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Picolinic acid is a bidentate chelating agent of elements such as chromium, zinc, manganese, copper, iron, and molybdenum in the human body. [5] [6] It is a substrate in the Mitsunobu reaction. In the Hammick reaction, picolinic acid reacts with ketones to give pyridine-2-carbonols: [7] NC 5 H 4 CO 2 H + R 2 C=O → NC 5 H 4 CR 2 (OH) + CO 2
The scope of the reaction is effectively limited to decarboxylating acids where the carboxyl group is α to the nitrogen, (reactivity has been reported when the acids are located elsewhere on the molecule but with low yields) [7] [8] thus suitable substrates are limited to the derivatives of α-picolinic acid [3] [9] including the α-carboxylic ...
He recognized the acid from β–picoline as Nicotinsäure (nicotinic acid or "niacin"), [12] which Weidel had discovered in 1873. [13] When Weidel decarboxylated the carboxylic acid of each isomer – by dry distilling its calcium salt with calcium oxide – the reaction yielded pyridine, thus showing that picoline was a mixture of three ...
Most of the reactions of picoline are centered on the methyl group. For example, the principal use of 2-picoline is as a precursor of 2-vinylpyridine. The conversion is achieved by condensation with formaldehyde: The copolymer of 2-vinylpyridine, butadiene and styrene is used as an adhesive for textile tire cord.
Evidence that the Cr 3+ center coordinates to the pyridine nitrogen comes from a shift in the IR spectra of a C=N vibration at 1602.4 cm −1 for free picolinic acid to 1565.9 cm −1 for chromium(III) picolinate. [11] The bond length between Cr 3+ and the nitrogen atom of the pyridine ring on picolinate ranges from 2.047 to 2.048 Å. [12]
The complex adopts an octahedral molecular geometry, containing two bidentate picolinate ligands (conjugate base of picolinic acid) and two aquo ligands. Additionally, two water of crystallization are present, thus the compound crystallizes with the formula Zn(NC 5 H 4 CO 2) 2 (H 2 O) 2 ·2H 2 O. [1] It is a colorless solid.
In the related Hammick reaction, uncatalyzed decarboxylation of a picolinic acid gives a stable carbene that attacks a carbonyl electrophile. Oxidative decarboxylations are generally radical reactions. These include the Kolbe electrolysis and Hunsdiecker-Kochi reactions. The Barton decarboxylation is an unusual radical reductive decarboxylation.
Water-reactive substances [1] are those that spontaneously undergo a chemical reaction with water, often noted as generating flammable gas. [2] Some are highly reducing in nature. [ 3 ] Notable examples include alkali metals , lithium through caesium , and alkaline earth metals , magnesium through barium .