tivation due to accumulation of P on the catalyst. For example, accumulation and catalytic deactivation. 6947 P from decomposed PH3 diffuses in and out of Pt( 1 1 1) above 300 K and is very difficult to remove by oxidation, espeically at high coverages7 The key to these oxidative processes is the removal of P by PO, formation and desorption before atomic P forms.In a recent study by Smentkowski et al.1° catalytic decomposition of DMMP was observed on Mo(l10) above 898 K in a 2:l 0,-DMMP molecular beam without accumulation of P or C on the surface. The Mo(l10) surface formed a stable oxide layer that catalyzed DMMP decomposition but prevented accumulation and bulk diffusion of P. Our results for DMMP decomposition on a-Fe2039 show that it is active for DMMP decomposition but deactivates as phosphate forms.Unlike Mo, Pt does not readily form a stable bulk oxide. Thus, removal of P can occur only when gas-phase oxygen is present to drive the formation of PO,. In the absence of 02, these PO, species are stable only below 500 K. The dominant PO, species observed in this study is PO. In the absence of 0, it decomposes with an activation barrier of 35.9 kcal/mol, about 23 kcal/mol lower than its desorption barrier from Pt." Thus removal of PO in a catalytic process of Pt will require high temperature to overcome the desorption barrier and high pressures of 0, to maintain P-O bonds. Our results suggest that, in the absence of 02, DMMP decomposition on Pt( 11 1) above 600 K will lead to phosphorus Summary(1) At 100 K on Pt(l1 l), DMMP adsorbs molecularly through the oxygen lone pairs of the -p--O group. This structure is stable to 300 K.(2) TPD after a multilayer exposure of DMMP at 100 K gives multilayer desorption (220 K) and 0.09 ML of DMMP decomposition. The products are 0.27 M L of C O (437, 505, 586 K), 0.79 ML of H2 (340,448, 504 K), surface P, and a small amount of surface C.(3) TPSSIMS results indicate that, between 300 and 500 K, DMMP decomposes in steps to PO,. Near 300 K PO-C bonds cleave, with some P-OC bond cleavage at high-DMMP coverages. At higher temperatures, P-C bonds cleave, leaving at least two PO, species on the surface.(4) The dominant PO, species is PO, which is characterized by a 1255-cm-I u(P=O) loss in HREELS and an intense PO' SSIMS signal. It is stable to at least 500 K. Acknowledgment.Abstract: The effects of substituents at the 0-carbon atom on the donor properties of primary amines and amino alcohols have been studied. Such substituted amino species have important applications in industrially relevant gas-separation processes. Qualitative molecular orbital arguments, along with detailed calculations at the MNDO level of theory, show that upon methyl substitution at the a-carbon atom the interactions of the methyl group orbitals with the nitrogen lone-pair orbital lead to subtle but significant changes in the donor properties of the amino species. Infrared spectroscopic data supporting the calculations are also described. The implications of changes in the donor properties of the amino speci...
Tcrom Ester of tert-Butoxycarbonyl-L-tyrosylglycylglycyl-L-phenylalaninyl-L-methionine. The tripeptide prepared above (210 mg, 0.30 mmol) was dissolved in dioxane (2 mL) and anisóle (0.5 mL) which had been saturated with hydrogen chloride. After 20 min at 25 °C the solvent was evaporated, and the residue was triturated with ether to give the hydrochloride salt of H-Gly-L-Phe-L-Met-OTcrom as a white powder (159 mg, 83%). This was dissolved in 5 mL of freshly distilled DMF containing tert-butoxycarbonyl-L-tyrosylglycine (88 mg, 0.26 mmol). The solution was cooled to 0 °C and treated with hydroxybenzotriazole (40 mg), triethylamine (36 mL), and dicyclohexylcarbodiimide (65 mg). After 2 h at 0 °C and 15 h at 25 °C, water and ethyl acetate were added, the slurry was filtered, and the filtrate was evaporated, ultimately at 0.1 mm. The resulting residue was taken up in ethyl acetate, washed with water, 0.5 M citric acid, 5% sodium bicarbonate, and water, and then dried and evaporated. The resulting oil was dried by repeated evaporation of acetonitrile, and the residue was triturated with ethyl acetate to give a white powder (143 mg, 64%) which was homogeneous by TLC (CHC13-CH30H, 9:1): [a}\ -11.5°( c 1.7, CH30H-CHC13, 3:1, v/v).
The X-ray structures of 1,8-bis(trimethylgermyl)naphthalene (4) and 1,8-bis(trimethylstannyl)naphthalene (5) have been determined. The structures of 4 and 5 are critically compared with those of 1,3,6,8-tetra-zerz-butylnaphthalene (1) and 1,8-di-ZérZ-butylnaphthalene (2). It is found that familial traits are shared by all the 1,8-bis(trimethylelement)naphthalenes: in each case a twist of the C1-C9-C8 and C4-C10-C5 planes about the C9-C10 axis imparts near C3 symmetry to the molecule, and the trimethylelement groups in the peri positions are further deflected away from each other and out of the average molecular plane. In each case, the effects of internal strain, brought about by repulsion between the (CH3)3Z groups, are felt most strongly near the peri positions, and it is there that the greatest distortions are localized. In this family of compounds, the skeletal distortion decreases in the order 1 (2) » 4 > 5, i.e., in the inverse order of the covalent radius of Z. The conformations adopted by the (CH3)3Z groups in 4 and 5 are almost the same, but distinctively different from those in 1 (2). Empirical force field calculations yield structures in good agreement with those obtained by X-ray diffraction; these calculations also predict that the conformation of the as yet unknown 1,8-bis(trimethylsilyl)naphthalene (3) resembles 4 and 5 more closely than 1 (2) maps had no peaks greater than ±0.5 and ±1.0 e A-3 for 4 and 5, respectively. Stereoviews of the final structures are given in
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