This organic acid also has a relatively non nuclephilic hydroxyl group. I need to activate a carboxylic acid.
Do not activate your acid, use anhydride of the acid or its ester /methyl- or ethyl-/, in the latter case a trans-esterification should proceed.
A question: do you want to esterify pentafluorphenol, some alcohol or another phenol? In the case of trans-esterification use much higher amount of alcohol than a stochiometric one.
You could prepare ester also via reaction of chloride of the acid /acylchloride/ with alcohol, phenol or maybe pentaflorphenol. Add to reaction mixture calcium or sodium carbonate to neutralize the arising HCl to avoid hydrolysis of the ester.
do u want to make an ester between pentafluorophenol and an carboxylic acid? if so, perhaps you could activate your carboxylic acid first to an acyl halide like acyl chloride (RCOCl) using phosgen or SOCl2. Acyl chlorides are very reactive because the chloride is a good leaving group and therefore your weak nucleophilic hydroxyl group of your pentafluorophenol can attack the carbonyl to form the ester. i think you also need a base to remove the hydrogen chloride byproduct in order to catalyze the reaction.
cheers
Pentafluorophenol is an alcool. You need an acid to form the ester. You can use in this purpose an acyl chloride (RCOCl), an anhydride (RCO-O-COR') or others reactions like the Yamaguchi esterification or using DCC/DMAP in anhydrous solvent.
Look this link, hope you will find something useful :
http://www.organic-chemistry.org/synthesis/C1O/esters/index.shtm
It's usually done activating the carboxylic acid with a carbodiimide such as EDCI or DIC.
Sebastien, pentafluorophenol is a derivatized phenol {Ar-OH} and not alcohol {R-OH}. Phenols are generally harder to esterify than alcohols.
R.S.
Rastislav, thank you I know the difference between both ! OH is in organic chemistry an alcohol group so phenol are part of alcohol compound. I did my PhD on aryl-dendrimers using multi-steps esterifications. In fact, it's really not hard to esterified phenols. I was using acyl chloride in anhydrous THF or DCC/DMAP in anhydrous DCM. For the first generations or on our mesogen, we've got really high yield over 90%.
Ok Sebastien, if you look at the rate and more specific conditions of reaction when eserifying phenolics, R-OH are still easier to esterify. I, and not only me, consider phenols to be aromatic hydroxyderivates.
R.S.
Of course aromatics have a huge influence on the OH group. The aromaticity have directly an effect on the pKa for this hydroxyl. Indeed, Ph-OH show a lower pKa than R-OH. For this reason you can proceed to a Williamson etherification with dry K2CO3 instead of NaOH or other strong base. Furthermore, in this case with 5 fluorines on the aromatic, pKa is really low compared to simple phenol. ( Currently fluorines is used in super acidic ion exchange resin as NAFION ). So for Patrik's question, the use of acyl chloride (RCOCl), anhydride (RCO-O-COR') or DCC/DMAP in anhydrous solvent should be strong enough for an esterification. You will find a lot of exemple using this 3 methods in literature. Just check the link I sent yesterday.
I understand well your reply, unforunatelly when you look at the question of the author specifying pentaflourphenol as an additive activating esterification we do not have to argue about the esterification of this compound /see the second "answer" of the author/. By the way, my firstly added answer dealt about esterification with anhydride, esther and acylhalogenide /acylchloride in the presence of sodium carbonate/. Compared to other answers, I am of the opinion the answer of mine was not any poor.
Kumar,
You want to prepare an active ester using pentafluorophenol is that right !
Here is the procedure:
"Pentafluorophenol (10 mmol) and 3.5 ml 2.6-lutidine (10 mmol) are dissolved in 15 ml dichloromethane. Under cooling acid chloride (10 mmol) is added and the whole mixture stirred for 3 h at 0 C. After removing the ice bath the reaction mixture is kept at room temperature overnight. After filtration of the solution to remove the precipitated 2.6-lutidine hydrochloride the filtrate was washed twice with 10 ml water and dried over MgSO4. The solvent was removed under reduced pressure. "
Please, see
---Marc Eberhardt, Ralf Mruk, Rudolf Zentel, Patrick The´ato, European Polymer Journal 41 (2005) 1569–1575 and reference# 6 cited therein.
Good luck
Convert pentafluorophenol to the trimethylsilyl ester by boiling in the hexamethyldisilazane and then leave to react with the acid chloride.
Thanks a lot guys. I performed the reaction in DMF using 1.2 eq of PFP-OTf and 1.2 eq of DIPEA for 20 minutes. I was able to successfully obtain my desired ester.
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