Thermal dehydration kinetics of disaccharides

The vacuum decomposition of sucrose and cellobiose has been observed in the 150–250°C temperature range. The predominant decomposition product of both sugars is H₂O with less than 5% CO, CO₂, CH₂O, CH₃CHO, CH₃OH, and C₂H₅OH formed. The detailed rates and temperature dependences suggest that with the possible exception of C₂H₅OH, the minor products are formed in secondary reactions of the dehydration products. Further it is shown that the so-called “melting with decomposition” of a sugar is in reality a high-temperature dissolution of the disaccharide in the eliminated water.     

Shock‐tube and modeling study of acetaldehyde pyrolysis and oxidation

Pyrolysis and oxidation of acetaldehyde were studied behind reflected shock waves in the temperature range 1000–1700 K at total pressures between 1.2 and 2.8 atm. The study was carried out using the following methods, (1) time‐resolved IR‐laser absorption at 3.39 μm for acetaldehyde decay and CH‐compound formation rates, (2) time‐resolved UV absorption at 200 nm for CH₂CO and C₂H₄ product formation rates, (3) time‐resolved UV absorption at 216 nm for CH₃ formation rates, (4) time‐resolved UV absorption at 306.7 nm for OH radical formation rate, (5) time‐resolved IR emission at 4.24 μm for the CO₂ formation rate, (6) time‐resolved IR emission at 4.68 μm for the CO and CH₂CO formation rate, and (7) a single‐pulse technique for product yields. From a computer‐simulation study, a 178‐reaction mechanism that could satisfactorily model all of our data was constructed using new reactions, CH₃CHO (+M) → CH₄ + CO (+M), CH₃CHO (+M) → CH₂CO + H₂(+M), H + CH₃CHO → CH₂CHO + H₂, CH₃ + CH₃CHO → CH₂CHO + CH₄, O₂ + CH₃CHO → CH₂CHO + HO₂, O + CH₃CHO → CH₂CHO + OH, OH + CH₃CHO → CH₂CHO + H₂O, HO₂ + CH₃CHO → CH₂CHO + H₂O₂, having assumed or evaluated rate constants. The submechanisms of methane, ethylene, ethane, formaldehyde, and ketene were found to play an important role in acetaldehyde oxidation. © 2007 Wiley Periodicals, Inc. 40: 73–102, 2008     

The thermal decomposition of azomethane. III. Kinetics of the noninhibited reaction

The thermal decomposition of azomethane (A) has been studied in a static system at temperatures between 250° and 320°C and at pressures between 5 and 402 torr, with particular attention to identification of products. Major products, in decreasing order of importance, were nitrogen, methane, ethane, methylethyldiimide, dimethylhydrazone, propane, tetramethylhydrazine, ethylene, methylpropyldiimide, and methylethylhydrazone. Carbon balance at the lowest pressure and highest temperature was 92%, but decreased with increasing pressure and decreasing temperature owing to the formation of a polymer. A fairly simple mechanism accounts reasonably well for a short chain in the decomposition, propagated by the radical CH₃N₂CH₂ (B), and for the five most abundant products, except ethane. It turns out that there is a second source of ethane, arising by C₂H₅ + A → C₂H₆ + B; this explains an anomalously high apparent activation energy for the reaction CH₃ + A → CH₄ + B. Ethyl radicals are also shown to be responsible for the formation of propane, ethylene, methylethylhydrazone, and methylpropyldiimide. The radical B decomposes to CH₃ + CH₂ + N₂, and the methylene radical (probably both singlet and triplet) is shown to yield C₂H₅ at low pressure and high temperature, and mostly polymer at high pressure and low temperature.     

Evaluated and estimated kinetic data for phase reactions of the hydroperoxyl radical

Methods are discussed for the production and detection of the hydroperoxyl radical for use in gas phase kinetic studies. Rate constants for gas phase reactions of the hydroperoxyl radical with itself, H₂, H₂O, CO, NO, SO₂, O₃, C₂H₆, C₃H₈, i-and n-C₄H₁₀, C₂H₄, i-C₄H₈, HCHO, C₂H₅CHO, n-C₃H₇CHO, Br, O, OH, and H are critically evaluated. Recommended or estimated rate constant expressions with associated error limits are given applicable over specified temperature ranges (normally 300–1000°K). The reactivity of HO₂ compared with OH, O, H, F, Cl, Br, CH₃, and CH₃O is presented in tabular form and the implications for atmospheric chemistry are discussed.     

A Theoretical Investigation of the Decomposition Reactions of Ethyl Formate in the S0 State

This study revisits the stability of the possible conformations and the decomposition reactions of ethyl formate in the S₀ state using the (U)MP2, MP4SDTQ, CCSD(T), and (U)B3LYP methods with various basis sets. The transition states of the decomposition channels to HCOOH + C₂H₄, CO + CH₃CH₂OH, CH₂O + CH₃CHO, HCOH + CH₃CHO, C₂H₆ + CO₂, and H₂ + CH₂CHOCHO are determined. The microcanonical rate constants derived from the RRKM theory are calculated for each of the decomposition reactions. The high‐pressure limit rate constants are calculated for the decomposition channels to HCOOH + C₂H₄, CO + CH₃CH₂OH, and CH₂O + CH₃CHO.     

Probing the pyrolysis of ethyl formate in the dilute gas phase by synchrotron radiation and theory

The thermal decomposition of the atmospheric constituent ethyl formate was studied by coupling flash pyrolysis with imaging photoelectron photoion coincidence (iPEPICO) spectroscopy using synchrotron vacuum ultraviolet (VUV) radiation at the Swiss Light Source (SLS). iPEPICO allows photoion mass-selected threshold photoelectron spectra (ms-TPES) to be obtained for pyrolysis products. By threshold photoionization and ion imaging, parent ions of neutral pyrolysis products and dissociative photoionization products could be distinguished, and multiple spectral carriers could be identified in several ms-TPES. The TPES and mass-selected TPES for ethyl formate are reported for the first time and appear to correspond to ionization of the lowest energy conformer having a cis (eclipsed) configuration of the O = C (H)– O – C (H₂)–CH₃ and trans (staggered) configuration of the O= C (H)– O – C (H₂)– C H₃ dihedral angles. We observed the following ethyl formate pyrolysis products: CH₃CH₂OH, CH₃CHO, C₂H₆, C₂H₄, HC(O)OH, CH₂O, CO₂, and CO, with HC(O)OH and C₂H₄ pyrolyzing further, forming CO + H₂O and C₂H₂ + H₂. The reaction paths and energetics leading to these products, together with the products of two homolytic bond cleavage reactions, CH₃CH₂O + CHO and CH₃CH₂ + HC(O)O, were studied computationally at the M06-2X-GD3/aug-cc-pVTZ and SVECV-f12 levels of theory, complemented by further theoretical methods for comparison. The calculated reaction pathways were used to derive Arrhenius parameters for each reaction. The reaction rate constants and branching ratios are discussed in terms of the residence time and newly suggest carbon monoxide as a competitive primary fragmentation product at high temperatures.     

Processing of Oil Refinery Gases: Oxidative Dehydrogenation of the Ethane–Ethylene Fraction

Oxidative transformations of the ethane–ethylene fraction of oil refinery gases, containing 20 vol % C₂H₄, on VMoTeNb oxide catalyst in the temperature interval 330–450°C were studied. Comparison with oxidative transformations of the individual components (oxidative dehydrogenation of C₂H₆ and oxidation of C₂H₄) shows that ethylene does not noticeably influence the ethane conversion, whereas ethane strongly suppresses the ethylene conversion. The maximal yield of ethylene from the ethane–ethylene fraction is close to that reached in oxidative dehydrogenation of ethane under similar conditions and amounts to 70–72%.     

Temperature-programmed desorption/pulse surface reaction (tpd/tpsr) studies of CH4, C2H6, C2H4, and CO over a cobalt/MWNTs catalyst

Summary Temperature-programmed desorption (TPD) of CH₄, C₂H₆, C₂H₄, and CO and temperature-programmed pulse surface reactions (TPSR) of CH₄, C₂H₆, C₂H₄, CO, and CO/H₂ over a Co/MWNTs catalyst have been investigated. The TPD results indicated that CH₄ and C₂H₆ mainly exist as physisorbed species on the Co/MWNTs catalyst surface, whilst C₂H₄ and CO exist as both physisorbed and chemisorbed species. The TPSR results indicated that CH₄ and C₂H₆ do not undergo reaction between room temperature and 450^oC. Pulsed C₂H₄ can be transformed into CH₄ at 400 ^oC whilst pulsed CO can be transformed into CO₂ at 100 or 150^oC. In gaseous mixtures of CO and H₂ containing excess CO, the products of pulsed reaction were CH₃CHO and CH₃OH. When the ratio of CO and H₂ was 1:2, pulsed CO and H₂ were transformed into CH₃CHO, CH₃OH and CH₄. In H₂ gas flow, pulsed CO was transformed into a mixture of CH₃CHO and CH₄ between 200 and 250^oC and was transformed into CH₄ only above 250^oC.     

Decomposition of Acetaldehyde in Atmospheric Pressure Filamentary Nitrogen Plasma

The removal of 500?ppm acetaldehyde in nitrogen at 1?bar is characterized in a pulse dielectric barrier discharge generating a spatial random distribution of plasma filaments. The identification and the quantification of numerous by-products are performed. At 20?°C, CH₃CHO is efficiently dissociated, probably owing to quenching of N₂ metastable states. The most abundant by-products are CO, H₂, and CH₄, in consistency with the three important exit channels for the quenching of the N₂(A³?? _u ⁺ ) state by CH₃CHO proposed by Faider et al. (2011). In order of importance, other products are HCN, C₂H₆, CH₃CN, HNCO, CO₂, CH₃COCH₃, C₂H₄, C₂H₅CN, NH₃, C₂H₂, and a group of nitriles and of ketones. An increase of the temperature from 20?°C up to 300?°C induces a strong decrease of the removal characteristic energy, but the by-products types remain unchanged. Probably the reaction of H with CH₃CHO plays a role in the removal of the molecule at 300?°C.     

Study of the solubility of components in the system Mg(ClO3)2-2NH2C2H4OH · H3C6H5O7-H2O

The solubility of components in the system Mg(ClO₃)₂-2NH₂C₂H₄OH · H₃C₆H₅O₇-H₂O was studied from the complete freezing temperature ?59.4°C to 20.0°C. A polythermal solubility diagram was constructed, in which the crystallization fields were determined for ice, Mg(ClO₃)₂ · 16H₂O, Mg(ClO₃)₂ · 12H₂O, Mg(ClO₃)₂ · 6H₂O, 2NH₂C₂H₄OH · H₃C₆H₅O₇ · H₂O, 2NH₂C₂H₄OH · H₃C₆H₅O₇, and two new compounds, [(HOC(CH₂COOH)₂COO)₂Mg · 2H₂O] and [HOC(CH₂COO)₂MgCOOH · 2H₂O], which were identified by chemical and physicochemical analysis methods.     

Novel Copolymers of Vinyl Acetate and Some Ring‐Substituted 2‐Phenyl‐1,1‐dicyanoethylenes

Electrophilic trisubstituted ethylene monomers, some ring‐substituted 2‐phenyl‐1,1‐dicyanoethylenes, RC₆H₄CH?C(CN)₂ (where R is 3‐C₆H₅O, 4‐C₆H₅O, 3‐C₆H₅CH₂O, 4‐C₆H₅CH₂O, 4‐CH₃CO₂, 4‐CH₃CONH, 4‐(C₂H₅)₂N) were synthesized by piperidine catalyzed Knoevenagel condensation of ring‐substituted benzaldehydes and malononitrile, and characterized by CHN elemental analysis, IR, ¹H‐ and ¹³C‐NMR. Novel copolymers of the ethylenes and vinyl acetate were prepared at equimolar monomer feed composition by solution copolymerization in the presence of a radical initiator (ABCN) at 70°C. The composition of the copolymers was calculated from nitrogen analysis, and the structures were analyzed by IR, ¹H and ¹³C‐NMR, GPC, DSC, and TGA. High T _g of the copolymers, in comparison with that of polyvinyl acetate, indicates a substantial decrease in chain mobility of the copolymer due to the high dipolar character of the trisubstituted ethylene monomer unit. The gravimetric analysis indicated that the copolymers decompose in the 190–700°C range.     

3,3′‐Seleno­bis­(propionic acid)

In contrast to Se[CH₂C(O)OH]₂versus S[CH₂C(O)OH]₂, the title compound, Se[CH₂CH₂C(O)OH]₂ or C₆H₁₀O₄Se, is structurally quite similar to its sulfur analogue. The mol­ecule has twofold symmetry. The C—Se—C bond angle is 96.48 (8)° and the Se—C bond lengths are 1.9610 (14) Å. The shortest Se?O intermolecular distance is 3.5410 (11) Å. The O?O distances in the carboxyl­ic acid dimers are 2.684 (2) Å. The temperature dependence of the IR spectrum suggests tautomerism in the solid state.     

Relative rate constants for the reactions of trichloropropenyl radical. Application of the two-parameter Taft equation

The relative rate constants for the hydrogen atom abstraction by CCl₃CH?CH· radical from CH₂Cl₂, CHCl₃, CH₃COCH₃, CH₃CN, C₆H₅CH₃, C₆H₅OCH₃, CH₃CHO, and CH₃OH in the liquid phase at 20°C have been measured. It was shown that these reaction rate constants are correlated by the two-parameter Taft equation with ρ* = 0.726 ± 0.096, r* = 1.22 ± 0.16. A relationship between r* and bond dissociation energy D(R? H) has been found for the abstraction reactions of different free radicals.     

Kinetics and mechanism associated with the reactions of hydroxyl radicals and of chlorine atoms with 1‐propanol under near‐tropospheric conditions between 273 and 343 K

Rate constants for the reactions of OH radicals and Cl atoms with 1‐propanol (1‐C₃H₇OH) have been determined over the temperature range 273–343 K by the use of a relative rate technique. The value of k(Cl + 1‐C₃H₇OH) = (1.69 ± 0.19) × 10^?12 cm³ molecule^?1 s^?1 at 298 K and shows a small increase of 10% between 273 and 342 K. The value of k(OH + 1‐C₃H₇OH) increases by 14% between 273 and 343 K with a value of (5.50 ± 0.55) × 10^?12 cm³ molecule^?1 s^?1 at 298 K, and further when combined with a single independent experimentally determined value at 753 K gives k(OH + 1‐C₃H₇OH) = 4.69 × 10^?17T^1.8 exp(422/T) cm³ molecule^?1 s^?1, which fits each data point to better than 2%. Two well‐established structure–activity relationships for H abstraction by OH radicals give accurate predictions of the rate constant for OH + 1‐C₃H₇OH, provided the β‐CH₂ group is given an increased reactivity of a factor of about 2 over that for the structurally equivalent CH₂ group in alkanes at 298 K. A quantitative product analysis was carried out at 298 K for the Cl‐initiated photooxidation of 1‐C₃H₇OH, using both FTIR and gas chromatography. HCHO, CH₃CHO, and C₂H₅CHO were the only major organic primary products observed, although HCOOH was found in much smaller amounts as a secondary product. A key characteristic of the analysis was that the initial values of the product ratio [CH₃CHO]/[C₂H₅CHO] were effectively constant for NO pressures between 0.15 and 0.3 Torr, but fell by about 35% as the pressure fell to 0.0375 Torr. From a detailed consideration of the mechanism for the oxidation, it is suggested that C₂H₅CHO, CH₃CHO (+HCHO), and 3 molecules of HCHO are formed uniquely from CH₃CH₂CHOH, CH₃CHCH₂OH, and CH₂CH₂CH₂OH radicals, respectively. On this basis, use of the product yields gives the branching ratios of 56, 30, and 14% for Cl atom reaction at the α‐, β‐, and γ‐C? H positions in 1‐C₃H₇OH at 298 K. Given the very low temperature coefficients involved, little change will occur over tropospheric temperature ranges. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 34: 110–121, 2002     

Synthesis and Polymerization of the Organometallic Monomer Series Based on Cymantrenylethyl Acrylate

{η⁵ -C₅H₄[CH(CH₃)OC(O)CH = CH₂])Mn(CO)3, {η⁵—C₅[CH-(CH₃)OC(O)C(CH₃)=CH₂]]Mn(CO)₃, and {η⁵—C₅H₄[CH(CH₃)-OC(O)CH=C(CH₃)2])Mn(CO)₃ were synthesized (63, 57, and 51%, respectively) from {η⁵—C₅H₄[CH(CH₃)OH])Mn(CO)₃, toluene-sulfonic acid, and the acrylic, methacrylic, and dimethylacrylic acids, and from (η⁵-C₅H₄[CH(CH₃)OH]}Mn(CO)₃, pyridine, and the acrylic, methacrylic, and dimethylacrylic acyl chlorides [26, 48, and 25% (impure), respectively]. No product was obtained when NaH was used as the base in the latter method. The acrylate and methacrylate monomers were bulk homopolymerized at 65°C with AIBN (75% yield, M_n = 88,550 g/mol; 78% yield, M_n = 349,350 g/mol, respectively). The dimethylacrylate did not polymerize under these conditions. The polymers lost vinylcymantrene upon heating to 257 and 279°C, respectively. The polymers did not exhibit a clear T_g but were observed to soften at 85 and 160°C, respectively, and they could be pulled into fibers.     

(η5‐Cyclo­penta­dienyl)(p‐fluoro­phenoxo)(nitro­syl)(tri­methyl­silyl­methyl)­molybdenum(II)

The title complex, [Mo(C₅H₅)(C₆H₄FO)(C₄H₁₁Si)(NO)], is formed by reacting CpMo(NO)(CH₂SiMe₃)₂, where Cp is cyclo­penta­dienyl, with one equivalent of p‐FC₆H₄OH. The complex exhibits the expected piano‐stool molecular structure, with a linear nitro­syl ligand [Mo—N—O 168.2 (2)°] having Mo—N and N—O distances of 1.764 (2) and 1.207 (3) Å, respectively. The phenoxo Mo—O distance of 1.945 (2) Å is suggestive of some multiple‐bond character.     

Synthesis of micro- and nanosized manganese oxides from hydrated manganese oxalates and products of their chemical modification with ethylene glycol

The reactions of ethylene glycol with manganese oxalates MnC₂O₄ · 2 H₂O and MnC₂O₄ · 3H₂O on heating in air were studied. At temperature below 100°C, ethylene glycol was found to displace water from oxalates to give a new solvate compound according to the reaction MnC₂O₄ · nH₂O + HOCH₂CH₂OH = MnC₂O₄(HOCH₂CH₂OH) + nH₂O↑. The crystals of the solvates retain the morphology of the initial oxalates, which is then inherited by the products of their thermolysis. Thus, thermolysis of MnC₂O₄ · 3H₂O and MnC₂O₄(HOCH₂CH₂OH) having quasi-unidimensional structure gave Mn₃O₄ and Mn₂O₃ nanowhiskers in air and MnO in an inert gas environment. Heating of MnC₂O₄ · nH₂O in ethylene glycol at temperatures above 100°C results in anhydrous manganese oxalate.     

Selected rate constants for H,O, N,and Cl atoms with substrates at room temperatures

Rate constants for H + Cl₂, H + CH₃CHO, H + C₃H₄, O + C₃H₆, O + CH₃CHO, and Cl + CH₄ have been measured at room temperature by the discharge flow—resonance fluorescence technique. The results are (1.6 ± 0.1) × 10^?11, (9.8 ± 0.8) × 10 ^?14, (6.3 ± 0.4) × 10^{?13) (2.00 torr He), (3.95 ± 0.41) × 10?12, (4.9 ± 0.5) × 10|su?13} and (1.08 ± 0.07) × 10^?13, respectively, all in units of cm³ molecule^?1 s^?1. Also N atom reactions with C₂H₂, C₂H₄, C₃H₄, and C₃H₆ were studied but in no case was there an appreciable rate constant. These results are compared to previous studies.     

Gel formation in cationic polymerization of divinyl ethers. I. 1,4-Bis(2-vinyloxyethoxy)benzene

Polymerization of 1,4-bis(2-vinyloxyethoxy)benzene (CH₂C O CH₂ CH₂ O C₆H₄ O CH₂CH₂ O CCH₂; 1 ) was investigated in CH₂Cl₂ at 0°C with the use of a variety of cationic initiators. SnCl₄, SnBr₄, AlEtCl₂, and BF₃OEt₂ (strong Lewis acids) and CF₃SO₃H (a strong protonic acid) yielded crosslinked insoluble polymers immediately after the polymerizations were initiated. The binary initiating systems such as HCl/ZnCl₂ and (C₆H₅O)₂P(O)OH/ZnCl₂ also produced insoluble poly( 1 )s. At the low initial concentration of ZnCl₂, however, the (C₆H₅O)₂P(O)OH/ZnCl₂ system gave the soluble polymers quantitatively, and gelation occurred only when the reaction mixture was stored for a long time after complete consumption of the monomer. The content of the unreacted pendant vinyl ether groups of the soluble polymers decreased with monomer conversion, and almost all the pendant vinyl ether groups were consumed in the soluble polymer obtained at 100% monomer conversion; this may be ascribed to frequent occurrence of intramolecular crosslinking. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 675–683, 1998     

The pyrolysis of acetaldehyde in the presence of nitric oxide

The kinetics of the acetaldehyde pyrolysis have been studied at temperatures from 450° to 525°C, at an acetaldehyde pressure of 176 torr and at 0 to 40 torr of added nitric oxide. The following products were identified and their rates of formation measured: CH₄, H₂, CO, CO₂, C₂H₄, C₂H₆, H₂O, C₃H₆, C₂H₅CHO, CH₃COCH₃, CH₃COOCH?CH₂, N₂, N₂O, HCN, CH₃NCO, and C₂H₅NCO. Acetaldehyde vapor was found to react with nitric oxide slowly in the dark at room temperature, the products being H₂O, CH₃COOCH₃, CO, CO₂, N₂, NO₂, HCN, CH₃NO₂, and CH₃ONO₂. The rates of formation of N₂ and C₂H₅NCO depend on how long the CH₃CHO-NO mixture is kept at room temperature before pyrolysis; the rates of formation of the other products depend only slightly on the mixing period. The pyrolysis of “clean” CH₃CHO–NO mixtures (i.e., the results extrapolated to zero mixing time, which are independent of products formed in the cold reaction) are interpreted as follows: (1) There are two chain carriers, CH₃ and CH₂CHO, their concentrations being interdependent and influenced by NO in different ways: the CH₃ radical is both generated and removed by reactions directly involving NO, whereas CH₂CHO is generated only indirectly from CH₃ but is also removed by direct reaction with NO. (2) An important mode of initiation by NO is its addition to the carbonyl group with the formation of which is converted into ; this splits off OH with the formation of CH₃NCO or CH₃ + OCN. (3) Important modes of termination are The steady-state equations derived from the mechanism are shown to give a good fit to the experimental rate versus [NO] curves and, in particular, explain why there is enhancement of rate by NO at higher CH₃CHO pressures and, at lower CH₃CHO pressures, inhibition at low [NO] followed by enhancement at higher [NO]. The cold reaction is explained in terms of chain-propagating and chain-branching steps resulting from the addition of several NO molecules to CH₃CHO and the CH₃CO radical. In the “unclean” reaction it is found that the rates of N₂ and C₂N₅NCO formation are increased by CH₃NO₂, CH₃ONO, and CH₃ONO₂ formed during the cold reaction. A mechanism is proposed, involving the participation of α-nitrosoethyl nitrite, CH₃CH(NO)ONO. It is suggested that there are two modes of behavior in pyrolyses in the presence of NO: (1) In the paraffins, ethers, and ketones, the effects are attributed to the addition of NO to a radical with the formation of an oxime-like compound. (2) In the aldehydes and alkenes, where there is a hydrogen atom attached to a double-bonded carbon atom, the behavior is explained in terms of addition of NO to the double bond followed by the formation of an oxime-like species.