With One Halogeno Substituent

Kinetics have been measured for the reactions of p-nitrophenoxide ion in methanol with equimolar quantities (0.01-0.024/) of 2-chloropyrazine, 3- and 4-chloropyridazines, and 2-, 4-, and 5-chloropyrimidines in the presence of a tenfold excess (0.1-0.24/) of p-nitriphenol (908). There was evidence for mild acid catalysis by the p-nitrophenol added to prevent concurrent methanolysis. The reactivity order observed was 2-chloropyrimidine 4-chloropyrimidine 4-chloropyridazine — 3-chloropyridazine — 2-chloropyrazine 5-chloropyrimidine, and corresponded with the theoretical order as modified by mild acid catalysis, more effective in the order ortho meta para to the point of substitution, and including the inverted order, 2- 4-chloropyrimidine, whereas the usual reactivity order with anionic reagents was 4- 2-chloropyrimidine (908). 

Replacement reactions of chloropyrazines with a large number of alkoxides have been observed. Some examples are 2-chloropyrazine with methoxide (974), perdeuteromethoxide (975), ethoxide and isopropoxide ions (668a), and as follows. Methoxide ion 2-chloro-3-methyl (49, 686, 687, 735, 736, 976) 2-chloro-5-deutero-3-methyl (687) 2-chloro-5-methyl (686, 735, 736) 2-chloro-6-methyl (686, 735, 736) 2-chloro-3,5-dimethyl (687, 844) 3-chloro-2,5-dimethyl (844, 977-979) 2-chloro-3-s-butyl (80, 649, 693) 2-chloro-3-isobutyl (80, 693)  

2- chloro-5-isobutyl (693) 2-chloro-5(and 6)-s-butyl (649) 2-chloro-3-isopropyl (80) 3-chloro-2-isopropyl-5-methyl (844) 3-chloro-2-isobutyl-5-isopropyl (740a)  

3- chloro-5-isobutyl-2-isopropyl (740a) 2-chloro-3-phenyl (817) 2-chloro-6-phenyl (365a) 2-chloro-3-benzyl (80, 366) 2-chloro-3-nonyl (649) 3-bromo-2,5-diphenyl (866) and 3-chloro-2,5-diisobutyl (980). Ethoxide ion 2 hloro (668a, 818) 

2- chloro-3-methyl (679, 978) 2-chloro-6-methyl (981) 2-chloro-3-ethyl (368) 

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