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一引言吡啶环中N-原子具有吸电效应,有许多事实根据,其中最有力的根据是吡啶与硝基苯取代反应非常相似。就亲电取代反应而言,吡啶与硝基苯的卤化,硝化和磺化,都此苯困难,而且都产生3—取代物。足见N—原子与NO_2—基因有钝化作用。例如,氯化或溴化吡啶,要超过300℃才能进行,产生3,5—二卤吡啶。硝化吡啶,通常采用H_2SO_4—KNO_3为硝化剂在330℃进行,产生15%3-硝基吡啶。氯化硝基苯要在催化剂FeCl_3参加下,在75℃～8℃才能进行,产生3-氯硝
I. INTRODUCTION The N-atom in the pyridine ring has an electric absorption effect and is based on many facts, the most powerful of which is that the pyridine and nitrobenzene substitution reactions are very similar. In the case of electrophilic substitution reactions, the halogenation, nitration and sulfonation of pyridine and nitrobenzene are both difficult and both produce 3-substituents. Sufficient to see N-atom and NO_2-gene passivation. For example, chlorination or bromination of bromine over 300 ° C yields 3,5-dihalopyridine. Nitration of pyridine, usually H_2SO_4-KNO_3 as nitrating agent at 330 ℃, resulting in 15% 3-nitropyridine. Chlorination of nitrobenzene to participate in the catalyst FeCl_3, 75 ℃ ~ 8 ℃ in order to produce 3 - chlorine nitrate