Benzotriazole

:File:Benzotriazole_synthesis_01.svg

Benzotriazole features two fused rings. It can in principle exist as tautomers, but X-ray crystallography establishes the depicted structure. The N=N and HN-N distances are 1.306 and 1.340 Å.{{cite journal |doi=10.1107/S1600536805025523 |title=Polymorph β of 1 H -benzotriazole |date=2005 |last1=Krawczyk |first1=Sławomir |last2=Gdaniec |first2=Maria |journal=Acta Crystallographica Section E: Structure Reports Online |volume=61 |issue=9 |pages=o2967–o2969 }}

Benzotriazole can be prepared by the monodiazotization of o-phenylenediamine using sodium nitrite and acetic acid.Robert A. Smiley "Phenylene- and Toluenediamines" in Ullmann's Encyclopedia of Industrial Chemistry, 2002, Wiley-VCH, Weinheim. {{doi|10.1002/14356007.a19_405}}{{cite journal |doi=10.15227/orgsyn.020.0016 |title=1,2,3-Benzotriazole |journal=Organic Syntheses |date=1940 |volume=20 |page=16|first1=R. E.|last1=Damschroder|first2=W. D.|last2=Peterson }}{{cite journal |last1=Pereira |first1=Claudio M. P. |last2=Stefani |first2=Helio A. |last3=Guzen |first3=Karla P. |last4=Orfao |first4=Aline T. G. |date=2007-07-31 |title=Improved Synthesis of Benzotriazoles and 1-Acylbenzotriazoles by Ultrasound Irradiation. |url=https://onlinelibrary.wiley.com/doi/10.1002/chin.200731104 |journal=ChemInform |volume=38 |issue=31 |doi=10.1002/chin.200731104 |issn=0931-7597|url-access=subscription }}{{cite web |url=http://chemceed.com/products/benzotriazole/ |title=Benzotriazole - Chemical Supplier Distributor Chemceed}}

File:CSD CIF BISNUM.pngBTA is a weak Bronsted acid with a pK_a = 8.2. It is a weak Brønsted base, as indicated by the low pK_a < 0 of its conjugate acid, [HBTA]⁺.

It is also a Lewis base, binding Lewis acids at the C-N=N center. A variety coordination complexes are known such as the tetrahedral 2:1 derivative with zinc chloride, ZnCl₂(BTA)₂.{{cite journal |doi=10.3891/acta.chem.scand.35a-0739 |title=Benzotriazole Complexes. II. The Crystal Structures of Benzotriazolium Tetrachlorocobaltate(II), Bis(benzotriazole)dichlorozinc(II) and Polymeric Tetrakis(benzotriazolato)dizinc(II) |date=1981 |last1=Søtofte |first1=Inger |last2=Nielsen |first2=Kurt |last3=Trysberg |first3=Lennart |last4=Uggla |first4=Rolf |last5=Nielsen |first5=P. H. |journal=Acta Chemica Scandinavica |volume=35a |pages=739–745 }} In some complexes, BTA binds metals as its conjugate base forming polymers and oligomers.{{cite journal |doi=10.1016/j.inoche.2009.01.003 |title=Synthesis, structure and luminescent properties of an Organic–Inorganic hybrid solid based on unprecedented flower-basket-shaped [] clusters with 1,2-bis(benzotriazole)ethane ligands |date=2009 |last1=Wang |first1=Yan |last2=Hu |first2=Man-Cheng |last3=Zhai |first3=Quan-Guo |last4=Li |first4=Shu-Ni |last5=Jiang |first5=Yu-Cheng |last6=Ji |first6=Wen-Juan |journal=Inorganic Chemistry Communications |volume=12 |issue=4 |pages=281–285 }} It binds to copper surfaces, serving as a corrosion inhibitor.{{cite journal |last=Sease |first=Catherine |title=Benzotriazole: A Review for Conservators |journal=Studies in Conservation |date=May 1978 |volume=23 |series=2 |pages=76–85 |jstor=1505798 |doi=10.2307/1505798 |issue=2}}

:File:AlkylnBTA.svg

Deprotonation of BTA followed by treament with alkyl halides gives a mixture of 1- and 2-alkyl derivatives. Aromatic aldehydes (ArCHO) in the presence of ethanol gives benzotriazole-based N,O-acetals:

:{{chem2|ArCHO + BtH + EtOH -> ArCH(OEt)(Bt) + H2O}}

These acetals are susceptible to deprotonation, giving access to acylsilanes{{cite journal |doi=10.1021/om950712b |title=Novel and Convenient Synthesis of Aroyl-, Heteroaroyl-, Alkenoyl-, and Alkynoylsilanes |date=1996 |last1=Katritzky |first1=Alan R. |last2=Wang |first2=Zuoquan |last3=Lang |first3=Hengyuan |journal=Organometallics |volume=15 |issue=2 |pages=486–490 }} and acylboranes.

N-amination of BTA with hydroxylamine-O-sulfonic acid gives 1-aminobenzotriazole. Oxidation of this amine with lead(IV) acetate affords benzyne, which rapidly dimerises to biphenylene.{{cite journal |first1=C.D. |last1=Campbell |first2=C.W. |last2=Rees |authorlink2=Charles Rees |journal=J. Chem. Soc. C |title=Reactive intermediates. Part I. Synthesis and oxidation of 1- and 2-aminobenzotriazole |volume=1969 |issue=5 |pages=742–747 |year=1969 |doi=10.1039/J39690000742}}

:File:Dehydrobenzol aus Aminobenztriazol.svg

Benzotriazole has been used as a restrainer (or anti-fogging agent) in photographic emulsions or developing solutions, and as a reagent for the analytical determination of silver. More importantly, it has been extensively used as a corrosion inhibitor in the atmosphere and underwater. BTA can be used as antifreezes, heating and cooling systems, hydraulic fluids, and vapor-phase inhibitors as well.{{cn|date=April 2025}}

Benzotriazole is an corrosion inhibitor for copper. It is known that a passive layer, consisting of a complex between copper and benzotriazole, is formed when copper is immersed in a solution containing benzotriazole. The passive layer is insoluble in aqueous and many organic solutions. There is a positive correlation between the thickness of the passive layer and the efficiency of preventing corrosion.{{cite journal |last=Finšgar |first=M. |author2=Milošev I. |title=Inhibition of copper corrosion by 1,2,3-benzotriazole: A review |journal=Corrosion Science |date=11 March 2010 |volume=52 |pages=2737–2749 |doi=10.1016/j.corsci.2010.05.002 |issue=9|bibcode=2010Corro..52.2737F }} BTA is used in heritage conservation, notably for the treatment of bronze disease.

File:PolyCubtri.svg from benzotriazolate and copper(I), the active ingredient in the BT-derived corrosion inhibition]]

Benzotriazole is fairly water-soluble, is not readily degraded, and has a limited sorption tendency. It is only partly removed in wastewater treatment plants and a substantial fraction reaches surface water such as rivers and lakes.{{cite journal |pmid=17180965 |year=2006 |last1=Giger |first1=W |last2=Schaffner |first2=C |last3=Kohler |first3=HP |title=Benzotriazole and tolyltriazole as aquatic contaminants. 1. Input and occurrence in rivers and lakes |volume=40 |issue=23 |pages=7186–92 |journal=Environmental Science & Technology |doi=10.1021/es061565j}} It is of low toxicity and a low health hazard to humans although exhibiting some antiestrogenic properties.{{cite journal |last1=Farré |first1=Marinel la |last2=Pérez |first2=Sandra |last3=Kantiani |first3=Lina |last4=Barceló |first4=Damià |title=Fate and toxicity of emerging pollutants, their metabolites and transformation products in the aquatic environment |journal=TrAC Trends in Analytical Chemistry |volume=27 |issue=11 |year=2008 |pages=991–1007 |issn=0165-9936 |doi=10.1016/j.trac.2008.09.010}} Benzotriazole (and tolyltriazole) is a common "polar organic persistent pollutant", often detected at >0.1 μg/L.{{cite journal |doi=10.1016/j.watres.2010.05.032 |title=Pan-European survey on the occurrence of selected polar organic persistent pollutants in ground water |date=2010 |last1=Loos |first1=Robert |last2=Locoro |first2=Giovanni |last3=Comero |first3=Sara |last4=Contini |first4=Serafino |last5=Schwesig |first5=David |last6=Werres |first6=Friedrich |last7=Balsaa |first7=Peter |last8=Gans |first8=Oliver |last9=Weiss |first9=Stefan |last10=Blaha |first10=Ludek |last11=Bolchi |first11=Monica |last12=Gawlik |first12=Bernd Manfred |journal=Water Research |volume=44 |issue=14 |pages=4115–4126 |pmid=20554303 |bibcode=2010WatRe..44.4115L }} One source of this pollution is their use as anti-icing/deicing agents in airports.{{cite journal |doi=10.1002/ep.10059 |title=Natural, cost-effective, and sustainable alternatives for treatment of aircraft deicing fluid waste |date=2005 |last1=Castro |first1=Sigifredo |last2=Davis |first2=Lawrence C. |last3=Erickson |first3=Larry E. |journal=Environmental Progress |volume=24 |issue=1 |pages=26–33 |bibcode=2005EnvPr..24...26C }}

Many modifications of benzotriazole have been reported.{{cite journal |doi=10.1021/cr900204u |title=Synthesis of Heterocycles Mediated by Benzotriazole. 1. Monocyclic Systems |date=2010 |last1=Katritzky |first1=Alan R. |last2=Rachwal |first2=Stanislaw |journal=Chemical Reviews |volume=110 |issue=3 |pages=1564–1610 |pmid=19799386 }}{{cite journal |doi=10.1021/cr200031r |title=Synthesis of Heterocycles Mediated by Benzotriazole. 2. Bicyclic Systems |date=2011 |last1=Katritzky |first1=Alan R. |last2=Rachwal |first2=Stanislaw |journal=Chemical Reviews |volume=111 |issue=11 |pages=7063–7120 |pmid=21894899 }}{{cite journal |doi=10.1021/acs.chemrev.1c00991 |title=1,2,3-Triazole and Its Analogues: New Surrogates for Diazo Compounds |date=2022 |last1=Akter |first1=Monalisa |last2=Rupa |first2=Kavuri |last3=Anbarasan |first3=Pazhamalai |journal=Chemical Reviews |volume=122 |issue=15 |pages=13108–13205 |pmid=35852917 }}{{cite journal |doi=10.1021/cr941170v |title=Properties and Synthetic Utility of N -Substituted Benzotriazoles |date=1998 |last1=Katritzky |first1=Alan R. |last2=Lan |first2=Xiangfu |last3=Yang |first3=Jason Z. |last4=Denisko |first4=Olga V. |journal=Chemical Reviews |volume=98 |issue=2 |pages=409–548 |pmid=11848906 }} Vorozole and alizapride are commercial drugs. Benzotriazole esters are used as mechanism-based inactivators to treat severe acute respiratory syndrome (SARS) by inhibiting the SARS 3CL protease of the SARS-CoV-1 virus.{{cite journal |last=Kale |first=Raju R. |author2=Virendra Prasad |author3=Prabhu P. Mohapatra |author4= Vinod K. Tiwari |title=Recent developments in benzotriazole methodology for construction of pharmacologically important heterocyclic skeletons |journal=Monatsh Chemistry |date=6 March 2010 |volume=141 |pages=1159–1182 |doi=10.1007/s00706-010-0378-1 |issue=11 |s2cid=93911988|doi-access=free }}

Tolyltriazole is a mixture of isomers or congeners that differ from benzotriazole by the addition of one methyl group attached somewhere on the benzene ring. Tolyltriazole has similar uses, but has higher solubility in some organic solvents.{{Citation needed|date=September 2022}}

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