Synthesis of arylacetic acid derivatives from mandelic acid derivatives by hydrogen transfer from H2OCO catalyzed by a PdCHCl system

✍ Scribed by G. Cavinato; L. Ronchin; L. Toniolo

• Publisher: Elsevier Science
• Year: 1995
• Tongue: English
• Weight: 416 KB
• Volume: 102
• Category: Article
• ISSN: 1381-1169
• DOI: 10.1016/1381-1169(95)00077-1

✦ Synopsis

A (\mathrm{Pd} / \mathrm{C}-\mathrm{HCl}) catalytic system is highly active and selective in the hydrogen transfer from (\mathrm{H}{2} \mathrm{O}-\mathrm{CO}) to (\mathrm{ArCHOHCOOH}) for the synthesis of (\mathrm{ArCH}{2} \mathrm{COOH}) ( Ar is para substituted with a (\mathrm{OH}) group). Typical reaction conditions are: temperature (50-70^{\circ} \mathrm{C}); (P_{\mathrm{CO}} 20-80 \mathrm{~atm} ;) solvent: acetonitrile; substrate (/ \mathrm{Pd} / \mathrm{HCl} / \mathrm{H}{2} \mathrm{O}=200-400 / 1 / 25-100 / 500-2000 ;[\mathrm{Pd}]=0.6-1.2 \mathrm{mmol} \cdot 1^{-1}). The reaction rate is approximately of the first order with respect to (\mathrm{ArCHOHCOOH}). The yield increases with the increasing of (P{\mathrm{CO}}) and of the temperature, as expected, and passes through a maximum with the increasing of the concentration of (\mathrm{H}{2} \mathrm{O}) and of (\mathrm{HCl}). The proposed catalytic cycle proceeds through the following steps. (i) (\mathrm{H}{2} \mathrm{O}) and (\mathrm{CO}) interact with the metal giving rise to an intermediate having a Pd-COOH moiety, which, upon (\beta)-hydride abstraction, gives off (\mathrm{CO}{2}) with formation of a Pd-H species. (ii) The starting substrate is in equilibrium, in the presence of (\mathrm{HCl}), with the corresponding chloride (\mathrm{ArCHClCOOH}), which adds to the metal forming an intermediate having a (\mathrm{Pd}-\mathrm{CH}(\mathrm{Ar}) \mathrm{COOH}) moiety. (iii) This species interacts with the hydride yielding the product (\mathrm{ArCH}{2} \mathrm{COOH}) and regenerating the catalyst. The reaction is compared to the closely related catalyzed water gas shift reaction.