Amphoterization reaction

The amphoteric reaction between two water molecules is endothermic, which means the reaction requires the input of heat energy in order to proceed ... 

Scheme 1 Solid-state amphoteric reaction of alumina...

The proteins vary markedly in chemical properties some are basic and form well characterized salts with active acids, and others are of distinctly acid character. The majority of proteins, however, are neither strongly acidic nor basic, and, consequently, form salts which are readily hydrolyzed by water. They possess an amphoteric reaction, acting as bases towards acids and as acids toward bases. 

The adsorption mechanism of H" and OH has long been attributed to the amphoteric reaction of the surface hydroxide groups -M-OH [4]. This is schematically represented as... 

An alternative derivation of Eq. (16), based on the amphoteric reactions of the surface hydroxide groups, given as Eq. (1), has been proposed by Levine and Smith [16]. Using the random mixing approximation for the distribution of the three types of surface sites [i.e., neutral, positive, and negative sites, as shown in Eq. (1)], these authors were able to derive an expression for the dependence of cm on the oxide surface. The derivation has also been outlined by Smith [2], and the modified Nemst equation can be written as... 

Other displacement reactions " 54-56 have been considered as amphoteric reactions ... 

A Pourbaix diagram also shows that permanganate ions must react with manganous ions, with the formation of manganese dioxide. Their preponderance areas are indeed disconnected. The reaction, which is a retrodismutation (or amphoterization) reaction, is... 

The use of polymeric acids and bases as catalysts has been reviewed by Sherrington, " and amphoteric reactions have been described. ... 

Amphoteric reactions such as those of the hydroxides of aluminum and zinc also occur in other solvents. When potassium hydroxide is added to insoluble aluminum hydroxide in water, the following reaction takes place ... 

A major difficulty in an inorganic text is to strike a balance between a short readable book and a longer, more detailed text which can be used for reference purposes. In reaching what we hope is a reasonable compromise between these two extremes, we acknowledge that both the historical background and industrial processes have been treated very concisely. We must also say that we have not hesitated to simplify complicated reactions or other phenomena—thus, for example, the treatment of amphoterism as a pH-dependent sequence between a simple aquo-cation and a simple hydroxo-anion neglects the presence of more complicated species but enables the phenomena to be adequately understood at this level. 

The dissociation, or autoprotolysis constant for a solvent, SH, relates the concentration of the protonated solvent, SH2, to that of the deprotonated solvent, S . For amphoteric solvents, which can act as both proton donors and proton acceptors, the autoprotolysis reaction is... 

Chloroacetic acid can be esterified and aminated to provide useful chemical intermediates. Amphoteric agents suitable as shampoos have been synthesized by reaction of sodium chloroacetate with fatty amines (4,5). Reactions with amines (6) such as ammonia, methylamine, and trimethylamine yield glycine [66-40-6J, sarcosine [107-97-17, and carhoxymethyltrimethylammonium chloride, respectively. Reaction with aniline forms /V-phenylglycine [103-01 -5] a starting point for the synthesis of indigo (7). 

Lead Monoxide. Lead monoxide (litharge), PbO, occurs as a reddish alpha form, which is stable up to 489°C where it transforms to a yellow beta form (massicot). The latter is stable at high temperatures. The solubihty of a-PbO ia water is 0.0504 g/L at 25°C the solubihty of the p-PbO is 0.1065 g/L at 25°C (40). Lead monoxide is amphoteric and dissolves ia both acids and alkahes. In alkahes, it forms the plumbite ion PbO - The monoxide is produced commercially by the reaction of molten lead with air or oxygen ia a furnace. Black or gray oxide is manufactured by the Barton process, by the oxidation of atomized molten lead ia air, as well as by the ball mill process, ia which metallic lead balls of high purity are tumbled ia the mill to form partially oxidized lead particles. 

Manganese Hydroxide. Manganese hydroxide [18933-05-6] is a weaMy amphoteric base having low solubihty in water. Mn(OH)2 crystals are reported to be almost pure white and darken on exposure to air. Manganese dihydroxide occurs in nature as the mineral pyrochroite and can also be prepared synthetically by reaction of manganese chloride and potassium hydroxide that is scmpulously free of oxygen. The entire reaction is conducted under reducing conditions (36). 

A wide variety of quaternaries can be prepared. Alkylation with benzyl chloride may produce quaternaries that are biologically active, namely, bactericides, germicides, or algaecides. Reaction of a tertiary amine with chloroacetic acid produces an amphoteric compound, a betaine. 

Imidazolinium Derivatives. Amphoteric imida2olinium derivatives are prepared from the 2-aLkyl-l-(2-hydroxyethyl)-2-imida2olines and from sodium chloroacetate. The most likely stmcture of the reaction product is as follows (109) ... 

Phenols. Phenols are unreactive toward chloroformates at room temperature and at elevated temperatures the yields of carbonates are relatively poor (< 10%) in the absence of catalysis. Many catalysts have been claimed in the patent Hterature that lead to high yields of carbonates from phenol and chloroformates. The use of catalyst is even more essential in the reaction of phenols and aryl chloroformates. Among the catalysts claimed are amphoteric metals or thek haUdes (16), magnesium haUdes (17), magnesium or manganese (18), secondary or tertiary amines such as imidazole (19), pyridine, quinoline, picoline (20—22), heterocycHc basic compounds (23) and carbonamides, thiocarbonamides, phosphoroamides, and sulfonamides (24). 

QuaterniZation. Choline chloride [67-48-1] was prepared ia nearly quantitative yield by the reaction of trimethylamine [121-44-8] with ethylene chlorohydrin at 90—105°C and 981—1471 kPa (10—15 kg/cm ) pressure (44). Precursors to quaternary ammonium amphoteric surfactants have been made by reaction of ethylene chlorohydrin with tertiary amines containing a long chain fatty acid group (45). 

Many of the surfactants made from ethyleneamines contain the imidazoline stmcture or are prepared through an imidazoline intermediate. Various 2-alkyl-imidazolines and their salts prepared mainly from EDA or monoethoxylated EDA are reported to have good foaming properties (292—295). Ethyleneamine-based imida zolines are also important intermediates for surfactants used in shampoos by virtue of their mildness and good foaming characteristics. 2- Alkyl imidazolines made from DETA or monoethoxylated EDA and fatty acids or their methyl esters are the principal commercial intermediates (296—298). They are converted into shampoo surfactants commonly by reaction with one or two moles of sodium chloroacetate to yield amphoteric surfactants (299—301). The ease with which the imidazoline intermediates are hydrolyzed leads to arnidoamine-type stmctures when these derivatives are prepared under aqueous alkaline conditions. However, reaction of the imidazoline under anhydrous conditions with acryflc acid [79-10-7] to make salt-free, amphoteric products, leaves the imidazoline stmcture essentially intact. Certain polyamine derivatives also function as water-in-oil or od-in-water emulsifiers. These include the products of a reaction between DETA, TETA, or TEPA and fatty acids (302) or oxidized hydrocarbon wax (303). The amidoamine made from lauric acid [143-07-7] and DETA mono- and bis(2-ethylhexyl) phosphate is a very effective water-in-od emulsifier (304). 

Correspondingly, amphoteric aluminum materials suffer active corrosion by the anodic partial reaction ... 

The primary corrosion product PbHj is unstable and decomposes in a subsequent reaction into lead powder and hydrogen gas. Figures 2-11 and 2-12 are typical examples of cathodic corrosion of amphoteric and hydride-forming metals. 

This last reaction is typical of many in which F3CIO can act as a Lewis base by fluoride ion donation to acceptors such as MF5 (M = P, As, Sb, Bi, V, Nb, Ta, Pt, U), M0F4O, Sip4, BF3, etc. These products are all white, stable, crystalline solids (except the canary yellow PtFe ) and contain the [F2CIO] cation (see Fig. 17.26h) which is isostructural with the isoelectronic F2SO. Chlorine trifluoride oxide can also act as a Lewis acid (fluoride ion acceptor) and is therefore to be considered as amphoteric (p. 225). For example KF, RbF and CsF yield M [F4C10] as white solids whose stabilities increase with increasing size of M+. Vibration spectroscopy establishes the C4 structure of the anion (Fig. 17.29g). 

The nitrile may best be saponified with methyl alcoholic potash while heating to 190° to 200°C with application of pressure. After the methyl alcohol has evaporated the salt is introduced into water and by the addition of dilute mineral acid until the alkaline reaction to phenolphthalein has just disappeared, the amphoteric 1-methyl-4-phenyl-piperidine-4-carbOxylic acid is precipitated while hot in the form of a colorless, coarsely crystalline powder. When dried On the water bath the acid still contains 1 mol of crystal water which is lost only at a raised temperature. The acid melts at 299°C. Reaction with ethanol yields the ester melting at 30°C and subsequent reaction with HCI gives the hydrochloride melting at 187° to 188°C. 

The data given in Tables 1.9 and 1.10 have been based on the assumption that metal cations are the sole species formed, but at higher pH values oxides, hydrated oxides or hydroxides may be formed, and the relevant half reactions will be of the form shown in equations 2(a) and 2(b) (Table 1.7). In these circumstances the a + will be governed by the solubility product of the solid compound and the pH of the solution. At higher pH values the solid compound may become unstable with respect to metal anions (equations 3(a) and 3(b), Table 1.7), and metals like aluminium, zinc, tin and lead, which form amphoteric oxides, corrode in alkaline solutions. It is evident, therefore, that the equilibrium between a metal and an aqueous solution is far more complex than that illustrated in Tables 1.9 and 1.10. Nevertheless, as will be discussed subsequently, a similar thermodynamic approach is possible. 

Reaction (22) shows that Al(OH)3 has the properties of an acid, since it reacts with the base OH-. A substance that acts as an acid under some conditions and as a base under other conditions is said to be amphoteric. The electronic situation in Al(OH)3 is such that it can either accept a proton (act as a base) or react with OH- (act as an acid). We will see in Chapter 22 that several other hydroxides also show amphoteric behavior. 

Combining volumes, law of, 26, 236 Combustion, heat of hydrogen, 40 Complex ions, 392 amphoteric, 396 bonding in, 395 formation, 413 geometry of. 393 in nature, 396 isomers, 394 linear, 395 octahedral, 393 significance of, 395 square planar, 395 tetrahedral, 394 weak acids, 396 Compound, 28 bonding in, 306 Concentration and equilibrium, 148 and E zero s, 213 and Le Chatelier s Principle, 149 effect on reaction rate, 126, 128 molar, 72... 

The product of the second reaction is sodium aluminate, which contains the alumi-nate ion, Al(OH)4. Other main-group elements that form amphoteric oxides are shown in Fig. 10.7. The acidic, amphoteric, or basic character of the oxides of the d-block metals depends on their oxidation state (Fig. 10.8 also see Chapter 16). 

---