Salicylic acid tests

Reactions of Aspirin, (i) Distinction from Salicylic acid. Shake up with water in two clean test-tubes a few crystals of a) salicylic acid, (0) aspirin, a very dilute aqueous solution of each substance being thus obtained. Note that the addition of i drop of ferric chloride solution to (a) gives an immediate purple coloration, due to the free —OH group, whereas (b) gives no coloration if the aspirin is pure. 

I. Methyl salicylate test. Heat i ml. of methanol with 0 5 g. of sodium sdicylate (or free salicylic acid) and a few drops of cone. H2SO4 gently for i minute. Cool, pour into a few ml. of cold water in a boiling-tube, and shake. Note the odour of methyl salicylate (oil of wintergreen). 

Salicylaldehyde gives a yellow coloration and forms salicylic acid very slowly. Cannizzaro s reaction is also given by formaldehyde but, owing to the difficulty in isolating the products, is not used as a test. 

Phthalein formation Fuse together carefully in a dry test-tube a few crystals of salicylic acid or of a salicylate with an equal quantity of phthalic anhydride rnoistened with 2 drops of cone. HjSO. Cool, dissolve in water and... 

This may be determined roughly by treating a small test portion with 3-4 ml. of hot water and acidifying with concentrated hydrochloric acid the absence of a precipitate in the warm solution indicates the essential completeness of the reaction. Salicylic acid is sparingly soluble and p-hydroxybenzoic acid is relatively soluble under these conditions. 

An additional useful test is to distil the acid or its sodium salt with soda lime. Heat 0.5 g. of the acid or its sodium salt with 0 2 g. of soda lime in an ignition tube to make certain that there is no explosion. Then grind together 0 5 g. of the acid with 3 g. of soda lime, place the mixture in a Pyrex test-tube and cover it with an equal bulk of soda hme. Fit a wide dehvery tube dipping into an empty test-tube. Clamp the tube near the mouth. Heat the soda lime first and then the mixture gradually to a dull-red heat. Examine the product this may consist of aromatic hydrocarbons or derivatives, e.g., phenol from salicylic acid, anisole firom anisic acid, toluene from toluic acid, etc. 

Another limitation to the studies in Table 1 is the small number of plant species tested. Primarily monocotyledonous plants have been studied, although McClure et al. (26) found ferulic acid inhibitory in soybean. The restriction of studies to monocots is probably because the mechanism of mineral absorption has been more fully elucidated with monocots. Harper and Balke (32) reported some minor differences in the inhibition of K+ absorption by salicylic acid among oats (Avena sativa L.), wheat (Triticum aestlvum L.), barley, and maize roots. 

Erdmann et al. (2000) report the fabrication of devices for the localized delivery of salicylic acid from the poly(anhydride-co-ester)s mentioned in Section II.C. A unique feature of this drug delivery system is that the drug compound is part of the polymer backbone. Devices were implanted intraorally and histopathology was reported (Erdmann et al., 2000). Chasin et al. (1990) review fabrication and testing of implantable formulations for other drugs including angiogenesis inhibitors for treatment of carcinomas and bethanechol for the treatment of Alzheimer s disease. 

In contrast to aspirin itself, the U.S.P. monograph for aspirin tablets has undergone considerable changes. For some reason, U.S.P. does not use the ferric salt test for free salicylic acid, as does the British Pharmacopeia of 1973. Apparently, certain excipients such as citric and tartaric acid interfere with this reaction.77 Already in 1913, a double titration method was developed78 which was made an official method in 1926.79 This method was used as the assay method when the aspirin tablets monograph was introduced into U.S.P. XII in 1942. 

Materials salicylic acid, methanol, distilled water, 10-mL graduated cylinder, Beral pipette, 250-mL beaker, concentrated sulfuric acid, top or bottom of a petri dish, cotton ball, small test tube, balance, weighing paper, hot plate, test-tube holder... 

Place 1.5 g of salicylic acid in a small test tube and add 3 mL of distilled water. Then add 3 mL of methanol and 3 drops of concentrated sulfuric acid to the test tube. CAUTION Sulfuric acid is corrosive. Handle with care. 

In a static-culture-flask screening test, naphthalene (5 and 10 mg/L) was statically incubated in the dark at 25 °C with yeast extract and settled domestic wastewater inoculum. After 7 d, 100% biodegradation with rapid adaptation was observed (Tabak et al, 1981). In freshwater sediments, naphthalene biodegraded to c/5-1,2-dihydroxy-1,2-dihydronaphthalene, 1-naphthol, salicylic acid, and catechol. 

Salicylic Acid Absorption. The apical 5 cm of the primary and two seminal roots from each of three plants were out into 1-cm segments to form an experimental unit (ca. 0.08 g). Incubation solution cc ijjtalned 0.5 mM KCl, 0.25 mM CaSOjj, 0.5 mM salicylic acid, 10 nCl/mL [ C]-sallcyllc acid, with 25 mM Tris and 25 mM Mes buffers mixed to obtain pH 6.5. Because the salicylic acid was dissolved in absolute ethanol, the final concentration of ethanol in the incubation solution was 1 (v/v). Root segments were transferred to test tubes containing 10 mL continuously aerated incubation solution. After the predetermined absorption time, segments were collected from the incubation solution by rapid filtration on Whatman No. 2 filter paper. 

The ability of an esterase or a -glucosidase to hydrolyze the in vitro generated metabolite was tested. An assay mixture that had been incubated for 22 h (ca. 50% conversion of salicylic acid) was incubated with either 10 units of hog-liver esterase (E.C. 3.1.1.1, Sigma Chemical Co.) at pH 8.0 or 20 units of -glucosidase (E.C. 3.2.1.21, Sigma) at pH 5.0 for 1 h at 37 °C. Salicylic acid and the metabolite were separated by thin layer chromatography with BAW and quantified by liquid scintillation chromatography. 

The application of a ruggedness test to the assay of Aspirin and its major degradation product, salicylic acid... 

The first case study we will consider is the assay of aspirin together with its major degradation product salicylic acid [19], This application study was selected as the HPLC assay of aspirin is well covered in the literature and we could select factors to test from the variety of HPLC conditions used in these published methods. This test was performed using a reflected saturated factorial design requiring a total of 15 experiments. 

Problem 19.26 Use simple test tube reactions to distinguish (a) p-cresol from p-xylene, (b) salicylic acid from aspirin (acetylsalicylic acid). ... 

Rarely are added benzoic or salicylic acids found in musts or wines although salicylic acid was widely used at the turn of the century. Sensitive color tests are available for their detection (3, 5, 6, 22, 74). 

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