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Primary amines are usually not used for enamine synthesis due to the preferential formation of the more thermodynamically stable imine species. [11] Methyl ketone self-condensation is a side-reaction which can be avoided through the addition of TiCl 4 [12] into the reaction mixture (to act as a water scavenger).
When R = H, the compound is a primary imine, when R is hydrocarbyl, the compound is a secondary imine. If this group is not a hydrogen atom, then the compound can sometimes be referred to as a Schiff base. [9] When R 3 is OH, the imine is called an oxime, and when R 3 is NH 2 the imine is called a hydrazone.
The mechanism of the Knorr pyrrole synthesis begins with condensation of the amine and ketone to give an imine. The imine then tautomerizes to an enamine, followed by cyclization, elimination of water, and isomerization to the pyrrole. Mechanism of Knorr pyrrole synthesis
Below is one published mechanism for the reaction: [5] Mechanism for the Hantzsch Pyrrole Synthesis. The mechanism starts with the amine (1) attacking the β carbon of the β-ketoesters (2), and eventually forming an enamine (3). The enamine then attacks the carbonyl carbon of the α-haloketone (4). This is followed by the loss of H 2 O, giving ...
The Stork enamine synthesis: formation of an enamine from a ketone; addition of the enamine to an alpha, beta-unsaturated aldehyde or ketone; hydrolysis of the enamine back to a ketone; The Stork enamine reaction. The reaction also applies to acyl halides as electrophiles, which results in the formation of 1,3-diketones (Stork acylation). [2]
The mechanism of the Mannich reaction starts with the formation of an iminium ion from the amine and formaldehyde. [4]: 140 The compound with the carbonyl functional group (in this case a ketone) will tautomerize to the enol form, after which it attacks the iminium ion.
Methanolamine, a simple hemiaminal. The adducts formed by the addition of ammonia to aldehydes have long been studied. [3] Compounds containing both a primary amino group and a hydroxyl group bonded to the same carbon atom are rarely stable, as they tend to dehydrate to form imines which polymerise to hexamethylenetetramine.
List [2] et al. theorize in their study that this restriction is primarily in the carboxylic-acid group next to the enamine attachment, which can stabilize the imine product. List also expands upon the role of the imine by listing its ratio with the aldehyde to be 1 using 1 H-NMR methods, indicating that the Michael Addition is rate-determining ...