My compound contains 2OH groups, I want to react my compound with acetic anhydride to obtain one OAc and one OH free ( mono acetyled product ) not two OAc.
That hardly depends on the type of alcohol and the environment of each OH.We need more information to properly answer that question.
For a symmetrical compound like that, is not gonna be easy, you can try working on substoichiometric conditions (0.5 eq of Ac2O) and you are going to obtain the statistical mixture. But the compound you need can be easily separated doing a basic extraction, then neutralize the aqueous phase, and extract the product.
I would recommend you keeping tightly to stechiometry. Use 1 eq of weak acetylating agent like: AcCl + DMAP, Et3N , AcCl + Pyridine, AcCl + imidazole or use Ac2O. Pay attention to concetration of solution = use diluted mixtures.
The AcCl/DMAP/Et3N combination is not a weak acetylating agent. For the mild conditions I would recommend Ac2O/Py or Ac2O/Et3N. Regardless, for this molecule with 1 equiv of Ac2O you will get a statistical mixture of starting material, mono- and di-acetylated products.
Perhaps the careful re-extractive work-up will allow to separate di-acetylated product from the mixture of mono/starting material, but ultimately, chromatographic separation will be required - hopefully not really difficult in this case.
If you use carefully 1,1 equivalent of acetylating reagent (and do prefer Vladimir's suggestion or Ac2O/DMAP room temperature, you should produce principally the monoacetylated derivative. Control from time to time your reacting medium, extracting an aliquot and TLC, to eventually stop the reaction when the diacetylated derivative begins to be formed. Since your compound looks to me symmetrical, there is only one monoacetylated derivative of it. Thus in the worst hypothesis, your will have to separe : unreacted compound from mono and eventually some diacetylated derivative. And this should be easy to carry out. Good luck
I suggest a little pre-experiment, try to explore if phenolates (Na+, K+) are water soluble. If so, it could help you to separate mono- (and maybe unreacted di-) phenolic compound (salts potentially water soluble) from diacylated (non-phenolic water insoluble) byproduct, using common A/B extractions...
That's a good idea Martin to process the reaction mixture after extraction.
Solve in methanol 1 eq of KOH. Add in this solution ½ eq of your bisfenol. Evaporate methanol in vacuo. Suspend the solid bisfenol monopotasium salt in the dry acetone or acetonitrile or DMF (weight ratio 1 : 5 – 1 : 10). Add to the suspension about 0.05 eq of DMAP, and next under good stirring 0.9 eq of acetyl chloride dropwise.
If you follow Pavel's suggestion, do it under the hood: acetyl chloride vapors are toxic ans stimulate cough. Do not drop acetyl chloride directly into the reacting medium because it may spit. Let it flow smoothly along a glass rod.
I would like to see very much if the method proposed by Pavel indeed provides mono-acetylation selectively. It is only possible if: a) mono-potassium salt has really low solubility in proposed solvents; b) the soluble part of the mono-potassuim salt salt undergoes acetylation before any disproportionation to mono/di salt and free bis-phenol happens. I used similar approach successfully for making mono-TBS derivative of 1,4-butanediol in THF in the presence of NaH (this procedure is reported in literature). Interested to see is it will work in this case as well.
There may be a useful a technology of supported reagents
- please check textbook http://www.amazon.com/Preparative-Chemistry-Using-Supported-Reagents/dp/0124371051
As support you may use silicagel, saturated in low-to-middle polarity solvent (like THF) by dihydroxy compound; it is better to use such acylation compounds that avoid building of acidic by-products (because acid will replace dihydroxy compound). As acid scavenger it can be used i-Pr2NEt, DMAP or N-methylimidazole in stoichiometric quantities. The last two compounds are also superior acylation catalysts, but N-methylimidazole is much cheaper than DMAP.
Mechanism is relative clear - stepwise acylation.
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