O=C(NC(NC(=S)Nc1cc(Cl)ccc1Cl)C(Cl)(Cl)Cl)c1ccco1
An acid's negative base-10 logarithmic dissociation constant (pKa) follows directly from its underlying thermodynamics; the negative pKa is directly proportional to its standard Gibbs free energy change. What is the negative pKa value of this molecule?