Decomposition residue

Table I. Mass Spectrometric Analysis of Decomposition Residues...

Further hydrolysis proceeds much slower with very small heat evolution (for R = Et and Bun its value is zero within the accuracy of the experiment, while for R = Pr1 it does not exceed 20% of the overall reaction heat). Composition of the hydrolysis products for all h values approximately corresponds to Ti01s(0R) yR0H, where y = 0.15-1 depending on the nature of alcohol and concentration of alkoxide. Solvating alcohol in the hydrolysis products was confirmed by chemical analysis and IR spectroscopy of the products of their thermal decomposition. Residual carbon on thermal treatment in air is eliminated in two steps — at 300°C with formation of amorphous black powder and then in the process of crystallization at 400 to 500. A mixture of anatase and rutile is usually thus formed, calcination at higher temperature gives pure rutile. 

Recent work by Cole-Hamilton and coworkers has demonstrated that stability and volatility are enhanced by the use of long-chain fluorinated p-diketonate ligands, that is those derived from Hdfhd (6) and Htdfhd (7). The hydrafed bis(/3-diketonate) complexes M(dfhd)2(H20) and M(tdftid)2(H20) were prepared for Cu, Ca, Sr, and Ba and were all found to sublime below 200 °C with weight loss ranging from 85 to 98% (see Table 15). In addition, the anhydrous compound Ba(tdfiid)2 was reported to melt at 196 °C and volatilize at 220 °C with essentially no decomposition (residual mass by TGA ca. 1%). 

Pharmaceutical products can be contaminated by a variety of substances such as contaminants associated with microbes, previous products (both active pharmaceutical ingredients (API) and excipient residues), residues of cleaning agents, airborne materials, such as dust and particulate matter, lubricants and ancillary material, such as disinfectants, and decomposition residues from ... 

The dinitrogen complex (Cp2TiR)2N2 liberates Nj and RH (R = Ph, m- or p-MeCgH4, or CH2Ph) on thermal decomposition, the decomposition residue evolves... 

TGA experiments under flowing argon, done on all samples, show that after an initial loss of water a thermally resistant component exists with no appreciable volatility up to 350 C. The final decomposition residue is crystalline orthorhombic V2O5. 

The decomposition residue should be compatible with the polymeric material, that is, it should not exudate or cause discoloration. 

Sodium alkoxides, namely, sodium methoxide, sodium ethoxide, sodium n-propoxide, and sodium iso-propoxide were synthesized and characterized by various analytical techniques. Thermal decomposition of these sodium alkoxides was studied under isothermal and non-isothermal conditions by thermogravimetric (TG) method. Non-isothermal experiments were carried out at different linear heating rates. Mass spectrometric technique was followed for identifying the evolved gases. The onset temperatures of decomposition of sodium methoxide, sodium ethoxide, sodium n-propoxide, and sodium iso-propoxide were found to be 623, 573, 590, and 545 K, respectively. These sodium alkoxides form gaseous products of saturated and unsaturated hydrocarbons and leave a mixture of sodium carbonate, sodium hydroxide, and free carbon as the decomposition residue. Activation energy and pre-exponential factor for the decomposition reactions were deduced from the TG data by model-dependent and model-independent (iso-conversion) methods. The probable decomposition mechanism of sodiiun alkoxides is described in this chapter. 

Stock solutions were made by dissolving about 100 mg samples from the decomposition residues of sodium alkoxides in dilute hydrochloric acid and distilled water. Necessary dilutions were made by taking aliquot from these stock solutions and used for sodium analysis using AES as explained previously. 

Confirmation test for carbonate radical In order to confirm the presence of carbonate in the decomposition residue of sodium alkoxides, the residues were taken in a suitable air tight glass vessel connected to a gas bubbler containing lime water. Addition of dilute hydrochloric acid to the decomposition residues of sodium alkoxides produced brisk effervescence indicating that the residue might contain carbonate. The evolved gas turned clear limewater solution to milky white, confirming that the residue contained sodium carbonate. 

Estimation ofNafCO and NaOH contents by volumetric method Volumetric titration method was resorted to estimate the quantity of sodium carbonate and sodium hydroxide to account for oxygen and the results are given in Table 15.5. About 100 mg of decomposition residue of sodium alkoxides were dissolved in distilled water and... 

Decomposition residue Soluble content/wt.% Insoluble content/ wL% Sodium content/wt.% ... 

Infrared analysis The decomposition residue of sodium methoxide was mixed with spectroscopic grade KBr and the mixture was then pelletized. The IR spectrum of the sample thus prepared was recorded using a FTIR spectrometer in the range of4000-400 cm" at 4 cm resolution as explained previously. Similar procedure was followed for recording IR spectra for other sodium alkoxide decomposition residues and the insoluble portions of decomposition residue. In order to compare the spectral features of the residue, IR spectrum was recorded for GR grade sodium carbonate (purity 99.8%) from M/s Sarabai Chemicals, India. 

IR spectrum of the decomposition residues and the commercially available sodium carbonate are shown in Figure 15.18. The spectral features obtained for the residues around 1450 and 870 cm match exactly with the features of sodium carbonate with that reported in the literature [26]. This confirms that the residues contain sodium carbonate. The IR spectra of insoluble black particles did not show any spectral feature of C-C or C-H bonding. It is clear that the black particles were free of hydrocarbons. 

Figure 15.18 Comparison of IR spectrum of sodium carbonate and decomposition residues of sodium alkoxides.

PXRD patterns of the decomposition residues of these sodium alkoxides are shown in Figure 15.19. All the peaks identified were found to match well with that of sodium carbonate and sodium hydroxide pattern reported in JCPDS file [38, 39]. The XRD pattern of the water insoluble and HCl insoluble black particles exhibited only background counts except a broad hump at 20 °. This indicates that the insoluble residue is amorphous carbon. 

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