Quenching direct

The reactivity of the bromo and amino functions in 4-bromo-l//-3-bcnzazepin-2-amine (8) has been investigated thoroughly.15-41 Acetylation with acetic anhydride at room temperature proceeds normally to give A%icetyl-4-bromo-17/-3-benzazepin-2-amine (72% mp 171 — 173CC), whereas in refluxing acetic anhydride, the diacetyl derivative 9 is produced. In each instance, the acetylated products are isolated by removal of the excess acetic anhydride and crystallization of the residue from a suitable solvent. If, however, the acetylation mixtures are quenched directly with water then only ring-opened products are formed.15... 

Fig. 32 Morphology of dispersed TE-5070 quenched directly into water after being held in the melt at 350 °C for (a) 5 min, (b) 10 min, (c) 20 min and (d) 60 min...

Any real molecule can only be approximated as a two-level system, since each electronic state involved in the transition contains a number of vibrational and rotational levels. In the (probably unrealistic)limit where quenching directly back to the single lower level pumped by the laser is much faster than rotational or vibrational relaxation, a two-level system with the... 

The presence of interfaces within a polymer LED can also introduce additional nonradiative decay channels. This is particularly important in proximity to a metal electrode. Excitons which are able to diffuse to the metal surface are liable to be quenched directly by interaction with the metal wave function. This mechanism is therefore active only within a few nanometers of the interface. At larger distances (up to about 100 nm), excited molecules can couple to the surface plasmon excitations in the metal, thus providing a further nonradiative decay channel. The combined effects of changes in the radiative and nonradiative rates in two-layer LED structures have been modelled by Becker et al.,83 who have been able to model the variation in EL efficiency with layer thickness due to changes in the efficiency of exciton decay. 

In general, however, one must be concerned with the possible dominance of chemistry by small amounts of dianions. Although not seen in electrochemistry, the naphthalene dianion has been reported in the literature ll l5°-159 167) and could dictate the results of quench reactions. In the specific case of sodium naphthalene in tetrahydro-furan, kinetic analysis of a water quench directly implicites the radical anion as the chemically dominant species 150 -158-167>. In the case of the larger aromatic molecule, perylene, however, the dianion and not the radical anion is the species quenched167a). 

With anions such as ester enolate anions, reaction occurs within minutes at -78 °C and the intermediate cyclohexadienyl complex can be observed spectroscopically [103]. The intermediates are exceedingly air sensitive and are generally quenched directly, without purification. In one case, from the addition of 2-lithio-l,3-dithiane, the adduct has been crystallized and fully characterized by X-ray diffraction analysis [103]. Oxidation with excess iodine (at least 2.5 mol-... 

Fig. 197. Rate of change of optical rotation with temperature of the gels mentioned in Fig. 196 (O) quenched directly to 5 °C ( ) quenched to 5 °C after holding for 24 h at 20 °C also shown are the results of a sample that was quenched to 20 °C only (A). Reproduced from Gums and Stabilisers for the Food Industry, Vol 4 [Ref. 478] by the courtesy of the authors and of Oxford University Press...

Densitometry is the instrumental measurement of visible or UV absorbance, fluorescence, or fluorescence quenching directly on the thin layer. Measurements are made either through the plate (transmission), by reflection from the plate, or by reflection and transmission simultaneously, and either single-beam, doublebeam, or single-beam-dual wavelength operation of scanning instruments has been used. 

Chromatographic agents, solvents, and samples can frequently reduce the luminous output produced by interactions between the radioactive sample and the fluor of the scintillation fluid. This effect, known as quenching, directly reduces the counting efficiency of the system and can result in significant quantitation errors if not taken into account. In addition to quenching, other interfering processes such as chemiluminescence, phosphorescence, and efficiency losses due to self-adsorption of labeled compounds on the TLC adsorbent can affect quantitative measurement (5,49,50,51). 

Previous works [98] have also revealed that (i) the nature of the precursors or (ii) the annealing kinetic parameters play a significant role for the stabilization of the metastable phase. Indeed, for chloride-based precursors, the pyrochlore structure is directly obtained. This is explained by the high affinity of Q anions relative to Ln ", which prevents the formation of the complex with 2,4-pentane-dione and thus the formation of a homogeneous gel. In addition, for the kinetic aspect, the layered perovskite phase is favored for rapid annealing or quenching directly at 950 °C. 

Direct Quench. Direct quench systems inject water or cool recycle gas into the hot raw gas leaving the gasifier. Essentially all moving-bed gasifiers use a total water quench to remove tars and oils from the raw gas before heat recovery. However, fluidized-bed and entrained-flow gasification processes often use partial gas or water quenches as well. 

In the first attempt, the full water quench directly downstream of the reaction chamber was designed as an internally wetted dip tube leading the raw gas through a water bath. Because the stability of the water film on the inner surface of the tube was disturbed due to temperature, pressure, or throughput fluctuations, slag deposition and corrosion occurred frequently (Franke, P. (2011) Shift... 

Consider the first dashed line A in Figure 14.4. The austenite is rapidly quenched directly into the martensitic region and is 100% converted to martensite. 

---