Acetals, identification

Diethyl Acetal. Identification of the Aldehydic and the Alcoholic Components... 

Aldehydes and ketones may frequently be identified by their semicarbazones, obtained by direct condensation with semicarbazide (or amino-urea), NH,NHCONH a compound which is a monacidic base and usually available as its monohydrochloride, NHjCONHNH, HCl. Semicarbazones are particularly useful for identification of con jounds (such as acetophenone) of which the oxime is too soluble to be readily isolated and the phenylhydrazone is unstable moreover, the high nitrogen content of semicarbazones enables very small quantities to be accurately analysed and so identified. The general conditions for the formation of semicarbazones are very similar to those for oximes and phenylhydrazones (pp. 93, 229) the free base must of course be liberated from its salts by the addition of sodium acetate. 

The above example serves to iUustrate the basis of the procedure employed for the characterisation of aUphatic esters, viz., hydrolysis to, and identification of, the parent acids and alcohols. Most esters are liquids a notable exception is dimethyl oxalate, m.p. 54°. Many have pleasant, often fruit-hke, odours. Many dry esters react with sodium, but less readily than do alcohols hydrogen is evolved particularly on warming, and a sohd sodio derivative may separate on coohng (e.j/., ethyl acetate yields ethyl sodioacetoacetate ethyl adipate gives ethyl sodio cj/cZopentanone carboxylate). 

The following give abnormal results when treated with chlorosulphonio acid alone, preferably at 50° for 30-60 minutes —fluobenzene (4 4 -difluorodiplienyl-sulphone, m.p. 98°) j iodobenzene (4 4 -di-iododiphenylsulplione, m.p. 202°) o-diclilorobenzene (3 4 3. -4 -tetrachlorodiphenylsulphone, m.p. 176°) and o-dibromobenzene (3 4 3 4 -tetrabromodiphenylsulphone, m.p. 176-177°). The resulting sulphones may be crystallised from glacial acetic acid, benzene or alcohol, and are satisfactory for identification of the original aryl halide. In some cases sulphones accompany the sulphonyl chloride they are readily separated from the final sulphonamide by their insolubility in cold 6N sodium hydroxide solution the sulphonamides dissolve readily and are reprecipitated by 6iV hydrochloric acid. 

Crystalline derivatives, suitable for identification and characterisation are dealt with in Section IV, 114, but the preparation of the following, largely liquid, derivatives will be described in the following Sections. When phenols are dissolved in aqueous sodium hydroxide solution and shaken with acetic anhydride, they undergo rapid and almost quantitative acetylation if the temperature is kept low throughout the reaction. This is because phenols form readily soluble sodium derivatives, which react with acetic anhydride before the latter undergoes appreciable hydrolysis, for example ... 

Norethindrone may be recrystakhed from ethyl acetate (111). It is soluble in acetone, chloroform, dioxane, ethanol, and pyridine slightly soluble in ether, and insoluble in water (112,113). Its crystal stmcture has been reported (114), and extensive analytical and spectral data have been compiled (115). Norethindrone acetate can be recrystakhed from methylene chloride/hexane (111). It is soluble in acetone, chloroform, dioxane, ethanol, and ether, and insoluble in water (112). Data for identification have been reported (113). The preparation of norethindrone (28) has been described (see Fig. 5). Norethindrone acetate (80) is prepared by the acylation of norethindrone. Norethindrone esters have been described ie, norethindrone, an appropriate acid, and trifiuoroacetic anhydride have been shown to provide a wide variety of norethindrone esters including the acetate (80) and enanthate (81) (116). 

Acetates. Because of the significant interest in selective acetylation reactions of sucrose, the need for a convenient and unambiguous method of identification has been recognized (34,35). The position of an acetyl group in a partially acetylated sucrose derivative can be ascertained by comparison of its H-nmr acetyl methyl proton resonances after per-deuterioacetylation with those of the assigned octaacetate spectmm. The synthesis of partially acetylated sucroses has generally been achieved either by way of selectively protected derivatives such as trityl ethers and cychc acetals or by direct selective acetylation and deacetylation reactions. 

Identification. When a solution of ferric chloride is added to a cold, saturated vanillin solution, a blue color appears that changes to brown upon warming to 20°C for a few minutes. On cooling, a white to off-white precipitate (dehydrodivanillin) of silky needles is formed. Vanillin can also be identified by the white to slightly yellow precipitate formed by the addition of lead acetate to a cold aqueous solution of vanillin. 

S. Eu, R. C. Medmd, and 1. Y. Chan, "The Identification and Characterization of Calcium Magnesium Acetate," in Abstracts, International Symposium on Calcium Magnesium Acetate, An Emerging Bulk Chemicalfor Environmental Applications, May 14—16, Northeastern University, Boston, Mass., 1991. 

At identification of cognacs and cognac alcohols on authenticity use the following characteristic attributes presence in them significant concentration of (15-150 mg/1) bytanol, the high level of acids - acetic, propionic and oil the high contents of polyphenolic bonds. 

Aconitine produces an intense tingling sensation when a drop of a solution, 1 in 10,000, is applied to the tip of the tongue. It also gives a characteristic unstable, crystalline precipitate when a few drops of potassium permanganate solution are added to a solution of the alkaloid in dilute acetic acid. The formation of acetic acid when the alkaloid is heated dry, or of benzoic acid when it is hydrolysed by alkali, have also been suggested as identification tests. For the recognition of minute quantities a biological test is probably the best procedure. ... 

Figure 10.9 Cliromatogi ams of foitified coconut oil obtained by using (a) normal-phase HPLC and (b) GPC/noimal-phase HPLC. Peak identification is as follows 1 (a,b), DL-a-toco-pheryl acetate, 2 (b), 2,6-di-tert-butyl-4-methylphenol 2 (a) and 3 (b), retinyl acetate 3 (a) and 4 (b), tocol 4 (a) and 5 (b), ergocalciferol. Reprinted from Analytical Chemistry, 60, J. M. Brown-Thomas et al., Determination of fat-soluble vitamins in oil matrices by multidimensional liigh-peiformance liquid cliromatography , pp. 1929-1933, copyright 1988, with permission from the American Chemical Society.

Nitroso-pinene may be prepared for identification purposes as follows To a solution of 12 grams of sodium in 30 c.c. of 90 per cent, alcohol, 100 grams of pinene-nitrosochloride are added. The mixture is boiled on a water-bath, under a reflux condenser, until the reaction is complete. Water is added, the-clear solution filtered from insoluble impurities, and the filtrate poured into excess of acetic acid. The nitroso-pinene separates as an oil which solidifies to a yellowish mass in a few days. This is broken up, washed with water, and dried on a porous plate. It can be recrystallised from acetic ether, when it is obtained in the pure condition, and then melts at 132°. 

The identification of camphene is best carried out by its conversion into isobomeol under the influence of acetic acid in the presence of sulphuric acid. In order to effect this conversion, 100 grams of the fraction containing the terpene in substantial quantity are mixed with 250 grains of glacial acetic acid and 10 grams of 50 per cent, sulphuric acid. Tne mixture is heated for two to three hours on a water-bath to a temperature of 50° to 60°. At first the liquid separates into two layers, bat soon becomes homogeneous and takes on a pale red colour. Excess of water is added, and the oil which is precipitated, and which contains the isobomeol in the form of its acetate, is well washed with water repeatedly. It is then saponified by heating with alcoholic potash solution on a water-bath. The liquid is then evaporated and extracted with water, and the residue recrystallised from petroleum ether. 

For the identification of limonene, one of the most useful compounds is the crystalline tetrabromide, Cj(,HjgBr. This body is best prepared as follows the fraction of the oil containing much limonene is mixed with four times its volume of glacial acetic acid, and the mixture cooled in ice. Bromine is then added, drop by drop, so long as it becomes decolorised at once. The mixture is then allowed to stand until crystals separate. These are filtered off, pressed between porous paper, and recrystallised from acetic ether. Limonene tetrabromide melts at 104 5° and is optically active, its specific rotation being + 73 3°. The inactive, or dipeutene, tetrabromide melts at 124° to 125°. In the preparation of the tetrabromide traces of moisture are advisable, as the use of absolutely anhydrous material renders the compound very diflftcult to crystallise. 

For the identification of terpinolene, its tetrabromide is the most characteristic compound. This body is prepared by adding gradually four atoms of bromine to a solution of the terpene in glacial acetic acid, maintained at a low temperature. Terpinolene tetrabromide, C], Hj,.Br., melts at 116° to 117°, when recrystallised from alcohol. 

Farnesal forms a semi-carbazone, which crystallises from acetic ether in fine flakes, which melt at 133° to 135°. This body is particularly useful for the identification of farnesol. 

It is suitable, not only for rose odours, but also for blending with almost any flower oil. Phenyl-ethyl alcohol forms a solid compound with chloride of calcium, which is very useful for its purification. On oxidation it is converted into a mixture of phenyl-acetaldehyde and phenyl-acetic acid. The last-named body forms an ethyl ester melting at 28°, which serves for its identification. 

Terpineol nitrosochloride, Cj Hj-OH. NOCl, is, perhaps, the most suitable derivative to prepare for the identification of terpineol. To a solution of 15 grams of terpineol in 15 c.c. of glacial acetic acid, 11 c.c. of ethyl nitrite are added. The mixture is cooled in ice, and 6 c.c. of hydrochloric acid mixed with 6 c.c. of glacial acetic acid are added drop by drop, with continual shaking. Care must be taken to avoid a rise in temperature. When the reaction is compdete, water is added to pjre-cipitate the nitrosochloride. The oily liquid soon solidifies and may be recrystallised from boiling acetic ether or from methyl alcohol. Ter-... 

Methyl Malonate.—This ester is an artificially prepared body, having a fruity odour, somewhat similar to the above-described esters of the fatty acids. It has the formula CH2(C02CHg)2, and boils at 181°. It may be prepared by treating potassium cyan-acetate with methyl alcohol and hydrochloric acid. On saponification with alcoholic potash it yields malonic acid, which melts at 132°, and serves well for the identification of the ester. 

For the identification of citronellal, the semi-carbazone is the easiest cry stalline compound to prepare. It results if an alcoholic solution of citronellal be well-shaken with a solution of semi-carbazide hydrochloride and acetate of sodium. It is purified by recrystallisation from a mixture of chloroform and petroleum ether, and then melts at 84°. It also forms a well-defined naphthocinchoninic acid, which is prepared in the same manner as the corresponding citral compound. It melts at 225°. 

This solution is extracted several times with 5% acetic acid, until the silico-tungstate test (an identification test for alkaloids) yields a negative result, and the acetic solutions are washed with 10 ml ether. 

The crystalline phenylboronate derived by similar treatment of methyl a-L-fucopyranoside was shown to possess the 3,4-cyclic structure (25). This assignment is based on oxidation of compound 25 with methyl sulfoxide-acetic anhydride and the chromatographic identification of... 

Identification of a characteristic set of isomers with differently branched nonyl substitutions of poorly biodegradable nonylphenoxyacetic acid and nonylphen-oxyethoxy acetic acid in sewage effluents was identified with high-resolution gas chromatography/mass spectrometry (HRGS-MS) and quantitative determination was done with HPLC [245]. 

The identification of bi-layer adsorption of polar solvents on the surface of silica gel arose from some work by Scott and Kucera (5) who measured the adsorption isotherms of the some polar solvents, ethyl acetate, isopropanol and tetrahydrofuran from n-heptane solutions onto silica gel. The authors found that the experimental results for the more polar solvents did not fit the simple mono-layer adsorption equation and, as a consequence, the possibility of bi-layer adsorption on the silica gel surface was examined. 

Note The three reagents should be applied as quickly as possible after each other. In combination with the Ry value, and with UV detection before application of the reagent sequence this procedure allows the identification of therapeutic quantities of thiazide diuretics and methyldopa in urine together with a series of other therapeutic agents. Mobile phase residues e. g. acetic acid, should be completely removed from the chromatograms before application of the reagent sequence. 

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