[Synthesis]
General procedure for the synthesis of 2,4,6-trimethylphenylhydrazine hydrochloride from homotrimethylaniline: Concentrated hydrochloric acid (0.125 L) and deionized water (0.100 L) were added to a 3.0 L three-necked, round-bottomed flask fitted with a mechanical stirrer and dosing funnel. The solution was cooled to -5°C in an ice/brine bath and 2,4,6-trimethylaniline (70 mL, 0.50 mol, 1.0 eq.) was added slowly and dropwise over 30 min, during which time the formation of a white precipitate was observed. After continuing to stir the mixture for 15-20 minutes, 52.5 mL of 9.5 M aqueous sodium nitrite (70 mL, 0.50 mol, 1.0 eq.) was slowly added dropwise for 30 to 45 minutes. The resulting brown solution was stirred for 30 minutes, followed by the slow addition of a 1:1 concentrated aqueous hydrochloric acid solution (0.455 L, 1.5 mol, 2.5 eq.) of 3.3 M stannous chloride dihydrate over a period of 4 hours under vigorous stirring. The addition of the stannous chloride solution results in the formation of a thick, light orange slurry, which may cause the mechanical stirrer to stall, at which point a small amount of deionized water may be added to restore stirring. The mixture was gradually brought to room temperature and stirred vigorously for 16 hours. Afterwards, the mixture was cooled to 0 °C and kept for 1 h. Subsequently, the mixture was filtered through a fine pore glass sintered Büchner funnel and the collected orange solid was washed with brine and ether. The orange solid was transferred to a 2L round-bottomed flask containing 10M NaOH aqueous solution (1.0 L) and ether (0.700 L) and cooled to -5°C. After the solid was almost completely dissolved (about 1 hour), the organic layer was separated and the aqueous layer was extracted with ether (2 x 0.400 L). The organic fraction was combined, dried over Na2SO4, filtered into a flame-dried 2.0 L round-bottomed flask, cooled to 0°C under N2 atmosphere, and treated with a 1,4-dioxane solution (0.125 L) in 4 M HCl. The white precipitate formed was collected by vacuum filtration, washed with ether and recrystallized from 200 standard ethanol to give the final 2,4,6-trimethylphenylhydrazine hydrochloride (50 g, 0.27 mol, 54% yield) as a white powder. The product was analyzed by 1H NMR (400 MHz, DMSO) δ 9.57 (3H, s, br, NH, exchanged), 6.89 (s, 2H), 2.33 (s, 6H), 2.21 (s, 3H); 13C NMR (100 MHz, DMSO) δ 138.06,136.20,135.01,129.17,20.54, 17.95; IR (thin film) v 3294,3002,2964,2911,2680,1564,1513,1481,852,825,753 cm-1; HRESI+/TOF-MS calculated value of C9H15N2+ [M]+ 151.1230, measured 134.0921 corresponds to the aniline anion radical ( 134.0975). |