[21050-95-3]  · C6H4ClN3  · 1-Chlorobenzotriazole  · (MW 153.57)

(positive halogen reagent for mild oxidations2,3 and selective chlorinations4)

Alternate Names: 1-chloro-1H-benzotriazole; N-chlorobenzotriazole; 1-CBT.

Physical Data: colorless needles; mp 104-106 °C; lmax 252 nm.

Solubility: sol CH2Cl2, CCl4, C6H6, MeCN, MeOH.

Analysis of Reagent Purity: solutions can be standardized by iodometric or potentiometric titration.1

Preparative Methods: treat benzotriazole with sodium hypochlorite in 50% aq acetic acid. The reagent quickly precipitates and is obtained in nearly quantitative yield after recrystallization from CH2Cl2/petroleum ether.2a

Handling, Storage, and Precautions: may ignite spontaneously;5 reacts explosively with DMSO;2b light sensitive; stable to air and moisture in brown bottles; storage recommended at 0 °C; discard or repurify if discoloration occurs. This reagent should be handled in a fume hood.

Oxidation of Alcohols and Nitrogen Compounds.

1-Chlorobenzotriazole (1-CBT) behaves similarly to positive halogen compounds such as N-Bromosuccinimide, N-Chlorosuccinimide, and Chloramine-T, acting as a source of halonium ion (Cl+) or halogen radical (Cl&bdot;). The reagent is convenient to use and prepare, and in some applications gives higher yields than t-Butyl Hypochlorite. Alcohols, hydrazones, 1,1- and 1,2-disubstituted hydrazines and aminobenzotriazoles are efficiently oxidized under extremely mild conditions by 1-CBT (Table 1).2 Reactions are typically carried out by warming equimolar amounts of substrate and 1-CBT in CH2Cl2, CCl4, or C6H6; reaction with hydrazines occurs readily in the cold. After a brief induction period a rapid exothermic reaction occurs, typical of a radical chain process, affording the oxidized product and benzotriazole hydrochloride which precipitates. Secondary alcohols are oxidized faster than primary alcohols, as is generally observed with N-halide oxidizing agents. Trace amounts of benzotriazole are easily removed from the product by washing with dilute aqueous sodium hydroxide.

Reaction with Sulfides.

Sulfides are efficiently oxidized to sulfoxides by 1-CBT in methanol or methylene chloride at -78 °C.3a The reaction is very fast and clean, giving no overoxidation to sulfones as is often observed with peroxy acids (e.g. m-Chloroperbenzoic Acid). The performance of the reagent is comparable to t-butyl hypochlorite. This transformation has been used in the conversion of steroidal thioacetals to ketones.3b The intermediate formed between 1-CBT and sulfides may also react with alcohols or primary and secondary amines. Treatment of the ensuing adduct with Silver(I) Tetrafluoroborate gives the corresponding amino- or alkoxysulfonium fluoroborate.3c

Chlorination of Heteroaromatics.

Indoles and other nitrogen heterocycles are selectively chlorinated by 1-CBT in high yield. This procedure often succeeds where the standard reagent t-butyl hypochlorite fails.4 Multiple equivalents of chlorine may be selectively incorporated simply by adjusting the initial amount of 1-CBT used (eq 1).4b The chlorination of some indoles is better effected by using 1-chloroisatin.4c

Other Applications.

The title reagent has been shown to undergo ready addition to alkenes, giving 1,2- and 2,2-chloroethylbenzotriazoles,6 as well as to effect a-chlorination of ketones.1 1-CBT has also been used in the preparation of other benzotriazole derivatives (1-nitro-, 1-bromo-, and 1-iodobenzotriazoles),7,8 as well as the selenium transfer reagent bis(1-benzotriazolyl) selenide.9

1. Hiremath, R. C.; Mayanna, S. M.; Venkatasubramanian, N. J. Sci. Ind. Res. 1990, 49, 122.
2. (a) Rees, C. W.; Storr, R. C. CC 1968, 1305. (b) Rees, C. W.; Storr, R. C. JCS(C) 1969, 1474.
3. (a) Kingsbury, W. D.; Johnson, C. R. CC 1969, 365. (b) Heaton, P. R.; Midgley, J. M.; Whalley, W. B. CC 1971, 750. (c) Johnson, C. R.; Bacon, C. C.; Kingsbury, W. D. TL 1972, 501.
4. (a) Lichman, K. V. JCS(C) 1971, 2539. (b) Bowyer, P. M.; Iles, D. H.; Ledwith, A. JCS(C) 1971, 2775. (c) Berti, C.; Greci, L.; Andruzzi, R.; Trazza, A. JOC 1982, 47, 4895.
5. Chem. Eng. News 1971, July 26, 3.
6. Rees, C. W.; Storr, R. C. JCS(C) 1969, 1478.
7. Ketari, R.; Foucaud, A. S 1982, 844.
8. Sasse, M. J.; Storr, R. C. JCS(P1) 1978, 909.
9. Ryan, M. D.; Harpp, D. H. TL 1992, 33, 2129.

Matthew P. Braun & Carl R. Johnson

Wayne State University, Detroit, MI, USA

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