Organic compounds -- part of the class 532-570 series – Organic compounds – Chalcogen in the nitrogen containing substituent
Reexamination Certificate
2000-03-24
2002-03-19
Raymond, Richard L. (Department: 1624)
Organic compounds -- part of the class 532-570 series
Organic compounds
Chalcogen in the nitrogen containing substituent
Reexamination Certificate
active
06359131
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is situated within the field of organic colorants and relates to an improved process for preparing dioxazine compounds. Dioxazine compounds are used to prepare valuable dyes and pigments (see Ullmann's Encyclopedia of Industrial Chemistry, Vol. A 3, p. 233). They are prepared industrially in a five-stage synthesis embracing the N-alkylation of carbazole, nitration, reduction, condensation and ring closure. In the final stage of the synthesis, compounds of the formula (II)
are cyclized to the dioxazine compounds using ring closure agents, such as benzenesulfonyl chloride or 4-toluenesulfonyl chloride, for example (DE-A 30 10 949). High temperatures are needed for the ring closure. Consequently, the only suitable reaction media for the ring closure are inert solvents whose boiling point under atmospheric pressure is more than 160° C. Proposed solvents of this type have included halogenated aromatic solvents, especially o-dichlorobenzene; nitrobenzene; polar aprotic solvents, such as quinoline; and halogenated monoalkyl-, dialkyl- and trialkylbenzenes, alkylnaphthalenes, and also alkanes and alkenes. Of these reaction media, the only one which has become established to date for the industrial preparation of dioxazine compounds is o-dichlorobenzene, since this solvent offers a number of advantages in both technical and economic respects. Significant advantages of o-dichlorobenzene are the high yields at all stages that can be achieved in this reaction medium, and also the easy phase separations and the resulting possibility of working without isolating the intermediates and without changing solvent. A procedure of this kind makes it possible to prepare the dioxazine compounds in a technically simple and economically advantageous way. Like other chlorinated aromatic solvents, however, o-dichlorobenzene has the disadvantage that the production wastewaters contain AOX and that, at the high reaction temperatures, toxic and environmentally harmful substances are formed in trace amounts, accumulate in the regenerated solvent in the production circuit and can also be detected in the product.
As environmental concerns acquired increasing importance therefore, a need came about for a preparation process which is advantageous to conduct over all stages of the synthesis—that is, which does not necessitate any isolation of intermediates or change of solvent—but which, unlike that using o-dichlorobenzene, is environmentally unobjectionable.
The halogen-free reaction media proposed to date have disadvantages which hinder their use in an industrial process for preparing dioxazine compounds. Polar aprotic solvents such as quinoline and dimethylformamide (JP-A-56-135 556) differ from o-dichlorobenzene in being soluble in water and are unsuitable as reaction media for all reaction stages of the synthesis. In these solvents, furthermore, the synthesis cannot be carried out without isolation of intermediates. When these solvents are used, it is necessary to isolate the condensation product prior to the ring closure and to change the reaction medium to allow substantially anhydrous operation and to give acceptable yields. Consequently, preparing dioxazine compounds using these solvents is technically complex and uneconomical.
Monoalkyl-, dialkyl- and trialkylbenzenes and alkylnaphthalenes (JP-A-7-331 097) and also alkanes and alkenes (JP-A-7-331 098) likewise have disadvantages in respect of the technical and economic preparation of the dioxazine compounds. In the preliminary stages, for example, the poorer solubilities of the intermediates, byproducts and the chloranil in these solvents in comparison with o-dichlorobenzene makes it necessary to employ substantially larger reaction volumes. Furthermore, the phases have to be separated in relatively large vessels. This makes the space yields significantly poorer than when working in o-dichlorobenzene. Furthermore, the use of these solvents gives rise to phase separation problems, resulting in long preparation times and thus poor time yields. If the synthesis is carried out without isolation of intermediates, the poor solubility of the excess chloranil and of the byproducts accumulated at the end of the synthesis in these solvents is a further serious disadvantage. Furthermore, following the isolation of the dioxazine compounds by filtration, they have to be washed with an organic solvent having better solvency in order to free the product completely from the byproducts and the unreacted starting products, which otherwise impair the performance properties. The product crystals are usually substantially smaller and of inferior morphology than when o-dichlorobenzene is used as the reaction medium; for this reason, in the course of the necessary washing with the additional polar solvent, there may be a drastic deterioration in the filtration form. Operating with a second organic solvent, moreover, represents an additional technical expense. The ring closure yields achievable in these halogen-free solvents are only moderate. Because of these disadvantages, the above-proposed halogen-free solvents have also been unable to replace the o-dichlorobenzene which has been preferred to date for the industrial preparation of the dioxazine compounds.
SUMMARY OF THE INVENTION
It has now surprisingly been found that certain aryl alkyl ethers which boil above 160° C. are especially suitable as a reaction medium for the complete synthesis of the dioxazine compounds.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention accordingly provides a process for preparing dioxazines by ring closure of a compound of the formula (II)
in which R
1
is hydrogen or C
1
-C
8
alkyl in the presence of a ring closure agent, which comprises using as reaction medium an aryl alkyl ether of the formula (Ill) or a mixture of aryl alkyl ethers of the formula (Ill)
in which n is an integer from 0 to 2 and R
2
is ethyl if n is 0 or is methyl if n is 1 or 2.
Preference is given to n =0 and R
2
=ethyl (phenetole), and to n=1 and R
2
=methyl. The methyl group is preferably positioned m or p with respect to the ether function. Particular preference is given to p-cresyl methyl ether (4-methylanisole).
C
1
-C
8
-alkyl R
1
can be straight-chain or branched and can for example be methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert.-butyl, pentyl, hexyl, heptyl or octyl. Preference is given to methyl, ethyl or propyl, especially ethyl.
The dioxazine compounds formed in the process of the invention can in principle possess a structure of the formula (a), (b) or (c) or can be a mixture of these compounds:
The aryl alkyl ether is judiciously used in an amount of from 3 to 20 times, preferably from 5 to 15 times, the amount by weight of the compound of the formula (II).
Examples of ring closure agents which can be used in the process of the invention are benzenesulfonyl chloride, 4-toluenesulfonyl chloride, nitro- or chloro-substituted benzenesulfonyl chloride, chloranil and pyridine N-oxide. A preferred ring closure agent is benzenesulfonyl chloride or 4-toluenesulfonyl chloride.
Benzenesulfonyl chloride, or substituted benzenesulfonyl chloride, is used preferably in amounts of from 0.5 to 2.0 mol, with particular preference from 1.0 to 1.5 mol, per mole of compound of the formula (II). Pyridine N-oxide is added preferably in an amount of from 1 to 3 mol, in particular from 1.2 to 2.5 mol, per mole of compound of the formula (II). Chloranil is added preferably in an amount of from 5 to 50 mol %, in particular from 10 to 40 mol %, based on the compound of the formula (II).
The reaction temperature is judiciously situated within the range from 140 to 200° C., preferably from 160 to 190° C. The reaction can be carried out under atmospheric pressure, superatmospheric pressure or reduced pressure. Reaction under atmospheric pressure is preferred. The reaction generally takes from 1 to 10 hours. Preference is given to a reaction time of from 3 to 7 hours.
In order to prepare the dioxazine compound
Bauer Wolfgang
Kempter Peter
Nagl Gert
Clariant GmbH
Hanf Scott E.
Jackson Susan S.
Patel Sudhaker B.
Raymond Richard L.
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