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Fischer esterification or Fischer–Speier esterification is a special type of esterification by refluxing a carboxylic acid and an alcohol in the presence of an acid catalyst. The reaction was first described by Emil Fischer and Arthur Speier in 1895. Most carboxylic acids are suitable for the reaction, but the alcohol should generally be primary or secondary. Tertiary alcohols are prone to elimination. Contrary to common misconception found in organic chemistry textbooks, phenols can also be esterified to give good to near quantitative yield of products. Commonly used catalysts for a Fischer esterification include sulfuric acid, p-toluenesulfonic acid, and Lewis acids such as scandium(III) triflate. For more valuable or sensitive substrates other, milder procedures such as Steglich esterification are used. The reaction is often carried out without a solvent or in a non-polar solvent to facilitate the Dean-Stark method. Typical reaction times vary from 1–10 hours at temperatures of 60-110 °C.
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3CF−
3 anions.
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Hafnium(IV) triflate or hafnium trifluoromethansulfonate is an inorganic substance with the idealized formula Hf(OSO2CF3)4, also written as Hf(OTf)4. Hafnium triflate is used as an impure mixture as a catalyst. Hafnium (IV) has an ionic radius of intermediate range (Al < Ti < Hf < Zr < Sc < Ln) and has an oxophilic hard character typical of group IV metals. This solid is a stronger Lewis acid than its typical precursor hafnium tetrachloride, HfCl4, because of the strong electron-withdrawing nature of the four triflate groups, which makes it a great Lewis acid and has many uses including as a great catalyst at low Lewis acid loadings for electrophilic aromatic substitution and nucleophilic substitution reactions.
References
- ↑ Harrowfield, J. M.; Keppert, D. L.; Patrick, J. M.; White, A. H. (1983). "Structure and stereochemistry in "f-block" complexes of high coordination number. VIII. The [M(unidentate)9] system. Crystal structures of [M(OH2)9] [CF3SO3]3, M = lanthanum, gadolinium, lutetium, or yttrium". Australian Journal of Chemistry . 36 (3): 483–492. doi:10.1071/CH9830483.
- ↑ Kobayashi, S.; Hachiya, I. (1994). "Lanthanide Triflates as Water-Tolerant Lewis Acids. Activation of Commercial Formaldehyde Solution and Use in the Aldol Reaction of Silyl Enol Ethers with Aldehydes in Aqueous Media". J. Org. Chem. 59 (13): 3590–6. doi:10.1021/jo00092a017.
- 1 2 Clark, J.; Macquarie, D. (2002). Handbook of Green Chemistry & Technology. Oxford, UK: Blackwell Science. ISBN 978-0-632-05715-3.
- ↑ Barrett, A.; Braddock, D. (1997). "Scandium(III) or Lanthanide(III) Triflates as Recyclable Catalysts for the Direct Acetylation of Alcohols with Acetic Acid". Chem. Commun. 1997 (4): 351–352. doi:10.1039/a606484a.
- 1 2 Engberts, J., Feringa, B., Keller, E. & Otto, S. 1996, “Lewis-acid Catalysis of Carbon Carbon Bond Forming Reactions in Water”, Recuil des Travaux Chimiques des Pays-Bas 115(11-12), 457-464
- 1 2 Kobayashi, S.; Manabe, K. (2000). "Green Lewis Acid Catalysts in Organic Synthesis". Pure Appl. Chem. 72 (7): 1373–1380. doi:10.1351/pac200072071373. S2CID 16770637.
- ↑ Wenhua Xie; Yafei Jin; Peng George Wang (1999). "Lanthanide triflates as unique Lewis acids". Chemtech . 29 (2): 23–29.
- ↑ Kobayashi, S.; Uchiro, H.; Fujishita, Y.; Shiina, I.; Mukaiyama, T. (1991). "Asymmetric Aldol Reaction between Achiral Silyl Enol Ethers and Achiral Aldehydes by use of a Chiral Promoter System". J. Am. Chem. Soc. 113 (11): 4247–4252. doi:10.1021/ja00011a030.
- ↑ Shu Kobayashi† and Kei Manabe. Green Lewis acid catalysis in organic synthesis. Pure Appl. Chem., Vol. 72, No. 7, pp. 1373–1380, 2000.
- ↑ Waller, F.J.; Barrett. A.G.M.; Braddock, D.C.; Ramprasad, D. "Lanthanide (III) Triflates as Recyclable Catalysts for Atom Economic Aromatic Nitration." Chem. Commun. 1997, 613-614.