Alcohols acid-base properties

The aim of this study is to develop model reaction for the characterization of the acidity and basicity of various transition aluminas, the experimental conditions being close to that for catalysis use. Among various model reactions, the transformation of cyclopentanol and cyclohexanone mixture was chosen for this work. Indeed, this reaction was well known for estimating simultaneously the acid-base properties of oxide catalysts [1], Two reactions take place the hydrogen transfer (HT) on basic sites and the alcohol dehydration (DEH) on acid sites. The global reaction scheme is shown in Figure 1. 

Di Cosimo et al. investigated the structural requirements and reaction pathways in condensation reactions of alcohols, using Mg/Al mixed oxides obtained by decomposition in N2 at 673 K for 4 h of LDH precursors with a wide range of composition [53], and found that the mechanistic pathway of the condensation reactions is affected not only by the catalyst acid-base properties but also by the chemical nature of the alcohols as well as steric factors. 

A good example of the use of the functional-group concept is for acid-base properties. Alcohols, ROH, are structurally related to water, HOH, in that both possess a hydroxyl function. We may then expect the chemistry of alcohols to be similar to that of water. In fact, both are weak acids because the OH group has a reactive proton that it can donate to a sufficiently strongly basic substance, written as B here ... 

Apart from zeolites and ion-exchange resins (Sections 4 and 5), the main classes of catalyst which are active for dehydration are salts (usually sulphates, phosphates, and to a lesser extent, carbonates) and oxides (single and mixed). A large proportion of research has been devoted to a correlation of acid-base properties with activity for dehydration and dehydrogenation of alcohols, the two reactions being closely associated. 

Usually these reactions have been studied in water or in other protic solvents such as the alcohols. Thus, the acid-base properties of the solvent are important in determining the relative strength of acids and bases which are solutes in water. This leads to the definition of two other types of proton transfer reaction, namely, the protolysis reaction,... 

Various solids consisting of magnesium and sodium-magnesium mixed orthophosphates were synthesized and used as catalysts in the transformation of 2-hexanol. The solids obtained were characterized by using various elucidation techniques. In particular, acid-base properties were determined by several methods. The solids were found to be active in the dehydration and dehydrogenation of the alcohol studied, and to be highly selective towards the dehydrogenation product in some instances. In addition to surface properties, the structure and composition of the catalysts -particularly their sodium content- appear to play essential roles in their catalytic behaviour. 

CH4, a major constituent of natural gases, can be an important carbon resource however, CH4 is a less valuable substance because of its low reactivity. It is important to utilize this stable substance by reaction with other stable and less valuable substances such as CO2 and H2O. Reactions between CH4 and CO2 or H2O lead to CO and H2 [1]. The mixture of CO and H2 is a raw material for synthesis of alcohols, carbonylatlon reactions, and the Fischer-Tropsch synthesis [2]. In this work, we studied basically CH4 reforming by CO2 and H2O over Pd, Pt, and Rh supported on several oxide carriers, and the main object was to stress the effect of acid-base properties of the carriers on the activity of the above metals for the CH4 reforming. 

Formation of the tetrahedral intermediate carbinolamine and subsequent elimination of water are amenable to acid-base catalysis and do not require a metal surface. The relative rates of adduct formation and subsequent dehydration to imine or enamine depend on the structure of alcohol and amine, and on the nature and strength of acidic and basic sites on the catalyst surface. It must be stressed that several side-reactions (e. g. dimerization and oligomerization, dehydration) are also acid or base-catalyzed, and good selectivity for the desired product requires proper tuning of the redox and acid-base properties of the catalyst. This is crucial in catalyst development when choosing a suitable support, additive, or modifier. Even traces of impurities remaining on the surface from the catalyst precursor can strongly influence product distribution [10]. 

It is shown in [4] that the presence of two types of centres possessing the discriminate reductive-oxidation and acid-base properties and participating in transformation processes of an alcohol molecule is an essential requirement to achieve high sensor response values when alcohol detection is mentioned. Alcohol detection is considered as a multi-step process involving both red-ox and acid-base interactions. Oxide phases within composites differ by oxygen-oxide surface bonding energy which can be the relative measure of oxide activity in oxidation reactions. The reactivity of... 

Previous results [4-8] for the same reaction on zirconia-, ceria-, and lanthana-based catalysts showed a correlation between the acid-base properties (in terms of both the concentration and the strength of the sites) of the samples and their catalytic behaviour. When the number of the acid sites is sensibly higher than that of the basic ones, the main product is the undesired 2-alkene, which forms through an El mechanism (Saytzeff orientation). The alcohol adsorbs on the oxide surface through the interaction between the OH group and an acid site the rupture of the C-OH bond leads to the carbocation which mainly gives the... 

CHEMICAL REACTIONS OF ALCOHOLS 13.5.1 Acid-Base Properties... 

Mg-Al mixed oxides obtained by thermal decomposition of anionic clays of hydrotalcite structure, present acidic or basic surface properties depending on their chemical composition [1]. These materials contain the metal components in close interaction thereby promoting bifunctional reactions that are catalyzed by Bronsted base-Lewis acid pairs. Among others, hydrotalcite-derived mixed oxides promote aldol condensations [2], alkylations [3] and alcohol eliminations reactions [1]. In particular, we have reported that Mg-Al mixed oxides efficiently catalyze the gas-phase self-condensation of acetone to a,P-unsaturated ketones such as mesityl oxides and isophorone [4]. Unfortunately, in coupling reactions like aldol condensations, basic catalysts are often deactivated either by the presence of byproducts such as water in the gas phase or by coke build up through secondary side reactions. Deactivation has traditionally limited the potential of solid basic catalysts to replace environmentally problematic and corrosive liquid bases. However, few works in the literature deal with the deactivation of solid bases under reaction conditions. Studies relating the concerted and sequential pathways required in the deactivation mechanism with the acid-base properties of the catalyst surface are specially lacking. 

The acid-base properties of amines are an extension of what you know about ammonia They are weaker acids and stronger bases than are water or alcohols. It will repay you many times over, however, to go over the information involving pAS/s of these molecules. The qualitative ability to handle acid-base concepts is one of the more useful capabilities you can take out of a course in organic chemistry. 

Attempts have been made of correlating the oxide acid-base properties, as determined by calorimetric techniques, and the corresponding catalytic activity and selectivity for the decomposition of propan-2-ol [126] and 4-methylpentan-2-ol [125]. As discussed in ref [127], however, this sort of correlations, in addition to the limitations inherent to the cleaning procedure applied in the calorimetric measurements, has a second difficulty under reaction conditions, the interaction of alcohols with the surface of rare earth sesquioxides leads to the formation of carboxilate and carbonate species which certainly will modify the acid-base properties of the actual catalytic surface. 

The acid-base properties of zeolites or oxides are often studied by measuring the selectivities to the different products in the decomposition of alcohols and particularly isopropanol. The rate of propene formation can very often be correlated to the number of acidic sites determined by ammonia adsorption. A relationship has been found between the strength of the acid sites of bulk oxides, as determined by ammonia adsorption microcalorimetry [95], and the activation energy of dehydration, while the activation energy of dehydrogenation was independent of the strength of the sites [149]. 

Magnesium indium oxide (Mglu204) is a multication oxide having two types of cation centers possessing different reductive-oxidative and acid-base properties. Also, participating in the processes of the alcohol molecule transformation causes high sensor response when alcohol detection is considered. The centers of one type can suitably participate in adsorption-desorption processes of alcohol molecules, whereas complete oxidation of intermediates proceeds effectively at the centers of another type. 

Polyacrylates as binders consist of copolymers of acrylate and methacrylate esters. Other unsaturated monomers (e.g., styrene and vinyltoluene) may also be incorporated, but usually to a lesser extent. Copolymers formed exclusively from acrylates and/or methacrylates are termed straight acrylics. The comonomers differ as regards the alcohol residues of the ester group, which also allow incorporation of additional functional groups. Choice of suitable monomers allows wide variation of the physical and chemical properties of the resulting polymer. Hydrophilicity, hydrophobic-ity, acid base properties as well as can be adjusted resins containing hydroxyl, amine, epoxy, or isocyanate groups can also be produced. 

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