Explain the following named reaction:

i) Sandmeyer reaction.

ii) Gattermann reaction.

Let's delve into two important reactions in organic chemistry: the Sandmeyer reaction and the Gattermann reaction. Both of these reactions involve the transformation of aryl halides, but they do so in distinct ways and for different purposes.

Sandmeyer Reaction

The Sandmeyer reaction is a method used to synthesize aryl halides from aryl amines. This reaction is particularly useful for converting an aniline derivative into a variety of substituted aromatic compounds. The general process involves the following steps:

• Starting Material: An aryl amine (like aniline).
• Treatment with Nitrous Acid: The aryl amine is first treated with nitrous acid (generated in situ from sodium nitrite and hydrochloric acid) to form a diazonium salt.
• Substitution Reaction: The diazonium salt can then undergo substitution with a copper(I) salt (like copper(I) bromide or copper(I) chloride) to yield the corresponding aryl halide.

For example, if we start with aniline and treat it with nitrous acid, we form benzenediazonium chloride. When this diazonium salt reacts with copper(I) bromide, we obtain bromobenzene. This reaction is particularly valuable because it allows for the introduction of halogens into aromatic systems, which can be further modified in subsequent reactions.

Applications of the Sandmeyer Reaction

The Sandmeyer reaction is widely used in the synthesis of pharmaceuticals, agrochemicals, and dyes. Its ability to selectively introduce halogens makes it a powerful tool in organic synthesis. Additionally, the reaction can be adapted to introduce other nucleophiles, such as cyanide or hydroxyl groups, by using different reagents.

Gattermann Reaction

On the other hand, the Gattermann reaction is a method for the formylation of aromatic compounds, which means it introduces a formyl group (-CHO) into the aromatic ring. This reaction is particularly useful for synthesizing aldehydes from aromatic compounds. Here’s how it works:

• Starting Material: An aromatic compound (like toluene).
• Treatment with Carbon Monoxide and Hydrochloric Acid: The aromatic compound is treated with carbon monoxide and hydrochloric acid in the presence of a Lewis acid catalyst, typically aluminum chloride.
• Formation of Aldehyde: The result is the introduction of a formyl group to the aromatic ring, yielding an aromatic aldehyde.

For instance, if toluene undergoes the Gattermann reaction, it can be converted into benzaldehyde. This reaction is particularly significant because it allows for the direct synthesis of aromatic aldehydes, which are important intermediates in organic synthesis.

Significance of the Gattermann Reaction

The Gattermann reaction is valuable in the production of various aromatic aldehydes, which are key components in fragrances, flavorings, and pharmaceuticals. The ability to introduce a formyl group directly into an aromatic system expands the toolbox for synthetic chemists, enabling the creation of complex molecules with relative ease.

In summary, both the Sandmeyer and Gattermann reactions are essential transformations in organic chemistry, each serving unique purposes in the synthesis of aromatic compounds. Understanding these reactions not only enhances your grasp of organic synthesis but also opens up pathways for creating a wide array of chemical products.