Organic compounds -- part of the class 532-570 series – Organic compounds – Nitriles
Reexamination Certificate
2000-09-22
2002-04-09
Higel, Floyd D. (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Nitriles
C252S299600
Reexamination Certificate
active
06369259
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a process for the preparation of 4,5,6-trichloro- and 2,4,5,6-tetrachloropyrimidine starting from 3-dimethylaminopropionitrile, to its use and also to a crystalline intermediate product form.
BACKGROUND OF THE INVENTION
According to US-A 3 509 032, 4,5,6-trichloro- and 2,4,5,6-tetrachloropyrimidine are obtained by chlorination of 3-dimethylaminopropionitrile with Cl
2
with irradiation by UV light, it being necessary for the temperature of the chlorination to sometimes be above 150° C., in particular from 180 to 220° C., in order to permit the desired products to form (see column 2, line 51 to 53 and Example 2 and 3). Such high chlorination temperatures are, however, disadvantageous when carrying out the procedure industrially.
According to DE-A 3 900 917, 4,5,6-trichloropyrimidine is prepared from the hydrochloride of 3-dimethylaminopropionitrile in a single-step chlorination at a temperature of from 120 to 130° C. However, some aspects of this procedure can still be improved upon, in particular as regards its suitability for large-scale batches.
Furthermore, most of the processes described in the prior art have the disadvantage that during subsequent distillation insoluble distillation residues are formed, which can only be removed from the distillation vessels at considerable expense. In addition, the resulting products gas very severely during distillation.
The object of the present invention was therefore to provide a process for the preparation of 4,5,6-trichloro- and 2,4,5,6-tetrachloropyrimidines starting from 3-dimethethylaminopropionitrile which does not have the above disadvantages.
DETAILED DESCRIPTION OF THE INVENTION
We have found a process for the preparation of 4,5,6-trichloro- and 2,4,5,6-tetrachloropyrimidine by reacting 3-dimethylaminopropionitrile with HCl and Cl
2
, which comprises
a) in a first reaction step reacting 3-dimethylaminopropionitrile in a solvent, preferably one inert towards HCl and Cl
2
, with HCl, preferably from 1 to 6 mol, and Cl
2
, preferably from 2 to 4 mol, in each case based on 1 mol of 3-dimethylaminopropionitrile, at a temperature of from −10 to 55° C., and
b) in a second reaction step reacting the reaction mixture from the first reaction step with Cl
2
, preferably from 3 to 5 mol, based on 1 mol of 3-dimethylaminopropionitrile used, at a temperature above 55° C., preferably from 65 to 120° C., optionally in the presence of a catalyst,
characterized in that the second reaction step is carried out in the presence of the reaction product from the first reaction step, which is in microcrystalline form with an average crystal size of ≦10 &mgr;m.
DETAILED DESCRIPTION OF THE INVENTION
The solvents which are inert towards HCl and Cl
2
under reaction conditions are preferably taken to mean those which are inert under the specified reaction conditions of the process according to the invention. Examples of suitable solvents are chlorinated, aliphatic and aromatic hydrocarbons, such as chloroform, tetrachloromethane, chlorobenzene, dichlorobenzene, isododecane, phosphorus oxychloride or mixtures thereof. Particular preference is given to phosphorus oxychloride (POCl
3
).
The first reaction step of the process according to the invention is preferably carried out at a temperature of from 15 to 25° C. It can, for example, be carried out batchwise or continuously.
The batchwise process variant involves, for example, initially introducing the 3-dimethylaminopropionitrile, preferably in the solvent inert towards Cl
2
and HCl, and passing HCl into it. The amount of HCl to be introduced is generally from 1 to 6 mol, preferably from 3 to 4 mol, based on 1 mol of the 3-dimethylaminopropionitrile used. The resulting HCl adduct of the nitrile is particularly readily soluble in the temperature range according to the invention when the solvent used is phosphorus oxychloride. The heat produced during HCl introduction with HCl adduct formation is preferably dissipated by cooling. This is then followed by the reaction with preferably from 2 to 4 mol of Cl
2
per mole of 3-dimethylaminopropionitrile. To this end, Cl
2
is passed into the reaction mixture for the HCl reaction with evolution of HCl. The introduction is preferably carried out at from 15 to 20° C.
The above-described batchwise variant preferably involves introducing from 1 to 2 mol of HCl before starting to introduce Cl
2
. The HCl adduct formation of the nitrile is then completed by the HCl formed during the chlorination.
The batchwise process variant is preferably chosen for small batches, in particular for batches smaller than 10 mol, based on 3-dimethylaminopropionitrile.
Particular preference is given to carrying out the reaction of the first reaction step of the process according to the invention continuously. In the continuous method, the solvent inert towards Cl
2
and HCl, in particular phosphorus oxychloride, 3-dimethylaminopropionitrile, HCl and Cl
2
are preferably brought together continuously in a reactor. The amount of HCl is preferably from 1 to 2 mol per mole of 3-dimethylaminopropionitrile.
The amount of Cl
2
corresponds to that mentioned at the outset. The HCl formed during the chlorination preferably remains in the reaction mixture and thus does not need to be fed in from outside. The heat which is liberated during the reaction is preferably dissipated by cooling. The temperature for the continuous method is particularly preferably maintained at from 15 to 25° C.
The reaction in the 1st reaction step is particularly preferably carried out completely continuously, this being taken to mean the continuous introduction of reactants and the continuous removal of reaction product.
If phosphorus oxychloride is used as preferred solvent, the reaction mixture in the first reaction step which is formed continuously is in the form of a solution at a temperature of from −10 to +55° C.
The reaction products formed in the first reaction step of the process according to the invention are preferably the hydrochlorides of the chlorinated 3-dimethylaminopropionitrile, which preferably conform to the formulae (I) and (II)
in which
x is a number from 1 to 3, preferably 3.
With particular preference, a product mixture is formed in which the compounds of the formulae (I) and (II) are present in a ratio of from 10:1 to 2:1.
The amount of solvent used can be varied over wide ranges. It is preferable to use from 4 to 10 parts of solvent per part of 3-dimethylaminopropionitrile used.
In a particularly preferred embodiment of the process according to the invention, the reaction mixture from the first reaction step and further Cl
2
are brought together semi-continuously at the temperature of the second reaction step, i.e. such that the bringing together, preferably in a second reactor, takes place for as long as the size of this reactor permits filling. In this connection, any catalyst which is used can, for example, be introduced with the introduced reaction mixture of the first reaction step or, for example, already be present in the reactor.
In the second reaction step HCl is formed. It is formed on the one hand during the chlorination and is, on the other hand, liberated from the HCl adduct of the first reaction step to form a monohydrochloride.
Transferring the reaction mixture of the first reaction step to the second step, preferably to the second reactor, results in crystalline precipitation. Furthermore, transfer to the second reaction step, which proceeds at a higher temperature (compared with the first reaction step) leads to the evolution of HCl. When the reaction mixture is transferred to the 2nd reaction step, coarse crystalline precipitations initially form. After a short time, finer crystals (microcrystals) can then be observed.
Both the coarse and also the fine crystals are crystals or mixed crystals of monohydrochlorides of the formulae (Ia) and/or (IIa).
These initially precipitate as relatively coarse crystals which have an average crystal size of >10 &mgr;m. These coarse crystals preferably precipitate in th
Hardenbicker Georg
Steffan Guido
Bayer Aktiengesellschaft
Eyl Diderico van
Gil Joseph C.
Higel Floyd D.
Sackey Ebenezer
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