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Sulfanilic acid can be produced by sulfonation of aniline with concentrated sulfuric acid. [5] This proceeds via phenylsulfamic acid; a zwitterion with a N-S bond. Eugen Bamberger originally proposed a mechanism involving a series of intramolecular rearrangements, with phenylsulfamic acid forming orthanilic acid, which rearranged to sulfanilic acid on heating.
Chlorosulfuric acid is also an effective agent: C 6 H 6 + HSO 3 Cl → C 6 H 5 SO 3 H + HCl. In contrast to aromatic nitration and most other electrophilic aromatic substitutions this reaction is reversible. Sulfonation takes place in concentrated acidic conditions and desulfonation is the mode of action in a dilute hot aqueous acid.
For example, reaction of aniline with sulfuric acid at 180 °C produces sulfanilic acid, H 2 NC 6 H 4 SO 3 H. If bromine water is added to aniline, the bromine water is decolourised and a white precipitate of 2,4,6-tribromoaniline is formed. To generate the mono-substituted product, a protection with acetyl chloride is required:
The reaction mechanism is not exactly known; two proposals are presented here. One possibility is at first an aldol condensation, starting from the enol form of the pyruvic acid (1) and the aldehyde, forming an β,γ-unsaturated α-ketocarboxylic acid (2). This is followed by a Michael addition with aniline to form an aniline derivative (3).
A 2006 study [6] proposes a fragmentation-recombination mechanism based on carbon isotope scrambling experiments. In this study 4-isopropylaniline 1 is reacted with a mixture (50:50)of ordinary pulegone and the 13 C-enriched isomer 2 and the reaction mechanism is outlined in scheme 2 with the labeled carbon
The Skraup synthesis is a chemical reaction used to synthesize quinolines. It is named after the Czech chemist Zdenko Hans Skraup (1850-1910). In the archetypal Skraup reaction, aniline is heated with sulfuric acid , glycerol , and an oxidizing agent such as nitrobenzene to yield quinoline.
The mechanism for the Gould–Jacobs reaction begins with a nucleophilic attack from the amine nitrogen follows by the loss of ethanol to form the condensation product. A 6 electron cyclization reaction with the loss of another ethanol molecule forms a quinoline (ethyl 4-oxo-4,4a-dihydroquinoline-3-carboxylate).
The reaction mechanism of the Gassman indole synthesis The first step is the oxidation of the aniline 1 using tert -butyl hypochlorite (tBuOCl) to give the chloramine 2 . The second step is the addition of the keto-thioether to give the sulfonium ion 3 , and is typically done at low temperatures (−78 °C).