Picolinic acid hydrochloride

A carboxyl group usually hinders electrophilic attack. It is, therefore, at first sight surprising to note that picolinic acid hydrochloride reacts with thionyl chloride to give 4-chloropicolinic acid in yields of up to 55%.182-184 Under more severe conditions a 35% yield of 4,6-dichloropicolinic acid is obtained.182 Sulfur dioxide in the reaction mixture favors 4-chloropicolinic acid formation.183 This suggests that the chlorination may actually involve a nucleophilic attack by chloride ion upon a complexed pyridinium salt1 ... 

PicoLiNic acid hydrochloride, 20, 79 Potassium acetate, 20, 33 Potassium amide, 20, 91 Potassium bromide, 20, 81, loi Potassium carbonate, 20, 21 Potassium cyanide, 20, 38, 44 Potassium permanganate, 20, 79 Pressure reaction, 20, 40, 81, loi 1,3-Propanedione, i,3-diphenyl-, 20,... 

Separation schemes for pyridinecarboxylic acids and nicotinic and isonicotinic acids are reported. Paper chromatography and gas chromatography of pyridinecarboxylic acids have been discussed, and the crystal structures of picolinic acid hydrochloride and picolinamide have been described. 

CgHsN02S, 2-Mercaptopyridine-4-carboxylic acid, 43B, 287 C6H6CINO2, Picolinic acid hydrochloride, 30B, 130 C6HgN20, Nicotinamide, 18, 752 CgHgN20, a-Picolinamide, 31B, 121... 

Trifluoromethylpyridine can be prepared ia 54% yield from picolinic acid and sulfur tetrafluoride—hydrogen fluoride (434). 2-Trifluoromethylpyridine is a weak base no hydrochloride salt is formed. However, 2-trifluoromethylpyridine 1-oxide [22253-71-0] (bp 132—133°C/2.7 kPa (20 mm Hg)) is prepared ia 81% yield usiag 30% hydrogen peroxide—acetic acid (438). 

In most of their reactions, the pyridine- and azinecarboxylic acids and their derivatives behave as any other acid (cf. Scheme 86). However, some acid chlorides can be obtained only as hydrochlorides, and we must also consider decarboxylation. Esterification of pyridine carboxylic acids can be usefully achieved via in situ generation of the acid fluoride. For example, treatment of picolinic acid with a stoichiometric amount of N,N,N,A-tetramethylfluoroformami-dinium hexafluorophosphate (TFFH) in dichloromethane and triethylamine leads to generation of the acid fluoride, which reacts with (3-methyloxetan-3-yl)methanol to give the corresponding ester in 95% yield <2004S2485>. 

Pyridine or picolinic acid chloride (66 R = H, COCI) reacts presumably with thionyl chloride to form a o--complex (67) that is attacked by a chloride ion to give 68. Elimination of HCI and SO, which disproportionate to sulfur and sulfur dioxide, ultimately furnishes the corresponding 4-chloropyridine hydrochloride (69). In the case of pyridine, the intermediate 4-chloropyridine (41) reacts with additional pyridine to form 65. The sometimes long initiation periods of these conversions (61 — 62 and 64— 65) indicate they may in reality be complicated radical reactions (cf. 8IS66I). 

Isonicotinic and picolinic acid are similarly obtained from 4- and 2-picoline, respectively, by oxidation with permanganate,391 yields being 50- 60% and 50% (as hydrochloride), respectively. 

C8-C20 alkyl sulfates and alkanesulfonates separation by increasing alkyl chain length Capillary isotachophoresis (CITE) FIFE, 0.55 mm x 22 cm Leading electrolyte 0.01 M L-histidine hydrochloride, apparent pH 4.88, 2% tetraethylene glycol Terminating electrolyte 0.01 M picolinic acid both in 80 20 MeOH/H20 Conductivity 1... 

It must be pointed out, however, that physical shielding takes place only when the nitrogen atom is not in an ionized form. Hydrogenations of pyridine and 2-substituted pyridines when carried out in acid solution or as salts show that pyridine is reduced first in comparison with other pyridines. For example, under the conditions used by Skita (9) pyridine was reduced more readily than 2-picoline. The same order of reducibility was observed in hydrogenations in acetic acid in the presence of Adams catalyst (55). In another comparison of the reduction of mixed hydrochloride salts (39) it was found that pyridine reduced first. This is further amplified in the reduction of equimolecular binary mixtures of hydrochloride salts in the presence of platinum oxide (40). 

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