Benzene and its derivatives are extremely important substances in modern chemical technologies. However, emissions of these substances have an extremely negative impact on the atmosphere and ecology. Benzene is a substance of the second class of danger and its effect on the human body is fraught with serious consequences. In the event of man-made disasters, it is an urgent task to convert benzene into less toxic substances. In this study, using a low-pressure flow reactor, the kinetic patterns of the reactions of atomic fluorine with benzene, fluorobenzene, and chlorobenzene at a temperature of T = 293 K and a pressure of 0.8–1.3 Torr are established. The concentrations of reagents and products are controlled by molecular beam mass spectrometry. To determine the reaction rate constants, the method of competing reactions is used. The reaction of fluorine atoms with cyclohexane is chosen as a competitor. As a result of the analysis using the experimental and published data, the following values of the rate constants of the studied reactions are obtained.

Halogenated acids are of anthropogenic and natural origin and play an important role in atmospheric processes. The global distribution and high stability of halogenated acids is concerning because they are toxic, accumulate in surface waters, and pose a threat to humans and the ecosystem. Knowledge of the reaction mechanism of halogenated acids in the gas phase makes it possible to explain and control many important processes occurring in the atmosphere and during combustion. In this paper, we experimentally study the reactions of atomic fluorine with monochloroacetic, dichloroacetic, trichloroacetic, trifluoroacetic, and pentafluoropropionic acids at a pressure of 1 Torr. The experiments are carried out using a flow reactor connected to a mass spectrometer with a modulated beam. The rate constants of these reactions at room temperature are determined by the method of competing reactions (MCR) using the available published data. It is shown that in this series the fastest reaction is F + CH 2 ClCOOH. In addition, the temperature dependences of the rate constants are obtained for F + CF 3 COOH and F + C 2 F 5 COOH reactions in the ranges of 258–343 and 262–343 K, respectively.

Галогензамещенные кислоты имеют антропогенное и природное происхождение и играют важную роль в атмосферных процессах. Глобальное распространение и высокая стабильность галогензамещенных кислот вызывают обеспокоенность в связи с тем, что они токсичны, накапливаются в поверхностных водах и представляют угрозу для людей и экосистемы. Знание механизма реакций галогензамещенных кислот в газовой фазе позволяет объяснить и управлять многими важными процессами, протекающими в атмосфере и при горении. В настоящей работе экспериментально исследованы реакции атомарного фтора с монохлоруксусной, дихлоруксусной, трихлоруксусной, трифторуксусной и пентафторпропионовой кислотами при давлении 1 Торр. Эксперименты проводили с помощью проточного реактора, соединенного с масс-спектрометром с модулированным пучком. Методом конкурирующих реакций с привлечением имеющихся литературных данных определены константы скорости указанных реакций при комнатной температуре. Показано, что в этом ряду наиболее быстрой является реакция F + CH 2 ClCOOH. Кроме того, для реакций F + + CF 3 COOH и F + C 2 F 5 COOH получены температурные зависимости констант скорости в диапазонах 258–343 и 262–343 K соответственно.

Benzyl and hydroxyethyl radicals play an important role in the combustion and oxidation of toluene and ethanol. As a result of their reactions with nitrogen oxides, a number of toxicants are formed, including soot particles. Establishing the mechanism of reactions of benzyl and hydroxyethyl radicals with nitrogen oxides will make it possible to explain many important chemical processes during combustion and in the atmosphere. In this work, using an experimental technique with a flow reactor and a time-of-flight mass spectrometer operating in the multiphoton ionization mode, we study the reactions of benzyl and hydroxyethyl radicals with nitric oxide in the temperature range of 253–353 K at a pressure of 1 mbar. Multiphoton dissociation spectra of hydroxyethyl radicals are obtained for different types of dyes from a tunable laser in the laser radiation wavelength range from 425 to 590 nm. The form of the temperature dependence of the ratio of the rate constants of the reactions of nitric oxide with benzyl and hydroxyethyl radicals has been experimentally established. Using the literature data by the method of competing reactions, the value of the rate constant of the reaction NO with C6H5CH2 at a temperature T = 299 K is found.

The mass spectra of negative ions of aqueous solutions of completely neutralized monochloroacetic acid (MCA), dichloroacetic acid (DCA), and trichloroacetic acid (TCA) with a concentration of 0.01 mol/L at 20°C are obtained by the mass spectrographic method of electrospraying electrolyte solutions in vacuum. In all the distributions according to the degree of hydration of the acid residue, the dependence of the ion current intensity on the number of water molecules in the ion current is found. At an acid concentration of 0.01 mol/L, the number of hydrated monochloroacetic and dichloroacetic ions decreases monotonically with the increasing degree of hydration. For a TCA solution, the ion current intensity reaches the maximum of the distribution for two water molecules in the ion.

The method of competing reactions is used to study the kinetics of the reaction of fluorine with benzene at a temperature of T = 293 K. The studies are carried out in a low-pressure flow reactor with the mass spectrometric detection of the reagents and reaction products. The reactions of fluorine atoms with cyclohexane, trifluoroacetic, and trichloroacetic acids are used as competing reactions. The ratios of the rate constants of benzene and these competing reactions with atomic fluorine are determined for the first time. The rate constant for the reaction of fluorine atoms with benzene is calculated based on the experimental data obtained and the reaction rate constants known from the literature: k 1 (293 K) = (2.0 ± 0.6) × 10 –10 cm 3 molecule –1 s –1 .

The structure of hydrated ions of dichloroacetic acid (DCA) is established by electrospraying aqueous solutions of DCA into the vacuum chamber of a mass spectrograph. At an acid concentration of 0.01 mol/L, the number of hydrated ions decreases monotonically with an increase in the degree of their hydration. The resulting mass spectrum provides information on the distribution of hydrated ions in solution, which makes the mass spectrographic method of spraying electrolytes in a vacuum applicable for determining the composition of electrolyte solutions in environmental studies.

The structure of hydrated ions of monochloroacetic acid was determined by electrospray of aqueous solution of monochloroacetic acid into the vacuum chamber of the mass spectrograph. It was found that the distribution of ions in degree of hydration depends on the concentration of acid in the initial solution. The number of the hydrated ions monotonically decreases with growth of their hydration shell at concentration of the acid of 10 mM. At acid concentrations <1 mM, the distribution is peaked on the hydration number n = 2. This maximum separates water molecules with a strong and weak bonding with the ion.

The kinetics of the reaction between fluorine and benzene is studied experimentally at T = 293 K. Competitive reactions are used to find a reaction rate constant. The interaction is studied in a low-pressure flow reactor, and mass spectrometry is used to control the concentration of reagents and products. The reaction between fluorine atoms and methane is used as a competitive one. The ratio of rate constants of the studied reaction (k1) and a competitive one (k2) is found for the first time: k1/k2 = 4.4 ± 0.3. A rate constant is calculated for the reaction of fluorine atoms with benzene using literature data: k1 (293 K) = (2.7 ± 0.5) × 10‒10 cm3 molecule−1 s−1.

Представлены результаты масс-спектрометрического исследования токсичных химических веществ - хлоруксусных кислот (монохлоруксусная, дихлоруксусная, трихлоруксусная кислоты) и пиридина с применением напуска исследованных веществ в виде модулированного молекулярного пучка. Преимуществом молекулярно пучкового напуска является сведение к минимуму образования в ходе анализа посторонних веществ, поскольку метод исключает столкновение молекул исследуемого вещества с нагретыми стенками ионного источника, на которых могут происходить реакции пиролиза и другие реакции образования новых веществ. Полученные масс спектры сравнивались с данными NIST Chemistry WebBook - крупнейшей базы данных, содержащей масс спектры органических и неорганических соединений. Результаты свидетельствуют о частичном расхождении масс спектров, полученных при молекулярно пучковом и традиционном молекулярном напуске анализируемых веществ в масс спектрометр. Показано, что в ряде случаев примененный метод позволяет уточнить масс спектр. Приведена полезная информация о характерных пиках других токсичных веществ, совпадающих с пиками масс спектров анализируемых соединений. Эти вещества могут искажать данные анализа при их одновременном присутствии в анализируемых пробах загрязненного атмосферного воздуха The paper presents results of mass spectrometric study of toxic chemicals - chloroacetic acids (monochloroacetic, dichloroacetic, trichloroacetic acid) and pyridine using modulated molecular beam inlet device for introducing analytes. The advantage of molecular beam inlet is minimizing emergence of foreign substances formed in the course of the analysis, since this type of device avoids collisions of examined analyte molecules with the heated walls of the ion source - the events that can result in pyrolysis and other reactions yielding new superfluous substances. The obtained mass spectra are compared with data taken from NIST Chemistry WebBook, the well known database containing mass spectra of organic and inorganic compounds. The results indicate a partial discrepancy between the mass spectra obtained with the use of the molecular beam technique and traditional mass spectrometer molecular inlets for the analyzed substances. In a number of cases, the applied method is shown to refine the mass spectrum of the analytes. Additionally, useful information is given on characteristic peaks of other toxic substances that coincide with the mass spectra peaks of the analyzed compounds. These substances can distort the analysis data when they are simultaneously present in the analyzed samples of polluted atmospheric air.

Аннотация - Реакции токсичного третичного амина пиридина изучались в основном в жидкой фазе, и только несколько исследований реакций пиридина были выполнены в газовой фазе. По этой причине установление его реакционной способности в газовой среде представляет значительный интерес. В связи с этим методом конкурирующих реакций с применением молекулярно-пучковой масс-спектрометрии была изучена кинетика реакции атомарного фтора с пиридином и 2-фторэтанолом. Впервые была определена константа скорости реакции пиридина с атомарным фтором, которая составила k = (8.0 ± 3.0)·1е-10 см3/мол · с. Установлены основные продукты этой реакции: пиридинил и фторпиридин. Abstract - The majority of reactions of toxic tertiary amine pyridine studied previously were carried out mainly in the liquid phase, and only a few studies investigated pyridine reactions in the gas phase. For that reason, determination of pyridine reactivity in a gaseous medium is of considerable interest. Therefore, the kinetics of the reaction of atomic fluorine with pyridine and 2-fluoroethanol was studied by competing reaction method using molecular-beam mass spectrometry. The rate constant for the reaction of pyridine with atomic fluorine was determined for the first time and was found to be k = (8.0 ± 3.0)∙1е-10 cm3/mol · s. The main products of this reaction were identified as pyridinyl and fluoropyridine.