USE OF CERTAIN TRANSITION METAL HYPERACCUMULATOR PLANTS FOR REDUCING ORGANIC COMPOUNDS IN A GREEN MANNER

Abstract

Disclosed is a method for reducing organic compounds using catalysts containing nickel (0) from metal hyperaccumulator plants. The method can be implemented in a green manner and is advantageous compared to methods using the known catalysts.

Claims

1-26. (canceled)

27. Process for the reduction of an organic compound wherein a metal catalyst comprising less than 2% by weight of carbon and of Ni(0) obtained by treatment with an organic acid, from the ashes of a calcined Ni-hyperaccumulator plant or of a part of a calcined Ni-accumulating plant that has accumulated Ni in a quantity at least equal to 100 ppm of calcined dehydrated plant, preferably greater than 1000 ppm of calcined dehydrated plant, a metal catalyst the Ni metal of which originates from said plant without the addition of Ni originating from an origin other than said plant, is reacted with said compound in the presence of a hydrogen donor.

28. Process according to claim 27, in which the organic compound reduction reaction is carried out in the absence of dihydrogen, hydrides, alanes, boranes, organometallics and metals with the degree of oxidation (0) as hydrogen donor.

29. Process according to claim 27, wherein the hydrogen donor is selected from an alcohol, a carbohydrate reducing agent, formic acid or a formic acid salt, a cycloalkene, an unsaturated heterocycle, phosphinic acid and a saline hydrophosphite.

30. Process according to claim 27, wherein the hydrogen donor is selected from an alcohol in the presence of a base, formic acid, a formic acid salt and a hydrophosphite.

31. Process according to claim 27, wherein the hydrogen donor is selected from isopropanol in the presence of a base, formic acid and a formic acid salt, preferably HCOONH.sub.4.

32. Process according to claim 27, in which the hydrogen donor is an alcohol, preferably isopropanol, in the presence of a base preferably selected from soda, hydrotalcite and alumina.

33. Process for the reduction of an organic compound according to claim 27 wherein the organic compound comprises one or more functions selected from the aldehyde, ketone, imine functions and the conjugated carbon-carbon bonds.

34. Process according to claim 33, wherein the organic compound comprises one or more functions selected from the aromatic aldehyde, aliphatic aldehyde, monosubstituted ketone, disubstituted ketone, trisubstituted ketone, aryl ketone, functionalized ketone, cyclic ketone, polycyclic ketone, imine functions, the carbonyl functions conjugated with carbon-carbon bonds or the conjugated carbon-carbon bonds.

35. Process according to claim 27, wherein the acid treatment to which the ashes of an Ni-hyperaccumulator plant is subjected is carried out with an organic acid selected from formic acid and oxalic acid.

36. Process according to claim 27, wherein the metal catalyst originates from the ashes of a nickel-hyperaccumulator plant selected from Psychotria douarrei, Geissois pruinosa, Alyssum fallicinum and Alyssum murale, Leucotron havanensis, Psychotria clementis, Phyllanthus balgooyi, Phyllanthus serpentinus, advantageously Psychotria douarrei, Geissois pruinosa, Alyssum fallicinum and Alyssum murale, preferably Alyssum murale.

37. Process according to claim 35 for the selective reduction of one of the reducible functions of an organic compound comprising several reducible functions, wherein the reaction is carried out in the presence of isopropanol and alumina or hydrotalcite.

38. Process according to claim 27 for the reduction of an organic compound comprising one or more unsaturated carbon-carbon bonds and an aldehyde or ketone function, preferably an ,-ethylenic aldehyde or an ,-ethylenic ketone, more preferentially selected from citral, cinnamaldehyde and pulegone characterized in that the aldehyde or ketone function is reduced to an alcohol function and the unsaturated carbon-carbon bond(s) is/are unchanged.

39. Process according to claim 27, wherein the reaction is carried out in the presence of isopropanol and alumina or hydrotalcite.

40. Process for the preparation of a catalyst comprising Ni(0), comprising the steps of: (a) calcination at a temperature from 250 to 500 C., more advantageously from 350 to 450 C., in particular of approximately 400 C. of an Ni-hyperaccumulator plant or of a part of an Ni-hyperaccumulator plant that has accumulated Ni at least equal to 100 ppm of dehydrated plant, preferably greater than 1000 ppm of dehydrated plant in order to obtain ashes, (b) treatment of the ashes obtained in step (a) with an organic acid, advantageously in order to isolate a precipitate containing at least one Ni(II) salt, (c) heat treatment at a temperature from 100 C. to 400 C., advantageously from 150 C. to 300 C., preferably at 240 C. of the product obtained in step (b) in order to obtain a metal catalyst comprising Ni(0).

41. Process according to claim 40, in which the Ni-hyperaccumulator plant is selected from Leucotron havanensis, Psychotria clementis, Phyllanthus balgooyi, Phyllanthus serpentinus, Psychotria douarrei, Geissois pruinosa, Alyssum fallicinum and Alyssum murale, advantageously Psychotria douarrei, Geissois pruinosa, Alyssum fallicinum and Alyssum murale, preferably Alyssum murale.

42. Process according to claim 40, in which the organic acid is formic acid or oxalic acid, preferably formic acid.

43. Metal catalyst comprising Ni(0) obtained by the process according to claim 40.

44. Metal catalyst according to claim 43, obtained by the process comprising or consisting of the steps of: (a) calcination of Psychotria douarrei that has accumulated Ni at least equal to 1000 ppm of dehydrated plant in order to obtain ashes, (b) treatment of the ashes obtained in step (a) with formic acid, in order to isolate a precipitate comprising nickel(II) oxalate, (c) optionally dissolving the precipitate comprising the nickel(II) oxalate in water, filtration of the solution and evaporation of the water, (d) heat treatment of the product obtained in step (c) at a temperature of 240 C., advantageously in paraffin, in order to obtain a metal catalyst comprising Ni(0).

45. A process for the reduction of an organic compound selected from the group constituted by the monoterpenes in which an ,-unsaturated aldehyde or ,-unsaturated ketone function is present, such as carvone, verbenone, citral, geranial, neral, 8-oxo-geranial, piperitone, pulegone and myrcenal, the monoterpenes in which an aldehyde or ketone function is present, such as citronellal, the retinoids, such as retinal and derivatives thereof, the substituted cyclopentanones, such as dihydrojasmone and derivatives thereof, and the substituted cyclopentenones, such as jasmone and derivatives thereof, advantageously selected from the group constituted by citral, cinnamaldehyde, substituted cyclopentanones, pulegone and retinal, wherein a metal catalyst comprising less than 2% by weight of carbon and of Ni(0) obtained by treatment with an organic acid, from the ashes of a calcined Ni-hyperaccumulator plant or of a part of a calcined Ni-accumulating plant that has accumulated Ni in a quantity at least equal to 100 ppm of calcined dehydrated plant, preferably greater than 1000 ppm of calcined dehydrated plant, a metal catalyst the Ni metal of which originates from said plant without the addition of Ni originating from an origin other than said plant, is reacted with said compound in the presence of a hydrogen donor, wherein a metal catalyst according to claim 44 is reacted with said compound.

46. Process according to claim 45, in which the hydrogen donor is selected from an alcohol in the presence of a base, preferably selected from hydrotalcite and alumina, formic acid, a formic acid salt, preferably HCOONH.sub.4 and a hydrophosphite.

Description

EXAMPLES

[0111] The reactivity of Eco-Ni(II) was first studied.

I. Green Reduction from the Phytoextract Ni(II), Eco-Ni (II)

[0112] The principle of the process of green reduction starting from the phytoextract Ni(II), Eco-Ni (II) is based on an adaptation of the reduction of the Meerwein-Pondorf-Verley type. It can be adapted to very diverse carbonyl-containing derivatives including the hindered and functionalized ketones. The method is compatible with the presence of CC double bonds.

[0113] Isopropanol is the preferred alcohol. The quantities of Eco-Ni involved are small but remarkably effective.

##STR00014##

[0114] The reaction conditions are not only very effective, but also very green; they generate very little waste, use a green solvent, isopropanol, and are very easy to implement. They present no industrial risk. This method is very advantageous with respect to Raney Ni or to the metals and hydrides conventionally used. It usefully replaces the precious metals or systems that are more complex than NiCl.sub.2(PPh).sub.3. The latter are less effective and require more Ni: the claimed Eco-Ni (II) system has a catalytic effect starting from 5% Ni, while liganded commercial NiCl.sub.2 requires 15% mol. (J. Chem. Soc., Chem Comm. 1995, 465-466, S. Iyer and Jos P. Vargehese). Here, no phosphine ligand is necessary, which makes it possible to work under aerobic conditions.

[0115] The reaction described is more rapid than with the conventional systems described as being the most effective (J. Chem. Soc., Chem Comm 2000, 1647-1648, M. D. Le Page and Brian R. James). The soda can be replaced with hydrotalcite, but here the prior conditioning and activation of the hydrotalcite at a high temperature is not necessary.

Experimental Part Relating to the Green Reduction from the Phytoextract Ni(II), Eco-Ni (II)

[0116] Typical experimental protocol for the reduction of cyclohexanone by the Eco-Ni(II)/iPrOH/NaOH system:

[0117] The following are introduced into a sealed tube provided with a magnetic stirrer: Eco-Ni(II) (17 mg; 0.05 mmol Ni), isopropanol (5 mL; 65.3 mmol), NaOH (20 mg; 0.5 mmol), cyclohexanone (103.5 L; 1.0 mmol). The reaction medium is heated at 85 C. by means of an oil bath, under stirring, for 3 hours. The composition of the reaction medium is analyzed by GC-MS, with an internal standard (biphenyl). Cyclohexanol is formed with a quantitative yield.

TABLE-US-00003 Reduction Substrate product Yield RC(O)R Conditions RR(CH)OH % [00015] Ni present in Eco-Ni(II): 6 mg (0.05 mmol Ni) iPrOH: 65.3 mmol NaOH: 4.25 mmol Substrate: 1 mmol 85 C./2 hours [00016] 100 [00017] Ni present in Eco-Ni(II): 6 mg (0.05 mmol Ni) iPrOH: 65.3 mmol hydrotalcite Substrate: 1 mmol 85 C./8 hours [00018] 92 [00019] Ni present in Eco-Ni(II): 6 mg (0.05 mmol Ni) iPrOH: 65.3 mmol NaOH: 4.25 mmol Substrate: 1 mmol 85 C./2 hours [00020] 98 [00021] Ni present in Eco-Ni(II): 6 mg (0.05 mmol Ni) iPrOH: 65.3 mmol hydrotalcite Substrate: 1 mmol 85 C./2 hours [00022] 100 [00023] Ni present in Eco-Ni(II): 6 mg (0.05 mmol Ni) iPrOH: 65.3 mmol NaOH: 4.25 mmol Substrate: 1 mmol 85 C./2 hours [00024] 100 [00025] Ni present in Eco-Ni(II): 6 mg (0.05 mmol Ni) iPrOH: 65.3 mmol NaOH: 4.25 mmol Substrate: 1 mmol 80 C./2 hours [00026] 77 [00027] Ni present in Eco-Ni(II): 6 mg (0.05 mmol Ni) iPrOH: 65.3 mmol NaOH: 4.25 mmol [00028] 91 Substrate: 1 mmol 85 C./24 hours [00029] Ni present in Eco-Ni(II): 6 mg (0.05 mmol Ni) iPrOH: 65.3 mmol NaOH: 4.25 mmol Substrate: 1 mmol 85 C./6 hours [00030] 88 [00031]

[0118] Other hydrogen donors can be used successfully when the reaction is catalyzed by Eco-Ni(II). The hydroxylanes form part of the most effective systems.

Reduction with the Hydrosiloxanes

[0119] The hydrosiloxanes are nowadays considered as substitutes for aluminium and boron hydrides. They may be a siloxane in the strict sense of the word or a hydrosilane, or a silazane containing one or more SiH groups. They can be linear, branched or cyclic. Systems such as 1,1,3,3-tetramethyldisiloxane (TMDS) or polymethylhydrosiloxane (PMHS) are the most useful. PMHS is considered as a safe and inexpensive co-product polymer of the silicon industry. It is inexpensive, non-toxic, air- and moisture-stable. It is ideal for the development of ecologically responsible reduction processes.

[0120] Combined with transition metals, PMHS has been used successfully for the reduction of various functional groups (carbonyl-containing derivatives, acid derivatives). The nature of the hydrosiloxanemetal combination makes it possible to modulate a significant role with respect to the chemoselectivity of the reactions implemented. It has recently been shown that certain nickel salts combined with phosphine ligands could catalyze the reduction of benzaldehyde by PMHS.

[0121] The present invention shows for the first time that the catalysts derived from the nickel-hyperaccumulator plants, the Eco-Ni(II)s allow such transformations. Surprisingly, Geissois pruinosa leads to results superior to those of the hypemickelophore Psychotria douarrei.

##STR00032##

TABLE-US-00004 Ni- hyperaccumulator Treatment of Yield* Ar plant the ashes ligand % Ph Psychotria douarrei AcOH [00033] 60 Ph Geissois pruinosa AcOH [00034] 73 Ph Psychotria douarrei HC1 [00035] 33 Ph Geissois pruinosa HC1 [00036] 57

[0122] Experimental protocol for the reduction of benzaldehyde by a hydrosiloxane: the Eco-Ni(II)/tricyclohexylphosphine/PMHS system:

[0123] The following are introduced into a sealed tube maintained under an inert atmosphere: Eco-Ni(II) (17 mg; 0.05 mmol Ni), tricyclohexylphosphine (28 mg; 0.10 mmol), anhydrous THF (2 mL), PMHS (average M.sub.n: 1700-3200) (179 L; 3.0 mmol of hydride), benzaldehyde (101.6 L; 1.0 mmol). The reaction medium maintained under an inert atmosphere is heated in an oil bath at 70 C. under stirring for 24 hours. After cooling down, a methanolysis is carried out by the addition of methanol (1 mL) and of a 2 M aqueous solution of sodium hydroxide (1.5 mL), then stirring at ambient temperature for 16 hours (a slight effervescence is produced). The medium is then extracted with cyclohexane then analyzed by GC-MS, with an internal standard (biphenyl). Benzyl alcohol is formed at a rate of 47% yield.

IIPreparation of Plant Ni(0), Eco-Ni(0), by Green Method and Study of its Reactivity

[0124] Organic acids such as formic acid, the formic acid salts including HCOOLi, HCOONa, HCOOK, HCOONH.sub.4, HCOONHEt.sub.3, but also oxalic acid which is more available naturally, phosphinic acid or its sodium salt, can be used to form complexes with the hyperaccumulated salts of the nickelophores. The complexes of the transition metals mainly precipitate. The heating thereof induces the reduction of the most reducible cation, nickel. The latter has very useful physico-chemical properties; thus for example, the metallic Ni(0)-cationsanions of plant originformates mixture leads to a material with outstanding reducing properties.

IIExperimental Part:

Preparation of Eco-Ni (0) by Reduction of Plant Ni(II) Using Formic Acid

[0125] 5 g of ashes of Psychotria douarrei obtained by heat treatment at 400 C. of the corresponding leaves, are dispersed in 150 mL of formic acid. The solution is stirred at 90 C. The solution becomes black fairly rapidly. After stirring for 30 hours, the reaction mixture is filtered on celite. A pale yellow solution and a grey residual solid are isolated and put aside. The solid residue deposited on the celite, composed partly of nickel formate is washed with boiling water. It is easily entrained (emerald green colour) and evaporated. 3.210 g of a light green solid is analyzed using ICP MS (Table 2). It is composed of 22% Ni. A pure catalyst would have had a level of 39%.

TABLE-US-00005 TABLE 2 ICP-MS data ppm (mg/kg) in the solid catalyst of plant origin Element .sup.23Na .sup.24Mg .sup.44ca .sup.52Cr .sup.55Mn .sup.56Fe .sup.59Co .sup.60Ni .sup.65Cu .sup.66Zn .sup.88Sr Ppm 47181 25189 30177 220 3462 5965 85 228030 121 158 341 (mg/kg)
Reduction of the Ni Formate from Psychotria douarrei to Eco-Ni(0) (FIG. 1).

[0126] 50 mg of the preceding catalyst and 3 mL of paraffin oil (d=0.82-0.89) are introduced into a 10 mL flask. The medium is first heated at 170 C. for 1 hour using a sand bath, then at 255 C. for 4 hours under a nitrogen atmosphere. After cooling down, the mixture is filtered then washed with hexane. A fine black powder is obtained and called Eco-Ni(0). It is stored under vacuum under P.sub.2O.sub.5.

[0127] The solid is characterized by measuring its porosity, specific surface area and scanning electron microscope (SEM) images. FIG. 2 shows the SEM images obtained, illustrating the porosity of the material obtained.

[0128] The specific surface area measured using the BET method is 109.2621 m.sup.3/g.

[0129] The volume and the size of the pores are 0.20 cm.sup.3/g and 75.06 respectively.

[0130] The particles of nickel have an average diameter of 20 nm.

[0131] The Ni(0) of Eco-Ni(0) can be generated by an organic acid that is more available naturally, oxalic acid, or a salt of the organic acids according to the same protocol.

[0132] These methods are very advantageous. The reduction of the Ni(II) is based on an effective use of natural organic acids and therefore of renewable resources. It also avoids the use of hazardous conditions, solvents and reagents contrary to the principles of green chemistry (metal lithium, arenes such as 4,4-di-tert-butylbiphenyl, THF etc.), which are still nonetheless very often used (F. Alonso, P. Riente, M. Yus' ACCOUNTS OF CHEMICAL RESEARCH Vol. 44, No. 5, 2011, 379-391 and cited references).

Reactivity of Eco-Ni(0)

[0133] The reactivity of Eco-Ni(0) has been tested vis--vis different carbonyl-containing derivatives.

##STR00037##

[0134] The experimental protocol is illustrated using the example of cyclohexanone:

[0135] The following are introduced into a sealed tube provided with a magnetic stirrer: Eco-Ni(0) (1.2 mg; 0.01 mmol Ni), isopropanol (5 mL; 65.3 mmol), basic alumina (Brockmann I type) (activated beforehand by heating at 300 C. for 15 minutes) (1 g; 9.8 mmol), cyclohexanone (103.5 L; 1.0 mmol). The reaction medium is heated at 85 C. by means of an oil bath, under stirring, for 2 hours. After cooling down to ambient temperature, the medium is filtered in order to recover the heterogeneous catalyst. The filtrate is analyzed using GC-MS, with an internal standard (biphenyl). Cyclohexanol is formed with a quantitative yield. The catalyst recovered by filtration is rinsed with isopropanol then dried in a desiccator under vacuum before being reused.

[0136] The following table shows a few examples of the structures studied:

TABLE-US-00006 Reduction Substrate Conditions product Yield [00038] Eco-Ni (0): 1.2 mg (0.01 mmol Ni) iPrOH: 65.3 mmol NaOH: 0.1 mmol Substrate: 1 mmol 85 C./24 hours [00039] 100 [00040] Eco-Ni (0): 1.2 mg (0.01 mmol Ni) iPrOH: 5 mL (65.3 mmol) Al.sub.2O.sub.3: 1 g Substrate: 1 mmol 85 C./18 hours [00041] 100 [00042] Eco-Ni (0): 1.2 mg (0.01 mmol Ni) iPrOH: 65.3 mmol Calcined hydrotalcite: 1 g Substrate: 1 mmol 85 C./8 hours [00043] 82 [00044] Eco-Ni (0): 1.2 mg (0.01 mmol Ni) iPrOH: 65.3 mmol NaOH: 0.1 mmol Substrate: 1 mmol 85 C./20 hours [00045] 100 [00046] Eco-Ni (0): 1.2 mg (0.01 mmol Ni) iPrOH: 65.3 mmol Al.sub.2O.sub.3: 1 g Substrate: 1 mmol 85 C./18 hours [00047] 97 [00048] Eco-Ni (0): 1.2 mg (0.01 mmol Ni) iPrOH: 65.3 mmol NaOH: 0.1 mmol Substrate: 1 mmol 85 C./24 hours [00049] 100 [00050] Eco-Ni (0): 1.2 mg (0.01 mmol Ni) iPrOH: 65.3 mmol NaOH: 0.1 mmol Substrate: 1 mmol 85 C./24 hours [00051] 100 [00052] Eco-Ni (0): 1.2 mg (0.01 mmol Ni) iPrOH: 65.3 mmol NaOH: 0.1 mmol Substrate: 1 mmol 85 C./24 hours [00053] 91 [00054] Eco-Ni (0): 1.2 mg (0.01 mmol Ni) iPrOH: 65.3 mmol NaOH: 0.1 mmol Substrate: 1 mmol 85 C./20 hours [00055] 86 [00056] Eco-Ni (0): 1.2 mg (0.01 mmol Ni) iPrOH: 65.3 mmol Al.sub.2O.sub.3: 1 g Substrate: 1 mmol 85 C./20 hours [00057] 78 [00058] Eco-Ni (0): 1.2 mg (0.01 mmol Ni) iPrOH: 65.3 mmol NaOH: 0.1 mmol Substrate: 1 mmol 85 C./24 hours [00059] 96 [00060] Eco-Ni (0): 1.2 mg (0.01 mmol Ni) iPrOH: 65.3 mmol Al.sub.2O.sub.3: 1 g Substrate: 1 mmol 85 C./18 hours [00061] 81 [00062] Eco-Ni (0): 1.2 mg (0.01 mmol Ni) iPrOH: 65.3 mmol Al.sub.2O.sub.3: 1 g Substrate: 1 mmol 85 C./18 hours [00063] 85 [00064] Eco-Ni (0): 1.2 mg (0.01 mmol Ni) iPrOH: 65.3 mmol Al.sub.2O.sub.3: 1 g Substrate: 1 mmol 85 C./18 hours [00065] 83 [00066] Eco-Ni (0): 1.2 mg (0.01 mmol Ni) iPrOH: 65.3 mmol NaOH: 0.1 mmol Substrate: 1 mmol 85 C./24 hours [00067] 75 [00068] Eco-Ni (0): 1.2 mg (0.01 mmol Ni) iPrOH: 5 mL (65.3 mmol) Al.sub.2O.sub.3 1 g Substrate: 1 mmol 85 C./6 hours [00069] 97 [00070] Eco-Ni (0): 1.2 mg (0.01 mmol Ni) iPrOH: 5 mL (65.3 mmol) Al.sub.2O.sub.3: 1 g Substrate: 1 mmol 85 C./4 hours [00071] 100 [00072] Eco-Ni (0): 1.2 mg (0.01 mmol Ni) iPrOH: 5 mL (65.3 mmol) Al.sub.2O.sub.3 1 g Substrate: 1 mmol 85 C./6 hours [00073] 98 [00074] Eco-Ni (0): 1.2 mg (0.01 mmol Ni) iPrOH: 65.3 mmol NaOH: 0.1 mmol Substrate: I mmol 85 C./20 hours [00075] 89 [00076]

[0137] The reaction can be extended to hindered substrates, such as di- or tri-substituted ketones. In this case, the Eco-Ni(0) catalyst supported on hydrotalcite constitutes a very effective solution if R has a function susceptible to alkaline hydrolysis (e.g.: carboxylic ester group).

##STR00077##

[0138] The high chemoselectivity of the reduction conditions is to be noted with interest: [0139] Aldehydes and ketones can be reduced; the high level of effectiveness of Eco-Ni(0) of plant origin contrasts with the particles of Ni(0) described in the literature. According to Alonso and Yus (Tetrahedron 64 (2008) 1847e1852), without additional ammonium formate, the benzaldehyde is reduced only to a level of 42% with the nanoparticles described in the article; the reduction of an aliphatic aldehyde is even more difficult (40%). [0140] The only systems that make it possible to achieve this level of reducing activity originate from complex treatment using hydrides in order to reduce Ni(II) (Kidway et al., Tetrahedron Letters 47 (2006) 4161-4165). With the biosourced reducing systems that are the subject of the present application, the yields are doubled (81-85%). The other metallic species present therefore lead to an enhancement of the reducing power of the nanoparticles of Eco-Ni(0). [0141] A carbonyl-containing derivative can be reduced in the presence of a nitro, nitrile, non-conjugated alkene and even an alkyne group. This last result shows the complementarity of selectivity with the method of Alonso and Yus which involves the reduction of the alkynes (Tetrahedron 63 (2007) 93-102). [0142] Finally, the reduction regioselectivity of an ,-ethylenic carbonyl-containing derivative is outstanding with plant Ni(0) in isopropanol. Contrary to the methods described (Page and James, Chem. Commun., 2000, 1647-1648, Alonso et al. Tetrahedron 64 (2008) 1847-1852), in this case it is possible to very selectively reduce the single carbonyl unit with the plant Ni (0)/iPrOH/Al.sub.2O.sub.3 system. This possibility is illustrated with the interesting example of the controlled reduction of citral to geraniol/nerol. Citral is a very demonstrative model, since it comprises 3 different reducible sites: two CC double bonds, one of which is conjugated, and an aldehyde function. Moreover, the reduction of citral to geraniol/nerol is of significant industrial interest in the field of the cosmetics given the rose fragrance of the geraniol/nerol mixture (Stolle et al. RSC Adv., 2013.3, 2112-2153). The result obtained is very original; it is clearly different from the H.sub.2/Ni/Al.sub.2O.sub.3 system which does not make it possible to orientate the reaction towards the controlled formation of the allyl alcohols or the hydrogenations with noble metals which lead to mixtures that are difficult to utilize. [0143] The examples such as the reduction of citral and of cinnamaldehyde show the general applicability of the method of the present application to structures of industrial interest. [0144] The presence of phosphine or of phosphite is not indispensable. The reactions are therefore clearly less sensitive and easy to implement. [0145] The isopropanol can be replaced with another alcohol, such as methanol or acetic acid. In these latter cases, it is useful to introduce a formic acid salt such as ammonium formate or a phosphinic acid salt such as sodium hydrophosphite as a hydrogen reservoir. For simple reasons of solubility they are preferred to hydrazine, or to easily re-aromatizable unsaturated rings.