2- Aminopyridine/acetic acid

The authors claim that these associations, which are destroyed in fixed compounds, play an important role in the calculation of Ty.The cases of 1,2,4-triazole-5-thiones 74 [97SA(A)699] and of pyridone dimers 15a-15a and 15a-15b were also studied [96MI(13)65]. (3) The recording of IR spectra in solution at different temperatures to determine the effect of the temperature on Kj-, for instance, in pyrazolinones [83JPR(325)238] and in cytosine-guanine base pairs [92MI(9)881]. (4) The determination of the equilibrium 2-aminopyridine/acetic acid 2-aminopyridinium acetate (see Section III.E) in the acid-base complex was carried out by IR (97NKK100). 

The formation energies of 2-aminopyridine dimer and 2-aminopyridine - 2-pyri-done complex were determined to be 6.0 and 10.6kcal/mol, respectively, in C6D6 solution by 11 NMR spectroscopy (84SA(A)623). The similar values were obtained by CNDO/2 calculations. The dynamics of amino-imino double proton-transfer tautomeric reaction of the 2-aminopyridine-acetic acid system in hexane was studied... 

Picosecond dynamics of amino-imino tautomerization in another host/guest system, 2-aminopyridine/acetic acid complex (Figure 3.16a), have been studied by Ishikawa et al. [47]. It has been shown that, upon exciting the doubly H-bonded... 

Sulphapyridine. Dissolve 18-8 g. of 2-aminopyridine in 40 ml. of dry pyridine (Section 11,47,22) in a 250 ml. flask and add 48 0 g. of p-acetamidobenzenesulphonyl chloride (4) the temperature rises to about 70°. Cool, add excess of water, filter the precipitated 2-(p-acet-amidobenzonesulphonamido)p3Tidine (s acetyl-sulphapyridine) at the pump and recrystallise it from 50 per cent, acetic acid. The yield of pm product, m.py. 224°, is 46-5 g. 

Cool and filter. Dissolve in the minimum volume of hot water, treat with about 0-5 per cent, by weight of decolourising carbon, filter, precipitate the base with 50 per cent, acetic acid imtil just acid to litmus (avoid an excess of acid), filter off the sulphapyridine at the pump, wash thoroughly with hot water, and dry to constant weight at 90° (about 12 horirs). Alternatively, the cold solution of the sodium salt may be just acidified with dilute hydrochloric acid with very vigorous stirring the presence of a local excess of acid must be avoided since sulphapyridine is hydrolysed by mineral acids to sulphanilic acid and 2-aminopyridine. 

A. 2-Ami/no-S-bromopyridine. In a 2-1. three-necked flask equipped with stirrer, dropping funnel, and condenser is placed a solution of 282 g. (3.0 moles) of 2-aminopyridine (Note 1) in 500 ml. of acetic acid. The solution is cooled to below 20° by immersion in an ice bath, and 480 g. (154 ml., 3.0 moles) of bromine dissolved in 300 ml. of acetic acid is added dropwise with vigorous stirring over a period of 1 hour. Initially the temperature is maintained below 20°, but after about half the bromine solution has been added it is allowed to rise to 50° to delay as long as possible the separation of the hydrobromide of 2-amino-5-bromopyridine. At 50° the hydrobromide usually begins to crystallize when about three-quarters of the bromine has been added. When addition of bromine is completed, the mixture is stirred for 1 hour and is then diluted with 750 ml. of water to dissolve the hydrobromide. The contents of the flask are transferred to a 5-1. beaker and are neutralized, with stirring and cooling, by the addition of 1.2 1. of 40% sodium hydroxide solution. 

Pyridylamine, see 2-Aminopyridine a-Pyridylamine, see 2-Aminopyridine p-Pyrine, see Pyrene Pyrinex, see Chlorpyrifos Pyroacetic acid, see Acetone Pyroacetic ether, see Acetone Pyrobenzol, see Benzene Pyrobenzole, see Benzene Pyrofax, see Butane Pyroligneous acid, see Acetic acid Pyromucic aldehyde, see Furfural Pyropentylene, see Cyclopentadiene Pyrophosphoric acid, tetraethyl ester, see Tetraethyl pyrophosphate... 

Iron in acetic acid at 100° reduced 4-nitropyridine oxide quantitatively to 4-aminopyridine [170], and 3-bromo-4-nitropyridine oxide to 3-bromo-4-aminopyridine in 80% yield [170]. Chromous chloride, on the other hand, failed in the deoxygenation of nitropyridine oxides and nitroquinoline oxides [191]. 

Pyrans 59 with ammonium acetate in acetic acid generally lead to 2-aminopyridines 267 (81JHC309) in 40-50% yields, probably, due to dis-proportionative aromatization (Scheme 105). 

Schiff base formation occurs normally with 3-aminopyridine (69CR(C)(269)1319> and aldehydes, but imines of 2-aminopyridine, though isolable, are less stable and bis(pyridyl-amino) compounds (e.g. 93) are readily formed. 9-Aminoacridine fails to react with benzal-dehyde. Nitrosobenzenes condense with aminopyridines in alkali (but not in acetic acid) to give azopyridines (Scheme 82). 

Reactions of 2-aminopyridines and diethyl 2-aryl-4-hydroxy-4-methyl-6-oxocyclohexane-l,3-dicarboxylate (309) in acetic acid for 4 h gave either ethyl 1,2-dihydro-l 1-oxo-l l//-pyrido[2,l -6]quinazoIine-2-carboxylates (310) or their isomeric ethyl 7,8-dihydro-6-oxo-6//-pyrido[l,2-a]quinazoline-8-carboxylates (311) (92PHA336). 

Other simple chelate ligands which have been found to give six-coordinate complexes NiX2L2 are 2-acetylpyridine N-oxide oxime,2495 2-acetamidopyridine,2496 pyridine-2-(acetic acid methyl ester)2497 and -substituted 2-aminopyridine N-oxides.2498... 

Reactions of 2-aminopyridines with /i-chlorovinyl ketones were surveyed by Fischer.16 He established that in a nonacidic medium (acetone-methanol mixture) the pyridinium salts (7) are formed, which can then be cyclized by acids (acetic acid and 70% perchloric acid) to the 2-substituted pyrido[l,2- ]-pyrimidinium salts (10).1415 in acidic media, however, the 4-substituted pyrido[l,2-a]pyrimidinium salts (9) are formed via the enamine (8).616... 

The one-step procedure, i.e., reaction of 2-aminopyridines and /J-oxo esters in the presence of an acid, generally gave higher yields. Thus, depending on the starting materials, the yields achieved were 10-60% in methyl cello-solve in the presence of p-toluenesulfonic acid,48,54 60 30-70% in acetic acid,49,61-64 and 44-98% in polyphosphoric acid8,41,49,64 73 or in a... 

Bohme and Weisel obtained 4-oxo-4//-pyrid o [ 1,2-a] pyrimidine (59) from 2-aminopyridine and ethyl 2-chloroacetoacetate. The yield was 10% in toluene in the presence of p-toluenesulfonic acid, 30% in acetic acid, and 59% in polyphosphoric acid. The triethylamine-catalyzed reaction in benzene led to the imidazo[l,2-a]pyridine 58.64 4-Oxo-4//-pyrido[ 1,2-a]-pyrimidine (59) was also prepared from 2-aminopyridine and 2-chloro-3-oxobutyronitrile.67... 

Cyclocondensation of 2-aminopyridines and ethyl 3-(dimethylamino)-2-(2-pyridyl)acrylate 143 in boiling glacial acetic acid afforded 3-(2-pyridyl)-4//-pyrido[ 1,2-a]pyrimidin-4-ones 144 (93JHC1253). 

Tisler and co-workers prepared 3-benzamido-4//-pyrido[l,2-a]-pyrimidin-4-ones 180 (R = H) in the reaction of 2-aminopyridines (R1 = H,3-NH2,4-Me) and 3-ethoxy-2-benzamidoacrylate 179 in refluxing acetic acid (90JHC359). From 2,3-diaminopyridine a condensed pyr-... 

Reaction of 2-aminopyridines with acrylic acid or methacrylic acid in boiling water for 2-20 hours gave betaine hydrates 262 (R3 = H) in 11-88% yields (Scheme 20) (92KGS80). When 2-aminopyridine reacted with methyl metharylate in acetic acid for 24 hours or 2-aminopyridine and its 5-bromo and 5-chloro derivatives reacted with acrylic acid in boiling toluene for 24 hours or 2-aminopyridine reacted with crotonic acid in boiling toluene for 20 hours, 3-(2-pyridylamino)propionic acid derivatives 263 were the products. When 5-chloro-2-aminopyridine reacted with acrylic... 

Methoxythiocarbonylamino-4//-pyridopyrimidin-4-one 704 (R = H) was obtained in 23% yield when A-methoxythiocarbonylglycine and triethyl orthoformate were reacted in acetic acid. The reaction mixture was evaporated in vacuo to dryness, the residue was dissolved in ethanol, and triethylamine and 2-aminopyridine were added. Then the reaction mixture was left to stand at room temperature for l week (94JHC125). The treatment of 3-methoxythiocarbonyl-8-methyl-4//-pyrido[l, 2-a]pyrimidin-4-one 704 (R = Me) with methyl iodide in methanolic sodium methylate at ambient temperature for 3 hours afforded 3-(l-methylthio-l-methoxymeth-yleneamino) (705) and 3-dimethoxymethyleneamino derivatives (706) in 23% and 3% yields, respectively. 

Fig. 6.6. Relationship between pKb(water) of N-bases and half - neutralization potential El/2 for potentiometric base titration in glacial acetic acid. 1) 4-aminopyridine (4.83), 2) morpholine (5.30), 3) 2,4,6-trimethylpyridine (6.68), 4) pyridine (8.85), 5) p-toluidine (8.88), 6) o-toluidine (9.61), 7) 3-acetylpyridine (10.82), 8) chloroaniline (11.36), 9) pyrazole (11.47), 10) diphenylamine (13.10) (Pawlak et al., 1985)...

Aminopyridines are useful substrates for the preparation of fused heterocycles. Imidazo[ 1,2- ]pyridines may be prepared in moderate to good yield by three-component coupling of 2-aminopyridine, aldehydes and isocyanides <1998S661>. The reaction proceeds by nucleophilic attack of the isocyanide onto an iminium species formed by condensation of 2-aminopyridine with the aldehyde component followed by 1,3-FI shift. For example, 2-aminopyridine reacts with benzylisocyanide and 2-hydroxyacetaldehyde in the presence of 2equiv of glacial acetic acid in methanol to give iiuidazo[2- ]pyridine 84 in 44% yield (Equation 57). 

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