Phenylpropiolic acids, hydration

The rates of hydration of substituted phenylpropiolic acids give a rho of —4.77 when plotted against a, comparable to Ihe acid-catalyzed isomerization of czs-cinnamic acid, with a rho value of —4.3. The solvent deuterium isotope effects are 3.7-S.2 for the isomerization of cinnamic acids at... 

The RuClj/aq. HCl system is effective for hydration of phenylpropiolic acid to give acetophenone and carbon dioxide via the P-keto acid (Eq. 6.53) [86]. 

The addition of hydrogen halides to propiolic acid (6 of Table 2) in water occurs by a mechanism entirely different from that of the acid-catalysed hydration of phenylpropiolic acid (see above). Here again vinyl cations are probably not involved as intermediates and the major mechanistic pathway is the one involving formation of 17 which stereospecifically adds a proton to form tram adducts following equation (7). 

---