Benzotriazole

Benzotriazole (BTA) is a heterocyclic compound with the chemical formula C6H5N3. Its five-membered ring contains three consecutive nitrogen atoms. This bicyclic compound may be viewed as fused rings of the aromatic compounds benzene and triazole. This white-to-light tan solid has a variety of uses, for instance, as a corrosion inhibitor for copper.[5]

Benzotriazole
Skeletal formula of benzotriazole
Space-filling model of the benzotriazole molecule
Names
Preferred IUPAC name
1H-1,2,3-Benzotriazole
Other names
1H-Benzotriazole; 1,2,3-Benzotriazole; BTA; BtaH
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.002.177
EC Number
  • 202-394-1
RTECS number
  • DM1225000
UNII
  • InChI=1S/C6H5N3/c1-2-4-6-5(3-1)7-9-8-6/h1-4H,(H,7,8,9) checkY
    Key: QRUDEWIWKLJBPS-UHFFFAOYSA-N checkY
  • InChI=1/C6H5N3/c1-2-4-6-5(3-1)7-9-8-6/h1-4H,(H,7,8,9)
    Key: QRUDEWIWKLJBPS-UHFFFAOYAH
  • n1c2ccccc2[nH]n1
Properties
C6H5N3
Molar mass 119.127 g·mol−1
Appearance White solid
Density 1.36 g/mL[1]
Melting point 100 °C (212 °F; 373 K)[2]
Boiling point 350 °C (662 °F; 623 K)[2]
20 g/L[2]
Acidity (pKa) 8.2[3][4]
Basicity (pKb) > 14[4]
Hazards
GHS labelling:
GHS07: Exclamation markGHS09: Environmental hazard
Warning
H302, H319, H332, H411, H412
P261, P264, P270, P271, P273, P280, P301+P312, P304+P312, P304+P340, P305+P351+P338, P312, P330, P337+P313, P391, P501
Related compounds
Related compounds
 Benzimidazole, Tolyltriazole
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☒N verify (what is checkY☒N ?)
Infobox references

Structure

Benzotriazole features two fused rings. Its five-membered ring can exist in tautomers A and B, and the derivatives of both tautomers, structures C and D, can also be produced:[6]

Benzotriazole tautomers and their derivatives

Various structural analyses with UV, IR and 1H-NMR spectra indicated that isomer A is predominantly present at room temperature. The bond between positions 1 and 2 and the one between positions 2 and 3 have proved to have the same bond properties. Moreover, the proton does not tightly bind to any of the nitrogen atoms, but rather migrates rapidly between positions 1 and 3. Therefore, the BTA can lose a proton to act as a weak acid (pKa = 8.2)[3][4] or accept a proton using the lone pair electrons located on its nitrogen atoms as a very weak Brønsted base (pKa < 0).[4] Not only can it act either as an acid or base, it can also bind to other species, utilizing the lone pair electrons. Applying this property, the BTA can form a stable coordination compound on a copper surface and behave as a corrosion inhibitor.[6]

Synthesis and reactions

Synthesis of benzotriazole involves the reaction of o-phenylenediamine, sodium nitrite, and acetic acid. The conversion proceeds via diazotization of one of the amine groups:[7]

Synthesis of benzotriazole

The synthesis can be improved when the reaction is carried out at low temperatures (5–10 °C) and briefly irradiated in an ultrasonic bath.[8] Typical batch purity is 98.5% or greater.[9]

Derivatives

Biphenylene and benzyne can be conveniently prepared from benzotriazole by N-amination with hydroxylamine-O-sulfonic acid. The major product, 1-aminobenzotriazole, forms benzyne in an almost quantitative yield by oxidation with lead(IV) acetate, which rapidly dimerises to biphenylene in good yields.[10]

Synthesis of Benzyne and Biphenylene from 1H-Benzotriazole

Applications

Benzotriazole has been known for its great versatility. It has already 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. Also, its derivatives and their effectiveness as drug precursors have been drawing attention. Besides all the applications mentioned above, the BTA can be used as antifreezes, heating and cooling systems, hydraulic fluids, and vapor-phase inhibitors as well.[6]

Corrosion inhibition

Benzotriazole is an effective corrosion inhibitor for copper and its alloys by preventing undesirable surface reactions. 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.[11] BTA is used in heritage conservation, notably for the treatment of bronze disease. The exact structure of the copper-BTA complex is controversial and many proposals have been suggested.

Chemical structure of the coordination polymer from benzotriazolate and copper(I), the active ingredient in the BT-derived corrosion inhibition

Drug precursor

Benzotriazole derivatives have chemical and biological properties that are versatile in the pharmaceutical industry. Benzotriazole derivatives act as agonists for many proteins. For instance, vorozole and alizapride have useful inhibitory properties against different proteins. 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. The methodology is not only limited to heterocyclization but was also successful for polynuclear hydrocarbons of small carbocyclic systems.[12]

Environmental relevance

Benzotriazole is fairly water-soluble, not readily degradable and has a limited sorption tendency. Hence, it is only partly removed in wastewater treatment plants and a substantial fraction reaches surface water such as rivers and lakes.[13] It is considered to be of low toxicity and a low health hazard to humans although exhibiting some antiestrogenic properties.[14]

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 better solubility in some organic solvents.

References

Media related to Benzotriazole at Wikimedia Commons

  1. "1H-Benzotriazole (CAS 95-14-7)". Archived from the original on 2020-10-24.
  2. 1H-Benzotriazole Archived September 27, 2007, at the Wayback Machine, SRC PhysProp Database
  3. Katritzky, A. R.; Rachwal S.; Hitchings G. J. (14 January 1991). "Benzotriazole: A novel synthetic auxiliary". Tetrahedron. 47 (16–17): 2683–2732. doi:10.1016/S0040-4020(01)87080-0.
  4. Katritzky, A. R. "Adventures with Benzotriazole" (PDF). Lecture presented at various locations in 2002. Florida Center for Heterocyclic Compounds. Archived from the original (PDF) on 26 April 2012. Retrieved 23 November 2011.
  5. "1,2,3-BENZOTRIAZOLE | CAMEO Chemicals | NOAA". cameochemicals.noaa.gov. Retrieved 2023-01-17.
  6. Sease, Catherine (May 1978). "Benzotriazole: A Review for Conservators". Studies in Conservation. 2. 23 (2): 76–85. doi:10.2307/1505798. JSTOR 1505798.
  7. Robert A. Smiley "Phenylene- and Toluenediamines" in Ullmann's Encyclopedia of Industrial Chemistry, 2002, Wiley-VCH, Weinheim. doi:10.1002/14356007.a19_405
  8. Pereira, Claudio M. P.; Stefani, Helio A.; Guzen, Karla P.; Orfao, Aline T. G. (2007-07-31). "Improved Synthesis of Benzotriazoles and 1-Acylbenzotriazoles by Ultrasound Irradiation". ChemInform. 38 (31). doi:10.1002/chin.200731104. ISSN 0931-7597.
  9. "Benzotriazole - Chemical Supplier Distributor Chemceed".
  10. Campbell, C.D.; Rees, C.W. (1969). "Reactive intermediates. Part I. Synthesis and oxidation of 1- and 2-aminobenzotriazole". J. Chem. Soc. C. 1969 (5): 742–747. doi:10.1039/J39690000742.
  11. Finšgar, M.; Milošev I. (11 March 2010). "Inhibition of copper corrosion by 1,2,3-benzotriazole: A review". Corrosion Science. 52 (9): 2737–2749. doi:10.1016/j.corsci.2010.05.002.
  12. Kale, Raju R.; Virendra Prasad; Prabhu P. Mohapatra; Vinod K. Tiwari (6 March 2010). "Recent developments in benzotriazole methodology for construction of pharmacologically important heterocyclic skeletons". Monatsh Chemistry. 141 (11): 1159–1182. doi:10.1007/s00706-010-0378-1. S2CID 93911988.
  13. Giger, W; Schaffner, C; Kohler, HP (2006). "Benzotriazole and tolyltriazole as aquatic contaminants. 1. Input and occurrence in rivers and lakes". Environmental Science & Technology. 40 (23): 7186–92. doi:10.1021/es061565j. PMID 17180965.
  14. Farré, Marinel la; Pérez, Sandra; Kantiani, Lina; Barceló, Damià (2008). "Fate and toxicity of emerging pollutants, their metabolites and transformation products in the aquatic environment". TrAC Trends in Analytical Chemistry. 27 (11): 991–1007. doi:10.1016/j.trac.2008.09.010. ISSN 0165-9936.
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