ethyl butyrate - pineapple ester
I wanted to preform this synthesis decades ago but it was postponed till today, when my dream came true.
reagents used: ethanol 95% denatured with 1% MEK and traces of denatonium benzoate, NaOH (only for purification of ethanol), butyric acid 95 %, conc.
H2SO4, NaCl, NaHCO3, anhydrous Na2SO4
glass: 500 ml round bottom flask, claisen condenser for reflux, 1 l separatory funnel, 250 ml erlenmeyer flask, 250 ml RBF, distillation adapter with
thermometer, claisen condenser (the same which used for reflux)
method:
purification of ethanol
shits were removed from denatured ethanol few days prior the main experiment this way:
600 ml of denatured ethanol was poured into 1 l flask and 2 g of NaOH added, the flask occasionally swirled about 10 times per day (NaOH dissolved
completely), ketone with b.p. close to ethanol reacted by aldol condensation into high boiling products that way, after 3 days the ethanol with
dissolved NaOH was refluxed for 30 minutes and then distilled (just simple distillation) - more ethanol purified than required for this ester
synthesis (I just would like to synthesize more esters)
the ethanol for the following esterification was used in 96 % concentration, it was not absolutized (though it would increase yield)
ester preparation:
To the 500 ml RBF was poured 101,5 g of 95% butyric acid (well I like to weigh liquids - empty flask and then flask with liquid and calculate the
weight difference, that's more exact than using measuring cylinder where unknown amount adheres to walls), 150 g of 96% ethanol (about 3-fold excess
as this chemical is very cheap, to shift equilibrium towards ester) and dropwise 5 ml of conc. H2SO4 using a pipette while swirling the flask in my
hand and boiling chips. Claisen condenser attached and then reflux for 2 hours. Allowed to stand for 1 hour to cool down (preparing and eating my
lunch, the drink after meal was made by mixing diluted solutions of NaHCO3 and citric acid with slight excess of the acid :-D ).
Transferred into 1 l separatory funnel and washed with 500 ml of saturated cold (4 C, from fridge) solution of NaCl, bottom water layer discarded and
upper organic layer processed further (this washing removed most of ethanol, H2SO4, some of butyric acid). Then washed thrice with NaHCO3 - every step
with 100 ml of saturated solution of NaHCO3 (CO2 evolution !!!) which removed H2SO4 completely and the residual unreacted butyric acid too (especially
the third washing was very thorough, 5 minutes of shaking) - this is the best method to remove butyric acid as it is hard to separate it by
distillation (azeotrope with ester) - if you do not remove butyric acid completely, then the smell of the product would be far(t) different from
expected ! Then washed with 100 ml of cold (4 C, from fridge) saturated NaCl solution (salt is necessary, solubility of ester is 4.9 mg/mL at 20 C,
addition of NaCl and low temp decreases loses of the product). NaHCO3 was not cold but used at room temperature as the NaHCO3 solubility at 0 C is
half of solubility at 20 C. Universal indicator paper showed neutral reaction (no acids) for both layers for the last washing. Upper ester layer
transferred into 250 ml Erlenmeyer flask and dried with anhydrous Na2SO4, the neck closed with a plastic foil, the flask swirled in hand occasionally
during 1/2 hour. Then transferred into 250 ml RBF, added boiling chips, attached distillation adapter with thermometer and Claisen condenser and
performed simple distillation, collected fraction 119-122 C, actual local atmospheric pressure 951,5 hPa (theoretical b.p. 120-121 C).
yields:
105,1 g after all washings
102,4 g after drying with Na2SO4
89,4 g after distillation (final yield)
I love pineapples !
Today we can post images but not yet fragrances, what's a pity. Maybe sometimes in the future...
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