Because the alkyl thiols RA-SH examined in this work are highly hydrophilic (MPA, coenzyme A, peptide or protein thiols), extracting the quenching thiol RQ-SH during the thiol-thioester exchanged step was envisioned as a simple mean for its removal from the reaction mixture. Liu's hydrazide method was initially developed using an excess of the aromatic thiol 4-mercaptophenylacetic acid (MPAA) to effect the thiolysis of the acyl azide intermediate. Although MPAA is known to be an excellent leaving group compared to alkyl thiols, it is not a suitable candidate as a quenching thiol in this work. Indeed, this compound is highly water-soluble at neutral pH, a property that precludes its extraction with an organic solvent under the working conditions of the thiol-thioester exchange step. Therefore, more hydrophobic arylthiols such as thiophenol or p-hydroxythiophenol were considered instead.