A PROCESS FOR THE SYNTHESIS OF AROMATIC CARBAMATES

Abstract

The present invention discloses a process for the synthesis of aromatic carbamates from amine with dialkyl carbonate in the presence of binary or ternary mixed metal oxide catalyst. The present invention further discloses the yield of said aromatic carbamate in the range of 60 to 99%. Further, the ratio of amine to dialkyl carbonate is in the range of 1:2 to 1:30.

Claims

1-10. (canceled)

11. A process for the synthesis of aromatic carbamate, the process comprising the step of reacting amine with dialkyl carbonate in the presence of a binary or ternary mixed metal oxide catalyst at a temperature in the range of 100 to 220 C. and for a period in the range of 1 to 15 hours to obtain corresponding aromatic carbamate, wherein yield of said aromatic carbamate is in the range of 60 to 99%.

12. The process as claimed in claim 11, wherein said process is carried out in presence of solvent.

13. The process as claimed in claim 11, wherein said amine is selected from compound of formula (I); ##STR00012## wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4 and R.sub.5 are same or different and are selected from hydrogen, alkyl, alkoxy, NH.sub.2, halide, NO.sub.2, ##STR00013##

14. The process as claimed in claim 13, wherein said amine is selected from aniline, 4-methylbenzene-1,3-diamine, 4,4-methylenedianiline, 2,4-dimethylaniline, 3,4-dimethylaniline, 2,6-dimethylaniline, 4-chloroaniline, 4-methoxyaniline, o-toluidine, m-toluidine, p-toluidine, toluene diamine or diaminodiphenyl methane.

15. The process as claimed in claim 11, wherein said dialkyl carbonate is selected from dimethyl carbonate or diethyl carbonate.

16. The process as claimed in claim 11, wherein said binary or ternary mixed metal oxide catalyst is X.sub.aY.sub.bZ.sub.cO.sub.d, wherein X is at least one metal selected from Group 3 elements, Y is at least one metal selected from transition metals of the Periodic Table, Z is at least one of the metal/metalloid selected from zirconium, aluminium and silica; a, b and c are the molar ratios of their respective components, a, b and c can vary from 0 to 3 respectively, and d is the number of oxygen atoms (O) necessary to satisfy the valence of the other components.

17. The process as claimed in claim 16, wherein said binary or ternary mixed metal oxide catalyst is selected from Ce:Zr, Zn:Zr, Y:Zr, Ce:Al, Zr:Y, Zn:Y, Zn:Al, Ni:Al, Co:Al, Ce:Fe, Zn:Fe, CeZnZr, Zn:Zr:Y, Y:Zn:Zr or La:Mg:Al.

18. The process as claimed in claim 17, wherein said catalyst is Ce.sub.3Zn.sub.0.5Zr.sub.1.

19. The process as claimed in claim 11, wherein the ratio of amine to dialkyl carbonate is in the range of 1:2 to 1:30.

20. The process as claimed in claim 11, wherein said aromatic carbamate is selected from N-methyl phenyl carbamate (MPC), dimethyl toluene-2,4,dicarbamate (TDC), methylene diphenyl-4,4-dicarbamate (MDC), methyl (2,4-dimethylphenyl)carbamate, methyl (3,4-dimethylphenyl)carbamate, methyl (2,6-dimethylphenyl)carbamate, methyl (4-chlorophenyl)carbamate, methyl (4-methoxyphenyl)carbamate, methyl o-tolylcarbamate, methyl m-tolylcarbamate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] FIG. 1: XRD patterns of Ce.sub.3Zn.sub.0.5Zr.sub.1 catalyst.

[0039] FIG. 2: (A) TEM image of Ce.sub.3Zn.sub.0.5Zr.sub.1 (B) SAED image of Ce.sub.3Zn.sub.0.5Zr.sub.1

DETAILED DESCRIPTION OF THE INVENTION

[0040] The present invention will now be described in preferred as well as optional embodiments so that the various aspects disclosed therein will be more clearly understood and appreciated.

[0041] In view of the above, the present invention provides a process for the synthesis of aromatic carbamate from amine and dialkyl carbonate in the presence of the mixed metal oxide catalyst of formula X.sub.aY.sub.bZ.sub.cO.sub.d, wherein X is at least one metal selected from Group 3 elements, Y is at least one metal selected from transition metals of the Periodic Table, Z is at least one of the metal/metalloid selected from zirconium, aluminium and silica; a, b and c are the molar ratios of their respective components, a, b and c can vary from 0 to 3 respectively, and d is the number of oxygen atoms (O) necessary to satisfy the valence of the other components.

[0042] In an embodiment, the present invention provides a process for the synthesis of aromatic carbamate comprises reacting amine with dialkyl carbonate in the presence of the binary or ternary mixed metal oxide catalyst at a temperature in the range of 100 to 220 C. for a period in the range of 1 to 15 hrs to obtain corresponding aromatic carbamate.

[0043] In one embodiment of the present invention, the process for the synthesis of aromatic carbamates is optionally carried out in presence of solvent.

[0044] In preferred embodiment, the solvent is selected from methanol or ethanol.

[0045] In another embodiment, the amine is selected from aromatic amine or substituted aromatic amine. Preferably, the amine is selected from compound of formula (I);

##STR00010##

[0046] Wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4 and R.sub.5 are same or different and are selected from hydrogen, alkyl, alkoxy, NH.sub.2, halide, NO.sub.2,

##STR00011##

[0047] In more preferred embodiment, the amine is selected from aniline, 4-methylbenzene-1,3-diamine, 4,4-methylenedianiline, 2,4-dimethylaniline, 3,4-dimethylaniline, 2,6-dimethylaniline, 4-chloroaniline, 4-methoxyaniline, o-toluidine, m-toluidine, p-toluidine, toluene diamine or diamine diphenyl methane, toluenediamine or diamonidiphenyl methane.

[0048] The dialkyl carbonate is selected from dimethyl carbonate or diethyl carbonate.

[0049] Ternary or binary metal oxides, (X.sub.aY.sub.bZ.sub.cO.sub.d) are used as catalysts for the synthesis of aromatic carbamates. X is at least one metal selected from Group 3 elements (including the Lanthanides and Actinides) i.e X is selected from cerium, samarium, lanthanum, yttrium, dysprosium, erbium, europium, gadolinium, holmium, lutetium, neodymium, praseodymium, promethium, scandium, terbium, thulium and ytterbium. And Y is at least one metal selected from transition metals of the Periodic Table, i.e zinc, cobalt, iron, manganese, nickel, tungsten or copper and Group 2 of the Periodic Table of Elements, such as magnesium, calcium, strontium or barium. Where Z is at least one of the metal/metalloid selected from zirconium, aluminium and silica; a, b and c are the molar ratios of their respective components, a, b and c can vary from 0 to 3 respectively, and d is the number of oxygen atoms (O) necessary to satisfy the valence of the other components.

[0050] The ternary/binary mixed metal oxides are synthesized by co-precipitation method followed by calcination at different temperatures in a range of 450 to 850 C. In a preferred embodiment, the synthesis of the ternary CeZnZr mixed metal oxide by co-precipitation method is disclosed. The molar ratio of Ce/Zr is 3:1 and concentration of Zn varied between 0-2.

[0051] CeZnZr mixed metal oxide is an efficient, stable, inexpensive and recyclable, heterogeneous catalyst. This catalyst is not dissociated under reaction conditions employed for the synthesis of carbamates.

[0052] In preferred embodiment, the binary or ternary mixed metal catalyst is selected from Ce:Zr, Zn:Zr, Y:Zr, Ce:Al, Zr:Y, Zn:Y, Zn:Al, Ni:Al, Co:Al, Ce:Fe, Zn:Fe, CeZnZr, Zn:Zr:Y, Y:Zn:Zr or La:Mg:Al.

[0053] The ratio of amine to dialkyl carbonate is in the range of 1:20 to 1:30 and the concentration of catalyst is in the range of 1-20 weight % of the amine.

[0054] The yield of the aromatic carbamate is in the range of 20 to 99% and preferably in a range of 60 to 99%.

[0055] The aromatic carbamate is selected from N-methyl phenyl carbamate (MPC), dimethyl toluene-2,4,dicarbamate (TDC), methylene diphenyl-4,4-dicarbamate (MDC), methyl (2,4-dimethylphenyl)carbamate, methyl (3,4-dimethylphenyl)carbamate, methyl (2,6-dimethylphenyl)carbamate, methyl (4-chlorophenyl)carbamate, methyl (4-methoxyphenyl)carbamate, methyl o-tolylcarbamate or methyl m-tolylcarbamate.

[0056] In a preferred embodiment, aromatic amines are reacted with DMC (aromatic amine:DMC mole ratio of 1:20), at catalyst concentration of 10 wt % relative to amine, for 2 h at 180 C. to obtain the corresponding aromatic N-methyl carbamates.

[0057] As shown in Table 2, aromatic amines screened are all compatible with this catalyst, leading to the corresponding N-methyl carbamates with good selectivity.

[0058] The process is carried out at 100 to 220 C. temperature with stirring speed in the range of 900 to 1200 rpm.

[0059] In another preferred embodiment, the present invention discloses synthesis of N-methyl phenyl carbamate from aniline and dimethyl carbonate using CeZnZr mixed metal oxide as a catalyst. The selectivity obtained towards MPC is greater than 90%.

[0060] The XRD pattern of Ce.sub.3Zn.sub.0.5Zr.sub.1 mixed metal oxide (MMO) catalyst is shown in FIG. 1. The peaks that appear at 28.8, 33.4, 48, 57 and 59.8 are the typical diffractions of Ce.sub.xZr.sub.1-xO.sub.2 material (PCPDF-28-0271). And the peaks related to ZnO appearing at 31.7, 34.4, 36.2, 47.4, 56.5, 68.9 and 67.8 (PCPDF-80-0075) was not observed indicating fine dispersion of ZnO on CeZr surface. XRD pattern of Ce.sub.3Zn.sub.0.5Zr.sub.1 material indicates the formation of crystalline structure with cubic symmetry.

[0061] To check the morphology and crystalline nature of the catalyst, TEM and SAED images of the catalyst is taken on carbon coated grid (FIGS. 2A and B). From FIG. 2A homogeneous distributions of small sized particles of 6-20 nm are observed. Poly crystalline nature of the synthesized material was observed from SAED image (FIG. 2B). The crystalline phases are in good agreement with the XRD pattern.

[0062] Further the reaction may be applied for the synthesis of MDC (methylenediphenyl dicarbamate) and TDC (Toluene dicarbamate) which are used in polyurethane foams.

Examples

[0063] Following examples are given by way of illustration and therefore should not be construed to limit the scope of the invention.

Example 1: General Process for Catalyst Preparation

[0064] Binary/Ternary mixed metal oxides were synthesized by co-precipitation method. The solution A contains binary or ternary mixture of metal precursors in appropriate molar ratios dissolved in distilled water. Solution B contains NaOH (1.2 M) and Na.sub.2CO.sub.3 (0.1 M) dissolved in distilled water. The solutions A and B were simultaneously added drop wise in 100 ml de-ionized water with vigorous stirring at 30 C. During addition, pH of the solution was maintained at 10-11 by addition of appropriate amount of solution B. The formed suspension was continuously stirred for 30 min and aged at 70 C. for 12 h. Finally the solid formed was separated by filtration and washed thoroughly with de-ionized water until pH of the water wash became neutral. Resultant solid was then dried at 100 C. for 12 h. The obtained solid power was calcined at 450-850 C. for 6 hours in air.

Example 2: Process for Preparation of Ce.SUB.3.Zn.SUB.0.5.Zr.SUB.1

[0065] Ternary Ce.sub.3Zn.sub.0.5Zr.sub.1 mixed metal oxides was synthesized by co-precipitation method. The solution A contains ternary mixture of metal precursors i.e Ce(NO.sub.3).sub.3.6H.sub.2O [30 mmol], Zn(NO.sub.3).6H.sub.2O [0.5 mmol], ZrO(NO.sub.3).sub.2.xH.sub.2O [10 mmol] dissolved in distilled water. Solution B contains NaOH (1.2 M) and Na.sub.2CO.sub.3 (0.1 M) dissolved in distilled water. The solutions A and B were simultaneously added drop wise in 100 ml de-ionized water with vigorous stirring at room temperature. During addition, pH of the solution was maintained at 10-11 by addition of appropriate amount of solution B. The formed suspension was continuously stirred for 30 min and aged at 70 C. for 12 h. Finally the solid formed was separated by filtration and washed thoroughly with deionized water until pH of the water wash became neutral. Resultant solid was then dried at 100 C. for 12 h. The obtained solid power was calcined at 550 C. for 6 hours in air.

[0066] Characterization of Ce.sub.3Zn.sub.0.5Zr.sub.1:

[0067] XRD:

[0068] The XRD pattern of Ce.sub.3Zn.sub.0.5Zr.sub.1 mixed metal oxide (MMO) catalyst is shown in FIG. 1. The peaks that appear at 28.8, 33.4, 48, 57 and 59.8 are the typical diffractions of Ce.sub.xZr.sub.1-xO.sub.2 material (PCPDF-28-0271). And the peaks related to ZnO appearing at 31.7, 34.4, 36.2, 47.4, 56.5, 68.9 and 67.8 (PCPDF-80-0075) was not observed indicating fine dispersion of ZnO on CeZr surface. XRD pattern of Ce.sub.3Zn.sub.0.5Zr.sub.1 material indicates the formation of crystalline structure with cubic symmetry.

[0069] TEM:

[0070] To check the morphology and crystalline nature of the catalyst, TEM and SAED images of the catalyst was taken on carbon coated grid (FIGS. 2A and B).

[0071] From FIG. 2A homogeneous distributions of small sized particles of 6-20 nm were observed. Poly crystalline nature of the synthesized material was observed from SAED image (FIG. 2B). The crystalline phases are in good agreement with the XRD pattern.

Example 3:Synthesis of Aromatic Carbamate (MPC)

[0072] The reaction of aniline and DMC was carried out in a 50 mL stainless autoclave (Parr reactor) with constant stirring. In a typical experiment aniline 16.64 mmol (1.55 m), DMC 333 mmol (30 m) and Ce.sub.3Zn.sub.0.5Zr.sub.1 mixed metal oxide catalyst 0.155 m (10 wt % relative to aniline), were charged to the reactor. The reactor was heated to 180 C. with slow stirring. The reaction was initiated by stirring the reactor at 900 rpm for desired time of 2 h. The reactor was cooled to 30 C., the catalyst was recovered by centrifugation, and the quantitative analysis of the reaction mixture was carried out using Agilent 6890 GC (FTD detector, Innowax column).

TABLE-US-00001 TABLE 1 Synthesis of MPC from aniline and DMC using different binary and ternary mixed metal oxides Conversion Selectivity Aniline MPC Sr. no. Catalyst (%) (%) 1 Ce:Zr (3:1) 50 56 2 Zn:Zr (3:1) 53 40 3 Y:Zr (3:1) 41.58 52 4 Ce:Al (3:1) 33 60 5 Zr:Y (3:1) 30.5 42 6 Zn:Y (3:1) 23.4 46 7 Zn:Al (3:1) 20.5 34.2 8 Ni:Al (3:1) 19.8 12.5 9 Co:Al (3:1) 26.3 58 10 Ce:Fe (3:1) 29.94 62 11 Zn:Fe (3:1) 31.58 42 12 Ce:Zn:Zr (3:0.5:1) 98.4 98.8 13 Zn:Zr:Y (3:0.5:1) 49 68 14 Y:Zn:Zr (3:0.5:1) 64 78 15 La:Mg:Al (3:0.5:1) 45 62 Reaction conditions: aniline: 1.55 gm, DMC: 30 gm, Catalyst: 10 wt % relative to aniline, Reaction Time: 2 h, Temperature: 180 C.

Example 4:Synthesis of Aromatic Carbamates Using Ce.SUB.3.Zn.SUB.0.5.Zr.SUB.1 .as the Catalyst

[0073] A set of aromatic amines were reacted with DMC under the optimized reaction conditions and the results of these experiments are presented in Table 2.

TABLE-US-00002 TABLE 2 Ce.sub.3Zn.sub.0.5Zr.sub.1 catalyzed synthesis of aromatic N-methyl carbamates Conversion Selectivity Entry Aromatic amine (%) (%) 1 O-Toluidine 82.5 94.2 2 m-Toluidine 86.8 95 3 p-Toluidine 89 95.7 Reaction conditions: Amine: 16.44 mmol, Amine: DMC = 1:20, Catalyst: 10 wt % relative to amine, Reaction Time: 2 h, Temperature: 180 C.

Example 5: Experimental Procedure for Recycle of CeZnZr Ternary Mixed Metal Oxide

[0074] Reaction of aniline and DMC was carried out as per the procedure described earlier. The catalyst from the reaction mixture was recovered by centrifugation, washed with DMC, and then dried overnight at 373 K for 12 h and calcined at 550 C./6 hin air. The recovered catalyst was used to perform a new reaction by charging aniline and DMC to the reactor. Catalyst was recycled two times using the same procedure and the results are presented in Table 3.

TABLE-US-00003 TABLE 3 Recycle study using CeZnZr ternary mixed metal oxide catalyst MPC Aniline Conversion (%) Selectivity (%) Fresh 98.4 98.8 Recycle 1 97.5 97.4 Recycle 2 94.1 97.2 Recycle 3 92 97.5 Recycle 4 91.4 96.6 Recycle 5 90.5 96 Reaction conditions: Amine: 16.44 mmol, Amine: DMC = 1:20, Catalyst: 10 wt % relative to amine, Reaction Time: 2 h, Temperature: 180 C.

Example 6: Synthesis of TDC

[0075] Reaction of TDA to TDC was carried out as per the procedure described earlier in example 3.

[0076] In this reaction TDA was used instead of aniline. The results are tabulated in table 4.

TABLE-US-00004 TABLE 4 Methoxycarbonylation of TDA to TDC Conversion Selectivity of TDC Entry Aromatic amine (%) (%) 1 TDA 96.8 18.6 2* TDA 79.2 5.7 Reaction conditions: TDA: 8.18 mmol, Amine: DMC = 1:30, Catalyst (Ce.sub.3Zn.sub.0.5Zr.sub.1): 30 wt % relative to TDA, Methanol (solvent) = 81.8 mmol, Reaction Time: 2 h, Temperature: 180 C. *Reaction conditions: TDA: 12.27 mmol, Amine: DMC = 1:30, Catalyst (Ce.sub.3Zn.sub.0.5Zr.sub.1): 10 wt % relative to TDA, Reaction Time: 2.5 h, Temperature: 190 C. In this reaction methanol was not used as solvent

Example 7: Synthesis of MDC

[0077] Reaction of DADPM to MDC was carried out as per the procedure described earlier in example 3. In this reaction DADPM was used instead of aniline. The results are tabulated in table 5.

TABLE-US-00005 TABLE 5 Methoxycarbonylation of DADPM to MDC Conversion Selectivity of MDC Entry Aromatic amine (%) (%) 1 DADPM 86.7 33.3 Reaction conditions: DADPM: 10.08 mmol, Amine: DMC = 1:30, Catalyst (Ce.sub.3Zn.sub.0.5Zr.sub.1): 30 wt % relative to DADPM, Methanol (solvent) = 100 mmol, Reaction Time: 3 h, Temperature: 180 C.

Example 8: Methoxycarbonylation of Aniline with Ce.SUB.3.Zn.SUB.0.5.Zr.SUB.1 .Catalyst

[0078] Reaction of aniline and DMC was carried out as per the procedure described earlier in example 3. The effect of various reaction parameters on the reaction conversion and selectivity such as effect of catalyst loading, effect of aniline:DMC molar ratio, effect of temperature is tabulated in table 6, 7 and 8 respectively.

TABLE-US-00006 TABLE 6 Effect of catalyst loading Catalyst Aniline loading Time conversion Selectivity (%) Entry (wt %) (h) (%) MPC MMPC NMA NNDMA 1 0 2 0 NA NA NA NA 2 5 2 87 95.8 1 2.3 0.39 3 10 2 98.4 98.6 0.1 1.2 0.09 4 15 2 96.3 96.6 1.6 1.5 0.2 Reaction conditions: Aniline: 1.55 gm, DMC: 30 gm, Aniline/DMC: 1/20, Catalyst(Ce.sub.3Zn.sub.0.5Zr.sub.1): 5-15 wt % relative to aniline, Reaction Time: 2 h, Temperature: 180 C.

TABLE-US-00007 TABLE 7 Effect of aniline: DMC molar ratio Molar Aniline ratio con- Selectivity (%) Aniline: Time version MPC Entry DMC (h) (%) sel. MMPC NMA NNDMA 1 1:5 2 96.6 87 2.6 7 3.2 2 1:10 2 89 93.2 0.67 3.4 0.8 3 1:20 2 98.4 98.6 0.1 1.2 0.09 Reaction conditions: Aniline: DMC molar ratio 1:5 to 1:20, Catalyst (Ce.sub.3Zn.sub.0.5Zr.sub.1): 10 wt %, Reaction Time: 2 h, Temperature: 180 C.

TABLE-US-00008 TABLE 8 Effect of Temperature Reaction Time Aniline Selectivity (%) Entry temperature (h) conv. (%) MPC MMPC NMA NNDMA 1 170 2 80.5 97 0.6 2.2 0.2 2 180 2 98.4 98.6 0.1 1.2 0.09 3 190 2 97.5 96 1.6 1.9 1 Reaction conditions: Aniline: 1.55 gm, DMC: 30 gm, Aniline/DMC:1/20, Catalyst (Ce.sub.3Zn.sub.0.5Zr.sub.1): 10 wt % relative to aniline, Reaction Time: 2 h, Temperature: 170-190 C.

ADVANTAGES OF THE INVENTION

[0079] Recyclability of the catalyst [0080] No leaching of catalyst during recovery process [0081] High conversion of starting materials