Nitration And Nitrosation Reactions Of Ester Salicylate Coordinated By Metal Nitrates

Nitric oxides play fundamental roles in biochemical processes. Therefore, the studies on their formation and elimination have been one of the most active research fields in biochemistry. The present study was focused on the formation and elimination of nitrogen oxides induced by the coordination between ester salicylate and metal nitrates, which may provide further understanding for the physiological function of nitric oxide in biosystems including plants and animals. At the same time, the nitration and nitrosation reactions relating to the elimination of nitric oxides are crucial for the synthesis of a vast of fine chemicals.First, we examined the typical coloration reactions of rare earth nitrates with ester salicylates in refluxing ethyl acetate by UV-vis spectra and identified the isolated green solid by means of MS, ¹H-NMR, IR, TG-DTA and cyclic voltammetry. The results show that the isolated green solid are nitrosated complexes of methyl salicylate with rare earths nitrates. These complexes can be transferred to red oximes when treated with concentration acids and further changed to nitrated methyl salicylates, methyl 3-nitrosalicylate and methyl 5-nitrosalicylate, when diluting the red solution. The basic union existed in green complexes is Ln(NO₃)(H₂O)(NO-MS), where the oxygen atoms of phenol, carbonyl group water and nitrate are all coordinated to rare earth ions. At the same time, passing NO into the warm ethyl acetate solution containing yttrium perchlorate and methyl salicylate under no oxide also resulted in the formation of green nitroso compound, indicating that complexes formed between rare earth ions and methyl salicylates can trap NO and form nitrosation compounds. Moreover, this observation also demonstrated that these complexes formed between rare earth ions and methyl salicylates can reduce nitrate to NO, not only to nitrite, and possess function similar to that of nitrate reductase. A possible mechanism is proposed, where salicylate was firstly coordinated with rare earth nitrates to form salicylate complex, then the electron of the complex was transferred to nitrate group to reduce nitrate to NO which is an effective nirosating reagent for rare earth salicylate complexes. Some experimental results were demonstrated by quatum chemical computation. The acivity energy of reaction between phenyl salicylate and yttrium nitrate is higher than that of methyl salicylate, which is in agreement with results that the reaction rate for phenyl salicylate was lower than that for methyl salicylate. The computational results also show nitroso compounds can easily be changed to oxime through a transition state.Secondly, the reaction mechanism of iron(III) nitrate and methyl salicylate in refluxing ethyl acetate solution was studied by means of Electric Absorption Spectra(EAS) and Electrospray Ionization Mass Spectra(ESIMS). This nitration reaction, which gives rise to forming methyl 3-nitrosalicylate and methyl 5-nitrosalicylate, was followed by the formation of red complex between iron and methyl salicylate, indicating that it is the red complexes participated in the nitration process. With the formation of nitrated compounds, the color of solution was transferred from red to yellow, and some brown solid were isolated, indicating that the complexes formed before were graduatly consumed with part of them transferred to iron oxides. Correspondingly, some of the iron(III) ions were reduced to iron (II) ions. With these evidences, we proposed a new radical formation mechanism explanation for nitration reaction mediated by coordination. The mechanism includes coordination, activation, radical formation,Ï€-complex formation,σ-complex formation, complex decomposition to nitrated methyl salicylates with the reduction and hydrolysis of iron(III). The coordination has been demonstrated by the directive detection of iron (III) methyl salicylate complexes using EAS and ESIMS approach. The activation process refers to the electron.transfer in inner coordination sphere promoted by heating. The splitting of O-N bonds in activated complexes then resulted in the liberation of·NO₂ radicals which have been detected using ESIMS method.·NO₂ radicals show strong affinity toward phenol ring of methyl salicylate to formÏ€-complex andσ-complex intermediates. These intermediates turn to final nitration products after being decomposed due to the reduction and hydrolysis of iron (III). At the same time, the effects of reaction time, mole ratio of iron(III) nitrate to methyl salicylate, acidity and basicity on the yield and regioselectivity of methyl 3-nitrosalicylate(O) and methyl 5-nitrosalicylate(P) were examined. With the optimum conditions, reaction time is 3h and the mole ratio of iron(III) nitrate and methyl salicylate is 2:3, the total yield and regioselectivity (P/O) are found to be 58.25% and 5.3. Furthermore, the differences of the the spectral properties of methyl salicylate and its nitration products, as well as the reaction regioselectivity were explained by quatum chemical computation.