Melting during decompositions

When heated, mercuric amido-chloride decomposes with loss of ammonia and nitrogen, leaving a residue of mercuric cliloride. It does not melt during decomposition, and if boiled with aqueous sodium hydroxide all the nitrogen is eliminated as ammonia. Water hydrolyses it, giving ammonium chloride and oxydimereuriamido-chloride thus ... 

The theory of solid state reaction kinetics includes no consideration of surface properties other than the recognition that crystal faces are the most probable location for nucleation in many reactions. Dehydration studies have provided evidence that, in many such processes, all surfaces are modified soon after the onset of chemical change [20,21], This is ascribed to a surface reaction that is limited in extent and can continue only at local sites of special reactivity where the recrystallization required for nucleation is possible. In other decompositions there is evidence that the modified reactivity associated with surfaces may influence the overall reaction [11] and may also preserve the identity of crystals. This, incidentally, masks the occurrence of melting during decomposition [22],... 

Sodium Levothyroxine. As one of the active principles of the thyroid gland, sodium levothyroxine [55-03-8] (levothyroxine sodium) can be obtained either from the thyroid glands of domesticated animals (10) or synthetically. It should contain 61.6—65.5% iodine, corresponding to 100 3% of the pure salt calculated on an anhydrous basis. Its chiral purity must also be ascertained because partial racemi2ation may occur during synthesis and because dl-T is available commercially. Sodium levothyroxine melts with decomposition at ca 235°C. It is prepared as pentahydrate [6106-07-6] from... 

The slow development of these materials is generally ascribed to the slow amidation reactions, the inability of many of the polymers to melt without decomposition and the tendency to colour during polymerisation. 

The decomposition temperature is somewhat influenced by the rate of heating. The material does not form a clear melt during the decomposition,... 

The alkali chlorates melt before decomposition [844], The catalytic properties of Co304 in promoting [865] the solid phase decomposition of NaC103 are attributed to the ability of the oxide to donate an electron to an oxygen atom, temporarily accepted at its surface from a CIO ion, prior to molecular oxygen formation and desorption. The progressive increase in E during reaction (from 120 to 200 kJ mole-1) is associated with systematic deactivation of the surface. 

Many of these salts melt or sublime before or during decomposition and reaction temperatures generally increase with molar mass. Thermal analyses for a selection of ammonium carboxylates have been given by Erdey et al. [915] who conclude that the base strength of the anion increases with temperature until it reaches that of NH3. Decompositions of ammonium acetate (>333 K) and ammonium oxalate (>473 K) proceed through amide formation. Ammonium benzoate and ammonium salicylate sublime (>373 K) without decomposition but ammonium citrate decomposes (>423 K) to yield some residual carbon. 

The same decomposition path was observed for KBH by Stasinevich and Egorenko [178] except that the melting and decomposition temperatures were much higher (by about 100°C). We performed ball milling for 5 h on the as-received NaBH but without any effect on its decomposition behavior. This is most likely due to the fact that NaBH exhibits a high structural stability during... 

DSC experiments were conducted up to 500 and 600°C for the ball-milled mixtures of NaBH with 12, 55, 73 and 92 wt%Mg (DSC traces not shown here). The temperatures of melting and decomposition peaks of NaBH are plotted in Fig. 3.46a. It is seen that the data points for the equivalent content of 12, 55 and 73 wt%Mg follow quite closely the data points for MgH. Only data points for the equivalent content of 92 wt%Mg show slightly higher decomposition temperature than their MgH counterpart and lie slightly above the ROM line for MgH. This behavior is probably related to different mechanical properties of Mg and MgH which results in different abilities to particle and grain size reduction during the milling process as can be seen in Fig. 3.47. The particle size reduction of ductile... 

The Mg particles melt at the burning surface and are partially oxidized by the fluorine produced by thermal decomposition of the Tf particles. Meanwhile, the Tf particles decompose completely to produce fluorine and other gaseous fragments. During decomposition of the Tf particles, some of the Mg particles melt and form agglomerates on and above the burning surface, while others are ejected into the gas phase whereupon they are rapidly oxidized by the fluorine. The oxidation of each Mg particle occurs at the molten layer on its surface. 

It is amazingly stable. Apparently, S12 exists in liquid sulfur, because it can be found in quenched melts (91), and it is formed in solutions of Sfl in toluene during decomposition under the influence of light (92). The vapor is, however, unstable thus, mass spectroscopic identiflcation proves to be difficult (12). The molecules have 2/m-C2ft symmetry in the crystal, but are close to Sm-Dg. Table II shows that the bond properties lie between those of Sg and Sg ... 

The spread of the explosion from the decomposed surface layer however depends on thermal factors, i.e. the heat liberated by the reaction is greater than that lost by self heating, conduction etc. The heat liberated during decomposition is sufficient to melt the surface of the azide and give rise to a reaction that will be self-supporting in the thermal sense. 

Cyanic acid, HOCN (boiling point (bp), 23.3°C melting point (mp), -86°C), is a dangerously explosive liquid with an acrid odor. The acid forms cyanate salts, such as NaOCN and KOCN. During decomposition from heat or contact with strong acid, cyanic acid evolves very toxic fumes. 

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