On the mechanism of dehydration of secondary alcohols over alumina catalyst. III. Dehydration of substituted 1-phenylethanols
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Dehydration reaction
Sorbitol dehydration in high temperature liquid water proceeded at 523–573 K without adding any acid catalysts. Anhydrosorbitols (1,4-anhydrosorbitol (1,4-AHSO), 2,5-anhydrosorbitol (2,5-AHSO) and 1,5-anhydrosorbitol (1,5-AHSO)) were produced by the monomolecular dehydration of sorbitol, and isosorbide was produced by the stepwise dehydration of 1,4-AHSO. The formation rates of 1,4-AHSO and 2,5-AHSO (five-membered cyclic ethers) from sorbitol dehydration were much larger than that of 1,5-AHSO (six-membered cyclic ether), and 1,4-AHSO was the main product of the monomolecular dehydration of sorbitol. The dehydration rate of sorbitol to 1,4-AHSO was faster than that of 1,4-AHSO to isosorbide; therefore, 1,4-AHSO could be obtained as an intermediate product. A kinetic analysis of sorbitol dehydration in high temperature liquid water showed that the maximum yield of 1,4-AHSO from the dehydration of sorbitol increased with decreasing reaction temperature (for example, 80% at 500 K) and that the maximum yield of isosorbide was 57% at 590 K for 1 h. 1,4-AHSO and isosorbide could be produced selectively from sorbitol dehydration in high temperature liquid water by controlling both the reaction temperature and reaction time.
Isosorbide
Dehydration reaction
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Dehydration reaction
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Abstract The dehydration of t-butyl alcohol (TBA) using various heteropoly compound (HPC) catalysts has been studied. Taking the adsorption of water on the surface of the catalyst into consideration, it is presumed that the dehydration of liquid TBA is governed by a Langmuir–Hinshelwood-like mechanism. Also, the change in the catalytic activity with the amount of HPC supported on the silica suggests that TBA is dehydrated through a pseudo-liquid mechanism in which a few layers of the HPC supported take part in the catalytic reaction. The layer thickness, regarded as a pseudo-liquid phase, depends markedly on the kind of HPC supported. For the dehydration of gaseous TBA, on the contrary, the reaction is found to be of the zero-order; it proceeds through in outer-surface mechanism in which only the outer layer of HPC is effective.
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The effect of pressure on the dehydration reaction of interlayer water in Na-montmorillonite (SWy-1)
The temperature of the dehydration of interlayer water of Na-montmorillonite (SWyl, American Clay Mineral Society Source Clay) is determined at pressures to I kbar, using differential thermal analysis (DTA). Two dehydration reactions occur, about 40 and 100C above the boiling curve of water. Above the critical point of water the dehydration reactions show only a modest increase of temperature with pressure. No significant differences in temperature were found using different heating rates and different size fractions, as defined by their hydraulic diameter. The presence of two dehydration reactions suggests that not all interlayer water is bonded equally; a distinction may be made between weakly bonded and strongly bonded water. It is concluded that hydrated Namontmorillonite is stable under normal pressure and temperature distributions in sedimentary basins; in these basins dehydration must involve more complex chemical interactions with pore fluids. The large increase in the stability of a hydrated montmorillonite with a modest increase in pressure may have important bearing in its use in nuclear waste disposal.
Dehydration reaction
Differential thermal analysis
Boiling point
Thermal Stability
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Dehydration reaction
Thermogravimetric analysis
Lithium hydroxide
Lithium chloride
Hydration reaction
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Dehydration reaction
Autocatalysis
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Dehydration reaction
Fluid catalytic cracking
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Following the dehydration of certain hydrated salts in high vacuum, an evolution of energy occurs. X-ray studies have shown that this energy liberation is due to an amorphous to crystalline transition in the products of dehydration. Measurements have been made of the integral heats of solution of the dehydration products of copper sulphate pentahydrate and zinc sulphate hexahydrate formed at a series of low dehydration pressures. From these measurements, the fractional amounts of relatively high energy amorphous products formed at a series of low dehydration pressures have been calculated. It has been found that as the water vapor pressure near the reaction interface is increased, the fractional amount of high energy product decreases to a minimum, then increases, passes through a maximum, followed by a slow decrease. These results are interpreted in terms of a possible dehydration mechanism, and an estimation made of the effect of water vapor pressure on the over-all reaction rate. In the course of this study, the integral heats of solution of the crystalline hydrates involved have been determined. The heats of transition of the amorphous to crystalline forms of copper and zinc sulphate monohydrates are reported.
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Gas phase dehydration of isoamylalcohol on spherical alumina catalyst was studied by a packed bed reactor. The reaction was operated under the constant conditions of 350°and the atmospheric pressure. The main products were 3-methyl-1-butene, 2-methyl-1-butene, 2-methyl-2-butene and water, and we could neglect the other byproducts for our calculation. The reverse process of dehydration reaction might be neglected. By the analysis of our results (Fig 3, 4), this dehydration reaction was summarised as equations (7)-(12), and we determined the rate-constants from our results.
Dehydration reaction
Butene
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Dehydration Reaction of Fructose to 5-Hydroxymethylfurfural over Various Keggin-type Heteropolyacids
Four Keggin-type heteropolyacids, (X = P and Si, M = W and Mo) that were substituted with heteroatom and polyatom were applied to the dehydration reaction of fructose to 5-hydroxymethylfurfural (HMF). The results showed that the acid became stronger when the heteroatom and polyatom were substituted with P and W than the cases of Si and Mo, respectively. However, the amount of acidic sites increased with the decrease in the acid strength, resulting in the change of the catalytic activity of heteropolyacids in the dehydration reaction. The experimental results revealed that four different heteropolyacids produced similar amounts of HMF via the dehydration reaction of fructose due to the counterbalancing effect between the amount of active sites, which is related to the catalytic activity of heteropolyacids, and the softness of polyanion. In addition, it was observed that the prepared heteropolyacids showed good structural stability after heat treatment at .
Heteroatom
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Keggin structure
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