Elguero, Jose et al. published their research in Compt. Rend. in 1963 | CAS: 15953-73-8

4-Chloro-3,5-dimethyl-1H-pyrazole (cas: 15953-73-8) belongs to pyrazole derivatives. Pyrazole is a weak base, with pKb 11.5 (pKa of the conjugated acid 2.49 at 25 °C).Pyrazole used as a ligand to prepare organometallic compounds. Pyrazoles can be selectively lithiated at different carbons and subsequently react with electrophiles depending on the substitution patterns.Category: pyrazoles-derivatives

Bromination of 2-pyrazolines was written by Elguero, Jose;Jacquier, Robert. And the article was included in Compt. Rend. in 1963.Category: pyrazoles-derivatives This article mentions the following:

N-Substituted pyrazolines brominate readily at position 3 but with difficulty at position 4, while pyrazolines not N-substituted give the corresponding pyrazoles, which brominate at the 4-position when this position is unsubstituted. Equimolar proportions of Br and 5-methylpyrazoline (I) in CHCl3 gave an unstable compound which had a nuclear magnetic resonance (n.m.r.) spectrum with a doublet at 7.32 p.p.m. and was apparently 1-bromo-3-methylpyrazoline (II). Without desiccation II rapidly liberated HBr to give a hydrobromide of 3-methylpyrazole, identified by n.m.r. spectrum. Bromination of I with 2 moles Br gave the hydrobromide of 3-methyl-4-bromopyrazole, m. 185-7°, identified by n.m.r. spectrum. Bromination of 3,5,5-trimethylpyrazoline (III) gave, in addition to a small amount of the hydrobromide of III, 1-bromo-3,5,5-trimethylpyrazoline (IV), b0.5 58°, m. 16°, in 83% yield. IV liberated iodine from aqueous acidic KI, precipitated AgBr from a pyridine solution of AgNO3, was reduced by SO2 to III, gave no NH band in its infrared spectrum, and in its n.m.r. spectrum gave bands at 8.55 (gem-dimethyl), 7.86 (3-methyl), and a quartet at 8.01 p.p.m. (2 protons at 4). IV, refluxed in AcOH, gave a black solid containing the hydrobromide of N-bromo-3,4,5-trimethylpyrazole, which was converted by MeONa in MeOH to the hydrobromide of 3,4,5-trimethylpyrazole (V), m. 257°. The change from IV to V is apparently a reverse pinacol transformation. Similarly, 1,3,5,5-tetramethylpyrazoline, b25 61° (from III and MeI), gave a 20% yield of 1,3,4,5-tetramethylpyrazole (picrate m. 192°). In the experiment, the researchers used many compounds, for example, 4-Chloro-3,5-dimethyl-1H-pyrazole (cas: 15953-73-8Category: pyrazoles-derivatives).

4-Chloro-3,5-dimethyl-1H-pyrazole (cas: 15953-73-8) belongs to pyrazole derivatives. Pyrazole is a weak base, with pKb 11.5 (pKa of the conjugated acid 2.49 at 25 °C).Pyrazole used as a ligand to prepare organometallic compounds. Pyrazoles can be selectively lithiated at different carbons and subsequently react with electrophiles depending on the substitution patterns.Category: pyrazoles-derivatives

Referemce:
Pyrazole – Wikipedia,
Pyrazoles – an overview | ScienceDirect Topics