Boiling Points of Fat and Oil molecules
Fat and oil molecules are roughly ‘tuning fork’ in shape with three limbs being hydrocarbon chains. If the chains are saturated, the molecules pack neatly together even at quite high temperatures. If the chains contain one or more double bonds the zig-zag chains become more distorted and the close packing of the molecules is less easy.
Fat-higher melting point(close packing strong LDF)
Oil-lower melting point(less packed weaker LDF)
-Fat molecules pack together tightly, making fats solid at room temperature.
-Double bonds in oil make them less compact
-less tightly packed molecules make oils liquid because the bonds between molecules are weaker
Hydrolysis of fats and oils
-Fats and oils can also be hydrolysed to form fatty acids and glycerol. This is the reverse of condensation just likes breaking esters. This hydrolysis reaction provides the body with essential fatty acids such as linoleic and linolenic acid, which are essential for blood coagulation and brain development.
-Usually the fats and oils will be hydrolysed with a dilute solution of sodium hydroxide to make sodium salts of the fatty acids ( see chemistry of toiletries later)
Hardening Oils
Remember the more saturated the fat or oil, the more solid it is. The key to converting liquid oil into a solid fat is to reduce the degree of unsaturation.
Reducing unsaturation means getting rid of some of the double bonds in the fatty acid sections of the ester molecules. Hydrogen molecules need to be added across these double bonds to reduce them to single bonds.
From Nat 5, the process of adding hydrogen is called hydrogenation and it is carried out using a catalyst, often nickel.
Hardening a fat or oil means hydrogenating it to increase its melting point.
When margarine is manufactured from vegetable oils, such as sunflower seed oil and olive oil, the extent of hydrogenation is carefully controlled. If the product were totally saturated it would be too hard to spread easily when taken straight from the fridge as well as again being unhealthy. If it were too unsaturated, it would be too runny at room temperature.
