Impurities, inorganic, removal

Metal impurities are removed from nanodiamond powders by dissolving them in mixtures of strong inorganic acids. 

Students are familiar with the general process of recrystallisa-tion from their more elementary inorganic work. Friefly, it consists in first finding a solvent which will dissolve the crude material readily when hot, but only to a small extent when cold. The crude substance is then dissolved in a minimum of the boiling solvent, the solution filtered if necessary to remove any insoluble impurities, and then cooled, when the solute will crystallise out, leaving the greater part of the impurities in solution. The crop of crystals is then filtered off, and the process repeated until the crystals are pure, and all impurities remain in the mother-liquor. 

Absolute diethyl ether. The chief impurities in commercial ether (sp. gr. 0- 720) are water, ethyl alcohol, and, in samples which have been exposed to the air and light for some time, ethyl peroxide. The presence of peroxides may be detected either by the liberation of iodine (brown colouration or blue colouration with starch solution) when a small sample is shaken with an equal volume of 2 per cent, potassium iodide solution and a few drops of dilute hydrochloric acid, or by carrying out the perchromio acid test of inorganic analysis with potassium dichromate solution acidified with dilute sulphuric acid. The peroxides may be removed by shaking with a concentrated solution of a ferrous salt, say, 6-10 g. of ferrous salt (s 10-20 ml. of the prepared concentrated solution) to 1 litre of ether. The concentrated solution of ferrous salt is prepared either from 60 g. of crystallised ferrous sulphate, 6 ml. of concentrated sulphuric acid and 110 ml. of water or from 100 g. of crystallised ferrous chloride, 42 ml. of concentrated hydiochloric acid and 85 ml. of water. Peroxides may also be removed by shaking with an aqueous solution of sodium sulphite (for the removal with stannous chloride, see Section VI,12). 

The exchange resins 6nd application in (i) the purification of water (cation-exchange resin to remove salts, followed by anion-exchange resin to remove free mineral acids and carbonic acid), (ii) removal of inorganic impurities from organic substances, (iii) in the partial separation of amino acids, and (iv) as catalysts in organic reactions (e.g., esterification. Section 111,102, and cyanoethylation. Section VI,22). 

The most common impurities are the corresponding acid and hydroxy compound (i.e. alcohol or phenol), and water. A liquid ester from a carboxylic acid is washed with 2N sodium carbonate or sodium hydroxide to remove acid material, then shaken with calcium chloride to remove ethyl or methyl alcohols (if it is a methyl or ethyl ester). It is dried with potassium carbonate or magnesium sulfate, and distilled. Fractional distillation then removes residual traces of hydroxy compounds. This method does not apply to esters of inorganic acids (e.g. dimethyl sulfate) which are more readily hydrolysed in aqueous solution when heat is generated in the neutralisation of the excess acid. In such cases, several fractional distillations, preferably under vacuum, are usually sufficient. 

Zincon (o-[l-(2-bydroxy-5-sulfo)-3-phenyl-5-formazono]-benzoic acid) [135-52-4] M 459.4. Main impurities are inorganic salts which can be removed by treatment with dilute acetic acid. Organic contaminants are removed by refluxing with ether. It can be recrystd from dilute H2SO4. [Fichter and Schiess Chem Ber 33 751 1900.]... 

As described 1 Eizember and Vogler (1980), many inorganic halides are effective in removal and destruction of nitrosamine impurities during in the synthesis of dinitroanilines. Nitrosamine destruction occurs during the synthesis of oryzalin and fluchloralin. Structures of oryzalin and fluchloralin are shown. 

For the large scale synthesis, the sodium salt of 2 formed in the NaCN-NaOH reaction could be purified by brominated polystyrene resin S P-207 chromatography to avoid acidic work-up which generates HCN. The SP-207 resin was first saturated with 1 M NaCl, and the crude reaction mixture was loaded onto the column. The column was then eluted with 1M NaCl to remove inorganic salts such as excess NaCN and NaOH and other polar impurities. Eluant switching to MeOH-H20 eluted the sodium salt of 2. Fractions containing >98.5 A% of... 

Post-combustion capture using chemical absorption by aqueous alkaline amine solutions has been used for C02 and H2S removal from gas-treating plants for decades [6]. Amines react rapidly, selectively and reversibly with C02 and can be applied at low C02 partial pressure conditions. Amines are volatile, cheap and safe in handling. They show several disadvantages as they are also corrosive and require the use of resistant materials. Furthermore, amines form stable salts in the presence of O2, SOx and other impurities such as particles, HC1, HF and organic and inorganic Fig trace compounds that extremely constrain the content of those compounds in the treated gas. 

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