Selective grignard addition to dialkyl oxalates: A flow chemistry approach

During the production of an intermediate of a major product at Bayer CropScience Schweiz AG in Muttenz, Switzerland, a side compound is formed that lowers the overall yield and requires intensive workup for its removal. In the reaction, the Grignard reagent 2 is reacted with dialkyl oxalate 3 to form an α-keto ester 3 (Fig. 1). Currently, a semi-batch operation mode is employed (Fig. 2).

As shown in Fig. 1 and Fig. 2, the desired compound 3 is synthesized, while the undesired side compound 4 can be formed through a second addition (overreaction) of the Grignard reagent 2 to compound 3.

The following potentials for improvement have been identified:

• The yield could be increased to enhance the overall efficiency of the process.

• The formation of the bis-alcohol (4) should be reduced to minimize both economic and environmental impacts.

• The process could be optimized and simplified to provide greater flexibility within the production plant at Bayer CropScience Schweiz AG in Muttenz.

• Moschen, L

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