Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2001-01-17
2002-05-21
Higel, Floyd D. (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
active
06392057
ABSTRACT:
The present invention relates to an improved process for the preparation of N,N′-carbonyldiazoles by reacting azoles with phosgene.
It has already been disclosed that N,N′-carbonyldiazoles can be obtained if azoles are reacted with phosgene (see DE-B 10 33 210). The solvents proposed here are tetrahydrofuran, other ethers and hydrocarbons, in particular anhydrous tetrahydrofuran and mixtures of tetrahydrofuran with benzene (see Chem. Ber. 96, 3374 (1963) and Org. Synth. Coll. Vol. IV, 201-204 (1968)). The reaction apparently takes place at room temperature, with phosgene being passed into an initially introduced solution of the azoles. This process requires solvents which have been freed from final traces of water. Since this requires the handling of metallic sodium, sodium hydride or calcium hydride, this means the use of extraordinary safety measures for work on an industrial scale. In addition, tetrahydrofuran and other ethers always entail the risk of the formation of explosive peroxides. Furthermore, the process can only be reproduced with difficulty.
These problems are circumvented in a more recent process (EP-A2 692 476) by working at temperatures of from 50 to 120° C. in an aromatic solvent, such as benzene, toluene or chlorobenzene, which has been dried by incipient distillation. In practice, the solvent is firstly dried by incipient distillation, the azole is then introduced and dissolved with warming, and phosgene is then passed in.
However, the procedure of passing phosgene into initially introduced azole solutions is accompanied by the following disadvantages:
If work is carried out at temperatures below 50° C., it is necessary to use solvents such as tetrahydrofuran, which causes problems for the above-mentioned reasons, since both of the azoles and the carbonyldiazoles are insufficiently soluble in the solvents that are simpler to dry and do not tend towards the formation of peroxide, such as benzene, toluene, xylenes or monochlorobenzene,
If work is carried out at temperatures above 50° C., the azole hydrochloride precipitate formed in the reaction is obtained as a viscous, tacky mass which adheres strongly to the reactor wall and stirrer and thereby considerably impairs stirrability. The heavy running of the stirrer then limits the maximum possible space yield to relatively low values. On solidification of the precipitate towards the end of the phosgene addition, hard beads then form, which can cause damage to the reaction vessel and its internals (for example stirrer, dip tubes, etc.).
There is therefore still a need for a process for the preparation of N,N′-carbonyldiazoles in which solvents that are difficult to handle and dry and at the same time tacky azole hydrochloride precipitates which cause problems are avoided.
A process has now been found for the preparation of N,N′-carbonyldiazoles of the formula (I)
in which
X
1
, X
2
and X
3
, independently of one another, are each CR
1
or nitrogen, where R
1
is hydrogen or C
1
-C
6
-alkyl, and
R
2
is hydrogen, or
X
1
and X
3
are CR
1
, where the R
1
located on X
1
is hydrogen or C
1
-C
6
-alkyl, and the R
1
located on X
3
, together with R
2
, forms a —CH═CH—CH═CH— bridge, and
X
2
is CR
1
or nitrogen, where R
1
is hydrogen or C
1
-C
6
-alkyl,
by reacting azoles of the formula (II)
in which the symbols used are as defined under the formula (I), with phosgene in a solvent, which process is characterized in that the azole of the formula (II) is metered with phosgene into an aromatic solvent which has been dried by incipient distillation, at such a rate that in the time in which 1 mol of azole of the formula (II) is metered in, from 0.17 to 0.34 mol of phosgene is metered in simultaneously.
In the process according to the invention, the azole hydrochloride (for example imidazole hydrochloride) precipitated in the reaction is, surprisingly, always formed and remains as a disperse, crystalline precipitate which does not form any deposits or adhesion to the stirrer or vessel wall. Due to the disperse habit of the precipitate, the stirring resistance is significantly lower than in the procedure which is not according to the invention. Significantly higher reactant concentrations than before can therefore be used in accordance with the invention, which results in a significantly improved space yield compared with the prior art. In accordance with EP-A 2 692 476, a reactant concentration of 12% by weight is used and a space yield of about 70 g/l is achieved, whereas in the process according to the invention, reactant concentrations of, for example, from 28 to 33% by weight are used and space yields of, for example, from 120 to 175 g/l can be achieved. Damage to the reactor and its internals due to hard azole hydrochloride conglomerates can also be excluded.
In the process according to the invention, the azole hydrochloride is in the form of a crystalline precipitate even towards the end of the metering of azoles of the formula (II) and phosgene. It can be washed easily and completely out of the reactor into a filtration device together with the reaction mixture. The filtration times are short owing to the crystallinity of the precipitate.
Preferably, only one azole of the formula (II) is employed in the process according to the invention, and thus a N,N′-carbonyldiazole of the formula (I) in which the two azole rings are identical is obtained.
It is furthermore preferred for one or two of the X
1
, X
2
and X
3
moieties in the formulae (I) and (II) to be nitrogen. It is also preferred for X
1
to be CH, X
2
to be nitrogen and X
3
to be CR
1
, where R
1
and R
2
together form a —CH═CH—CH═CH— bridge.
Particular preference is given in the process according to the invention to imidazole, benzimidazole, pyrazole or 1,2,4-triazole as the azole of the formula (II). Very particular preference is given to imidazole here.
Phosgene can be employed in the usual technical-grade quality. It is advantageous to employ from 0.2 to 0.3 mol, in particular from 0.22 to 0.27 mol, of phosgene per mole of the azole of the formula (II). It is particularly preferred to employ 0.25 mol of phosgene per mole of the azole of the formula (II).
It is an essential feature of the present invention that the azole of the formula (II) and phosgene are fed to the reaction mixture in a type of simultaneous metering.
Examples of suitable aromatic solvents are benzene, toluene, xylenes, monochlorobenzene, dichlorobenzenes, trichlorobenzenes and mixtures of these solvents. They are dried in a simple manner by incipient distillation before the reaction of the azoles of the formula (II) with phosgene.
The incipient distillation for drying of the solvents can be carried out, for example, by heating the respective solvent, before use, at the boiling point at atmospheric or reduced pressure until discharge of water is no longer observed. In general, from 0.1 to 5% by weight, preferably from 0.5 to 2% by weight, of the solvent are distilled off in this operation.
The azole used can be metered in in the form of a solution or suspension having a temperature of, for example, from 20 to 120° C., preferably from 60 to 100° C., in the above-mentioned solvents or as a melt. Monitoring of the metering rate is simplified by this type of metering.
The process according to the invention can be carried out, for example, at temperatures of from 50 to 120° C., preferably at from 70 to 100° C.
It is advantageous to initially introduce up to 10% by weight, preferably from 0.1 to 1% by weight, of the total amount of the azole into the reaction vessel before commencing the simultaneous metering of the azole and the phosgene, and then to commence the simultaneous metering of azole and phosgene. Thus, the unfavourable situation of phosgene being present in a significant excess (molar ratio phosgene:azole=0.3 or greater) cannot occur, even at the beginning of the reaction. This is because such high molar ratios favour decomposition of the azole with darkening of the reaction mixture.
It is generally advanta
Klausener Alexander
Scherer Johannes
Söllner Robert
Bayer Aktiengesellschaft
Gil Joseph C.
Henderson Richard E. L.
Higel Floyd D.
Shameem Golam M. M.
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