Organic Chemistry Brief Notes by chong56 on Scribd
Alcohols
Introduction
• Alcohols are a family of organic compounds containing carbon , hydrogen and oxygen.
• The general formula of alcohols is CnH2n+1OH (n = 1, 2, 3, 4…)
• The reacting group (or functional group) is the hydroxyl group, -OH.
• The names of an alcohol end with –ol.
• Propanol has 2 isomers.
Formation of ethanol
• Ethanol is obtained by
• (a) fermentation
• (b) catalytic addition of steam to ethene
• (a) Fermentation breaks down the sugar into ethanol and carbon dioxide. Yeast is used as a catalyst.
• C6H12O6 --> 2C2H5OH + 2CO2
sugar ethanol
Temperature of 37oC is used. Temperature is important in fermentation.
• (b) Addition of steam to ethene at high temperature (300oC) and pressure (67 atm) produces ethanol. Phosphoric acid is used as a catalyst.
• CH2=CH2 + H2O --> CH3-CH2OH
Reactions of alcohols
• Alcohols undergo 3 important reactions:
• (a) Combustion
• (b) Oxidation
• (c) Esterification
Combustion of alcohols
• Alcohols burn in oxygen to produce carbon dioxide and water.
• C2H5OH + 3O2 --> 2CO2 + 3H2O
Oxidation of alcohols
• Alcohols are oxidised to carboxylic acids.
• The number of carbon atoms remain the same in oxidation.
• CH3CH2OH + 2[O] --> CH3COOH + H2O
• The oxidation is carried out by using
• (i) oxygen
• (ii) acidified K2Cr2O7
• (iii) acidified KMnO4
Oxidation of alcohols
• During the oxidation:
– Acidified K2Cr2O7 turns from orange to green
– acidified KMnO4 is decolourised.
Esterification
• Alcohols react with organic acids to form esters. Esters are sweet fruity-smelling compounds.
• Word equation :
• Alcohol + carboxylic acid --> ester + water
Uses of ethanol
• As a solvent
• As a fuel
• As a constituent of wine and beer
• Human consumption of wine and beer can lead to alcohol addiction.
A model of an ethanol molecule
• Ethanol, C2H5OH, is used in beer making.
Carboxylic Acids
• Carboxylic acids are a family of organic compounds containing carbon, hydrogen and oxygen.
• The general formula of carboxylic acids is CnH2n+1COOH (n = 0, 1, 2, 3, 4…)
• The functional group is the –COOH group.
• Carboxylic acids end with –oic acid.
Carboxylic acid
• Butanoic acid has 2 isomers.
• Formation of ethanoic acid
– Ethanoic acid is formed by the oxidation of ethanol.
• By using atmospheric oxygen:
• CH3CH2OH + O2 --> CH3COOH + H2O
• By using acidified K2Cr2O7.
• CH3CH2OH + 2[O] à CH3COOH + H2O
• The orange dichromate (VI) solution changes from orange to green.
• A vinegar smell is detected.
Reactions of carboxylic acids
• Two important reactions of carboxylic acids are :
– Acid reactions
– Esterification
Acid reactions
- A carboxylic acid is a weak acid. When dissolved in water, it dissociates to produce H+ ions.
- Eg. CH3COOH <--> CH3COO- + H+
Reactions of carboxylic acids
• Carboxylic acids react with bases to form salt and water only.
• Carboxylic acids react with carbonate to produce carbon dioxide gas.
Reaction of acid - Esterification
• In the presence of a catalyst concentrated sulfuric acid, carboxylic acids react with alcohols to form a sweet-smelling compound, called an ester.
• Eg. Ethanoic acid + ethanol --> ethyl ethanoate + water
•
Esters
• The functional group of an ester is –COO- (there is a C=O bond and a C-O bond; refer to textbook on how the ester functional group looks like)
Esters are produced when an organic acid reacts with an alcohol, with a catalyst that is concentrated sulfuric acid.
Organic acid + alcohol --> ester + water
Esters
• Esters are neutral compound with a sweet smell.
• Esters are present in fruits.
• Uses of esters
– Artificial flavouring
– Solvents for organic compounds
– Vegetable oils
Macromolecules
• Macromolecules are very large molecules built up from joining together thousands of small units.
• The process of joining together thousands of small units is called polymerisation.
• The small units are called monomers.
• The large molecule formed is called a polymer.
• There are 2 groups of macromolecules:
• - synthetic polymers
• - natural macromolecules
Synthetic Polymers
• These are man-made polymers made by
–Addition polymerisation
–Condensation polymerisation
• Polymers made from addition polymerisation are called addition polymers.
• Polymers made from condensation polymerisation are called condensation polymers.
Addition Polymers
• Addition polymers are made from unsaturated monomers.
• The monomers are linked ( or added ) together to form a large molecule without the loss of any atoms. The monomers are joined together by an ADDITION reaction.
• Plastics are addition polymers formed using alkene molecules as monomers.
• Poly(ethene) is made from ethene monomers.
Condensation Polymers
• Condensation polymers are made from monomers containing alcohol, carboxylic acid or amino (-NH2) functional groups.
• The monomers are linked together to form a large molecule with the ELIMINATION of small molecules like water. The monomers are joined together by a condensation reaction.
Examples of condensation polymers
• Two examples of condensation polymers are
– Nylon
– Terylene
Formation of nylon
• The monomers used are carboxylic acids and amines
• The monomers are joined together by amide linkages to form a polyamide. A molecule of water is eliminated.
Formation of Terylene
• The monomers used are carboxylic acids and alcohols.
• The monomers are joined together by ester linkages to form a polyester. A molecule of water is also eliminated. Terylene and nylon are examples of condensation polymers.
Uses of nylon and terylene
• Nylon and terylene are made into synthetic fibres.
• Nylon fibres are used to make ropes, fishing lines, strings for rackets and cloth for making raincoats, tents and parachutes.
• Terylene fibres are used to make clothings.
Pollution caused by plastics
• Plastics are non-biodegradable and cannot be decomposed by bacteria in the environment.
• Plastic objects accumulate and pollute the environment.
• Plastics are carbon-based polymers which burn easily to release toxic fumes.
Natural Polymers
• Natural polymers are important substances found in all plants, animals and food.
• Food is made up of 3 types of polymers:
– Proteins needed for growth
– Carbohydrate which provide the body with energy
– Fats which also provide the body with energy.
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