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The Schmidt reaction is an important organic transformation in which carboxylic acids, aldehydes, or ketones react with hydrazoic acid (HN₃) under strongly acidic conditions (usually concentrated sulfuric acid) to form amines or amides with loss of nitrogen gas (N₂).

In the case of carboxylic acids, the reaction produces primary amines with one carbon less (decarboxylation). With ketones, it forms amides, while aldehydes give nitriles. The reaction proceeds through the formation of an acyl azide intermediate, which undergoes rearrangement involving migration of an alkyl or aryl group from carbon to nitrogen.

A key step is the evolution of nitrogen gas, which drives the reaction forward and makes it highly favorable. The migrating group retains its configuration, indicating a concerted rearrangement mechanism.
Overall, the Schmidt reaction is useful for chain shortening and synthesis of nitrogen-containing compounds, widely applied in organic and pharmaceutical chemistry.

The Reimer–Tiemann reaction is an important organic reaction used to introduce a formyl group (–CHO) into aromatic compounds, especially phenols. In this reaction, phenol is treated with chloroform (CHCl₃) and a strong base like aqueous NaOH or KOH, followed by acidification. The reaction mainly produces salicylaldehyde (o-hydroxybenzaldehyde) as the major product.

The mechanism involves the formation of a highly reactive intermediate called dichlorocarbene (:CCl₂), generated from chloroform under basic conditions. This intermediate attacks the activated aromatic ring of phenol, preferably at the ortho position due to the directing effect of the –OH group. After hydrolysis, the intermediate is converted into an aldehyde group.

This reaction is significant in organic synthesis because it provides a simple method to prepare aromatic aldehydes. It also demonstrates key concepts like electrophilic substitution, carbene chemistry, and ortho-directing effects in aromatic systems.

Four basic copolymers structures.