Perchloric Acid determination with

Dissolve 0.35 g of miconazole nitrate in 75 mL of anhydrous acetic acid R, with slight heating, if necessary. Titrate with 0.1 M perchloric acid determining the end point potentiometrically, according the general method (2.2.20). Carry out a blank titration. One milliliter of 0.1 M perchloric acid is equivalent to 47.91 mg of Ci8H15Cl4N304. 

Dissolve 0.2 g of primaquine phosphate in 40 mL of anhydrous acetic acid R, heating gently. Titrate with 0.1 M perchloric acid determining the endpoint... 

A weighed sample of the product (approximately 1 g.) is dissolved in a 3 % perchloric acid solution, with gentle heating in a water bath if necessary. To determine ehromium-(YI), aliquot portions of the solution are acidified with 10%... 

Assay Dissolve about 130 mg of sample, previously dried at 130° for 3 h and accurately weighed, in 3 mL of formic acid and 50 mL of glacial acetic acid, and titrate with 0.1 N perchloric acid, determining the endpoint potentiometrically. 

Macro quantities of selenium can be determined gravimetrically after reduction to the elemental form by various reagents such as tin (II) chloride, potassium iodide, or ascorbic acid (I). Ooba described a technique whereby the element is precipitated from perchloric acid solution with hydrazine (2). Selenium may be titrated with standard solutions of sodium thiosulfate, iodide, and ferrous, chromous, or trivalent titanium salts after oxidation to Se(VI) (I). Photometric and fluorometric methods based on formation of the piaselenol with diaminobenzidine or 2,3-diaminonaphthalene has been used for the determination of selenium (I, 3,4,5). Interfering elements such as As, Co, Cr, Cu, Fe, Hg, and Ni, are masked with EDTA or other chelating agents. 

Under these first-order conditions the rates of nitration of a number of compounds with acetyl nitrate in acetic anhydride have been determined. The data show that the rates of nitration of compounds bearing activating substituents reach a limit by analogy with the similar phenomenon shown in nitration in aqueous sulphuric and perchloric acids ( 2.5) and in solutions of nitric acid in sulpholan and nitro-methane ( 3.3), this limit has been taken to be the rate of encounter of the nitrating entity with the aromatic molecule. 

Eluorspar assay may be completed by fluoride determination alone, because the mineralogical grouping rarely iacludes fluorine minerals other than fluorite. Calcium can be determined as oxalate or by ion-selective electrodes (67). SiUca can be determined ia the residue from solution ia perchloric acid—boric acid mixture by measuriag the loss ia weight on Aiming off with hydrofluoric acid. Another method for determining siUca ia fluorspar is the ASTM Standard Test Method E463-72. 

Analytical Methods. The official NIOSH recommended method for determining sulfur dioxide in air consists of drawing a known prefiltered volume of air through a bubbler containing hydrogen peroxide, thus oxidising the sulfur dioxide to sulfuric acid. Isopropyl alcohol is then added to the contents in the bubbler and the pH of the sample is adjusted with dilute perchloric acid. The resultant solution is then titrated for sulfate with 0.005 M. barium perchlorate, and Thorin is used as the indicator. 

This procedure can now be repeated with a base D that is slightly weaker than C, using C as the reference. In this stepwise manner, a series of p determinations can be made over the acidity range from dilute aqueous solution to highly concentrated mineral acids. Table 8-18 gives pS bh+ values determined in this way for nitroaniline bases in sulfuric and perchloric acid solutions. This technique of determining weak base acidity constants is called the overlap method, and the series of p kBH+ values is said to be anchored to the first member of the series, which means that all of the members of the series possess the same standard state, namely, the hypothetical ideal 1 M solution in water. 

UOP Test Method 313 is commonly employed to determine the basic nitrogen content of FCC feed. The feed sample is first mixed 50/50 with acetic acid. The mixture is then titrated with perchloric acid. 

The above procedure may be adapted to the determination of molybdenum in steel. Dissolve a 1.00 g sample of the steel (accurately weighed) in 5 mL of 1 1 hydrochloric acid and 15 mL of 70 per cent perchloric acid. Heat the solution until dense fumes are evolved and then for 6-7 minutes longer. Cool, add 20 mL of water, and warm to dissolve all salts. Dilute the resulting cooled solution to volume in a 1 L flask. Pipette 10.0 mL of the diluted solution into a 50 mL separatory funnel, add 3 mL of the tin(II) chloride solution, and continue as detailed above. Measure the absorbance of the extract at 465 rnn with a spectrophotometer, and compare this value with that obtained with known amounts of molybdenum. Use the calibration curve prepared with equal amounts of iron and varying quantities of molybdenum. If preferred, a mixture of 3-methylbutanol and carbon tetrachloride, which is heavier than water, can be used as extractant. 

The method can be applied to the determination of phosphorus in a wide variety of materials, e.g. phosphate rock, phosphatic fertilisers and metals, and is suitable for use in conjunction with the oxygen-flask procedure (Section 3.31). In all cases it is essential to ensure that the material is so treated that the phosphorus is converted to orthophosphate this may usually be done by dissolution in an oxidising medium such as concentrated nitric acid or in 60 per cent perchloric acid. 

Discussion. Hydroxyl groups present in carbohydrates can be readily acetylated by acetic (ethanoic) anhydride in ethyl acetate containing some perchloric acid. This reaction can be used as a basis for determining the number of hydroxyl groups in the carbohydrate molecule by carrying out the reaction with excess acetic anhydride followed by titration of the excess using sodium hydroxide in methyl cellosolve. 

As the acetonitrile may contain basic impurities which also react with the perchloric acid, it is desirable to carry out a blank determination on this solvent. Subtract any value for this blank from the titration values of the amines before calculating the percentages of the two amines in the mixture. 

Note. Evaporation with perchloric acid or perchlorates should be carried out in a fume cupboard which is kept clean and free from combustible materials. In the presence of carbon and easily oxidisable organic compounds a violent explosion may occur on heating. The determination is not suitable for the beginner and should only be carried out by an experienced analyst. 

Iodide. A 0.01 M solution of potassium iodide, prepared from the dry salt with boiled-out water, is suitable for practice in this determination. The experimental details are similar to those given for bromide, except that the indicator electrode consists of a silver rod immersed in the solution. The titration cell may be charged with 10.00 mL of the iodide solution, 30 mL of water, and 10 mL of the stock solution of perchloric acid + potassium nitrate. In the neighbourhood of the equivalence point it is necessary to allow at least 30-60 seconds to elapse before steady potentials are established. 

In view of the foregoing remarks, it is clear that all glassware used in the preliminary treatment of samples to be subjected to stripping voltammetry, as well as the apparatus to be used in the actual determination, must be scrupulously cleaned. It is usually recommended that glassware be soaked for some hours in pure nitric acid (6 M), or in a 10 per cent solution of pure 70 per cent perchloric acid, followed by washing with de-ionised water. 

The rate-determining step in the diazotization of aniline in aqueous perchloric acid below concentrations of 0.05 m (pH >0.7) is the formation of N203. The following A-nitrosation step is faster (rate equation of Scheme 3-12). However, with aromatic amines that are weaker nucleophiles than aniline, e.g. 4-nitroaniline, nitrosation is slower than the formation of N203, and the rate is second-order with respect to nitrous acid and first-order in amine (Scheme 3-13, Larkworthy, 1959). 

The UV absorption spectra of sodium nitrite in aqueous solutions of sulfuric and perchloric acids were recorded by Seel and Winkler (1960) and by Bayliss et al. (1963). The absorption band at 250 nm is due either to the nitrosoacidium ion or to the nitrosyl ion. From the absorbancy of this band the equilibrium concentrations of HNO2 and NO or H20 —NO were calculated over the acid concentration ranges 0-100% H2S04 (by weight) and 0-72% HC104 (by weight). For both solvent systems the concentrations determined for the two (or three) equilibrium species correlate with the acidity function HR. This acidity function is defined for protonation-dehydration processes, and it is usually measured using triarylcarbinol indicators in the equilibrium shown in Scheme 3-15 (see Deno et al., 1955 Cox and Yates, 1983). 

De la Mare and Hilton198 measured the rates at 25 °C of bromination of benzene, benzoic acid, phthalic acid, 2-nitrobenzoic acid, trimethylanilinium perchlorate and nitrobenzene by hypobromous acid with sulphuric or perchloric acids as catalysts, in some cases in aqueous dioxan, in an attempt to discover if Br+ or H2OBr+ was the appropriate brominating species since the logarithm of the rates should then follow the acidity functions H0 or HR (J0) respectively. The results, however, were inconclusive and relative rates of bromination were determined (see Table 53). 

The rates of mercuration of a number of aromatic hydrocarbons have been determined using mercuric acetate in acetic acid, in some cases using perchloric acid as catalyst. Rate coefficients for benzene and alkylbenzene have been determined under both conditions at a range of temperatures and the data are gathered in Tables 117 and 118441 -4 8 in the absence of perchloric acid, mercuric acetate reacted with the solvent at a rate that was not insignificant compared with the rate of aromatic mercuration, and a correction was made for this side reaction. 

The detritiation of [3H]-2,4,6-trimethoxybenzene by aqueous perchloric acid was also studied, the second-order rate coefficients (107/c2) being determined as 5.44, 62.0, and 190 at 0, 24.6, and 36.8 °C, respectively, whilst with phosphate buffers, values were 3.75, 13.8, and 42.1 at 24.6, 39.9, and 55.4 °C, respectively. The summarised kinetic parameters for these studies are given in Table 134, and notable among the values are the more negative entropies of activation obtained in catalysis by the more negative acids. This has been rationalised in terms of proton transfer... 

A further kinetic investigation of the rates of cleavage of diphenylmercury (and some dialkylmercurials) showed similar kinetic features608. The first-order rate for the reaction of diphenylmercury with acetic acid at 25 °C was 4.98 x 10", which agreed quite well with the value from the above determination (2 x 10-4 at 42 °C with dioxan). In the presence of perchloric acid, second-order kinetics were found to be obeyed (for dineophyl mercury and presumably for diarylmercurials as well) for a twofold concentration change in both mercurial and perchloric acid. Two separate mechanisms were proposed for the reactions in the absence, and presence, of perchloric acid. Under the former conditions an SEi process (244) was... 

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