A synthesis of some new 4-arylidene-5(4 H )-oxazolone azo dyes and an evaluation of their solvatochromic behaviour

Nine novel 4-arylidene-5(4 H )-oxazolone azo dyes were synthesized in good yield by reacting sodium 2-[4-{2-[4-(dimethylamino)phenyl]-1-diazenyl}benzoylamino]acetate with suitable aldehydes in the presence of Ph 3 P/CCl 4 and acetonitrile at room temperature. Sodium 2-[4-{2-[4-(dimethylamino)phenyl]-1-diazenyl}benzoylamino]acetate was obtained by diazotization of 4-aminohippuric acid and coupling with N,N -dimethylaniline. These dyes were characterized by elemental and spectral analyses and the solvatochromic behaviour in various solvents was evaluated.


Introduction
Many heterocyclic compounds are used extensively in disperse dye chemistry for textile or nontextile applications.These dyes are now marketed to produce a full range of dispersed dyestuffs without the use of colorants based on heteroaromatic diazo components.Most of the heterocyclic dyes are derived from the diazo components consisting of five-membered rings containing one or more nitrogen heteroatoms, with the rings being fused into another aromatic ring. 1,2he azo dyes containing heterocyclic rings result in brighter and often deeper shades than their benzene analogs.][5][6][7][8][9] The 5(4H)-oxazolones are important synthons for the synthesis of several biologically active molecules.Also, they are precursors of amino acids containing an aromatic side chain.A number of methods are available for the synthesis of azlactones including the use of acetic anhydride and sodium acetate, acetic anhydride and lead acetate, polyphosphoric acid, sulfur trioxide/dimethyl formamide complex, perchloric acid, and carbodiimides.1][12][13][14][15] .
It is well known that triphenylphosphane in combination with tetrachloromethane provides reagents that have manifold uses and are finding increasing application in preparative chemistry for halogenation, dehydration, and P-N linking reagents.Of more general importance is the tertiary phosphane/tetrachloromethane system, as chlorinating and dehydrating agent for sensitive substrates to the aggressive and readily hydrolyzed acid chlorides such as PCl 5 , P(O)Cl 3 , thionyl chloride and sulfonyl chloride.][18] Herein, we wish to report a novel method for synthesis of some new 4-arylidene-5(4H)oxazolone azo dye derivatives from sodium 2-[4-{2-[4-(dimethylamino)phenyl]-1-diazenyl} benzoylamino]acetate and corresponding aldehydes in the presence of PPh 3 and CCl 4 at room temperature.acetate with corresponding aldehydes in presence of acetic anhydride and sodium acetate under refluxing condition (method A).In method B, We found that Ph 3 P/CCl 4 reagent easily converted the compound 2 to 4-arylidene-5(4H)-oxazolone azo dyes (3a-i) under refluxing with corresponding aldehydes and NEt 3 in CCl 4 .In this investigation, at first triphenylphosphane reacts with carbon tetrachloride to give triphenylphosphonium chloride.Next compound A is formed along with the generation of triphenylphosphane oxide.Then aromatic aldehydes are condensed with A to give the 4-arylidene-5(4H)-oxazolone azo dye products.A reasonable mechanism is shown in Scheme 1.In method C, we investigated the effect of acetonitrile as a solvent on the Ph 3 P/CCl 4 reaction.It was seen that with Ph 3 P/CCl 4 / MeCN an excellent yield of highly pure product was obtained at room temperature and short time whereas two previous methods were carried out at high temperature, long time and moderate yields (Table1).The choice of acetonitrile was based on a review by Appel 19,20 where it was pointed out that acetonitrile can have marked accelerating effect on Ph 3 P/CCl 4 reactions, owing to its high dielectric constant and solvating ability compared to CCl 4 itself.Other merit of this method is for sensitive substrates to hydrolyze in the acidic solution.

Results and Discussion
ARKAT USA, Inc.The absorption spectra of these oxazolone azo dyes 3a-i were recorded in various solvents at the concentration of 10 -6 M, and the results are given in Table 2.We found that the electronic absorption of these oxazolone azo dyes indicated a regular variation with the polarity of solvents, which did not change significantly.These dyes, apparently, did not exhibit a strong solvent dependence.The maximum absorption of these dyes shifted in the order: DMF > acetone > chloroform.The spectral shifts of dye 3a in various solvents are shown in Fig 1 .The maximum absorption of dye 3a showed bathochromic shift in DMF and acetone, with respect to the maximum absorption in chloroform (e.g.λ max is 494 nm in DMF, 492 nm in acetone, and 490 nm in chloroform).The same trends of absorption shifts in various solvents were observed for the entire series of dyes 3a-i, as shown in Table 2.The substituent effects of the heterocyclic azo dyes 3a-i were evaluated.The spectral shifts of dyes 3a-i in chloroform at a concentration of 10 - 6 are given in Table 3.We found that the dyes 3d and 3e contain an electrondonor group methoxy on the 4th and 2nd position of phenyl group substituted on the 4th position of oxazolone ring, so that the λ max of dye 3d and 3e showed hypsochromic shift of -6 and -2 relative to the dye 3a, respectively.
Dye 3g contains an electron acceptor group (nitro) in the 3rd position of the phenyl group substituted on the 4th position of the oxazolone ring, so that the λ max of dye 3g showed bathochromic shift of +13 nm relative to 3a, λ max of dyes 3b and 3c is +4 nm and +10 nm longer than that of dye 3a, due to weaker electron acceptor of chloro group in the para and ortho, para positions of phenyl group substituted on the 4th position of oxazolone ring, respectively, λ max of dye 3h showed bathochromic shift of +3 nm relative to 3a and λ max of dye 3i is +4 nm longer than that of dye 3a.

Experimental Section
General Procedures.Melting points were determined on a Gallenkamp melting point apparatus and are uncorrected.IR spectra were recorded with the MATTSON 1000 FT-IR spectrophotometer.Nuclear magnetic resonance spectra were recorded on the BRUKER DRX-500 AVANCE spectrometer using tetramethylsilane (TMS) as an internal standard.Mass spectra were obtained by SHIMADZU QP 1100EX.Elemental analyses were performed by the Iranian Oil Company using a Heracus CHN-O-Rapid analyzer.UV spectra were recorded using a GBC Scientific Equipment (CINTRA 5) UV visible spectrometer.

General preparative procedures Sodium 2-[4-{2-[4-(dimethylamino)phenyl]-1-diazenyl} benzoyl amino] acetate.
In a 125-mL Erlenmeyer flask, 4-aminohippuric acid (0.01 mol) was added to 2% sodium carbonate solution (30 mL) until it was dissolved by boiling.The solution was then cooled and sodium nitrite (0.01 mol) was added, with stirring, until it was dissolved.The solution was cooled by placing it in an ice bath, and then concentrated hydrochloric acid (2 mL) and water (3 mL) were added.By acidifying the solution, a powdery yellow precipitate of the diazonium salt was separated.
N,N-Dimethylaniline (0.01 mol) and glacial acetic acid (0.01 mol) was mixed.The solution of N,N-dimethylaniline acetate was added to suspension of diazotized hippuric acid, with stirring, and acid-stable form of the dye was separated.A stiff paste was formed in 5-10 min and then sodium hydroxide (5g) was added to produce the orange sodium salt.The product was collected using saturated sodium chloride solution.The crude product was crystallized from water (2).Orange crystals, decomposed >270 yield is 81%.IR (KBr): υ = 3354, 1716 cm -1 .).The solvent was evaporated after the reaction system was refluxed for 6h.The residue was precipitated in water and ethanol and then was purified with toluene to give the corresponding 4arylidene-5(4H)-oxazolone azo dye products.

Table 2 .
Absorption spectra of dyes 3a-i in various solvents

Table 3 .
Substituent effect of dyes 3a-i in chloroform a Relative to 3a.ARKAT USA, Inc.