Mixed melting-point

DETERMINATION OF MELTING POINT - MIXED MELTING POINTS... 

The structure of epimelibiose was established58 through periodate oxidation, and by comparison of its osazone with that of melibiose (melting point, mixed melting point, and x-ray diffraction pattern). 

Crystalline 2-desoxy-D-glucitol was obtained through a crystalline pyridine complex, in approximately 5 % yield, from a commercial product rich in sorbitol, manufactured by the electro-reduction of D-glucose at pH 7-10. It was identified by comparison of melting points, mixed... 

Using a procedure similar to that for cobalt, 2.38 g. of NiCl2 6H20 in 200 ml. of dimethylformamide gives Ni(hfa)2(dmf)2 in 50-75% yield after recrystallization. The melting point, mixed melting point, and infrared spectrum are identical to those of the product of Method A. Anal. Found C, 31.07 H, 2.45. 

The resolution of synthetic di-sparteine was achieved by Leonard and Beyler (278, 279) by means of i- and d-jS-camphorsulfonic acid, and both optically active forms of sparteine were obtained. The free bases were not isolated but each enantiomorph was identified through the formation of two known derivatives. The derivatives used to identify Lsparteine were the d-jS-camphorsulfonate and the dipicrate. The former salt was characterized by melting point, mixed melting point with an authentic sample, and specific rotation. The latter salt was characterized by melting point and mixed melting point with authentic I-sparteine dipicrate. d-Sparteine i- 3-camphorsulfonate had a specific rotation equal and opposite to its enantiomorphic Z-sparteine d-/3-camphorsulfonate. Characterization of d-sparteine was accomplished by conversion of the camphor-sulfonate salt to the dipicrate and monoperchlorate, both of which were... 

Identificatioii by Mixed Melting-points. It will be clear that melting-point determinations afford a ready method of identifying minute quantities of a solid compound, if the probable identity of this compound is already suspected. Thus if there is reason to believe that a particular substance is, for example. 

In addition to the use of a melting point determination as a criterion of purity, an equally valuable application is for the identification of oiganic compounds. If the melting point is known within one degree, the major proportion of possible substances is immediately eliminated from consideration. The study of the general chemical properties of the compound and a mixed melting point determination (Section 1,17) will largely establish the identity of the compound. 

The application of mixed melting point determinations to the identification of organic compounds has been described in Section 1,17. In order to gain experience the student should carry out the following simple experiment. 

Determine the melting point of pure cinnamic acid (133°) and pure urea (133°). Intimately mix approximately equal weights (ca. 01 g.) of the two finely-powdered compounds and determine the melting point a considerable depression of melting point will be observed. Obtain an unknown substance from the demonstrator and, by means of a mixed melting point determination, discover whether it is identical with urea or cinnamic acid. 

It is instructive for the student to construct a rough melting point diagram (compare Section 1,13 and Fig. 1,12, 1) for mixtures of cinnamic acid and urea. Weigh out 1 00 g. each of the two finely powdered components, and divide each into ten approximately equal portions on a sheet of clean, smooth paper. Mix 4 portions of cinnamic acid (A) with 1 portion of urea B) intimately with the aid of a spatula on a glass slide, and determine the melting point (the temperature at which the mixture just becomes completely fluid is noted). Repeat the procedure for 3 parts of A and 2 parts oiB 2 parts of A and 3 parts of B and 1 part of A and 4 parts of B. Tabulate your results as follows —... 

With some acids (e.g., succinic acid and sulplianilic acid) more satisfactory results are obtained by reversing the order of mixing, i.e., by adding the solution of the so um salt of the acid to the reagent. It should be pointed out that the melting points of the derivatives as determined on the electric hot plate (Fig. II, 11, 1) may differ by 2-3° from those obtained by the capillary tube method. In view of the proximity of the melting points of the derivatives of many acids, the mixed m.p. test (Section 1,17) should be applied. 

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