4-Hydroxy-TEMPO

{{Chembox

|Watchedfields = changed

|verifiedrevid = 456502836

|ImageFile = 4-Hydroxy-TEMPO.svg

|ImageSize = 175

|ImageAlt = Skeletal formula of 4-hydroxy-TEMPO

|ImageFile1 = 4-Hydroxy-TEMPO radical ball.png

|ImageSize1 = 175

|ImageAlt1 = Ball-and-stick model of the 4-hydroxy-TEMPO molecule

|PIN = (4-Hydroxy-2,2,6,6-tetramethylpiperidin-1-yl)oxyl

|OtherNames = tempol; tanol; TMPN; 4-Oxypiperidol; nitroxyl 2; HyTEMPO

|Section1={{Chembox Identifiers

|CASNo_Ref = {{cascite|correct|CAS}}

|CASNo = 2226-96-2

|UNII_Ref = {{fdacite|correct|FDA}}

|UNII = U78ZX2F65X

|ChEMBL_Ref = {{ebicite|correct|EBI}}

|ChEMBL = 607023

|PubChem = 137994

|ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}

|ChemSpiderID = 121639

|ChEBI = 180664

|SMILES = CC1(C)CC(O)CC(C)(C)N1[O]

|InChI = 1S/C9H18NO2/c1-8(2)5-7(11)6-9(3,4)10(8)12/h7,11H,5-6H2,1-4H3

|InChIKey = UZFMOKQJFYMBGY-UHFFFAOYSA-N

|StdInChI_Ref = {{stdinchicite|correct|chemspider}}

|StdInChI = 1S/C9H18NO2/c1-8(2)5-7(11)6-9(3,4)10(8)12/h7,11H,5-6H2,1-4H3

|StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}

|StdInChIKey = UZFMOKQJFYMBGY-UHFFFAOYSA-N

}}

|Section2={{Chembox Properties

|C=9|H=18|N=1|O=2

|Appearance = Orange crystals

|MeltingPtC = 71–73

|MeltingPt_ref = {{cite journal|last1=Zakrzewski|first1=Jerzy|last2=Krawczyk|first2=Maria|title=Reactions of Nitroxides. Part XII [1]. – 2,2,6,6-Tetramethyl-1-oxyl- 4-piperidyl Chloroformate – A New Reactive Nitroxyl Radical. A One-pot Synthesis of 2,2,6,6-Tetramethyl-1-oxyl-4-piperidyl N,N-Dialkyl-carbamates|journal=Zeitschrift für Naturforschung B|date=1 January 2011|volume=66|issue=5|pages=493–498 |doi=10.1515/znb-2011-0509|s2cid=51802316 |doi-access=free}}

|Solubility = 629.3 g/L (20 °C)}}

|Section3={{Chembox Hazards

|GHSPictograms = {{GHS07}}{{Sigma-Aldrich|id=176141|name=4-Hydroxy-TEMPO|accessdate=2015-08-24}}

|GHSSignalWord = Warning

|HPhrases = {{H-phrases|302|315|319|335}}

|PPhrases = {{P-phrases|261|305+351+338}}

}}

}}

4-Hydroxy-TEMPO or TEMPOL, formally 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl, is a heterocyclic compound. Like the related TEMPO, it is used as a catalyst and chemical oxidant by virtue of being a stable aminoxyl radical. Its major appeal over TEMPO is that it is less expensive, being produced from triacetone amine, which is itself made via the condensation of acetone and ammonia. This makes it economically viable on an industrial scale.{{cite journal|last1=Ciriminna|first1=Rosaria|last2=Pagliaro|first2=Mario|title=Industrial Oxidations with Organocatalyst TEMPO and Its Derivatives|journal=Organic Process Research & Development|date=15 January 2010|volume=14|issue=1|pages=245–251|doi=10.1021/op900059x}}

File:4-Hydroxy-TEMPO synthesis01.svg, which is itself made from acetone and ammonia]]

In biochemical research, 4-hydroxy-TEMPO has been investigated as an agent for limiting reactive oxygen species. It catalyzes the disproportionation of superoxide, facilitates hydrogen peroxide metabolism, and inhibits Fenton chemistry.{{cite journal | doi = 10.1124/pr.108.000240 | title = Chemistry and Antihypertensive Effects of Tempol and Other Nitroxides | year = 2008 | last1 = Wilcox | first1 = C. S. | last2 = Pearlman | first2 = A. | journal = Pharmacological Reviews | volume = 60 | issue = 4 | pages = 418–69 | pmid = 19112152 | pmc = 2739999}} 4-Hydroxy-TEMPO, along with related nitroxides, are being studied for their potential antioxidant properties.{{cite journal | doi = 10.3390/ijms18112490 | title = Nitroxides as Antioxidants and Anticancer Drugs | year = 2017 | last1 = Lewandowski | first1 = M | last2 = Gwozdzinski | first2 = K. | journal = International Journal of Molecular Sciences | volume = 18 | issue = 11 | pages = 2490 | pmid = 29165366 | pmc = 5713456| doi-access = free }}

On an industrial-scale 4-hydroxy-TEMPO is often present as a structural element in hindered amine light stabilizers, which are commonly used stabilizers in plastics, it is also used as a polymerisation inhibitor, particularly during the purification of styrene.

It is a promising model substance to inhibit SARS-CoV-2 RNA-dependent RNA polymerase.{{cite journal | doi = 10.1126/science.abi5224 | title = Fe-S cofactors in the SARS-CoV-2 RNA-dependent RNA polymerase are potential antiviral targets | year = 2021 | last1 = Maio| first1 = N. | last2 = Lafont| first2 = B.A.P. | last3 = Sil| first3 = D. | last4 = Li| first4 = Y. | last5 = Bollinger | first5 = M. | last6 = Krebs | first6 = C. | journal = Science | volume = 373 | issue = 6551 | pages = 236–241 | pmid = 34083449 | pmc = 8892629 | doi-access = free }}