Compounds amphoteric

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... 

J. R. Veraait, C. Gooijer, H. Lingeman, N. H. Velthorst and U. A. Th Brinkman, At-line solid-phase exti action coupled to capillary electi ophoresis deteitnination of amphoteric compounds in biological samples , 7. High Resolut. Chromatogr. 22 183-187(1999). 

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. 

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. 

Commercial mixtures of surfactants comprise several tens to hundreds of homologues, oligomers and isomers of anionic, nonionic, cationic and amphoteric compounds. Therefore, their identification and quantification in the environment is complicated and cumbersome. The requirement of more specific analytical methods has prompted a replacement of many of the separate steps in traditional methods of analysis, usually non-chromatographic, by chromatographic tools. 

Another ion chromatography pharmaceutical application is the analysis of amines and amphoteric compounds such as choline (see Figure 19). Such compounds may be present either as counterions, as mentioned above, or as synthesis by-products. In either case, ion chromatography can be advantageously utilized for this class of compounds due to the limited utility of gas chromatography and the lack of a UV chromophore for such compounds. Again, screening for such compounds in pharmaceutical preparations can be best accomplished... 

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... 

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). 

Lead forms amphoteric compounds in +2 and +4 valence states, forming plumbous and plumbic salts, such as PbCL and PbCL, as well as plumbites and plumbates, such as Na4Pb03 and Ca2Pb04,. Over a thousand compounds of lead are known which include divalent and tetravalent salts, complexes, and organometaUics. Divalent compounds of lead are far more numerous than the tetravalent compounds. Most compounds, however, result from the reactions involving other lead compounds, rather than elemental lead. Only the reactions involving elemental lead are outlined briefly below. 

In 1896 Pinnow and Samann reported that diazotization of o-amino-benzamidoxime (17) gave the amphoteric compound (18) as the sole reaction product. Structural assignment was based on chemical evidence which was erroneously interpreted, and reinvestigation of this reaction by Parnell has established that the correct structure for this... 

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... 

Biagi et ai. [28] studied the relationship between Kow and reversed-phase TLC retention factor for 28 phenols substituted with alkyl, halogen, methoxy, and nitro groups. Budvari-Barany et al. [29] compare the HPLC and TLC retention method to estimate Kovl for a class of heterocyclic compounds (imidazoquinoline derivatives). Takacs-Novak et al. [30] has demonstrated the similarity between the pH-dependent Kow and the pH-related retention (C i8 /methanol-water) pattern of eight amphoteric compounds in the pH range 4 to 9. 

Takacs-Novak, K., et al., Relationship Study Between Reversed Phase HPLC Retention and Octanol/Water Partition Among Amphoteric Compounds. J. Liquid Chromatogr., 1995 18, 807-825. 

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... 

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. 

Even though conventional extraction has been useful in testing of dosage forms, there are drawbacks. The primary difficulty is with the low extraction efficiencies that are common for highly ionic or amphoteric compounds. A review of 37 literature references that used conventional extraction techniques for analytes of drug products quoted recoveries of lower than 80% in 7 of the references reviewed [23]. 

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