Atmospheric chemistry of dimethyl phosphonate, dimethyl methylphosphonate, and dimethyl ethylphosphonate

Rate constants for the reactions of OH radicals and NO3 radicals with dimethyl phosphonate [DMHP, (CH3O)2P(O)H], dimethyl methylphosphonate [DMMP, (CH3O)2P(O)CH3], and dimethyl ethylphosphonate [DMEP, (CH3O)2P(O)C2H5] have been measured at 296 +/- 2 K and atmospheric pressure using relative rate methods. The rate constants obtained for the OH radical reactions (in units of 10(-12) cm3 molecule(-1) s(-1)) were as follows: DMHP, 4.83 +/- 0.25; DMMP, 10.4 +/- 0.6; and DMEP, 17.0 +/- 1.0, with a deuterium isotope effect of k(OH + DMMP)/k(OH + DMMP-d9) = 4.8 +/- 1.2. The rate constants obtained for the NO3 radical reactions (in units of 10(-16) cm3 molecule(-1) s(-1)) were as follows: DMHP, < 1.4; DMMP, 2.0 +/- 1.0; and DMEP, 3.4 +/- 1.4. Upper limits to the rate constants for the O3 reactions of < 8 x 10(-20) cm3 molecule(-1) s(-1) for DMHP and < 6 x 10(-20) cm3 molecule(-1) s(-1) for DMMP and DMEP were determined. Products of the reactions of OH radicals with DMHP, DMMP, and DMEP were investigated in situ using atmospheric pressure ionization mass spectrometry (API-MS) and, for the DMMP and DMEP reactions, Fourier transform infrared (FT-IR) spectroscopy. API-MS analyses showed the formation of products of molecular weight 96 and 126, attributed to CH3OP(O)(H)OH and (CH3O)2P(O)OH, respectively, from DMHP; of molecular weight 110, attributed to CH3OP(O)(CH3)OH, from DMMP; and of molecular weight 124 and 126, attributed to CH3OP(O)(C2H5)OH and (CH3O)2P(O)OH, respectively, from DMEP. FT-IR analyses showed formation (values given are % molar yields) of the following: from DMMP, CO, 54 +/- 6; CO2, 5 +/- 1 in dry air; HCHO, 3.9 +/- 0.7; HC(O)OH, < 1.4 in dry air; RONO2, approximately 4; and formate ester, approximately 8; and from DMEP, CO, 50 +/- 7; CO2, 11 +/- 4; CH3CHO, 18 +/- 8; HCHO, < 7; HC(O)OH, < 6; RONO2, < or = 5; and formate ester, 5.0 +/- 1.5. Possible reaction mechanisms are discussed.     

Shock‐tube studies on the reactions of dimethyl ether with oxygen and hydrogen atoms

The reactions of dimethyl ether (CH₃OCH₃, DME) with O(³P) and H atoms have been studied at high temperatures by using a shock tube apparatus coupled with atomic resonance absorption spectroscopy (ARAS). The rate coefficients for the reactions CH₃OCH₃ + O(³P) → CH₃OCH₂ + OH (1) and CH₃OCH₃ + H → CH₃OCH₂ + H₂ (2) were experimentally determined from the decay of O(³P) and H atoms as: These results show that DME can react with O(³P) atoms more easily than with H atoms. By combining these results with the previous lower temperature data, we obtained the following modified Arrhenius expressions applied over the wide temperature range between 300 and 1500 K: Both reactions of DME are faster than those of ethane, because the dissociation energy of the C? H bond in DME is smaller. Furthermore, the rate coefficients for reactions ( 1 ) and ( 2 ) were calculated with the transition‐state theory (TST). Structural parameters and vibrational frequencies of the reactants and the transition states required for the TST calculation were obtained from the MP2(full)/6‐31G(d) ab initio molecular orbital (MO) calculation. The energy barrier, E^?₀, was adjusted until the TST rate coefficient most closely matched the observed one. The fitting results of E(1) = 23 kJ mol^?1 and E(2) = 34 kJ mol^?1 were in agreement with the G2 energy barriers, within the expected uncertainty, demonstrating that the experimentally determined rate coefficients were theoretically valid. © 2006 Wiley Periodicals, Inc. 39: 97–108, 2007     

Dual-level direct dynamics studies for the reactions of dimethyl ether with hydrogen atom and methyl radical

The dual-level direct dynamics approach is employed to study the dynamics of the CH(3)OCH(3) + H (R1) and CH(3)OCH(3) + CH(3) (R2) reactions. Low-level calculations of the potential energy surface are carried out at the MP2/6-311+G(d,p) level of theory. High-level energetic information is obtained at the QCISD(T) level of theory with the 6-311+G(3df,3pd) basis set. The dynamics calculations are performed using variational transition state theory (VTST) with the interpolated single-point energies (ISPE) method, and small-curvature tunneling (SCT) is included. It is shown that the reaction of CH(3)OCH(3) with H (R1) may proceed much easier and with a lower barrier height than the reaction with CH(3) radical (R2). The calculated rate constants and activation energies are in good agreement with the experimental values. The calculated rate constants are fitted to k(R1) = 1.16 x 10(-19) T(3) exp(-1922/T) and k(R2) = 1.66 x 10(-28) T(5) exp(-3086/T) cm(3) mol(-1) s(-1) over a temperature range 207-2100 K. Furthermore, a small variational effect and large tunneling effect in the lower temperature range are found for the two reactions.     

Theoretical methodology for prediction of tropospheric oxidation of dimethyl phosphonate and dimethyl methylphosphonate

Rate constants for the reactions of OH radicals with dimethyl phosphonate [DMHP, (CH(3)O)(2)P(O)H] and dimethyl methylphosphonate [DMMP, (CH(3)O)(2)P(O)CH(3)] have been calculated by ab initio structural methods and semiclassical dynamics modeling and compared with experimental measurements over the temperature range 250-350 K. The structure and energetics of reactants and transition structures are determined for all hydrogen atom abstraction pathways that initiate the atmospheric oxidation mechanism. Structures are obtained at the CCSD/6-31++G** level of chemical theory, and the height of the activation barrier is determined by a variant of the G2MP2 method. A Transfer Hamiltonian is used to compute the minimum energy path in the neighborhood of the transition state (TS). This calculation provides information about the curvature of the potential energy surface in the neighborhood of the TS, as well as the internal forces that are needed by the semiclassical flux-flux autocorrelation function (SCFFAF) dynamics model used to compute the temperature-dependent reaction rate constants for the various possible abstraction pathways. The computed temperature-dependent rate curves frequently lie within the experimental error bars.     

Hydrolysis of dimethyl 1-acetoxy-2,2,2-trichloroethyl phosphonate

Conclusions The hydrolysis of chloroacetophos in water includes the parallel cleavage of acetic acid, hydrochloric acid and methanol. The ratio of the products, formed in the parallel steps, was determined, and we also determined the total rate constant for the hydrolysis of chloroacetophos.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2336–2338, October, 1971.     

Copper-catalyzed remote C-H monofluoromethylation of 8-aminoquinolines with dimethyl phosphonate as reductant

A simple and efficient copper-catalyzed monofluoromethylation of 8-aminoquinolines with 2-bromo-2-fluoroacetate has been described with HPO(OMe)₂ (dimethyl phosphonate) as reductant. The reaction tolerates a variety of quinoline amides and monofluoroalkyl bromides. Significant advantages of this protocol include synthetic convenience and high reaction efficiency.     

Resolution and absolute configuration of dimethyl hydroxy-(ferrocenylmethyl)phosphonate

Racemic dimethyl hydroxy-(ferrocenylmethyl)phosphonate rac-1 was resolved via the formation of diastereomeric esters with (S)-α-methoxy-α-phenylacetic acid. The diastereomers, separated by column chromatography, were stereospecifically hydrolyzed by dissolution in trifluoroacetic acid at −30 °C and quenching with water. The absolute configuration of one enantiomer of 1 was assigned by X-ray diffraction.     

Catalytic reactions of dimethyl disulfide with thiophene and benzene

The gas-phase reaction of dimethyl disulfide with thiophene proceeds under the action of acid catalysts under atmospheric pressure at 160–350°C and a residence time of τ = 0.6–21 s to form thioalkylation and alkylation products. Dimethyl disulfide reacts with benzene to form only alkylation products. Catalysts containing both strong protic and Lewis acid sites, as well as basic sites of moderate strength, are the most active ones.     

The photo-Arbuzov rearrangement of dimethyl 9-anthrylmethyl phosphite and the photodimerization of the corresponding phosphonate

Upon irradiation, 9-anthrylmethyl phosphite ( 2 ) undergoes the photo-Arbuzov rearrangement to give the corresponding phosphonate 3 . Prolonged irradiation led to the clean formation of the centrosymmetric, head to tail, [4 + 4] photocycloaddition product 4 as indicated by X-ray crystallographic analysis. The same photodimer results on irradiation of phosphonate 3 itself in solution or in the solid phase. Phosphite 2 does not undergo photodimerization to 6 . © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9:155–160, 1998     

Structure and stability of solvation complexes of trimethyl phosphate and dimethyl methyl phosphonate

The presently used electrolytes in Lithium ion batteries, dimethyl carbonate (DMC), and ethylene carbonate are flammable. Trimethyl phosphate (TMP) and dimethyl methyl phosphonate (DMMP) have been shown to be potential nonflammable electrolytes. Density functional theory is used to calculate the structure and stability of the solvation complexes of TMP and DMMP. The calculations indicate that TMP and DMMP can form a solvation complex of the form Li⁺(X)₄ where X is the TMP or DMMP molecule. Calculations of the solvation energy and bond dissociation energies to remove one TMP and DMMP from the solvation complexes are compared with the same calculations on DMC. The results indicate that TMP and DMMP are considerably more stable than DMC.     

Thermodynamic parameters of urethane formation reactions and concomitant processes

Thermodynamic parameters of reactions of methyl and phenyl isocyanates with a series of compounds were determined by quantum-chemical calculations. The products of these reactions model for various functional groups present in commercial polyurethanes. The thermodynamic stability series for compounds formed from aliphatic and aromatic isocyanates were constructed.     

Selective ion-molecule reactions of lactams with dimethyl ether ions

The ion-molecule reactions of dimethyl ether ions CH₃OCH₃ ⁺ and (CH₃OCH₃)H⁺, and four- to seven-membered ring lactams with methyl substituents in various positions were characterized by using a quadrupole ion trap mass spectrometer and a triple-quadrupole mass spectrometer. In both instruments, the lactams were protonated by dimethyl ether ions and formed various combinations of [M + 13] ⁺, [M + 15] ⁺, and [M + 45] ⁺ adduct ions, as well as unusual [M + 3] ⁺ and [M + 16] ⁺ adduct ions. An additional [M + 47] ⁺ adduct ion was formed in the conventional chemical ionization source of the triple-quadrupole mass spectrometer. The product ions were isolated and collisionally activated in the quadrupole ion trap to understand formation pathways, structures, and characteristic dissociation pathways. Sequential activation experiments were performed to elucidate fragment ion structures and stepwise dissociation sequences. Protonated lactams dissociate by loss of water, ammonia, or methylamine; ammonia and carbon monoxide; and water and ammonia or methylamine. The [M + 16] ⁺ products, which are identified as protonated lactone structures, are only formed by those lactams that do not have an N-methyl substituent. The ion-molecule reactions of dimethyl ether ions with lactams were compared with those of analogous amides and lactones.     

Complexation and reactions of molecular iodine with dimethyl and diethyl sulfoxides

The complexation and reactions of molecular iodine with dimethyl sulfoxide and diethyl sulfoxide in the neat sulfoxides and in their mixtrues with water were studied by conductometry, pH-metry, argentometric titration, UV spectroscopy, and GLC analysis. According to the results obtained, molecular iodine initially forms a charge-transfer complex with the sulfoxide, which subsequently undergoes chemical transformations to hydrogen iodide and the corresponding sulfones. A possible reaction mechanism was suggested.     

Theoretical study of hydrogen bonded complexes of dimethyl disulfide or dimethyl peroxide with nitric acid

Ab initio and DFT calculations performed on the title systems revealed two types of structures for both DMDS-HNO₃ and DMDO-HNO₃ complexes. In both structures two hydrogen bonds are formed between the OH group interacting with one of sulfur (or oxygen) atoms and methyl CH group being a proton donor to one of the oxygen atoms of the NO₂ group of nitric acid. Depending on the location of the interacting methyl group with respect to the S or O acceptor of the main O-H?S(O) bond, the seven or eight-membered ring structures are formed. For all the structures, the most pronounced changes in geometric parameters upon interaction are observed for the proton donor molecule. The calculated binding energies are between −20.86 and −29.95 kJ/mol at MP2 and between −17.52 and −27.47 kJ/mol at B3LYP using the 6-311++G(2d,2p) basis set. The complexes involving disulfide are slightly weaker by ca. 6.7-8.6 kJ/mol than the corresponding peroxide complexes. The performed NBO analysis reveals that the charge transferred to σ*(OH) orbital of the nitric acid molecule comes mainly from the high p-character lone pair orbital of sulfur or oxygen atom being the hydrogen bond acceptor site in the disulfide or peroxide molecule.     

Kinetics of the reactions of the hydroxyl radical with dimethyl ether and diethyl ether

Absolute rate coefficients for the reactions of the hydroxyl radical with dimethyl ether (k₁) and diethyl ether (k₂) were measured over the temperature range 295–442 K. The rate coefficient data, in the units cm³ molecule^?1 s^?1, were fitted to the Arrhenius equations k₁ (T) = (1.04 ± 0.10) × 10^?11 exp[?(739 ± 67 cal mol^?1)/RT] and k₂(T) = (9.13 ± 0.35) × 10^?12 exp[+(228 ± 27 kcal mol^?1)/RT], respectively, in which the stated error limits are 2σ values. Our results are compared with those of previous studies of hydrogen-atom abstraction from saturated hydrocarbons by OH. Correlations between measured reaction-rate coefficients and C? H bond-dissociation energies are discussed.     

The reactions of atomic hydrogen and active nitrogen with hydrogen azide

Detection of atoms by mass spectrometry has been used to study the reactions of hydrogen azide, HN₃, with H atoms and active nitrogen, in a fast flow reactor at pressures of about 1 torr. Stoichiometry and products of the H + HN₃ reaction have been determined and the rate constant of the initial step, assumed to be H + HN₃ → NH₂ + N₂, was found to be 2.54 × 10^?11 exp (?4600/RT) cm³ molecule^?1 s^?1, in the temperature range of 300–460K. The formation of NH₃ and H₂ products has been discussed from the different secondary steps which may occur in the mechanism. For the reaction of active nitrogen with HN₃, evidence has been found for the participation of excited nitrogen molecules produced by a microwave discharge through molecular nitrogen. The influence of excited nitrogen molecules has been reduced by lowering the gas flow velocity. It was then possible to study the N + HN₃ reaction for which the rate constant of the initial step was found to be 4.9 × 10^?15 cm³ molecule^?1 s^?1 at room temperature. Finally, the occurrence of these elementary reactions has been discussed in the mechanism of the decomposition flame of HN₃.