Regioselective mono and dihalogenations of amino, hydroxy and methoxy pyridines (2-, 3-, and 4-substituted) as well as 2,6-dimethoxy pyridine with N-bromosuccinimide in different solvents have been studied. Reactivity of the substrates decreases in the order amino>hydroxy>methoxy and regioselectivity depends on the position of the substituent (2-substituted > 3-substituted). In most of the cases we obtained monobrominated derivatives regioselectively and in high yields. Hydroxy and amino pyridines can also be dibrominated in almost quantitative yield with 2 equivalents of NBS.Polyfunctional pyridines are very useful compounds which have found applications as precursors of pharmacological compounds, 1 in the synthesis of liquid crystals 2 and polymers, 3 as well as ligands for different transition metal cations. 4 The wide range of halopyridines, 5,6 which are able to undergo metal-halogen exchange with n-BuLi, nucleophilic substitutions and oxidative additions with Pd(0) allowing the introduction of many functional groups to the pyridine ring, means they are of great interest from a synthetic point of view. Moreover, halopyridines are themselves important final products as herbicides, 7 insecticides 8 and fungicides. 9 As a consequence of these features the regioselective synthesis of halopyridines is a matter of great interest.Data published in the literature up to 1970 showed that bromination of activated pyridines must be carried out with bromine in polar protic solvents, such as water or ethanol. 10 Several years later, it was reported the bromination of aminopyridines and N-oxides 11 with bromine in mixtures of CH 3 CN/CH 2 Cl 2 , while bromination of methoxypyridines 10,12 was carried out in acetic acid. Also tetrabromocyclohexa-2,5-dienone 10 has been used for the bromination of 3-aminopyridine. In most of these papers, the formation of mixtures of monohalo and dihalo derivatives is reported but their relative proportions as well as their 1 H NMR characterisation is omitted. Recently, Br 2 / NaOH has successfully been employed by Schnatterer et al. 13 for the highly regioselective bromination of 3-hydroxypyridine to yield exclusively 2-bromo-3-hydroxypyridine but, to our knowledge, the authors have not extended this study to other pyridine derivatives.N-Halosuccinimides have previously been reported as reagents for the nuclear bromination of 8-quinolinol and its copper (II) chelate 14 but they have scarcely been used on pyridines bearing activating groups. 15 By contrast, radical brominations at lateral chains of alkylpyridines with NBS in the presence of radical initiators have been widely documented. 16 The good results obtained by our group in the regioselective bromination of methoxybenzenes and methoxynaphtalenes, 17 as well as phenols and napthols 18 under very mild conditions with NBS, prompted us to investigate the behaviour of activated pyridines. In this paper we report a systematic study of the bromination with NBS of pyridines bearing OH, NH 2 , and OMe groups at different positions and under ...

[reaction: see text] The reactions of the lithium (S)-alpha-(methylthio)-2-(p-toluenesulfinyl)benzyl carbanion with (S)-N-p-tolylsulfinyl aldimines evolve in a completely stereoselective manner providing a one-step synthesis of enantiomerically pure anti-1,2-disubstituted 1,2-amino sulfide derivatives.

This work presents experimental studies performed on a low-pressure auxiliary air fluid pulverization burner fueled with refined vegetable oils to research the impact of the fatty acid profile on combustion and regulated emissions. The vegetable oils used were coconut, palm, rapeseed, sunflower, and soya. First, the fatty acid profile and the degree of unsaturation of these vegetable oils were determined by high-resolution nuclear magnetic resonance spectroscopy. The physicochemical properties (density, kinematic viscosity, heating value, and elemental analysis) were also determined and correlated with the degree of unsaturation. It was found that the higher heating value of vegetable oils increases as the degree of unsaturation also increases. In this experimental study, the influence of varying fuel flow rate at three input air flows on combustion efficiency and flue gas emissions was investigated. The nitric oxide and carbon oxide emissions obtained in all the tests performed are well below the permitted minimum levels. Combustion efficiencies equal to or above 80% were achieved for soya, sunflower, and rapeseed oils. A comparison between the degree of unsaturation of the vegetable oils and some combustion parameters is also established. In most of the experiments carried out, it was found that carbon oxide emissions decrease and combustion efficiency increases as the degree of unsaturation of vegetable oils increases.

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Sulfinylimine and (S)-N-sulfinylimine react with the ylide derived from (S)-dimethyl-[2-(ptoluenesulfinyl)phenyl]sulfonium salt, affording trans-2,3-disubstituted aziridines. A complete trans selectivity in low facial diastereoselectivity is observed when the configuration at the sulfur atoms of the reagents is the same. Otherwise, when their configurations are different, the reaction evolved with total facial diastereoselectivity and the cis/trans ratio ranged between 1/4.2 and 1/9. Theoretical calculations indicate the reaction proceeds mainly by evolution of a planar free carbanion. The relative stability of the transition states predicts a trans/cis ratio that is in excellent agreement with the experimental results.