2-Picoline-N-oxide

The N-oxide function has proved useful for the activation of the pyridine ring, directed toward both nucleophilic and electrophilic attack (see Amine oxides). However, pyridine N-oxides have not been used widely ia iadustrial practice, because reactions involving them almost iavariably produce at least some isomeric by-products, a dding to the cost of purification of the desired isomer. Frequently, attack takes place first at the O-substituent, with subsequent rearrangement iato the ring. For example, 3-picoline N-oxide [1003-73-2] (40) reacts with acetic anhydride to give a mixture of pyridone products ia equal amounts, 5-methyl-2-pyridone [1003-68-5] and 3-methyl-2-pyridone [1003-56-1] (11). 

Metallation of 2-picoline N-oxide [931-19-1] with butyUithium followed by addition of the elertrophilir cyclohexanone leads to two carbinol products (47) (4% (49) [34277-46-8] (50) [34277-59-3]). 

Peroxomolybdenum-Picolinate N-oxide complex (1). The complex is prepared from Na2Mo04-2H20, H202, picolinic acid N-oxide, and Bu4NOH. It is obtained... 

In the coordination of 4-picoline N-oxide (MPNO) to a series of [VO(/3-diketonato)2]... 

Absorption spectral analysis of 4f-4f bands in the adducts between lanthanide triflu-oroacetates and 2-picoline N-oxide along with parametrization showed the existence of electrostatic interactions between lanthanides and ligand [216]. 

The oxidation of alkyl halides to carbonyl compounds with pyridine or 2-picoline N-oxide is a popular and general method, applicable even to unactivated substrates. The reaction may be performed in two ways. In the first, the halide is heated with the N-oxide in the presence of a base such as sodium hydrogen carbonate. In the second, the intermediate N-alkoxypyridinium salt is isolated before base treatment. The reaction has been shown by labeling to proceed via the pyridinium ylide, or, in the case of picoline N-oxide, via the anhydrobase (Scheme 8). Some typicd examples are shown in equations (23)-(25). ... 

Picoline-N-oxide complexes have been reported in some detail. (160-162) Complexes are of the general type LnLg X3nH20 (L = picoline-/V-oxides n = 0 or 2 X = Br or I). The isotropic shifts possess both contact and pseudocontact contributions. For LnLgIs a square antiprismatic geometry is assumed. Complexes of La, Nd, Er, and Lu with EDTA-type ligands are reported (163,164) and structural differences are discussed. Aqueous solutions of dysprosium perchlorate have been examined. (16 Contact and pseudocontact shifts are separated using a least-squares method based on the different... 

Picohne s 2.8 g 3-picoline s 2.8 g catalyst s 0.30 g adamantane (internal standard s 0.5 g 1 = 4 h Products 2 isonicotinic acid (4-picolinic acid) 3 4-picoUne N-oxide 4 isonicotinic acid N-oxide 2A nicotinic acid (3-picoUnic acid) 3A 3-picoline N-oxide 4A nicotinic acid N-oxide O others... 

The results for the oxidation of 4- and 3-picoline with these catalysts are shown in Table 21.2. In the case of 4-picoline, the overall conversion falls by an order of magnitude (ca 2.5 times), but more significantly, the selectivity for the target (desired) product (isonicotinic acid) was greatly diminished. Interestingly, substantial amounts (almost tenfold) of 4-picoline N-oxide and isonicotinic acid N-oxide were formed, whereas with the microporous host, containing the redox-active site in high oxidation (Mn ") state, 92% selectivity for the desired isonicotinic acid was maintained. In the case of 3-picoline, the results were even more pronounced there was almost a fivefold decrease in the conversion and virtually no nicotinic acid was produced. 

Phthalic acid, 259 Phthalic anhydride, 104 a-Picoline, 161 a-Picoline N-oxide, 161 Picolinic acid, 16 Picramic acid, 271 Picric acid, 271 Pinacol reduction, 7 Pinosylvin, 31 Piperazines, 322 Piperidine, 33, 291 2-Piperidone, 194 Pivaldehyde, 105 Podophyllotoxin, 337 Podophyllotoxone, 337 Polonovski reaction, 308 Polyisoprenoids, 300-301 Polymethoxybenzophenones, 30—31 Polymethylhydrosiloxane, 294 Polyphosphate ester (PPE), 229-230 Polyphosphoric acid, 227, 231—232 Potassium, 232, 233 Potassium acetate, 96 Potassium amide, 232—233, 310 Potassium azodicarboxylate, 100 Potassium r-butoxide, 26, 45, 47, 77-78, 85, 133, 188, 212, 222, 225, 233-234, 236, 246... 

The method was suggested in a paper by Chinese chemists2 which reported that the reaction of a-picoline N-oxide and iodine at 95-100° formed a gum which on pyrolysis decomposed to 2-pyridine aldehyde (16% yield) and a-picoline (37%). 

Hadzi (42) reported a similar spectrum from the basic salt. HBr, where B = a-picoline-N-oxide, and predicted a similar structure. This was confirmed by X-ray work (43). The crystal contains the dimeric ion (14), with a hydrogen bond (0 0 f=i2.40 A) Isdng across a... 

Figs. 19 and 20 show the infrared spectra of some acid salts and related crystalline compounds. The spectrum in Fig. 19(a) is from an acid salt of Type B, and it approximates to a superposition of the spectra of free acid and neutral salt. The other spectra are all of Hadzi s T5q>e (ii), which is shown in its starkest form in Fig. 19(c) (sodium hydrogen diacetate) with a window near 950 cm h Potassium hydrogen malonate, a Type A structure, has a similar spectrum (20 (a)). The picoline-N-oxide hemi-hydrobromide (19(d)) is a T5q>e A basic salt Cook s basic salt (Sect. XI) is of pseudo-Type A and gives the spectrum (20(b)). Sodium bicarbonate (20(c)) and potassium hydrogen oxalate (20(d)) are acid sdts of intermediate character (see Sect. XV and XVI A). 

Fig. 19. Infrared spectra of some crystalline acid salts and related compounds (a) potassium hydrogen di-p-nitrobenzoate (Type B) (b) rubidium hydrogen di-o-nitrobenzoate (Type A) (c) sodium hydrogen di-acetate (d) a-picoline-N-oxide hemi-hydrobromide...

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