Changing elementElement A into elementElement B requires changing the number of protons in each atom of elementElement A. There is NO chemical process that can affect the number of protons in any atom.
Chemical processes can be used to concentrate or dilute gold atoms mixed among others. Chemical processes can bond or separate gold atoms locked in compounds. But no chemical process can change another element into gold.
...assuming your alchemist is honest, of course. Any charlatan worthy of the name can whip up a convincing transmutation swindle.