The COLBERT reaction appears to proceed by a modified nucleophilic thiol attack according to the following mechanism. Initially, the thiol proton partially protonates the benzoxazine nitrogen to create an ammonium cation. The thiophenoxide sulfur then attacks the adjacent methylic carbon located between that nitrogen and the oxygen. The carbon-oxygen bond of the benzoxazine is severed while the sulfur-carbon bond is created. The nitrogen then transfers the proton to the oxygen to complete the phenol. Scheme 9 illustrates the proposed mechanism.