Kinetic Evidence for the Coexistence of Zwitterionic (T ± ), Neutral (T 0 ) and Anionic (T − ) Intermediates during Rearrangement of S -(2-Oxotetrahydrofuran-3-yl)- N -(4-methoxyphenyl)isothiuronium Bromide to 5-(2-Hydroxyethyl)-2-(4-methoxyphenylimino)-1,3-thiazolidin-4-one