Question

Give chemical reactions to show the action of `CO_2` & ethanal on methyl magnesium bromide and methyl lithium?

Answer 1

The metal reagent and carbon dioxide gives a carboxylate salt (a carboxylic acid on work up). With acetaldehyde, a secondary alcohol results.

Explanation:

In fact one of the best ways of making a carboxylic acid is by pouring the Grignard mixture onto dry ice:

`R-MgX + CO_2 rarr R-C(=O)-O^(-)(MgX)^+`;
`R-C(=O)-O^(-)(MgX)^+ + HX rarr RCO_2H + MgX_2`

The reaction would also occur with methyl lithium.

With acetaldehyde or ethanal, `H_3C-C(=O)H`, `C-C` bond formation again occurs and a isopropanol will result after workup:

`H_3C-C(=O)H + Li-CH_3 rarr H_3C-C(O^(-)Li^+)CH_3`
`H_3C-CH(O^(-)Li^+)CH_3 + HX rarr H_3C-CH(OH)CH_3 + LiX`

Note that `C-C` bond forming reactions are exceptionally rare, which is why the utility of these reactions is stressed in undergraduate studies.