Grignard reagent with sulfur dioxide

Question

I have studied that the Grignard reagent $\ce{RMgX}$ reacts with $\ce{CO2}$ to form $\ce{RCOOH}$ after acid hydrolysis. But does the same apply for sulfur dioxide?

Grignard reagents are good bases and also good nucleophiles. So the alkyl anion will attack the electron deficient carbon atom in $\ce{CO2}.$

But in the case of $\ce{SO2}$ the following conditions aren't present. First of all, sulfur is more electronegative than carbon. Secondly, sulfur has a lone pair of electrons which the carbon lacks. So this should further discourage an attack by the Grignard's alkyl anion.

So, what actually will happen when Grignards are treated with $\ce{SO2}?$

Answer 1

You get sulfinic acids $\ce{RSO2H}.$

This paper by Dowson et al. [1] states that Grignard plus $\ce{SO2}$ gives sulfinic acids and as a reference quotes an older article by Allen Jr. et al. [2] which states

The reaction between sulfur dioxide and Grignard reagent has been widely used for the preparation of aromatic and aliphatic sulfinic acids.

I would suggest you read [2] and the references it quotes.

References

1. Dowson, G. R. M.; Dimitriou, I.; Owen, R. E.; Reed, D. G.; Allen, R. W. K.; Styring, P. Kinetic and Economic Analysis of Reactive Capture of Dilute Carbon Dioxide with Grignard Reagents. Faraday Discuss. 2015, 183, 47–65. https://doi.org/10/gf9hvn. (Research Gate — PDF)
2. Allen, Jr., Paul.; Rehl, W. Richard.; Fuchs, P. E. Sulfone Formation during Sulfination of the Alkyl Grignard Reagent. J. Org. Chem. 1955, 20 (9), 1237–1239. https://doi.org/10/d42z3x.