CATALYST FOR THE CATALYTIC SYNTHESIS OF UREA

Abstract

A ruthenium-phosphine complex can be used as a catalyst in a method for the catalytic synthesis of urea. The method may comprise more particularly a reaction of formamide or of formamide with ammonia in the presence of the catalyst to form urea and hydrogen. Through the use of the ruthenium-phosphine complex as the catalyst, catalytic preparation of urea from formamide or from formamide with ammonia is provided for the first time. This allows for synthesis under mild conditions and virtually no formation of byproducts. Further, using an acid as a cocatalyst in the catalytic synthesis or the reaction can lead to an improvement in urea yield.

Claims

1.-15. (canceled)

16. A method of performing catalytic synthesis of urea, the method comprising using a ruthenium-phosphine complex as a catalyst.

17. The method of claim 16 comprising reacting formamide or formamide and ammonia in the presence of the catalyst to form urea and hydrogen.

18. The method of claim 16 wherein the ruthenium-phosphine complex comprises at least one monophosphine, one diphosphine, one triphosphine, or one compound having more than three phosphine groups, with the monophosphine having a formula PR.sup.1R.sup.2R.sup.3 in which R.sup.1, R.sup.2, and R.sup.3 independently of one another are in each case substituted or unsubstituted alkyl, substituted or unsubstituted aryl, or substituted or unsubstituted heteroaryl.

19. The method of claim 18 wherein R.sup.1 is alkyl and R.sup.2 and R.sup.3 independently of one another are substituted or unsubstituted heteroaryl and/or substituted or unsubstituted aryl.

20. The method of claim 16 wherein the ruthenium-phosphine complex comprises one or more nonphosphine ligands that is selected from carbenes, amines, amides, phosphites, phosphoamidites, phosphorus-containing ethers or esters, sulfides, trimethylenemethane, cyclopentadienyl, allyl, methylallyl, ethylene, cyclooctadiene, acetylacetonate, acetate, hydride, halide, phenoxide, carbon monoxide, or a combination thereof.

21. The method of claim 16 wherein the ruthenium-phosphine complex comprises one or more nonphosphine ligands that is selected from trimethylenemethane, cyclopentadienyl, allyl, methylallyl, ethylene, cyclooctadiene, acetylacetonate, acetate, hydride, halide, phenoxide, carbon monoxide, or a combination thereof.

22. The method of claim 16 wherein the ruthenium-phosphine complex is a ruthenium-triphosphine complex, wherein the triphosphine has a general formula I: ##STR00020## wherein R.sup.1 to R.sup.6 independently of one another are substituted or unsubstituted aryl or substituted or unsubstituted heteroaryl, wherein R.sup.7 is hydrogen, alkyl, cycloalkyl, or aryl.

23. The method of claim 16 wherein the ruthenium-phosphine complex has a general formula II of (A)Ru(L).sub.3, in which A is a triphosphine of a general formula I: ##STR00021## wherein R.sup.1 to R.sup.6 independently of one another are substituted or unsubstituted aryl or substituted or unsubstituted heteroaryl, wherein R.sup.7 is hydrogen, alkyl, cycloalkyl, or aryl, wherein L in each case independently of one another are monodentate ligands, wherein two monodentate ligands L are replaceable by one bidentate ligand or wherein three monodentate ligands L are replaceable by one tridentate ligand.

24. The method of claim 17 wherein a concentration of the ruthenium-phosphine complex is in a range from 0.05 mol % to 10 mol % based on a molar amount of formamide.

25. The method of claim 16 wherein the catalytic synthesis is performed at a temperature in a 50 to 250° C. range.

26. The method of claim 16 wherein the catalytic synthesis is performed at a pressure in a range from ambient pressure to 150 bar.

27. The method of claim 16 wherein an amount of ammonia used in equivalents, based on formamide, is in a range from 1 to 300 eq.

28. The method of claim 16 wherein a reaction time of the catalytic synthesis is in a range from 1 minute to 24 hours.

29. The method of claim 16 wherein the catalytic synthesis is performed in one or more organic solvents or one or more ionic liquids.

30. The method of claim 16 wherein the catalytic synthesis performed in one or more organic solvents or one or more ionic liquids, with the solvent being cyclic and noncyclic ethers, substituted and unsubstituted aromatics, alkanes, or halogenated hydrocarbons, with the solvent being dioxane, 1,4-dioxane, toluene, or THF.

31. The method of claim 17 wherein the reaction of formamide or formamide and ammonia is a homogeneous catalytic reaction.

32. The method of claim 17 wherein the reaction of formamide or formamide and ammonia is a heterogeneous catalytic reaction.

33. The method of claim 17 wherein the reaction of formamide or formamide and ammonia is performed continuously.

34. The method of claim 17 wherein the reaction of formamide or formamide and ammonia is performed batchwise.

35. The method of claim 16 comprising using an acid as a cocatalyst in the catalytic synthesis.

Description

EXAMPLES

Synthesis of [Ru(Triphos)(Tmm)]

[0075] A 35 mL Schlenk tube was filled with 319 mg (1.00 mmol) of [Ru(cod)(methylallyl)] (cod=1,5-cyclooctadiene) and 624 mg (1.17 mmol) of 1,1,1-tris(diphenyl-phosphinomethyl)ethane in 20 mL of toluene. The reaction mixture was stirred and was heated at 110° C. for 2 h, cooled to room temperature and concentrated under reduced pressure. Following treatment with 15 mL of pentane, the precipitating complex was isolated, washed with pentane (3×10 mL) and dried under reduced pressure overnight, to give [Ru(triphos)(tmm)] as a pale yellow powder (0.531 g, 0.678 mmol, 68% yield). The identity was confirmed by .sup.1H, .sup.13C APT and .sup.31P NMR spectra.

Examples 1-9

[0076] Synthesis of Urea from Formamide and Ammonia with Ru(Triphos)(Tmm)

[0077] The urea was synthesized in accordance with the following equation:

##STR00007##

[0078] High-pressure batch experiments were performed in a 10 mL stainless steel autoclave fitted with a glass insert and a magnetic stirring rod. When 2 mL of 1,4-dioxane and 0.6 g of NH.sub.3 were used, the reaction pressure was about 30 bar in the hot state (at 150° C. reaction temperature) and the pressure in the cold state (room temperature) was about 8-10 bar. Before being used, the autoclave was evacuated for at least 30 minutes and filled repeatedly with argon. The catalyst [Ru(triphos)(tmm)] (7.8 mg, 0.01 mmol) was weighed under an argon atmosphere into a Schlenk tube and dissolved in 1,4-dioxane (2.0 mL). Following addition of formamide (40 μL, 1.00 mmol), the reaction mixture was transferred to the autoclave with a cannula under an argon countercurrent. Liquid NH.sub.3 (between 0.5 g and 1.0 g) was introduced into the autoclave, and the autoclave was sealed. The reaction mixture was stirred and was heated to the respective reaction temperature in an aluminum cone for the respective reaction time. After cooling to room temperature, the autoclave was cautiously let down with air. Following removal of the solvent under reduced pressure, the reaction solution obtained was analyzed by .sup.1H and .sup.13C NMR spectroscopy, using mesitylene as internal standard, and the yield of urea relative to formamide was determined.

[0079] The experiment was repeated a number of times, with the catalyst loading, solvent, reaction temperature and reaction time being varied as shown in table 1 below. Table 1 also shows the yield of urea obtained.

[0080] The catalyst loading is the amount of catalyst used in mol %, relative to the amount of formamide used (in mol).

TABLE-US-00001 TABLE 1 Ru-catalyzed synthesis of urea from formamide and ammonia* Catalyst Reaction Reaction loading temperature time Ex. [mol %] Solvent [° C.] [hours] Yield 1 1.00 1,4-Dioxane 150 5 44 2 1.00 1,4-Dioxane 150 10 64 3 1.00 1,4-Dioxane 150 15 57 4 1.00 1,4-Dioxane 130 10 12 5 1.00 1,4-Dioxane 110 10 1 6 0.50 1,4-Dioxane 150 10 26 7 0.25 1,4-Dioxane 150 10 14 8 1.00 Toluene 150 10 53 9 1.00 THF 150 10 47 *Reaction conditions: [Ru(triphos)(tmm)], 1 mmol formamide, 2 mL solvent, 0.5-1.0 g NH.sub.3

Example 10

Preparation of Ru(Triphos)(Tmm) In Situ for Synthesis of Urea

[0081] The catalyst Ru(triphos)(tmm) was formed in situ from the catalyst precursor [Ru(cod)(methylallyl).sub.2] and triphos.

[0082] For this, 1 mol % of [Ru(cod)(methylallyl).sub.2], 1.3 mol % of triphos, 1 mmol of formamide, 2 mL of 1,4-dioxane and 0.6 g of NH.sub.3 were reacted at 150° C. for 10 h. The pressure was about 8 bar in the cold state and about 30 bar at 150° C. The yield of urea was 51%.

Example 11

[0083] Synthesis of Urea from Formamide in the Absence of Ammonia

[0084] 1 mol % of [Ru(triphos)tmm], 1 mmol of formamide and 2 mL of 1,4-dioxane were reacted at 150° C. and 15 bar for 10 h. The yield of urea was 7%.

Examples 12 to 18

Catalytic Activity of Ru-Phosphine Complexes as a Function of the Ligands on the Phosphorus

[0085] The catalytic activity of various Ru-phosphine complexes in the synthesis of urea from formamide and ammonia was tested as a function of the ligands on the phosphorus. Table 2 indicates the complexes (catalysts) studied, the reaction conditions and the yields obtained. In the experiments the reaction pressure was about 30 bar at the reaction temperature and the pressure in the cold state was about 8 bar, except in ex. 15.

[0086] Ruthenium-triphosphine complexes with the following structure were studied:

##STR00008##

[0087] The nature of the substituent R is shown in table 2 below; where not all of the substituents R on the three phosphorus atoms are the same, the substituents R on a first P atom are identified as R.sup.1, on a second P atom as R.sup.2, and on a third P atom as R.sup.3. For example, the complex of ex. 17 has two phenyl groups on two phosphine groups, and the third phosphine group has two isopropyl groups.

[0088] The ruthenium-triphosphine complex additionally possesses the tridentate ligand trimethylenemethane.

[0089] The pressures reported in the table relate to room temperature (about 23° C.). The autoclave was charged at room temperature and then brought to reaction temperature and reaction pressure.

TABLE-US-00002 TABLE 2 Urea Ex. R = Reaction conditions yield 12 [00009] 1 mol % cat., 1 mmol formamide, 2 mL 1,4- dioxane, 0.6 g NH.sub.3, 150° C., 10 h 64% 13 [00010] 0.5 mol % cat., 1 mmol formamide, 2 mL 1,4- dioxane, 8 bar NH.sub.3, 150° C., 20 h 8% 14 [00011] 0.5 mol % cat., 1 mmol formamide, 2 mL 1,4- dioxane, 8 bar NH.sub.3, 150° C., 20 h 8% 15 [00012] 1 mol % cat., 2 mol % B(C.sub.6F.sub.5).sub.3, 1 mmol formamide, 2 mL 1,4- dioxane, 4 bar NH.sub.3, 150° C., 20 h 16% 16 [00013] 0.5 mol % cat., 1 mmol formamide, 2 mL 1,4- dioxane, 8 bar NH.sub.3, 150° C., 20 h 2% 17 R.sup.1, R.sup.2: 1 mol % cat., 1 mmol 30% [00014] formamide, 2 mL 1,4- dioxane, 8 bar NH.sub.3, 150° C., 20 h R.sup.3: [00015] 18 R.sup.1, R.sup.2: 0.2 mol % cat., 5 mmol 6% [00016] formamide, 4.0 g NH.sub.3, 150° C., 20 h R.sup.3: [00017]

Examples 19 to 21

Catalytic Activity of Ru-Phosphine Complexes as a Function of the Additional Ligands on Ruthenium (Nonphosphine Ligands)

[0090] The catalytic activity of various Ru-phosphine complexes in the synthesis of urea from formamide and ammonia was tested as a function of the nonphosphine ligands on the ruthenium. Table 3 indicates the complexes (catalysts) studied, the reaction conditions and the yields obtained. In the experiments the pressure was about 30 bar at the reaction temperature and the pressure in the cold state (room temperature) was about 8-10 bar. Example 19 corresponds to example 12.

[0091] Ruthenium-triphosphine complexes with the following structure were studied:

##STR00018##

[0092] The three ligands L are shown in table 3 below, with one ligand L being designated L.sup.1, a second ligand L L.sup.2, and a third ligand L L.sup.3. In example 19 the three ligands L are formed together by the tridentate ligand trimethylenemethane (tmm). The pressures reported in the table relate to room temperature (about 23° C.). The autoclave was charged at room temperature and then brought to reaction temperature and reaction pressure.

TABLE-US-00003 TABLE 3 Ex. L = Reaction conditions Urea yield 19 L: 1 mol % cat., 1 mmol 64% [00019] formamide, 2 mL 1,4-dioxane 0.6 g NH.sub.3, 150° C., 10 h 20 L.sup.1 = CO; 1 mol % cat., 1 mmol 18% L.sup.2 = H; formamide, 2 mL 1,4-dioxane, L.sup.3 = Cl 8 bar NH.sub.3, 150° C., 20 h 21 L.sup.1 = CO; 1 mol % cat., 1 mmol 24% L.sup.2, L.sup.3 = H formamide, 2 mL 1,4-dioxane, 0.7 g NH.sub.3, 150° C., 10 h

Examples 22 to 28

Catalytic Activity of Ru-Phosphine Complexes as a Function of Catalyst Concentration

[0093] The catalytic activity as a function of the catalyst concentration was tested for the following reaction conditions:

[0094] Catalyst: [Ru(triphos)(tmm)], 1 mmol formamide, 2 mL 1,4-dioxane, 0.6 g NH.sub.3, 150° C., 10 h, with the catalyst concentration being varied. The reaction pressure was about 30 bar at the reaction temperature and the pressure in the cold state was about 8-10 bar.

[0095] Table 4 indicates the catalyst concentration (in mol % based on formamide) used under these reaction conditions, and the yields obtained.

TABLE-US-00004 TABLE 4 Ex. c(cat.) [mol %] Urea yield [%] 22 0.05 <1 23 0.25 16 24 1 40 25 5 63

[0096] The catalytic activity as a function of the catalyst concentration was additionally tested for the following reaction conditions:

[0097] Catalyst: [Ru(triphos)(tmm)], 1 mmol formamide, 2 mL 1,4-dioxane, 4 bar NH.sub.3 at room temperature (around 23° C.), 150° C., 20 h, with the catalyst concentration being varied.

[0098] Table 5 indicates the catalyst concentration (in mol % based on formamide) used under these reaction conditions, and the yields obtained.

TABLE-US-00005 TABLE 5 Ex. c(cat.) [mol %] Urea yield [%] 26 0.25 25 27 0.5 30 28 2 33

Examples 29 to 35

Catalytic Activity of Ru-Phosphine Complexes as a Function of the Solvent Concentration

[0099] The catalytic activity as a function of the solvent concentration was tested for the following reaction conditions:

[0100] Catalyst: 1 mol % [Ru(triphos)(tmm)], 1 mmol formamide, 0.6 g NH.sub.3, 150° C., 10 h, with the solvent concentration being varied. The reaction pressure was about 30 bar at the reaction temperature and the pressure in the cold state was about 8-10 bar. The solvent was 1,4-dioxane.

[0101] Table 6 indicates the amount of 1,4-dioxane used under these reaction conditions, in ml (V(1,4-dioxane) [mL]), and the yields obtained.

TABLE-US-00006 TABLE 6 Ex. V(1,4-dioxane) [mL] Urea yield [%] 29 0.5 53 30 0.8 45 31 1.1 50 32 1.4 60 33 1.7 42 34 2.3 37 35 2.6 31