Benzotriazole ring

Instead of sodium nitrite, isoamyl nitrite is sometimes used as a nitrosating agent in synthesis of the benzotriazole ring. With this reagent, the reaction conditions are very mild allowing survival of acid sensitive groups. In an example of such a reaction, methyl 3,4-diamino-2-methoxybenzoate 1286 is treated with isoamyl nitrite at room temperature. The reaction is fast and provides methyl 4-methoxybenzotriazole-5-carboxylate 1287 in 62% yield, isolated by simple filtration off the precipitate (Equation 31) <2006JME4762>. 

Some carbon-13 chemical shifts of benzotriazoles polysubstituted at both N- and C-atoms of the benzotriazole ring are listed in Table 8. They are generally assigned by comparison to literature values and by careful selective decoupling experiments. The contribution of C-substituents to the chemical shifts of benzotriazoles is much large than that of V-substituents. 

The structures of a number of commercially available 2-hydroxyphenylbenzotriazoles are summarised in Table 2. Substituents in both the phenol ring and the benzotriazole ring affect the absorption characteristics and the stability of these compounds. The size of the substituents is also important in determining the volatility of these stabilizers and their compatibility with polymer systems. 

The benzotriazole ring system is remarkably stable toward alkali under the conditions of the Anil Synthesis, and hence relatively high reaction temperatures (up to 100°C) may be employed. 

L = l-(N-salicylideneamino)-2-aminoethane, shows vasN3 at 2036 cm-1.178 IR bands due to vasN3 for [Cu(L)(N3)2]n and [Cu(Me-L)(N3)4]n, where L = 2-(pyrazol-l-ylmethyl)pyridine, Me-L = 2-(3-methylpyrazol-l-ylmethyl)pyri-dine, show the presence of both end-on and end-to-end bridging azido groups.179 SERS data for benzotriazole, (47), in an aqueous silver sol show coordination to Ag via nitrogen atoms of the benzotriazole ring.180... 

A number of polymerizable ultraviolet stabilizers have been synthesized and their homo- and copolymerization studied. The initial work consisted of the synthesis of vinyl derivatives of methyl salicylate (three isomers), 2, -dihydroxy-benzophenone, and ethyl a-cyano-p-phenylcinnamate. More recently, vinyl derivatives (two isomers) and one isopro-penyl derivative of 2(2-hydroxyphenyl)2H-benzotriazole have been prepared. A number of benzotriazoles with more than one benzotriazole ring in the molecule, or compounds with both benzo(or aceto)phenone and 2(2-hydroxyphenyl)2H-benzo-triazole groups in one molecule, have also been synthesized. Acryloyl and methacryloyl derivatives of benzotriazole-substituted polyphenols have been prepared and homo- and copolymerized. 

Polymerizable 2(2-Hydroxyphenyl)2H-Benzotriazole Ultraviolet Stabilizers. Synthesis. Some of the most important ultraviolet stabilizers belong to the class of 2(2-hydroxyphenyl)2H-benzotriazoles. Ever since the early work on benzotriazoles by Elbs (25,24), a number of 2(2-hydroxyphenyl)2H-benzotriazoles [2H-benzotriazole-2-yl)2-hydroxy-benzene] have been prepared (25). Even some polymerizable compounds of this class had been synthesized. The benzotriazole stabilizing groups had in the past been attached to a polymerizable group via a phenolic hydroxyl group placed in the benzotriazole ring (26). 

Obviously, the incorporation of an electron-withdrawing substituent in the polymer-supported benzotriazole ring should enhance its reactivity. Thus, the sulfonamide-substituted HOBt resin 34 (Section 7.3) has been obtained by reaction of aminomethylated divinylbenzene cross-linked polystyrene with the sulfonyl chloride 116 to give supported sulfonamide 117, followed by typical hydroxybenzo-triazole formation (Scheme 7.37) [128]. The effect induced by the sulfonamide group was determined by measuring the acidity of non-polymeric analogues, showing a pKa of 3.59 for the sulfonamide-substituted HOBt, and a pKa of 4.64... 

The transfer of halogen from nitrogen to a benzotriazole ring takes place in the reaction of N-chlorotriazole 36a with l-azabicyclo[2.2.2.]octane through the intermediate formation of a 1-chloroazonium derivative [76JCS(P1)741] (Scheme 33). 

A new arylpiperazine derivative was recently published as a pure antagonist at 5-HTlx receptors. This compound, containing a benzotriazole ring at a distance of three carbon atoms of the basic nitrogen atom, however is not highly selective with respect to GCj-adrenoceptors (ratio 5-HT1A/a=4.6) [54] (Table 9). 

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