I was going to give comments on Chromics proposed preliminary method posted in Post 473746 (https://www.thevespiary.org/talk/index.php?topic=8892.msg47374600#msg47374600)
(Chromic: "Uhm", Methods Discourse) but never did. I think it sounds ok although a little low in bromide compared to literature, there is also no mention of the volume of water to be used.
Here is a method strictly based on the Soviet electrocatalytic and the US elemental halogen THF oxidation patents. This is theoretical, small scale, and has not been tested. It uses little water volume which of course might cause problems with THF evaporation in some circumstances (lack of a reflux condenser etc), but is a good thing considering scale-up. If the water volume is to be increased the amount of sulfuric acid should be scaled proportionally as the optimal pH is around 1. The amount of the bromide salt is quite conservative, molar 20% of the amount of THF.
Now, my main concern is that the THF gets salted out of the solution in these conditions or that there is a problem with salt solubility -- and even if that happened the reaction might still work well, who knows? Experiment is king. Comments appreciated.
90 mL H2O
0.15 mol bromide salt (17.8 g KBr or 15.4 g NaBr)
0.92 g 96% H2SO4
0.75 mol THF (60.8 mL)
To a well-stirred mixture described above is added 107 mL of 30% H2O2 (1.65 mol, 1.1 equivalents) at such a rate that the temperature does not rise past 40°C. Work-up as usual.
The conversion of THF to GBL was recently tried in the two phase Br2 / H2O2 oxydation system described in: Organic Process Research & Development 2(4), 261-269 (1998) (https://www.thevespiary.org/rhodium/Rhodium/pdf/br-cat.h2o2-oxidation.pdf)
(https://www.thevespiary.org/rhodium/Rhodium/pdf/br-cat.h2o2-oxidation.pdf)
DOI:DOI:10.1021/op980028j (http://dx.doi.org/DOI%3A10.1021/op980028j)
Post 468078 (missing)
(moo: "Oxidations and brominations w/ H2O2/Br2/HBr", Methods Discourse)
Post 468126 (https://www.thevespiary.org/talk/index.php?topic=8892.msg46812600#msg46812600)
(Rhodium: "THF to GBL in 75% yield in 4h using H2O2/Br2", Methods Discourse)
Unfortunately yealds were low.
The procedure:
0,12mol Br2 was generated in situ by dissolving 33g KBr (slight excess) in 150ml water, than carefully adding 24g of 50% H2SO4 (0,12mol) followed by 16ml of 30% H2O2. To this yellow solution 150ml DCM and 25ml (0,3mol) THF was added. The two phase system was refluxed for 1h w/ intensive stierring (efficent condenser is required!), than 18ml 30% H2O2 was added followed by another hour of reflux and another 18ml of 30% H2O2 and finally 2h of reflux.
The DCM phase was separeted and the aq. phase further extracted w/ 2x 50ml DCM. The combined organic extracts were washed with 200ml of 15% NaHSO3 sol. Followed by 2x 150 ml of water washes. Dried (MgSO4) and stored overnight over some anhydrous Fe2SO4 (this precaution is most likely non necessery since the bisulfite wash should remove possible peroxides. Note that the used Fe2SO4 did not turn red at all.)
After stripping off DCM, the dark brown residue was distilled yealding 2,5ml clear liquide
(~11% Yeld). Sucks!!! :(
Further trials are to be expected in order to improve the yield! :)
What do you think, could the bisulfite remove some of the GBL from the DCM phase through the adduct?
Bobo find this unlikely, since significant amounts of bisulfite adduct dont form from DCM phase without PTC. OTOH GBL is somewhat water soluable (10% w/v). :-[
Next time Na2S2O3 might be used to remove Br2...
(Edit:) BTW bioessay of product was convincing... ;)