allyl hexanoate - pineapple ester
another beautiful pineapple scenting ester
63,5 g of hexanoic acid (0,55 mol)
47,8 g 80-90% allyl alcohol (I used a fraction boiling from b.p. of azeotrope to b.p. of anhydrous allyl alcohol which I collected as a forerun before
main anhydrous allyl alcohol fraction started to distill) (40,6 g of 100% alcohol if asssuming 85% alcohol = 0,70 mol = slight excess, 0,15 mol more =
8,7 g of alcohol are allowed to be lost until esterification with removal of all water, water present 15% * 47,8 = 7,2 g)
20 ml isohexanes, b.p. 60-65 C (medicinal petrolether, hydrogenated benzin) must be more than the volume of Dean-Stark trap apparatus
0,5 ml 96% H2SO4 (catalyst, no need more, maybe half would be enough too)
To 250 ml RBF was poured 63,5 g of hexanoic acid + 47,8 g 80-90% allyl alcohol + 20 ml isohexanes + 0,5 ml 96% H2SO4. Boiling stones (glass balls)
added, 10 ml Dean-Stark trap apparatus attached with condenser and the reaction mixture was refluxed. After 1 hour 21,0 g removed from the trap (9,9 g
reaction water, 7,2 g water present in 85% allyl alcohol and remaining 3,9 g should be allyl alcohol loses which is below the used 8,7 g excess of the
allyl alcohol). No more bottom phase collected after extra half an hour of refluxing.
Cooled down to room temperature, transferred into 250 ml separatory funnel.
Washed with:
washed with 100 ml of cold tap water
washed with 100 ml of cold tap water, emulsion formed, broken by addition of 50 ml of 5% NaHCO3, effervescence of CO2, sep funnel venter much more
frequently than when washing with only H2O
washed with 75 ml of 5% NaHCO3
washed with 75 ml of 5% NaHCO3, when it stopped evolving pressure and CO2 it was a sign that all the H2SO4 and possibly unreacted hexanoic acids were
removed, emulsion of water bottom phase observed, gently moving (not shaking) helped to break the emulsion faster
washed with 100 ml of tap H2O, emulsion, broken by occasional gentle moving (1 hour required)
washed with 100 ml of tap H2O, emulsion, broken by occasional gentle moving (1 hour required)
Upper phase always kept and bottom water phase discarded.
Transferred into 250 ml FBF, added anhydrous Na2SO4 and magnetically stirred for 1 hour, let to sit overnight and the next day again magnetically
stirred for 1 hour.
Filtered into 250 ml RBF through a glass funnel with a plug of mineral cotton.
Isohexanes distilled out using water aspirator vacuum.
Distilled using oil rotary vacuum pump at pressure approximately 4 kPa (-96 kPa when valve fully closed, -92 kPa when valve partially open during
ditillation), main fraction collected 74-75 C, yield 66,3 g 77% (first 10 ml forerun separated, residuum in flask cca 5 ml). Oil bath temp 110-115 C.
apparatus for the reaction
the level of upper isohexanes phase and bottom water + a little of allyl alcohol phase, I had to drain the bottom phase more times as my Dean-Stark
trap apparatus has only 10 ml volume, I collected totally 21,0 g of mixture of water + allyl alcohol (that's why I used excess of allyl alcohol for
the esterification) during 1 hour, then no more bottom phase collected after extra half an hour of reflux
first washing with tap water, no problem in separation, the organic phase is very dark as I used 2 years old hexanoic acid which was in original
plastic bottles (2x35 ml, https://fichema.cz/produkty/1565-kyselina-kapronova-35-ml-85...), maybe using less of H2SO4 catalyst could also help in less dark organic phase?,
but no worry, crystal clear product obtained after the final distillation
second washing with tap water, nasty emulsion
the emulsion was broken by adding 50 ml of 5% NaHCO3 (CO2 effervescence and increasing of pressure in the separatory funnel)
third washing, with 75 ml of 5% NaHCO3, no problem
fifth washing, with 100 ml of tap water, emulsion again, to break it a weak movement with the separatory funnel helped (not shaking!), the same on
sixth final washing with 100 ml of tap water
   
vacuum distillation, I had to partially open the valve to reduce the vacuum strength of my vacuum pump, the fraction collected boiling in range 74-75
C at vacuum level approximately 4 kPa (the manometer showed -92 kPa and when the valve fully closed it shows -96 kPa, it is 2-stage oil rotary vacuum
pump capable of vacuum below 1 Pa at which the manometer shows -96 kPa)
 
video of vacuum distillation:
https://www.youtube.com/watch?v=lieDF_4KgNE
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