Case studies Sulphuric acid

It is not surprising to find therefore that acids such as perchloric lnd sulphuric are more efficient initiators than, say, simple hydrogen halides. As already pointed out, the polymerization of styrene by these acids has been widely studied [10—22, 68], In the case of sulphuric acid in ethylene dichloride, there is an initial fast reaction which stops abruptly before all the monomer is consumed [11]. Pepper et al. [11] have analysed this non-stationary state polymerization employing the scheme... 

The first three of a series of papers by Ridd and co-workers on Inductive and Field effects in Aromatic Substitution have appeared. Results of studies of the nitration of 4-phenylp5nidine and of 4-benzylpyridine in aqueous sulphuric acid were reported and use of the usual criteria (para 8.2) showed that in each case the conjugate acid was the species undergoing nitration. The values of where fm refers to the corresponding homocyclic compound (biphenyl or diphenylmethane) when plotted against r, the distance between the... 

The use of maleic anhydride as a compatiblizer between wood particles and bisphenol A-based polyesters resins has been investigated (Han etal., 1991). In this study, the MA was added directly to the composition of woody matrix filler and resin rather than by pre-modification of the wood. It was found that composite properties were improved by addition of MA, probably due to esterification of the wood occurring during the kneading process. The modification of sawdust using maleic anhydride has been performed in order to provide a compatible filler for polyester resins (Marcovich etal., 1996). Modification was performed at room temperature using a solution of maleic anhydride in acetone, in some cases catalysed with sulphuric acid. It was claimed that bonding occurred under these mild conditions from IR spectroscopic evidence only. 

The reduction of benzoic acid at a lead cathode in aqueous sulphuric/citric acids yields the two-electron products benzaldehyde and the four-electron product benzyl alcohol rather than one-electron hydrodimer. In all cases studied by the authors they found that ultrasound favoured the process involving the smaller number of electrons per molecule. This is the opposite of the sonoelectrochemical effect seen in carboxylate electrooxidation [57,59,60] where the process involving the greater number of electrons was favoured by ultrasound. 

While this possibility cannot be ruled out, it is not sufficient to explain the behaviour of /-butyl acetate. The hydrolysis of this ester has been studied by many authors. Some recent results for aqueous sulphuric acid at 25°C ire available from Bunton et al.56, and these data are included in Fig. 6. The plot for this ester shows a very strongly negative slope, which can be shown to be in the region of— 9 to — 10 by a plot on expanded scales. This is ail aberration from the behaviour expected by Yates and McClelland, and could arise from a breakdown of their approximations in the case of this ester, or from a factor not allowed for by them. Since all the other acetate esters used seem to behave... 

V. Sihvonen studied the electrolysis of nitric acid with platinum or copper cathodes, with a cathode of mercury in phosphoric or sulphuric acid at 25°-40° and also the electrolysis of hydroxylamine with the same cathodes. His idea of the mechanism of the reactions in the two cases is illustrated by ... 

The relationship is unusual in the former case, in that it involves migration of an electron from the tr-bond into the 77-system when the proton is lost. That such reactions do not occur in 100% sulphuric acid sets a limit on the pK values for the radicals studied, and it would appear that one method of stabilization of the neutral radicals would be to protonate them in an acidic medium. 

Brand Mid his co-workers [17] CMiied out extensive studies on the absorption spectra of Momatic compounds in sulphuric acid solutions, i.e. in a strongly proto-nizing solvent. They found that under the influence of the sulphuric acid the maximum of the nitro group shifted. These shifts were most pronounced in the case of mononitro compounds, Mid the least in the case of trinitro compounds. They were smaller when sulphuric acid was used as a solvent, Mid larger when oleum was used. The absorption curves for 2,4-dinitrotoluene Me shown in Fig. 

It was first suggested by Edeleanu (41), in die case of stainless steels, that a potentiostat approach permits a quantitative study of electroetching. The potential of an electrode immersed in a given electrolyte can be maintained constant with the potentiostat such as that used by Roberts (42). There is a simple relationship between the potential of the electrode and the dissolution rate. Fig. 15 shows the type of curve obtained with an 18/8 stainless steel in 20% sulphuric acid solution at 25°C. The concentration of the electrolyte, temperature, and the composition of the steel are important parameters. If the... 

Simpler procedures are of course available for the preparation and characterisation of carbenium ions in solution, particularly for the more stable ones. Concentrated sulphuric acid was extensively used as protogenic medium before the superacid mixtures were shown to be superior, but many of the spectroscopic assignements in those earlier studies were later proved erroneous, particularly in the case of such reactive entities as the 1-phenylethylium ion Model monomers which cannot polymerise because of steric hindrance can generate fairly stable carbenium ions by interacting with Lewis or Br nsted acids in normal cationic polymerisation conditions. Thus, 1,1-diphenylethylene and its dimer, and 1,1-diphenylpropene give rise to typical visible absorption bands from which the concentration of the corresponding diphenyl-methylium ions can be accurately calculated. As for carbenium ions capable of forming stable salts, their synthesis and characterisation is obviously easy. 

Shi JP, Khan A A, Harrison RM (1999) Measurements of ultrafine particle concentration and size distribution in the urban atmosphere. Sci Total Environ 235 51-64 Siefert RL, Pehkonen SO, Erel Y, Hoffmatm MR (1994) Iron photochemistry of aqueous suspensions of ambient aerosol with added organic-acids. Geochim Cosmochim Acta 58 3271-3279 Sievering H, Boatman J, Gorman E, Kim Y, Anderson L, Ennis G, Luria M, Pandis S (1992) Removal of sulphur from the marine boimdaiy layer by ozone oxidation in sea-salt aerosols. Nature 360 571-573 Siffert C, Sulzberger B (1991) Light-induced dissolution of hematite in the presence of oxalate-A case-study. Langmuir 7 1627-1634... 

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