Ethylene → Styrenesulfonic acid

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Although the use of supported palladium catalysts is mentioned in EP-A 0 508 264 A1 page 4, lines 2 to 3, it is only referred to in one case, namely in the reaction of aniline-2-sulfonic acid with ethylene to give styrene-2-sulfonic acid (Example 6). However, as a comparison with Example 4 carried out using Pd(OAc)2 shows, the yield decreases significantly when a palladium-containing supported catalyst (10% Pd on charcoal) is used (Example 4: 87% yield; Example 7: 74% yield). In both examples, the reaction is carried out using a base which is used in excess based on aniline-2-sulfonic acid. As the experimental findings prove (see comparative trial in the experimental part), the procedure practised in the examples of EP-A 0 508 264 to prepare the aryldiazonium salts in situ and then to further process them, cannot generally be applied to preparation of a cinnamic ester by a palladium-containing supported catalyst. The comparative trial verifies that the desired cinnamic ester is not even formed in small amounts. These experimental findings do not let it be expected that palladium-containing supported catalysts are suitable for the preparation of the cinnamic acids and cinnamic esters according to the invention.

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