Surfactant aided reductive carbonylation of nitrobenzene in water catalyzed by Pd complexes

Surfactant aided reductive carbonylation of nitrobenzene in water catalyzed by Pd complexes

Andrea Vavasori^a*, Lucio Ronchin^a, Giuseppe Quartarone^a, Claudio Tortato^a, Leonardo Campagnaro^a.

a Department of Molecular Sciences and Nanosystems, Ca’ Foscari University of Venezia, Dorsoduro 2137 – 30123 – Venezia, Italy.

*vavasori@unive.it

The catalytic carbonylation of nitroarenes is a field of high interest from a technological point of view, since provides an environmentally benign route to a number of important industrial products, such as isocyanates, carbamates, ureas, azoarenes and azoxyarenes, amines, amides, oximes and several types of heterocyclic compounds [1-3]. The reductive carbonylation of nitrobenzene in water carried out by using Pd(II)-solvable catalyst precursors, leads to aniline, as major product [4]. In the present paper we propose the micellar catalytic reductive carbonylation of nitrobenzene in water. The Pd(II) catalyst precursors tested are synthesized by using cheaper commercial insolvable ligands, such as triphenylphosphine (PPh3), 1,3- bis(diphenylphosphino)propane (dppp) and 1, 10-phenantroline (phen). The influence on the conversion and on the selectivity of such precursors has been evaluated in combination with commercial anionic (SDS), cationic (TBAB) and non ionic (Triton X 100) surfactants (Tab.1).

Pd(OAc)2(PPh3)2 Pd(OAc)2(phen) Pd(OAc)2(dppp)

SDS 60 55 15

Triton X 100 20 19 -

CTAB 80 60 -

Table 1. Influence on the nitrobenzene conversion (molar %) of different precursors and surfactants

Pd: 3.10^-3 mmol, T: 90°C, P: 45 atm, V: 30 mL, NaOH: 30% in H2O. CTAB: cetyl trimethylammonium bromide, SDS: Sodium Dodecylsulfate, Triton X-100: octylphenol poly(ethyleneglycolether)x.

We have found that all the Pd(II) complexes in the Table 1 are efficiently dissolved in each O/W emulsions but the conversion is strongly influenced by the nature of ligand. By using Pd(OAc)2(PPh3)2, high selectivity towards azo- and azo-oxybenzene has been obtained. The influence of some reaction parameters has been further evaluated and optimized.

References

[1] F. Paul, Coord. Chem. Rev., 203 (2000) 269–323.

[2] F. Ragaini, Dalton Trans., (2009) 6251–6266.

[3] A. Vavasori, L. Ronchin, Pure Appl. Chem., 84 (2012) 473-484.

[4] A. M. Tafesh, M. Beller, Tetrahedron Letters, 36 (1995) 9305-9308.