Salicylic acid, melting point

The chief derivative of salicylic acid (melting point 159°C, boiling point 211°C, density 1.565), which is used as a drug, is the methyl acetyl ester, known as aspirin. 

Figure 20 shows the results of carrying out such measurements at different points marked in Figure 19. It is evident that the material examined at points 1 and 3 has a lower melting temperature than the other locations. Since benzoic acid melts at 122 °C and salicylic acid melts at 159 C, the results from such measurements are sufficient to identify the distribution of these materials within the image.

Other routes for hydroxybenzaldehydes are the electrolytic or catalytic reduction of hydroxybenzoic acids (65,66) and the electrolytic or catalytic oxidation of cresols (67,68). (see Salicylic acid and related compounds). Sahcylaldehyde is available in drums and bulk quantities. The normal specification is a freezing point minimum of 1.4°C. 4-Hydroxybenzaldehyde is available in fiber dmms, and has a normal specification requirement of a 114°C initial melting point. More refined analytical methods are used where the appHcation requires more stringent specifications. 

The existence of two polymorphs was reported for a NO-releasing derivative of acetyl-salicylic acid [28]. Selection crystallization of one form or the other was achieved from a number of solvent systems (14 solvents and 3 preparative methods), but several systems were identified that yielded mixtures of the two forms. The single-crystal structure of Form I was reported, but the habit of the Form II crystals precluded their characterization. The transition point of the two forms was calculated from intrinsic dissolution data to be higher than the melting points of both polymorphs and thus the two forms bear a monotropic relationship. 

SALICYLIC ACID AND RELATED COMPOUNDS. [CAS 69-72-7], Salicylic acid or C H4(OH)(COOH) is a white solid, melting points 159°C, sublimes at 76°C, insoluble in cold water, soluble in hot water, alcohol, or ether. With ferric chloride solution, salicylic acid solutions are colored violet (distinction from benzoic acid). 

Dilute nitric acid When a salicylate or the free acid is boiled with dilute nitric acid (2m) and the mixture poured into 4 times its volume of cold water, a crystalline precipitate of 5-nitrosalicylic acid is obtained. The precipitate is filtered off and recrystallized from boiling water the acid, after drying, has a melting point of 226°. 

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. 

To 50 mg of sublimed caffeine in a tared test tube add 38 mg of scilicyclic acid and 2.5 mL of dichloromethane. Heat the mixture to boiling and add petroleum ether (a poor solvent for the product) dropwise until the mixture just turns cloudy, indicating the solution is saturated. If too much petroleum ether is added then clarify it by adding a very small quantity of dichloromethane. Insulate the tube in order to allow it to cool slowly to room temperature, and then cool it in ice. The needle-like crystcils are isolated by removing the solvent while the reaction tube is in the ice bath. Evaporate the last traces of solvent under vacuum and determine the weight of the derivative and its melting point. Caffeine salicylate is reported to melt at 137°C. 

Test the solubility of your sample in toluene and in hot water and note the peculiar character of the aqueous solution when it is cooled and when it is then rubbed against the tube with a stirring rod. Note also that the substance dissolves in cold sodium bicarbonate solution and is precipitated by addition of an acid. Compare a tablet of commercial aspirin with your sample. Test the solubility of the tablet in water and in toluene and observe if it dissolves completely. Compare its behavior when heated in a melting point capillary with the behavior of your sample. If an impurity is found, it is probably some substance used as binder for the tablets. Is it organic or inorganic To interpret your results, consider the mechanism whereby salicylic acid is acetylated. 

Bile Acids, Sterols, and Steryl Esters Many of these compounds have high melting points, making them unsuitable for melt applications. Exceptions are the salicylic acid-cholic acid system formed by a melt-granulation technique reported by Froemming and Vetter.f The system provided a sustained release in acid media (pH 1-3.5). 

The addition of dilute mineral acids to moderately concentrated solution of salicylates produces a white crystalline precipitate of the salicylic acid which when washed with cold water and dried, has the melting point of salicylic acid (1). 

Decomposes when heated above melting point, 536°F/280°C, producing toxic fumes of arsenic, lead. Lead arsenates may be subject to redox reactions. Both arsenic and lead are known human carcinogens. PLUMBOUS ACETATE (6080-56-4) Pb(CjH302)2 3H,0 Contact with acids forms acetic acid. Incompatible with oxidizers, bases, acetic acid alkalis, alkylene oxides, ammonia, amines, bromates, carbonates, citrates, chlorides, chloral hydrate cresols, epichlorohydrin, hydrozoic acid, isocyanates, methyl isocyanoacetate, phenols, phosphates, salicylic acid sodium salicylate, sodium peroxyborate, potassium bromate resorcinol, salicylic acid, strong oxidizers, sulfates, sulfites, tannin, tartrates, tinctures trinitrobenzoic acid, urea nitrate. On small fires, use dry chemical, Halon, or CO2 extinguishers. 

CE is the equilibrium curve for the compound A,fiy— in the example under consideration x = and y = 1—with the submerged maximum at D. The point D is not realised in practice because the compound decomposes completely at E into sohd picric acid and liquid benzene. The point E is spoken of as the incongruent melting point of the compound (since the composition of the liquid is not the same as that of the original compound) or as the transition point. The ctuve EB represents the equilibrium between solid B and the liquid. This system is rarely encountered among compounds, but other examples are acetamide - salicylic acid and di-methylpyrone - acetic acid it is, however, comparatively common in alloy systems e.g., gold - antimony, AuSbj). 

Because aspirin will not give the color reaction with ferric chloride, the presence of salicylic acid in the final product is easily detected. The purity of your product will also be determined by obtaining the melting point. 

According to Kofler [358], microsublimation is any sublimation procedure in which the sublimate is caught on a smooth plate-usually a small slide-for purposes of microscopic examination (melting point, refraction, crystal structure). Many substances can be directly sublimed in crystalline form from drugs containing them, e. g., caffeine coumarin umbelliferone benzoic, ferulic, salicylic and cinnamic acids emodin etc. 

The portion of both oils which was soluble in alkali consisted of pure methyl salicylate. The acid separated therefrom had a melting-point of precisely 155 5 C., which is that of pure salicylic acid, and it did not contain a trace of benzoic acid. 

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