Question

How do you titrate Grignard reagents?

Answer 1

Simply take a known volume of the Grignard, dump it into water, and then titrate to a stoichiometric endpoint.

Explanation:

From above, we drop a solution of `RMgX` into water to give `R-H` and `MgXOH`; an aqueous titration to a stoichometric endpoint follows with standardized `HCl(aq)`.

Alternatively, there are indicators that you could dissolve up in dry ether, and titrate to an endpoint with the Grignard in ethereal solution. This is a bit more of a pfaff, but is still doable. The Grignard could even be used as the titrant; in which case we would typically use a `1` `mL` syringe with `0.01*mL` graduations. Diphenyl acetic acid, `Ph_2CHCO_2H`, in ether is used as the standard. Addition of `1` `"equiv Grignard"` gives `Ph_2CHCO_2^(-)MgBr + RH`. The second equiv of Grignard gives `Ph_2C^(-)CO_2^-`, which is noticeably yellow. Other such reagents exist.