The catalytic system Pd/C-HCl is highly active in the redn. of mandelic acid derivs. to phenylacetic acid derivs. with carbon monoxide when the arom. ring is para-substituted with a hydroxy group. Typical reaction conditions are: 70-110°, 20-100 atm of carbon monoxide, benzene-ethanol as reaction medium, substrate(vanillomandelic acid)/Pd = 102-104/1, HCl/substrate = 0.3-0.8/L. The proposed catalytic cycle proceeds as follows: the chloride ArCHClCOOR, formed in situ upon reaction of ArCHOHCOOR with hydrochloric acid, oxidatively adds to a Pd(0) species with formation of a catalytic intermediate having a Pd-[CH(Ar)COOR] moiety, which inserts a CO mol., yielding an acyl intermediate of the type Pd- [COCH(Ar)COOR]. The nucleophilic attack of H2O on the carbon atom of the carbonyl ligand gives back the Pd(0) complex to the catalytic cycle and yields a phenylmalonic acid deriv., which produces the final product, ArCH2COOR, upon CO2 evolution. Alternatively, protonolysis of the intermediate having a Pd-[CH(Ar)COOR] moiety yields directly the final product and a Pd(II) species, which is then reduced by CO to Pd(0). Moreover, no catalytic activity is obsd. when the Pd/C-HCl system is used in combination with any one of the above diphosphine ligands, probably because these ligands block the sites on the catalyst able to promote the catalytic cycle or because they prevent the redn. of Pd(II) to Pd(0). The influence of the following reaction parameters has been studied: concn. of HCl, PPh3, palladium and substrate, pressure of carbon monoxide, the temp., reaction time and solvent.

Influence of the reaction parameters on the palladium-hydrogen chloride catalyzed synthesis of phenylacetic acidderivatives via reduction of mandelic acid derivatives with carbon monoxide

TONIOLO, Luigi
1993-01-01

Abstract

The catalytic system Pd/C-HCl is highly active in the redn. of mandelic acid derivs. to phenylacetic acid derivs. with carbon monoxide when the arom. ring is para-substituted with a hydroxy group. Typical reaction conditions are: 70-110°, 20-100 atm of carbon monoxide, benzene-ethanol as reaction medium, substrate(vanillomandelic acid)/Pd = 102-104/1, HCl/substrate = 0.3-0.8/L. The proposed catalytic cycle proceeds as follows: the chloride ArCHClCOOR, formed in situ upon reaction of ArCHOHCOOR with hydrochloric acid, oxidatively adds to a Pd(0) species with formation of a catalytic intermediate having a Pd-[CH(Ar)COOR] moiety, which inserts a CO mol., yielding an acyl intermediate of the type Pd- [COCH(Ar)COOR]. The nucleophilic attack of H2O on the carbon atom of the carbonyl ligand gives back the Pd(0) complex to the catalytic cycle and yields a phenylmalonic acid deriv., which produces the final product, ArCH2COOR, upon CO2 evolution. Alternatively, protonolysis of the intermediate having a Pd-[CH(Ar)COOR] moiety yields directly the final product and a Pd(II) species, which is then reduced by CO to Pd(0). Moreover, no catalytic activity is obsd. when the Pd/C-HCl system is used in combination with any one of the above diphosphine ligands, probably because these ligands block the sites on the catalyst able to promote the catalytic cycle or because they prevent the redn. of Pd(II) to Pd(0). The influence of the following reaction parameters has been studied: concn. of HCl, PPh3, palladium and substrate, pressure of carbon monoxide, the temp., reaction time and solvent.
File in questo prodotto:
Non ci sono file associati a questo prodotto.

I documenti in ARCA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10278/35583
Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus ND
  • ???jsp.display-item.citation.isi??? ND
social impact