Can someone decipher this for me?

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SUMMARY

The forum discussion centers on the synthesis of esters, specifically the methyl ester and 2,2,2-trifluoroethyl ester of 10-undecylenic acid. The procedures involve refluxing the acid with methanol or 2,2,2-trifluoroethanol in the presence of sulfuric acid, followed by a workup process that includes washing with sodium bicarbonate, water, and NaCl, and drying over magnesium sulfate. The identity of the products was confirmed using proton NMR and fluorine NMR techniques. The term "workup" refers to the isolation and purification steps taken after the reaction completion.

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  • Familiarity with NMR spectroscopy, specifically proton and fluorine NMR.
  • Knowledge of reflux techniques and the use of a Dean-Stark apparatus.
  • Experience with purification methods such as vacuum distillation and drying agents like magnesium sulfate.
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seang
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Hi,

I am an electrical engineer, but I have to complete the following procedure:


Synthesis of Esters. (a)

Methyl Ester. The methyl ester of 10-
undecylenic acid was prepared similarly to the method used by Sieval.
The 10-undecylenic acid was dissolved in methanol and allowed to
reflux for 3 h with a small amount of sulfuric acid. Excess methanol
was removed by vacuum. The crude product was dissolved in ether,
washed with a saturated sodium bicarbonate solution, water, then a
saturated NaCl solution, and dried over magnesium sulfate. The identity
of the vacuum distilled product was confirmed using proton NMR.
1H NMR: ä 5.73-5.89 (m, 1H), 4.89-5.04 (m, 2H), 3.67 (s, 3H),
2.25-2.35 (t, 2H), 1.99-2.09 (m, 2H), 1.54-1.69 (m, 2H), 1.23-
1.44 (m, 10H).

(b) 2,2,2-Trifluoroethyl Ester. The fluorinated ethyl ester of 10-
undecylenic acid was prepared similarly to the methyl ester. To 30 g
of 10-undecylenic acid was added 22 g of 2,2,2-trifluoroethanol
dissolved in 40 mL of toluene. This mixture was allowed to reflux
with a small amount of sulfuric acid for 3 h using a Dean-Stark
apparatus. Workup similar to the methyl ester produced a crude product
that was further purified by vacuum distillation. Proton, COSY, and
fluorine NMR confirmed the identity of the product.
1H NMR: ä 5.70-5.90 (m, 1H), 4.86-5.06 (m, 2H), 4.38-4.51
(q, 2H), 2.35-2.45 (t, 2H), 1.98-2.10 (m, 2H), 1.55-1.75 (m, 2H),
1.20-1.50 (m, 10H). Fluorine NMR: single triplet.That word there, WORKUP, is kinda ambiguous to me as an EE. Not sure what part of procedure a.) they are referring to. My best guess is "...washed with a saturated sodium bicarbonate solution, water, then a saturated NaCl solution, and dried over magnesium sulfate."

Any ideas?
 
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seang said:
Hi,

I am an electrical engineer, but I have to complete the following procedure:


Synthesis of Esters. (a)

Methyl Ester. The methyl ester of 10-
undecylenic acid was prepared similarly to the method used by Sieval.
The 10-undecylenic acid was dissolved in methanol and allowed to
reflux for 3 h with a small amount of sulfuric acid. Excess methanol
was removed by vacuum. The crude product was dissolved in ether,
washed with a saturated sodium bicarbonate solution, water, then a
saturated NaCl solution, and dried over magnesium sulfate. The identity
of the vacuum distilled product was confirmed using proton NMR.
1H NMR: ä 5.73-5.89 (m, 1H), 4.89-5.04 (m, 2H), 3.67 (s, 3H),
2.25-2.35 (t, 2H), 1.99-2.09 (m, 2H), 1.54-1.69 (m, 2H), 1.23-
1.44 (m, 10H).

(b) 2,2,2-Trifluoroethyl Ester. The fluorinated ethyl ester of 10-
undecylenic acid was prepared similarly to the methyl ester. To 30 g
of 10-undecylenic acid was added 22 g of 2,2,2-trifluoroethanol
dissolved in 40 mL of toluene. This mixture was allowed to reflux
with a small amount of sulfuric acid for 3 h using a Dean-Stark
apparatus. Workup similar to the methyl ester produced a crude product
that was further purified by vacuum distillation. Proton, COSY, and
fluorine NMR confirmed the identity of the product.
1H NMR: ä 5.70-5.90 (m, 1H), 4.86-5.06 (m, 2H), 4.38-4.51
(q, 2H), 2.35-2.45 (t, 2H), 1.98-2.10 (m, 2H), 1.55-1.75 (m, 2H),
1.20-1.50 (m, 10H). Fluorine NMR: single triplet.


That word there, WORKUP, is kinda ambiguous to me as an EE. Not sure what part of procedure a.) they are referring to. My best guess is "...washed with a saturated sodium bicarbonate solution, water, then a saturated NaCl solution, and dried over magnesium sulfate."

Any ideas?

Looks like a standard transesterification. Workup is everything after the reaction is completed to isolate the desired product. Therefore, according to what you have, the workup is... "The crude product was dissolved in ether (the trifluoroester may or may not be soluble in ether), washed with a saturated sodium bicarbonate solution, water, then a saturated NaCl solution, and dried over magnesium sulfate. The identity of the vacuum distilled product was confirmed using proton NMR."
 
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Thanks for your help!