Benzoic acid, crystallization melting point

Melting point, subl > 100. Benzoic acid starts to sublime (go directly from a solid to a vapor) over 100 °C, before any crystals left melt at 122.4°C. 

A mixed melting point experiment involves mixing a little of the product with some pure compound. In carrying out a mixed melting point experiment for the benzoic acid obtained by the hydrolysis of ethyl benzoate, some crystals of the laboratory-synthesised benzoic add are mixed with pure benzoic acid. If the two compounds are Identical, then a melting point of the correct temperature range will be obtained. If the melting point is lower than expected, then it is likely that the product is either impure or Is not benzoic acid. 

IV.41 BENZOATES, C6H5COO" OR C7H502 Solubility Benzoic acid, C6H5COOH or H.C7H502, is a white crystalline solid it has a melting point of 121°. The acid is sparingly soluble in cold water, but more soluble in hot water, from which it crystallizes out on cooling it is soluble in alcohol and in ether. All the benzoates, with the exception of the silver and basic iron(III) salts, are readily soluble in cold water. 

Antifebrin.— Acetanilide is a common medicinal substance much used as a fever reducer under the name of antifebrin. It is a solid, crystallizing in glistening plates melting point 112°. It is slightly soluble in cold water, readily in hot water. Though not an ester it easily hydrolyzes reforming aniline and acetic acid. Other known anilides formed from aniline and formic acid, oxalic acid and benzoic... 

A) Melting Point of a Known Substance. In the preceding experiment one or two substances were purified by crystallization. The determination of the melting point of each batch of crystals is required as a criterion of its purity. In this way the student ob-taiis practice in melting-point determination. It is advisable to repeat the determination of the melting point of benzoic acid, or acetanilide, or naphthalene until the student is sure of the repro-ductibility of his results. 

Melting point not below 183° C.Add five drops of a solution of chromium trioxide (1 in 20) to 5 cc. of a solution of Cocaine Hydrochloride (1 in 50) a yellow precipitate is produced which redissolves on shaking the mixture. On the addition of 1 cc. of hydrochloric acid, a permanent, orange-colored, crystalline precipitate is formed. A solution of about 0.01 Gm. of Cocaine Hydrochloride in 1 cc. of distilled water yields on the addition of 2 cc. of tenth-normal potassium permanganate a violet, crystalline precipitate which appears brownish-violet when collected on a filter, and shows characteristic, crystalline aggregates under the low power of a microscope. Heat about 0.1 Gm. of powdered Cocaine Hydrochloride with 1 cc. of sulphuric acid for five minutes, then cautiously mix with 2 cc. of distilled water the aromatic odor of methyl benzoate is noticeable and on cooling crystals of benzoic acid separate. Silver... 

Crystallize your entire product from hot water in an Erlenmeyer flask using a hot plate as the heating source. Be sure to add the hot water in small portions to the crude product. Add the hot water until the solid just dissolves. Then allow the flask to cool slowly. After the flask cools to room temperature, place it in an ice bath to complete the crystallization. Collect the solid on a small Hirsch funnel and wash it with a small amount of cold water. Set the crystals aside to air-dry at room temperature until the next laboratory period before determining the melting point of the purified benzoic acid (literature value, 122°C). Also determine the recovered yield in grams. Submit the sample to the instructor in a properly labeled vial. 

Isolation and Drying Collect the crystals on a Buchner or Hirsch funnel by vacuum filtration (Fig. 2.54) and wash the filter cake with two small portions of co/d water. Press the crystals as dry as possible on the funnel with a clean cork or spatula. Spread the benzoic acid on a watchglass, protecting it from airborne contaminants with a piece of filter paper, and air-dry it at room temperature or in an oven. Be certain that the temperature of the oven is 20-30 "C below the melting point of the product ... 

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. 

Ephedrine occurs as white, rosette, needle, and crystals. It is soluble in water, alcohol, chloroform, ether, and in liquid petrolatum [12] and has a melting point of 187 °C-188 °C. It is marketed as ephedrine hydrochloride and may be found some traces of benzoic acid as a by-product of the process [42],... 

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