Acidic character

Eigure 1.7) [59]. Similarly, benzeneboronic adds of type 15 (Equation 5), which benefit from anchimeric partidpation of the ortho-dialkylaminomethyl group, display a relatively low pK of about 5.2 [61]. In this case, the actual first pK is that of ammo- 

Figute1.7 Ionization equilibrium for special types of boronic acids. 

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Notice that the acidic character is associated with the ability of aluminium to increase its covalency from three in the oxide to six in the hydroxoaluminate ion, [Al(OH)g] the same abihty to increase covalency is found in other metals whose oxides are amphoteric, for example... 

The reason for this relative lack of reactivity of 2-methylthiazoIium is probably due to the too-weak nucleophilic character of its carbon-2. For example, any /S-alkoxyalcene (29) derivatives resulting from the condensation of o-ester could never have been isolated, whereas they constitute the essential intermediate step in trimethine syntheses for rings of acidic character (64). However, even if a negative 5-substituent such as ethoxy-carbonyl increases the yield (61) by promoting independently the possible formation of the methylene base, it may be stressed that the presence of this base is not the essential condition of the reaction, since the isolated anhydrobase itself is not reactive toward the o-ester (Scheme 41). 

The higher members of the series decrease the surface tension of aqueous solutions well below the point possible with any type of hydrocarbon surfactant, although in practice because of their strong acid character and solubiUty characteristics, more commonly salts and other derivatives are employed. A 0.1% solution of C F COOH has a surface tension of only 19 mN/m (dyn/cm) at 30°C (6). 

The aromatic ring of alkylphenols imparts an acidic character to the hydroxyl group the piC of unhindered alkylphenols is 10—11 (2). Alkylphenols unsubstituted in the ortho position dissolve in aqueous caustic. As the carbon number of the alkyl chain increases, the solubihty of the alkah phenolate salt in water decreases, but aqueous caustic extractions of alkylphenols from an organic solution can be accomphshed at elevated temperatures. Bulky ortho substituents reduce the solubihty of the alkah phenolate in water. The term cryptophenol has been used to describe this phenomenon. A 35% solution of potassium hydroxide in methanol (Qaisen s alkah) dissolves such hindered phenols (3). 

The acidic character of siUca is shown by its reaction with a large number of basic oxides to form siUcates. The phase relations of numerous oxide systems involving siUca have been summarized (23). Reactions of siUca at elevated temperatures with alkaU and alkaline-earth carbonates result in the displacement of the more volatile acid, CO2, and the formation of the corresponding siUcates. Similar reactions occur with a number of nitrates and sulfates. Sihca at high temperature in the presence of sulfides gives thiosiUcates or siUcon disulfide, SiS2. 

The weakly acidic character of acycHc polyhydric alcohols increases with the number of hydroxyl groups, as indicated by the piC values in aqueous solution at 18°C (13). 

The acidic character of the hydrogen atoms of C-methyl groups linked to the pyrazolium ring (Figure 22 Section 4.04.2.1.1(11)) facilitates a number of reactions difficult to carry out with neutral pyrazoles. Since efficient methods of dealkylation have been described (Section 4.04.2.3.lO(ii)), the synthesis via the pyrazolium salt is a useful alternative. The same behaviour is observed for indazolium salts, for example, nucleophilic addition to aromatic aldehydes (78JOC1233). 

It was noted that the content of functional groups on the surface of studied A1,03 was 0,92-10 mol/g of acid character for (I), FOS-IO mol/g of basic character for (II). The total content of the groups of both types was 1,70-lO mol/g for (III). The absence of appreciable point deviations from a flat area of titration curves in all cases proves simultaneously charges neutralization character on the same adsoi ption centers and non-depending on their density. The isoelectric points of oxide surfaces have been detenuined from titration curves and have been confirmed by drift method. 

Sulplianilic Acid.—The acid characters of this substance, whuh is both base. and acid, are more piominently dereloped than the basic character. Neveithcless it leacts with nitrous aud like a primary amine, and forms a diazoniiim s.alt, which has the follovving constitution (sec Piep. 62, p. 161)... 

It years, there has been a considerable growth of interest in the catalysis of organic IS by inorganic reagents supported on high surface areas, Envirocat, a new family of supported reagents, which exhibits both Bronstead and Lev/is acid character, are ideal for environmentally friendly chemistry. These reagents are non-toxic powders that can be easily... 

Ursaure, /. a urelde of acid character, as barbi turic or oxaluric acid, a -uric acid. 

Those salts which hydrolyse to give an acid solution, e.g. the strong acid salts of aluminium, iron and, to a lesser extent, calcium, give solutions which may be very corrosive to cast iron, particularly if they are well aerated. When oxidising salts are also present in these acid solutions, a particularly dangerous system may be created. It is owing to this combination of oxidising and acidic character that mine waters are so corrosive. 

In addition to their concern regarding spray residues of the lead arsenate and organic types, canners whose fruits are sprayed with lime sulfur have reason for concern over the presence of sulfur in their canned products. The presence of elemental sulfur or simple compounds of reduced sulfur in canned foods, especially in those products having an acid character, is objectionable, not only because it may be the source of sulfide flavor and staining, but also because it may actively accelerate the formation of hydrogen by the corrosive action of the product on the container. 

One limitation of these noncatalyzed allyl(trialkyl)- and allyl(triaryl)stannane-aldehyde reactions is the high temperature required unless the aldehyde is activated towards nucleophilic attack. Allyltin halides are much more reactive because of their enhanced Lewis acid character however 2-butenyltin halides show reduced syn I anti selectivity45, and give other products including linear homoallylic alcohols and tetrahydropyrans47. 

TABLE 10.7 Acidic Character and ICa Values of Common Cations in Water ... 

The pattern of oxidation states correlates with the pattern of acid-base behavior of d-metal oxides. Although most d-metal oxides are basic, the oxides of a given element show a shift toward acidic character with increasing oxidation number, just as the oxoacids do (recall Section 10.10). The family of chromium oxides is a good... 

The range of oxidation states of a d-block element increases toward the center of the block. Compounds in which the d-block element has a high oxidation state tend to be oxidizing those in which it has a low oxidation state tend to be reducing. The acidic character of oxides increases with the oxidation state of the element. 

Metallation and oxymetallation reactions have been observed with the salts of only a few metals, namely mercury(II) (66, 67), thallium(III) (66,67), lead(IV) (66, 67), palladium(II) (100), gold(III) (63), and platinum-(II) (29). These facts correlate well with what Chatt (1) has termed class b, and Pearson (130) has called "soft acid character. Soft acids are characterized by low charge, large size, and, often, d electrons in their outer shell. No class b metal is known, in fact, which contains fewer than five d... 

Since aromatic substitutions, aliphatic substitutions, additions and conjugate additions to carbonyl compounds, cycloadditions, and ring expansion reactions catalyzed by Fe salts have recently been summarized [17], this section will focus on reactions in which iron salts produce a critical activation on unsaturated functional groups provided by the Lewis-acid character of these salts. 

The A1 atom in AICI3 has Lewis acid character, whereas the Cl atoms are Lewis bases. The compound... 

C21-0058. Prepare a list of the industrial reactions described In Section 21-1 that exploit the Brc )nsted acid character of sulfuric acid. 

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