Chemistry – Organic chemistry - Alkanes | e-Consult
Organic chemistry - Alkanes (1 questions)
The mixture of products is formed because the substitution of hydrogen atoms in propane by chlorine is a free radical reaction. This reaction is non-selective, meaning that chlorine can substitute any hydrogen atom in the propane molecule. The products are formed through a series of successive substitution reactions.
The proportion of each product changes as the reaction proceeds as follows:
| Stage | Product formed |
| Initial (low Cl2:propane ratio) | Methyl chloride (CH3Cl) - primarily one chlorine atom substituted |
| Intermediate (increasing Cl2:propane ratio) | Dichloro propane (e.g., CH2ClCH2CH3) - two chlorine atoms substituted |
| Late (high Cl2:propane ratio) | Trichloro propane (e.g., CHCl2CH2CH3) - three chlorine atoms substituted |
As the reaction continues and more chlorine is added, the proportion of methyl chloride decreases, while the proportions of dichloro propane and trichloro propane increase. This is because the reaction is statistically more likely to substitute a second and then a third hydrogen atom as the reaction progresses. Eventually, the reaction will produce a mixture of all possible chlorinated propane products, but the relative proportions will be determined by the ratio of chlorine to propane used in the reaction.