Next Article in Journal
5,5′-Oxybis(1,3,7-trihydroxy-9H-xanthen-9-one): A New Xanthone from the Stem Bark of Garcinia porrecta (Clusiaceae)
Previous Article in Journal
Phenethyl Esters and Amide of Ferulic Acid, Hydroferulic Acid, Homovanillic Acid, and Vanillic Acid: Synthesis, Free Radicals Scavenging Activity, and Molecular Modeling as Potential Cholinesterases Inhibitors
Open AccessShort Note

3,5-Dimethoxy-2-[(4-methoxyphenyl)diazenyl]phenol

Department of Industrial Chemistry “Toso Montanari”, Alma Mater Studiorum—Università di Bologna, Viale del Risorgimento 4, 40136 Bologna, Italy
*
Authors to whom correspondence should be addressed.
Molbank 2020, 2020(3), M1152; https://doi.org/10.3390/M1152
Received: 16 July 2020 / Revised: 4 August 2020 / Accepted: 6 August 2020 / Published: 11 August 2020

Abstract

3,5-Dimethoxy-2-[(4-methoxyphenyl)diazenyl]phenol was synthesized by an azo-coupling reaction between 3,5-dimethoxyphenol and 4-methoxy benzenediazonium tetrafluoroborate. The structure of newly synthesized compound was elucidated based on 1H NMR, 13C NMR, ESI-MS, UV-Vis and FT-IR.
Keywords: benzenediazonium salt; 3,5-dimethoxyphenol; azo-coupling reaction benzenediazonium salt; 3,5-dimethoxyphenol; azo-coupling reaction

1. Introduction

Azo compounds are a well-known class of compounds widely used in industry as colorants in textile, cosmetics, and paper-printing fields [1,2]. The principal method for the synthesis of azoic compounds is the azo-coupling reaction, a kind of electrophilic substitution reaction, that is one of the most important and versatile methodologies in organic synthesis [3,4]. From many years, we are studying aromatic substitution reaction, both electrophilic and nucleophilic, including azo-coupling reaction [5,6,7,8]. Now we report the synthesis, by azo-coupling reaction, of a novel azo compound, namely 3,5-dimethoxy-2-[(4-methoxyphenyl)diazenyl]phenol.

2. Results

The synthesis of 3,5-dimethoxy-2-[(4-methoxyphenyl)diazenyl]phenol (3) (Scheme 1) was performed by reaction between 3,5-dimethoxyphenol (1) and 4-methoxy benzenediazonium tetrafluoroborate (2) in acetonitrile at 80 °C. The reaction progress was monitored by TLC (RF of product 0.53 in CH2Cl2), and precipitation of a solid was observed. At the end of the reaction, the solid was collected and its 1H NMR spectrum showed only signals ascribable to compound 3 (52% yield). The TLC analyses of the mother liquor showed the presence of the compound 3, that was isolated and purified by column chromatography on silica gel using dichloromethane as eluent (31% yield) providing a combined yield of 83%. The structure of newly synthesized compound was elucidated based on FT-IR, UV-Vis, 1H NMR, 13C NMR and ESI-MS spectroscopy (All spectra are reported in supplementary materials).
Among the above cited techniques, the most diagnostic were NMR spectroscopy and mass spectrometry. In particular, 1H NMR spectrum showed different signals for all three methoxy groups and also two separated signals for CH on the phenol ring.
Further, compound 3 showed an interesting solid state fluorescence [9,10,11] when it was exposed to the UV lamp at 366 nm (Figure 1).
Figure 2 and Figure 3 show the UV-Vis spectrum and emission spectra, respectively.
A similar compound, namely 1-(4-methoxyphenyl)-2-(2,4,6-trimethoxyphenyl)diazene 4 (Figure 4) has been reported [12] as red dye. The reported synthesis was made starting from 1,3,5-trimethoxyphenyl lithium and 2 in THF at −78 °C under inert atmosphere; to the best of our knowledge, no information about fluorescence of it has been reported. We synthesized compound 4 under the experimental conditions currently reported for the preparation of 3, and no fluorescence was observed.
The only difference between compound 3 and 4 is the presence, in the latter, of a methoxy group instead of an hydroxy group. Probably, the presence of the hydroxy group in the ortho position with respect to the aza-group in compound 3 is able to block, through an intramolecular hydrogen bond, the isomerisation of the aza group, thus giving to the molecule fluorescent characteristics [9,10,11].

3. Materials and Methods

The 1H-, 13C NMR spectra were recorded on a Mercury 400 (Varian, Palo Alto, CA, USA) spectrometer operating at 400 MHz (for 1H NMR), at 100.6 MHz (for 13C NMR). Chemical shifts are referenced to the solvent for 1H- and 13C NMR (7.26 and 77.0 ppm, respectively for CDCl3 and 2.50 and 39.50 ppm, respectively for DMSO-d6). Signal multiplicities were established by DEPT experiments. Chemical shifts have been measured in δ (ppm). J values are given in Hertz. Electron spray ionization mass spectrum (ESI–MS) was recorded with a WATERS 2Q 4000 instrument (Waters, Etten-Leur, The Netherlands). IR spectrum was recorded using a Fourier transform spectrophotometer PerkinElmer (Waltham, MA, USA) FT-IR spectrometer Spectrum Two in the 4000−500 cm−1 wavelength range, using a NaCl cell. UV-Vis spectrum was recorded using a PerkinElmer (Waltham, MA, USA) UV-Vis spectrometer Lamba 12. Chromatographic purifications (FC) were carried out on glass columns packed with silica gel (Merck grade 9385, 230−400 mesh particle size, 60 Å pore size) at medium pressure. Thin layer chromatography (TLC) was performed on silica gel 60 F254 coated aluminium foils (Fluka, Darmstadt, Germany). 3,5-Dimethoxyphenol and 4-methoxy benzenediazonium tetrafluoroborate were purchased by Sigma-Aldrich (Darmstadt, Germany).

Synthesis of 3,5-Dimethoxy-2-[(4-methoxyphenyl)diazenyl]phenol (3)

In a round bottom flask equipped with a condenser, under magnetic stirring, 3,5-dimethoxyphenol (0.200 mmol, 30.8 mg) and 4-methoxybenzenediazonium tetrafluoroborate (0.200 mmol, 44.4 mg) were added in 2 mL of acetonitrile. The reaction was heated to reflux. The reaction was monitored by TLC (eluent CH2Cl2). During the reaction, a precipitate was formed. After 12 h, the solid was collected by filtration. The mother liquor was concentrated under vacuum, and the product was purified by silica gel column chromatography (eluent CH2Cl2). The product obtained by filtration and that obtained by chromatography are combined to give 83% total yield.
Red plates m.p.: 209.1–209.8 °C (MeCN); yield 48 mg, 83%; 1H NMR (400 MHz, DMSO-d6, 25 °C) δ ppm: 8.36 (d, J = 9.0 Hz, 2H), 7.95 (d, J = 9.0 Hz, 2H), 6.25 (s, 2H), 4.00 (s, 3H), 3.91 (s, 3H), 3.75 (s, 3H); 13C NMR: (100.6 MHz, DMSO-d6, 25 °C) δ ppm: 164.7 (C), 160.8 (C), 159.6 (C), 157.0 (C), 143.7 (C), 123.2 (C), 122.8 (CH), 114.8 (CH), 93.6 (CH), 91.5 (CH), 56.2 (CH3), 55.8 (CH3), 55.6 (CH3); 1H NMR (400 MHz, CDCl3, 25 °C) δ ppm: 7.75 (d, J = 9.0 Hz, 2H), 6.97 (d, J = 9.0 Hz, 2H), 6.06 (d, J = 2.3 Hz, 1H), 6.03 (d, J = 2.3 Hz, 1H), 3.95 (s, 3H), 3.86 (s, 3H), 3.84 (s, 3H); 13C NMR: (100.6 MHz, CDCl3, 25 °C) δ ppm: 165.1 (C), 160.8 (C), 159.7 (C), 159.4 (C), 143.7 (C), 124.2 (C), 122.8 (CH), 114.5 (CH), 93.8 (CH), 91.5 (CH), 56.3 (CH3), 55.6 (CH3), 55.5 (CH3); ESI-MS (m/z): 289 (M + H)+, 311 (M + Na)+, 327 (M + K)+; FT-IR (cm−1): 3686, 3614, 3020, 2400, 1605, 1525, 1421, 1223, 1211, 790, 725, 672, 515; UV-vis (CHCl3) λmax = 390 nm, ε390 = 21,445 L mol−1 cm−1; Elemental analysis for C15H16N2O4 calculated C 62.49; H 5.59; N 9.72; O 22.20, found C 62.69; H 5.61; N 9.73.

Supplementary Materials

The following are available online, Figure S1. 1H NMR spectrum of compound 3 in CDCl3; Figure S2. 13C NMR spectrum of compound 3 in CDCl3; Figure S3. DEPT spectrum of compound 3 in CDCl3; Figure S4. 1H NMR spectrum of compound 3 in DMSO-d6; Figure S5. 13C NMR spectrum of compound 3 in DMSO-d6; Figure S6. DEPT spectrum of compound 3 in DMSO-d6; Figure S7. ESI-MS spectrum of compound 3; Figure S8. FT-IR spectrum of compound 3.

Author Contributions

Methodology, G.M. and D.T.; writing—original draft preparation G.M. and C.B.; supervision and funding C.B. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by Alma Mater Studiorum-Università di Bologna.

Acknowledgments

Many thanks to Luca Zuppiroli for mass spectra.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Zollinger, H. Color Chemistry, 3rd ed.; Wiley-VCH: Weinheim, Germany, 2003. [Google Scholar]
  2. Broadbent, A.D. Basic Principles of Textile Coloration, 1st ed.; Society of Dyers and Colourists: Bradford, UK, 2001. [Google Scholar]
  3. Zollinger, H. Diazo Chemistry I, 1st ed.; VCH: Weinheim, Germany, 1994. [Google Scholar]
  4. Chehimi, M. Aryl Diazonium Salts; Wiley-VCH Verlag and Co.: Weinheim, Germany, 2012. [Google Scholar]
  5. Boga, C.; Cino, S.; Micheletti, G.; Padovan, D.; Prati, L.; Mazzanti, A.; Zanna, N. New azo-decorated N-pyrrolidinylthiazoles: Synthesis, properties and an unexpected remote substituent effect transmission. Org. Biomol. Chem. 2016, 14, 7061–7068. [Google Scholar] [CrossRef] [PubMed]
  6. Boga, C.; Micheletti, G.; Cino, S.; Fazzini, S.; Forlani, L.; Zanna, N.; Spinelli, D. C–C coupling between trinitrothiophenes and triaminobenzenes: Zwitterionic intermediates and new all-conjugated structures. Org. Biomol. Chem. 2016, 14, 4267–4275. [Google Scholar] [CrossRef] [PubMed]
  7. Del Vecchio, E.; Boga, C.; Forlani, L.; Tozzi, S.; Micheletti, G.; Cino, S. Ring Closure of Azo Compounds to 1,2-Annulated Benzimidazole Derivatives and Further Evidence of Reversibility of the Azo- Coupling Reaction. J. Org. Chem. 2015, 80, 2216–2222. [Google Scholar] [CrossRef] [PubMed]
  8. Micheletti, G.; Boga, C.; Pafundi, M.; Pollicino, S.; Zanna, N. New electron-donor and -acceptor architectures from benzofurazans and sym-triaminobenzenes: Intermediates, products and an unusual nitro group shift. Org. Biomol. Chem. 2016, 14, 768–776. [Google Scholar] [CrossRef] [PubMed]
  9. Fujino, T.; Arzhantsev, S.Y.; Tahra, T. Femtosecond Time-Resolved Fluorescence Study of Photoisomerization of trans-Azobenzene. J. Phys. Chem. A 2001, 105, 8123–8129. [Google Scholar] [CrossRef]
  10. Yoshino, J.; Kano, N.; Kawashima, T. Synthesis of the most intensely fluorescent azobenzene by utilizing the B–N interaction. Chem. Commun. 2007, 6, 559–561. [Google Scholar] [CrossRef] [PubMed]
  11. Kano, N.; Furuta, A.; Kambe, T.; Yoshino, J.; Shibata, Y.; Kawashima, T.; Mizorogi, N.; Nagase, S. 2,2′-Diborylazobenzenes with Double N–B Coordination: Control of Fluorescent Properties by Substituents and Redox Reactions. Eur. J. Inorg. Chem. 2012, 2012, 1584–1587. [Google Scholar] [CrossRef]
  12. Hansen, M.J.; Lerch, M.M.; Szymanski, W.; Feringa, B.L. Direct and Versatile Synthesis of Red-Shifted Azobenzenes. Angew. Chem. Int. Ed. 2016, 55, 13514–13518. [Google Scholar] [CrossRef] [PubMed]
Scheme 1. Synthesis of compound 3 from 3,5-dimethoxyphenol (1) and 4-methoxy benzenediazonium tetrafluoroborate (2).
Scheme 1. Synthesis of compound 3 from 3,5-dimethoxyphenol (1) and 4-methoxy benzenediazonium tetrafluoroborate (2).
Molbank 2020 m1152 sch001
Figure 1. Solid-state fluorescence of compound 3 at 366 nm.
Figure 1. Solid-state fluorescence of compound 3 at 366 nm.
Molbank 2020 m1152 g001
Figure 2. UV-Vis spectrum of compound 3 in CHCl3 (Concentration a. 7.64 × 10−5 mol L−1; b. 3.82 × 10−5 mol L−1; c. 1.91 × 10−5 mol L−1; d. 7.64 × 10−6 mol L−1).
Figure 2. UV-Vis spectrum of compound 3 in CHCl3 (Concentration a. 7.64 × 10−5 mol L−1; b. 3.82 × 10−5 mol L−1; c. 1.91 × 10−5 mol L−1; d. 7.64 × 10−6 mol L−1).
Molbank 2020 m1152 g002
Figure 3. (a) Emission spectrum of compound 3 in CH3CN (Concentration 3.47 × 10−4 mol L−1 λmax = 508 nm); (b) Solid state emission spectrum of compound 3max 680 nm).
Figure 3. (a) Emission spectrum of compound 3 in CH3CN (Concentration 3.47 × 10−4 mol L−1 λmax = 508 nm); (b) Solid state emission spectrum of compound 3max 680 nm).
Molbank 2020 m1152 g003
Figure 4. 1-(4-Methoxyphenyl)-2-(2,4,6-trimethoxyphenyl)diazene.
Figure 4. 1-(4-Methoxyphenyl)-2-(2,4,6-trimethoxyphenyl)diazene.
Molbank 2020 m1152 g004
Back to TopTop