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Author: Subject: ethyl hexanoate - pineapple ester
Fery
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[*] posted on 20-2-2020 at 09:47
ethyl hexanoate - pineapple ester


this ester has more pleasant scent than ethyl butyrate

the synthesis is similar

98% hexanoic acid 94,0 g = 0,81 mol (thx fichema.cz)
96% ethanol 120 g (denatured: 95% ethanol + 1% MEK + ppm denatonium benzoate purified by NaOH and distillation, the same is in ethyl butyrate) - 3-fold excess
5 ml conc. H2SO4 (catalyst)

rfx 2 h

cooled down to RT

washed 1x500 ml cold 4 C conc. solution NaCl
washed 3x100 ml conc. solution of NaHCO3 (room temp 20 C), until no CO2 evolution
washed 2x100 ml cold 4 C conc. solution NaCl
universal indicator paper showed neutral reaction for both layers

dried with anhydrous Na2SO4 for 1 hour - 92,8 g of crude product

simple distillation, fraction collected 166-170 C
b.p. 168 °C (lit.)

yield: 76,2 g 65% (M=144.21 g/mol, 0,53 mol)

[Edited on 20-2-2020 by Fery]




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Tsjerk
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[*] posted on 20-2-2020 at 10:59


What is the % yield? I'm interested because you do specify the 3x molar excess.
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[*] posted on 20-2-2020 at 13:53


Theoretical yield or % yield is per definition based on the limiting reagent or reactant. As is clearly specified in this preparation the limiting reactant is the acid.

But yes %yield is always a statistic and as the saying goes there are lies, gross lies and statistics. Without defining what your %yield is based on you might end up in the latter two categories. Also failing to check purity those numbers might be inflated.

Although with this synthesis and purification I'd say it's about right. Conversion was probably good (70-90%) and the main losses occurred during purification (distillation).

Ideally you'd want an in process control to check that conversion or some other estimate of purity in the crude product before distillation.
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Fery
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[*] posted on 21-2-2020 at 00:40


65% yield (0,53 mol) calculated from the amount of hexanoic acid (0,81 mol)
ethanol added in 3-fold excess as it is very cheap (to shift equilibrium towards the ester so more of expensive hexanoic acid reacted) - on the first washing it is necessary to use a lot of water to wash out unreacted ethanol (some NaCl also crystallized out as ethanol entered into water phase)
cost of the hexanoic acid 12 EUR for 3x35 ml from this supplier, cost of ethanol negligible from this supplier




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