Eric Fache

Selective hydrogenation of α,β-unsaturated aldehydes catalyzed by supported aqueous-phase catalysts and supported homogeneous catalysts

Abstract Selective hydrogenations of different α,β-unsaturated aldehydes into allylic alcohols with immobilized homogeneous catalysts are reported. Different kinds of catalysts were used: supported aqueous-phase catalysts (RuCl2(TPPTS)3/SiO2 and RuH2(TPPTS)4/SiO2) and supported homogeneous catalysts (especially phosphino-iridium catalysts like IrCl3{(C6H5)P[(CH2)3SiO 3 2 ]2·2N[(CH2)3SiO 3 2 ]3·2SiO2}3). Some of them are good alternatives to homogeneous catalysts since they are chemoselective, sometimes stereoselective and easy to recover.

Selective access to hydroquinone: «Fuchsone route

Publisher Summary Hydroquinone (HQ, 4-hydroxyphenol) and catechol (PC, 2-hydroxyphenol or pyrocatechol) are industrially prepared by: (1) selective access to HQ by aniline oxidation using manganese dioxide in sulphuric medium. Yields are high, but the process suffers from the stoichiometric co-production of mineral salts which is the cause of serious environmental problems, (2) selective access of HQ through autoxidation of p. diisopropylbenzene in corresponding dihydroperoxide, which is then converted in HQ and acetone through a acid catalysis. This is a complex process involving a very high conversion of diisopropyl benzene and co-production of corresponding hydroxy hydroperoxide and dicarbinol which compels the acid scission to be performed in the presence of hydrogen peroxide in order to convert these products to HQ, and (3) Simultaneous access to HQ and PC through phenol hydroxylation by hydrogen peroxide in the presence of either a homogeneous or heterogeneous catalyst.

Addition of alcohols to isoprene catalyzed by hydrated rhodium trichloride: A way to improve the 1,4-addition regioselectivity

Abstract Synthesis of alkoxyolefins from alcohols and dienes can be achieved in the presence of hydrated rhodium trichloride. Because of the probable intermediate formation of π-allylic rhodium complexes, the regioselectivity of the addition varies according to the reaction conditions. Without any additives, the greatest selectivity in 1,4-addition is 53% for a 78% isoprene conversion. In the presence of zinc chloride, 1,4-addition is significantly increased (68% for a 70% conversion).

Oxidation of alkylphenols to hydroxybenzaldehydes

4-methylphenol is oxidized into p-hydroxybenzaldehyde by oxygen or air, in water/acetic acid media, in the presence of catalysts like Pd/C or Pd-Sn/C (66% selectivity for total conversion). The former catalysts are not able to yield ohydroxybenzaldehyde from 2-methylphenol. However, good performances are reach with a Pd-Pt/C catalyst (60% selectivity for total conversion)