MXPA99011062A - Reduction of carbonyl compounds by a silane in the presence of a zinc catalyst - Google Patents

Abstract

The object of the present invention is a process for the preparation of alcohols by reduction of the carbonyl function in substrates belonging to the class of aldehydes, ketones, esters or lactones, which substrates may contain unsaturated functions other than carbonyl, comprising:a) the reaction of the carbonyl substrate with stoichiometric amounts of a silane in the presence of catalytic amounts of an active zinc compound which is monomeric and not a hydride, b) the hydrolysis of the thus-obtained siloxane with a basic agent, and c) the separation and purification, if necessary, of the thus-obtained alcohol. The catalytically active compound is generally obtained by the reaction of an oligomeric or polymeric precursor compound of zinc with a complexing agent.

Description

esters and lactones. All reagents mentioned above are used in stoichiometric quantities and show the disadvantage of hydrogen release during the course of the reaction or, when they come into contact with moisture, to lead to explosion risks and require the use of inert medium of the reactors. used. In addition, the use of these reagents is expensive since they are required in stoichiometric amounts. Thus, there is ongoing research for other systems that are more economical and easier to use. ~ Several publications describe the use of silanes as reducing agents for carbonyl substrates, together with a metallic catalyst. A preferred silane for this type of reductions is polymethylhydrosiloxane or P? HS, according to the general formula Does US Pat. 3,061 ^ 424 to Nitzsche and ick describe the reduction of aldehydes and ketones with PMHS and a salt of mercury, iron, copper, titanium, nickel, zironium, aluminum, zinc, lead, cadmium and, as the mode preferred, tin. This reducing system requires the activation by a source of protons, without. which the reaction does not proceed. However, the system is not effective for the reduction of esters and lactones. ^ US Patent 5,220,020 to Buch ald et al. describes a method for the preparation of alcohols by reducing carbonyl compounds using a system composed of a silane reducing agent and a metal catalyst of the formula M (L) (L1) (L11) or MÍLÍ L1) (L11) (L111) (L1V) (LV), where M is a metal that • belongs to any * of groups 3, 4, 5 or 6 of the periodic table, a lanthanide or an actinide, while ( L1) to (L *) represent hydrogen, an alkyl group, an aryl group, a silyl group, a halogen atom, or a '-OR, -SR or -NRÍR1 group), R and R1 are hydrogen, an alkyl group or one aril. Among the preferred catalysts, the cited patent mentions isopropylate or titanium (IV) ethylate or tpclorotitanium (IV) isopropylate. Such a system is said to be appropriate for the reduction of esters, lactones, amides, or iates. More recently, Breedon and Law ence (Synlett., 1994, 833) and Reding and Buchwald YES > -β (J. Org. Chem., 1995, 60, 7884) have described a similar process, that is to say the use of non-activated titanoxides of titanium as catalysts for the reduction of esters by means of PMHS. three * mentioned references requires the use of large quantities, at least 25 mol% with respect to the substrate, of catalyst. Barr, Ber and Buchwald (J. Org. Chem., 1994, 59, 4323) have shown that the Cp2TiCl2 complex, when reduced by means of butyl lithium or ethyl magnesium bromide, could catalyze the reduction of esters in alcohols. corresponding with good ^^ * = £ -comes, but this technique requires reagents that probe and difficult to use on a large scale, as is the case of industrial organic synthesis. As the closest prior art, one should cite the international application WO 96/12694 of the Applicant, which describes the reduction of aldehydes, ketones, esters and lactones by a reducing system composed of silanes and a metal hydride, which leads to the corresponding alcohols with good yields This system requires only a very small amount of catalyst, p. ex. the metal hydride, in the order of 1 mol% with respect to the substrate. The hydride is formed by the reaction of a salt of the respective metal with an appropriate reducing agent, preferably NaBH 4. Zinc salts, cobalt, manganese and iron salts are also used as precursors for the generation of metal hydrides. According to another preferred embodiment, PMHS was used as a silane reducing agent.

Description of the Invention TSe has now successfully developed a process for * "the reduction of carbonyl compounds with silanes, catalyzed by metal derivatives which are not hiarides and which, consequently, do not require the use of a reducing agent as , for example, NaBH4. "The objective of the invention is a process for the preparation of alcohols by reducing the carbonyl function in substrates belonging to the class of aldehydes, ketones, esters or lactones, these substrates could contain unsaturated functions different from the carbonyl group, where a) the carbonyl substrate reacts with an effective amount of a silane, preferably PMHS, in the presence of catalytic amounts of an active zinc compound that is monomeric and not a hydride, - "* # form a siloxane, b) the siloxane thus obtained is hydrolyzed with a basic agent to form an alcohol, and c) the resulting alcohol is separated and purified, if necessary. Another object of the invention is a reducing system comprising a) a silane, preferably PMHS, and b) an active zinc compound that is monomeric and is not a hydride. The present invention is based on the surprising fact that the use of a monomeric zinc species considerably increases the reactivity of a reducing system for carbonyl compounds, which contain a silane and a zinc compound. Thus, the reducing system containing a zinc salt and a silane, as described in J.a US Pat. No. 3,061,424 of Nitzsche and Wick that have been cited before, is faith less reactive than the system according to the present application. In particular, the system as described in the prior art is not capable of reducing esters and lactones, in contrast to the reducing system of the present invention. On the other hand, although the document cited earlier WO 96/12694 of Applicant shows that it is possible to increase the reactivity of a silane for the reduction of "carbonyl substrates by the addition of zinc salts or complexes, the latter requires the activation of a reducing agent." As a reducing agent, compounds such as NaBH4 , LiAlH4, lithium or aluminum alkyls or Grignard compounds were used to generate a highly reactive species, ie a hydride The present invention, however, uses zinc compounds such as salts or complexes that do not require activation by means of a reducing agent and which, when employed in stoichiometric quantities and together with * a silane, catalyzes the reduction of all species of carbonyl compounds. "The chemistry of zinc is generally characterized by the tendency of the metal to reach a number of coordination greater than 2 which_ is a consequence of its valence state +2. Zinc may reach the highest coordination number if it is to be obtained by oligo-or polymerization, after which a "tetra- or hexacoordination" is generally observed, for these reasons zinc salts or complexes are in most cases oligo- or polymeric, and as examples, zinc carboxylates and halides are mentioned herein, however, an electronically unsaturated class of compounds are the dialkyl- and diaryl zinc compounds.They are not capable of achieving a higher coordination number of 2 by oligo- or polymerization because the alkyl and aryl groups can not act as bridge-forming ligands.The dialkyl- and diaryl zinc compounds are therefore ionionic, and show a linear structure. "It has been established that all compounds The above-mentioned species show no activity or very low activity when used for carbonyl reduction, however, these polynuclear species, as well as such as dialkyl or diaryl zinc compounds, when treated with an appropriate complexing agent that is capable of generating a monomeric active species, become highly effective catalysts for the reduction of aldehydes, ketones, esters and lactones by a silane. According to the invention, an oligo- or polymeric precursor compound or a dialkyl- or diaryl zinc compound can be used, which is converted into a salt or active complex by treatment with an appropriate complexing agent. that complexes or monomeric salts may also be shown which "" become active in the process of the invention, but whose activity has completely passed without being noted until now. "As the parent compound, practically any known zinc compound may be used in accordance to the general formula ZnX2, in this formula, X is placed for any anion. The preferred X anions are defined below. The active catalyst of the invention can be described by the general formula ZnX2Ln. The catalyst can be obtained in situ, in the reaction medium, or can be prepared separately from a zinc compound such as /, for example, a salt or a complex complex of general formula Znx2, mentioned above. ZnX2 formula of the precursor compound and ZnX2Ln of the active catalyst, X is preferably any anion selected from the group consisting of carb xylates, β-diketonates, enolates, amides, silylamides, halides, carbonates and cyanides, and organic groups such as alkyl groups, cycloalkyl, alkoxy, aryl, aryloxy, alkoxyalkyl, alkoxyaryl, aralkoxy, aralkyl and alkylaryl, among which a zinc carboxylate of formula Zn (RC02) 2 such as, for example, acetate, propionate, butyrate, isobutyrate, ispvalerate, diethylacetate, benzoate, 2-ethylhexanoate, stearate or naphthenate; a zinc alkoxide of the formula Zn (OR) 2, wherein R is a group "C ± - to C20 alkyl, preferably from C1 to C5 such as, for example, methoxide, ethoxide, isopropoxide, * - 10-tert-butoxide , ter-pentoxide or 8-hydroxyquinoline, a zinc ß-diketonate such as, for example, acetllacetonate, substituted or unsubstituted, or tropolonate, a compound of the type alkyl zinc, aryl zinc, alkyl (alkoxy) zinc or aryl (alkoxy) ) zinc comprising from 1 to 20 carbon atoms, preferably from 1 * to 5 carbon atoms or a derivative thereof such as, for example, dimethyl zinc, diethyl zinc, dipfophenyl zinc, dibutyl zinc, diphenyl zinc, methyl (methoxy) zinc or methyl (phenoxy) zinc, or a derivative r * of the iodide halide (alkyl) zinc., - In the formula ZnX2Ln, n is an integer from 1 to 6. The ligands L may be identical or different and they are selected from the group consisting of amines, polyamines, imines, polyimines, aminoalcohols, amine oxides, phosphoramides and amides. r an aliphatic, alicyclic or aromatic primary, secondary or tertiary amine comprising from 2 to 30 carbon atoms. Non-limiting examples include aniline, triethylamine, "" * "** t ribut i lamina, N, N-dime t i lani 1 ina, morpholine, piperidine, pyridine, picolines, lutidines, 4-tert-butylpyridine, dimethylaminopyridine, quinoline and N-methylmorpholine. The polyamines could comprise from 2 to 6 primary, secondary or tertiary amine groups, and from 2 to 30 carbon atoms such as, for example, ethylenediamine, 1,2- and 1,3-propylenediamine, 1,2-, 1 , 3- and 1,4-butanediamine, hexamethylenediamine, N, N-di-methyl-ethylenediamine, diethylene triamine, di-p-trientriamine, triethylene tetra, tetramethylethylenediamine, N, N-dimethylpropylendiami, N, N, N '-trimethyl ethylenediamine, N, N, N ', N' -tetramethyl-1,3-propanediamine, hexamethylenetetramine, diazabicyclononane, sparteine, ortho-enantroline, 2,2'-bipyridine and neocuproin. The aminoalcohols could comprise one or more functions of primary, secondary or tertiary amine together with one or more primary, secondary or tertiary alcohol functions as in, for example, etholamine, diethanolamine, triethanolamine, dimethylaminoethanol, diethylaminoethanol, dim ilaminomethanol, diethylaminomethanol, 2-aminobutanol, ephedrine, prolinol, valinol, cinchonidine, quinine and quinidine. "As ligands belonging to the family of imines or diimines and capable of activating the derivatives or compounds zinc in the context of the present invention, there may be mentioned, as non-limiting examples, the families of the compound according to the formulas [I] to [V] below, in which the groups R1 to R6 each represents a hydrogen atom or an alkyl group, cycloalkyl, alkoxy, aryl, aryloxy, alkoxyalkyl, alkoxyaryl, aralkoxy, aralkyl, alkylaryl or aralkyl comprising from 1 to 20 carbon atoms. ; [l] [II] [IV] M "Other ligands capable of activating zinc compounds and derivatives include still amides such as, for example, dimethylformamide, dimethylacetamide or N-methylpyrrolidone, phosphoramides such as, for example, hexamethylphosphoramide, phosphine oxides, such as, for example, Rhodium phosphine oxide, tributyl or trioctylphosphine oxide, amine oxides such as, for example, pyridine N-oxide, 4-picoline N-oxide, N-methyl-morpholine N-oxide, and sulfoxides as , for example, dimethyl- or diphenylsulfoxide. The invention also relates to mondimeric zinc complexes that become active in the process of the invention A preferred class of compounds are the monomeric zinc carboxylates. described in the chemical literature, with the exception of the compound Zn (02CCH3) 2 (pyridine) 2, see J. Am. Chem. Soc. 119, 7030, "(1997). To or preferred compounds between these complexes, mention is made here of [Zn (benzoate) 2 (Me 2 NCH 2 CH 2 OH) 2], [Zn (_-diethylacetate) 2 (2,2 * -bipyridyl)], [Zn (diethyl acetate) 2 (1 , 2-diaminopropane) 2] and [Zn (benzoate) 2 (TMEDA)] (TMEDA = tetramethyl-ethylenediamine). The preparation and characterization of these compounds is described below. ? A large number of silanes can be used in the A process according to the present invention. Such silanes are known to one skilled in the art, and will be screened according to their ability to effectively reduce carbonyl substrates in the process according to the present invention. As non-limiting examples, mention may be made of trialkylsilanes, dialkylsilanes or trialkoxysilanes. More specific examples include dimethylsilane, diethylsilane, trimethoxysilane and triethoxysilane. PMHS will preferably be used due to its effectiveness, availability and price. The process according to the present invention is outlined in the following reaction schemes, which apply to the particular and preferred case of using PMHS as a reducing agent. _ Reduction of aldehydes (Rx = alkyl, aryl, R2 = H) and ketones (Rlf R2 = alkyl, aryl) Reduction of esters and lactones (Rx, R2 - alkyl, aryl) -s * The concentration of the catalyst ZnX2Ln, is given in% mol with respect to the substrate, in general is from 0.1 to 10%, "preferably from 1 to 5% Typically 2 mol equivalents of PMHS will be consumed per ester or lactone function, and one equivalent for the reduction of aldehydes and ketones For practical reasons, a slight excess of PMHS will preferably be used with respect to the stoichiometric amounts, generally of the order of 10 to 40% excess, based on the stoichiometric amount. According to the invention, it is also carried out when the silane is used in sub-stoichiometric amounts, but this results in a decrease in the conversion, therefore, according to the invention the term "effective amount" means an amount of sufficient silane to induce the reduction of the substrate. - The alcohol obtained as a product of the reaction can be obtained by hydrolysis of the polysilylether formed. to be performed by adding to the reaction mixture an aqueous or alcoholic solution of a basic agent such as, for example, sodium or potassium hydroxide, lime or sodium or potassium carbonate. The ratio of the base to the PMHS used will be approximately 1 to 2 mole equivalents. After completion of the hydrolysis, the formation of two phases will generally be observed. The desired alcohol is in the organic phase and can be obtained by evaporation of the solvent that could be present. The residue obtained could be distilled for further purification. The reduction can be carried out without a solvent or in a solvent such as, for example, an ether (eg methylter-butyl ether, diisopropyl ether, dibutyl ether, ter-amyl ethyl ether, tetrahydrofuran or dioxane), an aliphatic hydrocarbon (eg heptane, petroleum ether, octane or cyclohexane) or an aromatic hydrocarbon (eg benzene, toluene, xylene or mesitylene), or mixture thereof. *. * As stated above, the reduction according to the invention it is applicable for various carbonyl compounds which could contain unsaturated functionalities different from the carbonyl group such as, for example, olefin, acetylene, nitrile or nitro groups which will not be affected by the reduction reaction.

As non-limiting examples of aldehyde substrates, butanal, pentanal, heptanal, octanal, decanal, dodecanal, linear or branched may be cited. Other aldehydes which are unsaturated and which can be selectively reduced in the corresponding saturated alcohols include acrolein, methacrolein, prenl, citral, retinal, canfolene aldehyde, cinnamic aldehyde, hexyl cinnamic aldehyde, formylpinan and prickly pear. Aromatic aldehydes such as, for example, benzaldehyde, cuminic aldehyde, vanillin, salicylaldehyde or heliotropine are also easily reduced to the corresponding alcohols. JCo or non-limiting examples of saturated and unsaturated ketones which can be reduced in the corresponding alcohols by means of silanes according to the invention, may be cited -hexan-2-one, octan-2-one, nonan-4-one, dodecan- 2-one, methyl vinyl ketone, mesityl oxide, acetophenone, cyclopentanone, cyclododecanone, cyclohexen-l-en-3-one, isofone, oxophorone, carvone, canfo r, beta-yonone, geranylacetone and 2 -pent'ylcyclopenten-2 -one As non-limiting examples of saturated and unsaturated esters or lactones which can be reduced in the corresponding alcohols by means of silanes according to the invention, there may be mentioned acetates, propionates, butyrates, isobutyrates, benzoates, ^ = - ^ acrylates and crotonates, cinnamates, cis-3-hexenoates, sorbates, salicylates, 10-undecylenates, oleates, and * linoates, any ester of natural fatty acids * - and mixtures thereof All esters cited before Is can be, for example, alkyl or aryl esters, preferably methyl esters Other non-limiting examples include lactones, such as e-caprslactone, decalactone, dodecalactone, diketene and sclareolide.

A remarkable property of the catalysts according to the invention is that they allow the reduction of natural triglycerides of fatty acids, such as those that form vegetable and animal oils. In the course of the reaction of a mixed triglyceride derivative of various fatty acids, saturated and unsaturated natural alcohols can be obtained simultaneously without any modification of the position or the stereochemistry of the olefinic double bonds. This is of particular value for olefinic bonds that show a cis configuration.

«-In Scheme (3) above, the substituents Rlf R2 and R3 are hydrocarbon groups which may be identical or different and which may contain from 1 to 20 carbon atoms. In the case where these groups contain one or more olefinic groups of a defined stereochemistry (which, in general, will be cis), the corresponding alcohol obtained after the reduction according to the invention will have the same stereochemistry. Thus, oils rich in linoleic and / or linolenic acid, such as linseed oil, will be transformed into mixtures rich in linoleic and / or linolenic alcohol. The conventional hydrogenation of these vegetable oils is generally carried out at high pressures and temperatures, in contrast to the present invention. In addition, because the methyl esters of the respective acids obtained by transestepfication of the oils with methanol are used in these conventional hydrogenations, in most cases a modification of the stereochemistry of the fatty esters precursors is observed in the course of the reaction of transesterification and of idorogenation. Among the triglycerides which can be reduced by the process according to the invention, there may be cited, as examples, non-limiting examples, tpolema, peanut oil, soybean oil, olive oil, rapeseed oil, sesame oil, seed oil grape, linseed oil, cocoa butter, palm oil, palm kernel oil, cottonseed oil, copra oil, coconut oil, and pork, cow, mutton and chicken fat. Other oils and fats which are found in nature and which are not triglycerides, but esters of unsaturated fatty acids and monovalent unsaturated alcohols, such as jojoba oil and sperm oil, can also be reduced according to the present invention, without any modification of the position of the stereochemistry of the double bonds present in the ester molecule. I_The reaction temperature may vary within a wide range of values, and will generally be in the range of -50 ° C to 250 ° C. The chosen temperature will depend on the reactivity of the substrate and can therefore be adjusted without difficulty. More generally, the reaction will be carried out at a temperature within the range of 50 to 110 ° C. The invention will now be illustrated in greater detail in the following examples, in which temperatures are indicated in degrees centigrade, yields in % mol, the chemical change d of the NMR result in ppm, with respect to tetramethyl-silane as internal reference, and the abbreviations have the usual meaning in the art.

MODES OF CARRYING OUT THE INVENTION * EXAMPLE 1 Synthesis of the complex [Zn (benzoate) -, (Me2NCH-, GH? OH?) 1: The compound was prepared as described below and is illustrated in the scheme (4) . To a suspension of 3.06 g (10 mmol) of zinc benzoate in 50 ml of dichloromethane was added 1.8 g (20 mmol) of dimethylaminoethane.1. An exothermic reaction was observed, followed by the complete solution of zinc benzoate. After 1 h of stirring at 20 ° C, the solvent was evaporated, and the solid residue obtained was crystallized from a minimum amount of dichloromethane. 3.9 g (80%) of the desired complex were obtained as white solid crystals, the structure of which could be obtained by analysis of X-ray structure from a single crystal.

NMR (* H): dH: 2.4 (12H, s); ~ 2.65 (2H, t, CH2-N); 3.85 - (2H, t, CH2-0); 7.35-7.5 (m, 6H, arom.); 8.1-8.2 (d, ~~ 4H, arom.); NMR (13C): 46.37 (q, CH,); 57.34 (t, CH2-N); 61.02 (t, ^ CH2-0); 127.88 (d); 129.9 (d); 131.19 (d); 135.36 (s); 174.36 (s, C02-) Example 2 Synthesis of the complex [Zn (diethylacetate) - (2, 2'-bjpyridyl) 1. This compound was prepared as described below, according to the scheme (5) [Zn (diethylacetate) 2] n (5) 3 g (10 mmol) of zinc diethylacetate were dissolved in 50 ml of diisopropyl ether. Then 10 mmol of the 2,2'-bipyridyl ligand were added, and then the mixture was stirred at 20 ° C. A precipitate formed rapidly, which was isolated by filtration and recrystallized with cyclohexane. The yield was 80%.

P.f. : 135 ° C. Analysis: C22H30N204Zn; calculated: C, 58.48; H, 6.69; N, 6.20; found: C, 58.6; H, 6.6; N, 6.15 NMR (* H): dH: 0.85 (12H, t, CH3); 1.45 (4H, m, CH2-); _1.60 (4H, m, CH2-); 2.21 (2H, m, CH =); 7.6 (m, 2H, arom.); 8.05 (m, 2H, arom.); 8.21 (m, 2H, arom.); - 9.03 (m, 2H, arom.) NMR_ (13C): 12.13 (q, CH3); 25.75 (t, CH2-); 50.01 (d, .. CH =); 121.02-149.91 (d, d, d, d, s, arom.); 185.47 (s, fcco2-).

Example 3 Synthesis of 1 complex or FZn (benzoate) (tetramethylethylenediamine) 1; This compound was prepared as described below and is fragranced in the scheme (6) [Zn (benzoate) 2] n - The reaction was carried out as described in example 1, using 1 equivalent of tetramethylethylene diamine instead of the 2 equivalents of dimethylaminoethanol. Performance: 85%.

NMR (* H): dH: 2.62 (12H, s, CH3N); 2.77 (4H, s, CH2-N); ^ 7.3-7.5 (m, 6H, arom.); 8.1 (d, 4H, arom.); NMR (13C): 46.57 (q, CH3N); 56.60 (t, CH2-N); 127-131 (d, d, d); 133.8 (s); 175 (s, C02-).

Example 4 Synthesis of comple j or rZn (diethylacetate), (1, 2-diaminopropane) -,] 2 This compound was prepared as described below, according to the scheme (7) [Zn (diethylacetate):] n + 2 The reaction was carried out as described in example 2, using 2 equivalents of 1,2-diam-nopropane instead of 1 equivalent of 2,2'-bipyridyl. Performance = 75%. I P.f. : 148 ° C. Analysis: ClsH42N404Zn; calculated:, 48.70; H, 9.54; N, 12.62; found: C, 48.6; H, 9.6; N, 12.5 NMR JXH): dH: 0.88 (12H, t, CH3); 1.13 (6H, d, CH3); 1.48 - (8H, m, CH2-); 2.0 (2H, n, CH =); 2.4 * (m, 2H); 2.8- 3.5 (m, 12H, NH2); 8.21 (m, 2H, arom.); 9.03 (m, ** 2H, arom. ) NMR ~ (13C): 12.57 (q, CH3); 21.44 (q, CH3); 26.05 (t, H2); 45.73 (t, CH2); 46.61 (d, CH =); 52.27 (d, CH =); 77.29 (d, CH =); 183.30 (s, C02-).

Reduction Reactions Example 5"In a 250 ml three-necked flask were charged 30 g of isopropyl ether and 27.2 g of methyl benzoate. (0.2 mol), followed by 4 mmol of the crystalline complex prepared according to example 2, e.g.

[Zn (diethylacetate) 2 (2, 2'-bipyridyl)]. The mixture was heated to 70 ° C (reflux) before adding 30 g of PMHS (0.44 mol) for 15 minutes. The mixture was stirred for an additional hour at reflux until the complete disappearance of the substrate (monitored by GC analysis).

The mixture was then cooled to 20 ° C before adding 66 g of a 45% aqueous solution of KOH (0.52 mol) with rapid stirring, followed by further stirring for 1 h. Then 100 g of water were added, and the mixture was decanted. The aqueous phase containing the potassium polymethylsiliconate was decanted, then the organic phase was washed with 50 ml of water. The solvent was removed by distillation to obtain 21 g of crude product. Distillation of the residue gave 20.5 g of benzyl alcohol in a purity greater than 98% (yield = 95%).

Example 6 (comparative) The reaction was carried out as in Example 5, with the exception that 1.12 g (4 mmol) of polymeric zinc diethylacetate were used as a catalyst. After 4_ h, no reaction of the methyl benzoate employed could be observed, which indicated that the presence of an appropriate ligand is essential for the depolymerization reaction and, therefore, the activation of the zinc dietary diettate for reduction of the ester.

Emplos 7 to 23 These examples, summarized in Table 1, illustrate the considerable influence that the addition of bidentate ligands has on the catalytic activity of zinc carboxylates in the reduction of methyl benzoate to benzyl alcohol by PMHS. The conditions of the reaction, resemble those of Example 5, are given at the end of. the board. This table also gives the position of the infrared bands v (C02) as and v (C02) s of the carbpxylate groups of the isolated complexes, which make it possible to identify the polymerization of the precursor zinc carboxylate before achieving its catalytic activity.

Table 1 Reduction of benzene from methyl to benzyl alcohol. Influence of the nature of the bidentate ligand.

[Zn (dietyl-1605 95 cetate) 2] n Me-N N-Me 1400 H H [Zn (d? Ethyla-1603 96 cetato) 2] n Ph Ph 1384 and NH HN- [Zn (diethylam- 1564 97 cetate) 2] n Me-N N-Me 1422 Me Me [Zn (2-Et 98 hexanoate) 2], Me-N N-Me Me Me [Zn (diethyl-1600 98 cetato) 2] n 1401 Reaction conditions: Methyl benzoate = 20 mmol, PMHS = 44 mmol, Zn (carboxylate) 2 = 0.4 mmol, Ligand = 0.4_mmol (if not stated otherwise), Solvent = diisopropyl ether (2 ml), 70 ° C , 4h, Et = ethyl.

And emplos 24 to 30"These examples, summarized in Table 2, illustrate the considerable influence of the addition of monomerized ligands on the catalytic activity of zinc carboxylates in the reduction of methyl benzoate by PMHS. The reactions are carried out as described in beforehand, using methyl benzoate as a substrate and 2% mol of zinc diethylacetate together with 4 mol% of the monodentate ligand.

Table 2 Reduction of methyl benzoate by PMHS in the presence of zinc ~ carboxylates complexed by monodentate ligands Reaction conditions: Methyl benzoate = 20 mmol, PMHS "= 44 mmol, Zn (carboxylate) 2 = 0.4 mmol, Ligand = 0.8 mmol, Solvent = diisopropyl ether (2 ml), 70 ° C, 4h, Et = ethyl.

Examples 31 to 36 These examples show that the favorable influence of the addition of the ligands specified above also exists with respect to the catalytic activity of zinc ß-diketonates, such as acet flacetonate, for the reduction of esters using PMHS. It is known that zinc acetylacetonate has a trimeric structure that becomes monomeric and octahedral when it is reacted with bidentate ligands, such as 2, 2'-bipyridine.

Table 3 below shows that zinc acetylacetonate alone has low activity in the reduction of esters by PMHS.

The addition of 1 equivalent of a primary or secondary diamine to zinc acetylacetonate makes it possible to obtain zinc complexes capable of catalyzing the complete conversion of methyl benzoate to the corresponding alcohol. ~~ Table 3 Reduction of methyl benzoate by PMHS in the presence of zinc acetylacetonate complexed by several ligands Reaction conditions: Methyl benzoate = 20 mmol, PMHS "= 44 mmol, [Zn (acac):] L = 0.4 mmol, Ligand = 0.4 mmol, acac = acetylacetonate Solvent = diisopropyl ether (2 ml), 70 ° C, 4 h, Ph = phenyl.

Examples 37 to 42 and In these examples, it will be shown that the favorable influence of the addition of the ligands specified above also exists with respect to the catalytic activity of dialkyl zinc compounds, such as diethyl zinc, for the reduction of esters using PMHS (Table 4) . The dialkyl zinc compounds have a monomeric linear structure with an angle of C-Zn-C being 180 ° and are non-reactive under the conditions of the invention. In the presence of a bidentate ligand L, such as a tertiary diamine, they form a monomeric complex of tetrahedral structure ZnR- > L [see O'Brien et al., J. Organo et. Chem., 1993, 449, 1 et 1993, 461, 5].

Table 4 Reduction of methyl benzoate by PMHS in the presence of diethyl zinc formed in complex by several 1 people Example Compound Ligand Rendimient precursor 2 mol% or PhCH2OH zinc% mol 2 mol% 37 ZnEt Reaction conditions: Methyl benzoate = 20 mmol, PMHS_ = 44 mmol, ZnEt2 = 0.4 mmol, Ligand = 0.4 mmol (0.8 ramol in Example 42) Solvent = diisopropyl ether (2 ml), 70 ° C, 4 h, Ph = phenyl, Et = ethyl.

Examples 43 to 47 In these examples, it will be shown that the favorable influence of the addition of the ligands specified above also exists with respect to the catalytic activity of zinc alkoxides for the reduction of esters using PMHS. Table 5 shows that the zinc ter-pentoxylate, formed in situ by the addition of 2 equivalents of potassium ter-pentoxide (in toluene solution) for one equivalent of anhydrous zinc chloride, does not show pronounced activity for the reduction of methyl benzoate by PMHS, while the addition of primary, secondary and tertiary diamines results in highly active catalysts.

Table 5 Reduction of methyl benzoate by PMHS in the presence of zinc alkoxides complexed by several ligands Reaction conditions: Methyl benzoate = 20 mmol, PMHS = 4 4 mmol, Zn (OC5Hn) 2 = 0.4 mmol, Ligand = 0.4 mmol, Solvent = diisopropyl ether (2 ml), 70 ° C, 4 h, Ph = phenyl.

Examples 48 to 52 . The reactions were carried out as described in Example 5, in diisipropyl ether under reflux, and using a mixture containing 2% mmol of zinc diethylacetate and 2% mmol of dimethylaminoethanol, each with respect to the substrate. 20 mmol of the respective ester was used which was reduced with 44 mmol of PMHS. The hydrolysis was carried out when the substrate had disappeared, using 60 mmol KOH (in the form of an aqueous 45% KOH solution). After decanting and evaporating the solvent, the alcohol formed was distilled. In all cases, the stereochemistry of the initial compound was not affected, as shown by the results presented in Table 6.

Table 6 Reduction of different esters by PMHS in the presence of zinc diethylacetate complexed by dimethylaminoethanol Reaction conditions: Ester = 20 mmol, PMHS = 44 mmol, Zn (diethylacetate) 2 = 0.4 mmol, Dimethylaminoethanol = 0_ ^ 4 mmol, Solvent = Di isopropyl ether (2 ml), 70 ° C, 4 h -L Examples' 53 to 59 The reactions were carried out as described in Example 5, in refluxing diisipropyl ether, and using a mixture containing 2% mmol of diethyl zinclacetate and 2% mmol of one of the ligands mentioned below in the Table 7, each one with respect to the substrate. As substrates, 20 mmol of the respective aldehyde or ketone was used, which was reduced with 22 mmol of PMHS. The hydrolysis was carried out after the substrate had completely disappeared, using 60 mmol KOH (in the form of a 45% aqueous KOH solution). After decanting and evaporating the solvent, the alcohol formed was distilled. The results of Table 7 show that, in all cases, the reduction of aldehydes and ketones proceeded with excellent yields, without any modification of the stereochemistry of the initial compound.

Table 7 Reduction of different aldehydes and ketones by PMHS in the presence of zinc diethylacetate complexed by several ligands Reaction conditions: Substrate = 20 mmol, PMHS = 22 mmol, Zn (diethylacetate) 2 = 0.4 mmol, Ligand = 0.4 mmol, Solvent = diisopropyl ether (2 ml), 70 ° C, 4 h.

- Examples 60 to 62 The reactions were carried out as indicated in example 5 and using ZnF2 as a catalyst. The results show that zinc halides are active in this type of reduction. ~~ Table 8 Reduction of methyl benzoate by PMHS in the presence of ZnF2 complexed by several ligands Reaction conditions: Methyl benzoate = 20 mmol, PMHS = 44 mmol, ZnX2 = 0.4 mmol, Ligand = 0.4 mmol, Solvent = diisopropyl ether (2 ml), 70 ° C, 4 h.

Ahem 63 Reduction of peanut oil A three 1-necked flask was charged with 200 ml of toluene, 11 g of zinc 2-ethexanoate (0.03 mol) and 5.34 g (0.06 mol) of di-ethylaminoethanol. Then 200 g of peanut oil was added and the mixture was heated to reflux (110 ° C). 200 g (0.5 mol) of PMHS were added during 1 h, and the mixture was refluxed for another 2 h. After this time, the GC analysis carried out on samples hydrolyzed by a "methanolic solution of 30% KOH showed that the amount of alcohol in the reaction mixture was constant.The mixture was then poured into 450 g of a methanolic solution of KOH and Afterwards, for a further 1 hour at 50 ° C., 300 g of water were added and the mixture was decanted, then the solvent was evaporated from the organic phase and the residue was distilled at 200-250 ° C./1 hPa to obtain 100 g of water. a mixture containing 14% l-hexadetanol, 55% alcohol -oleic and 17% linoleic alcohol. i5 Example 64 Reduction of ethyl sorbate A 1 1 three-necked flask equipped with a reflux condenser, internal thermometer, syringe pump and magnetic stirrer was charged with 13.3 g (4 mol% of the substrate) of Z (2-ethylhexanoate) 2.4 g (4% _ mol) of dimethylaminoethanol, 10 ml of toluene and heated to 80 ° C. Then 210.1 g (1.5 mol) of ethyl sorbate, 0.42 g of BHT (2,4-di-tert-but-il-p-i-cresol), toluene (ca 200 ml) were added and the solution was brought to reflux . 213 g (corresponding to 2.1 equivalents) of PMHS were then added over 90 min, and the reaction mixture was then heated to reflux for another 30 min. The mixture was poured into 630 g of an aqueous solution of 30% NaOH until complete hydrolysis, before decanting the organic phase and washing with water. The crude product was distilled in a Vigreux type column (10 hPa) to obtain 120.7 g (83.4%) of hexa-2,4-dien-1-ol.

Example 65 Reduction of jojoba oil A 250 ml three-neck flask equipped with a reflux condenser, internal thermometer, syringe pump and magnetic stirrer was charged with 50 g of jojoba oil, 0.2 g of Zn (2-ethyl-hexanoate) ) 2, (corresponding to approximately 4 mol% by ester function), 0.06 g of dimethylaminoethanol (approximately 4% _mol) and 50 ml of toluene. The mixture was heated to reflux and ^ 6.5 g (0.1 moles, approximately 2.2 equivalents) of PMHS were added for 45 min. The reflux was continued for another 30 min, and the reaction mixture was poured into 50 g of an aqueous solution of 30% strength NaOH. After completing the hydrolysis, the organic phase was decanted and washed with water. The crude product thus obtained was distilled in a flask flask apparatus at 250V1 hPa, to obtain 48.4 g (95%) of a product containing 6.4% of (Z) -9-octadecen-l-ol, 59.3% of (Z) -9-icosen-1-ol, 26.8% (Z) -9-docosen-1-ol and 3.9% (Z) -9-tetracosen-1-ol.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (52)

CLAIMS Having described the invention as above, the content of the following claims is claimed as property:

1. Process for the preparation of alcohols by reducing the carbonyl function in substrates belonging to the class of aldehydes, ketones, esters or lactones, these substrates could contain unsaturated functions other than the carbonyl group, characterized in that it comprises a) the reaction of the carbonyl substrate with an effective amount of a silane compound in the presence of catalytic amounts of an active zinc compound that is monomeric and is not a hydride, to form a siloxane, b) the hydrolysis of the siloxane obtained with an agent basic to form an alcohol, and c) the separation and purification, if necessary, of the alcohol thus obtained.

2. Process according to claim 1, characterized in that the silane is polymethylhydrosiloxane (PMHS).

~ 3. Process according to claim 1, characterized in that the zinc active compound is formed from an oligomeric or polymeric zinc precursor compound, or a dialkyl zinc or diaryl zinc compound, and a complexing agent.

4. Process according to claim 1 0 2, characterized in that the active compound is of general formula ZnX2Ln, wherein X is an anion selected from the group consisting of carboxylates, β-diketonates, enolates, amides, silylamides, alkyl, cycloalkyl, alkoxy, aryl, aryloxy, alkoxyalkyl, alkoxyaryl, aralkoxy, aralkoyl and alkylaryl having from 1 to 20 carbon atoms, halides, carbonates and cyanides, the ligand L is selected from the group consisting of amines, polyamines, amino acids, polyimines, aminoalcohols, amine oxides, phosphoramides and amides, and wherein the X anions and the L ligands may be identical or different and the ligand / zinc ratio, expressed by the integer n, is 1 to 6.

Process according to claim 4 characterized in that X is selected from the group consisting of acetate, propionate, butyrate, isobutyrate, isovalerianat or, diethyl acetate, benzoate, 2-ethexanoate, stearate, methoxide, ethoxide, isopropoxide, tert-butoxide, ter-pentoxide, 8-hydroxyquinoline or, naphthenate, substituted and unsubstituted acetylacetonate, tropolonate, a methyl group, an ethyl group, a propyl group, a butyl group and an aryl group.

6. Process according to claim 4, characterized in that the ligand L is selected from the group consisting of ethylenediamine, N, N'-dimethylethylenediamine, tetramethylethylenediamine, ethanolamine, diethanolamine, dimethylamide, dimethylformamide, dimethylacetamide. , hexamethylphosphatria ida, dimethylsulfoxide or 4-tert-but and Ipi ridine.

., - 7. Process according to claim 1, characterized in that the concentration of the zinc active compound, expressed in% mol with respect to the substrate, is from about 0.1 to about 10%. '

8. Process according to claim 7, characterized in that the concentration of the zinc active compound, expressed in% mol with respect to the substrate, is from about 1 to about 5%.

9. Process according to claim 1, characterized in that the carbonyl substrate is a ketone or aldehyde, linear or branched, aliphatic or cyclic, saturated or unsaturated selected from the group consisting of butanal, pentanal, hexanal, trans-hex-2-en -l-al, heptanal, octanal, decanal, dodecanal, acrolein, methacrolein, crotonaldehyde, prenal, citral, retinal, canfolinic aldehyde, cinnamic aldehyde, hexyl cinnamic aldehyde, formylpinan, prickly pear, benzaldehyde, cuminic aldehyde, vanillin, salicylic aldehyde, hexan- 2-one, octan-2-one, nonan-4-one, dodecan-2-one, methyl vinyl ketone, mesityl oxide, acetophenone, cyclopentanone, cyclohexanone, cyclododecanone, cyclohex-1-en- 3-one, isophorone, oxophorone, carvone, camphor, beta-yonone, geranylacetone, 3-met-il-cyclopenta-1,5-dione, 3,3-dimet-il-5- (2, 2, 3-trimethyl-cyclo) ? ent-3-en-l-yl) -pent-4-en-2-one and 2-pentyl-cyclopenten-2-one.

10. Process according to claim 1, characterized in that the carbonyl substrate is an ester or lactone selected from the group consisting of acetates, propionates, "butyrates, isobutyrates, benzoates, acrylates, crotonates, cinnamates, cis-3-hexenoates, sorbates, salicylates, alkyl and aryl 10-undecylenates, oleates and linoleates, fatty esters of natural or synthetic origin, caprolactone, butyrolactone, dodecalactone, diketene and sclareolide.

11. Process according to claim 1, characterized in that the substrate is an animal or vegetable fat.

12. Process according to claim 11, characterized in that the substrate is a triglyceride of a fatty acid of formula H2C-0-C (0) R 'I HC - O - C (OR) R2 I H2C - O - C (0) R3 wherein R1, R2 and R3 are hydrocarbon groups which are identical or different, linear or branched, saturated or unsaturated, and which may contain from 1 to 20 carbon atoms.

"~ 13. Process according to claim 12, characterized in that the triglyceride is a vegetable oil.

14. Process according to claim 13, characterized in that the vegetable oil is selected from the group consisting of triolein, peanut oil, sunflower oil, soybean oil, olive oil, rapeseed oil, sesame oil, seed oil grape, linseed oil, cocoa butter, cottonseed oil, copra oil, palm oil, palm kernel oil.

15. Process according to claim 11, characterized in that the animal fat is fat of pig, cow, sheep and chicken.

- Process according to claim 11, characterized in that the fat is selected from the group consisting of jojoba oil and whale sperm oil.

17. Process according to claim 1, characterized in that the hydrolysis of the siloxane obtained after the reduction is carried out by treating the reaction mixture with sodium or potassium hydroxide, lime or sodium carbonate.

18. Process according to claim 1, characterized in that the reduction reaction is carried out in an inert organic solvent selected from the group consisting of aliphatic and aromatic hydrocarbons.

. 19. Process according to claim 1, characterized in that the reduction reaction is carried out at a temperature from about -50 ° C to about 250 ° C, and preferably from about 50 ° to about 110 ° C.

20. A reducing system capable of mixing together to effect the reduction of carbonyl compounds to the corresponding alcohols, characterized in that it comprises a) a silane, and b) an active zinc compound that is monomeric and is not a hydride, wherein the components (a) and (b), when mixed together, allow the reduction of carbonyl compounds.

21. Reducing system according to claim 20, characterized in that the active zinc compound is formed by the reaction of i) an oligomeric or polymeric zinc precursor compound or a dialkyl zinc or diaryl zinc compound, and ii) a complexing agent .

22. Reducing system according to claim 20, characterized in that the silane agent is polymethylhydroxy siloxane (PMHS).

23. Reducing system according to claim 20, characterized in that the active compound is a compound of the general formula ZnX2Lr ?, wherein X is any anion selected from the group consisting of carboxylates, β-diketonates, enolates, amides, silylamides, alkyl groups , cycloalkyl, alkoxy, aryl, aryloxy, alkoxyalkyl, alkoxyaryl, aralkoxy, aralkoyl and alkylaryl having from 1 to 20 carbon atoms, halides, carbonates and cyanides, L is a ligand selected from the group consisting of amines, polyamines, imines, polyimines, aminoalcohols, amine oxides, phosphoramides and amides, and wherein the X anions and the L ligands can be identical or different and the "ligand / zinc ratio, expressed by the integer n, is from 1 to 6.

24. Reducing system according to claim 20, characterized in that X is selected from the group consisting of acetate, propionate, butyrate, isobutyrate, isovalerianate, diethylacetate, Benzoate, 2-ethylhexanoate, stearate, methoxide, ethoxide, isopropoxide, tert-butoxide, tert-pentoxide, 8-hydroxyquinolone, naphthenate, substituted and unsubstituted acetylacetonate, tropolonate, a methyl group, an ethyl group, a propyl group, an butyl group and an aryl group.

25. Reducing system according to claim 20, characterized in that the ligand L is selected from the group consisting of ethylenediamine, N, N-dimethylethylene diamine, tetramethylethylenediamine, 20 ethanolamine, diethanolamine, dimethylaminoet anol, dimethe formamide, dimethe lacetamide, hexamet i 1 fosfort riamide, dimethyl sulfoxide or 4-tert-butylpyridine.

26. Reducing system according to claim 20, characterized in that the concentration of the active zinc complex, expressed in% mol with respect to the substrate, is 0.1 to 10%.

27. Reducing system according to claim 20, characterized in that the silane is used in a stoichiometric amount essentially with respect to the carbonyl substrate.

; Reducing system according to claim 20, characterized in that the catalyst is used in a molar ratio of reducing agent to metal of 1 to 2.

29. Reducing system for the reduction of carbonyl compounds, characterized in that it consists essentially of the product of the reaction of: a) an effective amount of a silane to effect the reduction of a carbonyl substrate to the corresponding alcohol, and b) an effective amount of a catalyst for To catalyze the reduction, the catalyst is an active zinc compound that is monomeric and is not a hydride.

30. Reducing system according to claim 29, characterized in that the active zinc compound is formed by the reaction of: i) "an oligo- or polymeric zinc precursor compound, or a dialkyl zinc or diaryl zinc compound, ii) an agent complex trainer

31. Reducing system according to claim 29, characterized in that the silane agent is polyhydroxyhydroxy loxane (PMHS).

32. Reducing system according to claim 29, characterized in that the active compound is composed of the general formula ZnXL. , wherein X is any anion selected from the group consisting of carboxylates, β-di ketonates, enolates, amides, silylamides, alkyl, cycloalkyl, akoxy, anlo, aploxy, alkoxy, alkoxyaryl, aralkoxy, aralcoiic and aikaryl having from 1 to 20 carbon atoms, halides, carbonates and cyanides, L is a ligand chosen from the group consisting of amines, eg, ammonia, amine, polymerase, aminoa 1 coholes, oxides of amine,: is fora i cas and amides, and donates anions? and ios l: gdnjos L pueae be identical or different and the re "l a i 1. gande ~ p, expresaa for the whole n, is from 1 to 6

33. Reducing system according to claim 29, characterized in that X is selected from the group consisting of acetate, propionate, butyrate, isobutyrate, isovalerianate, diethylacetate, benzoate, 2-ethylhexanoate, stearate, methoxide, ethoxide, isopropoxide, tert-butoxide, ter pentaoxide, 8-hydroquinoline, naphthenate, substituted and unsubstituted acetylacetonate, tropolonate, a methyl group, an ethyl group, a propyl group, a butyl group and an aryl group.

3 . A reducing system according to claim 29, characterized in that the ligand L is selected from the group consisting of ethylenediamine, N, Nj-dimethylethylenediamine, tetramethylethylenediamine, ethanolamine, die anolamine, dimethylaminoet anol, dimethylamine, d imet The acetamide, hexameth, and 1-fluoride, dimethyl, and isulfide or 4-tert-butylpyridine.

35. Reducing system according to claim 29, characterized in that the concentration of the active zinc complex, expressed in% mol with respect to the substrate, is 0.1 to 10%.

36. Reducing system according to claim 29, characterized in that the silane is used in a stoichiometric amount essentially with respect to the carbonyl substrate.

- 37. Reducing system according to claim 29, characterized in that the catalyst is used in a molar ratio of reducing agent to metal of 1 to 2.

38. Catalyst capable of reacting together with a silane to effect the reduction of a carbon substrate to the corresponding alcohol, characterized in that it consists essentially of: a) an effective amount of a catalyst to catalyze the reduction, the catalyst is an active zinc compound that it is monomeric and is not a hydride, and b) the carbonyl substrate that is to be reduced.

. 39. Catalyst system according to claim 38, characterized in that the active zinc compound is formed by the reaction of: i) an oligo- or polymeric zinc precursor compound, or a dialkyl zinc or diaryl zinc compound, ii ) a complexing agent.

40. A reaction product produced by the catalytic reduction of a carbonyl substrate by a silane to an alcohol before recovering the alcohol, characterized in that it consists essentially of: a) a catalyst, the catalyst is an active zinc compound that is monomeric and not is a hydride, and b) the reaction product of a carbonyl substrate with a silane.

41. The reaction product according to claim 40, characterized in that the active zinc compound consists essentially of the reaction product of: i) an oligo- or polymeric zinc precursor compound, or a dialkyl zinc or diaryl zinc compound, i) a complexing agent.

42. Reaction product according to claim 41, characterized in that the silane is pol i et i Ihydrosi loxane (PMHS).

43 A catalyst system capable of reacting together to effect the reduction of a carbonyl substrate by a silane, characterized in that the catalyst consists essentially of a mixture of: i) an oligo- or polymeric zinc precursor compound, or a dialkyl zinc compound or diaryl zinc, and ii) a complexing agent.

44. A catalyst consisting essentially of a zinc compound which is monomeric and is not a hydride, characterized in that it is the product of the reaction of: i) an oligo- or polymeric zinc precursor compound, or a dialkyl zinc or diaryl zinc compound , and ii) a complexing agent.

45. Catalyst according to claim 44, characterized in that the precursor compound is a compound of general formula ZnXr, wherein X is any anion selected from the group consisting of ca boxylates, β-diketonates, enolates, amides, silylamides, alkyl groups, cycloalkyl, alkoxy, aryl, aryloxy, alkoxyalkyl, alkoxyaryl, aralkoxy, aralkyl and alkylaryl having from 1 to 20 carbon atoms, halides, carbonates and cyanides

46 The catalyst according to claim 44, characterized in that X is selected from the group consisting of acetate, propionate, butyrate, isobutyrate, isovalerianate, diethylacetate, benzoate, 2-ethylhexanoate, stearate, methoxide, ethoxide, isopropoxide, tert-butoxide , ter-pentoxide, 8-hydroxyquinoline, naphthenate, substituted and unsubstituted acetylacetonate, tropolonate, a methyl group, an ethyl group, a propyl group, a butyl group and an aryl group.

47. Catalyst according to claim 44, characterized in that the carpel-forming agent or accplLejapte is separated from the group that contains cer amines, polyamines, imines, polyimines, aminoalcohols, amine oxides, phosphoramides and amides.

48. Catalyst according to claim 44, characterized in that the complexing agent is selected from the group consisting of et-lendiamine, N, N'-dimethylethylenediamine, tetramethylethylenediamine, ethanolamine, diethanolamine, di meil am in oe tanol, di me tilfo rmam i da, dimet i lacetamide, hexamethylphosfortriidamide, dime i lsul f oxide or 4-tert-but i lpyridine.

49. Catalyst according to claim 44, characterized in that the catalyst is of general formula ZnX2Ln, wherein X is any anion as defined in claim 45, L is a complexing agent as defined in claim 47, and wherein X and L can be identical or different and the ligand / zinc ratio, expressed by the integer n, is from 1 to 6.

50. A monomeric carboxylate of zinc, with the proviso that the complex [Zn (O.CCH) - (pyridine) J is excluded.

51. Co or a carboxylate according to claim 50, a) [Zn (benzoate) (dimethylaminoethanol):] b) [Zn (benzoate) _ (tetrame i let i lendiamine)] c) [Zn (diethyllacetate) ( 1, 2-d? Am? Nopropane) 2] d) fZn (diet and lacetate) (2,2'-b? P? D? Lo)].

52. Process for the preparation of carboxylates according to claim 50, characterized in that it comprises the reaction of a suitable oligo- and co-polymeric precursor compound of zinc with a complexing or complexing agent.