Laser Flash Photolysis Studies of Metal Carbonyls in Supercritical CO2 and Ethane

Abstract

The ring-closure reaction of M(C0)5L-L (M = W, Mo) where L-L denotes a bidentate ligand was chosen for its comparative independence of solvent properties to demonstrate the repulsive (or intrinsic) part of the activation volume. The ring-closure reaction rate constant was determined in supercritical CO;? and in supercritical ethane over the range between 1000 and 3500 psi at several temperatures (35, 42, 48, and 60 "C). The activation volume was observed to be as high as +7000 cm3/mol just above the critical point in each of these solvents. The ring-closure activation volume was also determined in liquid C02 and in several other liquid solvents for comparison. These studies demonstrate a huge repulsive contribution to the activation volume in these two supercritical fluids.

Probing the Scale of Local Density Augmentation in Supercritical Fluids: A Picosecond Rotational Reorientation Study

“…In supercritical fluids, the physicochemical properties of the fluid are a strong function of pressure and temperature, thus an increase in fluid pressure (or density) produces a concomitant increase in the fluid refractive index. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] If a single exponential decay law governs the radiative decay (see Figures 2 and 3) and the BTBP quantum yield is unity, 40 a simple plot of 1/τ vs n 2 can confirm Strickler-Berg behavior. Analysis of the Figure 3 data (results not shown) yields a straight line (r 2 ) 0.98) and confirms that the majority of the decrease in τ is simply due to the change in fluid refractive index.…”

“…Supercritical fluids, in contrast, are substantially more flexible and provide one with the means to actually tune the physicochemical properties simply by adjusting the fluid temperature and/or pressure. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] Thus, a supercritical fluid is generally considered a continuously tunable solvent.…”

“…26 Following from this exciting discovery, many researchers have used a myriad of approaches and techniques in an effort to understand these special intermolecular interactions and the scale of these solute-fluid clusters. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][27][28][29][30][31][32][33][34][35][36][37][38] Spectroscopy has proven an excellent tool to probe the solute-fluid clustering and to provide a more clear molecular-level view of solvation in supercritical fluids. [1][2][3][4][5][6]10,11,13,14,[27][28][29][30][31][32][33]35,36 Static optical methods (e.g., absorbance, fluorescence) and solvatochromic solutes have been used to characterize the local solute environment.…”

Kinetic study of the metalation reaction of 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin with water and methanol adducts of bis(1,1,1,5,5,5-hexafluoropentane-2,4-dionato)zinc(II) in supercritical carbon dioxide: specific cosolvent effect on the metalation

“…The solvent effect on chemical reactions in supercritical fluid is obviously different from that in liquid solvents. For example, the activation volumes in liquids are typically between −30 and 30 cm 3 mol −1 [8], but those in supercritical fluids can be thousands of cm 3 mol −1 negative or positive [9][10][11][12]. In order to study the potential influences of supercritical fluid solvents on chemical reactions, the simple unimolecular and bimolecular reactions are usually selected as the mechanistic probes [12].…”

Novos tensoativos não-iônicos para CO2-supercrítico: síntese e estudo de algumas propriedades

“…Resultados obtidos mostram que o volume molar parcial, ʋ 2 , se torna muito alto e negativo conforme nos aproximamos do ponto crítico do solvente (Debenedetti, 1987;Eckert et al, 1986;Fariss, 1969;Ji et al, 1995;Haynes, 1987;Peck;Mehta;Johnston, 1989;Simmons;Mason, 1972; Abboud;Taft, 1977;Kamlet et al, 1979), pireno (escala Py) Winnik, 1982Winnik, , 1984 …”