Depression of melting point

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. 

The major difference between the two gluco-alkaloids and also between the two aglycones, lies in their melting-points and those of their derivatives. For convenience of comparison these are summarised in the following table, which includes mixed melting-points to illustrate the difficulty met with in this series, that a mixture of two distinct members of the group may not show depression of melting-point. 

Reaction of Ethylenediamine. Using 0.015 mole of diamine, 0.9 gram (61%) of bisacetylacetoneethylenediiminocopper(II) was obtained. Red platelets, m.p. 138-41° (dilute ethanol). There was no depression of melting point on admixture with authentic sample. Using 0.005 or 0.01 mole of amine, a mixture of blue and gray crystals was obtained, suggesting hydrolysis and, certainly, the absence of amine exchange. 

Advantage is taken of the depression of melting points of mixtures to prove whether two compounds having the same melting points are identical. If X and Y are identical, then a mixture of the two will have the same melting point but if X and Y are not identical, then a small amount of X in Y or of Y in X will cause the melting point to be lowered. 

Fine, glistening plates from ether, mp 212.8-216,8 gives no depression of melting point when mixed with cortisone. Very sparingly sol in water, ether. Sol in acetone, methanol, alcohol. Gives a carmine-red fluorescence reaction with coned. H2SOt. Reduces ammoniacal silver nitrate soln at room temp, uv max 242 nm (E 500). Oxidation with chromic acid in glacial acetic acid yields 4-androstene-3.17-dione. 

A new application for naphthalene with considerable growth potential is the production of alkylated naphthalenes, especially that of diisopropylnaphthalenes. Resulting from the mutual depression of melting-points, the mixture of diisopro-pylnaphthalene is liquid and can therefore be used as a high-value solvent for dyes in the production of carbonless copy papers. The solvents for dyes must meet certain preconditions, i. e. exhibit high solvent power, be free from odor, be toxico-... 

It is kix3wn that a melting point d ression results in a miscible blend. Paul and ccworkers32 34 recently reported such results for blends of polyvir lidene flixoride with various ca en-cemtaining polynners, such as polymethyl itethacrylate, polymethylacrylate, polyvinyl acetate, etc. Since in the present study novolac forms miscible blends with polyesterimide, similar depression of melting point of the blend was expected. On the contrary. 

In the equilibrium states of polymer crystals, the chain ends can be regarded as the crystalline defects in the infinitely large crystals formed by extended chains, which will apparently result in a depression of melting points with the increase of concentrations of chain ends, or in other words, with the decrease of chain lengths. 

Lateral substituents in core units have to be kept small in order to preserve liquid crystallinity and the most generally useful lateral substituent is fluoro. The special features of fluoro substitution, which separately or in combination may be useful, include the following (a) a small size which usually has only a small effect on nematic thermal stability (b) electron-attraction which may give compounds of negative dielectric anisotropy (c) the ability to diminish or destroy anti-parallel molecular association and increase positive dielectric anisotropies (d) a depression of melting point (e) a reduction in the prominence of ordered smectic phases, frequently, with the consequent relevation of a nematic phase and... 

Depression of Melting Point of Semicrystalline Polymer by the Addition of Low-Molecular-Weight Soluble Diluent... 

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