Organic compounds -- part of the class 532-570 series – Organic compounds – Isocyanate esters
Reexamination Certificate
1999-12-14
2002-11-26
Rotman, Alan L. (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Isocyanate esters
C560S342000, C568S932000
Reexamination Certificate
active
06486346
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an improved process for the preparation of 2,3,5,6-tetramethyl-1,4-diisocyanatobenzene (hereinafter referred to as “durene diisocyanate”) by (1) reaction of 1,2,4,5-tetramethyl-benzene (hereinafter referred to as “durene”) with nitric acid in sulfuric acid, (2) catalytic hydrogenation of the resultant 2,3,5,6-tetramethyl-1,4-dinitrobenzene (hereinafter referred to as “dinitrodurene”), and (3) phosgenation of the resultant 2,3,5,6-tetramethyl-1,4-diaminobenzene (hereinafter referred to as “durene diamine”).
The preparation of durene diisocyanate is known. One of the known processes is described in British Patent Specification 779,806. In accordance with British Patent 779,806, durene diamine is dissolved in chlorobenzene, then reacted with gaseous hydrogen chloride to form durene diamine dihydrochloride, and the latter is further reacted as a suspension in chlorobenzene with phosgene at elevated temperature.
Durene diamine has been known for a long time and is normally prepared from dinitrodurene by reduction. The hydrogenation of dinitrodurene to durene diamine in ethanol with the addition of Raney nickel as catalyst is described, for example, in the
Journal of the American Chemical Society,
Vol. 70, p. 2227 and Vol. 72, p. 132.
Dinitrodurene has similarly been known for a long time and is normally prepared by nitration of durene. An improved process for the preparation of dinitrodurene is described in U.S. Pat. No. 3,153,099. In accordance with U.S. Pat. No. 3,153,099, a suspension of durene inconcentrated aqueous sulfuric acid is reacted with a nitric acid-sulfuric acid-water mixture in the absence of organic solvents at temperatures from 5° to 10° C., the resultant suspension is then stirred into an ice-water mixture and the dinitrodurene is filtered off, washed with water, and dried at 60° to 70° C.
U.S. Pat. No. 3,153,099 teaches, the obvious procedure of dissolving durene in an organic solvent and subjecting this solution to a nitration has a considerable number of disadvantages. The most significant of these disadvantages are the small yields of dinitrodurene and the large amounts of by-products. These disadvantages are illustrated in Example 1 (comparison example) of the present patent specification.
Admittedly, the nitration of durene in sulfuric acid suspension represents an improvement over the nitration of a solution in an organic solvent. However, the process described in U.S. Pat. No. 3,153,099 has serious disadvantages. For example, the reaction temperature range of 5° to 10° C., which is said to be preferred, results in uneconomically long reaction times. This is also confirmed by Example 2 (comparison example) of the present patent specification.
A further disadvantage of the process disclosed in U.S. Pat. No. 3,153,099 is that the end reaction mixture is stirred into an ice-water mixture. Although this use of ice to dilute concentrated sulfuric acid with water in order to control the heat of mixing that is generated is a conventional and practicable method for laboratory scale operations, it is unsuitable for large-scale production processes. This method requires the availability and handling of large amounts of ice, coupled with the considerable technical effort and expenditure involved in producing and transporting the ice. This method also requires processing the ice in large capacity containers, optionally using comparatively powerful stirrer motors. One of the consequences of this process step is that all of the sulfuric acid used for the reaction becomes diluted and must either be disposed of as a valueless waste acid or be reconcentrated (a complicated and expensive process).
A further disadvantage of the process described in U.S. Pat. No. 3,153,099 is that the crude dinitrodurene filtered off is purified only by washing with water. Consequently, impurities such as sulfuric acid trapped in the dinitrodurene particles are not separated. On the other hand, a minimum quality of the dinitrodurene is necessary, especially if the dinitrodurene is to be used to produce durene diamine by reduction as taught at column 3, lines 47 to 50. This generally means that the dinitrodurene that is prepared must be purified in a further process step, for example, by recrystallization.
Only catalytic hydrogenation is technically feasible as a commercial process for the reduction of dinitrodurene to durene diamine. Although other known processes, such as the conversion of dinitrodurene with ammonium sulfide, with zinc or with tin (II) chloride are suitable for conversions on a laboratory scale, for economic and ecological reasons they are unsuitable for large-scale preparation of durene diamine.
The known processes for catalytic hydrogenation in a protic solvent such as ethanol have the disadvantage as regards the conversion of durene diamine with phosgene that the solvent must be substantially completely removed from the reaction mixture. If the solvent is not substantially removed, undesirable reaction products of the solvent with phosgene will be formed during the phosgenation. This means that the solution of durene diamine must be completely evaporated in a complicated process step and the remaining solid durene diamine then must be re-dissolved in an aprotic solvent.
The process described in British Patent 779,806 for the preparation of durene diisocyanate by reacting durene diamine dihydrochloride with phosgene is also affected by serious disadvantages. For example, preparation of durene diamine dihydrochloride using gaseous hydrogen chloride is costly and time-consuming. Likewise, the reaction of the dihydrochloride with phosgene in suspension is laborious and also results in contamination of the process waste gas with comparatively large amounts of hydrogen chloride.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a technical process for the preparation of durene diisocyanate.
It is also an object of the present invention to provide a process for the production of durene diisocyanate in higher yields without uneconomically long reaction times.
It is a further object of the present invention to provide a process for the production of durene diisocyanate without generating large quantities of waste and by-products.
It is an additional object of the present invention to provide a process for the production of durene diisocyanate that does not require considerable technical effort and expenditure.
It is a further object of the present invention to provide a process for the production of durene diisocyanate in which the individual reaction steps and process stages are matched to one another.
These and other objects which will be apparent to those skilled in the art are accomplished by (1) reacting durene with nitric acid in the presence of sulfuric acid. (2) diluting the resultant reaction mixture with water to form a suspension; (3) mixing the resultant suspension with an aprotic organic solvent to dissolve the dinitrodurene and to form two liquid phases; (4) separating the liquid phases to recover a solution of dinitrodurene in organic solvent; (5) hydrogenating the dinitrodurene in the presence of a catalyst; (6) removing water and catalyst from the hydrogenated mixture; and (7) phosgenating the diaminodurene from (5).
DETAILED DESCRIPTION OF THE INVENTION
The present invention is an improved process for the preparation of durene diisocyanate by reaction of durene with nitric acid in sulfuric acid, catalytic hydrogenation of the dinitrodurene that is formed, and phosgenation of the resultant durene diamine. In this process, after the reaction of durene with nitric acid in sulfuric acid has been completed, the liquid phase of the reaction mixture, which is composed substantially of sulfuric acid, is diluted by mixing it with water. The resultant suspension is intensively mixed with an aprotic organic solvent that is substantially immiscible with water and is inert with respect to hydrogen to dissolve the dinitrodurene in the solvent and form a mixture composed of two liquid pha
Heitkämper Peter
Jost Klaus
Penninger Stefan
Bayer Aktiengesellschaft
Gil Joseph C.
Oh Taylor V.
Rotman Alan L.
Sloane Carolyn M.
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