Phase transition azides

The variations of dielectric constant and of the tangent of the dielectric-loss angle with time provide information on the mobility and concentration of charge carriers, the dissociation of defect clusters, the occurrence of phase transitions and the formation of solid solutions. Techniques and the interpretation of results for sodium azide are described by Ellis and Hall [372]. 

Ammonium azide is a colorless, crystalline substance. Some of its properties are given in Table 19. No phase transitions are found between 90 and 348 K. Sublimation of ammonium azide begins at 406 K, recondensation of the vapors at 418 K. Ammonium azide vapors decompose, similar to other ammonium salts, to ammonia and HN3 at 418 K (A// = -1-67.7 kJmol ). In the solid state, all ammonium ions are tetrahedrally connected to azide ions via hydrogen bonds with an NH -N distance of 297.5(4) and 296.7(3) pm. ... 

Temperature and pressure effects on azides have been studied with the emphasis being on the alkali-metal salts of relatively simple structure. Phase transitions have been observed, but studies of the dynamics of the transitions have only recently been started via Raman scattering experiments. These aspects are reviewed below. 

The ESR spectrum of Mn in sodium azide [28] shows a remarkable similarity to that of Mn in sodium chloride. In both cases the divalent manganese ion is located substitutionally at a monovalent sodium ion site, and the extra positive charge is compensated by a cation vacancy. The same mobility and coagulation effects are seen for both materials, and multiple sets of Mn —cation vacancy complexes are also observed. Vacancy hopping, which produces lifetime broadening of the resonance lines, is observed in NaNa (as well as in potassium and rubidium azides). As mentioned earlier. Miller and King [13] used the ESR spectrum of Mn " to observe the phase transition at 19°C. 

Hou D, Zhang E, Ji C et al (2011) Series of phase transitions in cesium azide under high pressure studied by in situ X-ray diffraction. Phys Rev B 84 064127... 

Winnik and coworkers [11] utilized an azide functional RAFT agent to synthesize azide functional linear PNIPAM followed by a thiol-ene Michael addition reaction with propargyl acrylate, producing a-alkyne-ou-azide PNIPAM. Consequently, the cyclization reaction by CuAAC was achieved in water with CUSO4 and ascorbic acid as the catalyst (Scheme 33). Further, the solution properties showed that the cyclic PNIPAM had higher phase transition temperature due to the endless chain structure of the cycUc compared to the linear counterpart with the same molecular weight. 

Fig. 3 presents differential scanning experiments on isolated micro-somes, and azide-inhibited, cultured cells from tomatoes. The temperature induced transitions for membranes are sharper than those for cells. The thermal transitions observed in cells and membranes probably represent lipid phase transitions. The transition temperatures agree quite well with the break in the Arrhenius plot of Fig. 2B. 

The nucleophilic attack of azide on 76b was also modeled at the pBP/DN //HF/ 6-31G level (Table 10, Fig. 23).44 In the gas phase the transition state is preceded by an ion-molecule complex (Fig. 23a) which is at a minimum on the reaction coordinate and in which the azide anion is 3.7 A from the amide nitrogen, and approaching the axis of the formyloxy-nitrogen (Nl-09) bond but in which the azide possesses all the anionic charge. 

The addition of carbenes and carbenoids to imines and nitriles continues to be a popular approach to aziridines and 2//-azirines. These processes have been well reviewed by Deyrup (B-83MI101-01). Dichlorocarbene and other dihalocarbenes have been added to a wide variety of imines to provide dihaloaziridines. A recent example is shown in Equation (64), illustrating the use of phase-transfer conditions <93H(36)69i). The treatment of azides with excess dichlorocarbene results in the formation of the 2,2,3,3-tetrachloroaziridines (92TL2339). Presumably, the azide is converted by dichlorocarbene to the imidoyl dihalide RN=CC12 which reacts further with dichlorocarbene. Transition metal-promoted reaction of a-diazoesters with imines provides 2-(alkoxycarbonyl)aziridines [Pg.46]

In sodium azide a transition occurs at 19 °C (9) and also on application of 1 kbar pressure 37a), in which the rhombohedral lattice transforms by a shearing motion of the azide ion layers to form a monoclinic unit ceU (9). The latter is isostructural with the unit cell of lithium azide shown in Fig. 2 b. Among the tetragonal rubidium, cesium and thallous azides a high temperature transformation in the range 151 °C to 315 °C to a cubic structure takes place (77), while at —40 °C a transition to an orthorhombic structure has been recently established for thallous azide 38). In the range 4 to 6 kbar, Pistorius 39) has observed pressure induced polymorphs of rubidium, cesium and thallous azides which are expected to be isostructural with the low temperature phase in thallous azide. 

Later workers accepted Porter s assignment without reservation [88], The gas phase spectrum was reproduced by Berry using phenyl azide as the precursor [25]. Laser-induced fluorescence attributed to triplet phenyl nitrene was observed upon pumping the 368 nm transition in ordinary gas phase experiments and in supersonic jet expansions where very highly resolved spectra could be generated [89a]. 

Simmons-Smith cyclopropanation, 456 Simmons-Smith reaction, 455 six-centered transition state, 264 Smiles-type rearrangement, 7 SOCI2, 19, 159 sodium azide, 365, 375 sodium borohydride, 416 sodium hexamethyldisilazide, 290 sodium hydride, 372, 375. 383 sodium in liquid ammonia, 440 sodium iodide, 379 sodium phenylselenide, 458 sodium trifluoroethoxide, 447 solid phase synthesis, 25 Sonogashira conditions, 409 Sonogashira coupling, 411 spartadienedione, 144 spontaneous csdodimerization, 23 S-shaped and C-shaped diastereomers, 83 stainless steel reactor, 283... 

They represent transitions occurring with increasing pressure. The high-pressure phases in NaNa and IJN3 are probably equivalent to their low temperature phases. Low-temperature phases in RbNa and CsNa have not been observed. The tetragonal-to-cubic transitions in Rb, Cs, and T1 azides were found to have transition temperatures which decrease linearly with increasing cationic radius [92] (Figure 18). This implies that the transition is primarily dictated by geo-... 

Recently, wave functions for an F center in sodium azide have been calculated using the point-ion model, and the electronic structure of the center has been elucidated [19]. In the monochnic phase the point symmetry at the anion site is C2h- There are two allowed transitions of the F center in this symmetry (corresponding to to A and A" to B transition). The calculation predicts that the bands due to these transitions should occur in the area of 730 nm and that the two bands would be very close, perhaps experimentally unresolvable. The calculation also predicts an absorption in the near-infrared due to the A" to B" transition. The energy levels of the F center in C2h symmetry of NaNa are depicted in Figure 6. 

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