The kinetic regularities of acetone oxidation by aqueous nitric acid solutions (5.86-58.31 wt.%) were studied using a differential automatic microcalorimeter. The critical phenomena were discovered, which manifest themselves as a abrupt change in the initial heat release rate at a minor change in the temperature or acid concentration. The abrupt change in the oxidative activity of the reactant at a minor change in the system parameter was assumed to be related to changes in the structure of the solution and, as a consequence, in the solvation energy of the reactants at a certain acid/water ratio in the solution.The reactions of nitric acid with organic compounds, mainly nitration reactions, which are widely used for syn thesis of dyes, drugs, explosives, gunpowders, etc., are being intensively studied in the modern organic chemis try. Nitration is almost always accompanied by a parallel oxidation reaction, whose rate under normal conditions is much lower, but the thermal effect is substantially higher. The change in the parameters of the process may result in an abrupt increase in the heat release rate in the system and in the loss of the thermal stability of the pro cess. According to the current knowledge, the kinetics and mechanism of liquid phase oxidation of different classes of organic compounds including ketones with molecular oxygen can be described by the regularities of chain reac tions with degenerate chain branching. 1 In turn, data on the kinetics and mechanism of ketone oxidation by bound oxygen, particularly, by the systems based on nitric acid solutions, are rather scarce, and the available works are mainly preparative. It was found 2-6 in a series of studies on the liquid phase oxidation of aliphatic hydrocarbons by nitric acid solutions that the process under study is classi fied as a reaction where acid base equilibria play a sub stantial and in many aspects determining role along with the radical steps characteristic of oxidation. A combination of radical irreversible and ion molecular reversible steps is the main specific feature of oxidation by systems based on nitric acid solutions. This opens new possibilities to control the rate of the overall process by shifting the acid base equilibria. ExperimentalAcetone (special purity grade) was used in experiments. Solutions of nitric acid were prepared from HNO 3 (reagent grade, † Deceased. c 34.7 mol.%), and their concentrations were determined by acidometric volumetric titration. The heat release rate during oxidation was measured with a differential automatic calorimeter 7 in glass sealed ampules without cold parts, which made it possible to retain all reaction components in the reaction bulk. The temperature interval studied was 17-99.4°С, and the concentra tion of HNO 3 solutions expressed as a molar ratio of water to acid (n H 2 O /n HNO 3 ) was 2.50-56.14. The investigated acetoneaqueous nitric acid system is homogeneous in the region of the studied concentrations of nitric acid solutions. A high HNO 3 excess with respect to acetone was use...
The equilibrium of nitration of cellulose was studied at 13.1 and 20 ~ in aqueous solutions of HNO 3 (77.3--80.5 wt.%) forming quasi-homogeneous solutions with cellulose. At 20 ~ under quasi-homogeneous conditions, the rates of cellulose nitration are comparable to those of homogeneous nitration of alcohols. The effective nitration constants differ substantially for heterogeneous and homogeneous reactions. Using IR spectra, the partial conversions in the nitration to the 2, 3 and 6 positions of the glucopyranose cycle and the effective equilibrium constants of formation of different isomeric nitrates were estimated.Key words: cellulose, nitration, equilibrium, constants.The equilibrium of the reaction of cellulose (1) nitration by aqueous solutions of HNO 3 has been studied in detail, t-3 but the equilibrium constants of reactions of formation of different isomeric nitrates have been determined only in 1980--1990 J,4 using J3C NMR spectroscopy. At concentrations of HNO 3 below ~75 wt.% and above -82 wt.%, the nitration of cellulose is heterogeneous, j which can be due to a specific influence of the solid phase. Therefore, it was of interest to study the regularities of nitration of cellulose by nitric acid under homogeneous or close to homogeneity (gellike) conditions. The purpose of this work is to estimate the duration of nitration of a part of cellulose soluble in HNO 3, to analyze the effect of heterogeneity of the system on the equilibrium constants, and to study them in the region of formation of a quasi-homogeneous solution, using more accessible and widely abundant IR spectroscopy for the estimation of equilibrium constants of the cellulose nitration. ExperimentalSolutions of nitric acid with different concentrations were prepared by dilution of a stock 88.48% solution of HNO 3, and their concentrations were calculated from the weight of the stock solution and distilled water added. The stock solution was prepared by dilution of the concentrated acid distilled from fuming HNO 3 at a reduced pressure. Cotton cellulose with an ash content of 0.07% containing 98.4% a-cellulose was used.To study the equilibrium of nitration at 13.1 ~ samples of nitrocellulose (2) were prepared in several stages: first, at room temperature cellulose was mixed with a solution of HNO3 in a weight ratio of 1:(40_+0.01). The mixture was thoroughly homogenized and filtered through an acid-resisting filter. The gel-like transparent mass obtained was placed in a vessel, which was thermostatted at 13.1 ~ and had on the bottom several thick-walled capillaries with an inner diameter of ~1 mm closed with a ground plate. A vessel with a solution of nitrocellulose was hermetically mounted above another vessel thermostat'ted at the same temperature, provided with a magnetic stirrer, and containing a ~30-fold (relative to a solution of nitrocellulose) amount of 10% acetic acid. After thermostatting for 30 rain, the vessel with aqueous acetic acid was evacuated, and a solution of nitrocellulose was added through capillaries with stirring to a...
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