Quinoline 1-oxides chlorination

In the Meisenheimer reaction of quinoline 1-oxides chlorine atoms usually enter the 2-and 4-positions, but not exclusively. 2,4-Dibromoquinoline 1-oxide was 6-chlorinated (57MI1), and the 5- and 6-nitroquinoline 1-oxides were 3-chlorinated to some extent (44JOC302). This reaction with phosphoryl chloride-phosphorus pentachloride has also been used in the preparation of chlorinated phenanthrolines (88YZ1148). 

These compounds are convenient starting materials for the preparation of a wide variety of platinum(II) complexes. The chlorine atoms can be replaced by other negative groups such as bromide, iodide, hydroxide, nitrate, nitrite, and thiocyanate. The ammonia molecules can be replaced by other bases such as pyridine, arylamines, and quinoline. Oxidation with aqua regia or chlorine yields the corresponding isomers of tetrachlorodiammineplatinum(IV) (synthesis 62). A supposedly third (7-) form has been shown to be a solid solution or mixture of the cis (jS-) and trans (a-) isomers. 

Quinoline Salicylic acid Silicon Dinitrogen tetroxide, linseed oil, maleic anhydride, thionyl chloride Iodine, iron salts, lead acetate Alkali carbonates, calcium, chlorine, cobalt(II) fluoride, manganese trifluoride, oxidants, silver fluoride, sodium-potassium alloy... 

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. 

Xanthurenic acid is determined in bicarbonate solution by the green color resulting from addition of small amounts of ferrous salt. Its determination is not influenced by kynurenic acid, whereas the presence of xanthurenic acid can interfere with that of kynurenic acid. To avoid such interference a brief and cautious oxidation with potassium permanganate is necessary to destroy exclusively xanthvu enic acid. Afterwards the unchanged kynurenic acid is extracted at pH 2 with isoamyl alcohol, chlorinated, and reacted with quinoline. 

Very mobile nitro groups can be replaced directly by chlorine or bromine, a reaction that has preparative importance for bromo- and chloro-pyridine and -quinoline derivatives. 5-Ethoxy-2-nitropyridine gives 2-bromo-5-ethoxy-pyridine when heated with HBr in glacial acetic acid in a sealed tube for 3 hours at 130°,1260 and 2-bromo-3-ethoxypyridine is obtained from the corresponding nitro compound and boiling 48% HBr.1261 It is particularly easy to introduce Cl or Br in place of a 4-nitro group in pyridine 1-oxide or quino-... 

Silicon and germanium require rather drastic reaction conditions for complexation to porphyrins. SiCU or GeCU must be heated with the porphyrin at 170°C for several hours in pyridine in a sealed tube, and the complex is obtained as the dimethoxy form, M (Por)(OMe)2, by crystallization in the presence of excess methanol after hydrolysis and chromatographic isolation. Ge(Por)Cl2 is also obtained by the reaction of GeC and porphyrin in quinoline at 230 °C. Sn and Pb porphyrins are easily prepared from the divalent metal salts in pyridine. Sn (Por) is air sensitive and oxidized to the Sn complex, Sn (Por)X2. In Sn(TPP)Cl2, the porphyrin ring is expanded to accommodate the large Sn atom (Sn—= 2.098(2) A). The Pb atom in Pb" meso-tetrapropylporphyrin (A(N ) 1.174 A, Pb—Np r 2.37A) is easily dissociated from it. Pb (Por) can be oxidized to Pb" (Por)Cl2 by chlorine. ... 

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