Ionic compounds, formation

A number of general methods for the synthesis of meso-ionic 1,2,4-triazol-3-ones are available. Sodium ethoxide-catalyzed cyclization of 1-benzoyl-l,4-diphenylsemicarbazide (201, R = R = R = Ph, X = O) yielded anhydro-3-hydroxy-1,4,5-triphenyl-1,2,4-triazolium hydroxide (200, R = R = R = Ph). A general route to meso-ionic 1,2,4-triazol-3-ones (200) is exemplified by the formation of the 1,4,5-triphenyl derivative (200, R = R = R = Ph) from A-amino-MA -diphenylbenzamidine (202, R = R = R = Ph) and phosgene. In contrast with this ready meso-ionic compound formation, the corresponding reaction of the iV-methylbenzamidine (202, R = Me, R = R = Ph) did not yield the meso-ionic 1,2,4-triazol-3-one (200, R = Me, R = R = Ph). The product was in fact 3,4-diphenyl-2-methyl-l,2,4-triazol-5-onium chloride (203), which on heating gave 3,4-diphenyl-1,2,4-triazol-5-one (204, R = Ph). The formation of the A-methyl derivative (200, R = Me, R = R = Ph, yield 79%) by heating the 7V-thiobenzoyl semicarbazide (201, R = Me, R = R = Ph, X = S) with potassium carbonate in methyl cyanide has been reported. Another synthesis of A-methyl derivatives (200, R = Me) involves methylation of 3-methyl-4-phenyl-l,2,4-triazol-5-one (204,... 

More than a single electron may be transferred when an ionic bond is formed. Two examples of ionic compound formation involving the transfer of more than one electron are the formation of calcium chloride and magnesium oxide ... 

Chapter 3 periodicity of eiectron arrangements in atoms importance of valence electrons Chapter 4 formation of ionic compounds, formation of covalent compounds... 

Formation of Ionic Compounds Formation of Covalent Compounds... 

Fig. 3-1 Matrix illustrating ionic compound formation. Columns represent the cations from Groups I, II, and III.

Note The actual formation of NaCl need not follow the above steps. The above steps are just a simplified and convenient way to analyse the energetics of ionic compound formation.]... 

Thus, the conditions favourable for ionic compound formation are -... 

Q Show that Fajans rules are consistent with the criteria for ionic compound formation described in Section 5.1.5. 

Ceramics and refractories are inherently brittle materials. The reason for this behavior is that the bonding in them is predominantly ionic or predominantly covalent. For plastic deformation, which is required for ductile fracture, there should be dislocation movement. In ionic compounds, formation of dislocation itself is difficult, because, for neutrality of the material, a pair of dislocations should simultaneously form. One should carry negative charge, and the other, positive. This is a difficult thing. If at all a dislocation forms, it requires simultaneous movement of the oppositely charged dislocations. This is still more difficult. In the case of covalent bonds, they are directional and strong. There is no question of any line defect, such as a dislocation, forming. Therefore, any question of dislocation movement does not arise. Ceramic and refractory materials fail by the sudden fracture of their atomic or ionic bonds. Hence, the failiue of ceramic and refractory materials can be discussed in terms of the failure of brittle materials. In other words, the theory of brittle materials fracture can be applied to ceramics and refractories. 

---