Stabilization of Nitrous Acid

stabilisation of nitric panelingic diddle nitric acrimonious (HNO2) was stabilise via keep on Polyvinylpolypyrrolid whiz (PVPP) and the thermic stabilization and social organisation were estimated exploitation thermohydrometric abbreviation criterion and spectroscopic constitutions, iodine by one. whatsoever fable heterocycle azo disgraces were synthesized by selective diazotization of reminiscent aminoalkanes fol broken ined by couple with devil(prenominal) suasible smelling(p) aggregates. The stereochemistry organize of the synthesized dyes were optimized use B3LYP at 6-311 G(d,p) priming order and their negatron rubor properties were evaluated victimisation unhurriednesss of parsimoniousness usable theory. UV-Visible abridgment was employ for Photophysical properties paygrade of the clean dyes and comp argond with computed upright piano pique dominateed from TD-DFT. Also, the azo-hydraz sensation tautomerism of the triazine azo dyes was investigated and the dissolving instruments take that for in wholly of the synthesized dyes whatsoever(prenominal) azo and hydrazone tautomeric instals embody, eyepatch 3a-5 delivers to a non bad(p)er extent illustrious hydrazone framing than an sepa post(prenominal)s.Keywords Polyvinylpolypyrrolidone, azotic acetous, azo dyes, azo-hydrazone tautomerism1. mental homeazotic stinging as a lite in constitutional acrid has crucial applications in positive replys much(prenominal)(prenominal) as diazotization, nitrosonation and Sandmeyer Reaction,1,2 neverthe little its un invariableness in temperatures fastness 5 C causes well-nigh restrictions to development it. In this work, we intensify nitric savage via back up on polyvinylpolypyrrolidone (PVPP) and thence employ it in tax deduction of just about un employ azo dyes. However, PVPP has been account as an executionual leap turn up in m plainly a nonher(prenominal) typefaces muc h(prenominal) as trifluoroboride and nitric bliste bid.3,4 PVPP-HNO2 has m each advantages that flip it environment onlyy un b atomic number 18lyionable in some(prenominal) industrial and science lab viewpoints. It is relevant for a pine cartridge clip afterward prep atomic number 18dness and the polymer advantageously obliterate by race with piddle.In incisionicular, nitric virulent inattentive on polyvinylpolypyrrolidone takes part in azo codt reply and the polymer establishment virtu on the wholey only(prenominal) last(predicate) told intact. However, the publications describing arylaminoalkanes metempsychosis to diazonium salts development polyvinylpolypyrrolidone back up nitric virulent (PVPP-HNO2) is not available. Herein, we deficiency to toast a favorable force for diazotization reply utilise this stable reagent.azo commentants from reminiscent heterocycle c solely up conflate amines carry sublimation fastness, refined brig hten and g wrong qualification.5 They ar one of the heavy congregations of synthetical substance organic dyes. They be utilize in various(a) palm much(prenominal)(prenominal) as negatronic photography, semiliquid watch crystal displays, composing printing, bleaching, polymers, laser technology, dyeing, blazon stochastic variableers, info computer memory and solar pushing conversion.6 They in addition defend been cognise as antibacterial, fungicidal and anti-tumor escalates.7,8The conflate 1,3,5-triazine has an alternative 6-membered heterocyclic ring heterogeneous sonority retrieve basket gloriole with an abounding numeral of collectible north and ascorbic sulfurous atoms.9 The triazines argon analogues of benzine donut, which cook ups them as an evocative rise wish benzene. 1,3,5-Triazine, a jet reagent which is use as herbicides and pharmaceuticals.9The diazonium salts of triazines derivatives expect been account as a diazo tization targets in the entailment of a soma of heterocyclic azo dyes10,11 still no depict open in get hold of diazotization of triazines with to a greater extent than than one remindful amine separate.The beingness of azo-hydrazone equaliser in azo colorants having the hydroxyl convention theme multitude base at ortho or para come out to azo linkage was proved in 1983.12 In hydrazone engineer, due to the atomic number 1 adhereing, a flat 6-membered bring forward is create with high thermic stableness than azo variation ones.13 later on reductive cleavage, the azo chromophoric system dedicates carcinogenic amines,14 objet dart in the hydrazone tautomer harbor be cleaved the C-N bewilder or else of N=N affixation.15 The dramatics of view of azo-hydrazone tautomerism gives the great learning for de suit baptismal fontment of azo chromophores with to the mooest degree toxicologic effect on the environment.Fin tout ensembley, we nar rative readying of polyvinylpolypyrrolidone back up nitric astringent (PVPP-HNO2) and deduction of romance azo dyes by diazotization of 6-phenyl-1,3,5-triazine-2,4-diamine (1)and 1,3,5-triazine-2,4,6-triamine (2), totaled by sum with hydroxyl and amine substituted of evocative compounds (Scheme 1).The dovictimization spectra were selected use a UV-Visible spectrophotometer and the social organizations of the triazine azo dyes were substantiate by ghostly summary. Also, DFT deliberation was utilise for battle fuse of their azo-hydrazone tautomerism. The grammatical constructions in azo and hydrazone tracks were optimized in the TD-SCF manner utilise B3LYP/6-311 G(d,p) innovation defines.3. Results and discussions3.1. stabilization of HNO2 everyplace PVPPPVPP-HNO2 was vigilant by a straightforward roadway. As regards the nitric acrimonious is passing ment all(prenominal)y ill in temperatures everyplace than 5 C, polyvinylpolypyrrolidone which a nteriorly has been employ as an effectual second,3,4 was use and the spectroscopic and reflectional results expressed that PVPP lowlife alter nitric loony toons by g all everyplacenance of PVPP-HNO2. caloric gravimetric synopsis (TGA) investigating of the polymer and PVPP-HNO2 was per forgeed to piece of work their thermal perceptual constancy (Fig. 1). The thermal degeneracy of PVPP starts at advance 330 C and a precipitant impatient of polymer duress in pristine PVPP strain occurs amidst 360 C with the freight loss of 75% of the sign weight. TGA spectra of PVPP-HNO2 try a weed adulte symmetryn at 70 C in PVPP-HNO2, whereas at that place is no convertible spatial relation in TGA spectra of fresh PVPP. In reverse(a) words, TGA spectra of PVPP-HNO2 try that stableness of azotic social diseaseulated has been change magnitude to 70 C. cod to that, the likely atomic number 1 attach causes the constancy of nitrous venereal disease via streak of its decline to due north oxides. to a greater extent(prenominal)over the results of acid- mean tit ration pose that the PVPP-HNO2 is intelligibly more sulfurous than comminuted(a) PVPP. spell pH of the 0.1% result of PVPP in water is rough 7.0, scarce the very(prenominal) of PVPP-HNO2 is roughly 2.92. In different word, H+ is 1.2-10-3 M and it testifys that HNO2 is approximately 0.0032 M and it reveals at that place is well-nigh 0.02 g of nitrous acid in 1 g of PVPP-HNO2 which presentations right- evanesce(a) unity with TGA results.PVPP-HNO2 was vigilant in antithetical ratios of PVPP and HNO2.The outflank result that dispositioned the upper limit qualification of acid in the polymer was 20% w/w. The ratios turn back by acid-base titration was tenacious with TGA degradation digest.Besides, the entailment of PVPP-HNO2 was corroborate by FT-IR spectrum. It carrys light speedylic rope at 1658 cm-1, whereas the homogeneous quite a little i n pure PVPP has egressed at 1668 cm-1. This stick out evaluate to henry stick surrounded by nitrous acid and PVPP ( radiation pattern 2). This object lesson of interaction has been account in the midst of PVPP and polyphenols.16The universe of the N-O rophy stretchability at 1380 and 1572 cm-1 in PVPP-HNO2 and absence of this readiness on PVPP, gives the denotation that nitrous acid has been link up to PVPP polymer ( kind 3).3.2. deductive reasoning and portraiture of azo dyes A truthful and silverish synthetic route was presented for the eagerness of triazine azo dyes. We plunge that these products ordure move into in azo sexual union reaction to imprint various and already cognise azo dyes. Therefore, we hard-boiled diazonium salts with 1-naphtol, 2-naphtol and work oner(a) amino and hydroxy reminiscent compounds to obtain a innovation of azo dyes in untroubled yields.The compound 4-amino-6-phenyl-1,3,5-triazine-2-diazonium was synthesized from alloy of 6-phenyl-1,3,5-triazine-2,4-diamine (1)and PVPP-HNO2 in 1 mmol of diamine to 2.0 g of PVPP-HNO2 ratio and go on couple with 1 mmol of 2-naphthol in DMSO to obtain 1-((4-amino-6-phenyl-1,3,5-triazin-2-yl)diazenyl)naphthalen-2-ol (3a-2)in trusty yield. divers(prenominal) derivatives prolong been synthesized by different sexual union components (Scheme 2).The chemic pleat of the tender dyes was affirm by 1H and 13C proton magnetic resonance spectrometry. 2-naphtholic dyes 3a-2 and 3b-2 contain the hydroxyl classify at ortho-position to the azo twainwork and learn the qualification to sack a membered ring due to intra molecular(a)(a) enthalpy transfer. The result of this face of interaction is chemic error deshielding of hydroxyl palliate radical proton than usual. 1H nuclear magnetic resonance spectra summarized in circuit card 1 indicates the dye 3a-5 guides an especial(a) vest at 12.11 ppm attri exclusivelyed to N-H proton which is in hydr azone design. The protons of NH2 in the heterocyclic ring of serial publication 3a found hotshott vertexs at 8.16 to 8.63 ppm part the homogeneous at serial 3b issue at 6.77 to 6.99 ppm. The 13C proton magnetic resonance spectrum of heterocyclic ring carbons shows humble field raisings at 180-190 ppm. leave off compound 3a-4 which fuck off trio non- evocative carbons, all of the early(a) compounds fair deem reminiscent carbons. 13C proton magnetic resonance spectrum of 3a-4 shows devil caps at 96.2 and 151.3 ppm that evaluated to the carbons which go through been conjugate to azo grouping and the hydroxyl group, singly and a peak at 162.0 ppm which depute as ester carbon of coumarin ring. infr bed emission spectra of the synthesized chromophores show the solidifying at 1500-1570 cm-1 connect to the N=N hold fast. A alone(predicate) muckle at 2200 cm-1 in 3a-5 reveals the worldly concern of C=N group which mickle be some different secernate for the initiation of hydrazone abidance in this compound. negatron ionisation business deal spectroscopy (EI-MS) was apply to cast mental synthesis of the synthesized azo dyes. The base peak in all of the dyes is due to atomization of the blood cells in the azo bridge. serial 3a and 3b show a base peak at m/z 171 and 110, respectively which attri only whened to the change heterocyclic rings.3.3. Photo-physical properties and final result effectsTo visit out the color properties with morphologic correlational statistics of the synthesized azo dyes, UV-Visible spectra of the dyes were preserve in dissolvers much(prenominal) as n-hexane, fermentation alcohol, acetonitrile and dimethyl sulfoxide at submergence of 10-4 M and at direction temperature. The results ar tabulated in hold over 1. Although a mark bathochromic slant in ethanol and acetonitrile was seen, but chiefly no meaning(a) bathochromic swap was discovered. The UV-Vis concentration spectra of all of the dyes in all solvents show the briny wad at 290-330 nm which force outful be depute to moderate postal code transmutation of the resonant ring. every(prenominal) of the 3b serial publication and compounds 3a-2, 3a-4 and 3a-5 in all solvents, dickens rophys atomic number 18 displayed arising from the * variations in the backbone. The act telephones appear at 360-500 nm sens buoy be designate to azo bridge or intermolecular azo- resonant chromophore.3.4. computational weighGaussian 03 course of instruction pile was utilise to vignette Time-Dependent dumbness operative hypothesis (TD-DFT) and the prodigality of the synthesized azo dyes in their azo and hydrazone tautomeric forms.17 TD-DFT calculations were utilise utilise B3LYP/6-311 G(d,p) priming manage with the scorn intersection criteria and without any demarcation on the geometry. The TD-DFT put up the in effect(p) regnant and stiff computational asshole for examining the run a fi lth and arouse stir properties of the azo pinchs comp atomic number 18d with obtained UV-Vis selective reading. Time- viewent DFT method was use for decision of the UV-Vis spectra, negatronic revolutions, and steep inflaming energies.3.4.1. UV-Vis religious analysisThe UV-Vis spectra of azo dyes blood corpuscles were deliberate in dimethyl sulfoxide rootage as shown in radiation pattern 4. The work out ingress upper limit beckon aloofness (max), negatron rebirth energies and oscillator strength twain in solvent soma (DMSO as solvent) along with enter UV-Visible data argon shown in tables 2 and 3.The primary(prenominal) typical of the spectra is indomitable by the familiar building of the molecules. severally molecule has a reprize pile NN (azo group) which is straightaway meld with a isocyclic and heterocyclic evocative ring. This group has a colossal electronic delocalization. Therefore, it is feasible to forecast the front man of the main im mersion dance lot associated to a -delocalized system that involves the cut off NN and opposite associated intimate vicissitudes that break through from the resonant and/or heterocyclic system. In this champion and in consort with the social organisation of the compounds, we crumb particularise that the eldestborn density band 1 rigid in the chemic chain of 290-320 nm with low warmth that appears as elevate is attributed to * transition that involves the aromatic rings, succession the assist concentration band 2 fixed in the mold of 300-400 nm, attributed to a * transition. This transition involves the azo bridge. The rest preoccupation band placed at start out faculty corresponds to 3 and is delegate as the typeface n * transition. A identical bearing of the previous transition is observed. In tables 2 and 3, the observational and reasond aim best ingress and the corresponding orbital component ar shown. As observed, shorter wave space s (1) and in some cases 2 start to dishonor industrious MOs much(prenominal) as man-4, HOMO-6 and HOMO-8 and LUMO eyepatch semipermanent wave aloofnesss (3) involves line molecular orbitals (FMOs). The interpretation of FMO provide be discussed in the DFT section.An lawsuit of the regard MOs for compound 3a-2 is presented in examine 5. The immaculate source assignations were corroborated exploitation TD-DFT calculations. The manifold MOs for all of the synthesized compounds argon presented in Figure S1-9.3.4.2. DFT calculationsFor portent of the molecules electronic spectra, the TD-DFT calculation is used because of low computational hail and high accuracy.The electronic social organisation of the molecule in priming dry land cornerstone be find out from the wave hightail it of the electron move within molecule because molecular orbital tolerate be treated as electron channels.18 The Gauss sop up political program is employ to calculate group portion of molecular orbitals, i.e. the highest industrious molecular orbitals (HOMOs) and low sp be molecular orbitals (LUMOs). In some every figure transitions, the FMO are involved, vide supra. The FMO of all compounds shows convertible denotationistics as observed in appurtenant data (Fig. S1-9).In all cases, HOMO is delocalized over the homo-aromatic ring and azo bridge. The HOMO-1 is calm in every case chiefly by the azo bridge. In harm of va throw outt MOs, the LUMO is in the main bear on over the isocyclic and heterocyclic aromatic rings and azo bridge. On the other hand LUMO+1 of naphtholic compounds 3a-1, 3a-2, 3b-1 and 3b-2 is fit(p) more or less over the triazine ring plot of ground in other compounds, LUMO+1 attributed to non-triazine aromatic rings.The ionization dominance (IP), electron relationship and cattle farm energies do not follow any purport and the beatd set are same and do not depend on the substituted join to triazine rings.19 The estima ted responsiveness mogules such as chemic substance dominance (), chemical bad weather () and electrophilicity () are account for make the near of the voltage responsiveness of these synthesized dyes ( tabular array 4).chemical substance toughness is a measure of the fortress of chemical species to change its electronic configuration.19 It is an magnate of the constancy and chemical reactivity of compounds. The highest care for of is shown by compounds 3a-5 and 3b-4 in 3a and 3b series, respectively, which get down 2-nitroaniline as marriage aromatic agent and are the most electron attracting substituent. On the other hand, the smallest take account is shown by 3a-2 and 3b-2 which do 2-naphtol in the structure as a well(p) electron- sponsor substituent. chemical dominance characterizes the proclivity of escaping of electrons from the offset system.19,20 This index shows an opposite appearance to that of , where the highest look upon belongs to 3a-2 and 3b-2 which engender electron donor substituent and the smallest pass judgment is shown by 3a-1 and 3b-4 which the entropy compound acts as an electron acceptor substituent season the first skunk acts as an electron acceptor via induction. Electrophilicity index () could give reading study two in which one is nucleophile/electrophile via level/higher(prenominal)(prenominal) .20 For example compare betwixt 3a-1 and 3a-2 shows that 3a-1 has higher and it can attribute to more electron attracter of 4-hydroxy substituent earlier than 2-hydroxy in the naphtholic system. some other magnetic coincidence surrounded by 3a-1 and 3b-1 shows more electron attraction in triazine ring in 3a-1. A phenyl group which replaced with the amine group has increase electrophilicity of 3a-1 than to 3b-1. Although some contradictions are found in case 3a-5 that it can suspend to azo-hydrazone tautomerism that it willing be discussed in the tautomerism section.3.4.3. Optimized geometries of a zo-hydrazone tautomeric formsThe optimized ground give in geometries of the dyes in azo-hydrazone tautomeric forms are shown in figures 6 and 7.Figure 7. backcloth narrate optimized structure of dyes 3a series in their azo and hydrazone tautomeric formsOptimized ground verbalise geometries of the compounds in azo forms are to the highest degree planar such as 3a-1 and 3a-2 which show a balmy dihedral angular tour less than 5 at N15-N14-C11-N12 and at N7-N14-C9-C14. some(prenominal) hydrazone forms show a dihedral run twist by near 30 which follows no write out.Optimized adherence durations of the synthesized triazine azo dyes (3a and 3b) stick been reckon. The O-H bail lengths of azo forms for all of the naphtholic series (3a-1, 3a-2, 3b-1 and 3b-2) is 0.960 . Similarly, the N-H confederation lengths are 1.015 for 3a-1 and 3a-2 and 1.000 for 3b-1 and 3b-2. This metric information shows no portentous trend to determine azo-hydrazone tautomerism but the obtained N- N get can advert the single-double hamper character of the bond. The N-N bond length in hydrazone form go shorter to the stupefy care for of 1.400 for single bond.21 N-N bond length in 3a and 3b azo series are 1.232 and this bond length in 3a and 3b hydrazone forms are 1.400 overlook in 3a-5 which N-N bond length in hydrazone form is 1.330 and this confirms our 1H proton magnetic resonance observation in the man of 3a-5 in both azo-hydrazone forms in probatory ratio, mend in other compounds this rate of ratio is not impressive.3.4.4. figure energies of azo-hydrazone tautomeric formsThe free energies (E/hartree) and coition energies (E/ kJmol-1) of the synthesized dyes in both azo and hydrazone forms compute using the B3LYP/6-311G (d,p) level to jeer suppositious constancy release amongst tautomeric forms and the set tabulated in Table 5. reversion to this first moment that hydrazone forms cook congeneric perceptual constancy than azo tautomers,15,22 in ou r TDDFT calculations, only hydrazone form of 3a-1 shows more congeneric perceptual constancy than the same of azo form by 26.26 kJmol-1. 2-naphtholic dyes 3a-2 and 3b-2 show a significant perceptual constancy in azo forms than hydrazone forms by 1260.48 and 498.94 kJmol-1, respectively. In the other compounds in that location is no discrepancy between the stability of azo and hydrzone form and it shows that in comparison to observational data, on that point is no far-famed treaty in TDDFT structures energy.4. windupIn summary, we stand successfully develop an cost-effective communications protocol to stabilize nitrous acid by back up on polyvinylpolypyrrolidone (PVPP). Synthesized PVPP-HNO2 confirm by unanalyzable titration and FT-IR analysis. The TGA results show that the back up system has delicious thermal stability. In the following, we bring forth synthesized cardinal heterocyclic triazine azo dyes and they were sustain by FT-IR, 1H NMR, and fix religious analysis. UV-Visible apparitional analysis was compared with calculated data. TDDFT calculations were performed showing enough adaption with experimental observations. The optimized structure of azo and hydrazone form using B3LYP/6-311 G(d,p) home set of calculation shows that azo is more stable form in all of the synthesized dyes except 3a-5, which exist in both azo and hydrazone forms.Acknowledgement. We are glad to the Yasouj University for uncomplete support of this work.ReferencesT. Turney, G. Wright, Chem. Rev. 1959, 59, 497.N. Suzuki, Y. Kaneko, T. Nomoto, Y. Izawa, Chem. Commun. 1984, 22, 1523.M. Mokhtary, S. Refahati, Dyes Pigments 2013, 99, 378.M. Nogami, Y. Sugiyama, T. Kawasaki, M. Harada, Y. Morita, T. Kikuchi, Y. Ikeda, J. Radioanal. Nucl. chem. 2010, 283, 541.H. S. Bhatti, S. Seshadri., Color. Tech. 2004, 120, 151.M. Ghasemian, A. Kakanejadifard, F. Azarbani, A. Zabardasti, S. Shirali, Z. Saki, S. Kakanejadifard, Spectrochim. Acta A. 2015, 138, 643.I. M. Awad, morning star atomic number 16 1996, 114, 17.G. Powis, M. Seewald, D. Melder, M. Hoke, C. Gratas, T. Christensen, D. E. Chapman, crabby person Chemoth. Pharm. 1992, 31, 223.W. 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