Melting point experimental determination

All melting points were determined on a Kofler micro-melting point apparatus and were uncorrected. Optical rotation were measured with WZZ polarimeter at room temperature. IR spectra were recorded with 5DX-FI spectrometer, and NMR spectra with Unity-400 spectrometer. The FAB- and EI-MS were determined on a VG-7070E spectrometer. Gas liquid chromatography (GLC) was run a Shimaz GC-6A unit equipped with a flame ionization detector (FLD). Experimental conditions for sugar TMS ether column, 5% SE-52 on chromosorb W, 3mmX2m column temp. 179°C injection temp. 200 C carrier gas(N )... 

An extensive series of studies for the prediction of aqueous solubility has been reported in the literature, as summarized by Lipinski et al. [15] and jorgensen and Duffy [16]. These methods can be categorized into three types 1 correlation of solubility with experimentally determined physicochemical properties such as melting point and molecular volume 2) estimation of solubility by group contribution methods and 3) correlation of solubility with descriptors derived from the molecular structure by computational methods. The third approach has been proven to be particularly successful for the prediction of solubility because it does not need experimental descriptors and can therefore be applied to collections of virtual compounds also. 

Full experimental details for the determination of melting and boiling points are given in Sections 11,10 and 11,11 respectively. The Tables II, 9, A and II, 9, B list suitable substances for the cabbration of thermometers by melting point or boiling point determinations respectively. Substances which are bracketed are alternative to each other. It need hardly be emphasised that only compounds of the highest purity should be employed. 

The student should read Sections 1,10 to 1,16 carefully before commencing any experimental work. A supply of melting point capillaries is prepared as described in Section 11,10 (compare Fig. 77, R , I). The apparatus illustrated in Fig. 77. 10, 2, a is assembled with concentrated sulphuric acid as the bath liquid the thermometer selected should have a small bulb. The melting points of pure samples of the following compounds are determined in the manner detailed in Section 11,10 —... 

Drop 1 g. of sodium into 10 ml. of ethyl alcohol in a small flask provided with a small water condenser heat the mixture until all the sodium has dissolved. Cool, and add 1 g. of the ester and 0-5 ml. of water. Frequently the sodium salt of the acid will be deposited either at once or after boiling for a few minutes. If this occurs, filter oflF the solid at once, wash it with a little absolute ethyl alcohol (or absolute methylated spirit), and convert it into the p-bromophenacyl ester, p-nitro-benzyl ester or S-benzyl-tso-thiuronium salt (for experimental details, see Section 111,85). If no solid separates, continue the boiling for 30-60 minutes, boil oflF the alcohol, allow to cool, render the product just neutral to phenolphthalein with dilute sulphuric or hydrochloric acid, convert the sodium salt present in solution into a crystalline derivative (Section 111,85), and determine its melting point. 

The normal boiling point of 2-methylthiazole is 17 0= 128.488 0.005°C. The purity of various thiazoles was determined cryometrically by Handley et al. (292), who measured the precise melting point of thiazole and its monomethyl derivatives. Meyer et al. (293, 294) extended this study and, from the experimental diagrams of crystallization (temperature/degree of crystallization), obtained the true temperatures of crystallization and molar enthalpies of fusion of ideally pure thiazoles (Table 1-43). 

If 31/1 is small and AF is a known function of temperature, Eq. (2.3) can be used to determine the melting point and surface free energy of a lamella from experimental data. For long chain molecules there are several difficulties in choosing the relevant form for AF, Therefore we first consider the limiting case... 

Logarithm of intrinsic solubility (mol L ) experimentally determined (pSOL) also logSexp Melting point Molecular weight... 

For crystalline compounds, they noted that an important factor to consider is the crystal lattice energy. From theoretical considerations and subsequent empirical studies, they discovered that melting point (mp) serves as an excellent proxy for this factor. While this is a significant advance in our understanding of water solubility, it falls short as a means to predict solubility from the chemical structure alone a compound must be made and a mp determined experimentally. 

However, for most studies, DTA has been mostly used in a qualitative sense as a means to determine the characteristic temperatures of thermally induced reactions. Owing to the experimental conditions used for its measurement, the technique is most useful for the characterization of materials that evolve corrosive gases during the heating process. The technique has been found to be highly useful as a means for compound identification based on the melting point considerations, and has been successfully used in the study of mixtures. 

There is a corresponding paucity of experimental determinations of the surface tension of solids, probably because no direct experimental method has been developed. A review of the work on the surface tension of solid metals has been given by Shaler 27). These values were obtained, in most cases, near the melting point of the metals and thermodynamic equilibrium was achieved. These experiments are thus quite different from those where the nonequilibrium state persists, with incomplete relief of surface stress. As this review is mainly concerned with high surface area adsorbents in a state of considerable surface stress in vacuo at least), the above results with metals will not concern us further. 

Stabilized by bulky organic cations such as EMI+ or BMI+ [BMI+ = butyl(methyl) imidazolium]. Nitrosomethanide-based ionic liquids are very hygroscopic and immediately absorb water when exposed to air. The experimentally determined melting points vary between —4°C and 35 °C (Figure 40, Table 11), with the BMI+ salts always possessing the lower melting point. ... 

In a nutshell, it may be concluded that DTA, DSC and TGA have been used mainly to determine the thermal properties of explosives like melting points, thermal stability, kinetics of thermal decomposition and temperatures of initiation and ignition etc. Further, the properties which can be calculated quantitatively from the experimentally obtained values are reaction rates, activation energies and heats of explosion. DTA data of some explosives are given [46] in Table 3.6. 

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