Physical properties of propane: propane is a colorless, odorless gas with melting point of -189.9 C and boiling point of -44.5 C. It is insoluble in polar solvents like water, but soluble in non polar solvents, such as alcohol, ether and benzene.
Chemical properties of propane: Like other alkanes, under ordinary conditions, propane too is quite inert towards common reagents such as acids, alkalis and oxidizing agents.
Propane undergoes halogenations such as chlorination in the presence of light, heat or catalyst.
Halogenation is an example of substitution reaction since it is brought about by the replacement of a H atom present in the molecule of propane by a halogen atom without the compound undergoing any change in its structure.
Propane has two types of H atoms-primary and secondary;
Chlorination gives the following two products with the indicated percentage yield:
CH3.CH2.CH3 + Cl2 --> CH3.CHCl.CH3 (60% )+ CH2.Cl.CH2.CH3 (40%)
So the conclusion we arrive at is that the secondary hydrogen atom is more reactive than the primary hydrogen atom. (According to Markownikoff’s rule, the order of stability is tertiary H> sec. H> primary H)
Nitration: propane reacts with nitric acid at temperatures between 150 – 475 C to give rise to various nitro substituted compounds by the replacement of Hydrogen’s; the ease with which the various hydrogen atoms are replaced is in accordance with the Markownikoff’s rule for halogenations.
CH3.CH2.CH3 + HNO3 (400C) --> CH3.CH.NO2.CH3 (major product)+ minor products (CH3.CH2.CH2.NO2 + CH3.CH2.NO2 + CH3.NO2)
Sulphonation is another reaction that occurs through substitution as in the instance of nitration, when propane is treated with oleum; a hydrogen atom is replaced by a sulphonic group –SO3H.
CH3.CH2.CH3 + OH.SO3.H(oleum) --> CH3.CH.(SO3H).CH3 + H2O.
Combustion of propane or burning of propane with a non luminous flame results in the formation of CO2 and H2O.
Oxidation of propane in the presence of catalysts such as vanadium oxides result in the formation of acetic acid or acrylic acid when carried out in the presence of water vapor.
CH3.CH2.CH3 + 5O2 --> 3CO2 + 4H2O + HEAT
Cracking of propane can also be carried out by passing the vapors through a hot metal tube at high temperature. This yields smaller products such as methane and ethylene.