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Benzotriazole
Chemical compound From Wikipedia, the free encyclopedia
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Benzotriazole (BTA) is a heterocyclic compound with the chemical formula C6H4N3H. It can be viewed as the fusion of a benzene and triazole rings. It is a white solid, although impure samples can appear tan. It is used as a corrosion inhibitor for copper.[5]
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Structure and synthesis
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.[1]
Benzotriazole can be prepared by the monodiazotization of o-phenylenediamine using sodium nitrite and acetic acid.[6][7][8]
Reactions
Acid-base behavior
BTA is a weak Bronsted acid with a pKa = 8.2.[3] It is a weak Brønsted base, as indicated by the low pKa < 0 of its conjugate acid, [HBTA]+.[4]
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.[9] In some complexes, BTA binds metals as its conjugate base forming polymers and oligomers.[10] It binds to copper surfaces, serving as a corrosion inhibitor.[11]
N-alkylation
Deprotonation of BTA followed by treament with alkyl halides gives a mixture of 1- and 2-alkyl derivatives.[12] Aromatic aldehydes (ArCHO) in the presence of ethanol gives benzotriazole-based N,O-acetals:
- ArCHO + BtH + EtOH → ArCH(OEt)(Bt) + H2O
These acetals are susceptible to deprotonation, giving access to acylsilanes[13] 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.[14]
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Applications
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.[citation needed]
Corrosion inhibition
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.[15] BTA is used in heritage conservation, notably for the treatment of bronze disease.
Environmental relevance
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.[16] It is of low toxicity and a low health hazard to humans although exhibiting some antiestrogenic properties.[17] Benzotriazole (and tolyltriazole) is a common "polar organic persistent pollutant", often detected at >0.1 μg/L.[18] One source of this pollution is their use as anti-icing/deicing agents in airports.[19]
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Benzotriazole derivatives
Many modifications of benzotriazole have been reported.[12][20][21][22] Alizapride is a commercial drug containing a benzotriazole ring system.
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]
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References
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