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Triethyl Orthoacetate: Applications in Organic Synthesis and Esterification

Aug 6,2025

Triethyl orthoacetate is the ethyl orthoester of acetic acid. It is an oily liquid with a pungent odor. Triethyl orthoacetate is used as a water scavenger and as intermediate for synthesis of pharmaceuticals. It is used in organic synthesis for the introduction of the acetate group to an alcohol and in the Johnson-Claisen rearrangement. Triethyl orthoacetate can be used for the synthesis of: Ordered mesoporous carbons for catalysis, electrochemistry and hydrogen storage applications; Esters of phosphonic acids, carboxylic acids and phosphinic acids; alk-4-enoates by Johnson–Claisen rearrangement reaction; Benzoxazoles, benzimidazoles and oxazolo[4,5-b]pyridines and Quinazolin-4(3H)-one derivatives. Triethyl orthoacetat is also used in organic synthesis to introduce the acetate group into an alcohol. It is involved in the Johnson-Claisen rearrangement.

Triethyl orthoacetate.png

Concurrent esterification and N-acetylation of amino acids with orthoesters

Orthoesters have been widely used in organic synthesis for a variety of reactions. However, the difference in reactivity between the most commonly used orthoesters, triethyl orthoacetate (TEOA) and triethyl orthoformate (TEOF), has not been clearly appreciated. A while ago, we reported that TEOA and trimethyl orthoacetate (TMOA) were more effective and superior in the esterification of carboxylic acids and sulfonic acids under mild reaction conditions than TEOF. The reaction of amines with orthoesters is quite complicated and is dependent on a number of variables including the nature of the amine and the orthoester, stoichiometry of the reagents, presence of an acid catalyst, and the reaction conditions, leading to the formation of a variety of nitrogen-containing products including amides, imidates, amidines and orthoamines. The use of Triethyl orthoacetat or TMOA for the esterification of carboxylic, phosphinic and phosphonic acids in ionic liquids (80°C, 100 min) has also been reported. Orthoesters have been used in the esterification of N-acylamino acids. In the microwave-assisted esterification of various N-protected amino acids, Triethyl orthoacetat was found to better effect the esterification than TEOF.[1]

The observed stoichiometry and stereochemical outcome of the TEOA reaction with proline and phenylalanine was surprising. It is interesting to point out that in the case of 3-aminobenzoic acid, the product isolated on reaction with Triethyl orthoacetat (2 eq.) was the imidate ethyl ester, and not the N-acetyl ester. This supports our mechanistic hypothesis that an imidate ester is involved in this process. In conclusion, we have shown that TEOA is an effective reagent for the concurrent and one pot N-acetylation and esterification of amino acids under neutral conditions. TEOF exhibits lower reactivity and performs poorly in this type of transformation. In the case of α-amino acids, one equivalent of Triethyl orthoacetat in refluxing toluene is sufficient to give the corresponding N-acetyl ethyl esters in good yields.  It is important in emphasize that the choice of TEOA or TEOF is important and may govern the success of the desired transformation. It is clear that further studies are required to delineate the differences in reactivity between Triethyl orthoacetat and TEOF with other substrates and transformations. Also, the use of other orthoesters may allow variation of the acyl or ester groups that are incorporated.

Selective Esterification of Phosphonic Acids

Organophosphonates are a relatively diverse and common group of compounds, which feature the presence of a stable C–P bond. In nature, they are present in microorganisms as well as in metazoans. The synthesis of organophosphorus esters from related phosphites in reaction with organic halides (Michaelis–Arbuzov reaction) is well-established chemistry. Here, we report straightforward and selective synthetic procedures for mono- and diesterification of phosphonic acids. A series of alkoxy group donors were studied and triethyl orthoacetate was found to be the best reagent as well as a solvent for the performed transformations. The application of triethyl orthoacetate as an ethoxy group donor resulting in high conversion, yielding 84%. In both cases, excellent selectivity towards monoesters 3a and 3b was observed.[2]

After the addition of triethyl orthoacetate and heating the reaction mixture for 1 h at 75 °C, the NMR spectra changed substantially. The signal associated with substrate phenylphosphonic diminished almost to zero and four new signals appeared on the spectra. The main peak at 26.5 ppm comes from diester Diethyl Benzylphosphonate. This readily explains why the larger amount of triethyl orthoacetate favors double esterification with respect to monoesterification. To a solution of butylphosphonic acid 1a (1 equiv., 7 mg, 0.05 mmol) or benzylphosphonic acid 1b (1 equiv., 9 mg, 0.05 mmol), 1 mL of respective solvent triethyl orthoacetate 2a (3 equiv., 25 mg, 0.15 mmol) was added and stirred at 30 °C for 24 h. The solvent and other volatile substances were evaporated under reduced pressure.

References

[1]Gibson S, Romero D, Jacobs HK, Gopalan AS. Concurrent esterification and N-acetylation of amino acids with orthoesters: A useful reaction with interesting mechanistic implications. Tetrahedron Lett. 2010 Dec 22;51(51):6737-6740. doi: 10.1016/j.tetlet.2010.10.081. PMID: 21286246; PMCID: PMC3030124.

[2]Trzepizur D, Brodzka A, Koszelewski D, Ostaszewski R. Selective Esterification of Phosphonic Acids. Molecules. 2021 Sep 17;26(18):5637. doi: 10.3390/molecules26185637. PMID: 34577108; PMCID: PMC8466293.

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Triethyl orthoacetate manufacturers

  • Triethyl Orthoacetate
  • 78-39-7 Triethyl Orthoacetate
  • $0.00 / 1kg
  • 2025-08-07
  • CAS:78-39-7
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  • Purity: 99.99%
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  • Triethyl orthoacetate
  • 78-39-7 Triethyl orthoacetate
  • $50.00 / 1KG
  • 2025-07-07
  • CAS:78-39-7
  • Min. Order: 1KG
  • Purity: 99%
  • Supply Ability: 5000KG