Quinoline 1-oxides halogenation

It has been stated that many halogen-free compounds, e.g., certain derivatives of pyridine and quinoline, purines, acid amides and cyano compounds, when ignited on copper oxide impart a green colour to the dame, presumably owing to the formation of volatile cuprous cyanide. The test is therefore not always trustworthy. The test is not given by duorides. 

The oxidative degradations of binuclear azaarenes (quinoline, isoquinoline, and benzodrazines) by hydroxyl and sulfate radicals and halogen radicals have been studied under both photochemical and dark-reaction conditions. A shift from oxidation of the benzene moiety to the pyridine moiety was observed in the quinoline and isoquinoline systems upon changing the reaction from the dark to photochemical conditions. The results were interpreted using frontier-orbital calculations. The reaction of OH with the dye 3,3,6,6-tetramethyl-3,4,6,7,9,10-hexahydro-(l,8)(2//,5//)-acridinedione has been studied, and the transient absorption bands assigned in neutral solution.The redox potential (and also the pA a of the transient species) was determined. Hydroxyl radicals have been found to react with thioanisole via both electron transfer to give radical cations (73%) and OH-adduct formation (23%). The bimolec-ular rate constant was determined (3.5 x lO lmoU s ). " ... 

Fig. 3.23 Oxidation of halogenated quinolines to halogenopyridine-2,3-dicarboxylic acids [260]...

Reduction of Sn(Pc)Cl2 with SnCl2 or H2 in quinoline gives Sn1](Pc), which is inert to weak acid (AcOH) and alkali (3 N NaOH) but is oxidized to Snlv(Pc)X2 by Br2 or I2.197,198 Cl2 halogenates the Pc ring as well. 

Pyridine-2,3-dicarboxylic acids containing a halogen in the 5- or 6-position were prepared by oxidation of the corresponding quinolines using either ozone/H202 or catalytic R.UO4. Diacids substituted in the 6-position by Cl or Br, or in the 5-position by F, Cl, or Br, respectively, were isolated in 46-71% yields. The yields of 6-fluoro and 6- or 5-iodo diacids were low (<30%) (Equation 40) <2001S2495>. 

Dimethyldioxirane (1) is a mild and efficient oxidant for pyridine pyiidines and quinolines have also been oxidized in good yield by r-pentylhydroperoxide in the presence of molybdenum(V) chloride. A(-Halogenation and other oxidative reactions of pyridines and related heterocycles have been re-viewed. " Thus, pyridines and some diazines can be aminated by mesitylenesulfonylhydtoxylamine... 

Puschel and Stefanac use alkaline hydrogen peroxide in the oxygen flask method to oxidize arsenic to arsenate. The arsenate is titrated directly with standard lead nitrate solution with 4-(2-pyridylazo) resorcinol or 8-hydroxy-7-(4-sulpho-l-naphthylazo) quinoline-5-sulphonic acid as indicator. Phosphorus interferes in this method. The precision at the 99% confidence limit is within 0.67% for a 3-mg sample. In another variation, Stefanac used sodium acetate as the absorbing liquid, and arsenite and arsenate are precipitated with silver nitrate. The precipitate is dissolved in potassium nickel cyanide (K2Ni(CN)4) solution and the displaced nickel is titrated with EDTA solution, with murexide as indicator. The average error is within 0.19% for a 3-mg sample. Halogens and phosphate interfere in the procedure. 

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