Classifying organic reactions by type highlights similarities between reactions that may at first appear different, and makes learning reaction chemistry easier.
Preparation of haloalkanes from alkenes and alcohols
The most useful preparations are those that result in introduction of halogen at specific carbon atoms with no change at other carbons. Examples of these are the addition (In addition reactions of organic substrates the two reactants combine to give a single product with no atoms left over.) and substitution reactions (A substitution reaction of an organic molecule is one in which a part of the organic molecule is changed for a part of the reagent. Two products result (RH + Cl–Cl → RCl + HCl). ) given below.
Reactions of haloalkanes to give alkenes, alcohols or amines.
Note that the reaction of haloalkanes to give alkenes is the reverse of the reaction above as is their substitution reaction to form alcohols.
Preparation of haloalkanes from alkenes and alcohols
The most useful preparations are those that result in introduction of halogen at specific carbon atoms with no change at other carbons. Examples of these are the addition (In addition reactions of organic substrates the two reactants combine to give a single product with no atoms left over.) and substitution reactions (A substitution reaction of an organic molecule is one in which a part of the organic molecule is changed for a part of the reagent. Two products result (RH + Cl–Cl → RCl + HCl). ) given below.
| addition Alkenes react with halogen (X2) or HX at multiply bonded carbons. CH2=CH2 + Br–Br  BrCH2–CH2BrCH2=CH2 + H–Cl HCH2–CH2Cl |
| substitution Alcohols react with a variety of halogen-containing reagents to substitute the OH for halogen. Common ones are SOCl2, PCl3 (PBr3), PCl5, conc HCl (HBr). The changes in the organic compound involved are shown below. Additional products formed depend on the reagent used. CH3CH2OH CH3CH2ClCH3CH2OH CH3CH2Br |
Reactions of haloalkanes to give alkenes, alcohols or amines.
Note that the reaction of haloalkanes to give alkenes is the reverse of the reaction above as is their substitution reaction to form alcohols.
| elimination Haloalkanes react with bases (commonly KOH or NaOH) to form alkenes. In order for elimination to occur the carbon adjacent to the carbon bearing halogen must bear H. HO– + HCH2–CH2Cl HOH + CH2=CH2 + Cl– |
| substitution Haloalkanes react with HO– to give alcohols or with a larger excess of NH3 to give amines. CH3CH2Cl + OH– CH3CH2OH + Cl–CH3CH2Cl + NH3 CH3CH2NH2 + HClThe HCl produced reacts with excess NH3 to give the ethylammonium chloride (NH4Cl). |