We performed this suzuki reaction in lab: The solution was heated to 80°C and re

Question

We performed this suzuki reaction in lab:

The solution was heated to 80°C and refluxed for an hour. A sample was taken every 10 minutes (6 in total per reaction) and the yield of the product of the 6 samples were measured with a GC-method. The yield of the product of the samples 1 till 4 were rising. However, the yield of the product of the samples 5 (after 50 minutes) and 6 (after 60 minutes) were decreasing compared to sample 4 (after 40 minutes). We expected that the yield of the reaction of samples 5 and and 6 would increase compared to the yield of sample 4 since the reaction is more complete. We performed the reaction 4 times and still faced the same problem.

What could be the cause of this problem? Has the GC-method something to do with it?

This reaction is not an equilibrium reaction!

Explanation / Answer

In the above reaction, the product after sample 4, may be combining with an excess of boronic acid substrate to form the biphenyl side product.

Did your GC show any other peak other than what you saw in sample 1-4.

Confirm the GC chart, compare it with sample 5 and sample 6 charts.

Excess product might be undergoing secondary reaction to form biphenyl rings and thus reduces the overall product yield of the reaction.

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