acetoxy group
{{Short description|Chemical group (–OC(O)CH3)}}
{{redirect|AcO|other uses|aco (disambiguation)}}
In organic chemistry, the acetoxy group (abbr. AcO– or –OAc; IUPAC name: acetyloxy{{cite book | title = Nomenclature of Organic Chemistry : IUPAC Recommendations and Preferred Names 2013 (Blue Book) | publisher = The Royal Society of Chemistry | date = 2014 | location = Cambridge | page = 805 | doi = 10.1039/9781849733069-00648 | isbn = 978-0-85404-182-4 |quote=The systematic name ‘acetyloxy’ is preferred to the contracted name ‘acetoxy’ that may be used in general nomenclature.}}), is a functional group with the formula {{chem2|\sOCOCH3}} and the structure {{chem2|\sO\sC(\dO)\sCH3}}. As the -oxy suffix implies, it differs from the acetyl group ({{chem2|\sC(\dO)\sCH3}}) by the presence of an additional oxygen atom. The name acetoxy is the short form of acetyl-oxy.
Functionality
An acetoxy group may be used as a protection for an alcohol functionality in a synthetic route although the protecting group itself is called an acetyl group.
=Alcohol protection=
There are several options of introducing an acetoxy functionality in a molecule from an alcohol (in effect protecting the alcohol by acetylation):
- Acetyl halide, such as acetyl chloride in the presence of a base like triethylamine{{Cite book |last=Ouellette |first=Robert J. |url=https://www.sciencedirect.com/book/9780128128381/organic-chemistry |title=Organic Chemistry |last2=Rawn |first2=J. David |year=2019 |isbn=978-0-12-812838-1 |edition=2nd |pages=665-710 |chapter=22 - Carboxylic Acid Derivatives |doi=10.1016/C2016-0-04004-4 |access-date=2024-05-08 |chapter-url=https://www.sciencedirect.com/science/article/abs/pii/B9780128128381500220 |url-access=limited}}
- Activated ester form of acetic acid, such as a N-hydroxysuccinimide ester, although this is not advisable due to higher costs and difficulties.{{Cite book |last=Cali |first=Khasim |url=https://www.sciencedirect.com/bookseries/methods-in-enzymology/vol/642/suppl/C |title=Odorant Binding and Chemosensory Proteins |last2=Tuccori |first2=Elena |last3=Persaud |first3=Krishna C. |date=2020-08-19 |editor-last=Pelosi |editor-first=Paolo |series=Methods in Enzymology |volume=642 |pages=435-468 |language=en |chapter=Chapter Eighteen - Gravimetric biosensors |doi=10.1016/bs.mie.2020.05.010 |issn=0076-6879 |access-date=2024-05-08 |editor-last2=Knoll |editor-first2=Wolfgang |chapter-url=https://www.sciencedirect.com/science/article/abs/pii/S0076687920302329}}
- Acetic anhydride in the presence of base with a catalyst such as pyridine with a bit of DMAP added.{{Cite book |url=http://www.ncbi.nlm.nih.gov/books/NBK593839/ |title=Glycoscience Protocols (GlycoPODv2) |date=2021 |publisher=Japan Consortium for Glycobiology and Glycotechnology |editor-last=Nishihara |editor-first=Shoko |location=Saitama (JP) |pmid=37590565 |editor-last2=Angata |editor-first2=Kiyohiko |editor-last3=Aoki-Kinoshita |editor-first3=Kiyoko F. |editor-last4=Hirabayashi |editor-first4=Jun}}
An alcohol is not a particularly strong nucleophile and, when present, more powerful nucleophiles like amines will react with the above-mentioned reagents in preference to the alcohol.{{Cite journal |last=Wall |first=Leo A. |last2=Pummer |first2=Walter J. |last3=Fearn |first3=James E. |last4=Antonucci |first4=Joseph M. |date=1963-09-01 |title=Reactions of polyfluorobenzenes with nucleophilic reagents |url=https://nvlpubs.nist.gov/nistpubs/jres/67A/jresv67An5p481_A1b.pdf |journal=Journal of Research of the National Institute of Standards and Technology |language=en |volume=67A |issue=5 |pages=481 |doi=10.6028/jres.067A.050 |issn=0022-4332 |pmc=5319811 |pmid=31580596}}
=Alcohol deprotection=
For deprotection (regeneration of the alcohol)
- Aqueous base (pH >9){{Cite book |last=Matyjaszewski |first=Krzysztof |url=https://www.sciencedirect.com/referencework/9780080878621/polymer-science-a-comprehensive-reference |title=Polymer Science: A Comprehensive Reference |last2=Möller |first2=Martin |publisher=Elsevier Science |year=2012 |isbn=978-0-08-087862-1 |volume=8 |pages=37-76 |language=en |chapter=8.03 - Photoresists and Advanced Patterning |doi=10.1016/B978-0-444-53349-4.00201-6 |chapter-url=https://www.sciencedirect.com/science/article/abs/pii/B9780444533494002016}}
- Aqueous acid (pH <2), may have to be heated{{Cite journal |last=Howard |first=Kyle T. |last2=Chisholm |first2=John D. |date=2016-01-02 |title=Preparation and Applications of 4-Methoxybenzyl Esters in Organic Synthesis |url=https://www.tandfonline.com/doi/full/10.1080/00304948.2016.1127096 |journal=Organic Preparations and Procedures International |language=en |volume=48 |issue=1 |pages=1–36 |doi=10.1080/00304948.2016.1127096 |issn=0030-4948 |pmc=4989276 |pmid=27546912}}
- Anhydrous base such as sodium methoxide in methanol. Very useful when a methyl ester of a carboxylic acid is also present in the molecule, as it will not hydrolyze it like an aqueous base would. (Same also holds with an ethoxide in ethanol with ethyl esters){{Cite journal |last=Banyikwa |first=Andrew Toyi |last2=Miller |first2=Stephen E. |last3=Krebs |first3=Richard A. |last4=Xiao |first4=Yuewu |last5=Carney |first5=Jeffrey M. |last6=Braiman |first6=Mark S. |date=2017-10-31 |title=Anhydrous Monoalkylguanidines in Aprotic and Nonpolar Solvents: Models for Deprotonated Arginine Side Chains in Membrane Environments |url=https://pubs.acs.org/doi/10.1021/acsomega.7b00281 |journal=ACS Omega |language=en |volume=2 |issue=10 |pages=7239–7252 |doi=10.1021/acsomega.7b00281 |issn=2470-1343 |pmc=6645140 |pmid=31457300}}