Structure and Spectroscopic Studies of Bis Azo Compounds with S/SO 2 Bridges and Containing Cyclic-1,3-Dicarbonyl Groups

A sequence of new bis azo dyes was synthesized using aromatic diamines with S/SO 2 bridges and cyclic-1,3-dicarbonyl compounds containing active methylene groups; 3,3-dimethyl-1,5-cyclohexadione (dimedone), 1,3-cyclohexadione and 2,2-dimethyl-1,3-dioxane-4,6-dione, and was obtained dyes 1-6 . Whether the reaction was complete and the purity of the compounds was controlled with TLC. The structure of the newly synthesized compounds was investigated by using, FT-IR, 1 H-NMR, LC–MS/MS and UV–Visible spectrophotometric methods, CH 3 OH was used in the LC-MS/MS experiments, and the molecular masses of the compounds were seen as M and M +1 protonated in the spectrum. In the absorption spectra of these compounds, the solvent effect by using different solvents and also the acid-base effect by adding HCl or KOH to the medium were investigated. The tautomeric equilibrium forms (enol-imine O-H….N, keto-amine O….H-N forms) of the compounds were investigated according to the electronic spectrum recorded in chloroform, dimethylformamide (DMF), acetic acid and methanol solvents. The results of the UV-visible and 1 H-NMR spectra indicated that the compounds in chloroform, dimethylformamide (DMF), acetic acid and methanol were found in the hydrazo tautomer (keto-amine O….H-N forms) of the proposed tautomeric forms.


Experimental Equipment (Deneysel Ekipman)
All chemicals purchased with Merck and Aldrich chemical companies were used with no purification. Melting points were determined on a Stuart-SMP30 instrument with the capillary tube and were not corrected. Thermo Nicolet 6700 FT-IR spectrometer (on ATR) at Hitit University was used for infrared spectra (4000-400 cm-1). Brucker Avance DPX-400 NMR device (solvent CDCl3; internal standard TMS) at Fırat University was used for proton nuclear magnetic resonance ( 1 H-NMR) spectra. LC-MS/MS was recorded by Thermo Scientific/TSQ Quantum Access Max at Scientific Technical Application and Research Center at Hitit University. Absorption spectra of compounds were recorded by a PG Instruments T80+ spectrophotometer.

General synthesis of the arylhydrazone derivatives (Arilhidrazon türevlerinin genel sentezi)
Diazonium salt: 4,4'-thiodianiline (0,010 mol) or 4,4'sulfonyldianiline (0.010 mol) was dissolved in conc. HCl (5.04 mL, 0.060 mol) and 20.00 mL of water. Then, the solution temperature was allowed down to around 0°C on an ice-salt bath and 1.38 g (0.020 mol) NaNO2 solution in water was slowly dropped to the diamine solution and, continued stirring for at least 30 min. The temperature of the mixture should not exceed 0-5°C. Azo coupling: Cyclic-1,3-dicarbonyl compounds (0.010 mol) in ethanol (20 mL) were added in portions to solution of the diazonium salt at 0-5°C. This mixture maintained 3h. The solid product was precipitated with saturated sodium acetate solution under pH control. The obtained solid crude was filtered, airdried and recrystallized using ethanol (for all compounds). The purities of the compounds were controlled with TLC (ethylacetate; n-hexane, 1:1).

FT-IR and 1 H-NMR Studies (FT-IR ve 1 H-NMR çalışmaları)
Three tautomeric forms that bis azo-dioxo (T1), bis hydrazo-dioxo (T2) and bis azo-enol-oxo (T3) were estimated for bis azo dyes regarding present FT-IR and 1 H-NMR data. The structures of 1-6 are confirmed by the presence of corresponding signals of the FT-IR and 1 H-NMR protons spectra. The estimated tautomeric forms are shown in Figure 3 on the bis azo compound 1.

UV-Vis Study
The UV-Vis spectra of the bis azo dyes were recorded in 4 different solvents; chloroform, DMF, acetic acid, and methanol ( Figure 4). Solvents in different polarities were preferred in our study. In addition, the acidic or basic medium impacts on the absorption spectra of bis azo dyes were investigated [38]. For this purpose, 2-3 mL of HCl (0.1 M) or KOH (0.1 M) solution was added to the bis azomethanol solution and scanned again. All measurements were recorded at room temperature (±25°C). The data obtained are listed in Table 1.

LC MS/MS Study
While the mass spectra were taken, the samples were dissolved in methanol and then filtered through the 0.45µm syringe filter. The structures of 1-6 bis azo dyes were proposed considering these LC-MS/MS data and the molecular weight information. The molecular ion cluster was determined at m/z 462.03 for 1, 517.00 for 2, 525.10 for 3, 494.89 for 4 ( Figure.

CONCLUSIONS (SONUÇLAR)
In the 1 H-NMR Spectrum, we can say that our compounds are in bishydrazo-dioxo form because NH protons come out in a very low field between 15.56-13.70 ppm. In the literature, the reaction of cyclic-1,3-dicarbonyl compounds with the aryldiazonium compounds gave the arylhydrazo derivatives and these compounds are in the arylhydrazo form via the intramolecular N-H-O=Chydrogen bonding [36,37]. Although bishydrazodioxo form (T2) appears in solution, in the FT-IR spectra, the solvent-free medium, has not been observed either. These results are in agreement with the literature [40,41]. According to the absorption data, it can be said that a single maximum absorption peak was observed in all solvents. This situation suggested that the bis azo dye solutions consisted of a single tautomeric form. According to our explanation based on the NMR data before, the compounds are thought to be mostly in the bis hydrazo-dioxo (T2) tautomeric form in the solution medium. Also, a shoulder peak at 500 nm is observed in the spectrum of compound 4 recorded in DMF. This situation suggests a mixture of the two tautomeric forms in DMF.
The acidic or basic medium impacts on the absorption spectra of dye solutions were investigated by adding HCl or KOH to the methanol solution. For all dye solutions, it has been observed hypsochromic shift (in values ranging from 4 to 8 nm) in absorption values in an acidic medium. Only a single absorption peak is observed in the acidic media spectra, suggesting that it is in a single tautomeric form. In basic medium, a bathochromic shift can be mentioned for all compounds, but long wavelength shouldering (>400 nm) was also observed in all recorded spectra. This situation shows that two different tautomeric forms coexist in the basic environment of dye solutions.

DECLARATION OF ETHICAL STANDARDS
(ETİK STANDARTLARIN BEYANI) The author of this article declares that the materials and methods they use in their work do not require ethical committee approval and/or legal-specific permission.

KATKILARI)
Gülnihal ERTEN: She conducted the experiments, analyzed the results and performed the writing process.
Naki ÇOLAK: He analyzed the results and performed the writing process.

CONFLICT OF INTEREST (ÇIKAR ÇATIŞMASI)
There is no conflict of interest in this study.