Organic compounds -- part of the class 532-570 series – Organic compounds – Sulfonic acids or salts thereof
Reexamination Certificate
2003-09-16
2004-09-07
Powers, Fiona T. (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Sulfonic acids or salts thereof
Reexamination Certificate
active
06787666
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for the preparation of 3,4-diaminobenzenesulphonic acid by sulphonation of 1,2-diaminobenzene with sulphuric acid which contains no SO
3
or only up to 1.0 mol of SO
3
per mole.
2. Brief Description of the Prior Art
The objective of the invention is to provide a simple process for the preparation of 3,4-diaminobenzenesulphonic acid (also called “orthaminic acid”) which is particularly useful as an intermediate product. Illustratively, this compound is useful as an intermediate for the preparation of dyes, crop protection compositions, pharmaceutical products, and cosmetic products, particularly of UV absorbents in light protection agents such as 2-phenylbenzimidazolemonosulphonic acid. Particularly pure products are required for the last-mentioned intended use in particular, since the end products should be pure white. The prior art processes for preparing the compounds and the associated disadvantages are described hereunder.
In accordance with the prior art, 3,4-Diaminobenzenesulphonic acid can be obtained, by reacting the HCl salt of 1,2-diaminobenzene with a large excess (about 11 mol/mol) of SO
3
-containing sulphuric acid (see J. Post, Liebigs Ann. Chemie 205 (1880), p. 100).
However, the use of the HCl salt leads to the evolution of considerable amounts of HCl gas, which has a corrosive action, requires the use of sealed apparatuses made of expensive materials and would hinder reuse of the sulphuric acid.
Moreover, it has hitherto not been possible to obtain orthaminic acid as isolated product from a sulphonation of free 1,2-diaminobenzene with excess sulphuric acid. Thus, it is necessary to precipitate out the entire excess of H
2
SO
4
with BaCl
2
and evaporate the mother liquor which remains. The product obtained in this way does not readily crystallize and has to be purified again, which is laborious.
For the isolation, aromatic sulphonic acids are often converted into Na salts, which are then less readily soluble than the pure sulphonic acid. Incidentally, this is not known of orthaminic acid.
A further possible route for the synthesis of orthaminic acid is the reduction of 2-nitroaniline-4-sulphonic acid or dinitroazobenzenedisulphonic acid with tin/HCl (Zincke and Kuchenbecker, Ann. 330, (1904), p. 23). However, these starting materials are not inexpensive and have to be synthesized via several stages. Orthaminic acid is obtained in the process as HCl salt, which decomposes readily (Nietzki, Lerch; Ber. d. deutsch. Chem. Ges. 21, 3220 (1888)). Also the orthaminic acid obtained by this route is impure, and darkly discolored, as such purification by recrystallization is necessary (loc.cit.). Moreover, since HCl is highly corrosive, the handling of acidic, decomposable HCl salts is therefore not preferred on an industrial scale.
The synthesis by sulphonation of 1,2-diaminobenzene would, by contrast, be advantageous since 1,2-diaminobenzene is obtainable in considerable amounts. In this synthesis it is desirable to isolate intermediates if they are to be obtained in the purest possible form and further processed.
Without intermediate isolation which (apart from starting materials and secondary products) can, as in this case, still comprise large amounts of sulphuric acid, it is not always possible to further process crude reaction solutions. This often leads to the formation of contaminated products and/or to poor yields in the subsequent stage. This is described in the example in EP-A 4 203 072, wherein a mixture of 1,2-diaminobenzene, benzoic acid and 96% strength sulphuric acid is mixed and heated to 200° C. In the subject process, 2-phenylbenzimidazole-5-sulphonic acid is obtained as the secondary product in a yield of 49% of theory. The product is isolated in a yield of 60%, with the process carried out in 86% strength sulphuric acid at 178°.
However, the formation or even isolation of orthaminic acid by this route is not described; the process, which is carried out with aqueous sulphuric acid and a particularly high temperature, does not therefore suggest the process according to the invention. In fact, the increase in the yield with increasing water content of the sulphuric acid in the examples described teaches away from the use of 100% strength or SO
3
-containing sulphuric acid.
Similarly EP-A 1167358 and EP-A 1167359 via the examples show that in the reaction of benzoic acid, 1,2-diaminobenzene and sulphuric acid in the presence of considerable amounts of SO
3
at a processing temperature of about 120°, considerable amounts of the disulphonic acids of 2-phenylbenzimidazole are obtained, even exclusively.
An intermediate isolation of orthaminic acid which has been obtained by sulphonation is nowadays highly desirable and required for the following economic and ecological reasons: Since the sulphonation is carried out in an excess of sulphuric acid (see J. Post, loc. cit.), contaminated sulphuric acid is formed in the process, the reutilization of which is desired. Spent sulphuric acid is nowadays either concentrated with oxidation of organic ingredients, or cleaved back at a high temperature to give SO
2
in order to be converted again into pure ready-to-use sulphuric acid. For this, the desired material-of-value must of course be largely removed beforehand, and contamination with inorganic ions (as in the precipitation of the sulphonic acid as e.g. Na or K salt) is unacceptable since that would lead to problems in the work-up.
Furthermore, it has been found that during the sulphonation of 1,2-diaminobenzene in sulphuric acid which comprises a super-stoichiometric amount of SO
3
, considerable amounts of disulphonic acid are produced.
It was therefore the object to find a way of preparing orthaminic acid by reacting 1,2-diaminobenzene with sulphuric acid and isolating it therefrom in the purest possible form, in a high yield and free from inorganic cations such that the sulphuric acid used can be reused and orthaminic acid can be obtained therefrom in a high purity and yield.
SUMMARY OF THE INVENTION
Surprisingly, it was then possible to find conditions to sulphonate 1,2-diaminobenzene with anhydrous sulphuric acid which comprises no SO
3
or only up to 1.0 mol of SO
3
per mole, and to work up the sulphonation mixture such that 3,4-diaminobenzenesulphonic acid is obtained in high yield and high purity, and that the separated-off sulphuric acid is free from inorganic cations which would impair reutilization.
This is particularly surprising since under otherwise identical conditions it was not possible to react the structurally very similar 1,3-diaminobenzene to give 1,3-diaminobenzenesulphonic acid such that it could be correspondingly isolated from the sulphonation mixture. In this case, the conversion achieves only about 50%.
The invention therefore provides a process for the preparation of 3,4-diaminobenzenesulphonic acid, characterized in that
a) 1,2-diaminobenzene is reacted with anhydrous sulphuric acid which optionally comprises SO
3
in up to stoichiometric amount, at a temperature in the range from 100 to 160° C. with stirring for a reaction time of from 1 to 20 hours,
b) water or ice is added to the reaction mixture, optionally with cooling, up to a sulphuric acid concentration in the range from 30 to 75% by weight, based on the total mixture,
c) the 3,4-diaminobenzenesulphonic acid precipitated out of the reaction mixture is filtered off, optionally washed with dilute sulphuric acid and worked up.
The product obtained by said process does not, in contrast to earlier findings about products of a different origin, decompose, but is stable.
The product which is obtained by this process is white to dark grey, generally pale grey. This is particularly surprising since 1,2-diaminobenzene is readily oxidizable and sulphuric acid acts as a strong oxidizing agent particularly at elevated temperature. It was therefore to be expected that the sulphonation would take place in parallel to oxidation and the formation of considerable amounts of darkly coloured secondary
Emde Herbert
Kissener Wolfram
Rauchschwalbe Günter
Bayer Chemicals AG
Deneavich Jill
Powers Fiona T.
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