Alkenes are prepared by alcohols, alkly halides, alkynes and more. Different reagents and physical conditions should be maintained according to thee using compound. Preparation of alkene is a lesson of organic chemistry in grade 12.
When alkyl halide compound is heated with alcoholic potassium hydroxide, an alkene is formed as the product. A H-X molecule is removed from alkyl halide to give alkene. Heated KOH is acted as an alkaline and remove a hydrogen atom which is linked to a carbon atom which is adjoin to the halogen linked to the carbon atom.
Alkynes are reduced to alkenes using Linda catalyst ( alladium- charcoal catalyst partially deactivated with poison like sulfur compounds or quinoline ) and hydrogen gas (H2).
When alcohols are heated with a dehydrator, a water molecule is eliminated from alcohol molecule and alkene is formed as the product. As a dehydrator one of the following substance can be used.
If there is no direct way, you have to find an alternative method. It may be longer than usual one.
Prepare an alkyl halide from alcohol using a suitable reagent like PCl3 or PBr3. Then, alkyl halide is heated with alcoholic KOH to produce alkene.
Ethanol is an alcohol which contains two carbon atoms. Therefore, you can prepare ethene which is the simplest alkene from ethanol. You need an dehydrator to convert ethanol to ethene.
1-propanol is a liquid at room temperature. When you prepare propene (an alkene with three carbon atoms) by heating 1-propanol with a dehydrator, a physical state change can be seen. Because, propene is a gas.