The preparation of Anthranilic acid derivative

The present invention relates to the selective preparation of anthranilic acid. Anthranilic acid is a valuable intermediate for the preparation of benzonorbornene fungicides, as described for example in WO 2007/048556.

According to WO 2007/031323, anthranilic acid (A) can be prepared according to the following scheme:

3-Nitro-phthalimide (E) is a useful starting material for the preparation of anthranilic acid(CAS NO.: 118-92-3), in particular for large scale manufacturing which requires high safety standards.

However, an efficient process for the preparation of anthranilic acid starting from 3- nitro-phthalimide has to avoid the form tion of the undesired regioisomer of formula (B) which reduces yield and quality of the product. Therefore, the process according to WO 2007/031323 is performed in two separate steps. In the scheme above, 3-nitro-phthalimide (E) is converted in a first step by reaction with an aqueous base, and by subsequent reaction with an aqueous acid, into 6-nitrophthalamic acid (D). During the precipitation of the amido acid, the desired isomer (D) is enriched. 

In a second step, 6-nitrophthalamic acid (D) is then converted to anthranilic acid (A). In that step, 6-nitrophthalamic acid may be reacted first with aqueous base, such as, for example, aqueous sodium hydroxide, and sodium hypochlorite, and then with aqueous acid, such as, for example, aqueous hydrochloric acid. The disadvantage of this prior art process is the relatively low yield in each of the two steps (70-73%). Further, isolation is required to enrich the desired isomer with additional filtration which leads to high waste generation and higher cycle time (energy inefficient). Also, a two step synthesis is undesired for large scale production.

The aim of the present invention is therefore to provide a novel process for the selective production of anthranilic acid that avoids the disadvantages of the known process and makes it possible to prepare anthranilic acid in high yields and good quality in an economically and ecologically advantageous way in a one-pot process with a high safety standard.

Thus, according to the present invention, there is provided a process for the preparation of a compound of anthranilic acid derivative

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