Tetraoxides

In the laboratory vicinal diols are normally prepared from alkenes using the reagent osmium tetraoxide (OSO4) Osmium tetraoxide reacts rapidly with alkenes to give cyclic osmate esters... 

Because osmium tetraoxide is regenerated m this step alkenes can be converted to vie mal diols using only catalytic amounts of osmium tetraoxide which is both toxic and expensive The entire process is performed m a single operation by simply allowing a solution of the alkene and tert butyl hydroperoxide m tert butyl alcohol containing a small amount of osmium tetraoxide and base to stand for several hours... 

Section 15 5 Osmium tetraoxide is a key reactant m the conversion of alkenes to vie mal diols... 

Examples P2O5, diphosphorus pentaoxide or phosphorus)V) oxide Hgj, mercury(I) ion or dimercury(2-l-) ion K2[Fe(CN)g], potassium hexacyanoferrate(II) or potassium hexacyanofer-rate(4—) PbJPb 04, dilead(II) lead(IV) oxide or trilead tetraoxide. 

Dimethipin. 2,3-Dihydro-5,6-dimethyl-l,4-dithiin-l,l,4,4-tetraoxide [55290-64-7] (dimethipin, oxidimetbiin, UBI-N252, Harvard) (25) is used as a cotton defoHant and has been used as an experimental desiccant in potato vines. In addition, it defoHates nursery stock, grapes, dry beans, and natural mbber and is used as a desiccant for seed of canola, flax (l lnum usitatlssimum), rice, and sunflower (He/lanthus annuus) (10). The product has been available since the mid-1970s and the experimental work was first reported in 1974 (44). 

Thermally unstable cycHc trioxides, 1,2,3-trioxolanes or primary o2onides are prepared by reaction of olefins with o2one (64) (see Ozone). Dialkyl trioxides, ROOOR, have been obtained by coupling of alkoxy radicals, RO , with alkylperoxy radicals, ROO , at low temperatures. DiaLkyl trioxides are unstable above —30° C (63). Dialkyl tetraoxides, ROOOOR, have been similarly produced by coupling of two alkylperoxy radicals, ROO , at low temperatures. Dialkyl tetraoxides are unstable above —80°C (63). 

From acrolein by oxidation with sodium chlorate and osmium tetraoxide. Neuberg, Biochem. Z. 255, i (1932). 

Overall, the reaction leads to addition of two hydroxyl groups to the double bond and is refened to as hydroxylation. Both oxygens of the diol come from osmium tetraoxide via the cyclic osmate ester. The reaction of OSO4 with the alkene is a syn addition, and the conversion of the cyclic osmate to the diol involves cleavage of the bonds between oxygen and osmium. Thus, both hydroxyl groups of the diol become attached to the sfflne face of the double bond syn hydroxylation of the alkene is observed. 

The blends are frozen in liquid nitrogen and then microtomed and stained with osmium tetraoxide, which stains only unsaturated elastomers. 

To illustrate how a relatively simple equation can be written and balanced, consider a reaction used to launch astronauts into space (Figure 3.4). The reactants are two liquids, hydrazine and dinitrogen tetraoxide, whose molecular formulas are N2H4 and N204, respectively. The products of the reaction are gaseous nitrogen, N2, and water vapor. To write a balanced equation for this reaction, proceed as follows ... 

This is the final balanced equation for the reaction of hydrazine with dinitrogen tetraoxide. Three points concerning the balancing process are worth noting. 

N2Os (dinitrogen pentaoxide) N204 (dinitrogen tetraoxide)... 

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