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The Baeyer–Drewsen indigo synthesis (1882) is an organic reaction in which indigo is prepared from 2-nitrobenzaldehyde and acetone [1] [2] The reaction was developed by von Baeyer and Viggo Drewsen in 1880 to produce the first synthetic indigo at laboratory scale. This procedure is not used at industrial scale.
This reaction is used to protect alkynes: the alkyne is either converted with acetone to a 2-hydroxyprop-2-yl-alkyne or a protected alkyne can be directly synthesized using the commercially available 2-methyl-3-butyn-2-ol as an alkyne source. [5]
Acetone (2-propanone or dimethyl ketone) is an organic compound with the formula (CH 3) 2 CO. [22] It is the simplest and smallest ketone (>C=O).It is a colorless, highly volatile, and flammable liquid with a characteristic pungent odour, very reminiscent of the smell of pear drops.
The original reaction was a mixture of the reagents phenol, chloroform, and acetone in the presence of a sodium hydroxide solution. [2] Prior to Bargellini's research, the product attributed to this multi-component reaction (MCR) had been described as a phenol derivative in chemistry texts at the time.
The concerted mechanism of this step is similar to the mechanisms of the Baeyer–Villiger oxidation [6] and Criegee rearrangement reactions, and also the oxidation step of the hydroboration–oxidation process. [7] In 2009, an acidified bentonite clay was proven to be a more economical catalyst than sulfuric acid as the acid medium.
The aldol addition product can be dehydrated via two mechanisms; a strong base like potassium t-butoxide, potassium hydroxide or sodium hydride deprotonates the product to an enolate, which eliminates via the E1cB mechanism, [9] [10] while dehydration in acid proceeds via an E1 reaction mechanism.
For example, two molecules of acetone condense to a single compound mesityl oxide in the presence of an ion-exchange resin: [1] 2 CH 3 COCH 3 → (CH 3) 2 C=CH(CO)CH 3 + H 2 O. For synthetic uses, this is generally an undesirable, but spontaneous and favored side-reaction of mixed aldol condensation, and special precautions are needed to ...
The rearrangement of acetone oxime in the Beckmann solution involved three acetic acid molecules and one proton (present as an oxonium ion). In the transition state leading to the iminium ion (σ-complex), the methyl group migrates to the nitrogen atom in a concerted reaction as the hydroxyl group is expelled.