Two extensive mechanisms are proposed for cyclotrimerization of nitriles to s-triazines under high pressure. The availability of these mechanisms is proven by synthesis of some new symmetrically substituted s-triazines; simultaneously, however, their limits are demonstrated. Furthermore, there were found rearrangement and cyclic degradation reactions as reaction possibilities for s-triazines under high pressure. Both reactions are based on an equilibrium in alcohol between symmetrically substituted s-triazine and iminoether