Purification, general procedures with sodium

The purification procedures to be applied depend on the monomer, on the expected impurities, and especially on the purpose for which the monomer is to be employed, e.g., whether it is to be used for radical polymerization in aqueous emulsion or for ionic polymerization initiated with sodium naphthalene. It is not possible to devise a general purification scheme instead the most suitable method must be chosen in each case from those given below. A prerequisite for successful purification is extreme cleanliness of all apparatus (if necessary, treating with hot nitrating acid and repeatedly thorough washing with distilled water). 

As a general procedure if the olefin is impure, the oxymercura-tion-reduction process may include an olefin purification step. Alternatively, this process may be used to purify the olefin for other purposes. - In such cases, acetone is substituted for ether and, after oxymercuration for the same length of time as suggested above, the solution is poured with stirring into two volumes of water containing one equivalent each of sodium bicarbonate and sodium chloride. The mercury derivative is filtered, recrystallized from ethanol-water, ether, dioxane, or ethyl acetate-heptane and then either reduced as described above (in 70-80% yield) to produce pure alcohol, or deoxy-mercurated with cold 6N HCl, with ethereal lithium aluminum hydride (added cautiously), or high concentrations of alkali halides - to produce the pure olefin. 

The earlier chemical procedures for iodine, which are of interest to radiochemists, have been reviewed by Kleinberg and Cowan (1960). A widely-accepted standard radiochemical procedure for iodine purification was developed by Glendenin and Metcalf (1951). The procedure uses sodium hypochlorite and hydroxylamine hydrochloride in successive steps to ensure radiochemical exchange with the iodine carrier (generally D), followed by carbon tetrachloride-aqueous extractions with nitrite and sulfite for the separation of iodine. The purified iodine is finally precipitated as silver iodide for weighing and counting. Since this procedure has been widely employed, a step-by-step procedure is described below. 

Quinazoline-4(3//)-thiones 13 are prepared in a very simple, one-step synthesis by treatment of 2-[(ethoxymethylene)amino] derivatives 12 with alcoholic sodium hydrosulfide. Numerous other hetero-fused pyrimidinethiones are also available by this procedure (Method Cyclization proceeds uniformly in very high yields, generally in excess of 90%. In some cases, since isolation and purification of (ethoxymethylene)amino derivatives results in the lowering of the overall yield, the one-step procedure, consisting of treatment of a 2-aminonitrile 11, either with a 1 1 mixture of triethyl orthofoimate and acetic anhydride or with triethyl orthoformate alone, to give an intermediate ethoxymethyleneamino derivative which, without isolation, is treated with an ethanolic solution of sodium hydrosulfide, is preferred for preparative purposes (Method B). In a few cases, conversion of the 2-aminonitrile to a 2-aminothioamide followed by cyclization with triethyl orthoformate (see p 47) competes favorably with the above procedure. 

When treated with concentrated alkali, acetoacetic ester is converted into two moles of sodium acetate, (a) Outline all steps in a likely mechanism for this reaction. (Hint See Sec. 21.11 and Problem 5.8, p. 170.) (b) Substituted acetoacetic esters also undergo this reaction. Outline the steps in a general synthetic route from acetoacetic ester to carboxylic acids, (c) Outline the steps in the synthesis of 2-hexanone via acetoacetic ester. What acids will be formed as by-products Outline a procedure for purification of the desired ketone. (Remember that the alkylation is carried out in alcohol that NaBr is formed that aqueous base is used for hydrolysis and that ethyl alcohol is a product of the hydrolysis.)... 

The ammonia is removed by distillation with steam, most of the byproduct hydroxy compounds going into solution as the sodium salt during this operation. The aminoanthraquinone is then filtered hot and washed with hot dilute alkaline solutions. Generally, no purification operation is required. The results obtained by the foregoing/procedure are set forth in Table 8-15. 

Distillation Methods Distillation methods have been widely used in iodine isotope production. Since iodine may be converted to a volatile form (I2), either wet distillation or dry distillation has been employed. A general distillation procedure for carrier-free purification has been reported earlier by Kahn and Freedman (1954). In a wet distillation method (IAEA, 1966), irradiated Te metal is dissolved in a chromic acid-H2S04 mixture. After complete dissolution, the iodate (IO3) formed is reduced to elemental iodine (I2) with oxalic acid and then distilled off from the solution. The distillate is trapped in alkaline sulfite solution. This solution is then purified by an oxidation-reduction cycle and finally redistilled into dilute alkaline solution. In another wet distillation method, irradiated Te02 is dissolved in NaOH and the sodium tellurite is oxidized with H2O2 in the presence of a catalyst, sodium molybdate. The mixture is then acidified with H2SO4 and the iodine is distilled off and trapped in ice-cold water. 

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