In this work, we developed a new signal amplification system based on allylic phosphonium ion 1, together with phosphine reduceable disulfide molecules for the detection of thiol compounds. The system is activated by the allylic substitution of TPPTS from 1 by a thiol analyte through a sub-stochiometric reaction. This reaction initiates a chain reaction that exponentially amplifies the input thiol signal. The experimental data is supported by a kinetic model that accurately describes the rates of any species involved in the amplification cycle and predicted individual component variations which allowed further insight into the system.