Describe the preparation and reactions of bromo cyclohexane in organic synthesis.

The preparation of bromocyclohexane typically involves the free radical halogenation of cyclohexane or the nucleophilic substitution of cyclohexanol. Here, we will discuss the preparation of bromocyclohexane through the nucleophilic substitution reaction, which is more common in a laboratory setting.

Step 1: Preparation of Cyclohexanol

Cyclohexanol can be prepared by the hydrogenation of phenol or the oxidation of cyclohexane. For the purpose of this explanation, let's assume we have cyclohexanol readily available.

Step 2: Conversion of Cyclohexanol to Bromocyclohexane

The conversion of cyclohexanol to bromocyclohexane is typically done through an SN1 or SN2 mechanism, depending on the reaction conditions. Here, we will use an SN1 reaction, which is common for secondary alcohols like cyclohexanol.

Materials Required:

- Cyclohexanol
- Hydrobromic acid (HBr)
- Sulfuric acid (H2SO4) (optional, as a catalyst)
- Distillation apparatus
- Ice bath
- Separatory funnel
- Anhydrous sodium sulfate (Na2SO4)

Procedure:

1. Reflux with Hydrobromic Acid:
Place cyclohexanol in a round-bottom flask equipped with a reflux condenser. Add an excess of hydrobromic acid to the flask. The reaction can be catalyzed by adding a small amount of concentrated sulfuric acid to promote the formation of the bromonium ion.

$$\text{Cyclohexanol}+\text{HBr}\to \text{Bromocyclohexane}+{\text{H}}_2\text{O}$$

2. Heating:
Heat the mixture under reflux for several hours to ensure complete reaction. The SN1 reaction involves the formation of a carbocation intermediate, which then reacts with the bromide ion from hydrobromic acid to form bromocyclohexane.

3. Distillation:
After the reaction is complete, distill the mixture to separate bromocyclohexane from water and excess hydrobromic acid. Bromocyclohexane, being less polar, will have a higher boiling point than water and can be collected separately.

4. Separation:
Use a separatory funnel to separate the organic layer (bromocyclohexane) from the aqueous layer. The organic layer is usually on top due to the lower density of bromocyclohexane compared to water.

5. Drying:
Dry the organic layer by adding anhydrous sodium sulfate, which will remove any remaining traces of water.

6. Purification:
Purify the bromocyclohexane by simple distillation or fractional distillation, collecting the fraction at the boiling point of bromocyclohexane (approximately 156°C).

Reactions of Bromocyclohexane in Organic Synthesis:

Bromocyclohexane is a versatile intermediate in organic synthesis. It can undergo various reactions, including:

1. Nucleophilic Substitution Reactions (SN2):
Bromocyclohexane can react with nucleophiles such as cyanide or azide ions to form corresponding cyclohexyl derivatives.

$$\text{Bromocyclohexane}+\text{Nucleophile}\to \text{Cyclohexyl derivative}+{\text{Br}}^{-}$$

2. Elimination Reactions (E2):
Under strong basic conditions, bromocyclohexane can undergo dehydrohalogenation to form cyclohexene.

$$\text{Bromocyclohexane}+\text{Base}\to \text{Cyclohexene}+\text{HBr}$$

3. Grignard Reaction:
Bromocyclohexane can be used to form Grignard reagents by reacting with magnesium in dry ether, which can then be used in various carbon-carbon bond-forming reactions.

$$\text{Bromocyclohexane}+\text{Mg}\to \text{Cyclohexylmagnesium bromide}$$

4. Coupling Reactions:
Bromocyclohexane can participate in palladium-catalyzed coupling reactions, such as the Suzuki or Stille coupling, to form biaryl compounds or other complex structures.

These are just a few examples of the reactions that bromocyclohexane can undergo in organic synthesis. Its reactivity as an alkyl halide makes it a valuable building block for the construction of more complex organic molecules.