Picoline V-oxide

Picoline-V-oxide (4-methylpyridine-l-oxide) [1003-67-4] M 109.1, m 182-184 , 185-186 , 186-188 , pK 1.29. Recryst from EtOH-EtOAc, Mc2C0-Et20 or C6H6. [Bullitt and Maynard 7 Am Chem Soc 76 1370 1954 Boekelheide and Linn J Am Chem Soc 76 1286 1954]. 

MeOpyNO. 4-ClpyNO, or 4-N02pyN0) and [FeL ](C104)2 (L = 4-picoline. V-oxide. 4-MeOpyNO, 4-ClpyNO, 4-N02pyN0, 4-CNpyNO, or 3-CNpyNO) have been prepared, and have been characterized by magnetic measurements and i.r. and electronic spectroscopy. ... 

Pyridine A-oxide (pyNO) (10) 2-Picoline /V-oxide (2-picNO) (11) 2,6-Lutidine A-oxide (2,6-lutNO)... 

The utilization of metal /3-diketonate complexes as organic-soluble NMR shift reagents was first explored in the mid-sixties with Ni(II) and Co(II) complexes of 2,4-pentanedione [(Ni(acac)2 and Co(acac)2] . Donor ligands such as triarylphosphines, isonitriles, pyridine V-oxides and picoline V-oxides bind to the metal ion. Relatively small shifts were observed in the NMR spectrum of the bound donor groups. These shifts were the results of contact (through-bond) and pseudocontact (dipolar or through-space) effects. 

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... 

Pyridine and quinoline /V-oxides react with phosphorus oxychloride or sulfuryl chloride to form mixtures of the corresponding a- and y-chloropyridines. The reaction sequence involves first formation of a nucleophilic complex (e.g. 270), then attack of chloride ions on this, followed by rearomatization (see also Section 3.2.3.12.5) involving the loss of the /V-oxide oxygen. Treatment of pyridazine 1-oxides with phosphorus oxychloride also results in an a-chlorination with respect to the /V-oxide groups with simultaneous deoxygenation. If the a-position is blocked substitution occurs at the y-position. Thionyl chloride chlorinates the nucleus of certain pyridine carboxylic acids, e.g. picolinic acid — (271), probably by a similar mechanism. 

V-oxide are heated, N-(2 -pyridyl)-2-pyridone (30%), 2,3 -dipyridyl ether, and JV-(4 -pyridyl)-2-pyridone are obtained.358 It was also observed that, when 3-picoline Y-oxide was heated with acetic anhydride and then water, 3-methyl-Y-(5 -methyl-2 -pyridyl)-2-pyridone (152) (4%) was isolated together with the expected 3- and 5-methyl-2-pyridones359 (see also Section V,B). When 3-picoline... 

Radical addition-elimination mechanism with participation of an electrophilic V(IV)-00 species was proposed for aromatic hydroxylation by a peroxo complex [V0(02)(pic)(Hj0)2] (pic=picolinate) that oxidizes benzene at room temperature in CH CN to produce phenol in a yield of 55%, without any coupling products (Scheme 14.4) [33]. A radical anion was suggested as an alternative hydroxylating species [34]. 

Equimolar solutions of picryl acetate and 2-picoline N-oxide both in dry benzene added with vigorous stirring simultaneously to dry benzene 1-acetoxy-2-methylpyridinium picrate. Y 95%. V. J. Traynelis, A. I. Gallagher, and R. F. Martello, J. Org. Ghem. 26, 4365 (1961). 

Vanadous picolinate, [V(pic)3], is the most effective outer-sphere reductant in the heterogeneous reaction with substitution inert iron(III) oxides.In removing these metal oxides from surfaces, these redox reagents may be more useful than the more conventionally used, strong acids and chelating agents. 

Vorob ev, P. B., Gabdrakipov, V. Z., Mikhailovskaya, T. R, and Sembaev, D. Kh. Reactivity of Isomeric Picolines in Oxidative Ammonoly sis on a Vanadium Oxide Catalyst. Russian J Gen Chem (Translation of Zhumal Obshchei Khimii) 71,605-607 (2001). 

Interesting hydrocarbon oxidations have been observed with Fe(II) catalysts with oxygen as the oxidant. These catalytic systems have become known as Gif chemistry after the location of their discovery in France.228 An improved system involving Fe(III), picolinic acid, and H202, has been developed. The reactive species generated in these systems is believed to be at the Fe(V)=0 oxidation level229... 

The highly distorted octahedral complex [mer-V (pic) 3] (pic = picolinic acid, a tryptophan metabolite) oxidizes over time to the [VO(pic)2] complex in aqueous solution [39]. Conductivity measurements revealed that the species is a nonelectrolyte, and voltammetry indicated a reversible oxidation at 0.635 V and reduction at — 1.01 V versus Ag/AgCl, values which are more positive than usually observed for comparable complexes. This feature was attributed to delocalization of d electrons [39]. 

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