Amphoteric compounds, solubility

Tetracyclines (TCs) are chemically characterized by a partially conjugated octahydronaphtacene four-ring skeleton with a carboxyamide functional group. They are amphoteric compounds soluble in polar and moderately polar solvents, and they show the ability to form strong complexes... 

Quinolones are amphoteric compounds soluble in polar organic solvents such as acetonitrile, methanol, ethanol, dimethylformamide, dichloromethane, and ethyl acetate. They are slightly soluble in water and insoluble in nonpolar solvents such as hexane, petroleum ether, and isooctane. Most of these drugs are fluorescent and are quite stable in aqueous solution toward light except nuloxacin, which is reported to be unstable. These inherent characteristics have made quinolones a difficult group of compounds to be analyzed by chromatographic methods. 

Chromium hydroxide is an amphoteric compound and exhibits minimum solubility in the pH range of 7.5 to 10.0. Effluents from chromium reduction processes should be neutralized to the range of zero solubility (pH 8.5 to 9.0) to minimize the amount of soluble chromium remaining in solution. 

Tetracycline antibiotics are closely related derivatives of the polycyclic naphtha-cenecarboxamide. They are amphoteric compounds with characteristic dissociation constants corresponding to the acidic hydroxyl group at position 3 (pK about 3.3), die dimethylamino group at position 4 (pK, about 7.5), and the hydroxyl group at position 12 (pK about 9.4). In aqueous solutions of pH 4-7, tetracyclines exist as dipolar ions, but as the pH increases to 8-9 marked dissociation of the dimethylamine cation occurs. They are soluble in acids, bases, and alcohols but are quite insoluble in organic solvents such as chloroform. Their ultraviolet spectra show strong absorption at around 270 and 360 nm in neutral and acidic solutions. Tetracyclines are readily transformed into fluorescent products in the presence of metal ions or under alkaline conditions. 

Imidazoles are amphoteric compounds with a basic, pyridine-type nitrogen (they are about 106 times more basic than oxazoles and 104 times more basic than thiazoles173), and (where the NH is unsubstituted) a weakly acidic, pyrrole-type amino nitrogen in the ring. In consequence, imidazoles readily form salts with acids and often form salts (or complexes) with metals. The sparingly soluble silver salts formed by imidazoles have been used by Giesemann et al.174 as intermediates in the synthesis of 1-triphenylmethylimidazoles. Normally, however, the salts formed with acids are more important in isolation and purification procedures. 

The solubility of amphoteric compounds should be determined at the isoelectric point if it occurs between pH 1.2 and 6.8. 

Beryllium oxide (BeO) is an extremely hard substance, much more so than the oxides of the other alkaline earths. Beryllium hydroxide (Be(OH)2) is an amphoteric compound, meaning that it is soluble in both acidic and basic solutions. In hydrochloric acid, the following reaction takes place ... 

Class B. Compounds insoluble in water and in alkali, which react with dilute HCI to yield soluble products. Amines are in this class. Diaryl- and triaiylamines are exceptions, being nearly neutral compounds. Amphoteric compounds are classed as A,(B) or A,(B). Water-insoluble acids such as calcium oxalate also are in Class B. Likewise, certain acetals, which are readily hydrolyzed by dilute acids, may fall in this class. 

A general method for estimating dissociation values, given a set of solubility and pH measurements for tyrosine and 2,8-dihydroxyadenine, is presented. Equations are derived extending solubility, pH and dissociation constant relationships from weak acids and bases to polyprotic, amphoteric compounds. Included in ttie estimation procedure is a subroutine for approximating ttiermodynamic dissociation constants."... 

Peck CC and Benet LZ, General method for determining macrodissociation constants of polyprotic amphoteric compounds from solubility measurements, /. Pharm. Sci, 67,12-16 (1978). NB Ionic strengths were NMT 0.07M and ttien extrapolated to zero. Intrinsic solubility. So = 2.89 iM. See Dihydroxyadenine for further details. 

Lead is found in nature in several minerals, but never in pure metallic form. Lead forms amphoteric compounds in +2 and +4 valence states. There are over 1,000 compounds of lead known. Most lead salts are only slightly soluble in water, and halides of lead are always anhydrous. 

Amphoteric Compounds such as amino acids that form salts with acids or bases. The hydroxides of aluminium, zinc, chromium and a few other elements are soluble in both acid and bases. Hence used to accomplish separations in water treatment. 

Students may have learnt about ionic precipitation reactions and the formation and properties of ammonia in the topic on Acids, bases and salts . They also need to draw upon knowledge of amphoteric compounds (those that react with both acids and alkalis) to understand the further reactions of the insoluble hydroxides of zinc, aluminium and lead with excess sodium hydroxide solution to form soluble salts. The reactions of the insoluble hydroxides of copper and zinc with excess ammonia solution are similar in that soluble salts are also formed. 

IR spectrum of symbioimine (35) showed absorption bands for hydroxyl (3450 cm ), iminium (1690 cm ), and sulfate (1240, 1140, 1050 cm ) groups. The NMR signal at 188.0 (C-5) implied the presence of an iminium functionality in this water-soluble amphoteric compound. Its structure, which consists of a characteristic 6,6,6-tricyclic iminium ring possessing an aryl sulfate moiety, was deduced by 2D-NMR analysis (Fig. 6). 

For the cationic compounds, the water solubility decreased in the following order A -lauroyl-L-lysine esters > A -lauroyl-L-arginine esters > N lauroyl-AlW Al -trimethyl-L-lysine esters. In contrast, for the amphoteric compounds, water solubility decreased in the following order sodium salt of At -lauroyl-AlWW -trimethyl-L-lysine > sodium salt of At -lauroyl-L-lysine > sodium salt... 

Basic, water-insoluble substances, soluble in 1.2 n HQ. Amines (except negatively substituted ones and diaryl- and triarylamines these are in group 7) (8, 10, 11, 20, 23, 29), amino acids (7, 8, 20, 23), amphoteric compounds (aminophenols, amino-thiophenols, aminosulfonamides) (20), arylsubstituted hydrazines (5, 16, 17)... 

In its chemistry, cadmium exhibits exclusively the oxidation state + 2 in both ionic and covalent compounds. The hydroxide is soluble in acids to give cadmium(II) salts, and slightly soluble in concentrated alkali where hydroxocadmiates are probably formed it is therefore slightly amphoteric. It is also soluble in ammonia to give ammines, for example Of the halides, cadmium-... 

Nloha.tes, Niobic acid is amphoteric and can act as an acid radical in several series of compounds, which are referred to as niobates. Niobic acid is soluble in solutions of the hydroxides of alkaH metals to form niobates. Fusion of the anhydrous pentoxide with alkaH metal hydroxides or carbonates also yields niobates. Most niobates are insoluble in water with the exception of those alkaH metal niobates having a base-to-acid ratio greater than one. The most weU-known water-soluble niobates are the 4 3 ad the 7 6 salts (base acid), having empirical formulas MgNb O c, (aq) and M24Nb2202y (aq), respectively. The hexaniobate is hydrolyzed in aqueous solution according to the pH-dependent reversible equiHbria (130), when the pH is ca 9. 

In general, the tetracyclines are yellow crystalline compounds that have amphoteric properties (Fig. 2) (15). They are soluble in both aqueous acid and aqueous base. The acid salts tend to be soluble in organic solvents such as 1-butanol, dioxane, and 2-ethoxyethanol In fact, 1-butanol is used to extract the salts from aqueous solution. 

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. 

If a compound contains nitrogen its solubility in dUute hydrochloric acid shoidd be tested also to ascertain whether it is amphoteric. 

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