Atmospheric samples, heterogeneous reactions

Surface Chemical Analysis. Electron spectroscopy of chemical analysis (ESCA) has been the most useful technique for the identification of chemical compounds present on the surface of a composite sample of atmospheric particles. The most prominent examples Include the determination of the surface chemical states of S and N in aerosols, and the investigation of the catalytic role of soot in heterogeneous reactions involving gaseous SO2, NO, or NH3 (15, 39-41). It is apparent from these and other studies that most aerosol sulfur is in the form of sulfate, while most nitrogen is present as the ammonium ion. A substantial quantity of amine nitrogen also has been observed using ESCA (15, 39, 41). 

The mass of a solid sample heated to a chosen temperature in a specific gaseous atmosphere is continuously measured via an electronic gravimetric device. This method is suitable for all heterogeneous reactions involving a solid and producing a variation in the number of gaseous moles. 

A 25-mL round-bottom flask was charged with l-[Val-Thr(Bzl)-Val-Thr(Bzl)-DMEDA]2 (180 mg, 102 pmol) dissolved in MeOH (2 mL) and formic acid (approx. 3 mL). The flask was flushed with N2 and 10% Pd/C (102 mg) was added. The N2 atmosphere was then replaced with an atmosphere of H2. The reaction was monitored by C18 RP-HPLC. After 4-5 h, the MeOH was removed under reduced pressure and the thick, heterogeneous soln was diluted with H20 (10 mL). The pH of the soln was adjusted to approx. 7 and the catalyst filtered using a 0.22-pm acetate membrane. The soln was analyzed by analytical C18 RP-HPLC and purified using semi-preparative C18 RP-HPLC. The MeCN in the column fractions was removed under reduced pressure and the sample lyophilized to afford the side-chain deprotected peptidomimetic 3 yield 58 mg (45%) ESI-MS rn/z- [M+H]+ calcd. 1253.5 found 1254.0. 

FIGURE 2.32 The DSC thermograms under nitrogen atmosphere (50 mL/min), sample mass 3 mg at 5 °C/min for chitin/chitosan samples obtained at different reaction times of thermochemical heterogeneous deacetylation. 

The first step in developing accurate IPCs is to obtain a representative sample of the reaction, one that accurately reflects the extent of reaction and the profile of impurities in the reactor at the time the sample was withdrawn. Two sets of parameters must be considered whether the reaction is homogeneous or heterogeneous, and the temperature of the reaction relative to the temperature of the sample preparation. All samples must be taken safely, with precautions where appropriate to protect operators and to exclude atmospheric moisture and 02 from both the reactor and the sample. 

The complexes were heterogenized from their aqueous and methanol solutions in the atmosphere of Ar, as described in [2]. The experiments were performed in a reaction vessel with a magnetic stirrer, equipped by a water jacket, reflux condenser, and sampling device [1]. We loaded 0.05 - 0.1 g of the catalyst (4.95 X 10- g-atom of Ru) and 0.025 g of NaBH4 into the reaction vessel, filled the system with Ar (or air), added 5 ml of propanol-2, stirred the reaction mixture at 82.5° for some definite time period to activate the catalyst, and then added p-BT (9.9 x 10- - 4.95 x 10- mole). The composition of the catalyzate was analyzed by gas-liquid chromatography. The activity of the catalysts was characterized by the initial specific rate of toluene formation (W, ... 

One additional ethyl acrylate copolymer (PEA-4VP) sample containing 21 mol% 4-vinyl pyridine (480 EW) was synthesized for the present study. The synthesis was performed in solution by free radical copolymerization. Ethyl acrylate (EA) and 4-vinyl pyridine (4-VP) monomers were purified by fractional distillation under reduced pressure and were subsequently stored under N2 atmosphere at -10prior to use. 216g of EA, 19g of 4-VP, 1.2g of benzoyl peroxide (BZ2O2) and 350g of benzene were used in the reaction. The polymerization was performed at 56 C for 6-1/2 hours and the conversion was kept low so that heterogeneity in the material was less than... 

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