Strongly acidic medium

The function of the sulphuric acid is to furnish a strongly acid medium and to convert the nitric acid into the highly reactive nitronium ion NOj+, which is the real nitrating agent ... 

The NMR determination in strongly acidic medium (trifluoroacetic acid) of the chemical shifts of the protons in the 4- or 5-position can be used to establish a reactivity scale. If the proton appears at low field, this indicates that this substitution site wiE be poorly or not at all nitrated (111). 

Masking by oxidation or reduction of a metal ion to a state which does not react with EDTA is occasionally of value. For example, Fe(III) (log K- y 24.23) in acidic media may be reduced to Fe(II) (log K-yyy = 14.33) by ascorbic acid in this state iron does not interfere in the titration of some trivalent and tetravalent ions in strong acidic medium (pH 0 to 2). Similarly, Hg(II) can be reduced to the metal. In favorable conditions, Cr(III) may be oxidized by alkaline peroxide to chromate which does not complex with EDTA. 

The stated amount of acid has been found sufficient to provide the strongly acidic medium which the reaction requires. 

Hydroxyl groups are stable to peracids, but oxidation of an allylic alcohol during an attempted epoxidation reaction has been reported." The di-hydroxyacetone side chain is usually protected during the peracid reaction, either by acetylation or by formation of a bismethylenedioxy derivative. To obtain high yields of epoxides it is essential to avoid high reaction temperatures and a strongly acidic medium. The products of epoxidation of enol acetates are especially sensitive to heat or acid and can easily rearrange to keto acetates. 

A solution of iodine in aqueous iodide has an intense yellow to brown colour. One drop of 0.05M iodine solution imparts a perceptible pale yellow colour to 100 mL of water, so that in otherwise colourless solutions iodine can serve as its own indicator. The test is made much more sensitive by the use of a solution of starch as indicator. Starch reacts with iodine in the presence of iodide to form an intensely blue-coloured complex, which is visible at very low concentrations of iodine. The sensitivity of the colour reaction is such that a blue colour is visible when the iodine concentration is 2 x 10 " 5 M and the iodide concentration is greater than 4x 10 4M at 20 °C. The colour sensitivity decreases with increasing temperature of the solution thus at 50 °C it is about ten times less sensitive than at 25 °C. The sensitivity decreases upon the addition of solvents, such as ethanol no colour is obtained in solutions containing 50 per cent ethanol or more. It cannot be used in a strongly acid medium because hydrolysis of the starch occurs. 

Research into the mechanism of diazotization was based on Bamberger s supposition (1894 b) that the reaction corresponds to the formation of A-nitroso-A-alkyl-arylamines. The TV-nitrosation of secondary amines finishes at the nitrosoamine stage (because protolysis is not possible), but primary nitrosoamines are quickly transformed into diazo compounds in a moderately to strongly acidic medium. The process probably takes place by a prototropic rearrangement to the diazohydroxide, which is then attacked by a hydroxonium ion to yield the diazonium salt (Scheme 3-1 see also Sec. 3.4). 

A method suitable for quantification of the functional class of bis(ethanol)amine antistatics, which lack UV chromophores, consists of reaction with methyl orange [53]. Atmer 163 (alkyl-diethanol amine) has been determined as a yellow complex at 415 nm after interaction with a bromophenol/cresole mixture [64]. Hilton [65] coupled extracted phenolic antioxidants with diazotised p-nitroaniline in strongly acidic medium and carried out identification on the basis of the visible absorption spectrum in alkaline solution. The antioxidant Nonox Cl in... 

A colorimetric procedure is described for the determination of small amounts of Compound 118 (1,2,3,4,10,10-hexa-chloro - 1,4,4a,5,8,8a - hexahydro - 1,4,.5,8 - dimethano-naphthalene). Reaction with phenyl azide to form a di-hydrotriazole derivative and subsequent treatment with diazotized dinitroaniline in strongly acid medium produce an intense red color. Amounts of the insect toxicant of 10 to 40 micrograms in the final 10-ml. aliquot are readily determined with a spectrophotometer. Commonly used insect toxicants do not interfere. 

The precipitation of arsenic with H2S gas in the normal condition could occur only in strongly acidic medium whereas another cation of the second group Cd(II), precipitates only in faintly acidic medium, therefore, the precipitation of both cadmium and arsenic with H2S gas in the same solution was not easily possible. To precipitate both in the same solution, the H2S gas is conventionally first passed into the strongly acidic original solution of basic radicals followed by its bubbling into the diluted solution. To examine the role of ultrasound on the precipitation of arsenic in faintly acidic or neutral medium, few experiments were carried out. The results obtained showed effective precipitation of arsenic even in mild reaction solutions, with their pH ranging from 5.1 to 8.8. under ultrasonic field. Hence Cd2+ and As3+/5+ both could be precipitated in the same solution at low pH under the... 

In a strongly acidic medium (FS03H—SbFs) methanesulfinic acid is readily protonated to give CH3S(OH) this species appears to be rather stable, showing no tendency to undergo cleavage reactions up to +65°C (Olah et al., 1970). 

Consequently, the equivalent amount of iodine generated by the above reaction may be conveniently assayed by titration against a standard sodium thiosulphate solution. In this context a point of caution must be observed while KI is being oxidized under a strongly acidic medium so as to avoid simultaneous oxidation of the iodide by atmospheric oxygen that may result high erroneous titer values leading to false estimations. 

Indirect electroreduction of allyl alcohols leading to the corresponding unsaturated hydrocarbons is attained using a mercury electrode in a strongly acidic medium containing an iodide salt [554]. The reaction involves transformation of the alcohol into the iodide, the reaction of the iodide with mercury, the protonation of the... 

Butanone was hydrogenated by [It(ti -C5Mes)(H20)3] in strongly acidic solution (25 °C, 5 bar H2, TOFmax at pH 2.5) [89]. At higher pH the Ir-catalyst dimerizes to an inactive species. It was speculated, that the strongly acidic medium assisted the formation of an intermediate carbocation which... 

The localization of electron density on heteroatoms is seen during the nitration of anilines which are A-nitrated in aprotic media. " Anilines can give abnormal o p-isomer ratios resulting from a process of A-nitration followed by rearrangement to the ring nitrated product, a process which often occurs in situ in the strongly acidic medium of mixed acid (Section 4.5). 

The Pourbaix diagram for cw-[Ru (0)2(Tet-Me6)] " " is shown in Figure 9. These electrochemical data show that for this system Ru is unstable with respect to disproportionation at pH 1, while Ru is unstable at pH.4.5. The Ru complex cw-[Ru qO)2(Tet-Meg)]+ has been isolated and is found to disproportionate in strongly acidic medium (Equation (36)). 

Classical methods use strongly acidic medium. Oximes may be converted to their ester or ether derivatives and these may be used to promote the rearrangement (less vigorous reaction conditions are usually needed). Some other milder reaction conditions and reagents may be used (Section VI.C). 

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