Alkali concentration reactions

The rate of removal of successive triethylsilyl groups in the sequence (11) - (12) - (13) can be measured and exact conditions of medium composition (MeOH—H2O), alkali concentration, reaction temperature and time worked out so as to optimize the yield of (12). The cleavage is then interrupted by lowering the pH, the monosilyltetrayne (12) is separated by column chromatography (silica gel) from (13) and residual (11) and oxidatively coupled to give the bis-silylocta-acetylene (14). Repetition of this sequence affords either pure octa-acetylene (16) or the hexadeca-acetylene (17) via (15). Variations on the whole procedure yield solutions of all the parent poly-ynes, H(C )nH, (n = 4 — 12) [21]. A further example (Fig. 1.14) of... 

PETP flakes produced from used soft drinks bottles were subjected to alkaline hydrolysis in aqueous sodium hydroxide. A phase transfer catalyst (trioctylmethylammonium bromide) was used to enable the depolymerisation reaction to take place at room temperature and under mild conditions. The effects of temperature, alkali concentration, PETP particle size, PETP concentration and catalyst to PETP ratio on the reaction kinetics were studied. The disodium terephthalate produced was treated with sulphuric to give terephthalic acid of high purity. A simple theoretical model was developed to describe the hydrolysis rate. 17 refs. 

The results of experiments with crude oil fractions in this study also suggest that several species were present in reaction interface. There are mainly long chain carboxylic acids. The difference in size and structure is expected to give them different pka values. As a result, different surface activity (i.e., IFT value) is obtained with different levels of alkali concentration. Crude oil fractions with lower surface activity only yield surface inactive salts that may appear as precipitates at the interface. 

The rate of reduction of a vat dye depends partly on the intrinsic chemical properties of the dye and partly on the size and physical form of the dispersed particles undergoing this reaction. The physical factors are much less important than the chemical aspects [26]. The vatting process entails conversion of the insoluble keto form into the soluble sodium enolate (section 1.6.1). The reaction takes place in two stages at ambient temperature. Extremely rapid reduction to the hydroquinone is followed by slower dissolution in the alkaline solution. At higher temperatures, however, the dissolution rate approximates more closely to the rate of reduction. Temperature and dithionite concentration are the important variables and the rate of reduction is much less dependent on dye or alkali concentration. 

The rate of decomposition is faster in mineral acids with evolution of methane. However, in hot concentrated alkalies the reaction is very rapid, forming alkali metal beryllate and methane ... 

The mechanism of the inhibitive action of LiOH proposed by Stark et al. [7] is attributed to the formation of lithium silicate that dissolves at the surface of the aggregate without causing swelling [7], In the presence of KOH and NaOH the gel product incorporates Li ions and the amount of Li in this gel increases with its concentration. The threshold level of Na Li is 1 0.67 to 1 1 molar ratio at which expansion due to alkali-silica reaction is reduced to safe levels. Some workers [22] have found that when LiOH is added to mortar much more lithium is taken up by the cement hydration products than Na or K. This would indicate that small amounts of lithium are not very effective. It can therefore be concluded that a critical amount of lithium is needed to overcome the combined concentrations of KOH and NaOH to eliminate the expansive effect and that the product formed with Li is non-expansive. 

In contrast to the results described so far, the temperature has little influence on particle size distribution. The increase in the velocity of the reaction which takes place as the temperature is raised (Figure 4, top) does not influence the position of the maximum at all. The peaks, however, become more pronounced indicating that more uniform crystals are formed (Figure 4, bottom). Thus, an increase in the alkali concentration of the liquid phase or in the Carman surface of the Si02 source raises both the speed of the reaction and the amount of fine particles in the crystalline product. Conversely the addition of even small amounts of K+ ions re-... 

Iodine dissolves without reaction in concentrated sulfuric acid and with concentrated nitric acid it reacts to form iodine pentoxide (47). Iodine reacts with alkali metal hydroxide solutions to form the corresponding hypoiodite and the rate of the reaction increases with the alkali concentration and temperature. At 50°C, the reaction is almost instantaneous ... 

Subsequently, the hypoiodite is oxidized to iodate, and this reaction is not influenced by the alkali concentration, temperature, or iodate concentration. 

Further investigations were completed by the development of conditions under which the synthesis of pyrroles and their /V-vinyl derivatives can be performed under atmospheric pressure in a simple apparatus equipped with a stirrer and a bubbler for acetylene supply (reaction temperature 93-97°C). For this purpose, the alkali concentration must be increased in the reaction mixture to 50% of the ketoxime mass the reaction must also be run approximately twice as long. In most cases the yield of pyrroles remains high 80% (cf. Sections III.A-D). 

The order of decreasing / —/ certainly follows the order expected, for water is a better nucleophile than formic acid, and better in neutral ethanol than in formic acid-dioxan, while iodide ion is better still. The interesting thing is that both the first two reactions are kinetically of type, the rates being unaltered by addition of sodium formate, while the third reaction is of intermediate type, the rate varying with addition of alkali but not being first order in alkali concentration. Yet if our analysis is correct, the second and third reactions must both involve strong nucleophilic participation. 

Ruthenium(VI)-catalysed oxidation of propane-1,2-diol, cyclohexane-1,2-diol, and propanetriol by alkaline HCF(III) exhibits a zero-order dependence on HCF(III) and first-order dependence on Ru(VI) and the rate increased with a decrease in alkali concentration. The reaction showed a Michaelis-Menten type of behaviour with respect to the reductant. A tentative mechanism has been proposed.63 In the ruthenium(in)-catalysed oxidation of sulfanilic acid by HCF(III) in alkaline medium, the proposed ruthenium(III) active species is [Ru(H20)50H]2+.64 Iridium(III) chloride-catalysed oxidation of diethylene glycol by alkaline HCF(III) is proposed to proceed through complex formation.65... 

Hexenuronic acid (i.e., 4-deoxy-L-threo-hex-4-enopyranosyl-uronic acid) is formed under alkaline conditions by elimination of methanol from side chain residues in xylans [65] (Scheme 10). The reaction is promoted by both increasing alkali concentration and temperature [66,67]. After kraft pulping, only... 

In the case of 2-halotropones, for instance, the reaction is believed to begin with the attack of hydroxide ion onto C-l or C-3, and it results in the formation of benzoic acid or salicylaldehyde, respectively. The balance between the two processes is affected by the alkali concentration More dilute alkali favors the second route. According to Pietra (79ACR132), the key step of the first route is ring closure in the initial hydroxide adduct to give a norcaradiene intermediate. 

AR = alumina ratio (alumina modulus). ASR = alkali silica reaction. LSF = lime saturation factor. SR = silica ratio (silica modulus). C, = analytical (total) concentration of x, irrespective of species, [x] = concentration of species x. x = activity of species x. RH = relative humidity. =... 

The kinetics of the xanthation of sucrose were studied in the same year by Cherkasskaya, Pakshver, and Kargin, who determined potentiometric-ally the concentrations of the dithiocarbonate derivative and also of inorganic sulfide and trithiocarbonate. The rate of formation of 0-(sodium thiol-thiocarbonyl)sucrose was found to pass through a maximum with increasing alkali concentration, presumably due to a shift of the equilibrium in favor of side reactions in strongly alkaline solution. This result appears to parallel the qualitative findings of Lieser and Hackl for polysaccharides. 

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