Researchers who often do experiments know that organic synthesis is a process of preparing more complex target molecules from simple raw materials through one or more chemical reactions. Generally, it requires fewer steps, and cheap raw materials. 3398-16-1, name is 4-Bromo-3,5-dimethylpyrazole, A new synthetic method of this compound is introduced below., Quality Control of 4-Bromo-3,5-dimethylpyrazole
General procedure: The corresponding pyrazole and thallium(I) borohydride in the appropriate ratio (see below) were added to a 500 mL Schlenk tube. The tube was closed with a rubber septum and three vacuum/nitrogen cycles were made. The septum was replaced with a reflux condenser fitted with a bubbler on top. The nitrogen flow was stopped and the stirred solid mixture was slowly warmed using an oil bath (fitted with a temperature regulator) until melting of the pyrazole was observed. At this point, evolution of hydrogen should initiate. The mixture was heated at the corresponding temperature for the required period and then cooled to r.t. During the reaction, some of the unreacted pyrazole sublimed and was deposited over the inside surface of the Schlenk tube. A heating gun was used to melt it and return it to the reaction mixture. The reaction mixture solidified during cooling and was dissolved in CHCl3 before filtration through neutral alumina. The alumina was washed with three portions of CHCl3. The resulting solution was submitted to low pressure in a rotary evaporator to remove the solvent, affording a white solid that was further purified by sublimation to remove the remaining pyrazole. The yields depended strongly on the degree of purity of the starting pyrazole: higher yields were obtained in all cases when the pyrazoles were purified by sublimation instead of by recrystallization prior to being employed as reactants. Thalium Hydrotris(3,5-dimethyl-4-bromopyrazol-1-yl)borate (TlTp*,Br) (1) 1H-4-Bromo-3,5-dimethylpyrazole (14 g, 80 mmol) and thallium(I) borohydride (4.4 g, 20 mmol) were used. The pyrazole melted at 170-175 °C and the reaction was heated at 180 °C for 4 h. Unreacted pyrazole was removed by sublimation (130 °C, 2 mbar) until no more pyrazole was collected. TlTp*,Br was obtained as a white solid in 90percent yield (13.5 g of TlTp*,Br). In contrast, when the initial pyrazole was purified by recrystallization from petroleum ether the final yield of 1 decreased significantly (71percent, 10.6 g of TlTp*,Br).1H NMR (500 MHz, CDCl3): delta = 4.76 (br s, 1 H), 2.37 (s, 9 H), 2.27 (s, 9 H). 11B{1H} NMR (160 MHz, CDCl3): delta = ?7.08 (d, JB-H = 96.6 Hz). 13C{1H} NMR (125 MHz, CDCl3): delta = 146.7 (d, JC-Tl = 33.6 Hz), 143.0, 95.6 (d, JC-Tl = 29.0 Hz), 12.5 (d, JC-Tl = 95 Hz), 12.1. Anal. Calcd for C15H19BBr3N6Tl: C, 24.40; H, 2.59; N, 11.38. Found: C, 24.65; H, 2.58; N, 11.25.
The basis of chemical reaction formula synthesis, the synthesis route is composed of some specific reactions and combined according to certain logical thinking. We look forward to the emergence of more reaction modes in the future.
Reference:
Article; Olmos, Andrea; Pereira, Ana; Belderrain, Tomas R.; Perez, Pedro J.; Synthesis; vol. 50; 17; (2018); p. 3333 – 3336;,
Pyrazole – Wikipedia,
Pyrazoles – an overview | ScienceDirect Topics