H O N N N Ph Ar Cl Cl O O N N Cl– Ar N HO N Ar 1a–j + + solvent HO R.T. Ar = Ph Ar = 2-MeC6H4 Ar = 3-MeC6H4 Ar = 4-MeC6H4 Ar = 2-MeOC6H4 Ar = 3-MeOC6H4 Ar = 4-MeOC6H4 Ar = 2-ClC6H4 Ar = 3-ClC6H4 Ar = 4-ClC6H4 a b c d e f g h i j 1,3,4 3a–j 4a,d,g,j NaOH 166 J. CHEM. RESEARCH (S), 1997 J. Chem. Research (S), 1997, 166–167† Reaction of Triazene 1-Oxides: Novel Synthesis of Solid Arenediazonium Chlorides† Shaaban K. Mohamed,* Mohsen A.-M. Gomaa and Ahmed M. Nour El-Din Chemistry Department, Faculty of Science, El-Minia University, El-Minia, A.R. Egypt Treatment of 1,3-diaryltriazene 1-oxides with oxalyl chloride in dry toluene at room temperature gives only solid arenediazonium chlorides; however, treatment with acetyl and benzoyl chlorides does not afford the corresponding diazonium chlorides. In previous reports1,2 we have shown that 1,3-diaryltriazene 1-oxides form stable charge-transfer complexes (1:1) with the electron-deficient tetracyanoethylene in different solvents.1 The photolysis of these 1,3-dipoles in aromatic and nonaromatic solvents leads to their decomposition2 giving 2-hydroxyazobenzene and mono- and di-substituted biaryls.These results prompted us to study the reactivity of these oxides towards different chemical reagents. Here we report the results of our investigations of the effect of acid chlorides on 1,3-diaryltriazene 1-oxides. It has been reported3 that the analogous 1,3-dipoles, nitrones, rearranged to the isomeric amides on treatment with acetyl chloride.However the reaction of N-aryl nitrones with oxalyl chloride led to the introduction of the chlorooxalyl group at the ortho position of the N-aryl group.4 In the present work, the reaction of the 1,3-dipoles 1,3-diaryltriazene 1-oxides 1a–i with acid chlorides behaved differently. Addition of oxalyl chloride to the 1,3-dipoles 1a–i in dry toluene at room temperature gave only the arenediazonium chlorides in good yields (80–95%), Table 1. The physical and spectral properties of the diazonium salts 3a–i are summarised in Table 1.The well known instability of diazonium compounds is one of their outstanding characteristics, and they usually explode on heating above their melting points, a property which complicates both their analyses and mass spectral fragmentation. The IR spectra of 3a–i in KBr disks showed a sharp absorption characteristic of the diazonium group ·+N�N at 2250–2280 cmµ1. Because of the instability of the diazonium salt, the 1H NMR spectra could not be recorded. Chemical evidence for the diazonium salt structure was provided by coupling the salts 3a,d,g,i with an ethanolic alkaline solution (NaOH) of 2-naphthol, which afforded the corresponding azo dyes5,6 4a,d,g,i (Scheme 1).Chromatographic separation of the mother liquors did not give any pure compounds. A rationale for the formation of the arenediazonium salts 3a–i is presented in Scheme 2.It is expected from the dipolar nature of the triazene 1-oxides that the oxygen of the azoxy function will behave as a nucleophile and may attack the electron-deficient carbonyl carbon of the oxalyl chloride to form the dipoles 5a–i. Proton shift followed by decomposition of 6a–i may give rise to the diazonium salts 3a–i, chlorooxalic acid 7 and nitrene 8. In previous work7 on the thermal characterization of triazene 1-oxides, we succeeded in capturing the nitrene species 8 which underwent dimerisation to form azobenzene in low yield (0.01%; GC–MS analysis).It was too difficult to separate the dimer by preparative TLC. However, the chloroxalic acid 7 could not be separated and although there are plenty of reports8 on this acid, reference to explain the separation was not found. In contrast to the oxalyl chloride reaction, treatment of triazene 1-oxides 1a–i with acetyl chloride and benzoyl chloride did not give the corresponding arenediazonium salts but instead gave resins.Chromatographic separation gave decomposed compounds in small quantities, which could not be isolated in a pure form. Experimental All melting points were recorded on a Galenkamp melting point apparatus and are uncorrected. Oxalyl chloride, benzoyl chloride and acetyl chloride were obtained from Aldrich. Toluene was distilled and dried following the method of Vogel.9 Triazene 1-oxides 1a–i were prepared according to literature methods.10 IR spectra *To receive any correspondence.†This is a Short Paper as defined in the Instructions for Authors, Section 5.0 [see J. Chem. Research (S), 1997, Issue 1]; there is therefore no corresponding material in J. Chem. Research (M). Table 1 Physical and spectral data of diazonium chlorides 3a–i Compound Yield Mp 3 (%) Colour °C vmax (KBr)/cmµ1 a bc def ghij 93 80 86 80 87 95 90 80 83 89 White Pink Buff Brown White White Grey Orange Brown White 59 (decomp.) 71–72 79–80 65 60–61 70–72 74–75 133–135 75–77 87–88 3000 (Ar–CH), 2280 (–N+�N) 3000 (Ar–CH), 2900 (aliph-CH), 2255 (–N+�N) 3030 (Ar–CH), 880 (aliph-CH), 2260 (–N+�N) 3030 (Ar–CH), 2850 (aliph-CH), 2250 (–N+�N) 3010 (Ar–CH), 2900 (aliph-CH), 2255 (–N+�N) 3030 (Ar–CH), 2885 (aliph-CH), 2265 (–N+�N) 3000 (Ar–CH), 2800 (aliph-CH), 2280 (–N+�N) 3000 (Ar–CH), 2265 (–N+�N), 775 (C–Cl) 3030 (Ar–CH), 2280 (–N+�N), 800 (C–Cl) 3030 (Ar–CH), 2260 (–N+�N), 780 (C–Cl) Scheme 1H O– N+ N N Ar Ph Cl O Cl O H O N+ N N Ar Ph C Cl O C Cl O O N N N Ar Ph C Cl O C Cl O N N Cl– Ar + – decomposition 1a–j Cl O HO O 2 5a–j –H+ – 6a–j + Ph N + 7 + 8 3a–j J.CHEM. RESEARCH (S), 1997 167 were recorded on Shimadzu 470 and Perkin Elmer 283 spectrophotometers (KBr disk). Synthesis of Solid Diazonium Chlorides 3a–i.·To a clear stirred solution of the unsymmetrical triazene 1-oxides 1a–i (1 mmol) in dry toluene (10 ml), oxalyl chloride 2 (1 mmol) in dry toluene (5 ml) was added dropwise. The reaction mixture became turbid and after 10 min at room temperature the solid diazonium chloride products precipitated.The diazonium chlorides 3a–i were separated by filtration in 80–95% yield. Reaction of Triazene 1-Oxides 1a–i with Acetyl Chloride and Benzoyl Chloride.·To a stirred solid cold (µ10 °C) solution of triazene 1-oxide (1 mmol) in dry toluene (10 ml), acid chloride (1 mmol) in dry toluene (5 ml) was added dropwise over 10 min. The reaction mixture was allowed to warm to room temperature and gradually became darker giving an oily viscous material.Separation of these resins by preparative TLC afforded multi-decomposed compounds in small quantities which could not be isolated in pure solid form. Preparation of the Azo Dyes 4a,d,g,i.·Addition of a solution of the solid diazonium salt 3a,d,g,i (1 mmol) in cold water (5 ml) to an ethanolic alkaline solution (10% NaOH) of 2-naphthol (1 mmol) at 0–5 °C gave a red precipitate. The reaction mixture was then allowed to stand at room temperature for 10 min and then filtered.The solid obtained was dried and then recrystallized from an appropriate solvent. The melting points of the product dyes were compared with those of authentic samples.5,6 4a: scarlet red (93%), mp 132 °C (lit.,5 132–133 °C). 4d: deeply red (96%), mp 133 °C (lit.,6 133–134 °C). 4g: red dye (87%), 140 °C (lit.,6 139–140 °C). 4i: bright red (94%), mp 156 °C (lit.,6 155–157 °C). Received, 17th July 1996; Accepted, 27th January 1997 Paper E/6/05013A References 1 A. M. Nour El-Din, A. A. Hassan, S. K. Mohamed, F. F. Abdel- Latif and H. A. El-faham, Bull. Chem. Soc. Jpn., 1992, 65, 553. 2 A. M. Nour El-Din, S. K. Mohamed and D. Doepp, Bull. Chem. Soc. Jpn., submitted for publication. 3 J. Hamer and A. Macaluso, Chem. Rev., 1964, 64, 473. 4 D. Liotta, A. D. Baker, N. L. Goldman and R. Engel, J. Org. Chem., 1975, 39. 5 R. P. Lastovsk and I. Zhur, J. Gen. Che.), 1948, 18, 921. 6 J. W. Raymond, Le Fevre and H. T. Liddicoet, J. Chem. Soc., 1951, 2743. 7 S. K. Mohamed, PhD Thesis, El-Minia University, 1994. 8 H. A. Abdel-Nabi, PhD Thesis, El-Minia University, 1992. 9 Text Book of Practical Organic Chemistry, ed. A. I. Vogel, Longman, London, 4th edn., 1978. 10 T. Mitsuhashi and O. Simamura, J. Chem. Soc. B, 1970, 705. Scheme 2