Group III

In this chapter, substitution, addition-dissociation, and intramolecular reactions of compounds of the non-metals will be covered. Simple compounds of the Group III and Group IV metals are also included complexes of these elements are mentioned in the appropriate sections of Chapters 6 and 8. Elements are discussed in Periodic Table order. 

Borohydride is rapidly oxidized by N3, Br2, and (SCN)2 (166). A UV/visible spectrum of the intermediate was obtained and attributed to BH4. It is not obvious to this writer that the species observed could 

The free-radical chemistry of aluminum has been discussed in Buxton and Sellers review (69). The only species mentioned is Al2+, and its only reported reaction is the dehalogenation of chloroethanol and bromoacetate. 

In+ is a species of limited stability, but, as discussed in Standard Potentials, there is a fairly reliable value of —0.126 V for the In+/In couple, where In is in the bulk state. The assumption of a hydration free energy of 13 kj/mol for atomic indium leads to AfG° = 222 kJ/mol for aqueous In and E° = —2.43 V for the In+/In couple. To our knowledge homogeneous reduction of In+ has not yet been reported. 

Latimer s discussion of In2+ (195), like that of Ga2+, is unreliable because it was based on the incorrect belief that InCl2 is a compound of In(II). In their study of the chemistry of aqueous In+, Taylor and Sykes found that In+ does not reduce Cr3+, and thus they estimated E°  

As discussed in Standard Potentials, the T1+/T1 potential is — 0.3363 V, in which T1 refers to the bulk metal. If the hydration free energy of atomic thallium is taken as that of xenon, we calculate AfG° = 161 kJ/mol for aqueous Tl, and E° = —2.00 V for the T1+/T1 couple. Thus it is quite reasonable that Tl+ is reported to be reduced by e q and H. Butler and Henglein estimated a potential of -1.9 V by similar methods, but they neglected the hydration energy of atomic thallium (S3). 

- As in previous years, organoboron chemistry has seen a considerable level of activity. Several review articles have appeared 

Reagent chemistry based on boron has seen some advances. Tetra- 

Reducing agents, both boranes and borates, have already found widespread use in a variety of situations, but new reagents and advances in asymmetric reduction continue to be developed. A convenient new synthesis of potassium trisisoamylborohydride (KSia BH) is based on the catalytic effect of (PriO)3B. 99 101 102 104 106 107 The hexylchloroborane complex (137) has been compared to both thexylborane 

This species acts as a Lewis acid and in the absence of (139), very low optical yields ( 4% e.e.) were observed.The degree of asymmetric induction in the reduction step was also shown to be dependent on the concentration of (139). Computational studies relevant to the proposed transition state for the asymmetric reduction step have also 

84-96% e.e. These ketones, e.g. 2,2-dimethylcyclopentanone or 2,2-dimethylcyclohexanone, are in general unreactive towards the more usual Alpineborane reagent. The reducing properties of a series of 9-alkoxy-9-BBN derivatives, prepared from 9-BBN and a chiral alcohol 

- The chemistry of organoboranes has seen significant developments across a range of different fronts. As with zinc, ultrasound has had an impact in the boron area. Alkyl and aryl halides react with Bp2.Et20 and Mg under ultrasonic conditions to 

Probably the most important aspect of boron chemistry this year concerns its use in the control of absolute stereochemistry. 

Allylic boranes generally undergo rapid allylic rearrangement, but hydroboration of cyclohexa-1,3-diene with (+)- or (-)-a-iso-pinocamphenylborane (Ipc BH) gives the first example of an optically active allylic borane (109) that is stable towards rearrange- 

Good levels of asymmetric induction have also been observed in 

The asymmetric reduction of carbonyl compounds using boranes has been further developed, principally by Brown s research group. (3-Pinanyl)-9-borabicyclo[3.3.1]nonane, Alpine borane, reduces 

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Group III with electronic configuration 5s 4d . The principal ore is gadolinite (a silicate also containing lanthanides). Y2O3 containing Eu is used as a red phosphor in colour television. Yttrium iron garnets are used as microwave filters. 

Wallace C H 1998 The rapid solid-state synthesis of group III and transition metal nitrides at ambient and high pressures PhD Dissertation University of California, Los Angeles... 

Two of the material systems shown in figure G2.16.3 are of particular importance. These are the ternary compounds fonned from group III elements such as A1 and Ga in combination with As and quaternary compounds fonned from Ga and In in combination with As and P [8,15,]. Ternary Al Ga s grown on GaAs is the best known of the general class of compounds Quaternary Ga In As grown on InP is... 

Gillis H P, Choutov D A and Martin K P 1996 The dry etching of Group iii-Nitride wide bandgap semiconductors J. Mater. 48 50-5... 

In Group III, boron, having no available d orbitals, is unable to fill its outer quantum level above eight and hence has a maximum covalency of 4. Other Group 111 elements, however, are able to form more than four covalent bonds, the number depending partly on the nature of the attached atoms or groups. 

The ability to act as a lone pair acceptor is not confined to Group III, and can occur wherever a quantum level is incomplete. This ability to accept electrons explains why covalent chlorides, with the exception of carbon tetrachloride, are readily hydrolysed, the apparently anomalous behaviour of carbon tetrachloride being readily explained by the fact that the carbon has a completed quantum level and is unable to form an intermediate complex with water. 

This is an exothermic process, due largely to the large hydration enthalpy of the proton. However, unlike the metallic elements, non-metallic elements do not usually form hydrated cations when their compounds dissolve in water the process of hydrolysis occurs instead. The reason is probably to be found in the difference in ionisation energies. Compare boron and aluminium in Group III ... 

A non-metal or weakly electropositive metal X in Group III of the periodic table would be expeeted to form a covalent volatile hydride XHj. In fact, the simplest hydride of boron is BjHf, and aluminium hydride is a polymer (AlHj) . 

Of the five Group III elements, only boron and aluminium are reasonably familiar elements. Aluminium is in fact the most abundant metal, the third most abundant element in nature, but the other elements are rare and boron is the only one so far found In concentrated deposits. 

The data in Table 7.1 show that, as expected, density, ionic radius, and atomic radius increase with increasing atomic number. However, we should also note the marked differences in m.p. and liquid range of boron compared with the other Group III elements here we have the first indication of the very large difference in properties between boron and the other elements in the group. Boron is in fact a non-metal, whilst the remaining elements are metals with closely related properties. 

In the absence of oxygen, gallium and indium are unaffected by water. Thallium, the most metallic element in Group III, reacts slowly with hot water and readily with steam to produce thallium(I) oxide, TI2O. 

Only thallium of the Group III elements is affected by air at room temperature and thalliumflll) oxide is slowly formed. All the elements, however, burn in air when strongly heated and, with the exception of gallium, form the oxide M2O3 gallium forms a mixed oxide of composition GaO. In addition to oxide formation, boron and aluminium react at high temperature with the nitrogen in the air to form nitrides (BN and AIN). 

Group III. Compounds insoluble in water, but soluble in dilute sodium hydroxide. This group may be further subdivided into Group IIIA—soluble in dilute sodium hydroxide and soluble in dilute sodium bicarbonate and Group IIIB—soluble in dilute sodium hydroxide and insoluble in dilute sodium bicarbonate. 

Group III. Carboxylic and sulphonic acids (also sym.-tribromophenol, 2 4-dinitrophenol and picric acid) are also soluble in dilute sodium bicarbonate solution. 

Solubility in 5 per cent, sodium hydroxide solution. Note whether there is any rise in temperature. If the compound appears insoluble, remove some of the supernatant liquid by means of a dropper to a semimicro test-tube (75 X 10 mm.), add 5 per cent, hydrochloric acid dropwise until acid, and note whether any precipitate (or turbidity) is formed. The production of the latter will place the compound in Group III. 

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