Title: Woodward's Reagent K

CAS Registry Number: 4156-16-5

CAS Name: 2-Ethyl-5-(3-sulfophenyl)isoxazolium inner salt

Additional Names: N-ethyl-5-phenylisoxazolium-3¢-sulfonate

Molecular Formula: C11H11NO4S

Molecular Weight: 253.27

Percent Composition: C 52.16%, H 4.38%, N 5.53%, O 25.27%, S 12.66%

Literature References: Prepd by reacting 5-phenylisoxazole with chlorosulfonic acid, followed by alkylation with triethyloxonium fluoroborate, and acid hydrolysis: Woodward et al., J. Am. Chem. Soc. 83, 1010 (1961).

Properties: Crystals, dec 207-208°. Stable. Non-hygroscopic.

Use: Peptide-bond former.