PRODUCTS

BENZOTRIAZOLE

CAS No. : 95-14-7
EC No. : 202-394-1

Synonyms:
BTA; 1H-Benzotriazole; 1,2,3-Benzotriazole; BtaH; 1,2,3-Benzotriazole; 1,2,3-1H-Benzotriazole; 1,2,3-triaza-1H-indene; 1,2,3-triazaindene; 1H-1,2,3-Benzotriazole [ACD/Index Name]; 1H-benzo[1,2,3]triazole; 1H-Benzo[d][1,2,3]triazole; 1H-Benzotriazol [German] [ACD/IUPAC Name]; 1H-Benzotriazole [ACD/IUPAC Name]; 1H-Benzotriazole [French] [ACD/IUPAC Name]; 202-394-1 [EINECS]; 4-26-00-00093 [Beilstein]; 95-14-7 [RN]; Benzotriazol; BTA; T56 BMNNJ [WLN]; 1,2,3-Benzotriazole(BTA); 1,2-aminoazophenylene; 1,2-Aminozophenylene; 112133 [Beilstein]; 1H-?Benzotriazole; 2,3-diazaindole; 2H-Benzo[d][1,2,3]triazole; azabenzimidazole; azaindazole; Azimidobenzene; aziminobenzene; benzene azimide; Benzisotriazole; benzo[1,2,3]triazole; Benzotriazole (VAN); Benzotriazole Granular 25kg bags; Benztriazole; Cobratec 35G; Cobtratec 99; Drometrizole [INN] [USAN]; Entek; Pseudoazimidobenzene; UNII-86110UXM5Y; DM1225000; 1,2,3-Benzotriazole, BtaH; 1,2,3-1H-Benzotriazole; 1,2,3-Benzotriazole, 1,2,3-Triaza-1H-indene, 1,2,3-Triazaindene, 1,2-AMINOAZOPHENYLENE, 1H-1,2,3-Benzotriazole; 1H-Benzotraizole, 1H-BENZOTRIAZOL, 1H-Benzotriazole, 2,3-Diazaindole; Azimidobenzene,Aziminobenzene; Benzene; azimide; Benzisotriazole; Benzotriazol; Benzotriazole; BLS 1326; BT 120; BT 120 (lubricant additive);BTA; BTA (corrosion inhibitor); C.V.I. Liquid; Cobratec 35G; Cobratec 99; CVI; D 32-108, Entek, Irgastab I 489, ISK 3; Kemitec TT, M 318; NSC 3058; Rusmin R; Seetec BT; Seetec BT-R, Verzone Crystal, 1,2,3-1H-Benzotriazole, 1,2,3-Benzotriazole,1,2,3-triaza-1H-indene; 1,2,3-triazaindene; 1H-1,2,3-Benzotriazole; 1H-benzo[1,2,3]triazole, 1H-Benzo[d][1,2,3]triazole; 1H-Benzotriazol;, 1H-Benzotriazole; 1H-Benzotriazole; Benzotriazol; BTA; 116421-31-9 [RN]; 25377-81-5 [RN], 27556-51-0 [RN]; 28880-01-5 [RN], 70644-74-5 [RN], 94160-69-7 [RN], 1,2,3-Benztriazole, 1,2-aminoazophenylene, 1,2-Aminozophenylene; 2,3-diazaindole; azabenzimidazole, azaindazole, Azimidobenzene; aziminobenzene; benzene azimide; Benzisotriazole; benzo[1,2,3]triazole; benzo[d][1,2,3]triazole; Benzotriazole (VAN); Benztriazole; C012771; Cobratec #99; Cobratec 35G; Cobratec No. 99; Cobtratec 99; D 32-108; DM1225000 [RTECS]; Drometrizole; Entek; Irgastab I 489; ISK 3; Pseudoazimidobenzene; titaniumisopropyloxide; WLN: T56 BMNNJ; Benzotriazole; ReagentPlus®, 99%; 1,2,3-Benzotriazole, 1H-Benzotriazole; Tolyltriazole; 5-METHYL-1H-BENZOTRIAZOLE; 5-METHYL-1H-BENZOTRIAZOLE(1,2,3); Ribavirin; 1-Hydroxybenzotriazole; 1,2,3-1H-Triazole Tolytriazole sodium salt 1,2,4-Triazole; 1-Hydroxybenzotriazole hydrate; RIBAVIRINA; BENZOTRIAZOLE; 1,2,3-benzotriazole-1h-benzotriazole; 1,2,3-Benztriazole; 1,2,3-Triaza-1H-indene; 1,2,3-Triazaindene; 1,2,-aminozophenylene 1,2-Aminoazophenylene 1,2-Aminozophenylene 1h-benzo 2,3-diazaindol 2,3-Diazaindole 2,3-Diazaindole; 1,2,3-triazaindene ADK STAB LA-32 Aziminobenzene Benzene azimide; benzeneazimide Benzisotriazole; 1H-benzotriazole; Benztriazol; Benztriazole; Cobratec; Cobratec 99; Cobratec No. 99; cobratec#99; NCI-C03521; NSC-3058; Preventol Cl 8; U-6233; COBRATEC(R) 99; AZIMIDOBENZENE BENZOTRIAZOLE; 1,2,3-1H-BENZOTRIAZOLE; 1,2,3-BENZOTRIAZOLE AMINOAZOPHENYLENE AKOS; 92210; 95-14-7; T706; TRIAZOLE; 1,2,3-benzor; REAGENTPLUS, 99%; REAGENT GRADE, 97%; 1,2,3-Benzotriazole, Flake; 1,2,3-Benzotriazole, Powder; Benzotriazole99.5%; 1,2,3-Benzotriazole(Bta) Benzotrichloride; ForSynthesis Benzotriazole,99% 1H-Benzotriazole, 99+%; BTA; 1,2,3-Benzotriazole (BTA); 1H-Benzotriazole, 1,2,3-Benzotriazole, BtaH; Azimidobenzene, Cobratec 99; 1H-1,2,3-Benzotriazole; 2,3-Diazaindole; 1,2-Aminozophenylene; 1,2,3-Benztriazole; 1,2,3-Benzotriazole; 1,2,3-Triaza-1H-indene; 1,2,3-Triazaindene; Benzene Azimide; Benzene azimide; Benzisotriazole; Azimidobenzene; Aziminobenzene; Benzene azimide; Benzisotriazole; Benzotriazole; Benztriazole; 1,2-Aminoazophenylene; 1,2,3-Benzotriazole; 1,2,3-Triaza-1H-indene; 1,2,3-Triazaindene; 1H-1,2,3-Benzotriazole; 2,3-Diazaindole; Cobratec No. 99; NCI-C03521; NSC-3058; U-6233; 1,2,3-Benztriazole; Cobratec 35G; 1,2,3-1H-Benzotriazole; Azimidobenzene; Aziminobenzene; Benzene azimide; Benzisotriazole; Benzotriazole; Benztriazole; Cobratec 99; 1,2-Aminoazophenylene; 1,2,3-Benzotriazole; 1,2,3-Triaza-1H-indene; 1,2,3-Triazaindene; 1H-1,2,3-Benzotriazole; 2,3-Diazaindole; Cobratec No. 99; NCI-C03521; NSC-3058; U-6233; 1,2-Aminozophenylene; 1,2,3-Benztriazole; 2,3-Diazaindole; 1,2,3-triazaindene; ADK STAB LA-32; Benzotriazole1H-benzotriazole; Cobratec; Preventol Cl 8; Related Analytes (1,2,3-Benzotriazole):1,2,3,4,6,7,8; Heptachlorodibenzofuran; 1,2,3,4,7,8-Hexachlorodibenzofuran-C13; aminobenzene, benzeneamine, phenylamine; 95-14-7; BTA; 1,2,3-Benzotriazole; 1,2-Aminoazophenylene; 1,2,3-Triazaindene; 1,2,3-Benzotriazole (BTA); Methybenzotriazole (TTA) ; 2-Mercaptobenzothiazole (MBT) ; T706 ; U-6233; 1h-benzo; Cobratec; NSC-3058; BLS 1326; RusMin R; Seetec BT; cobratec99; NCI-C03521; 95-14-7(1H-Benzotriazole); Ribavirin 1-Hydroxybenzotriazole 1,2,3-1H-Triazole Tolytriazole sodium salt 1,2,4-Triazole 1-Hydroxybenzotriazole hydrate RIBAVIRINA; 1,2,3-benzotriazole-1h-benzotriazole; 1,2,3-Benztriazole 1,2,3-Triaza-1H-indene; 1,2,3-Triazaindene; 1,2,-aminozophenylene; 1,2-Aminoazophenylene; 1,2-Aminozophenylene 1h-benzo; 2,3-diazaindol; 2,3-Diazaindole

Benzotriazole

Benzotriazole (BTA) is a heterocyclic compound containing three nitrogen atoms, with the chemical formula C6H5N3. This aromatic compound is colorless and polar and can be used in various fields.

Structure of Benzotriazole
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 also can be produced.

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 benzotriazole 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 Bronsted 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 benzotriazole can form a stable coordination compound on a copper surface and behave as a corrosion inhibitor.

Synthesis and reactions of Benzotriazole
A synthesis of the benzotriazole involves the reaction of o-phenylenediamine, sodium nitrite and acetic acid. The conversion proceeds via diazotization of one of the amine groups.

USES of Benzotriazole
The use of benzotriazole as a corrosion inhibitor for copper
Benzotriazole is a specific corrosion inhibitor for copper and copper alloys. It is now widely used in industry to reduce the corrosion of these alloys under both atmospheric and immersed conditions. Corrosion of copper may produce a surface stain or tarnish, pitting of surfaces of pipes or promote pitting of other metals, such as aluminium, which are in contact with dissolved copper in the water. Benzotriazole is used to reduce these forms of attack and the methods by which it is applied are discussed in this paper.

Use of BTA for Stabilizing Bronze Objects
Use: Benzotriazole (BT) is an anticorrosive agent well known for its use in aircraft deicing and antifreeze fluids
Use of Benzotriazole as antimicrobial agents
Use of Benzotriazole as a ligand of choice
Benzotriazole is inexpensive and stable. It behaves as an acid (pKa 8.2) and is highly soluble in basic solutions. It is soluble in ethanol, benzene, toluene, chloroform, and DMF. As one of the most useful synthetic auxiliary, it displays the following characteristics:

•It can be easily introduced into molecules and activates then toward various transformations.
•It is stable during various operations,
•It is easy to remove and can be recovered and used again.

Production and use
Benzotriazole is used as a component of aircraft de-icing fluid, pickling inhibitor in boiler scale removal, restrainer, developer and antifogging agent in photographic emulsions, corrosion inhibitor for copper, chemical intermediate for dyes, in pharmaceuticals, and as fungicide. (HSDB 1998).
Tolyltriazole is used as inhibitor of corrosion of copper and copper alloys, in antioxidants, and photographic developers (NTP 1991b). In Denmark, benzotriazole and tolyltriazole are reported to be used in small amounts (0.1-0.2 %) in de-icing fluids, e.g. propylene glycol (MST 1999). They are also used as a corrosion inhibitor in antifreeze chemicals containing glycol (MST 2000).

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.[7] Typical batch purity is 98.5% or greater
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.

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 in photographic emulsions 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 benzotriazole can be used as antifreezes, heating and cooling systems, hydraulic fluids and vapor phase inhibitors as well.

Corrosion inhibitor of benzotriazole
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.[10] Benzotriazole is used in 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 and benzotriazole esters have been reported to work as mechanism-based inactivators for severe acute respiratory syndrome (SARS) 3CL protease. The methodology is not only limited to heterocyclization but was also successful for polynuclear hydrocarbons of small carbocyclic systems.

Environmental relevance of benzotriazole
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.[12] It is considered to be of low toxicity and a low health hazard to humans although exhibiting some antiestrogenic properties.

Benzotriazole as a ligand of choice
Benzotriazole is inexpensive and stable. It behaves as an acid (pKa 8.2) and is highly soluble in basic solutions. It is soluble in ethanol, benzene, toluene, chloroform, and DMF. As one of the most useful synthetic auxiliary, it displays the following characteristics:
•Benzotriazole can be easily introduced into molecules and activates then toward various transformations.
•Benzotriazole is stable during various operations,
•Benzotriazole is easy to remove and can be recovered and used again.

Benzotriazole possesses both electron-donor and electron-acceptor properties. N-Substituted derivatives of benzotriazole also have some interesting properties. We now summarize some of the work done using benzotriazole and its derivatives as ligands (Scheme 3).
Some derivatives of benzotriazole used as a ligand for metal-catalyzed coupling between electron-rich or electron-neutral arylhalides and N-heterocycles (indoles, pyrrole, carbazole, imidazole, etc.), alkynes, boronic-acids, and thiols are in Scheme 4.
benzotriazole appears as white to light tan crystals or white powder. No odor. (NTP, 1992)
Benzotriazole is the simplest member of the class of benzotriazoles that consists of a benzene nucleus fused to a 1H-1,2,3-triazole ring. It has a role as an environmental contaminant and a xenobiotic.

USAGE areas of Benzotriazole
- Corrosion inhibitor
- Stabilizing Bronze Objects
- Antimicrobial agents
- ligand of choice
- anticorrosive agent

Benzotriazole, which plays a crucial role in the study of organic chemistry. The author takes up a US patent related to one specific component of organic chemistry and provides other details of the patent for further clarification. This chapter discusses one patent and that is the method of synthesizing t-amido-substituted 2-(2-hydroxyphenyl) benzotriazole compounds in a one-step process. The chapter provides information about the patent's assignee, utility designation, reactions, derivatives, experimental details, and notes. The assignee of this patent is Eastman Kodak Company and the utility designation for the same is UV-light-absorbing coating additive. The notes mentioned help in shedding some more light on the subject. Moreover, relevant prior art US patent references are incorporated at the end of the chapter.

Uses: It can be used in many applications for the protection of copper and copper alloys. In circulation cooling systems such as cooling towers, air conditioning systems, cutting and grinding fluids; in functional fluids (hydraulic fluids, automotive refrigerants and special lubricants); direct treatment (such as fabrication and decorative parts, sculptures); soaps, detergents and strong acid and alkaline cleaners.
Thermal stability: Excellent thermal resistance, stable at normal application temperature. Benzotriazole decomposes exothermically above 160 oC when the pure substance is heated.

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 Benzotriazole can lose a proton to act as a weak acid (pKa = 8.2) or accept a proton using the lone pair electrons located on its nitrogen atoms as a very weak Bronsted base (pKa < 0) 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 Benzotriazole can form a stable coordination compound on a copper surface and behave as a corrosion inhibitor.

Chemical structure of the coordination polymer from benzotriazolate and copper(I), the active ingredient in the BT-derived corrosion inhibition.
It is also used in photographic developers and emulsion as a restrainer.
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.
Studies of tautomerism by hydrogen transfer in benzotriazole (e.g., Tinuvin P, TIN) show that torsional libration of the p-cresol ring relative to the benzotriazole ring and hydrogen out-of-plane bending and/or hydrogen stretching vibration of the intramolecular hydrogen bond in the excited TIN(intra) molecule are responsible for its rapid radiationless deactivation.1 These rapid deactivation processes are the origin of the high efficiency of this UV stabilizer.1 Figure 5.1 characterizes the processes of energy dissipation using Jablonski's diagram.

Benzotriazole (BTA) and benzimidazole (BZI) are common chemicals used for many different purposes. Benzotriazole is generally used as a corrosion inhibitor, hydraulic fluid, dishwashing detergent, aircraft deicer, antiulcer fluid, and stabilizer for bronze objects, whereas BZI is widely used as an antiviral, antiulcer, antibacterial, and antifungal chemical.4,117 Recently, metal azolate frameworks (MAFs), a subclass of MOFs, have drawn significant interest because of their robust chemical and thermal stability121 as well as their high hydrophobicity122 and their potential for use in water purification applications.118 In their study, Sarkar et al. used MAF-5, a Co-based metal azolate to remove Benzotriazole and BZI from aqueous solutions. The results were compared with those obtained using ZIF-8-Zn, ZIF-67-Co, and conventional AC. The adsorption efficiency of the adsorbents for Benzotriazole adsorption increased in the order: AC < ZIF-8-Zn < ZIF-67-Co < MAF-5-Co, whereas for BZI: ZIF-8-Zn < AC < ZIF-67-Co < MAF-5-Co. Although the MAF-5-Co has the lowest surface area and pore volume of all the studied adsorbents, it had the highest adsorption capacity which indicated the existence of a special interaction between MAF-5-Co and Benzotriazole or BZI.

The adsorption isotherm followed the Langmuir model, and the Qo values for the adsorption of Benzotriazole and BZI by MAF-5-Co are 389 and 175 mg g−1, respectively. These values are much higher than those for ZIF-8-Zn and ZIF-67-Co as well as higher/more competitive than other reported adsorbents (see Table 2.2). An insight into the adsorption mechanism can be found from the effect of the solution pH and pHzpc of the adsorbent. The pHzpc of MAF-5-Co is 8.2 and, depending on the solution pH, Benzotriazole can be protonated (when pH <1.6), neutral (when the pH is 1.6–8.6), and deprotonated (when pH >8.6) (see Fig. 2.11). A significant amount of adsorption (over 100 mg g−1) throughout the experimental pH range (particularly, at pH <1.6 and pH >12) indicated the presence of other interactions, which played a vital role in addition to electrostatic interaction. The hydrophobicity of MAF-5-Co is higher than that of ZIF-67-Co, and this interaction might contribute to the adsorption, as evidenced by the higher adsorption of Benzotriazole on MAF-5-Co (389 mg g−1) compared to ZIF-67-Co (272 mg g−1). In addition to the electrostatic and hydrophobic interactions, π–π interactions (between the imidazole ring of MAF-5-Co and the aromatic ring of benzotriazole) also contribute to the adsorption process.

During the last 67 years there has been considerable interest in the triazole class of compounds, containing 3 N atoms. Molecules such as 1H-benzotriazole (BTAH, C6H5N3), as shown in Figure 9.3-35a, and tolytriazole (TTA, C7H7N3), shown in Figure 9.3-35b have received the most attention among these aromatic three-N passivating agents. Tolytriazone is actually a mixture of 4- and 5-methylbenzotriazole [234].
The general inhibiting mechanism of the 1H-triazole compounds is that they polymerize as a Cu-triazole structure on an oxidized Cu surface. Effective protective films are usually thinner rather than thicker. Thicker protective films are more likely to be disturbed by physical processes, i.e.; high velocity fluid movement and CMP polishing processes, thereby exposing the underlying surface to corrosion. Under certain conditions, the formation of a thick, multilayered coating has been confirmed [235].

Other studies [236] indicate that Benzotriazole is first adsorbed onto a Cu2O film followed by polymerization to the Cu(I)–Benzotriazole complex. Figure 9.3-36 shows the Pourbaix diagram for the Cu-Benzotriazole /H2O system at 25°C and 1 × 10–4 mol Benzotriazole . Benzotriazole is the protonated form of Benzotriazole . The diagram shows that Benzotriazole forms a film with the Cu(I) oxide. Depending on the Cu ion concentrations in solution (1 × 10–2 to 1 × 10–4 mol), the passivation film can be stable between pH ∼2 and 10. SEM and FTIR spectroscopy examined the morphology of these surfaces with and without Benzotriazole . Notoya and co-workers [237] have conducted SIMS analysis of Cu surfaces treated with Benzotriazole under various pH conditions. The data indicated that the positive fragments were composed of (Cu2(C6H4N3))+, (Cu3(C6H4N3)2)+, etc. Tamilmani [238], determined compositions with similar results to Notoya's, using XPS data.

Tamilmani believed that the Cu values were distorted by deeper penetration of the X-rays into the Cu substrate. His data did indicate that the bulk of the Benzotriazole was associated with the cuprous, Cu(I), state. Other studies have used extended X-ray absorption fine structure (EXAFS) methods [240]. Xu et al. [241], using STM methods, observed that Benzotriazole polymerized in long, thin irregular rectangles. The morphology of the film became flatter and smoother, but there were “groves” between the Benzotriazole polymeric films, which could be sites of corrosion. Brusic et al. [242] have done an extensive study of the Cu–Benzotriazole with electrochemical methods, in situ ellipsometry, TOF-SIMS and high-temperature mass spectrometry methods to characterize these films. Marsh [234] has recently reviewed a number of film characteristics for Benzotriazole , TTA, and mixtures of the two inhibitors. Other electrochemical studies have indicated that the TTA and Benzotriazole , besides having a dielectric nature [243, 244], also have a hydrophobic characteristic, which enhance their inhibitor properties. Tamilmani [238] determined the contact angle on bare Cu and a Cu-Benzotriazole sample; the Cu-Benzotriazole was hydrophilic compared to the bare Cu: πbareCu = 45°, πCu-Benzotriazole = 74°. Ward et al. [245] compared the performance of benzotriazole and tolyltriazole under similarly controlled test conditions and concluded that tolyltriazole forms very strong, thin, hydrophobic films on Cu. Benzotriazole films are somewhat weaker, but are composed of many Benzotriazole molecule layers.

As with most passivating agents, halide ions can destroy the triazole film's inhibiting power by penetrating the film. The halide ion effect is inversely related to anion size: Cl–> Br–>> I–. The halide effect is not as pronounced with the thicker Benzotriazole films, though the film can eventually fail. Modestov et al. [246], using a variety of electrochemical techniques, showed that unless a proper Cu(I)–Benzotriazole film thickness is achieved, Cl–will diffuse through the Cu(I)–Benzotriazole layer to form solid CuCl on top of the oxide film which destroys the inhibitor properties. Huang [247] suggested that Cu metal in Cl–solutions can be better protected if the solution's pH is ∼8; surfactants had little beneficial effect for enhancing corrosion protection. A synergistic effect was found when Benzotriazole and potassium ethylxanthate (KEX) were used in a NaCl solution [248]. At a pH of 7–11 (0.1 M NaCl solution) the Benzotriazole –KEX mixture showed good passivation, which was believed to be caused by a more compact passivation layer.

Recent XPS studies of Cu–Benzotriazole films after chemical mechanical polishing [249] and immersion for 2 hours at 23°C indicated that the film thickness was between 25 and 75-Å; thick. Marsh [234] using phase-modulated spectroscopic ellipsometer reported that Benzotriazole , TTA and a commercial mixture (Cobrate® 939) of the two inhibitors prepared from 50 to 60°C NMP (N-methyl-2-pyrrolidone) solutions, had corresponding film thickness of 27, 13 and 6.5 Å;, respectively.

A number of Benzotriazole -derivatives have been studied to understand how side chain groups can influence inhibitor performance. Derivatives with primary alkyl side chain groups (C1 to C12) [250], generally increased protective performance due to the increased hydrophobic effect of the side chains on the metal surface. A variety of analytical methods including EIS, surface enhanced Raman scattering spectroscopy, cyclic voltammetry photocurrent measurements, intensity modulated photocurrent spectrum analysis and laser-scanning photoelectrochemical microscopic methods have been used to study the carboxyl ester side group's destabilized passivation [251–254]. Benzotriazole -derivatives that contained short chain alkyl groups with amino groups [255, 256] had a wider pH range for corrosion inhibition. The amino group could interact with the oxide film while the aliphatic side chains provided better solubility in the solution and hydrophobicity on the oxide layer. Electrochemical and XPS measurements have been used to study these interactions.

This chapter discusses benzotriazole, which plays a crucial role in the study of organic chemistry. The author takes up a US patent related to one specific component of organic chemistry and provides other details of the patent for further clarification. This chapter discusses one patent and that is the method of synthesizing t-amido-substituted 2-(2-hydroxyphenyl) benzotriazole compounds in a one-step process. The chapter provides information about the patent's assignee, utility designation, reactions, derivatives, experimental details, and notes. The assignee of this patent is Eastman Kodak Company and the utility designation for the same is UV-light-absorbing coating additive. The notes mentioned help in shedding some more light on the subject. Moreover, relevant prior art US patent references are incorporated at the end of the chapter.

Corrosion Inhibition
Benzotriazole and its derivatives have found widespread use as corrosion inhibitors for copper and its alloys. A huge number of patents have appeared since the mid-1980s. Polymeric tapes or sheets coated with adhesive containing acrylic polymer emulsions of benzotriazole and tripolyphosphate salts can protect copper and copper alloys against discoloration 〈87JAP8707780〉. Benzotriazoles with an alkyl group, especially n-butyl, at the benzene ring have been used to inhibit corrosion of copper in aqueous systems 〈88EUP258021〉. An inhibitor mixture consisting of triethanolamine, NaNO2, benzotriazole, sodium salicylate, and polyethylene glycol protects copper, solder, brass, steel, cast iron, and aluminum in heating systems 〈81JAP81108882〉.
5-Alkoxybenzotriazoles are effective corrosion inhibitors of copper and copper alloy 〈90EUP397455〉. The anticorrosion of benzotriazole on copper has been studied by surface-enhanced Raman spectroscopy, ellipsometry, and electrochemical techniques 〈86MI 401-01〉.
Benzotriazole has also been used as an additive in anticorrosive coatings for silver layered on plastic film 〈89JAP8909733〉. An anticorrosive, electromagnetic wave-shielding coating containing tolyltriazole has been developed for aluminum 〈91EUP437979〉.

Some derivatives of benzotriazole used as a ligand for metal-catalyzed coupling between electron-rich or electron-neutral arylhalides and N-heterocycles (indoles, pyrrole, carbazole, imidazole, etc.), alkynes, boronic-acids, and thiols are in Scheme 4.
3.2 Designing metal catalyst using benzotriazole and its derivatives
We synthesized and screened a number of structurally related benzotriazole-based N,N- and N,O-bidendate ligands having more donating sites with bulkiness (Figure 1). These ligands are believed to have more electron-donating capability and more bulk. They were designed as sites having lone pair(s) approachable to the metal to make temporary bonds. Complexes generated from these ligands couple a broad range of N-heterocycles with arylhalides with high turnover numbers and tolerance of functional groups. The designed ligands were synthesized by standard methods.

Benzotriazole (BTAH) is widely used for polishing and plating purposes to prevent Cu and relevant alloys from corrosion because Benzotriazole can form a coordination polymer film on the surface of Cu to prevent its oxidation.88 Gewirth’s group employed SHINERS technique for real-time investigation of processes involving formation of Benzotriazole− film at Cu(hkl) and Cu(poly) electrode surfaces.50 Fig. 5 clearly exhibits the peak around 1020 cm− 1 which is assigned to benzene skeletal and Csingle bondH bend, and the peak around 1190 cm− 1 is attributed to triazole ring breathing mode (Csingle bondCsingle bondC in-plane bending). During the positive scanning process at Cu(hkl) electrode surfaces, the Raman intensities of both the above-mentioned peaks increased; however, the similar phenomenon at Cu(poly) electrode surface was not observed during the same scanning process. Furthermore, the peak intensities ratio of 1190/1140 increased with the increase in the potential at Cu(100) and Cu(111) electrodes surfaces. The peak at 1140 cm− 1 is assigned to Nsingle bondH bending mode of adsorbed Benzotriazole at Cu electrode surfaces. However, SHINERS results indicated different interpretation for both single crystal surfaces.

The intensities ratio corresponding to 1190/1140 stopped increasing later for Cu(111) electrode surface compared to Cu(100) at the negative scanning direction, and the correlated stop potentials were − 0.3 and − 0.2 V, respectively. During the negative scanning direction at Cu(poly) electrode surface, the SHINERS results again exhibited different phenomena compared to the single crystal electrode surface, thus indicating different growth behaviors for the Benzotriazole-Cu(I) film formation at different Cu electrodes surfaces. The film formation was found to be irreversible at single crystal Cu(hkl) electrodes, while it was reversible at Cu(poly) surfaces. The systematic research reveals that different crystallographic orientation of Cu(hkl) electrodes surfaces, with evident effect on Benzotriazole-Cu(I) film growth, and the presence of grain boundaries together lead to the cathodic degradation of Benzotriazole-polymeric films at Cu(poly) electrode.

Benzotriazole is a bicyclic nitrogen heterocycle formed by the fusion of the benzene ring with the 4,5-positions or the “d” site of 1H-1,2,3-triazole. It is also known as 1H-benzo[d]-1,2,3-triazole and exists in two tautomeric 1H- and 2H- forms in which the 1H- form predominates (99.9%) over the 2H- form at room temperature in both gas and solution phases.
Benzotriazole is a very weak base with a pKa of 8.2, but NH is more acidic than indazole, benzimidazole, and 1,2,3-triazoles. It is quite a stable molecule because the fused benzene ring gives additional strength to the stability of the conjugate base.
There are numerous benzotriazole-based clinically used drugs in the market for the treatment of various diseases. Some of the anticancer, antifungal, and antibacterial drugs are depicted in the following scheme.

Synthesis
There are numerous methods for the synthesis of benzotriazole but only the important and general routes of this ring system are depicted here.
1. o-Phenylenediamine on treatment with NaNO2 in acetic acid undergoes intramolecular cyclization to yield benzotriazoles.
2. Dehydrobenzene (benzyne) generated in situ by a slow addition of anthranilic acid to an alkyl nitrite followed by addition of alkyl, aryl, and acyl or sulfonyl azides afforded benzotriazoles.
3. 1-Chloro-2-nitrobenzene or 1,2-dinitrobenzene on reaction with hydrazine produced benzotriazol-1-ol via 2-nitrophenylhydrazine.
4. The reaction of 1,3-dihydrobenzimidazol-2-one with sodium nitrite and water under high temperature (190–300°C) and pressure afforded 1-sodium benzotriazole, which on acid treatment gave 1H-benzotriazole in high yields.
An alternative way to prepare N-aryl benzotriazole has been reported by treating a diazotized solution derived from 2-chloroaniline with aryl amine followed by intramolecular cyclization in the presence of CuI and CsCO3.

Reaction of 1H-benzotriazole with different methylating agents such as methyl sulfate, diazomethane, and methyl halide gave a mixture of 1-methyl- and 2-methylbenzotriazole in the ratio of 5:17. Alkylation of 1H-benzotriazole with alkyl halide using NaOH or NaOEt as a base gave 1-alkylbenzotriazole as a major product and 2-alkylbenzotriazole and 1,3-dialkylbenzotriazolium salts as minor products.
1H-Benzotriazole on reaction with diarylmethanols in the presence 4-toluenesulfonic acid as catalyst yielded a mixture of the corresponding 1- and 2-diarylmethylbenzotriazoles.

Acylation: 1H-Benzotriazoles reacting with acid chloride or acid anhydride afforded 1-acylbenzotriazoles.
Arylation: 1H-Benzotriazole on reaction with activated aryl and heteroaryl halides afforded 1-arylbenzotriazole. However, 1-chloro-2-nitrobenzene reacting with 1H-benzotriazole gave a mixture of 1- and 2-(2-nitrophenyl)benzotriazole.
Reaction of 1H-benzotriazole with α,β-unsaturated ketones underwent 1,3-conjugated addition to give a mixture of 1-H- and 3-(2H-benzo[d][1,2,3-triazol-2-yl)-1,3-diphenylpropan-1-one,712 but reaction with aliphatic aldehyde afforded 1-hydroxyalkyl benzotriazole as an addition product.713 However, reaction with ketone in the presence of dialkyl amine delivered 1-(dialkylaminoalkyl)benzotriazole.

Halogenation
1H-Benzotriazole is readily transformed to 1-chlorobenzotriazole on reaction with sodium hypochlorite in aqueous acetic acid.715 Analogously, 1H-benzotriazole reacting with sodium hypoiodite in aqueous NaOH provided 1-iodobenzotriazole. 1-Methylbenzotriazole chlorinated on refluxing in aqua regia for 3 h gave 4,5,6, 7-tetrachloro-1H-tetrazole in 87% yields, while under analogous conditions 2-methylbenzotriazole is chlorinated to yield 2-methyl-4,5,6,7-tetrachloro-2H-benzotriazole.
Sulfonation: 1H-Benzotriazole on reaction with trifluoromethanesulfonic anhydride in dry DCM and dry pyridine at − 78°C afforded 1-(trifluoromethyl)sulfonyl-1H-benzotriazole in 87% yields.
Nitration: 1H-Benzotriazole has been nitrated with a mixture of concentrated nitric acid and sulfuric acid at room temperature to give 4-nitro-1H-benzotriazole in 50% yields.

Benzotriazoles (BTs) are xenobiotic contaminants widely distributed in aquatic environments and of emerging concern due to their polarity, recalcitrance, and common use. During some water reclamation activities, such as stormwater bioretention or crop irrigation with recycled water, Benzotriazoles come in contact with vegetation, presenting a potential exposure route to consumers. We discovered that Benzotriazole in hydroponic systems was rapidly (approximately 1-log per day) assimilated by Arabidopsis plants and metabolized to novel Benzotriazole metabolites structurally resembling tryptophan and auxin plant hormones; <1% remained as parent compound. Using LC-QTOF-MS untargeted metabolomics, we identified two major types of Benzotriazole transformation products: glycosylation and incorporation into the tryptophan biosynthetic pathway. Benzotriazole amino acid metabolites are structurally analogous to tryptophan and the storage forms of auxin plant hormones. Critical intermediates were synthesized (authenticated by (1)H/(13)C NMR) for product verification. In a multiple-exposure temporal mass balance, three major metabolites accounted for >60% of Benzotriazole. Glycosylated Benzotriazole was excreted by the plants into the hydroponic medium, a phenomenon not observed previously. The observed amino acid metabolites are likely formed when tryptophan biosynthetic enzymes substitute synthetic Benzotriazole for native indolic molecules, generating potential phytohormone mimics. These results suggest that Benzotriazole metabolism by plants could mask the presence of Benzotriazole contamination in the environment. Furthermore, Benzotriazole-derived metabolites are structurally related to plant auxin hormones and should be evaluated for undesirable biological effects.

IDENTIFICATION: 1,2,3-Benzotriazole is a white to light tan, crystalline powder with no odor. It is slightly soluble in water. USE: 1,2,3-Benzotriazole is used as an anticorrosive in metalworking, water-cooling systems and dry-cleaning equipment. It is used as a tarnish remover and a protective coating in the construction industry. It is an ingredient in auto and home use products. 1,2,3-Benzotriazole is a component of some aircraft de-icing fluids. EXPOSURE: Workers that produce or use 1,2,3-benzotriazole may breathe in dust or have direct skin contact. The general population may be exposed by dermal contact with products in which it is used. If 1,2,3-benzotriazole is released to the environment, it will be in or on particles that eventually fall to the ground. It will be broken down in air by reaction with hydroxyl radicals and by sunlight. It will not volatilize into air from soil and water surfaces. It is expected to have very high to moderately mobility in soil. It is not expected to be broken down by microorganisms, and is not expected to build up in fish. RISK: Workers developed dermatitis from skin exposure of oil containing 1,2,3-benzotriazole. Data on the potential for 1,2,3-benzotriazole to produce other toxic effects in humans were not available. Data on the potential for 1,2,3-benzotriazole to cause cancer, birth defects or reproductive effects in laboratory animals were not available. The potential for 1,2,3-benzotriazole to cause cancer in humans has not been assessed by the U.S. EPA IRIS program, the International Agency for Research on Cancer, or the U.S. National Toxicology Program 14th Report on Carcinogens.

Benzotriazole has also been used as an additive in anticorrosive coatings for silver layered on plastic film. An anticorrosive, electromagnetic wave-shielding coating containing tolyltriazole has been developed for aluminum .
Benzotriazole is a specific corrosion inhibitor for copper and copper alloys. Benzotriazole is now widely used in industry to reduce the corrosion of these alloys under both atmospheric and immersed conditions. Corrosion of copper may produce a surface stain or tarnish, pitting of surfaces of pipes or promote pitting of other metals, such as aluminium, which are in contact with dissolved copper in the water. Benzotriazole is used to reduce these forms of attack and the methods by which Benzotriazole is applied are discussed in this paper.

Properties: 1,2,3-Benzotriazole insoluble in water, soluble in ethanol. Benzotriazole is a main ingredient for producing UV absorbers. Benzotriazole and its derivatives are versatile substances involved in the production of anti-corrosion agents, antiperspirant agents for metals, antiseptic and anticoagulant agents, anti-fog for photography, UV absorbers, photocondensers, photocondensation systems, drugs, pesticides and other specialty chemicals.
Uses: It can be used in many applications for the protection of copper and copper alloys. In circulation cooling systems such as cooling towers, air conditioning systems, cutting and grinding fluids; in functional fluids (hydraulic fluids, automotive refrigerants and special lubricants); direct treatment (such as fabrication and decorative parts, sculptures); soaps, detergents and strong acid and alkaline cleaners.
Thermal stability: Excellent thermal resistance, stable at normal application temperature. Benzotriazole decomposes exothermically above 160 oC when the pure substance is heated.

As an emerging contaminant, 1-H-benzotriazole (1H-Benzotriazole) has been detected in the engineered and natural aquatic environments, which usually coexists with heavy metals and causes combined pollution. In the present study, wild-type and transgenic zebrafish Danio rerio were used to explore the acute toxicity as well as the single and joint hepatotoxicity of cadmium (Cd) and 1H-Benzotriazole. Although the acute toxicity of 1H-Benzotriazole to zebrafish was low, increased expression of liver-specific fatty acid binding protein was observed in transgenic zebrafish when the embryos were exposed to 5.0 uM of 1H-Benzotriazole for 30 days. Besides, co-exposure to 1H-Benzotriazole not only reduced the acute toxic effects induced by Cd, but also alleviated the Cd-induced liver atrophy in transgenic fish. Correspondingly, effects of combined exposure to 1H-Benzotriazole on the Cd-induced expressions of several signal pathway-related genes and superoxide dismutase and glutathione-s-transferase proteins were studied. Based on the determination of Cd bioaccumulation in fish and the complexing stability constant (beta) of Cd-Benzotriazole complex in solution, the detoxification mechanism of co-existing 1H-Benzotriazole on Cd to the zebrafish was discussed.

A bioassay of 1H-benzotriazole for possible carcinogenicity was conducted by administering the test chemical in feed to Fischer 344 rats and B6C3F1 mice. Groups of 50 rats of each sex were administered 1H-benzotriazole at one of two time weighted average doses, either 6,700 or 12,100 ppm for 78 wk. Except for five control and five high dose rats of each sex, which were /sacrificed/ at wk 78, all animals surviving at that time were observed for 26-27 additional wk. Controls consisted of groups of 50 untreated rats of each sex and were observed for 105-16 wk. All rats surviving to wk 104-106 were then /sacrificed/. Groups of 50 mice of each sex were administered 1H-benzotriazole at one of two time weighted average doses, either 11,700 or 23,500 ppm for 104 wk, then observed for 2 additional wk. Controls consisted of groups of 50 untreated mice of each sex and were observed for 109 wk. All mice surviving to wk 106-109 were then /sacrificed/. In female B6C3F1 mice there was an incr incidence of alveolar/bronchiolar carcinomas, suggesting a possible carcinogenic effect of 1H-benzotriazole. In Fischer 344 rats there was an incr incidence of brain tumors, suggesting a possible carcinogenic effect. However, there was no convincing evidence that under the conditions of this bioassay 1H-benzotriazole was carcinogenic in B6C3F1 mice or Fischer 344 rats of either sex. Levels of Evidence of Carcinogenicity: Male Rats: Equivocal; Female Rats: Equivocal; Male Mice: Negative; Female Mice: Equivocal.

1,2,3-Benzotriazole's production and use as an anticorrosive in metalworking, as a tarnish remover and protective coating in the construction industry, as a corrosion inhibitor in water-cooling systems and in dry-cleaning equipment, use in some formulations of automatic dishwasher detergents, use in electrolytic and photographic processing and use as chemical intermediate may result in its release to the environment through various waste streams. Its use as a component of aircraft de-icing fluid will result in its direct release to the environment. If released to air, an estimated vapor pressure of 2.5X10-5 mm Hg at 25 °C indicates 1,2,3-benzotriazole will exist in both the vapor and particulate phases in the atmosphere. Vapor-phase 1,2,3-benzotriazole will be degraded in the atmosphere by reaction with photochemically-produced hydroxyl radicals; the half-life for this reaction in air is estimated to be 16 days. Particulate-phase 1,2,3-benzotriazole will be removed from the atmosphere by wet or dry deposition. 1,2,3-Benzotriazole absorbs at wavelengths >290 nm and, therefore, may be susceptible to direct photolysis by sunlight. If released to soil, 1,2,3-benzotriazole is expected to have very high to moderate mobility based upon an experimentally derived Koc range of 10-500. Sorption in soil is influenced by surface complexation of the neutral species, pH, ion exchange and metal content in the soil. Volatilization from moist soil surfaces is not expected to be an important fate process based upon an estimated Henry's Law constant of 1.5X10-7 atm-cu m/mole. 1,2,3-Benzotriazole is not expected to volatilize from dry soil surfaces based upon its vapor pressure.

The results of screening tests and soil degradation studies indicated that 1,2,3-benzotriazole is stable with regard to biodegradation in soils under environmental conditions with a half-life >180 days. A compilation of biodegradation rate constants in soil and groundwater for 1,2,3-benzotriazole yields a half-life range of 43 to 693 days. If released into water, 1,2,3-benzotriazole may have some adsorption to suspended solids and sediment based upon the Koc. A 2% of theoretical BOD using activated sludge in the Japanese MITI test indicates that 1,2,3-benzotriazole is not readily biodegradable. Volatilization from water surfaces is not expected to be an important fate process based upon this compound's estimated Henry's Law constant. A measured BCF range of 1.1 to 15 in carp suggests bioconcentration in aquatic organisms is low. Hydrolysis is not expected to be an important environmental fate process since this compound lacks functional groups that hydrolyze under environmental conditions (pH 5 to 9). 1,2,3-Benzotriazole has been shown to be slowly photodecomposed in aqueous solutions by irradiation at 300 nm. Occupational exposure to 1,2,3-benzotriazole may occur through inhalation and dermal contact with this compound at workplaces where 1,2,3-benzotriazole is produced or used. Monitoring and use data indicate that the general population may be exposed to 1,2,3-benzotriazole via inhalation of ambient air and dermal contact with consumer products containing 1,2,3-benzotriazole.

Benzotriazole as a ligand of choice
Benzotriazole is inexpensive and stable. It behaves as an acid (pKa 8.2) and is highly soluble in basic solutions. It is soluble in ethanol, benzene, toluene, chloroform, and DMF. As one of the most useful synthetic auxiliary, it displays the following characteristics:
•Benzotriazole can be easily introduced into molecules and activates then toward various transformations.
•Benzotriazole is stable during various operations,
•Benzotriazole is easy to remove and can be recovered and used again.

Based on a classification scheme(1), an experimentally derived Koc range of 10 to 500(2,3) indicates that 1,2,3-benzotriazole is expected to have very high to moderate mobility in soil. Sorption in soil is influenced by surface complexation of the neutral species, pH, ion exchange(3) and metal content in the soil(2). The pKa of 1,2,3-benzotriazole is 8.37(4), indicating that this compound will exist partially in anion form in the environment and anions generally do not adsorb more strongly to soils containing organic carbon and clay than their neutral counterparts(5). Results of sorption tests at pH 5.2 to 8.6 indicated that 1,2,3-benzotriazole existed primarily as the neutral species(3). Volatilization of 1,2,3-benzotriazole from moist soil surfaces is not expected to be an important fate process(SRC) given an estimated Henry's Law constant of 1.5X10-7 atm-cu m/mole, using a fragment constant estimation method(6). A 2% of theoretical BOD using activated sludge in the Japanese MITI test(7) indicates that 1,2,3-benzotriazole is not readily biodegradable. The results of other screening tests and soil degradation studies indicated that 1,2,3-benzotriazole is stable with regard to biodegradation in soils under environmental conditions with a half-life >180 days(8). A compilation of biodegradation rate constants in soil and groundwater for 1,2,3-benzotriazole has a range of 0.001 to 0.016/day(9) which has a corresponding half-life range of 43 to 693 days.

1,2,3-Benzotriazole, present at 100 mg/L, reached 2% of its theoretical BOD in 4 weeks using an activated sludge inoculum at 30 mg/L in the Japanese MITI test(1); this classified the compound as not readily biodegradable(1). Using OECD Guideline 301D (Ready Biodegradability: Closed Bottle Test) in tests using both adapted and non-adapted activated sludge inocula, 1,2,3-benzotriazole reached 0% degradation after 28 days of incubation(2). Using OECD Guideline 301B (Ready Biodegradability: CO2 Evolution Test) with an adapted activated sludge inoculum, 1,2,3-benzotriazole (at 10 mg/L) reached 0-4% degradation after 29 days of incubation(2). Based on the results of several soil degradation studies, it was concluded that 1,2,3-benzotriazole is stable with regard to biodegradation in soils under environmental conditions with a half-life >180 days(2). 1,2,3-Benzotriazole was found to be persistent in controlled laboratory degradation studies using sediment core samples taken from the infiltration zone of a bank filtration site in Berlin Germany(3). In large-scale laboratory columns used in mimic aquifer recharge under anaerobic conditions, 1,2,3-benzotriazole had a biological lag-time of approximately 30-60 days before achieving a biodegradation half-life of 29 days(4). A compilation of biodegradation rate constants in soil and groundwater for 1,2,3-benzotriazole has a range of 0.001 to 0.016/day(5) which has a corresponding half-life range of 43 to 693 days(SRC).

The rate constant for the vapor-phase reaction of 1,2,3-benzotriazole with photochemically-produced hydroxyl radicals has been estimated as 1.0X10-12 cu cm/molecule-sec at 25 °C(SRC) using a structure estimation method(1). This corresponds to an atmospheric half-life of about 16 days at an atmospheric concentration of 5X10+5 hydroxyl radicals per cu cm(1). 1,2,3-Benzotriazole is not expected to undergo hydrolysis in the environment due to the lack of functional groups that hydrolyze under environmental conditions(2). 1,2,3-Benzotriazole absorbs at wavelengths >290 nm(3) and, therefore, may be susceptible to direct photolysis by sunlight(SRC). It has been shown to be slowly photodecomposed into aniline and o-anisidine by irradiation at 300 nm in aqueous solutions(4). Phenazine and aniline were identified as metabolites in a UV-irradiation study that also found that photodegradation in water occurred more rapidly at lower pHs (7 and below) where 1,2,3-benzotriazole exists almost entirely as a neutral species(3); the pKa is 8.37(5). An aqueous solution study using simulated solar irradiation found 1,2,3-benzotriazole to be relatively photostable(6).