Combustion Reaction: Carbon and carbon compounds give carbon dioxide, vapor, heat and light on burning in air. Following are some of the examples of combustion reaction of organic compounds:
C + O2 ⇨ CO2 + Heat + Light
CH4 + 2O2 ⇨ CO2 + 2H2O + Heat + Light
CH3CH2OH + O2 ⇨ CO2 + H2O + Heat + Light
In combustion reaction, carbon compounds are oxidized in the presence of oxygen. The following example is different because alkaline KMnO4 is the oxidizing agent in this reaction.
CH3CH2OH + (Alkaline KMnO4/Acidified K2Cr2O7) ⇨ CH3COOH
Formation of larger molecules by addition of more radicals is known as addition reaction. For example; ethene is converted into ethane when heated with the catalyst nickel.
CH2=CH2 + H2 + (Nickel catalyst) ⇨ CH3−CH3
When ethene undergoes addition reaction with chlorine, it gives dichloroethane.
Replacement of a functional group or any atom by another atom or functional group is known as substitution reaction. Substitution reactions are single displacement reactions.
When methane reacts with chlorine gas in the presence of sunlight, it gives chloromethane and hydrogen chloride.
CH4 + Cl2 + Sunlight ⇨ CH3Cl + HCl
Similarly, ethane gives chloroethane when it reacts with chlorine in the presence of sunlight.
C2H6 + Cl2 + Sunlight ⇨ C2H5Cl + HCl
Some Important Organic Compounds
- Ethanol is commonly known as alcohol and spirit.
- General name of ethanol is ethyl alcohol.
- Ethanol is the main constituent of all alcoholic drinks
- Ethanol is soluble in water
- Ethanol is a very good solvent
- Ethanol is used in manufacturing of medicines, such as tincture iodine, cough syrup, etc.
- Taking even small quantity of pure ethanol may prove lethal
- Taking dilute ethyl alcohol can cause drunkenness
Reaction of ethanol with sodium metal:
When ethanol reacts with sodium, it gives sodium ethoxide and hydrogen gas.
2CH3CH2OH + 2Na ⇨ 2CH3CH2ONa + H2
Oxidation of ethanol: Ethanol gives ethanoic acid on oxidation.
CH3CH2OH + (Alkaline KMnO4/Acidified K2Cr2O7) ⇨ CH3COOH
Dehydration of ethanol: Ethanol gives ethene and water when it is heated with concentrated sulphuric acid.
CH3CH2OH + Conc. H2SO4 ⇨ CH2=CH2 + H2O
Ethanoic Acid (CH3COOH)
Structural formula of ethanoic acid is as follows:
- General name of ethanoic acid is acetic acid.
- Melting point of ethanoic acid is 290K.
- Ethanoic acid freezes in winter and hence it is also known as glacial acetic acid.
- Ethanoic acid is a colorless liquid.
- 5% to 8% solution of acetic acid in water is known as vinegar.
- Vinegar is used as preservative in pickles.
- Carboxylic acids are weak acid compared to mineral acids.
Reaction of ethanoic acid with base: Ethanoic acid gives sodium acetate when it reacts with sodium hydroxide.
CH3COOH + NaOH ⇨ CH3COONa + H2O
Esterificaiton of ethanoic acid: Ethanoic acid gives ethyl acetate when it reacts with ethanol in presence of conc. sulphuric acid. This reaction is called esterification reaction.
CH3COOH + C2H5OH ⇨ CH3COOC2H5 + H2O
The IUPAC name of Ethyl acetate is Ethyl Ethanoate. Ethyl acetate is also known as ester. Ester is a sweet smelling compound. It is used in making perfumes and as a flavouring agent. When ethyl ethanoate reacts with a base or acid, it gives back ethanol and ethanoic acid.
CH3COOC2H5 + NaOH ⇨ CH3COOH + C2H5OH
Hydrolysis of ester (Ethyl ethanoate): Ethyl ethanoate gives parent alcohol and sodium ethanoate when heated with sodium hydroxide solution.
CH3COOC2H5 + NaOH ⇨ CH3COONa + C2H5OH
Saponification: Ester of higher fatty acids gives sodium salt of higher fatty acid; when heated with glycerol and sodium hydroxide. Sodium salts of higher fatty acid are known as soaps. This reaction is called saponification (soap making).
Reaction of ethanoic acid with sodium carbonate and sodium bicarbonate:
Ethanoic acid gives sodium acetate, water and carbon dioxide when reacts with sodium carbonate or sodium bicarbonate (sodium hydrogen carbonate).
2CH3COOH + Na2CO3 ⇨ 2CH3COONa + CO2 + H2O
CH3COOH + NaHCO3 ⇨ CH3COONa + CO2 + H2O
Soaps and Detergents:
Soap: Sodium salts of long chain fatty acids are called soap. It is manufactured by the reaction of easter of higher fatty acid with sodium hydroxide. The sodium salt so formed has cleansing property.
Detergent: Soap cannot form lather in hard water. To overcome this problem, detergents were introduced. Detergent is also known as soapless soap. Detergent is sodium salt of benzene sulphonic acid or sodium salt of long chain alkyl hydrogen sulphate.
Cleansing action of soap:
Soap molecule has two ends. One end is hydrophilic and another end is hydrophobic. In other words, one end is lipophobic (hydrophilic) and another end is lipophilic (hydrophobic). When soap is dissolved in water and clothes are put in the soapy solution, soap molecules converge in a typical fashion to make a structure; called micelle. The hydrophobic ends of different molecules surround a particle of grease and make the micelle; which is a spherical structure. In this, the hydrophilic end is outside the sphere and hydrophobic end is towards the centre of the sphere. That is how, soap molecules wash away dirt and grease by making micelles around them.
Soap and Hard Water: Hard water often contains salts of calcium and magnesium. Soap molecules react with the salts of calcium and magnesium and form a precipitate. This precipitate begins floating as an off-white layer over water. This layer is called scum. Soaps lose their cleansing property in hard water because of formation of scum. Detergents are used; instead of soaps; in hard water to overcome the problem. Detergents are usually ammonium or sulphonate salts of carboxylic acids. The charged ends of these compounds do not form precipitate with calcium or magnesium salts in hard water. Hence, detergents retain their cleansing property in hard water.