Formylation of Aromatic Rings
This reaction is called the Reimer-Tiemann reaction after its discoverers. It is carried out on phenol and its mechanism involves a carbene, generated from chloroform by the action of hydroxide.
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A carbene is a neutral species with a carbon that forms only two bonds and keeps one lone pair: it has six electrons in its valence shell, lacks a complete octet and is therefore very reactive and electrophilic. Dichlorocarbene, :CCl2, forms when hydroxide removes the proton of chloroform and the resulting CCl3− anion loses a chloride. The very electron-rich phenoxide attacks it at the ortho position. The video explains the mechanism in more detail.
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Its discoverers: Karl Ludwig Reimer and Ferdinand Tiemann.