Melting point sublimation

MELTING POINT = sublimes at 300°C BOILING POINT = decomposes at 390°C DENSITY = 1.4 g/cm3 (calculated)... 

Physical properties of chemicals melting point, sublimation, and boiling point... 

The physical properties most commonly listed in handbooks of chemical data are color, crystal form (if a solid), refractive index (if a liquid), density (discussed in Experiment 3), solubility in various solvents (discussed in Experiment 17), melting point, sublimation characteristics, and boiling point. When a new compound is isolated or synthesized, these properties almost always accompany the report in the literature. 

Action of heat Salicylic acid, when gradually heated above its melting point, sublimes. If it is rapidly heated, it is decomposed into carbon dioxide and phenol. Salicylates char on heating and phenol is evolved. 

Before initiating the design of a formulation and method of preparation, additional physico-chemical properties of the active substance should be defined such as particle size and particle size distribution, salt, polymorphism, aqueous solubility in dependence on pH, hygroscopicity, melting point, sublimation behaviour, water of crystallisation, dehydration temperature. The properties of the raw material are also relevant to the physical and chemical stability and the compatibility with the excipients and packaging. Furthermore, compatibility with other active substances has to be investigated when the new substance is to be administered through the same infusion line. 

Melting point Sublimes without melting at 613C. 

Thiosahcyhc 2Lcid[147-93-3] (o-mercaptobenzoic acid), a sulfur-yeUow sohd that softens at 158°C, has a melting point of 164°C. It sublimes, is slightly soluble in hot water but freely soluble in glacial acetic acid and alcohol, and yields dithiosahcyhc acid [527-89-9] upon exposure to air. 

The acid occurs both as colorless triclinic prisms (a-form) and as monoclinic prisms ( 3-form) (8). The P-form is triboluminescent and is stable up to 137°C the a-form is stable above this temperature. Both forms dissolve in water, alcohol, diethyl ether, glacial acetic acid, anhydrous glycerol, acetone, and various aqueous mixtures of the last two solvents. Succinic acid sublimes with partial dehydration to the anhydride when heated near its melting point. 

Elemental arsenic normally exists in the a-crystaUine metallic form which is steel-gray in appearance and britde in nature, and in the P-form, a dark-gray amorphous soHd. Other aHotropic forms, ie, yellow, pale reddish-brown to dark brown, have been reported (1), but the evidence supporting some of these aHotropes is meager. MetaUic arsenic, heated under ordinary conditions, does not exhibit a discrete melting point but sublimes. Molten arsenic can be obtained by heating under pressure. 

Properties. Under nitrogen pressure hexagonal boron nitride melts at about 3000°C but sublimes at about 2500°C at atmospheric pressure. Despite the high melting point, the substance is mechanically weak because of the relatively easy sliding of the sheets of rings past one another (3). The theoretical density is 2.27 g/mL and the resistivity is about 10 H-cm. 

The melting point of indazole has been reported at various temperatures in the range of 145 to 149 °C. Indazole boils at 269-270 °C at 743 mmHg and 146 °C at 15 mmHg, can be readily sublimed on a water bath and is also steam-volatile. Its two A-methyl derivatives have similar melting points 1-methyl (106), m.p. 61 °C, 2-methyl (107), m.p. 56 °C, but they are easily separated by fractional distillation [(106), 120/15 (107), 141/15]. 

N-tert-Butyl urea [1118-12-3] M 116.2, m 182°, 185°(dec). Possible impurity is A,A -di-rcr/-butyl urea which is quite insol in H2O. Recrystd from hot H2O, filter off insol material, and cool to 0° to -5° with stirring. Dry in vac at room temp over KOH or H2SO4. If dried at higher temperatures it sublimes slowly. It can be recrystd from EtOH as long white needles or from 95% aq EtOH as plates. During melting point determination the bath temp has to be raised rapidly as the urea sublimes slowly above 100° at 760mm. [Org Synth Coll Vol III 151 1955.]... 

Chlorobenzaldehyde [J04-88-]] M 140.6, m 47 . Crystd from EtOH/water (3 1), then sublimed twice at 2mm pressure at a temperature slightly above the melting point. 

Methylaminoanthraquinone [82-38-2] M 237.3, m 166.5°, pK ,t-2. Crystd to constant melting point from butan-l-ol, then crystd from EtOH. It can be sublimed under vacuum. 

Melamine, a non-hygroscopic, white crystalline solid, melts with decomposition above 347°C and sublimes at temperatures below the melting point. It is only slightly soluble in water 100 ml of water dissolve 0.38 g at 20°C and 3.7 g at 90°C. It is weakly basic and forms well-defined salts with acids. 

This table shows that the similarity of the two aglycones is most marked in their salts, but they do not appear to be dimorphic forms giving identical salts, for the melting-points of the bases are unchanged after sublimation, the rotations of the two bases in solution are different, though those of the two hydrochlorides are identical within the limits of experimental error, and all attempts at interconversion of the two bases... 

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