Acids amphoteric compounds

Figure 3 shows a typical example of the pH-mobility curve for a monobasic drug, donepezil hydrochloride. The observed mobilities at different pHs were well in agreement with the regressed values from Eq. (17). The obtained pKa value is 9.2, which is consistent with the result via the UV method (9.1). Similar results were reported for weak acids, amphoteric compounds, as well as peptides with seven ionic groups (20). 

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. 

Primary fatty amines also add (Michael addition) to esters of acryUc acid, H2C=CHCOOH, methacrylic acid, H2C=C(CH2)COOH, or crotonic acid, CH2CH=CHC00H. Hydrolysis of the Michael ester forms an amphoteric surfactant. Crotonic acid can be used to form the amphoteric compound... 

Hydroxypyrazoles are amphoteric compounds which form salts with alkalies and with mineral acids (B-76MI40402). The 4-hydroxy group directs electrophilic substitution towards... 

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... 

Anionic and cationic products generally tend to interact with each other, usually diminishing the surface-active properties of both and often resulting in precipitation of the complex formed. Amphoteric compounds can also be incompatible with anionics in acid solution but are generally compatible with cationics and nonionics. Interaction between anionic and cationic agents can sometimes be prevented by addition of a nonionic. In some cases, if an ethoxylated sulphate or phosphate is used as the anionic component a cationic compound produces no obvious precipitation, since the oxyethylene chain acts as dispersant for any complex that may be formed. 

Amphoteric. Compounds having the capability of acting as an acid or a base. Amino acids are amphoteric—their molecules contain both an acid group (-COOH) and a basic group (-NH2). 

Amphoteric compounds are compounds that may function as either acid or base, depending upon conditions. We have already met this concept in Section 4.5.4, where simple alcohols and amines have two pATa values according to whether the compound loses or gains a proton. Of course, with alcohols and amines, acidity and basicity involve the same functional group. Other amphoteric compounds may contain separate acidic and basic groups. Particularly... 

The stability of several -lactam antibiotic in aqueous solutions is pH dependent. Optimum stability for monobasic penicillins in general is exhibited at pH 6-7, while for the amphoteric penicillins this coincides with the isoelectric point (18). A fast degradation occurs at both acidic and basic conditions. At pH 2.6, acid-labile -lactams such as penicillin G, methicillin, and nafcillin disappear almost completely while acid-resistant compounds like penicillin V and isoxazolyl penicillins survive (19). 

Quinolone carboxylic acid antibacterials are synthetic compounds whose basic nuclear structure includes a quinolone ring and a carboxylic acid group. Fluoroquinolones are second-generation quinolones that contain in their molecule a fluorine and a piperazine ring. Quinolones are amphoteric compounds slightly soluble in polar solvents such as water, and insoluble in nonpolar solvents such as benzene and hexane. Most of these drugs are fluorescent and are quite stable in aqueous solution toward light, except miloxacin, which is reported to be unstable. 

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. 

PROTON AFFINITY OF ACIDS AND BASES The division between acids and bases is not a very sharp one it has been remarked already that the borderline between the two groups is formed by the amphoteric compounds, that have both weak acid and weak basic properties, and thus behave as acids in the presence of strong bases and as bases in the presence of strong acids. To a... 

The product in this case is sodium aluminate, a compound that contains the aluminate ion, [Al(OH)4]. Because aluminum oxide reacts with both acids and bases, it is classified as amphoteric. Other main-group elements that form amphoteric oxides are shown in Fig. J.3. As you can see, these elements lie in a diagonal band across the table from beryllium to polonium. The acidic, amphoteric, or basic character of the oxides of the d-block metals depends on their oxidation state (see Chapter 16). 

Ion pair mixture QAS + anionic, nonionic, or amphoteric compound, for example, dodecylbenzenesulfonic acid (DDBSA) + quaternary ammonium compound (with appendages <6 carbons) Baker Petrolite (Crosby et al., 2005)... 

Amphoteric compounds such as amino acids can be resolved as acid or amine forms after deriving corresponding esters or N-acyl compounds. Racemic alcohols and amines are also resolved by use of optically active isocyanates, where the alcohols and amines are derived the corresponding diastereomeric urethanes or ureas. 

Amphoteric compounds that contain both basic (e.g., -NH2) and acidic (e.g., -COOH) groups, such as amino acids. 

This is an amphoteric compound because it behaves as both an acid and a base in the Bronsted definition. As an acid, it can donate an H+ and becomes the conjugate base ... 

Amphoteric compound (Section 26.2) A compound that can act as either an acid or a base. 

Amino acids are amphoteric compounds i.e., they contain both acidic and basic groups. Because of this, they arc capable of bearing a net electrical charge, which depends on the nature of the solution. 

If a strong acid is added to water, the water acts as a base and is protonated by the acid to become H30+. If we added a strong base to water, the base would deprotonate the water to give hydroxide ion, OH, and here the water would be acting as an acid. Such compounds that can act as either an acid or a base are called amphoteric. 

Ampholyte — A substance that can react both as an acid and as abase is called an ampholyte, or amphoteric compound. Usually this property refers to the - Bronsted acid-base theory. An example is HCOj which can act as a proton acceptor and as a proton donator. An ampholyte can be a zwitterion, as in case of amino acids in the range between pH = pJCai and pH = pfCa2, they exist as [+(H3N)HRC-COO-]. 

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. 

Acidity and basicity are relative properties. Many compounds are amphoteric and behave as acids or as bases according to a partner. Metal oxides are classified as acidic, amphoteric or basic. Experimentally, this classification corresponds to the adsorption of probe molecules[7, 8]. NH3 is a base probe molecule that reacts with the electron deficient metal atoms (Lewis acid) or the protons adsorbed on the hydrated surface, CO2 is usually considered as acidic and thus it is expected to adsorb more strongly on basic sites. According to this classification, Ti02 belongs to an amphoteric species and MgO to a basic species. A general difficulty for such classifications is that the order can vary with the choice of the probe. The Hard and Soft Bases and Acids theory[9, 10] responds to the necessity to refine the model with a second scale it is better to couple... 

Amino acids constitute a particularly important class of bifiinctional compounds the two functional groups in an amino acid are, respectively, basic and acidic, the compounds are amphoteric, and in fact exist as zwit-terions or inner salts. For example, glycine, the simplest amino acid, exists mosdy in the zwitterion form shown first, rather than as aminoacetic acid... 

Chromic hydroxide is an amphoteric compound and exhibits acidic properties in combining with basic oxides to form chromites, to which the general formula M-jO.CrjOg is given, and which are isomorphous with the corresiiouding aluminium compounds known as spinels. They may be considered as derived from an acid, HCrOj the monohydrate, CrjOj.HjO, has this empirical formula. From a study of the action of sodium hydroxide on chromium hydroxide for prolonged periods and the rate of the formation of chromate by the oxidation of dissolved chromite, it would appear that the chronlic hydroxide acts as a poly basic acid. 

We call compounds, like amino acids, that can act as acids or bases depending on their environment amphoteric compounds. The body uses this dual property in the stomach, as the protein stomach juices and lining can react to mop up any adverse effects of overeating or drinking (within reason). If the system is overloaded you might have to help a bit by taking a Rennie or stomach powder to help restore the correct acidity to the stomach. 

There are about 4-5 surface hydroxy groups per square nanometer on anatase and these are of two different types. One type is basic in nature and can be exchanged by F". This type of site is responsible for the adsorption of acidic species onto the surface and initiates the adsorption of base sensitive compounds such as Mo02(acac)2. The second type of surface hydroxide is acidic. It interacts strongly with base and initiates the adsorption of acid sensitive compounds such as Fe(acac)3.2 This amphoteric nature of titania is illustrated by the zeta potential versus pH curve shown in Fig. 9.9. Cationic catalyst precursers are adsorbed at pH values greater than 7-8 and anionic species from solutions having a pH less than about 5. 

Several drugs and amino acids, peptides and proteins are amphoteric, displaying both basic and acidic characteristics. Frequently encountered dmgs in this category are the sulfonamides and the tetracyclines. If, for simplicity, one were to use a generalised stmcture for an amphoteric compound... 

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