[darkdevil]

Hi there,
I am performing the following Schotten Bauman esterification to make an ATRP initiator:


What I did was to first mix the acid bromide and propargyl alcohol in ether, and then slowly adding aqueous NaOH solution to the mixture to give a two phase equilibrium system. I then removed the solvents and performed an NMR analysis for the crude product. And the NMR spectrum is shown below:


I first thought I got my product correctly from the NMR spectrum but then the MALDI analysis gave me this, which it doesnt make sense at all... the molecular weight of the ester should be ~205 but I couldnt find it there, and I couldnt think of any possible structures that relate to the dominant 508m/z peak (or other peaks)


is there anything wrong with my reaction?? I just couldnt figure out what happened!! Any help would be greatly appreciated. Thank you!!

[discodermolide]

Well I see your problem, or rather I don't. The spectra are not visible.
The uploading them using additional options, just below the posting window.

[Archer]

I wouldn't use those reaction conditions. You only need a very weak, non-nucleophillic, base to mop up the HBr produced by the reaction. NaOH may be removing other acidic protons.

Your NMR is fairly inconclusive, your integrals are not sufficient for identification.

I would use plain GC-EI-MS too, fragmentations may tell you something about the product(s) while also showing how many products you have.

[MOTOBALL]

Please post your MALDI MS, with the molecular ion region (m/z 508) clearly shown, and also any lower mass fragment ions.

What was the MALDI matrix ??

[MOTOBALL]

Without seeing the MALDI spectrum, I would speculate that since you have sampled the crude rxn. mixture you possibly have a proton bound dimer of the Ester/HBr adduct and the Ester/H2O adduct.  This would give m/z 507, 509 as a 1:1 doublet for the molecular ion.

If not a doublet, then all bets are off.

[darkdevil]

Thanks for the reply, I think Archer is right. NaOH may be too nucleophilic and side reactions may have occured. I used triethylamine instead,  This time I purified it with flash column chromatography, and the proton NMR spectrum is below.

which is similar to the previous one.

I even did a carbon NMR and here are the results:




I can see 6 kinds of carbons ( while the triplet splitting in 76-78 ppm is CCl3 carbon) which is correct for my desired compound, but I am still waiting for the MALDI result for a final confirmation. WHat do you think???

[discodermolide]

Why am I only seeing "?" marks in little blue boxes instead of your spectra?

[darkdevil]

Why am I only seeing "?" marks in little blue boxes instead of your spectra?

let me check

[darkdevil]

Why am I only seeing "?" marks in little blue boxes instead of your spectra?

can you see them now?

[darkdevil]

Without seeing the MALDI spectrum, I would speculate that since you have sampled the crude rxn. mixture you possibly have a proton bound dimer of the Ester/HBr adduct and the Ester/H2O adduct.  This would give m/z 507, 509 as a 1:1 doublet for the molecular ion.

If not a doublet, then all bets are off.

Hi there I think this is interesting.. but can you clarify how does the structure look like if i have a " a proton bound dimer of the Ester/HBr adduct and the Ester/H2O adduct" ?

[MOTOBALL]

I have not used MALDI-MS, but based my response on much experience with ESI-MS.  Since you sampled the reaction mixture directly by MALDI, you will (in general) expect to get an MS response for each organic component of the mixture.

1) I assumed that your desired ester product was formed initially, but had then reacted as shown below,

                 Ester + HBr ====> Ester/HBr adduct

                 Ester + H₂O ====> Ester/H₂O adduct

2) Your mass spectrum might then be expected to give signals for

                 [Ester/HBr adduct + H]⁺     (1:1 doublet)           

                 [Ester/H2O adduct + H]⁺     (singlet)

and the proton-bound dimer,

[Ester/HBr adduct]--- H⁺ ---[Ester/H2O adduct]
at m/z 507,509 (1:1 doublet).

If you can, please post your MALDI spectrum with the high mass region at ca. m/z 500 clearly resolved.
If not, please post a table of m/z vs. Relative Abundance.