Melting point mixtures

A mixture of 4.98 g of acetoacetic acid N-benzyl-N-methylaminoethyl ester, 2.3 g of aminocrotonic acid methyl ester, and 3 g of m-nitrobenzaldehyde was stirred for 6 hours at 100°C in an oil bath. The reaction mixture was subjected to a silica gel column chromatography (diameter 4 cm and height 25 cm) and then eluted with a 20 1 mixture of chloroform and acetone. The effluent containing the subject product was concentrated and checked by thin layer chromatography. The powdery product thus obtained was dissolved in acetone and after adjusting the solution with an ethanol solution saturated with hydrogen chloride to pH 1 -2, the solution was concentrated to provide 2 g of 2,6-dimethyl-4-(3 -nitrophenyl)-1,4-dihydropyridlne-3,5-dicarboxylic acid 3-methylester-5- -(N-benzyl-N-methylamino)ethyl ester hydrochloride. The product thus obtained was then crystallized from an acetone mixture, melting point 136°Cto 140°C (decomposed). 

The next 1 liter of eluent yielded no alkaloids, but the following 1 liter yielded the second alkaloid (1.78 g), which was crystallized from alcohol-hexane to yield 0.855 g of needles, mp 119-120°. This was identified as (+)-glauclne by direct comparison (melting point, mixture melting point, TLC, IR, and circular dichroism) with an authentic reference sample of (+)-glaucine. (+)-Glaucine was reported previously to be the major alkaloidal constituent of the heartwood (8). 

Llrlodenine from Fractions 33-40 - Crystallization of the residue of these fractions (118 mg) from chloroform yielded 85 mg of yellow needles, mp 280-281°. The melting point, IR, and UV data were consistent with that reported for the yellow alkaloid, llrlodenine, previously reported from the heartwood (9). Direct comparison (melting point, mixture melting point, IR, and UV) with an authentic sample of llrlodenine confirmed the identity. Antimicrobial assay showed llrlodenine to be the active component present in these fractions (Table II). 

In a second Walden cycle, germane S -3 was converted to the chloro derivative R-13, which was reduced by LiAlPLt to the enantiomeric germane R-32. The configuration of the chloride J -13 was assigned by mixture melting point with the known R sila analogue and from consideration of Brewster s rales. Thus, chlorination must proceed with retention and hydride reduction with inversion of configuration. 

Actually, taking a mixture melting point, the melting point of a mixture, is more correct. But I have seen this expressed both ways. 

Another dimer was isolated from both sugar maple and Norway spruce and obtained in pure form by chromatography on a nylon powder column. The individual melting points and mixture melting point of the substance obtained from the two woods were 77°-78°C. The compound acetylated... 

Testing the component and mixture melting points was done by the ASTM-D-127 method. Vaseline penetration testing was done by ASTM-D-937, and that of ozocerite, paraffin and the mixture by ASTM-D-1321 method. Calculations by Eq. (3.29) offered these values of regression coefficients ... 

Physical chemistry. Identity and physico-chemical properties of the substance. This includes the structural formula of the chemical or the components of a mixture, melting point, boiling point, water and fat solubility, vapour pressure, partition coefficient and data on flammability and explosion characteristics. This involves a great deal of detailed analytical work all of which must be carried out to the highest standard, for instance using Good Laboratory Practice (GLP) in a quality assured laboratory. 

It forms an eutectic mixture (melting point 100 °C =212°F) when mixed with an equal amount of ammonium nitrate. 

Amino-4-r-butylphenol and 2-amino-4-chlorophenol behaved similarly under identical conditions. A solid product was obtained in each case which melted at 205.5-207 C (4) and 206-207 C (5), respectively. A mixture melting point determination of a mixture of the two materials melted over a range (179-186 C) to confirm the individual identities. Spectral data for both products are in the Experimental. 

This alkaloid, C17H21NO4, has been isolated from several Nareissv hybrids (90a). It crystallized from acetone as prisms, m.p. 253-254 dec., and from methanol in the same crystalline form, m.p. 221 . It contains the same functional groups as methylpseudolycorine, and a mixture melting point of the lower melting polymorph with methyl-pseudolycorine was not depressed. However, the infrared spectra of Base M and methylpseudolycorine, although very similar, were not identical. The hydroperchlorates of Base M and methylpseudolycorine showed no correlation. From the similarities between the two alkaloids, it is possible that they either are identical and differ only in state of purity or are closely related. 

The initial RJRT PAH investigation involved eleven PAHs in the MSS from nonfiltered cigarettes (3240, 3244) [(see Table 1 in (3262)]. Naphthalene, anthracene, pyrene, fluoranthene, and B[fl]P, isolated in crystalline form, were characterized by UV absorption spectral data as well as by classical chemical means (mixture melting point, IR spectra, derivatization, and derivative properties). The other six PAHs were identified on the basis of agreement of their UV absorption spectra with those of authentic samples or with published UV data. 

In 1959 Katsui and his co-workers (69, 70) isolated a diterpenoid alkaloid, designated initially as base D and later as isodelphinine, from the mother liquors accumulated during the isolation of miyaconitine and miy-aconitinone from the roots of A. miyabei Nakai, a plant native to Hokkaido, Japan. On the basis of chemical studies, they reported that base D contains an N-methyl, a benzoxyl, an acetoxyl, a hydroxyl, and four methoxyl groups. On treatment with acetyl chloride, base D gave a monoacetate, mp 188-190°. The data indicated that base D has the same empirical formula and functional groups as delphinine (31), but differs from delphinine by the mixture-melting point (mmp) and infrared spectra. On the basis of an infrared analysis and chemical studies, Katsui postulated that isodelphinine is a C-14 epimer of delphinine. 

This alkaloid (mp 162° [ajp —72° in EtOH) was isolated in low yield from an unidentified Hippeastrum species. A mixture melting point with 2-0-methyllycorine (I R = H, Ri = CH3) obtained by partial synthesis was not depressed 31). 

Finding a crystallization solvent Mixture melting point Critical thinking application... 

In Experiment 3D of this experiment, you will determine the identity of an unknown using the melting point technique. The mixture melting point technique is introduced in this part. 

A rigid and final test for identifying an unknown can be made if an "authentic" sample of the compound is available for comparison. One can compare infrared and NMR spectra of the unknown compound with the spectra of the known compound. If the spectra match, peak for peak, then the identity is probably certain. Other physical and chemical properties can also be compared. If the compound is a solid, a convenient test is the mixture melting point (see Technique 9, Section 9.4). Thin-layer or gas-chromatographic comparisons may also be useful. For thin-layer analysis, however, it may be necessary to experiment with several different development solvents to reach a satisfactory conclusion about the identity of the substance in question. 

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