Answer:

1. The Reimer-Tiemann reaction is a chemical reaction used for the preparation of ortho-hydroxyaryl aldehydes or ketones from phenols. The procedure involves the treatment of phenol with chloroform (CHCl3) and a strong base such as sodium hydroxide (NaOH) or potassium hydroxide (KOH) in the presence of a catalyst, usually copper (Cu). The reaction mechanism involves the formation of a carbonyl intermediate followed by rearrangement to the final product.
2. The Hell-Volhard-Zelinsky reaction is a chemical reaction used for the α-bromination of carboxylic acids. The procedure involves the treatment of a carboxylic acid with bromine (Br2) in the presence of a phosphorus halide, usually phosphorus tribromide (PBr3), and a catalyst such as iron (Fe) or iodine (I2). The reaction mechanism involves the formation of an acyl bromide intermediate followed by halogen exchange to the final product.
3. The Stephen aldehyde synthesis is a chemical reaction used for the preparation of aldehydes from nitriles. The procedure involves the treatment of a nitrile with a reducing agent, usually lithium aluminum hydride (LiAlH4), in the presence of an acid catalyst such as sulfuric acid (H2SO4). The reaction mechanism involves the reduction of the nitrile to an imine intermediate, followed by hydrolysis to the final product.
4. The Gattermann-Koch reaction is a chemical reaction used for the preparation of aryl aldehydes from benzene derivatives. The procedure involves the treatment of a benzene derivative with carbon monoxide (CO) and hydrogen chloride (HCl) in the presence of a catalyst such as copper (Cu) or aluminum chloride (AlCl3). The reaction mechanism involves the formation of a carbonyl intermediate followed by hydrolysis to the final product.
5. The Cannizzaro reaction is a chemical reaction used for the disproportionation of aldehydes into a carboxylic acid and an alcohol. The procedure involves the treatment of an aldehyde with a strong base such as sodium hydroxide (NaOH) or potassium hydroxide (KOH). The reaction mechanism involves the formation of a carbanion intermediate followed by transfer of a hydride ion to another molecule of the same aldehyde, resulting in the formation of a carboxylic acid and an alcohol.

Explanation:

Verified answer

Continuing the journey from @mradityabhau ( Since, the student wrote all the main points of these reactions. )

1) The Reimer Tiemann reaction.

■. In the attachment 1, common example of the Reimer Tiemann reaction is the conversion of phenol to salicylaldehyde (2-hydroxy benzaldehyde) as shown above.

2) The Halfmann bromide reaction.

■. In the 2nd attachment, common example of the Halfmann bromide reaction is the conversion of Acetamide to methanamine and the conversion of propanamide to ethanamine

3) The Stephen aldehyde synthesis.

■. An example where the Stephen reaction is used is when acetaldehyde is produced from methyl cyanide.

4) The Gattermann Koch's reaction.

■. benzaldehyde is formed from the treatment of benzene with carbon monoxide and hydrochloric acid in the presence of aluminium chloride and copper chloride.

5) The Cannizzaro reaction.

■. In the 3rd and last attachment, there is the example of this reaction where, the products that are formed in a Cannizzaro reaction include primary alcohols and carboxylic acids. The carboxylate anion is protonated to afford the carboxylic acid whereas the alkoxide anion is protonated by water to yield alcohol.

I have listed out only the examples of each hydro-organic reaction. ^_^.