Group As„+ cations

Figure 5.1 Change in transport number of calcium ions relative to sodium ions, mobility ratio and ion exchange equilibrium constant between calcium ions and sodium ions in a cation exchange membrane having salicylic acid groups as cation exchange groups (condensation type) with the pH of a mixed salt solution. (O) PNaC i (A) KNaCa ( ) UCu/UNa. Electrodialysis of the mixed solution of 0.375 N sodium chloride and 0.125 N calcium chloride (chloride ions 0.500 N), the pH of which was adjusted, was carried out using a cation exchange membrane prepared from condensation polymerization of salicylic acid, phenol and formaldehyde.

Group As cation As anion As ligand organic compounds... 

Surfactants can be classified by the charge of the hydrophilic group as cationic, anionic, neutral, and zwitterionic (includes positive and negative charges in the same molecule). The use of surfactants for the removal of COC by electrokinetics has been demonstrated in literature [17]. Several surfactants have been used such as Brij 35, TritonX-100, Sodium dodecyl sulfate, Tween 80, and Igepal CA-720, but COC removal results largely depend on surfactant nature and dosage, characteristics of the soil and contaminant, and operation conditions. Therefore, it is necessary to test the surfactant for each application [8]. 

To illustrate how aldol condensation may be coupled to functional group modifi cation consider the synthesis of 2 ethyl 1 3 hexanediol a compound used as an insect repellent This 1 3 diol is prepared by reduction of the aldol addition product of butanal... 

Carboxylate exchangers contain —COOH groups which have weak acidic properties and will only function as cation exchangers when the pH is sufficiently high (pH > 6) to permit complete dissociation of the —COOH site. Outside this range the ion exchanger can be used only at the cost of reduced capacity. 

Higher order aUphatic quaternary compounds, where one of the alkyl groups contains - 10 carbon atoms, exhibit surface-active properties (167). These compounds compose a subclass of a more general class of compounds known as cationic surfactants (qv). These have physical properties such as substantivity and aggregation ia polar media (168) that give rise to many practical appHcations. In some cases the ammonium compounds are referred to as iaverse soaps because the charge on the organic portion of the molecule is cationic rather than anionic. 

Basic Dyes. These are usuaUy the salts of organic bases where the colored portion of the molecule is the cation. They are therefore sometimes referred to as cationic dyes. They are appHed from mild acid, to induce solubUity, and appHed to fibers containing anionic groups. Thein main outiet is for dyeing fibers based on polyacrylonitrile (see Fibers, acrylic). 

Recently developed trifluoromethylatmg agents capable of transferring the trifluoromethyl group as a cation to strongly nucleophilic compounds such as carbanions and sulfur and phosphorus nucleophiles are prepared from o-biphenyl trifluoromethyl sulfoxide [164] and are shown in equation 141... 

EDTA, leading to a postulate that more than one equivalent of Ca2+ can be captured by X (e.g. one Ca2+ sequestered by the three amines and the three carboxylates and another Ca2 + by the remaining half the donor groups), as the Dreiding model suggests. The fact that there was no interaction at neutral pH of X with phosphate or oxalate anions was separately confirmed. Thus, the dissolution of Ca3(P04)2 and Ca(C204) is entirely due to the cation complexation mechanism. 

The structures of LiCl and NaCl are typical of all the alkali halides (Group 1 cation, Group 17 anion) except those of cesium. Because of the large size of the Cs+ ion, CsCl crystallizes in a quite different structure. Here, each Cs+ ion is located at the center of a simple cube outlined by Cl- ions. The Cs+ ion at the center touches all the Cl- ions at the comers the Cl- ions do not touch each other. As you can see, each Cs+ ion is surrounded by eight Cl- ions, and each Cl- ion is surrounded by eight Cs+ ions. 

Group III sulfides and hydroxides. /Left) Five Group III cations precipitatB as sulfides. These are NiS. CoS. and FeS (all of which are black], MnS (salmon), and ZnS (white). (Right) Jvio cations precipitate as hydroxides. AIIOHfo (white) and Cr(0H)3 (gray-green). 

Group IV cations have soluble chlorides and sulfides, so they are still in solution at this point. The alkaline earth cations (Mg2, Ca2+. Ba2+) are precipitated as carbonates... 

The transition metals, unlike those in Groups 1 and 2, typically show several different oxidation numbers in their compounds. This tends to make their redox chemistry more complex (and more colorful). Only in the lower oxidation states (+1, +2, +3) are the transition metals present as cations (e.g., Ag+, Zn2+, Fe3+). In higher oxidation states (+4 to +7) a transition metal is covalently bonded to a nonmetal atom, most often oxygen. 

---