Lithium compounds with oxygen

If lithium combines with oxygen to form an ionic compound, then two lithium ions, each with -i-l chcirge, are required to neutralize the -2 charge of the oxide anion. So the ncime lithium oxide implies the formula Li20, because a two-to-one ratio of lithium cation to oxide anion is necessary to produce a neutral compound. 

The anion is assumed to exist preferentially in the anti conformation A, which offers a stabilizing 7rc -> minimizes steric interactions69,71 11. The nonplanar nature of the carhanionic center and coordination of the lithium to the oxygen atom could be demonstrated for a related compound by an X-ray analysis72. Usually, the electrophile attacks the carhanionic center with stereoinversion. 

The principal product of the reaction of the alkali metals with oxygen varies systematically down the group (Fig. 14.15). Ionic compounds formed from cations and anions of similar radius are commonly found to he more stable than those formed from ions with markedly different radii. Such is the case here. Lithium forms mainly the oxide, Li20. Sodium, which has a larger cation, forms predominantly the very pale yellow sodium peroxide, Na202. Potassium, with an even bigger cation, forms mainly the superoxide, K02, which contains the superoxide ion, O,. ... 

Geurink and Klumpp measured the protodelithiation enthalpies of 3-lithiopropyl methyl ether, 3-lithiobutyl methyl ether, 5-lithiopentyl methyl ether and 7-5yn-methoxy-2-exo-lithionorbornane in the same study that was discussed in an earlier section for the non-oxygenated compounds n-propyl lithium, n-butyl lithium, 5ec-butyl lithium and 2-norbornyl lithium. The reaction enthalpies for the oxygen-containing lithium species with 5ec-butyl alcohol in benzene were —190 2, —199 4, —190 3 and —199 2 kJmoU, respectively, where all of the lithiated ethers purportedly exist as tetrameric species. 

The strong preference for oxygen over carbon as a donor atom is shown by the rapid decomposition in water of most compounds with a covalent M—C bond or an ionic M+. .. C- interaction. The effect of the differences in electronegativity is shown in the structures of methyl lithium and methyl potassium. The methyl lithium tetramer, (39), has a cubane ... 

Lithiation of dibenzofuran with butyllithium and mercuration both occur at the 4-position. Thallation occurs at the 2-position, however (57IZV1391). The mercury and thallium derivatives serve as a source of the iodo compounds by reaction with iodine. Bromodibenzofurans undergo bromine/lithium exchange with butyllithium and the derived lithio compounds may be converted into phenols by reaction with molecular oxygen in the presence of a Grignard reagent, into amines by reaction with O-methylhydroxylamine, into sulfinic acids by reaction with sulfur dioxide, into carboxylic acids by reaction with carbon dioxide and into methyl derivatives by reaction with methyl sulfate (Scheme 100). This last reaction... 

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