New media in homogeneous catalysis: wet sodium or tetrabutylammonium hydrogensulfate salts for reppe syntheses catalyzed by a ru(ii) carbonyl complex

Abstract

The ruthenium(II) complex fac-[Ru(CO)₂(H₂O)₃(C(O)C₂H₅)][CF₃SO₃] dissolved in aqueous tetrabutylammonium hydrogensulfate ([(CH₃(CH₂)₃)₄N][HSO₄]) or sodium hydrogensulfate (NaHSO₄) catalyzes the hydrocarboxylation of ethylene to propionic acid and additionally produces minor amounts of hydrocarbonylation products (diethyl ketone and propanal), under water-gas shift reaction conditions. This system is stable with a selectivity of 90% to propionic acid for high ethylene conversion. A turnover frequency of propionic acid, TOF(C₂H₅CO₂H)/24 h = 5 × 10³ (TOF (C₂H₅CO₂H) = ([(moles of C₂H₅CO₂H)/(moles of Ru) × rt)] × 24 h) was achieved for Ru = 7.45 × 10⁻⁴ mol, [(CH₃(CH₂)₃)₄N][HSO₄] = 80 g (2.36 × 10⁻² mol); H₂O = 40 g (2.22 mol); CO = C₂H₄ = 20 g (total pressure = 88 atm); T = 150°C by a reaction time (rt) of 2.87 h. The countercation (sodium or tetrabutylammonium), the ruthenium concentration and the hydrogensulfate/H₂O ratio of the medium affect the catalytic reaction. A nonlinear dependence on total ruthenium concentration was shown. The data are discussed in terms of a potential catalytic cycle. Formation of propionic acid comes from hydrolysis, and formation of diethyl ketone and propanal comes from hydrogenolysis of the Ru-ketyl and Ru-acyl complexes, respectively.

Keywords:

• Reppe synthesis
• Ruthenium complex
• Ethylene
• Carbon monoxide
• Propionic acid
• Diethyl ketone

Acknowledgements

We thank Mr. F. Del Cima for skillful technical assistance and Chimet SpA for a gift of ruthenium. CL and AJP thank the CDCH-UCV for sabbatical leave scholarships.