Sulfuric acid active medium-concentration

The application of A-type GIC materials in rechargeable batteries has frequently been investigated, namely in metal/graphite cells in concentrated sulfuric acid by Fujii (Me = Pd) [153,154] and in acids of medium concentration by Beck and Krohn (Me = Pb or Zn) [155-157]. The latter electrolytes have an improved compatibility with the negative metal electrode. Metal-free accumulators with GIC as a positive electrode were built with anthraquinone in aqueous acids [80] and with polypyrrole in aprotic electrolytes [58,158,159]. General discussions of the potentialities of graphite-type active materials in rechargeable batteries have been published by Besenhard and Fritz [160] and Beck et al. [5-10]. At the end of this review (Section 9) the discussion relevant to batteries will be summarized. 

The bomb contents are digested with concentrated hydrochloric acid, and material still undissolved is then digested with potassium hydroxide and hydrogen peroxide. A crude separation is made by a sulfide precipitation from the combined digestion solutions. The sulfides are dissolved in aqua regia, the solution is evaporated, and antimony in the residue is reduced to antimony (III) with hydroxylamine hydrochloride. The sample, in ammonium thiocyanate-hydrochloric acid medium, is loaded onto a Dowex 2 column (SCN" form). Arsenic and other impurities are eluted with aliquots of more dilute ammonium thiocyanate-hydrochloric acid solutions. Antimony is eluated with sulfuric acid and fixed in solution by addition of hydrochloric acid. The activity of the solution caused by the 0.56 MeV y-ray of 2.8-day 122Sb is counted. 

The oxidation of L-norleucine, L-leucine, L-isoleucine, and r.-r-leucine with permanganate in strong acid medium showed an autocatalysis by Mn(II), except in the case of L-leucine. For the autocatalytic activity to initiate, a certain concentration of Mn(II) is required. Moreover, the autocatalytic phenomenon vanishes in concentrations of sulfuric acid that are greater than 4.3 mol dm-3. The oxidation showed a good correlation in a biparametric equation, with p = -4.57 and Sc = 2.23 at 318 K.43... 

A solution of 17 g (0.1 mole) of 3-(4-hydroxyphenyl)propionic acid in 500 mL methanol and 2 mL concentrated sulfuric acid were placed in a Soxhlet extractor charged with 3A molecular sieves. The solution was refluxed for 72 hours and the sieve were exchanged at 24 hour intervals. The reaction medium was then evaporated to an oil which was dissolved in 100 mL toluene and extracted with 100 mL water (3 times). The toluene phase was dried over magnesium sulfate, treated with activated charcoal and evaporated to provide 15 g (80%) of a clear oil. The NMR spectrum was consistent with the methyl 3-(4-hydroxyphenyl)propionate. 

By increasing the concentration of sulfuric acid in water, the thermodynamic activity of the water can be strongly decreased. If the acidity of a solution of a predominantly (or partly) hydrated cation is. progressively increased, the amount of free water remaining in the medium for hydration of the organic molecule is correspondingly decreased, and the spectrum thus becomes more similar to that of the anhydrous cation. In quinazoline, for example, bands present in the 271 and 305 mp r on at pH 7, which are associated with the predominantly anhydrous neutral species, disappear at pH 1 (because the hydrated cation is formed) but reappear on increasing the acidity to Hq — 3.5 (because the anhydrous monocation is formed). A similar effect is observed with quinazoline 3-oxide (see Fig. 4) and 3-nitro- and 8-... 

The rate-increasing portion of the nitration rate profile can readily be explained by the increasing concentration of nitronium ion up to about 90% sulfuric acid, at which point the nitric acid is essentially completely converted to nitronium ion. It is not clear exactly why the nitration rate declines thereafter however, it has been suggested that the effects of the medium on the aromatic activity coefficients are responsible. (13)... 

Kinetic data show that in seawater medium S42 reacts about 20-30 times faster than HS with acrylic acid, whereas the reaction of S42 with acrylonitrile is only about 4-6 times higher than with HS. However, in any environment, the importance of polysulfide versus bisulfide reactions is also dependent on their relative concentrations. In a situation where polysulfide and bisulfide ions are present in similar concentrations, our results imply that polysulfide ions, rather than bisulfide, are the important sulfur nucleophiles for reactions with activated unsaturated molecules having a terminal carboxyl group (e.g. acrylic acid, cinnamic acid). However, for neutral molecules such as fucoxanthin, in addition to polysulfide ions, reactions with bisulfide ions will also be of importance. 

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