1-(4-Benzenesulfonic acid)pyrazole synthesis

Yield:18336-38-4 37%

Reaction Conditions:

with sulfuric acid;sulfur trioxide at 0 - 35; for 1 h;

Steps:

2.1

A solution was prepared by adding 1-phenylpyrazole (1.3 ml, 9.8 mmol) to concentrated sulfuric acid (2 ml). To this solution, fuming sulfuric acid (5 ml, 30% SO3) was added gradually over at least 5 minutes at 0° C. The resultant mixture was heated to 35° C., and this temperature was kept for 1 hour. This mixture then was cooled to 0° C. by pouring it over crushed ice, thereby causing sulfate to precipitate. This sulfate was collected by filtration and then vacuum-dried. Thus, a desired compound, 4-(1H-pyrazole-1-yl)benzenesulfonic acid, was obtained in the form of a white solid (the yield calculated based on 1-phenylpyrazole: 37%). The instrumental analysis values of 4-(1H-pyrazole-1-yl)benzenesulfonic acid are shown below.¹H-NMR (DMSO-d₆, 298 K): δ (ppm) 6.55 (d, d, J=1.5 Hz, J=2.6 Hz, 1H), 7.68 (d, J=2.4 Hz, 2H), 7.75 (d, J=1.5 Hz, 1H), 7.80 (d, J=2.4 Hz, 2H), 8.52 (d, J=2.6 Hz, 1H).

References:

US2012/321550,2012,A1 Location in patent:Page/Page column 28