Oxides, compared with nitrogen analogs

Andrews and co-workers have used the matrix reaction between lithium atoms and some inorganic compounds to produce species of spectroscopic interest. Reaction of lithium with molecular oxygen [301] produces, in addition to the molecule Li02, the molecule LiO and a dimer Li2 02. Reaction with nitric oxide produced a nitroxide compound [302], but analysis of the infrared spectrum indicated that in this compound the lithium atom was bound to the oxygen atom (LiON), rather than to the nitrogen atom (LiNO), as would be expected by analogy with the known compounds HNO and RNO. The matrix deposition of lithium and nitrous oxide [303] leads to the formation of LiO and LijO. The other alkali metals have also been reacted in the same way with nitrous oxide [304]. Potassium, rubidium and caesium all led to the formation of the compounds MO and M2O. No sodium oxides were produced when sodium and nitrous oxide were co-deposited. This is to be compared with the mechanism advanced for the sodium-catalysed gas-phase reaction between N2O and CO, where sodium is assumed to react with N2O, (Section 4, ref. 

Aminopyridines, aminopyridine oxides, and 3-aminoquinoline are obviously diazotized by analogous mechanisms. Kalatzis (1967 b) studied the diazotization of 4-aminopyridine over a very large range of acid concentrations (0.0025-5.0 m HC104). This compound is comparable to 2-aminothiazole in its acid-base properties the heterocyclic nitrogen is easily protonated at pH 10, whereas the amino group is a very weak base (pKa = -6.5). Therefore, the kinetics indicate that the (mono-protonated) 4-aminopyridinium ion reacts with the nitrosyl ion. The... 

Sulfur compounds with divalent sulfur functionalities are much more prone to dioxirane oxidation on account of their higher nucleophilicity compared to the above-presented oxygen-type nucleophiles. Examples of this type of dioxirane oxidation abound in the literature. Such a case is the oxidation of thiols, which may be quite complex and afford a complex mixture of oxidation products, e.g. sulfinic acids, sulfonic acids, disulfides, thiosulfonates and aldehydes , and is, therefore, hardly useful in synthesis. Nevertheless, the oxidation of some 9i/-purine-6-thiols in the presence of an amine nucleophile produces n >( -nucleoside analogs in useful yields (equation 19). This reaction also displays the general chemoselectivity trend that divalent sulfur functionalities are more reactive than trivalent sp -hybridized nitrogen compounds P. 

The role played by coordination complexes as templates and catalysts in these reactions is somewhat more difficult to discern, although several important results have been reported. Some early work by Bahadur showed that amino acids were formed in the reaction of potassium nitrate with paraformaldehyde in the presence of light. Many amino acids were produced, but the highest yields were found when the reaction was carried out in the presence of iron(lll) chloride as a catalyst. Later work extended analogous findings to colloidal molybdenum oxide as the catalyst. Molecular nitrogen was fixed in this case, a reaction in a sense comparable to the... 

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