I activated the magnesium to form the Grignard reagent with 1,2-dibromoethane and then added paraformaldehyde to make an alcohol but now I'm afraid that I have added too much dibromoethane and that the Grignard will react with it. Is it likely or will the reaction proceed mostly with paraformaldehyde?
Hmm, don't you typically do Grignard reagent preps in ethereal solvents? I can't vouch for this source, but it looks like paraformaldehyde is insoluble in ether: http://www.chemicalland21.com/industrialchem/organic/PARAFORMALDEHYDE.htm
Typically paraformaldehyde depolymerizes to formaldehyde (and hence can participate in the Grignard reaction) in water, which if present in any substantial quantity would certainly react with your Grignard reagent.
In any case, to my knowledge the Grignard reaction requires a carbonyl in the other reagent, and since 1,2-dibromoethane doesn't have one you can be reasonably sure that it won't react with any Grignard reagent that has formed.
It can also react with alkyl halides and attack the alpha-carbon in relation to the halogen atom, displacing the latter. That is why I was worried.
Many protocols do Grignard reactions in THF with paraformaldehyde.
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