Gattermann - Koch Reaction: Mechanism, Limitations and Examples

Ans. Ludwig Gattermann (1860–1920), a German chemist, developed it in 1890.

Ans. Benzaldehyde or substituted benzaldehyde is formed when benzene or one of its derivatives is treated with hydrogen chloride and carbon monoxide in the presence of cuprous chloride or anhydrous aluminium chloride.

The Gattermann Koch response is the name for this reaction.

Ans. The Gattermann Koch Reaction Mechanism begins with the production of reactive species using acid as a catalyst. The reaction's ultimate goal is to attach a formyl group (-CHO group) to an aromatic system, resulting in the formation of an aromatic aldehyde as a product.

Benzaldehyde is produced when benzene is reacted with carbon monoxide in an acidic solution in the presence of anhydrous aluminium chloride. In this process, anhydrous aluminium chloride functions as a catalyst. An electrophilic substitution reaction is what occurs.

Ans. The mechanism of the Gattermann - Koch reaction is as follows:

Step 1: Carbon monoxide functions as a Lewis base, accepting a proton from hydrochloric acid to produce a positively charged molecule with various resonance configurations. One of these has a positive charge on the carbon and reacts with the aromatic ring as an electrophile. The chloride ion in hydrochloric acid, on the other hand, attacks it nucleophilically.

Carbon monoxide reacts with hydrochloric acid to create formyl chloride, which is the first step in the process.

Step 2: The formyl chloride generates an electrophile or aldehyde intermediate when it interacts with anhydrous aluminium chloride, which acts as a catalyst.

Step 3: The electrophile or aldehyde group finally interacts with the benzene ring to produce the end product, benzaldehyde. The aromatic ring acts as a nucleophile, giving the formyl cation an electron pair. The simultaneous ejection of a proton resolves the transient loss of aromaticity. Hydrochloric acid and aluminium chloride are both eliminated as a result of this reaction.

Ans. The Gattermann – Koch process is one of the most popular aromatic chemistry procedures utilized in the production of aryl ketones. When stoichiometric quantities of Lewis acid are used, a complex form at the conclusion of the reaction between the aryl ketone produced and the Lewis acid.

Ans. Phenol and phenol ether substrates are not suitable for the Gattermann-Koch reaction. If we employ zinc chloride as a catalyst in the Gattermann – Koch reaction, we must additionally add traces of copper(I) chloride, which acts as a co-catalyst, enhancing the activity of catalysts. 

Ans. The electron density of the ring is significant because it usually starts with a nucleophilic assault by the aromatic group. Regioselective formylation is known to occur in certain aromatic compounds, such as pyrrole. The Gattermann reaction and the Gattermann-Koch reaction may both be used to formylate benzene rings.

Other electron-rich substrates such as mesitylene, pyrrole, or fused aromatic rings might also be anticipated to react since they can be quickly deprotonated to produce phenoxides, which are good nucleophiles. Under strong circumstances, benzene will react, although deactivated rings like pyridine are difficult to formylate efficiently.

Many formylation methods would produce just the ortho result, whereas phenol would generally produce a mixture of ortho and para molecules (e.g. 2-hydroxybenzaldehyde). This can be explained through the strong attractive forces that exist between the formylating reagent and phenoxide during the reaction, such as ionic interactions with the nitrogen centers that are cationic in the Vilsmeier–Haack reaction and Duff reaction, or coordination to metals of high oxidation in the Rieche formylation (Kolbe–Schmitt reaction) and the Casiraghi formylation.

The Casiraghi formylation allows phenol to react directly with paraformaldehyde; all earlier techniques utilized disguised forms of formaldehyde, in part to prevent the production of phenol-formaldehyde resins. Because aldehydes are highly deactivating, phenols usually only react once; nevertheless, some reactions, such as the Duff reaction, might result in multiple additions.

Ans. The Gattermann – Koch reaction is a variation of the Gattermann reaction that uses carbon monoxide (CO) instead of hydrogen cyanide. It is named after German scientists Ludwig Gattermann and Julius Arnold Koch.

Ans. A variant of the Gattermann response is the Gattermann Koch reaction. The main distinction between the Gattermann and Gattermann Koch reactions is that the former utilizes a combination of hydrogen cyanide and hydrochloric acid, whilst the latter uses carbon monoxide instead of hydrogen cyanide.

Ans. As phenol and phenol ethers "could not be effectively formylated at atmospheric pressure in benzene as a solvent," the Gattermann-Koch Reaction is not applicable to them. "The insolubility of the cuprous chloride in the reaction mixture was blamed for the failure to react."