Free precipitation

The dark-brown and chloride-free precipitate, [ TcN(0H)(H20) 2(p-0)2], can be formed by hydrolysis of Cs2[TcNCl5] in a large amount of water [36]. In... 

Precipitation by ethanol in the cold was used effectively by J.Mellanby in 1908 to obtain diptheria antitoxin two years later Hardy and Gardiner reported the precipitation of plasma proteins by cold ethanol or acetone. The resulting proteins remained soluble in water, i.e. they were not denatured, and subsequent estimation of protein as nitrogen was helped by the use of nitrogen-free precipitants. Separations using organic solvents were considerably extended by Edsall,... 

In order to observe the size and shape of the particles formed by free precipitation, a control sample was prepared with 0.015 M of HAuCU solution to which gradually the reducing agent NaBH4 (0.01 M) was added drop wise and mixed well. The yellow solution gradually transformed into a purple solution, indicating gold nanoparticle formation. 

Fig. 7 Irregularly shaped particles form during the free precipitation reaction of HAuCU with NaBH4...

Fig. 8 a Facetted particles formed without reducing agent, b spherical particle produced by the use of a reducing agent, c irregular shaped particles obtained by free precipitation... 

The old analytical chemistry literature is rich with methods involving homogeneous precipitation from solution, the purpose being to obtain dense (therefore easily filterable), contamination-free precipitates for purposes of analyses. The... 

Pich et al. [111] reported synthesis of microgel-clay composite particles by one-step surfactant-free precipitation polymerization (unpublished results). Laponite NPs present in the reaction mixture become encapsulated during the microgel... 

Tetramethylzirconium was prepared (59) by the reaction of stoichiometric amounts of methyllithium and zirconium tetrachloride in an ether-toluene solvent mixture at —45°C. Methylation is accompanied by the appearance of a yellow color and precipitation of lithium chloride. The red liquid was recovered in poor yield by vacuum distillation at —30°C. The product decomposes at —15°C with the evolution of methane and the formation of a black color. When a mole ratio of ZrCl 4 LiCH g( 1 6) is used, the addition of hexane to the ether/toluene solution results in a chloride-free precipitate whose elementary analysis corresponds to the composition Li2[Zr(CH3)g]. This product decomposes at 0°C. 

Rietveld structure refinements have also been undertaken on synthetic precipitated COsAps as model systems for biological apatites. The reduction in apparent PO4 volume, and P and Ca2 occupancies seen in dental enamel were also seen in Na-free precipitated COsAps with CO3 contents of 4 wt % produced by the reaction between CaCOs and CaHP04 at 100°C (Morgan et al. 2000). COsAps precipitated in the presence of Na ions... 

Microscopic analysis of received suspensions showed that particles of BaS04 posses pronounced anisometry (they represent sticks with length-to-diameter ratio about 4, that explains the sigmoid shape of sedimentation curves with extreme) (Fig. 5.19). At the initial moment of sedimentation the rotation of stick-shaped particles is possible, that determines additional resistance to sedimentation proceeding (analogously to viscosity increase) and slowing down of rate of deposition accumulation. Moreover, at free precipitation particles of spherical form are oriented in movement direction in that way to create maximum resistance to movement. This also reduces the precipitation rate of solid particles in liquid and embarrasses the definition of their actual sizes. In this connection, equivalent radius re (radius of spherical particle precipitating with the same rate) was determined by results of sedimentation analysis. 

Anunonitjm Salts. Addition of formaldehyde to ammonium salt solu tions at room temperatui-e results in the liberation of acid. When this acid is neutralized or removed, hexametliylenetetramine is obtained. In the case of ammonium borate, the boric acid which is set free precipitates in the same manner as if a strong acid had been added . With ammonium cai bonate, carbon dioxide is liberated as a gas and when the solution is e aporated under reduced pressure, a residue of hexamethylenetetramine i-emains. When excess alkah is added to solutions containing ammonium salts of strong acids plus an excess of fonnaldehyde, the acid which was originally combined Adth ammonia may be accurately determined by measuring the amount of alkah consumed. A volumetric method for the determination of ammonium nitrate is based on the reaction shown below. ... 

CH2CI-CO-CH3. Colourless lachrymatory liquid b.p. 119°C. Manufactured by treating propanone with bleaching powder or chlorine. It is used as a tear gas and is usually mixed with the more potent bromoacetone. chloro acids Complex chloroanions are formed by most elements of the periodic table by solution of oxides or chlorides in concentrated hydrochloric acid. Potassium salts are precipitated from solution when potassium chloride is added to a solution of the chloro acid, the free acids are generally unstable. 

Hydrolysis of Potassium Ethyl Sulphate. Dissolve about i g. of the crystals in about 4 ml. of cold distilled water, and divide the solution into two portions, a) To one portion, add barium chloride solution. If pure potassium ethyl sulphate were used, no precipitate should now form, as barium ethyl sulphate is soluble in water. Actually however, almost all samples of potassium ethyl sulphate contain traces of potassium hydrogen sulphate formed by slight hydrolysis of the ethyl compound during the evaporation of its solution, and barium chloride almost invariably gives a faint precipitate of barium sulphate. b) To the second portion, add 2-3 drops of concentrated hydrochloric acid, and boil the mixture gently for about one minute. Cool, add distilled water if necessary until the solution has its former volume, and then add barium chloride as before. A markedly heavier precipitate of barium sulphate separates. The hydrolysis of the potassium ethyl sulphate is hastened considerably by the presence of the free acid Caustic alkalis have a similar, but not quite so rapid an effect. 

Boil 5 ml. (5-1 g.) of benzonitrile and 75 ml. of 10% aqueous sodium hydroxide in a 200 ml. flask under a reflux water condenser until no more oily drops of unchanged nitrile run down from the condenser (usually about 40 minutes). Th detach the condenser and boil the solution in the open flask for a few minutes to remove free ammonia, Cool the liquid, and add concentrated hydrochloric acid cautiously until precipitation of benzoic acid is complete. Cool the mixture again thoroughly, filter off the benzoic acid at the pump, and wash well with cold water. Yield, 5 8 g. (almost theoretical). Confirm the identity of the benzoic acid by the tests given on p. 347. The benzoic acid obtained in this way should be pure and have m.p. 121 a portion may if desired be recrystallised from hot water. 

The use of lead nitrate in place of silver nitrate is to be avoided, for the precipitated lead sulphide occludes most of the free acid. 

Transfer the quinoline chlorozincate to a beaker, add a small quantity of water, and then add 10% sodium hydroxide solution until the initial precipitate of zinc hydroxide completely redissolves, and the free quinoline separates. Transfer the mixture to a separating-funnel, wash out the beaker with ether, adding the washings also to the solution in the funnel, and then extract the quinoline twice with ether. Dry the united ethereal extracts by adding an ample quantity of powdered potassium hydroxide and... 

Colorations or coloured precipitates are frequently given by the reaction of ferric chloride solution with.(i) solutions of neutral salts of acids, (ii) phenols and many of their derivatives, (iii) a few amines. If a free acid is under investigation it must first be neutralised as follows Place about 01 g. of the acid in a boiling-tube and add a slight excess of ammonia solution, i,e., until the solution is just alkaline to litmus-paper. Add a piece of unglazed porcelain and boil until the odour of ammonia is completely removed, and then cool. To the solution so obtained add a few drops of the "neutralised ferric chloride solution. Perform this test with the following acids and note the result ... 

Succinate, benzoate, phthalate and cinnamate give buff or brownish coloured precipitates of the basic ferric salts in the cold. Add dil. H2SO4. The basic ferric succinate dissolves giving a clear solution the other basic ferric salts also dissolve, but simultaneously a white precipitate of the free acid is also formed. 

A brisk effervescence of COg without the formation of a precipitate indicates urea (if the NaOH used is free from carbonate). 

Colorations or precipitates given by phenols and many derivatives of phenols by neutral salts of acids by some amines. (The FeCl, solution can be added directly to a small quantity of the phenol or to its aqueous solution free acids must first be neutralised.)... 

Add 1 ml. of the alcohol-free ether to 0-1-0-15 g. of finely-powdered anhydrous zinc chloride and 0 5 g. of pure 3 5-dinitrobenzoyl chloride (Section 111,27,1) contained in a test-tube attach a small water condenser and reflux gently for 1 hour. Treat the reaction product with 10 ml. of 1-5N sodium carbonate solution, heat and stir the mixture for 1 minute upon a boiling water bath, allow to cool, and filter at the pump. Wash the precipitate with 5 ml. of 1 5N sodium carbonate solution and twice with 6 ml. of ether. Dry on a porous tile or upon a pad of filter paper. Transfer the crude ester to a test-tube and boil it with 10 ml. of chloroform or carbon tetrachloride filter the hot solution, if necessary. If the ester does not separate on cooling, evaporate to dryness on a water bath, and recrystallise the residue from 2-3 ml. of either of the above solvents. Determine the melting point of the resulting 3 5 dinitro benzoate (Section 111,27). 

N-Benzylamides are recommended when the corresponding acid is liquid and/or water-soluble so that it cannot itself serve as a derivative. Phe benzylamides derived from the simple fatty acids or their esters are not altogether satisfactory (see Table below) those derived from most hydroxy-acids and from poly basic acids or their esters are formed in good yield and are easily purified. The esters of aromatic acids yield satisfactory derivatives but the method must compete with the equally simple process of hydrolysis and precipitation of the free acid, an obvious derivative when the acid is a solid. The procedure fails with esters of keto, sul phonic, inorganic and some halogenated aliphatic esters. 

Cellulose. This is insoluble in water, hot and cold. It dissolves in a solution of Schweitzer s reagent (precipitated cupric hydroxide is washed free from salts and then dissolved in concentrated ammonia solution), from which it is precipitated by the addition of dilute acids. Cellulose is not hydrolysed by dilute hydrochloric acid. 

Method 1. From ammonium chloroplatinate. Place 3 0 g. of ammonium chloroplatinate and 30 g. of A.R. sodium nitrate (1) in Pyrex beaker or porcelain casserole and heat gently at first until the rapid evolution of gas slackens, and then more strongly until a temperature of about 300° is reached. This operation occupies about 15 minutes, and there is no spattering. Maintain the fluid mass at 500-530° for 30 minutes, and allow the mixture to cool. Treat the sohd mass with 50 ml. of water. The brown precipitate of platinum oxide (PtOj.HjO) settles to the bottom. Wash it once or twice by decantation, filter througha hardened filter paper on a Gooch crucible, and wash on the filter until practically free from nitrates. Stop the washing process immediately the precipitate tends to become colloidal (2) traces of sodium nitrate do not affect the efficiency of the catalyst. Dry the oxide in a desiccator, and weigh out portions of the dried material as required. 

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