The reaction of an aromatic heterocycle with a proton is called a protonation. One of articles about this theory is 《Synthesis of 5- and 6-haloindoles from indoline》. Authors are Ikan, R.; Hoffmann, E.; Bergmann, E. D.; Galun, A..The article about the compound:5-Fluoroindolinecas:2343-22-8,SMILESS:FC1=CC2=C(NCC2)C=C1).Quality Control of 5-Fluoroindoline. Through the article, more information about this compound (cas:2343-22-8) is conveyed.
cf. Terent’ev, et al., CA 54, 10991c. A mixture of 240 g. indoline and 2 1. concentrated H2SO4 stirred 1 hr. below 0° with a mixture of 90 ml. HNO3 and 2 h H2SO4 gave 95% 6-nitroindoline, m. 66-7° (BuOH); NAc derivative (I) m. 156-7°. I (250 g.) suspended in 600 ml. isoPrOH and hydrogenated over 10% Pd-C at 70°/80 lb./in.2 gave 85% 6-amino-1-acetyfindole (II), m. 181°. II (500 g.) suspended in a mixture of 760 ml. H2O and 760 ml. concentrated HCl and diazotized at 0-5° by a solution of 208 g. NaNO2 in 420 H2O, gave on stirring 1 hr. at 0-5° with a solution of 580 g. NaBF4 in 1 1. H2O a diazonium salt, which, filtered and washed successively with aqueous NaBF4 solution, cold EtOH, and Et2O and then dried, was extracted with iso-PrOH to give 55% 6-fluoro-1-acetylindole (III), b1 180°, b0.5 165°, m. 79-80°. III refluxed 1 hr. with 10 parts concentrated HCl gave quant. 6-fluoroindoline (IV), b0.3 70-2°, n29D 1.5533, also obtained directly by adding 1.5 moles NaOH/mole II to the iso-PrOH extract of the decomposition product of the diazonium fluoborate, and subsequent distillation A mixture of 7 1. xylene, 470 g. chloranil, and 194 g. IV refluxed 5 hrs. gave 60% 6-fluoroindole (V), m. 74.5-5.5°. IV (50 g.) dehydrogenated by 20-min. treatment at 180-200° with 3 g. 10% Pd-C gave 35% V. Dropwise addition of 170 ml. fuming HNO3 to 220 g. indoline in 3 1. Ac2O at 10-12° gave 350 g. orange solid when the product was poured on ice. After removing the small amount of dinitroacetylindoline by refluxing the product with 10 parts concentrated HCl 1 hr. and then filtering off the more acidic dinitroindole which precipitated, the filtrate was made alk. to aqueous NaOH solution and the precipitate refluxed 3 hrs. with Ac2O to give 73% 5-nitro-1-acetylindoline, m. 175-6° (AcOH), which hydrogenated over 10% Pd-C at 70° gave 85% the 5-amino analog (VI), m. 185-6° (aqueous EtOH). VI, diazotized and subjected to a Schiemann reaction, gave 55% 5-fluoro-1-acetylindoline, b8 170°, m. 110-11°, which was deacetylated quant. to 5-fluoroindoline, b15 116-18°, n24D 1.5559, and converted into 5-fluoroindole, m. 45-6°, by the above method. II (176 g.) was suspended in a mixture of 250 ml. H2O and 250 ml. concentrated HCl and diazotized at 0° with a solution of 70 g. NaNO2 in 150 ml. H2O, and the resulting diazonium solution added slowly at 0° to a Cu2Cl2. solution prepared from 310 g. CuSO4.5H2O and 81 g. NaCl in 1 1. H2O, 66 g. NaHSO3 and 44 g. NaOH in 0.5 1. H2O, and 500 ml. concentrated HCl, and the mixture heated to 45° slowly, stirred 2 hrs., cooled to 0°, and filtered gave 56% 6-chloro-1-acetylindoline, m. 127-8°, 85 g. of which refluxed 1 hr. with 850 ml. concentrated HCl gave 6-chloroindoline-HCl, m. 210°; the free base (VII) b28 156-8°, n29D 1.5984. Dehydrogenated with chloranil VII gave 60% 6-chloroindole, m. 89-90°. Similarly, 5-amino-1-acetylindoline gave 60%, the 5-chloro analog, m. 115-16° (EtOH), which was deacetylated to 94% 5-chloroindoline, b20 132-5°, n24D 1.5996, and in turn dehydrogenated to 62% 5-chloroindole, m. 69-70°, by chloranil. Ultraviolet data for these compounds were given.
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