HETEROGENEOUS CATALYSTS FOR THE SYNTHESIS OF CARBAMATES

Abstract

The present invention relates to a catalyst for preparing carbamates, in particular aromatic carbamates, comprising a binary oxide having the formula L.sub.1-xM.sub.xO.sub.2, wherein L is a metal selected from the lanthanoid series and M is a metal selected from the group consisting of Sc, Y, Ti, Zr, Hf, metals from the lanthanoid series and metals from the actinoid series, and wherein x ranges from 0.01 to 0.05. The present invention also relates to a method for producing said catalysts and a method of utilizing said catalysts in the production of carbamates, in particular aromatic carbamates.

Claims

1. A catalyst for preparing carbamates comprising a binary oxide having the formula L.sub.1-xM.sub.xO.sub.2, wherein L is a metal selected from the lanthanoid series and M is a metal selected from the group consisting of scandium, yttrium, titanium, zirconium, hafnium, a metal from the lanthanoid series and a metal from the actinoid series, and wherein x ranges from 0.01 to 0.05.

2. The catalyst of claim 1, wherein L is cerium.

3. The catalyst of claim 1, wherein M is selected from the group consisting of yttrium, zirconium, hafnium, lanthanum, praseodymium, samarium, europium and terbium.

4. The catalyst of claim 3, wherein M is zirconium.

5. The catalyst of claim 1, wherein x ranges from 0.01 to 0.045.

6. A method for preparing the catalyst of claim 1, comprising: I. precipitating a catalyst precursor by combining an aqueous solution of a salt of the metal L and an aqueous solution of a salt of the metal M in the presence of an oxidizing agent; II. separating off the catalyst precursor precipitated in step I; and III. calcining the catalyst precursor separated off in step II to yield the catalyst.

7. The method of claim 6, wherein the oxidixing agent is selected from the group consisting of hydrogen peroxide, nitric acid, perchloric acid, peroxydisulphuric acid, peroxymonosulphuric acid, chlorite, chlorate, perchlorate, hypochlorite, sodium perborate, and mixtures thereof.

8. The method of claim 6, wherein the salt of the metal L and the salt of the metal M are independently of one another selected from the group consisting of nitrates, chlorides, sulphates and hydroxides.

9. The method of claim 6, wherein the precipitating in step I comprises adjusting the pH of the combined solutions of the salt of the metal L and the salt of the metal M to a value of from 7.0 to 14.0.

10. The method of claim 9, wherein the adjusting of the pH is affected by addition of a base.

11. A method of producing a carbamate compound, comprising reacting an organic amine with an organic dicarbonate in the presence of the catalyst of claim 1.

12. The method of claim 11, wherein the organic dicarbonate comprises one or more of dipropyl carbonate, diethyl carbonate, and dimethyl carbonate.

13. The method of claim 11, wherein the reaction is carried out at a molar ratio of organic dicarbonate to organic amine of from 10:1 to 50:1.

14. The method of claim 11, wherein the reaction is carried out under autogenous pressure.

15. The method of claim 11, wherein the organic amine comprises aniline, 2,4-diamino-N-phenylaniline, o-, m-, or 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-, or 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, 4,4ethylenedianiline, 2,4-bis(4-aminobenzyl)aniline, 4,4-methylenebis(N,N-dimethylaniline), 4,4methylenebis(N-methylaniline), benzidine; N,N,N,N-tetramethylbenzidine, bis(3,4-diaminophenyl)methane, bis(3-methyl-4-aminophenyl)methane, 2,2-methylene dianiline, 2,4-methylene dianiline, 4,4-methylene dianiline, 1,6-hexamethylene diamine, isophorone diamine, (2-aminocylohexyl)-(4-aminocylohexyl)-methane, bis-(4-aminocyclohexyl)-methane or a mixture of two or more of the aforementioned organic amines, whereby in case the organic amine comprises methylene dianiline, higher oligomers of methylene dianiline having three or more six-membered aromatic rings are optionally also contained in the organic amine.

16. A process for producing an isocyanate, comprising producing a carbamate compound according to the method of claim 11 and subjecting the carbamate to thermal or catalytic cleavage.

Description

EXAMPLES

[0090] General Remarks

[0091] The catalytic results presented below are based on a series of experiments employing the different heterogeneous catalysts that have been prepared according to Examples 1 to 7. Catalytic assays were at least duplicated (a minimum of two reactions per catalyst were performed). Furthermore, two samples for HPLC quantitative analysis were made up for each reaction mixture and were quantified by HPLC analysis using calibration curves of external standards.

[0092] As test substrates for carbamate production, 2,4-TDA and dimethyl carbonate were used, as shown in the following scheme:

##STR00003##

[0093] Reactions were performed in an autoclave under nitrogen atmosphere. The reaction time of 7 hours refers to the time the reaction is allowed to proceed after the desired temperature has been reached. Heating-up the autoclave takes 30 min for reactions at 140 C.

[0094] Dimethyl carbonate (99%) was purchased from Aldrich and was dried with 4 molecular sieves. Water content analysis of the organic carbonates (Karl Fischer method) was performed; water concentration was always below 30 ppm. 2,4-TDA (98%) was purchased from Aldrich used without further purification.

[0095] Crude product mixtures derived from the methoxycarbonylation reaction of 2,4-TDA were analysed by quantitative HPLC analysis using calibration curves of external standards. The analytical conditions were as follows:

[0096] Kromasil 100 C18 5 m 4.6150 mm, 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.

[0097] Preparation of the Catalyst

Example 1 (According to the Invention)

[0098] The binary oxide Ce.sub.0.98Zr.sub.0.02O.sub.2 with a zirconium molar fraction of 2% was prepared by co-precipitation in the presence of H.sub.2O.sub.2. Ce(NO.sub.3).sub.3.6H.sub.2O (Acros, 99.5%) and the corresponding amount of zirconyl nitrate solution (Aldrich, 35% in dilute nitric acid) were dissolved in deionized water (in a weight ratio of (Ce precursor+Zr precursor)=1:10) under stirring at room temperature, H.sub.2O.sub.2 was poured into the solution to obtain a molar H.sub.2O.sub.2:(Ce+Zr) ratio of 3. The precipitation was obtained by adding aqueous ammonia solution until a pH of 10.5 was reached. The slurry was stirred for 4 hours at room temperature, and the precipitate formed was separated by filtration, washed with deionized water until neutral pH, dried at 100 C. in static air for 12 hours, and calcined at 500 C. (5 C. min.sup.1) in static air for 5 h. Phase composition was confirmed by XRD (X-Ray diffraction), crystallite size was 9 nm calculated from the Scherrer equation, and BET surface area was 69 m.sup.2 g.sup.1. The resulting catalyst was named catalyst A.

Example 2 (According to the Invention)

[0099] Following the procedure of Example 1, the binary oxide Ce.sub.0.95Zr.sub.0.05O.sub.2 with a zirconium molar fraction of 5% was prepared. Phase composition was confirmed by XRD (X-Ray diffraction), crystallite size was 9 nm calculated from the Scherrer equation, and BET surface area was 79 m.sup.2 g.sup.1. The resulting catalyst was named catalyst B.

Example 3 (According to the Invention)

[0100] Following the procedure of Example 1, the binary oxide Ce.sub.0.95Eu.sub.0.05O.sub.2 with an europium molar fraction of 5% was prepared, employing Eu(NO.sub.3).sub.3.6H.sub.2O (ABCR-Chemicals, 99.9%) as precursor. Phase composition was confirmed by XRD (X-Ray diffraction), crystallite size was 8 nm calculated from the Scherrer equation, and BET surface area was 73 m.sup.2 g.sup.1. The resulting catalyst was named catalyst C.

Example 4 (According to the Invention)

[0101] Following the procedure of Example 1, the binary oxide Ce.sub.0.98Y.sub.0.02O.sub.2 with an yttrium molar fraction of 2% was prepared, employing Y(NO.sub.3).sub.3.6H.sub.2O (ABCR-Chemicals, 99.9%) as precursor. Phase composition was confirmed by XRD, crystallite size was 9 nm calculated from the Scherrer equation, and BET surface area was 71 m.sup.2 g.sup.1. The resulting catalyst was named catalyst D.

Example 5 (According to the Invention)

[0102] Following the procedure of Example 1, the binary oxide Ce.sub.0.98Sm.sub.0.02O.sub.2 oxide with a samarium molar fraction of 2% was prepared, employing Sm(NO.sub.3).sub.3.6H.sub.2O (Acros Organics, 99.9%) as precursor. Phase composition was confirmed by XRD, crystallite size was 10 nm calculated from the Scherrer equation, and BET surface area was 73 m.sup.2 g.sup.1. The resulting catalyst was named catalyst E.

Example 6 (According to the Invention)

[0103] Following the procedure of Example 1, the binary oxide Ce.sub.0.98Hf.sub.0.02O.sub.2 with a hafnium molar fraction of 2% was prepared, employing HfCl.sub.4 (Strem Chemicals, 99.9%) as precursor. Phase composition was confirmed by XRD, crystallite size was 9 nm calculated from the Scherrer equation, and BET surface area was 84 m.sup.2 g.sup.1. The resulting catalyst was named catalyst F.

Example 7 (Comparative Example)

[0104] CeO.sub.2 was precipitated from a Ce(NO.sub.3).sub.3.6H.sub.2O (Acros, 99.5) solution following the procedure of Example 1 with the exception that no M dopant was used. Phase composition was confirmed by XRD, crystallite size was 12 nm calculated from the Scherrer equation, and BET surface area was 64 m.sup.2 g.sup.1. The resulting catalyst was named catalyst G.

[0105] Preparation of Aromatic Carbamates

Example 8 (According to the Invention)

[0106] 0.40 g 2,4-toluenediamine, 8.8 g dimethyl carbonate, and 0.84 g of catalyst A were placed with a magnetic stirrer in a PTFE vessel in a 25 mL autoclave. The reaction was performed after reaching an internal temperature of 140 C. and maintained at this temperature for 7 hours under autogenous pressure. After the completion of the reaction, the autoclave was cooled down and the reaction mixture analysed by HPLC.

[0107] Biscarbamate yield: 88%. Combined yield of mono- and biscarbamates: 95%.

Example 9 (According to the Invention)

[0108] 0.40 g 2,4-toluenediamine, 8.8 g dimethyl carbonate, and 0.82 g of catalyst B were placed with a magnetic stirrer in a PTFE vessel in a 25 mL autoclave, otherwise following the reaction procedure of Example 8.

[0109] Biscarbamate yield: 82%. Combined yield of mono- and biscarbamates: 93%.

Example 10 (According to the Invention)

[0110] 0.40 g 2,4-toluenediamine, 8.8 g dimethyl carbonate, and 0.89 g of catalyst C were placed with a magnetic stirrer in a PTFE vessel in a 25 mL autoclave, otherwise following the reaction procedure of Example 8.

[0111] Biscarbamate yield: 82%. Combined yield of mono- and biscarbamates: 93%.

Example 11 (According to the Invention)

[0112] 0.40 g 2,4-toluenediamine, 8.8 g dimethyl carbonate, and 0.89 g of catalyst D were placed with a magnetic stirrer in a PTFE vessel in a 25 mL autoclave, otherwise following the reaction procedure of Example 8.

[0113] Biscarbamate yield: 84%. Combined yield of mono- and biscarbamates: 93%.

Example 12 (According to the Invention)

[0114] 0.40 g 2,4-toluenediamine, 8.8 g dimethyl carbonate, and 0.89 g of catalyst E were placed with a magnetic stirrer in a PTFE vessel in a 25 mL autoclave, otherwise following the reaction procedure of Example 8.

[0115] Biscarbamate yield: 83%. Combined yield of mono- and biscarbamates: 93%.

Example 13 (According to the Invention)

[0116] 0.40 g 2,4-toluenediamine, 8.8 g dimethyl carbonate, and 0.77 g of catalyst F were placed with a magnetic stirrer in a PTFE vessel in a 25 mL autoclave, otherwise following the reaction procedure of Example 8.

[0117] Biscarbamate yield: 81%. Combined yield of mono- and biscarbamates: 93%.

Example 14 (Comparative Example)

[0118] 0.40 g 2,4-toluenediamine, 8.8 g dimethyl carbonate, and 1.01 g of catalyst G were placed with a magnetic stirrer in a PTFE vessel in a 25 mL autoclave, otherwise following the reaction procedure of Example 8.

[0119] Biscarbamate yield: 83%. Combined yield of mono- and biscarbamates: 90%.

[0120] Table 1 summarizes the results of examples 8-14.

TABLE-US-00001 TABLE 1 Methoxycarbonylation reactions of 2,4-TDA using catalysts A G..sup.[a] Conver- Combined BCMe sion Yield Yield Alk. Carb. Ex. Catalyst (%) (%) .sup.[b] (%) .sup.[c] ( area %) .sup.[d] 14 CeO.sub.2.sup.[e] G >99 90 83 3 8 Ce.sub.0.98Zr.sub.0.02O.sub.2 A >99 95 88 3 9 Ce.sub.0.95Zr.sub.0.05O.sub.2 B >99 93 82 3 10 Ce.sub.0.95Eu.sub.0.05O.sub.2 C >99 93 82 3 11 Ce.sub.0.98Y.sub.0.02O.sub.2 D >99 93 84 3 12 Ce.sub.0.98Sm.sub.0.02O.sub.2 E >99 93 83 3 13 Ce.sub.0.98Hf.sub.0.02O.sub.2 F >99 93 81 4 .sup.[a]Values expressed as an average of all independent runs. Catalyst loading was adjusted to reach a catalyst surface area of 20 m.sup.2/mmol 2,4-TDA. (The catalysts were dosed based on their surface area. The specific surface area of each catalyst was measured prior to the catalytic reaction and then the catalyst was dosed based on a fixed and predetermined ratio of surface area per mmol of the substrate which was 20 m.sup.2/mmol 2,4-TDA in these experiments.) .sup.[b] Combined yield stand for the sum of the yield of the target biscarbamate and its precursors (i.e. the two corresponding monocarbamates). .sup.[c] Yield of biscarbamate. .sup.[d] Sum of the percentage of peak areas of all alkylated carbamates. .sup.[e]Catalyst prepared following the procedure of examples 1-6 in the absence of metal M.

[0121] As can be seen from Table 1, the combined yields of mono and biscarbamates are significantly higher in case of the inventive catalysts as compared to CeO.sub.2.

Example 15 (According to the Invention)

[0122] Five consecutive catalytic tests were conducted with the catalyst A and the catalyst G under the conditions described in Example 8. After each run, the used catalyst was recovered by filtration, washed with acetone (55 mL), and dried at 120 C. in static air for 2 hours. Prior to the next catalytic test, the BET surface area was determined and the required amount of catalyst was calculated to be constant at 20 m.sup.2/mmol 2,4-TDA in all the experiments.

[0123] Table 2 summarizes the results.

TABLE-US-00002 TABLE 2 Results of the consecutive methoxycarbonylation reactions of 2,4-TDA using catalysts A and G..sup.[a] Conver- Combined BCMe Alk. Carb. sion Yield Yield ( area Catalyst Code Cycle (%) (%).sup.[b] (%).sup.[c] %).sup.[d] CeO.sub.2.sup.[e] G #1 >99 90 83 3 #2 >99 92 83 3 #3 >99 86 60 4 #4 99 66 43 7 #5 89 42 8 15 Ce.sub.0.98Zr.sub.0.02O.sub.2 A #1 >99 96 88 3 #2 >99 90 76 4 #3 >99 92 79 4 #4 99 80 40 7 #5 98 54 22 12 .sup.[a]Values expressed as an average of all independent runs. Catalyst loading was adjusted to reach a catalyst surface area of 20 m.sup.2/mmol 2,4-TDA. (The catalysts were dosed based on their surface area. The specific surface area of each catalyst was measured prior to the catalytic reaction and then the catalyst was dosed based on a fixed and predetermined ratio of surface area per mmol of the substrate which was 20 m.sup.2/mmol 2,4-TDA in these experiments.) .sup.[b]Combined yield stand for the sum of the yield of the target biscarbamate and its precursors (i.e. the two corresponding monocarbamates). .sup.[c]Yield of biscarbamate. .sup.[d]Sum of the percentage of peak areas of all alkylated carbamates. .sup.[e]Catalyst prepared following the procedure of examples 1-6 in the absence of metal M.