SILICA-BASED ZINC CATALYSTS, THEIR PREPARATION AND USE IN THE ALKOXYCARBONYLATION OF AMINES

Abstract

The present invention relates to silica-based heterogeneous zinc compounds which are suitable as catalysts in the reaction of amines with dialkyl carbonates to produce carbamates. The catalysts have the formula [SiO.sub.2]CH.sub.2CHRXCOOZn[Y], wherein [SiO.sub.2] represents a silica carrier selected from the group consisting of ordered mesoporous silica and irregular amorphous narrow pore silica, R represents a moiety selected from the group consisting of hydrogen, CH.sub.3, and CH.sub.2CH.sub.3, preferably hydrogen, X is an aliphatic chain of 2 to 11 carbon atoms that optionally comprises ether moieties and [Y] represents a mono anion. The invention is also directed towards a method for the preparation of the aforementioned compounds and towards method for the alkoxycarbonylation of amines.

Claims

1. A silica-based zinc compound of the formula
[SiO.sub.2]CH.sub.2CHRXCOOZn[Y] wherein [SiO.sub.2] represents a silica carrier selected from the group consisting of ordered mesoporous silica and irregular amorphous narrow pore silica, said silica carrier [SiO2] being covalently bound to the terminal CH.sub.2 group of CH.sub.2CHRXCOOZn[Y]; R represents a moiety selected from the group consisting of hydrogen, CH.sub.3, and CH.sub.2CH.sub.3; X is an aliphatic chain of 2 to 11 carbon atoms that optionally comprises ether moieties; and [Y] represents a mono anion.

2. The silica-based zinc compound according to claim 1, wherein X is an aliphatic chain of 2 to 9 carbon atoms that optionally comprises ether moieties.

3. The silica-based zinc compound according to claim 2, wherein X is selected from the group consisting of (CH.sub.2).sub.2, (CH.sub.2).sub.9 and CH.sub.2O(CH.sub.2).sub.2.

4. The silica-based zinc compound according to claim 1, wherein said compound (a) has a structure A in which the mono anion [Y] comprises a carboxylate group, the carboxylate oxygen atoms coordinating to the zinc atom and the carboxylate carbon atom being covalently connected to the silica carrier [SiO.sub.2] via a chain of the same structure as CH.sub.2CHRX, or (b) has a structure B in which the mono anion [Y] is not covalently connected to the [SiO.sub.2] carrier, or (c) exists as a mixture of structures A and B.

5. The silica-based zinc compound according to claim 4, wherein the mono anion of structure B is selected from the group consisting of chloride, bromide, iodide, acetate, naphthenate, octanoate, propionate, salicylate, pivalate, acrylate, p-chlorobenzoate, phenolate, formate, chloroacetate, acetylacetonate, oxalate, and trifluoroacetate.

6. The silica-based zinc compound according to claim 5, wherein the mono anion of structure B is acetate.

7. The silica-based zinc compound according to claim 1, wherein the ordered mesoporous silica is selected from the group consisting of SBA-1, SBA-2, SBA-3, SBA-6, SBA-8, SBA-11, SBA-12, SBA-15, SBA-16, MCM-41, MCM-48, and FSM-16, and the irregular amorphous narrow pore silica is a silica gel with an average pore diameter in the range of 2.5 nm to 7.5 nm, and particle sizes in the range of 35-500 m.

8. A method for producing the silica-based zinc compound according to claim 1, comprising: A) reacting an unsaturated carboxylic acid of the formula CH.sub.2CRXCOOH, where R represents a moiety selected from the group consisting of hydrogen, CH.sub.3, and CH.sub.2CH.sub.3 and X is an aliphatic chain of 2 to 11 carbon atoms that optionally comprises ether moieties, with a trialkyloxy silane or triaryloxy silane or mixed alkyl-aryloxy trisubstituted silane in the presence of a catalyst to yield a silicon-containing addition product; B) impregnating a silica carrier selected from the group consisting of ordered mesoporous silica and irregular amorphous narrow pore silica with a solution of the silicon-containing addition product in a solvent to yield a silica-based carboxylic acid; and C) ion-exchanging the silica-based carboxylic acid with a zinc salt to yield the silica-based zinc compound.

9. The method according to claim 8, wherein the zinc salt is selected from the group consisting of zinc(II) chloride, bromide, iodide, acetate, naphthenate, octanoate, propionate, salicylate, pivalate, acrylate, p-chlorobenzoate, phenolate, formate, chloroacetate, acetylacetonate, oxalate, and trifluoroacetate.

10. A method of producing carbamate compounds, comprising reacting an organic amine with a dialkyl carbonate in the presence of a catalyst, wherein the catalyst is the silica-based zinc compound according to claim 1.

11. The method according to claim 10, wherein the dialkyl carbonate is selected from the group consisting of propyl carbonate, ethyl carbonate, and methyl carbonate.

12. The method according to claim 10, wherein the reaction of the organic amine with the dialkyl carbonate is carried out at a molar ratio of organic amine to Zn catalyst ranging from 10:1 to 20:1.

13. The method according to claim 10, wherein the reaction of the organic amine with the dialkyl carbonate is carried out at a temperature ranging from 150 C. to 200 C. for a reaction time ranging from 0.5 h to 6 h.

14. The method according to claim 10, wherein the organic amine is an aromatic amine selected from the group consisting of aniline, 2,4-diamino-N-phenylaniline, o-, m-, and p-phenylenediamine, 2,4-diaminotoluene, 2,6-diaminotoluene, 1,2,4,5-tetraaminobenzene, 4-methoxy-m-phenylenediamine, 4-amino-N-phenylaniline, 2-amino-N-methylaniline, N-isobutyl-p-phenyldiamine, o-, m-, and p-xylylenediamine, N-isoamyl-p-phenylenediamine, N-benzyl-p-phenylenediamine, N-cyclohexyl-p-diphenylenediamine, N,N-di(n-propyl)-p-phenylenediamine, N-(n-butyl)-N-benzyl-p-phenylenediamine, N,N-dibenzyl-p-phenylenediamine, N-ethyl-m-phenylenediamine, N-ethyl-o-phenylenediamine, N-methyl-m-phenylenediamine, N,N-diethyl-p-phenylenediamine, N-methyl-N-(n-propyl)-p-phenylenediamine, 4,4-oxydianiline, 4,4-ethylenedianiline, 2,4-bis(4-aminobenzyl)aniline, 4,4-methylenebis(N,N-dimethylaniline); 4,4-methylenebis(N-methylaniline); benzidine; N,N,N,N-tetramethylbenzidine, bis(3,4-diaminophenyl)methane, bis(3-methyl-4-aminophenyl)methane, 2,2-, 2,4- or 4,4-methylene dianiline, 1,6-hexamethylene diamine, isophorone diamine, (2-aminocylohexyl)-(4-aminocylohexyl)-methane, bis-(4-aminocyclohexyl)-methane and mixtures of the aforementioned organic amines.

15. The method according to claim 14, wherein the organic amine is selected from the group consisting of aniline, 2,4-diaminotoluene, 2,6-diaminotoluene, and mixtures thereof or wherein the organic amine is selected from the group consisting of 2,2-, 2,4-, 4,4-methylene dianiline, and mixtures thereof.

Description

EXAMPLES

[0105] A. Preparation of Silica-Based Zinc Compounds

Example A.1

[0106] Preparation of Irregular Amorphous Narrow Pore [SiO.sub.2](CH.sub.2).sub.3O(CH.sub.2).sub.2COOZn[Y]

[0107] Under an inert atmosphere, triethoxysilane (3.39 g, 97%, 20.0 mmol) was added dropwise to a mixture of 3-allyloxypropionic acid (2.74 g, 95%, 20.0 mmol), dry THF (3.0 mL) and PtO.sub.2 (4.6 mg, 0.02 mmol) at 0 C. The mixture was stirred at 0 C. for 6 h followed by another 10 h at RT. After the reaction was complete, the mixture was filtered through a PTFE syringe filter and the filtrate evaporated in vacuo to give the corresponding alkoxy silane carboxylic acid (5.83 g). A minor by-product, whose structure was determined to be the corresponding cyclic ester by .sup.1H-NMR analysis, was also observed (16%). This reaction mixture was used without any further purification.

[0108] .sup.1H NMR: 11.26 (s, 1H), 3.67 (q, 6H, J=7.0 Hz), 3.59-3.51 (m, 2H), 3.33-3.24 (m, 2H), 2.49-2.42 (m, 2H), 1.61-1.46 (m, 2H), 1.07 (t, 9H, J=7.0 Hz), 0.55-0.42 (m, 2H) ppm; .sup.13C{.sup.1H}NMR: 176.3, 73.1, 65.5, 58.2, 34.6, 22.6, 18.0, 6.2 ppm; .sup.29Si{.sup.1H} NMR: 49.4 ppm.

[0109] Then, 4.40 g of silica gel (irregular amorphous narrow pore, 40-63 m particle size, pore volume: 0.73 mL/g, 435 m.sup.2/g, average pore diameter 6.7 nm, Merck) previously dried (120 C. overnight) were impregnated with a solution of the previously obtained 3-(3-(triethoxysilyl)propoxy)propanoic acid (1.94 g, 84%, 5.57 mmol) and dry toluene (ca. 2 mL toluene; the overall volume of the final solution was 3.2 mL). The impregnation was carried out by slowly adding the alkoxy silane carboxylic acid solution over the silica support while stirring vigorously with a vortex stirrer (3000 rpm). Once the addition was complete, the material was left at RT for 3 h and then heated for 15 h at 120 C. in vacuo (10 mbar). The material was then sequentially washed with toluene, dichloromethane, hexane, and diethyl ether (20 mL each) and dried for 3 h at 120 C. in vacuo (10 mbar) to yield 5.68 g of a white powder.

[0110] The resulting carboxylic acid containing material was subjected to ion exchange employing aqueous zinc acetate solutions. To a portion of 2.0 g of the latter material, a zinc acetate solution (0.4 M; 40 mL; 20 mL/g) was added, the mixture was then heated with stirring at 65 C. for 1 h and the aqueous solution was filtered off and discarded. This process was repeated two more times with a zinc acetate solution, as that indicated above. The zinc-containing material was thoroughly washed with deionized water (850 mL), filtered and dried for 3 h at 120 C. in vacuo (10 mbar) to yield 1.8 g of a white powder corresponding to the [SiO.sub.2](CH.sub.2).sub.3O-(CH.sub.2).sub.2COOZn[Y]_material, whose zinc content was determined to be 0.78 mmol [Zn]/g, (complexometric titration with EDTA).

[0111] Characterization Data of [SiO.sub.2](CH.sub.2).sub.3O(CH.sub.2).sub.2COOZn[Y]

[0112] TGA (air, 30-550 C., 5 C./min): mass loss at 80 C. (2.62%) and 270 C. (9.14%); XRPD (2 range 5-70): no diffraction peaks observed; BET surface area analysis (N.sub.2 adsorption-desorption isotherm): 0.46 mL/g total pore volume, 290 m.sup.2/g specific surface area; complexometric titration: 0.78 mmol [Zn]/g; ion chromatography: 0.014 mmol ACO.sup. groups/g (<2% of ACO.sup. groups with respect to [Zn] present in the modified SiO.sub.2); .sup.13C CP-MAS NMR: 182.1, 73.1, 67.2, 37.0, 23.0, 8.6 ppm; .sup.29Si CP-MAS NMR: 51.2, 59.4, 68.3, 94.1, 104.0, 113.3 ppm; FT-IR (ATR, solid, v/cm.sup.1): 2945 (out-of-phase stretch CH.sub.2), 2882 (in-phase stretch CH.sub.2), 1568 (asym. stretch COO), 1445 (deformation CH.sub.2), 1420 (sym. stretch COO), 1054 (asym. stretch SiOSi); zinc content: 0.78 mmol [Zn]/g.

[0113] Repetitions of the reactions described above yielded products with the same spectroscopic and analytical data and with the following zinc contents:

[0114] Batch #2: 0.75 mmol [Zn]/g

[0115] Batch #3: 0.79 mmol [Zn]/g

[0116] Average value: 0.77 mmol [Zn]/g; standard deviation: 0.02 mmol [Zn]/g.

[0117] The analytical data (ion exchange) available for [SiO.sub.2](CH.sub.2).sub.3O(CH.sub.2).sub.2COOZn[Y] indicates predominantly (98 mass percent, based on the total mass of the silica-based zinc compound) a structure of type A, i.e. a structure in which the mono anion [Y] comprises a carboxylate group, the carboxylate oxygen atoms coordinating to the zinc atom and the carboxylate carbon atom being covalently connected to the silica carrier [SiO2] via a chain of the same structure as CH.sub.2CHRX. A minor amount (2 mass percent, based on the total mass of the silica-based zinc compound) exists in structure of type B, the mono anion [Y] being acetate (the counter ion of the zinc salt used in the ion exchange step). Thus, the catalyst [SiO.sub.2](CH.sub.2).sub.3O(CH.sub.2).sub.2COOZn[Y] when prepared as described above is of variant (c). The predominant structure of type A may be visualized as follows:

##STR00007##

[0118] Scheme 1: Possible structure of type A of [SiO.sub.2](CH.sub.2).sub.3O(CH.sub.2).sub.2COOZn[Y] catalyst. It should be noted that the extract of the structure of the silica carrier [SiO.sub.2] shown here is not to be understood as limiting. Deviations therefrom are possible.

[0119] The less dominant structure of type B may be visualized as follows:

##STR00008##

[0120] Scheme 2: Possible structure of type B of [SiO.sub.2](CH.sub.2).sub.3O(CH.sub.2).sub.2COOZn[Y] catalyst. It should be noted that the extract of the structure of the silica carrier [SiO.sub.2] shown here is not to be understood as limiting. Deviations therefrom are possible.

Example A.2

[0121] Preparation of Irregular Amorphous Narrow Pore [SiO.sub.1]-(CH.sub.2).sub.4COOZn[Y]

[0122] 5-(Triethoxysilyl)pentanoic acid was prepared following the same experimental protocol as that described above for Example 1, with the following amounts of reagents: triethoxysilane (4.32 g, 97%, 25.0 mmol), pent-4-enoic acid (2.50 g, 25.0 mmol), dry THF (3.0 mL) and PtO.sub.2 (5.7 mg, 0.025 mmol).

[0123] Along with the desired compound, the corresponding cyclic ester was also observed as a minor by-product (4%). The alkoxy silane carboxylic acid was obtained as an oil (6.44 g, 96%, 23.4 mmol, 94% yield) and used without any further purification.

[0124] .sup.1H NMR: 11.34 (s, 1H) , 3.72 (q, 6H, J=7.0 Hz), 2.29-2.20 (m, 2H), 1.64-1.52 (m, 2H), 1.45-1.32 (m, 2H), 1.12 (t, 9H, J=7.0 Hz), 0.61-0.49 (m, 2H) ppm; .sup.13C{.sup.1H} NMR: 179.5, 58.2, 33.6, 27.8, 22.2, 18.1, 10.0 ppm; .sup.29Si{.sup.1H} NMR: 45.4 ppm.

[0125] 5-(Triethoxysilyl)pentanoic acid was attached to SiO.sub.2 following the same experimental protocol as that described for Example 1, with the following amounts of reagents: Silica gel (4.09 g, irregular amorphous narrow pore, 40-63 m particle size, pore volume: 0.73 mL/g, 435 m.sup.2/g, average pore diameter 6.7 nm, Merck) previously dried (120 C. overnight), 5-(trimethoxysilyl)pentanoic acid (2.00 g, 96%, 7.25 mmol) and dry toluene (ca. 1.7 mL toluene; the overall volume of the final solution was 3.0 mL). The COOH-containing silica gel was obtained as a white powder (5.19 g).

[0126] The resulting carboxylic acid containing material was subjected to ion exchange following the same experimental protocol as that described for [SiO.sub.2](CH.sub.2).sub.3O(CH.sub.2).sub.2COOZn[Y], with the following amounts of reagents: COOH-containing silica gel (1.5 g) and aqueous zinc acetate (0.4 M; 30 mL; 20 mL/g). [SiO.sub.2](CH.sub.2).sub.4COOZn[Y] was obtained as a white powder (1.4 g).

[0127] Characterization Data for [SiO.sub.2](CH.sub.2).sub.4COOZn[Y]

[0128] TGA (air, 30-550 C., 5 C./min): mass loss at 80 C. (2.36%) and 460 C. (9.35%); XRPD (2 range 5-70): no diffraction peaks observed; BET surface area analysis (N.sub.2 adsorption-desorption isotherm): 0.43 mL/g total pore volume, 282 m.sup.2/g specific surface area; complexometry: 1.00 mmol [Zn]/g, ion chromatography: 0.016 mmol ACO.sup. groups/g (<2% of ACO.sup. groups with respect to [Zn] present in the modified SiO.sub.2); FT-IR (ATR, solid, v/cm.sup.1): 2936 (out-of-phase stretch CH.sub.2), 2877 (in-phase stretch CH.sub.2), 1557 (asym. stretch COO), 1454 (deformation CH.sub.2), 1423 (sym. stretch COO), 1052 (asym. stretch Si-O-Si); zinc content: 1.00 mmol [Zn]/g.

Example A.3

[0129] Preparation of Ordered Mesoporous [SiO.sub.2](CH.sub.2).sub.4COOZn[Y]

[0130] Previously obtained 5-(triethoxysilyl)pentanoic acid was attached to ordered mesoporous silica SBA15 following the same experimental protocol as that described for Example 1, with the following amounts of reagents: SBA15 silica gel (2.10 g, mesostructured [average pore diameter 5.8 nm,], pore volume: 0.94 mL/g, 656 m.sup.2/g, Aldrich) previously dried (120 C. overnight), 5-(trimethoxysilyl)pentanoic acid (1.26 g, 96%, 4.57 mmol) and dry toluene (ca. 1.0 mL toluene; the overall volume of the final solution was 1.9 mL). The COOH-containing silica gel was obtained as a white powder (2.65 g).

[0131] The resulting carboxylic acid containing material was subjected to ion exchange following the same experimental protocol as that described for [SiO.sub.2](CH.sub.2).sub.3O(CH.sub.2).sub.2COOZn[Y], with the following amounts of reagents: COOH-containing silica gel (1.5 g) and aqueous zinc acetate (0.4 M; 30 mL; 20 mL/g). Ordered mesoporous [SiO.sub.2](CH.sub.2).sub.4COOZn[Y] was obtained as a white powder (1.4 g).

[0132] Characterization Data for Ordered Mesoporous [SiO.sub.2](CH.sub.2).sub.4COOZn[Y]

[0133] TGA (air, 30-550 C., 5 C./min): mass loss at 80 C. (2.67%) and 460 C. (10.32%); XRPD (2 range 5-70): no diffraction peaks observed; BET surface area analysis (N.sub.2 adsorption-desorption isotherm): 0.56 mL/g total pore volume, 350 m.sup.2/g specific surface area; complexometric titration: 1.25 mmol [Zn]/g, ion chromatography: 0.015 mmol ACO.sup. groups/g (<2% of ACO.sup. groups with respect to [Zn] present in the modified SiO.sub.2); FT-IR (ATR, solid, v/cm.sup.1): 2935 (out-of-phase stretch CH.sub.2), 2868 (in-phase stretch CH.sub.2), 1557 (asym. stretch COO), 1457 (deformation CH.sub.2), 1423 (sym. stretch COO), 1056 (asym. stretch SiOSi); zinc content: 1.25 mmol [Zn]/g.

Example A.4

[0134] Preparation of Irregular Amorphous Narrow Pore [SiO.sub.2](CH.sub.2).sub.11COOZn[Y]

[0135] 12-(Triethoxysilyl)dodecanoic acid was prepared following the same experimental protocol as that described above for Example 1, with the following amounts of reagents: triethoxysilane (2.56 g, 97%, 15.1 mmol), dodec-11-enoic acid (3.00 g, 15.1 mmol), dry THF (3.0 mL) and PtO.sub.2 (3.4 mg, 0.015 mmol). Along with the desired compound, the corresponding cyclic ester was also observed as a minor by-product (12%). The alkoxy silane carboxylic acid was obtained as an oil (5.32 g, 88%, 12.9 mmol, 86% yield) and used without any further purification.

[0136] .sup.1H NMR: 11.54 (s, 1H) , 3.71 (q, 6H, J=7.0 Hz), 2.26-2.18 (m, 2H), 1.57-1.46 (m, 2H), 1.36-1.26 (m, 2H), 1.26-1.14 (m, 14H), 1.11 (t, 9H, J=7.0 Hz), 0.56-0.47 (m, 2H) ppm;.sup.13C{.sup.1H} NMR: 179.4, 58.1, 33.9, 33.0, 29.4, 29.4, 29.3, 29.1, 29.1, 28.9, 22.6, 22.6, 18.1, 10.2 ppm; .sup.29Si{.sup.1H} NMR: 44.7 ppm.

[0137] 12-(Triethoxysilyl)dodecanoic acid was attached to SiO.sub.2 following the same experimental protocol as that described for Example 1, with the following amounts of reagents: Silica gel (3.40 g, irregular amorphous narrow pore, 40-63 m particle size, pore volume: 0.73 mL/g, 435 m.sup.2/g, average pore diameter 6.7 nm, Merck) previously dried (120 C. overnight), 12-(triethoxysilyl)dodecanoic acid (1.48 g, 88%, 3.57 mmol) and dry toluene (ca. 1.6 mL toluene; the overall volume of the final solution was 2.5 mL). The COOH-containing silica gel was obtained as a white powder (4.12 g).

[0138] The resulting carboxylic acid containing material was subjected to ion exchange following the same experimental protocol as that described for [SiO.sub.2](CH.sub.2).sub.3O(CH.sub.2).sub.2COOZn[Y], with the following amounts of reagents: COOH-containing silica gel (2.0 g) and aqueous zinc acetate (0.4 M; 40 mL; 20 mL/g). [SiO.sub.2](CH.sub.2).sub.11COOZn[Y] was obtained as a white powder (1.9 g).

[0139] Characterization Data for [SiO.sub.2]13 (CH.sub.2).sub.11COOZn[Y]

[0140] TGA (air, 30-550 C., 5 C./min): mass loss at 80 C. (2.05%) and 430 C. (16.36%); XRPD (2 range 5-70): no diffraction peaks observed; BET surface area analysis (N.sub.2 adsorption-desorption isotherm): 0.30 mL/g total pore volume, 268 m.sup.2/g specific surface area; complexometric titration: 0.81 mmol [Zn]/g, ion chromatography: 0.015 mmol ACO.sup. groups/g (<2% of ACO.sup. groups with respect to [Zn] present in the modified SiO.sub.2); FT-IR (ATR, solid, v/cm.sup.1): 2925 (out-of-phase stretch CH.sub.2), 2854 (in-phase stretch CH.sub.2), 1557 (asym. stretch COO), 1456 (deformation CH.sub.2), 1418 (sym. stretch COO), 1054 (asym. stretch SiOSi); zinc content: 0.81 mmol [Zn]/g.

Example A.5

[0141] Preparation of a Siliceous Catalyst without Zinc Groups (Comparison)

[0142] With the aim of assessing the methoxycarbonylation background reaction mediated by the solid support (a siliceous material), (MeO).sub.3SiMe was grafted to irregular amorphous narrow pore silica gel following an identical procedure to that employed for covalently linking COOZn groups to the inorganic supports (see Example 1). Thus, a modified silica gel (SG-Me) was prepared by grafting identical amounts of (MeO).sub.3SiMe. The work-up and purification procedures employed were also the same than those employed for preparing the real catalysts. It should be noted that this material (SG-Me) is based on the same siliceous support and has the same functionalization degree as the real catalysts (with irregular amorphous narrow pore silica carriers), however it lacks zinc groups.

[0143] B. Alkoxycarbonylations of Aromatic Amines

[0144] General Procedure

[0145] The catalytic results presented below are based on a series of experiments employing the four different heterogeneous catalysts that have been prepared according to Examples A.1 to A.4 and the comparison catalyst prepared according to Example A.S. Catalytic assays were at least duplicated (a minimum of two reactions per catalyst and substrate were performed). Furthermore, two samples for HPLC quantitative analysis were made up for each reaction mixture and were analysed with the corresponding quantitative HPLC analytical method. The aromatic amines used as substrates were aniline, MDA and 2,4-TDA, as shown in the following scheme:

##STR00009##

Crude product mixtures derived from the methoxycarbonylation reaction of aniline were analyzed by NMR using internal standards whereas crude product mixtures derived from the methoxycarbonylation reaction of MDA and TDA were analyzed by quantitative HPLC analysis using calibration curves. The analytical conditions for MDA and 2,4-TDA derivatives were as follows:

[0146] MDA-derivatives: Kromasil 100 C18 5 m 4.6150 column, RT, 1.0 mL/min, Injection=5 L, UV detection 254 nm, Eluent A:100 mL CH.sub.3CN, 900 mL H.sub.2O, 0.01M NH.sub.4Ac. Eluent B: 900 mL CH.sub.3CN, 100 mL H.sub.2O, 0.01M NH.sub.4Ac. Gradient: 0 min 60% A, 40% B; 15 min 60% A, 40% B; 25min 100% B; 30 min Stop. Retention times: Rt(MDA)=4.1 min, Rt(MDA-MCMe)=6.4 min, Rt(MDA-MMe)=8.4 min, Rt(MDA-BCMe)=10.0 min, Rt(MDA-BMe)=19.0 min.

[0147] 2,4-TDA-derivatives: Kromasil 100 C18 5 m 4.6150, RT, 1.0 mL/min, Injection=5 L, UV detection 225 nm, Eluent A:100 mL CH.sub.3CN, 900 mL H.sub.2O, 0.01M NH.sub.4Ac. Eluent B: 900 mL CH.sub.3CN, 100 mL H.sub.2O, 0.01M NH.sub.4Ac. Gradient: 0 min 100% A, 22 min 100% A; 48 min 80% A, 20% B; 60 min 55% A, 45% B; 80 min Stop. Retention times: Rt(2,4-TDA)=7.5 min, Rt(2,4-TDA-M-oMe)=15.0 min, Rt(2,4-TDA-M-pMe=20.0 min, Rt(2,4-TDA-MC-oMe)=22.4 min, Rt(2,4-TDA-MC-pMe)=30.8 min, Rt(2,4-TDA-BMe)=42.0 min, Rt(2,4-TDA-BCMe)=45.1 min.

[0148] The reaction conditions that were used in the catalytic studies were based on the ones disclosed in WO 2014/187756 Al (Example 2 in page 12, line 12), with the exception of the catalyst loading employed. The reaction conditions for each substrate are indicated below and catalyst loadings are expressed in molar ratio of dimethyl carbonate (DMC), amine and catalyst (based in [Zn] content). [0149] Aniline: molar ratio DMC: amine: catalyst=25:1:0.05, T=180 C. [0150] MDA: molar ratio DMC: amine: catalyst=25:1:0.05, T=180 C. [0151] 2,4-TDA: molar ratio DMC: amine: catalyst=30:1:0.10, T=190 C.

[0152] In order to recover and reuse the catalysts after the alkoxycarbonylation reactions, the crude reaction mixtures were filtered. The recovered heterogeneous catalysts were washed with acetone, and the solid residue was dried at 120 C. prior to its reuse. The results are indicated in each case and are labelled as cycle #2 in the Tables that summarise the results on catalysis in Examples B.2 to B.6 below. In the methoxycarbonylation of MDA, considerable amounts of insoluble and non-analysable materials were formed. The catalysts were separated from the reaction mixture together with these MDA-derived insoluble compounds, which could not be separated from the catalyst during the catalyst recycling process. Thus, catalytic studies with recycled catalyst implied adding these impurities to the reaction mixture.

Examples B.1 and B.2 (Comparisons)

[0153] Catalyst From Example A.5 and No Catalyst, Respectively

[0154] The results are summarised in Table 1.

TABLE-US-00001 TABLE 1 Methoxycarbonylation reactions using a blank catalyst (SG-Me, Example A.5) or no catalyst. Conver- High. Poss. Yield Reaction sion Yield (%) (%) Ex. conditions Substrate (%) (SD) (SD) .sup.[a] (SD) .sup.[b] B.1 190 C., 2 h, 2,4-TDA 73 8 <1 DMC, SG-Me as catalyst B.2 190 C., 2 h, 2,4-TDA 73 5 1 DMC No catalyst .sup.[a] Highest possible yield. Sum of the yield of the target biscarbamate and its intermediates. .sup.[b] Yield of the desired biscarbamate.

Example B.3

[0155] Irregular Amorphous Narrow Pore [SiO.sub.2](CH.sub.2).sub.4COOZn[Y] (of Example A.2) as Catalyst

[0156] Table 2 summarises the results.

TABLE-US-00002 TABLE 2 Methoxycarbonylation reactions using irregular amorphous narrow pore [SiO.sub.2](CH.sub.2).sub.4COOZn[Y] as the catalyst..sup.[a] High. Alk. Poss. Amines Conver- Yield Yield (%)/Alk. Ex. sion (%) (%) Carb. ( B.3.- Substrate Cycle (%) (SD) (SD) .sup.[b] (SD) .sup.[c] area %).sup.[d] 1 Aniline #1 >99 (0) 95 (0) 95 (0) 4/2 2 Aniline #2 >99 (0) 98 (0) 98 (0) 2/0 3 MDA #1 >99 (0) 57 (2) 42 (3) 4/29 4 MDA #2 97 (2) 54 (7) 32 (11) 7/23 5 2,4-TDA #1 >99 (0) 46 (1) 33 (2) 4/32 6 2,4-TDA #2 >99 (1) 36 (1) 11 (2) 18/28 .sup.[a]Values expressed as an average of all independent runs. Standard deviations are indicated in brackets. .sup.[b] Highest possible yield: sum of the yield of the target carbamate and its precursors (i.e. the corresponding monocarbamates). .sup.[c] Yield of the desired carbamate. .sup.[d]Sum of areas of alkylated carbamates.

[0157] In comparison, the wide-pore supported catalyst described in Catal. Sci. Technol. 2015, 5, 109 and CN 102872912 A is said to give yields with aniline as reactant of up to 91.6%.

Example B.4

[0158] Ordered Mesoporous [SiO.sub.2](CH.sub.2).sub.4 COOZn[Y] (of Example A.3) as Catalyst

[0159] Table 3 summarises the results.

TABLE-US-00003 TABLE 3 Methoxycarbonylation reactions using ordered mesoporous [SiO.sub.2](CH.sub.2).sub.4 COOZn[Y] as the catalyst..sup.[a] Aik. High. Poss. Amines (%)/ Ex. Conversion Yield (%) Yield (%) Aik. Carb. B.4.- Substrate Cycle (%) (SD) (SD) .sup.[b] (SD) .sup.[c] ( area %).sup.[d] 1 Aniline #1 >99 (0) 94 (0) 94 (0) 4/2 2 Aniline #2 >99 (0) 97 (0) 97 (0) 3/1 3 MDA #1 99 (1) 54 (2) 34 (6) 6/26 4 MDA #2 97 (2) 47 (5) 23 (1) 8/22 5 2,4-TDA #1 >99 (0) 43 (1) 28 (1) 5/40 6 2,4-TDA #2 96 (1) 38 (6) 12 (4) 17/31 .sup.[a]Values expressed as an average of all independent runs. Standard deviations are indicated in brackets. .sup.[b] Highest possible yield: sum of the yield of the target carbamate and its precursors (i.e. the corresponding monocarbamates). .sup.[c] Yield of the desired carbamate. .sup.[d]Sum of areas of alkylated carbamates.

Example B.5

[0160] Irregular Amorphous Narrow Pore [SiO.sub.2](CH.sub.2).sub.11 COOZn[Y] (of Example A.4) as Catalyst

[0161] Table 4 summarises the results.

TABLE-US-00004 TABLE 4 Methoxycarbonylation reactions using irregular amorphous narrow pore [SiO.sub.2](CH.sub.2).sub.4COOZn[Y] as the catalyst..sup.[a] Aik. High. Poss. Amines (%)/ Ex. Conversion Yield (%) Yield (%) Aik. Carb. B.5.- Substrate Cycle (%) (SD) (SD) .sup.[b] (SD) .sup.[c] ( area %).sup.[d] 1 Aniline #1 >99 (0) 93 (0) 93 (0) 4/4 2 Aniline #2 >99 (0) 98 (0) 98 (0) 1/1 3 MDA #1 98 (0) 57 (0) 34 (1) 6/23 4 MDA #2 97 (2) 50 (2) 27 (6) 7/21 5 2,4-TDA #1 65 (1) 3 (1) <1 (0) 45/10 6 2,4-TDA #2 / .sup.[a]Values expressed as an average of all independent runs. Standard deviations are indicated in brackets. .sup.[b] Highest possible yield: sum of the yield of the target carbamate and its precursors (i.e. the corresponding monocarbamates). .sup.[c] Yield of the desired carbamate. .sup.[d]Sum of areas of alkylated carbamates.

Example B.6

[0162] Irregular Amorphous Narrow Pore [SiO.sub.2](CH.sub.2).sub.3O(CH.sub.2).sub.2COOZn[Y] (of Example A.1) as Catalyst

[0163] Table 5 summarises the results.

TABLE-US-00005 TABLE 5 Methoxycarbonylation reactions using irregular amorphous narrow pore [SiO.sub.2](CH.sub.2).sub.3O(CH.sub.2).sub.2COOZn[Y] as the catalyst..sup.[a] Aik. High. Poss. Amines (%)/ Ex. Conversion Yield (%) Yield (%) Aik. Carb. B.6.- Substrate Cycle (%) (SD) (SD) .sup.[b] (SD) .sup.[c] ( area %).sup.[d] 1 Aniline #1 >99 (0) 93 (0) 93 (0) 6/2 2 Aniline #2 >99 (0) 97 (0) 97 (0) 2/1 3 MDA #1 99 (0) 56 (3) 40 (4) 4/28 4 MDA #2 >99 (0) 68 (5) 57 (5) 2/24 5 2,4-TDA #1 >99 (0) 46 (2) 37 (1) 3/39 6 2,4-TDA #2 >99 (0) 67 (1) 55 (2) 1/26 .sup.[a]Values expressed as an average of all independent runs. Standard deviations are indicated in brackets. .sup.[b] Highest possible yield: sum of the yield of the target carbamate and its precursors (i.e. the corresponding monocarbamates). .sup.[c] Yield of the desired carbamate. .sup.[d]Sum of areas of alkylated carbamates.

[0164] Recycled catalyst of Example A.1 mediated the methoxycarbonylation of 2,4-TDA with higher selectivity, reaching 55% and 67% yield of the desired biscarbamate and biscarbamate plus intermediates (i.e. 2- and 4-monocarbamates derived from 2,4-TDA; compare Examples B.6.5 and B.6.6 in Table 5). Despite containing MDA-derived impurities, recycled catalyst of Example A.1 gave slightly better results in the second cycle (for instance, yield in the desired biscarbamate increased from 40% in the first cycle to 57% in the second; compare entries B.6.3 and B.6.4 in Table 5).

[0165] Zinc leaching after each catalytic cycle was also investigated for catalyst of Example A1, [SiO.sub.2](CH.sub.2).sub.3O(CH.sub.2).sub.2COOZn[Y]. As indicated in Table 6, zinc leaching was found to be negligible after two catalytic cycles, with leaching values around 1 mol% with respect to the original [Zn] loading present in the reaction.

TABLE-US-00006 TABLE 6 [Zn] leaching in the methoxycarbonylation of 2,4-TDA..sup.[a] Leaching Entry Substrate Cycle (mol % [Zn]) .sup.[b] 1 2,4-TDA #1 1.1 2 2,4-TDA #2 0.8 .sup.[a][Zn] content determined by complexometric titration with EDTA as reagent and Eriochrome T as final point indicator. .sup.[b] Leaching expressed as mol % [Zn] respect to the initial Zn content in the catalyst.

Summary of Examples B.2 to B.6

[0166] Total conversion of the substrates was observed for almost each combination of substrate and catalyst. The different catalysts prepared within this co-operation performed similarly in the alkoxycarbonylation of aniline The four explored catalysts gave excellent results, with an average yield of 94% towards the corresponding carbamate.