Organic compounds -- part of the class 532-570 series – Organic compounds – Isocyanate esters
Reexamination Certificate
2000-09-19
2004-08-24
Seaman, D. Margaret (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Isocyanate esters
C560S345000
Reexamination Certificate
active
06781010
ABSTRACT:
TECHNICAL FIELD
The present invention pertains to the industrial production of organic isocyanates.
BACKGROUND ART
Organic isocyanates have widespread industrial use. The isocyanates manufactured in the largest volume are the organic di- and polyisocyanates employed in polymer manufacture, particularly in the production of polyurethanes, polyurethane/ureas, polyisocyanurates, and related polymers. However, monoisocyanates are useful as well, particularly as intermediates in the pesticide, pharmaceutical, and fine chemical industries. The term “isocyanate” herein refers to monoisocyanates and to di- and polyisocyanates, unless indicated to the contrary.
Both aryl as well as aliphatic isocyanates are useful. Aryl isocyanates such as 2,4- and 2,6-toluene diisocyanate (TDI) and 4,4′-diphenylmethane diisocyanate (MDI) dominate isocyanate production because of cost considerations, their reactivity profiles, and their use in polyurethane molded and slabstock foam. However, aliphatic isocyanates such as 1,6-hexane diisocyanate and isophorone diisocyanate are particularly useful where high photolytic stability is desired, and where a flexible aliphatic hydrocarbon chain is desired, for example in paints and coatings.
The manufacture of most commercial isocyanates involves reaction of the corresponding primary amine with phosgene to form the carbamoyl chloride followed by thermolysis to the isocyanate. In the process, two molecules of hydrogen chloride are generated for each isocyanate group created. This byproduct, as hydrochloric acid, has limited commercial value. Additionally, the phosgene used in isocyanate production is expensive and quite hazardous. Hence, the industry has long sought viable non-phosgene methods of isocyanate production. A wide variety of such methods have been proposed, but all thus far have significant drawbacks which, with the exception of isophorone diisocyanate production, have prevented their commercial use.
Numerous processes involve condensation reactions with urea or urea precursors to form a variety of ureas and carbamates, often complex mixtures containing oligomeric or even polymeric species as well. The ureas or carbamates are then pyrolyzed to produce the isocyanate. The pyrolysis of O-substituted carbamates is reasonably efficient. However, to be efficient overall, precursor synthesis must be efficient as well.
Typical of processes suggested for manufacture of thermolyzable carbamate isocyanate precursors is the reaction of amines with dialkylcarbonate in the presence of a suitable catalyst. For example, PCT published application WO 99/47493 discloses the reaction of amines with organic carbonates in excess, preferably in the presence of a heterogenous metal based catalyst. However, yields appear to be quite low.
U.S. Pat. Nos. 4,713,476; 4,611,079; and 4,851,565, disclose the co-condensation of aryl or aliphatic di- or polyamines with urea and excess alcohol to produce di- or poly(O-alkyl) carbamates. A variety of substituted ureas and other products are also produced. Some of the byproducts are necessarily recycled back to the process in order to raise the overall efficiency and diminish waste production. Thus, the overall process is complicated and requires numerous separation and purification steps. Nevertheless, such a process is believed currently employed in the production of isophorone diisocyanate (IPDI).
In U.S. Pat. No. 3,960,914, alkyl or aryl fomamides are converted directly to isocyanates in the presence of precious metal catalysts. However, the reaction proceeds with both low yield and low selectivity. Numerous byproducts are also produced. In U.S. Pat. Nos. 5,155,267 and 5,686,645, asymmetric substituted ureas and carbamates are prepared by reaction of a primary formamide with a dialkylamine or an alcohol in the presence of large amounts of Group VIII transition metal catalyst. Although the yields of disubstituted ureas are relatively high, carbamates are produced in only low yields. The large amount of expensive precious metal catalyst is a considerable disadvantage when commodity isocyanate production is contemplated.
It would be desirable to provide a non-phosgene method of producing isocyanates and their direct precursors on an industrial scale, employing readily available starting materials, which produces the desired products in high yield and with efficient recycling of byproducts.
DISCLOSURE OF INVENTION
It has now been surprisingly discovered that organic isocyanates may be obtained directly by the synthesis and thermolysis of the reaction product of the corresponding formamide and a diorganocarbonate. Major byproducts may themselves be thermolyzed to isocyanates or may be recycled to generate additional raw materials. Thus, the overall process is efficient and generates little waste.
BEST MODE FOR CARRYING OUT THE INVENTION
The process of the present invention is directed to the synthesis of organic isocyanates and substituted O-carbamate analogs by the reaction of an organic formamide with a diorganocarbonate. In the specification which follows, terms such as “corresponding amine”, “corresponding isocyanate” and like terms pertain to related compounds of the same structure but with different functional groups obtained by reaction of the “corresponding” functional group. Thus, 2,4-toluene diamine (1) is the “corresponding amine” to 2,4-toluene diamine bis(formamide) (2), 2,4-toluene dilsocyanate (3), and 2,4-toluene diamine bis(organocarbamate) (4). These “corresponding” compounds are represented structurally below, from which their chemical relationship may easily be discerned.
In the overall process of the present invention, a formamide, i.e., (2) generates the corresponding isocyanate (3) as well as a lesser quantity of the corresponding O-organocarbamate (4) which itself may be pyrolyzed to additional isocyanate (3). The amine (1) may serve as a starting raw material for the production of the formamide (2).
The formamides useful in the subject invention are aliphatic and aryl formamides with at least one formamide group. While there is no theoretical upper limit to the number of formamide groups, it is preferable that the starting formamide contain from 1 to 10 formamide groups, more preferably 1 to 5, and most preferably 2 to 4 formamide groups. Mixtures of compounds such as the formamides of polymethylenepolyphenylenepolyamines having structure
where n is 0 to 10 or higher are useful, for example. In such mixtures, the largest population of molecules are those with values of n from 0 to 4, with n=0 and n=1 generally predominating.
Thus, the formamides preferably correspond to the formula
R&Parenopenst;NHCHO)
n
where n is an integer of at least 1, preferably in the range of 1 to 10, more preferably in the range of 1-5, and most preferably in the range of 2-4.
The organo group R may be any organic group to which the formamide groups may be bound in a stable fashion such that they may be handled in an industrial setting. Non-limiting organo groups R include aryl groups; alkaryl groups; aralkyl groups; linear, branched, and cyclic aliphatic groups, both saturated and unsaturated; and any of the foregoing groups substituted with non-interfering substituents or having ring or chain interspersed heteroatoms. By “non-interfering” is meant that the substituents (or heteroatoms) should not participate unduly in the reaction with diorganocarbonate unless this reaction is desired. Modest reaction which does not substantially impede recovery of the desired product can be tolerated.
Non-limiting examples of suitable substituents include cyano; alkoxy, preferably C
1-4
alkoxy and more preferably methoxy; halo, particularly chloro and fluoro; halogenated alkyl, i.e., trifluoromethyl, hexafluoropropyl and heptafluoropropyl; nitro; alkylthio; acyl, preferably C
1-4
lower acyl (—C(O)—R), and the like.
Also suitable for organo groups R are the various silanes and siloxanes, including oligomeric and polymeric species thereof, in which the formamide groups are not bound directly to silicon, but are bound to a hydr
Brooks & Kushman P.C.
Lyondell Chemical Company
Oh Taylor V
Seaman D. Margaret
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