METHOD FOR CONVERTING MONOISOCYANATES TO UREAS

Abstract

Organic isocyanates are converted to ureas by heating in the presence of certain cobalt, magnesium, chromium and lanthanide series organometallic catalysts. The process requires no water or other reactants. The process is particularly useful for removing small quantities of monoisocyanates from a solvent stream recovered from a polyisocyanate manufacturing process. The urea compounds in some instances can be recycled back into the polyisocyanate manufacturing process and reacted with polyisocyanate compounds to form biurets.

Claims

1. A method for converting an organic isocyanate comprising a phenyl isocyanate to one or more urea compounds in the presence of a non-polar organic solvent, comprising reacting a solution of the organic isocyanate in a liquid nonpolar solvent in the presence of at least 0.025 wt.-% of a organometallic catalyst, based on the weight of the organic isocyanate, wherein the organometallic catalyst includes at least one metal ion bonded to at least one organic ligand and the metal ion is selected from one or more of Co(II), Mg(II), Y(III), Cr(III) and a lanthanide series metal ion in the 3+ oxidation state, to convert at least a portion of the organic isocyanate to the one or more urea compounds.

2. The method of claim 1 wherein the metal ion is Co(II) or Mg(II).

3. The method of claim 2 wherein at least one organic ligand is an arene ligand.

4. The method of claim 3 wherein the arene ligand is cyclopentadienyl or methylcyclopentadienyl.

5. The method of claim 1 wherein the metallic catalyst is one or more of bis(cyclopentadienyl) Co(II), bis(cyclopentadienyl) Mg(II), bis(cyclopentadienyl) Cr(II), tris(cyclopentadienyl) Gd(III), tris(cyclopentadienyl) Y(III), tris(cyclopentadienyl) La(III), tris(cyclopentadienyl Ru(III), bis(methylcyclopentadienyl) Co (II), bis(methylcyclopentadienyl) Mg(II), bis(methylcyclopentadienyl) Cr(II), tris (methylcyclopentadienyl) Gd(III), tris (methylcyclopentadienyl) Y(III), tris(methylcyclopentadienyl) La(III), tris(methylcyclopentadienyl) Ru(III), a tris(cyclopentadienyl) lanthanide serial metal and a tris(methylcyclopentadienyl) lanthanide series metal.

6. The method of claim 2 wherein at least one organic ligand is a β-diketone.

7. The method of claim 6 wherein the metallic catalyst is one or more of Co(II) acetylacetonate and bis(2,4-pentanedionato) Mg(II).

8. The method of claim 1 wherein the organic isocyanate includes phenyl isocyanate.

9. The method of claim 1 wherein the solution of the organic isocyanate in a liquid nonpolar solvent is or includes a process stream from an isocyanate manufacturing process, which process stream is obtained by separating a process solvent from a polyisocyanate product produced by reacting a polyamine with phosgene in solution in the process solvent.

10. The method of claim 9 wherein the polyamine is MDA and/or PMDA.

11. The method of claim 10 wherein at least a portion of the one or more urea compounds is recycled into the isocyanate manufacturing process and reacted with a polyisocyanate to form one or more biuret compounds.

12. The method of claim 11 wherein the step of reacting the one or more urea compounds with the polyisocyanate to form one or more biuret compounds is performed during a step of separating the polyisocyanate product from the process solvent.

13. The method of claim 1 further comprising the step of separating at least a portion of the one or more organic solvents from the one or more urea compounds.

14. An MDI and/or polymeric MDI manufacturing process, comprising the steps of: a) reacting aniline with formaldehyde to produce a mixture of methylene dianiline (MDA), one or more polymethylene polyanilines having at least three aniline groups (PMDA) and unreacted aniline in the solvent; b) distilling aniline from the mixture produced in step a) to produce a process stream containing the MDA, PMDA and residual aniline; c) phosgenating the process stream from step b) in a non-polar solvent to form an isocyanate process stream containing the non-polar solvent, MDI, one or more polymethylene polyphenylisocyanates that have at least three phenyl isocyanate groups (PMDI) and phenyl isocyanate; d) separating MDI and PMDI from the isocyanate process stream obtained in step c) by distillation to produce a solvent stream containing the non-polar solvent, 0.2 to 10 weight percent phenyl isocyanate based on the weight of the solvent stream and up to 5 weight percent, based on the weight of the solvent stream, of MDI and/or PMDI; e) reacting the solvent stream obtained in step d) in the presence of at least 0.025 wt.-% of an organometallic catalyst, based on the weight of the phenyl isocyanate, wherein the organometallic catalyst includes at least one metal ion bonded to at least one organic ligand and the metal ion is selected from one or more of Co(II), Mg(II), Y(III), Cr(III) and a lanthanide series metal ion in the 3+ oxidation state, to convert at least a portion of the phenylisocyanate to 1,3-diphenylurea and optionally aniline, and optionally to thermally deactivate the organometallic catalyst; and f) recycling 1,3-diphenylurea, aniline, and optionally non-polar solvent and optionally residues from the thermal deactivation of the catalyst, from step e) directly or indirectly into step d), whereby at least a portion of the 1,3-diphenylurea reacts with at least a portion of the MDI and/or PMDI to form biuret compounds and at least a portion of the aniline, if any, reacts with least a portion of the MDI and/or PMDI to form urea compounds.

Description

EXAMPLES 1-4

[0060] General procedure: A standard solution of about 2 wt.-% phenyl isocyanate in chlorobenzene is prepared. A sample of the standard solution is combined with the catalyst under nitrogen in a 3 neck, 100 milliliter, round bottom, glass reactor equipped with a chilled condenser (0° C.), thermocouple/heating mantle/temperature controller assembly, overhead nitrogen inlet (0.2 LPM), and magnetic stirring. The resulting mixture is heated over 9-12 minutes to 80° C. and maintained at that temperature. The reaction is followed by taking samples periodically and analyzing them for phenyl isocyanate, aniline, and 1,3-diphenylurea, using an externally calibrated gas chromatograph.

[0061] In each of Examples 1-4, the catalyst is bis(cyclopentadienyl)cobalt (II). The amount of catalyst (as a percentage of the weight of phenyl isocyanate solution) is as reported in Table 1.

TABLE-US-00001 TABLE 1 Example Catalyst Concentration, wt-% 1 Bis(cyclopentadenyl) Co(II) 0.365% 2 Bis(cyclopentadenyl) Co(II) 0.16% 3 Bis(cyclopentadenyl) Co(II) 0.048% 4 Bis(cyclopentadenyl) Co(II) 0.0385%

[0062] In each case, the amount of phenyl isocyanate is reduced by greater than 50% within a few minutes after the start of the reaction. After 5-6 hours of reaction time, the concentration of phenyl isocyanate is reduced to about 0.06% or less in each case. A similar amount of aniline is detected at that time. A strong 1,3-diphenylurea peak is detected in each case beginning at about 30-40 minutes of reaction time.

[0063] The reaction solutions from Examples 2 and 4 are each subjected to further processing to thermally deactivate the catalyst. In each case, the solution is heated to reflux (133.7-133.9° C.) over 13 minutes. Some fine brown particles are observed suspended in the solution, indicating that the catalyst has been thermally deactivated. After 3 hours heating at reflux, heating is discontinued and the reactor is allowed to cool to room temperature. Chlorobenzene is removed from each of the resulting solutions using a rotary evaporator operated to final conditions of 75° C. and 0.9-1.6 mm Hg. In each case, a brown solid is recovered, which consists mainly of 1,3-diphenylurea, and deactivated catalyst residues.

[0064] 0.5 parts of solids thus obtained in each case are combined under nitrogen with 100 parts of a commercial grade polymeric MDI (PAPI™ 27, from The Dow Chemical Company) at a weight ratio. The solution is heated over 35 minutes to 100° C. and held at that temperature for 20 minutes, further heated to 125° C. over 16 minutes, and held at that temperature for 1 hour. Biuret compounds form under these conditions as confirmed by Matrix-Assisted Laser Desorption/Ionization Mass Spectral (MALDI-TOF MS) analysis. The solutions are in each case then cooled to 109° C. and vacuum filtered. The supernatant fluid is a transparent amber brown colored solution that is liquid at room temperature.

[0065] The isocyanate content of the supernatant liquid is determined by titration. For comparison, a quantity of the polymeric MDI is heated in similar manner by itself, and its isocyanate content then measured. Viscosity is measured using a cone-and-plate viscometer with a 40 mm cone and 54 μm gap at 25.6° C. and 100° C. Number and weight average molecular weights are measured by gel permeation chromatography against a 1000 mw polyethylene glycol standard. Results are as indicated in Table 2.

TABLE-US-00002 TABLE 2 Isocyanate Viscosity, content Pa .Math. s, M.sub.n/M.sub.w/ Designation (wt.-%) 25.6° C./100° C. Polydipersity Polymeric MDI 32.65 0.20/0.01 450/574/1.276 Polymeric MDI 31.73 0.22/0.01 449/578/1.286 biuret-modified with Ex. 2 Polymeric MDI 31.91 0.25/0.01 452/581/1.286 biuret-modified with Ex. 4

[0066] As the data in Table 2 shows, modifying a polymeric MDI with a small (in this case, 0.5 wt-%) amount of the 1,3-diphenylurea containing residues from the deactivation of the organometallic catalyst results in at most a very small change in isocyanate content, viscosity and molecular weight. Isocyanate functionality is also essentially unchanged. The data also demonstrates that the residues from the deactivated organometallic catalyst have little, if any, effect on the properties of the polymeric MDI. This data indicates that biuret-modified polyisocyanates produced by reaction with a small quantity 1,3-diphenylurea are useful in the same manner and in the same applications as the unmodified polyisocyanates.

EXAMPLES 5-6

[0067] The general procedure is repeated, replacing the cobalt catalyst of Examples 1˜4 with various quantities of bis(cyclopentadienyl)magnesium (II). The amount of catalyst and results are as indicated in Table 3:

TABLE-US-00003 TABLE 3 Bis(cyclo- Desig- pentadienyl) nation Mg (II), wt.-% Results 5 0.36 Phenyl isocyanate and aniline levels are each below 0.1 wt.-% after 300 minutes; large 1,3-diphenylurea peak detected. 6 0.076 Phenyl isocyanate concentration reduces to 1.47 wt.-% with 0.02 wt.-% aniline after 2 hours and further to 0.93 wt-% phenyl isocyanate and 0.03 wt.-% aniline after 23 hours; 1,3-diphenylurea peak detected.

[0068] The data in Table 3 demonstrates the effect of catalyst concentration.

EXAMPLE 7

[0069] The general procedure is repeated using a concentration of 0.020 wt.-% bis(cyclopentadienyl)magnesium (II). The solution is heated over 16 minutes to reflux (133° C.) and sampled for externally calibrated gas chromatographic analysis, demonstrating a decrease in phenyl isocyanate from 1.99 to 1.80 w.-%, with no aniline detected. Some fine orange particles are observed suspended in the solution, indicating that the catalyst has been thermally deactivated. After heating at reflux for an additional 6 hours phenyl isocyanate and aniline concentrations are unchanged.

[0070] The general procedure is repeated using a concentration of 0.012 wt.-% bis(cyclopentadienyl)magnesium (II). The solution is heated over 12 minutes to 80° C. and sampled for externally calibrated gas chromatographic analysis after holding at 80° C. for 7 hours, demonstrating a decrease in phenyl isocyanate from 2.06 to 1.74 w.-%, with 0.014 w.-% aniline detected. After heating at reflux for an additional 16.35 hours phenyl isocyanate decreases to 1.44 w.-% with 0.022 w.-% aniline detected.

[0071] The results demonstrate thermal deactivation of the bis(cyclopentadienyl)magnesium (II) catalyst at 133° C., with no additional decrease in phenyl isocyanate concentration after this temperature is achieved. Even when a lower catalyst concentration (0.012 wt.-%) is employed, phenyl isocyanate concentration continues to decline at 80° C.

EXAMPLES 8-13 AND COMPARATIVE SAMPLES C-N

[0072] The general procedure is repeated, substituting other catalysts for the catalyst of Examples 1-4. Results are as indicated in Table 4.

TABLE-US-00004 TABLE 4 Desig- Wt.-% nation Catalyst Catalyst Result  8 Bis(cyclopentadienyl) 0.36 Phenyl isocyanate concen- Cr(II) tration < 1.4 wt.-% after about 5 hours.  9 Tris(cyclopentadienyl) 0.36 Phenyl isocyanate concen- Gd (III) tration < 1.4 wt.-% after about 3 hours. 10 Co(II) acetylacetonate 0.36 Phenyl isocyanate concen- tration < 1.3 wt.-% after about 5 hours. 11 Tris(cyclopentadienyl) 0.36 Phenyl isocyanate concen- Y(III) tration < 1.5 wt.-% after about 71 minutes. 12 Bis(2,4- 0.36 Phenyl isocyanate concen- pentanedionato) tration < 1.4 wt. % after Mg(II) about 190 minutes. 13 Tris(cyclopentadienyl) 0.36 Phenyl isocyanate concen- La(III) tration < 1 wt-% within 129 minutes. C* Bis (cyclepentadienyl) 0.17 No reaction after over 5 Fe(II) hours. D* Bis (cyclopentadienyl) 0.36 No reaction after 6 hours. Fe(II) E* Methylcyclopentadienyl 0.36 No reaction after 7 hours. Mn(I) tricarbonyl F* Bis(cyclopentadienyl) 0.36 No reaction after 7 hours. Ru(II) G* Bis(cyclopentadienyl) 0.36 Minimal reaction after 6 V(II) hours. H* Bis*cyclopentadienyl) 0.36 No reaction after 7 hours. Mo(IV) dichloride I* Fe(II) acetylacetonate 0.36 No reaction after 7 hours. J* Co(III) acetylacetonate 0.36 No reaction after 7 hours. K* Cyclopentadienyl Co(I) 0.36 No reaction after 7 hours. dicarbonyl L* Bis(cyclopentadienyl 0.36 Minimal reaction after 400 Ni(II) minutes. M* Bis(cyclopentadienyl) 0.36 Minimal reaction after 435 dimethyl Zr (IV) minutes. N* Co(II) chloride 0.36 No reaction after 4½ hours. O* Cobalt (II) 0.05 No reaction after 2½ hours, phthalocyanine at 80° C. or 2 hours addi- tional at 134° C.

[0073] The data in Table 4 shows the effect of catalyst selection. The Cr(II), Gd(III), Y(III), and La(III) cyclopentadienyl compounds all exhibit significant activity. Co(II) and Mg(II), when complexed with dione ligands, also exhibit significant activity.

[0074] Surprisingly, the Co(I) and Co(III) compounds tested do not exhibit catalyst activity in this reaction, suggesting that the oxidation state of those metals is important to their catalytic performance. Similarly, the inorganic Co(II) salt (cobalt dichloride) perform poorly, suggesting that the organic ligand is important to catalytic activity. Likewise Co (II) phthalocyanine dp not exhibit catalytic activity, apparently due to partial bonding between the Co(II) and the nitrogen atoms of the phthalocyanine.

[0075] Other organometallic catalysts tested perform poorly or not at all.

Recycling Method Model Reaction

[0076] To further simulate and evaluate the effect of recycling urea compounds and aniline obtained in the process of the invention, the following model reaction is performed.

[0077] Aniline (0.248 gram, 2.663 milliequivalents amine) in chlorobenzene (8.01 grams) is combined with a solution prepared by combining 0.05 wt-% diphenylmethane diisocyanates (MDI), 2 wt-% phenyl isocyanate, and 97.95 wt-% chlorobenzene (25.072 grams, 4.309 NCO milliequivalents). The diphenylmethane diisocyanates used are an approximate 50 wt-% 4,4′- and 50 wt-% 2,4′-isomer mixture. After holding at reflux, followed by cooling, vacuum filtration of the slurry on a fritted glass funnel, and drying at 100° C. in the vacuum oven, a white powder is recovered.

[0078] Matrix Assisted Laser Desorption Ionization Mass Spectrometry (MALDI)-Orbitrap analysis of a portion of the reaction product is completed, examining the region from 50-650 Daltons (Da). The major peak intensities are due to (DPU)H.sup.+ at 213.1022 Da and (DPU)Na.sup.+ at 235.0842 Da (DPU=diphenylurea). The minor peak intensities are due to (aniline)H.sup.+ at 94.0651 Da, (DPU with a single biuret linkage)Na.sup.+ at 354.1213 Da, (bis[urea]MDI)Na.sup.+ at 459.1792 Da, and (bis[urea]MDI with a single biuret linkage)Na.sup.+ at 578.2163 Da.

[0079] This data confirms the reaction products of the process of the invention form mainly compounds having a single biuret linkage or none at all. A portion of the 1,3-diphenylurea produced in the inventive process does not react further under these conditions.