Organic compounds -- part of the class 532-570 series – Organic compounds – Isocyanate esters
Reexamination Certificate
2002-03-04
2004-01-27
Shippen, Michael L. (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Isocyanate esters
Reexamination Certificate
active
06683204
ABSTRACT:
The invention relates to a process for the preparation of mono- and oligoisocyanates by reacting primary amines with phosgene in the presence of a catalyst.
Isocyanates are industrial products which have a large number of uses in the field of polyurethane plastics. However, certain isocyanates are also used in the preparation of pharmaceutical active ingredients.
The synthesis of isocyanates by reacting amines with phosgene has been known for some time. In principal, two processes are described in the literature, one of which is carried out at atmospheric pressure and the other is carried out at increased pressure. Phosgenation under increased pressure is disadvantageous since it requires much more complex industrial apparatus to control the increased safety risk, the release of phosgene.
For sulfonyl isocyanates, U.S. Pat. No. 3,371,114 and U.S. Pat. No. 3,484,466 disclose a preparation process at atmospheric pressure in which a solution of a sulfonylamide and an isocyanate as catalyst in an inert solvent is reacted with phosgene. In the process, the corresponding sulfonylurea is formed as an intermediate, which reacts with phosgene to give the desired sulfonyl isocyanate.
Alkyl and aryl isocyanates are usually prepared by the phosgenation process, described, for example, in Houben-Weyl, Methoden der organischen Chemie [Methods in Organic Chemistry], 4th Edition, Volume E4, pages 741-751, Georg Thieme Verlag Stuttgart, 1983, from the corresponding amines in two phases at atmospheric pressure. In the first phase, the cold phosgenation, the amine is reacted with an excess of phosgene in very dilute solution and at low temperatures to give the corresponding carbamyl chloride, from which, in the second phase at elevated temperature, the hot phosgenation, the isocyanate forms. Aliphatic and cycloaliphatic primary amines are more difficult to phosgenate because of their increased basicity compared with aromatic amines, and lead to an increased formation of byproducts. A disadvantage of these processes is, in addition to the fact that the phosgenation is carried out in two phases, the formation of an intermediate solids suspension of sparingly soluble carbamyl chloride and amine hydrochloride, which in turn renders an increased dilution of the reaction medium necessary in order to prevent deposits and blockages of parts of the equipment. Because of the accumulation of solids which occurs, this process cannot be carried out continuously at atmospheric pressure. Furthermore, symmetrically N,N′-substituted urea forms as a byproduct, the formation of which can only be suppressed at the expense of drastically reduced space-time yields.
Aliphatic and cycloaliphatic amines are frequently used in the form of their salts in the cold/hot phosgenation. However, these salts are sparingly soluble in the reaction medium, meaning that additional reaction stages and very long reaction times are necessary.
Furthermore, it is known from GB 1 114 085, U.S. Pat. No. 3,492,331 and H. Ulrich, Chemistry & Technology of Isocyanates, Wiley & Sons, 1996, pages 328-330, to optimize the reaction of primary amines with phosgene by the addition of catalysts such as dimethylformamide, phenyltetramethylguanidine, 2,4,6-trimethylpyridine or carbodiimidazole. Some of these catalysts must be used in equimolar amounts and form sparingly soluble salts under the reaction conditions.
It is an object of the present invention to provide a process, which can be used for aliphatic, cycloaliphatic, araliphatic and aromatic primary amines, for the preparation of the corresponding mono- and oligoisocyanates using phosgene which can be carried out either continuously or batchwise at atmospheric pressure, does not have the above disadvantages and provides the corresponding mono- and oligoisocyanates in good yields and high selectivities.
We have found that this object is achieved by a process for the preparation of aliphatic, cycloaliphatic, araliphatic and aromatic mono- and oligoisocyanates by phosgenation of the corresponding primary amines at atmospheric pressure, in which
a) a catalytic amount of a monoisocyanate (isocyanate a) is introduced into an inert solvent together with phosgene,
b) the primary amine is added, and
c) the resulting reaction mixture is reacted with phosgene.
The net equation underlying the process is given in scheme 1 below.
The process according to the invention has the advantage that it can be used for a large number of amines. The phosgenation is carried out according to the invention, while avoiding a division into cold and hot phosgenation, in a narrow temperature interval and at atmospheric pressure, the intermediate formation of sparingly soluble suspensions being avoided. The desired isocyanate is formed in the process, with complete conversion of the amine, in high yields and high selectivity in significantly shortened reaction times without symmetrically substituted N,N′-urea being formed from the amine as a byproduct. Since the formation of urea from the amine is not observed, it is possible by means of the process according to the invention to significantly increase the concentration of the amine in the reaction solution and thus the space-time yields. In addition, it is advantageous that the process according to the invention can be carried out either batchwise or continuously since there is no accumulation of solids.
The process according to the invention gives aliphatic, cycloaliphatic, araliphatic and aromatic mono- and oligoisocyanates of the formula I
R
1
−N=C=O (I)
The radical R
1
in formula I corresponds to the radical R
1
in formula IV of the amines used in the process according to the invention, which are discussed later and to which reference is made here. Preference is given to preparing mono- and diisocyanates by the process of the invention. Of lesser importance in practice, but preparable in principle are isocyanates having 3 and more isocyanate groups.
The sole catalyst used is a monoisocyanate of the formula II (isocyanate a)
R
2
−N=C=O (II)
or mixtures thereof, in which R
2
is aliphatic, cycloaliphatic, aromatic or araliphatic radicals. These can be substituted by heteroatoms, or their carbon chains can be interrupted by heteroatoms, such as oxygen and sulfur. The radical R
2
must, however, be inert toward phosgene, thus excluding radicals which carry NH, OH and SH groups. The aliphatic radicals can be arbitrarily branched or unbranched, saturated or unsaturated. They contain 3 to 30 carbon atoms, preferably 3 to 10 carbon atoms. Examples of aliphatic radicals are methyl, ethyl, propyl, n-butyl, isobutyl and sec-butyl.
Suitable cycloaliphatic radicals are those which have 3 to 20 carbon atoms, preferably 3 to 10 carbon atoms, such as, for example, cyclopentyl and cyclohexyl.
The aromatic radicals can be unsubstituted or arbitrarily substituted by alkyl or aryl substituents or heteroatoms. Preference is given to the aromatic radicals which are mono- or disubstituted. Examples of aromatic radicals are phenyl, chlorophenyl, o-, m- and p-tolyl.
Suitable araliphatic radicals are radicals having 7 to 12 carbon atoms, such as, for example, benzyl, although preference is given to a radical of the formula III
in which R
3
and R
4
can be identical or different and can be hydrogen or an aliphatic, cycloaliphatic, araliphatic or aromatic radical, in which case these may be substituted by heteroatoms, or their carbon chains can be interrupted by heteroatoms, such as oxygen and sulfur. The radicals R
3
and R
4
must, however, be inert toward phosgene, thus excluding radicals carrying NH, OH and SH groups. The aliphatic radicals can be arbitrarily branched or unbranched, saturated or unsaturated. They contain 1 to 30 carbon atoms, preferably 1 to 10 carbon atoms. Examples of aliphatic radicals are methyl, ethyl, propyl, n-butyl, isobutyl and sec-butyl.
Suitable cycloaliphatic radicals are those which have 3 to 20 carbon atoms, preferably 3 to 10 carbon atoms, such as, for example, cyclopentyl and
Henkelmann Jochem
Kneuper Heinz-Josef
Stamm Armin
Thil Lucien
BASF - Aktiengesellschaft
Keil & Weinkauf
Shippen Michael L.
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