Highly Efficient Synthesis of New 2 H-chromene Dyes Using Cu-SBA-15 SHIRIN

In this work, some new azotated 2H-chromene derivatives were successfully synthesized by use of mesoporous Cu-SBA-15 as nanocatalyst leading short reaction times and high yields. By this research, the scope of azo compounds was increased.

Azo compounds are very considerable in dyes and pigments industry 21 .They are the main class of all synthetic dyes that are widely used in the world 22 .The importance of azo dyes returns to their significant physicochemical features such as stability 23 , optical properties 24,25 and their extensive applications in chemosensors 26,27 , liquid crystals 28 and nanotubes 29 .
Recently, an enhancing attention has been concentrated on the development of new synthetic paths in processes employing functionalized mesoporous catalysts 30 .
Mesoporous material has been grown in academia because of its extraordinary surface area, narrow size distribution of porosity, heat resistance and mechanical stability that make them outstanding catalysts 31,32 .
In this work, we use them for the synthesis of new class of azo dyes in very good conditions.

General information
In this research, 5-Phenylazo-salicylaldehyde 1 was synthesized similar to the repor ted methods 33,34 , but optimized, and also the mesoporous Cu-SBA-15 catalyst was prepared by literature 35 .
All of the chemicals and solvents were purchased from Merck (Germany), Sigma-Aldrich (United States) and Fluka (Switzerland) corporations.They were used without anymore purification.TLC was performed on precoated plastic sheets (25DC UV-254 ).Melting points totally were weighed on an electrothermal Gallenkamp melting point apparatus and are not corrected.Elemental analysis for C, H and N were done using a Thermo Finnigan Flash EA1112 instrument.IR spectra were obtained on a Shimadzu FT-IR-4300 spectrophotometer as KBr discs. 1 HNMR and 13 CNMR spectra were analyzed on a Bruker 300 MHz spectrometer (but 2a, 2c and 2d compounds were analyzed on a Bruker 250 MHz spectrometer) in CDCl 3 , and DMSO-d 6 , solutions and chemical shifts were noted in d units by using TMS, as standard.

General procedure for the synthesis of 5-phenylazo-salicylaldehyde (1)
To a solution of substituted aniline (0.05 mol) in a small portion of water was slowly added 7 ml of 37% aq HCl solution at 0-5 0 C with rapid stirring.15 ml of 5 M aq NaNO 2 solution was added dropwise to afford yellowish diazonium salts.Then the solution of salicylaldehyde (3-methoxy salicylaldehyde, 0.05 mol) in 2% aq KOH solution (100 mL) was added very slowly in 1 hour.The mixture was stirred for 30 minutes.The brown solid was filtered and washed with sufficient water.Finally it was recrystallized from ethanol to get the pure product.
In order to recovery of the catalyst, the product was dissolved in acetonitrile (10 ml) and shaken for 5 min.then the catalyst was filtered and washed with enough ethyl acetate and the filtrate was evaporated to gain crude product.It was recrystallized from ethanol to obtain orange pure crystals, mp, 134-136 o C.
The similar procedure was used leading 2b-f.

Diazotization of substituted aniline and a coupling reaction with 2-hydroxybenzaldehyde or its derivative (3-methoxysalicylaldehyde) yielded
The structures of the new azo chromene dyes were deduced from their IR, 1 HNMR, 13 CNMR spectra, and also CHN analysis data.The 1 H decoupled 13 CNMR spectrum for each derivate is completely coincident with the product structure.Due to low solubility, we could not provide 13 CNMR spectra for 2f compound.Fig. 1 illustrates the number of carbon atoms for structure 2. It is helpful for 1 HNMR interpretation in spectral data section.
The infrared spectra (IR) of these 2Hchromene dyes show a decreasing intense carbonyl bands due to conjugated carbonyl systems appearing at 1650-1670 cm -1 .The broad bands in region of 3250-3480 cm "1 are referred to n (O-H) vibrations.The peaks appearing at 1000-1200 cm -1 are attributed to n (C-O) aromatic and aliphatic stretching vibration.The spectra also exhibit the existence of (-N=N-) group at 1400-1450 cm -1 .
To explain the reaction mechanism, should focus on catalyst.The catalyst has lewis acid sites for polarizing carbonyl groups in both reagents, acetylacetone and 5-phenylazo-salicylaldehyde 1, via the nonbonding electrons on their oxygens.This coordination is more important for acetylacetone because it can lead the equilibrium to enol substance in a suitable solvent.
Since b-dicarbonyl compounds such as acetylacetone have keto-enol tautomerization, less polar solvents will move the equilibrium toward the enol form.In examine about effect of solvents, better yields were observed by using mixture of dichloromethane and low amount of a protic solvent.2:1 volume ratio of dichloromethane and ethanol was most suitable according to the high yields (Table 1).
The effect of temperature was also examined.When the reaction warm up to room temperature or higher, the efficiency will decrease.So using ice bath is necessary in whole of the reaction.

CONCLUSIONS
In summary, a new series of azo-chromene dyes 2a-f were synthesized by use of mesoporous nanocatalyst, Cu-SBA-15, leading short reaction times, very simple methodology, high efficiency, easy purification, minimal production of waste and performing reactions in the mild conditions.
However, the diverse characteristics of these azo dye compounds need further investigations.