Pyridine chlorides

A large number of Brpnsted and Lewis acid catalysts have been employed in the Fischer indole synthesis. Only a few have been found to be sufficiently useful for general use. It is worth noting that some Fischer indolizations are unsuccessful simply due to the sensitivity of the reaction intermediates or products under acidic conditions. In many such cases the thermal indolization process may be of use if the reaction intermediates or products are thermally stable (vide infra). If the products (intermediates) are labile to either thermal or acidic conditions, the use of pyridine chloride in pyridine or biphasic conditions are employed. The general mechanism for the acid catalyzed reaction is believed to be facilitated by the equilibrium between the aryl-hydrazone 13 (R = FF or Lewis acid) and the ene-hydrazine tautomer 14, presumably stabilizing the latter intermediate 14 by either protonation or complex formation (i.e. Lewis acid) at the more basic nitrogen atom (i.e. the 2-nitrogen atom in the arylhydrazone) is important. 

In the former Soviet Union much use is made of industrial by-products to prepare acid inhibitors. The PB class is obtained by treating technical butyraldehyde with ammonia and polymerising the resulting aldehyde-ammonia. PB-5, for example, with O-Ol-O-15% of an arsenic salt is used in 20-25% HCl. A mixture of urotropine (hexamethyleneimine, hexamine) with potassium iodide, a regulator and a foaming agent is the ChM inhibitor. BA-6 is prepared from the condensation product of hexamine with aniline. A more recent development is the Katapin series which consists of /7-alkyl benzyl pyridine chlorides Katapin A, for example, is the /7-dodecyl compound. 

Sonogashira coupling of acetylenes with 24 and with the triflate 25 have also been reported (Equation 11) <2003RCB441>. The latter substrate is formed by treatment of the trione 26 with trifluoromethanesulfonic anhydride and pyridine chloride and triflate are comparable in respect of cross-coupling yields. 

ReClN402C2oH2o, Rhenium(V), dioxotetra-kis(pyridine)-, chloride, trans-, 21 116 ReClN406C2oH2o, Rhenium(V), dioxotetra-kis(pyridine)-, perchlorate, trans-, 21 117... 

ClN402ReC20H2(J, Rhenium(V), dioxo-tetrakis(pyridine)-, chloride, trans-,... 

ReCINjOjC oHa, Rhenium(V), dioxotetra-kis(pyridine)-, chloride trans-, 21 116 ReCIN406CxlHa, Rhenium(V), dioxotetra-kis(pyridine)-, perchlorate, trans-, 21 117 RhAs4ClC2oH32, Rhodium(l +), bis[o-phenyl-enebis(dimethylarsine)]-, chloride, 21 101 RhAs4C102C21H32, Rhodium( 1 +), (carbon dioxide)bis[o-phenylene-bis(dimethylarsine)]-, chloride, 21 101 RhBN4C44H56, Rhodium(l), tetrakis( I-isocyano-butane)-, tetraphenylborate(l -), 21 50 RhN,S Hl2, Rhodate(III), tris(pentasulfido)-, triammonium, 21 15... 

H2O2—hydrogen peroxide HRP—horseradish peroxidase PVP—poly(4-vinylpiridine) CpFeC2B9Hii—3i-cyclopentadiennyl-3i-dicarbollyliron Ru(NH3)5py(PFg)—pentaammine-pyridineruthenium(II) ttb-CuPc— tetra-tert-butyl-copper phtalocyanine GA—glutaraldehyde BSA—bovine serum albumin mPEG—methoxypolyethylene [Os(bpy)2pyCl] -—Osmium dibypyridine pyridine chloride cation. 

Lingane and Page (56) have determined cobalt in a pyridine-chloride electrolyte by deposition into a mercury cathode at —1.20 V vs. SCE. At a pH of 6.4 or above, the average error did not exceed 0.4 mg for samples in the 10-100 mg range. Tanaka (57) deposited cobalt quantitatively on platinum cathodes from a 1.2 N ammonium hydroxide —0.2 m ammonium chloride electrolyte at —0.85 V vs SCE. Similar experiments were reported by Wilkens and Hibbs (58) who deposited cobalt from a sulphate-sulphite electrolyte held at 70-90° C on platinum electrodes at —0.80 to —0.85 V vs. SCE. 

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