Investigation of aerosol formation during benzaldehyde photolysis

The kinetics of photolysis and photonucleation of benzaldehyde (BA) vapor in the air and in an inert gas is investigated, along with the physical and chemical characteristics of the resulting aerosol particles. Short-lived free radicals that accompany the BA photonucleation process were identified by means of spin trapping. Numerical simulation of BA photonucleation, combined with the proposed chemical mechanism, allowed us to calculate the rate of generation of initial particles and to estimate the aerosol quantum yield.     

Detection of benzaldehyde and formaldehyde in the UV photolysis of gas-phase methyl benzoate

The excitation of gas-phase methyl benzoate at 240 nm leads to the observation of phosphorescence. The dispersed phosphorescence spectrum has an assigned origin of 25 270 cm⁻¹ and a prominent C=O progression of 1720 cm⁻¹, consistent with literature reports of gas-phase benzaldehyde spectroscopy. Weaker bands, which correspond to formaldehyde ν₁₇ and ν₂₅, are also evident. Time-resolved IR diode laser absorption spectroscopy has been used to probe formaldehyde. Excitation of methyl benzoate at 222 nm clearly indicates the generation of formaldehyde as a photoproduct. The temporal profile of the formaldehyde signal is consistent with significant nascent vibrational excitation in this product. The ratio of formaldehyde initially in the ground vibrational state to that in the excited vibrational states is estimated to be 0.6 ± 0.1. The proposed elimination mechanisms are analogous to those postulated for the formation of CO₂ and acetaldehyde from pyruvic acid.     

Water vapor as a carrier gas in capillary gas chromatography

The use of water vapor as carrier gas in capillary chromatography is analyzed. Under equivalent conditions, a comparison of water vapor and helium as a mobile phase was performed during the separation of diesel fuel components. The advantage of water vapor was demonstrated. The resolutions of peaks were calculated for a pair of substances, C₁₈-iso and C₂₀ (4.4 for water vapor and 3.9 for helium). The Van Deemter dependences were measured, and it was demonstrated that the substantially lower viscosity of the water vapor compared to helium makes it possible to perform the separation of substances in a broader range of linear velocities, comparable to hydrogen used as mobile phase. The prospects for using water vapor was demonstrated in chromatographic analysis of hydrocarbons.     

Water vapor clustering in the field of a chlorine anion occurring in a planar nanopore with structureless walls

The Monte Carlo bicanonical statistical ensemble method has been employed to calculate the free energy, entropy, and work of Cl^? ion hydration in model planar pores 0.5 and 0.7 nm wide at 298 and 400 K. A detailed model of many-body interactions with the ion has been used, the model being matched to experimental data with respect to the free energy and enthalpy of attachment reaction in water vapor. Under the conditions of a restricted volume, the equilibrium size of a hydration shell substantially decreases, with the effect becoming stronger in the range of moderate and large sizes. In moderately supersaturated vapors, under the conditions of a nanopore, the ion loses its hydration shell as the temperature is decreased. In supersaturated vapors, the hydration shell formed on the ion is thermodynamically stable, while the stability crisis shifts to the region of larger sizes. The enhancement of the thermodynamic stability in the pore results from a rise in the chemical potential of molecules due to the deficiency of closet neighbors and a reduction in the entropy under the conditions of the restricted volume. As the temperature is elevated, the effect of ion displacement out of its hydration shell is leveled. The regularities derived in terms of the estimation model based on the capillary approximation are in qualitative agreement with the results of computer simulation.     

Time-resolved CIDNP effects in the reaction of hydrogen atom transfer in photolysis of benzaldehyde in solution

We have studied the dependence of CIDNP effects on the concentration of the starting material in photolysis of a solution of benzaldehyde in cyclohexane-D₁₂ and in benzene-D₆. Using an excimer laser (=308 nm), we have investigated the time evolution of the CIDNP signals with time resolution 1 sec. We have determined the rate constant k₁ for transfer of a hydrogen atom from the hydroxybenzyl radical to the ground-state benzaldehyde molecule and also the rate constant for recombination of two hydroxybenzene radicals.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 3, pp. 324–329, May–June, 1988.The authors thank Doctor of Chemical Sciences L. N. Krasnoperov for useful discussions.     

Water vapor transport in a series of polyarylates

Water vapor sorption and transport properties are presented for a series of polyarylates. The effect of making various structural changes in the polymer backbone has been studied, by comparing the transport properties to those of the base polymer bisphenol A isophthalate. All the polymers exhibit an upturn in the sorption isotherm at moderate to high activities, which in most cases is caused by plasticization of the polymer by water vapor. The response of water vapor to the structural changes is compared to that of the permanent gases reported previously for these materials. A good correlation is established between the diffusion and permeability coefficients and the fractional free volume. A similar behavior is seen in gases. However, the solubility coefficient, which decreases with increase in the fractional free volume, shows an opposite effect. Water vapor has the ability to hydrogen bond with itself and interact strongly with the polymer. In the case of solubility, the water vapor–polymer interaction plays an important role and overrides the effect of the increase in fractional free volume. The structural changes described here have similar effects on the permeation of water in a series of polysulfones reported earlier, as seen here for the polyarylates.     

Mechanism of the long wavelength photolysis of CS2 vapor

It is proposed that in the long wavelength (λ ≥ 290 nm) photolysis of CS₂ vapor the observed CS and S₂ are produced in the reaction sequence:      

Consecutive processes in the photolysis of dimethyl-s-tetrazine molecules in the vapor phase

Experimental studies of the variation of the fluorescence yield and photochemical product yield are presented for dimethyl-s-tetrazine (DMT) at 0.6 Torr and 300 K. Results are also reported for the variation of these yields upon adding argon buffer gas. The fluorescence yield decreases with increasing excitation energy (0 to 4200 cm^?1 vibrational energy excess in the first excited singlet state) but the decrease is insufficient to account for the corresponding increase in product yield. Added gas (600 Torr argon) quenches the photochemistry but not the fluorescence. The results imply that the photo-dissociation involves a bottleneck (B) in the non-radiative singlet decay. The molecules in B can be relaxed by collisions, relax to photostable DMT molecules without collisions, or undergo photodissociation.     

The kinetics and mechanism of n-butyraldehyde photolysis in the vapor phase at 313 nm

The photolysis was investigated at 313 nm wavelength, 253–529 K temperatures, and 4 × 10^?11-2 × 10^?9 mol·photon/cm²·sec light intensities by determining the quantum yields of 20 reaction products. Primary quantum yields for the seven primary processes and rate constant ratios, rate constants, and Arrhenius parameters for secondary processes were derived on the basis of the suggested reaction scheme. The dependence of the quantum yields of the four major primary processes on experimental conditions was established.     

Synthesis of azide-fluoro-dehydrocoelenterazine analog as a photoaffinity-labeling probe and photolysis of azide-fluoro-coelenterazine

A photosensitive azide-fluoro-dehydrocoelenterazine analog (Az-F-DCT) was synthesized, starting from 4-fluorophenylacetic acid, as a photoaffinity-labeling probe in order to analyze symplectin active site. To examine the photo-reactivity of Az-F-DCT, azide-fluoro-coelenterazine analog (Az-F-CT) was used as a potent symplectin chromophore model. Photolysis of Az-F-CT in 2,2,2-trifluoroethanol afforded nitrene intermediate to give an insertion product. The structure of this product was confirmed through spectroscopic analyses particularly by using a proton/deuterium (H/D) exchange experiments with ESI-Q-TOF-MS and -MS/MS measurement.     

Dimethylsulphide as a nitrene trap in the photolysis of some phosphinic azides

When PhRP(O)N₃ (R = Ph or t-Bu) is photolysed in dimethylsulphide substantial amounts (22 – 32%) of PhRP(O)N:SMe₂ and PhRP(O)NHCH₂SMe are produced and rearrangement is less important than in benzene.     

Water vapor sorption and diffusion in glassy polymers

By establishing relationships between polymer structure and gas permeation behavior, significant advances have been made in designing materials for membrane separation of gas mixtures. However, the situation is not so well understood when water vapor is one of the components since water molecules may interact with the polymer (plasticization) or each other (clustering) in ways that complicate the structure-property relationships. In addition, accurate measurement of water sorption, diffusion, and permeation is more complicated than for gases because of the unique hydrogen bonding capability of water, e.g., its tendency to strongly adsorb on high-energy surfaces and high heat of vaporization. A progress report on a broad program to understand water sorption and diffusion in glassy polymers that may be of interest for membrane applications is outlined; specific strategies include studies of structurally related polymers and miscible blends of hydrophobic/hydrophilic polymer pairs.     

The photolysis of water vapor at 1470 Å. H2 production in the primary process

The primary processes in the photolysis of water vapor at 1470 Å are due to H₂O + hν(λ = 1470 Å) → H₂ + O(¹D), H₂O + hν(λ = 1470 Å) → H + OH with the H₂ yield of the first process accounting for 23% of the overall H₂ production. The quantum yield of this process is estimated to be 0.08 by using O₂ as a scavenger for H-atoms. Secondary reactions involving the photolytic products and added O₂ are discussed.     

Chlorosulfonylisocyanate as a chlorinating agent

CSI rather than adding to the double bond in 1, chlorinates the aromatic ring.     

Water vapor nucleation on a crystal surface in a strong electric field

Water vapor nucleation at 260 K in a transverse electric field has been simulated by the Monte Carlo method under conditions corresponding to an internal wall of a spatially extended microcrack in a silver iodide crystal. The bicanonical statistical ensemble method has been employed to calculate, at the molecular level, the free energy of addition and the work of formation of dense phase nuclei in fields with different strengths. In a moderate field, the film mechanism of nucleation characterized by intense distortions on the film surface remains preserved. A domain structure of a film layer in contact with the surface exhibits a high stability with respect to an external field and remains preserved until the film is completely destroyed. In a strong electric field, the nucleation mechanism is fundamentally changed; i.e., the film is destroyed to yield threadlike structures. Therewith, the area of the contact with the surface drastically decreases. The orientation of nanothreads along the electric field lines overcomes a low free energy barrier. The point of equilibrium of nanothreads with vapor depends on the presence of hydrogen bonds, while their stability is determined by longer-range dipole-dipole interactions. The observed form of existence of the condensate as polarized nanothreads seems to be analogous to the superpolarized state previously revealed for water microdroplets, the transition to which has the character of the first-order phase transition.     

Silatrane as a reducing agent

Silatrane has been shown to have potential as a reducing agent for some organic compounds, including halides, carbonyl compounds, and azoxybenzene.     

Water vapor sorption and diffusion in sulfonated aromatic polyamides

In this contribution polyamides with different sulfonation degrees were directly synthesized from a combination of sulfonated and nonsulfonated diamines and isophthaloyl chloride. They were then used as dense membranes to study water sorption and mass transport properties. The polymers were characterized by their inherent viscosity and by spectroscopic methods, and the water vapor unsteady sorption phenomena were studied using a gravimetric technique. The effect of sulfonation substitution concentration in these polymers produces very interesting and original results in a number of properties such as the ionic exchange capacity, water equilibrium sorption and diffusivity. Obtained results are discussed and explained in the light of existing theories. Sorption behavior for polymers with a low sulfonation degree, up to 30%, can be explained with Langmuir equation. With larger substitution degree (40 and 60%) an additional mechanism must be assumed to explain sorption data. Assuming the presence of two phases helps to explain the observed diffusivity results. The mass transport mechanism is assumed to be Fickian. When water activity is low diffusivity systematically decreases as the degree of sulfonation increases. However, as water activity increases less sulfonated and nonsulfonated (PA0, PA20 and PA30) behave completely different from PA40 and PA60. The first group of polymers shows a tendency to decrease the rate of diffusion as water activity increases while the second group shows the opposite behavior, with a maximum in diffusivity at intermediate water activities. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2007–2014, 2007