Replacement of oxygen

Replacement of Oxygen by Other Chalcogens. Acids derived from oxoacids by replacement of oxygen by sulfur are called thioacids, and the number of replacements are given by prefixes di-, tri-, and so on. The affixes seleno- and telluro- are used analogously. 

In the geochemistry of fluorine, the close match in the ionic radii of fluoride (0.136 nm), hydroxide (0.140 nm), and oxide ion (0.140 nm) allows a sequential replacement of oxygen by fluorine in a wide variety of minerals. This accounts for the wide dissemination of the element in nature. The ready formation of volatile silicon tetrafluoride, the pyrohydrolysis of fluorides to hydrogen fluoride, and the low solubility of calcium fluoride and of calcium fluorophosphates, have provided a geochemical cycle in which fluorine may be stripped from solution by limestone and by apatite to form the deposits of fluorspar and of phosphate rock (fluoroapatite [1306-01 -0]) approximately CaF2 3Ca2(P0 2 which ate the world s main resources of fluorine (1). 

Manganese dioxide reacted incompletely but KMnO released oxygen quantitatively. Complete replacement of oxygen took place with oxides of B, Ti, V,... 

The course of thiation (replacement of oxygen by sulfur) of dioxo-... 

The reactions in this section are grouped into classifications based on bone changes, similar to those used for the oxidation reactions. These sections are (A reactions involving replacement of oxygen by hydrogen, (B) reactions in whicr... 

Carius (8) replaced the oxygen in phosphoryl chloride by sulfur. This may be somewhat analogous to the replacement of oxygen in a carbonyl group by sulfur using phosphorus pentasulfide. Prinz (8) used thionyl chloride in his reaction with phosphorus sulfide and De Fazi (2) used carbon tetrachloride in a very interesting preparation of this important intermediate. 

Dialkylaminosulfur trifluorides are widely used as a safe substitute for SF4 in the replacement of oxygen by fluorine in many types of organic compounds, for example, converting alcohols to fluorides, or aldehydes and ketones to gem-difluorides. The most familiar of these reagents is DAST, while an increasingly popular one (considered safer to use than DAST) is bis(2-methoxyethyl)aminosulfur trifluoride (Deoxo-Fluor Reagent) (Scheme 7.15). 

Figure 16 Relaxation changes of chemiluminescence intensity for oxidized polyisoprene during replacement of oxygen by nitrogen and vice versa.

A more common usage of phosphorus pentasulfide is to effect replacement of oxygen atoms in an acyclic compound. The thiated intermediate—which may be a fairly complex derivative containing phosphorus, sulfur, and oxygen atoms—then cyclizes with elimination. Except in one case, mentioned below, the intermediates seem not to have been studied in any detail. 

For the replacement of oxygen by hydrogen in ketones and aldehydes the method of Kishner and Wolff is used as often as is that of Clemmensen. In the former method the hydrazone or semicarbazone of the carbonyl compound is heated for several hours—preferably in the presence of hydrazine hydrate—in a sealed tube or autoclave with sodium ethoxide at about 160°. The explanation of the reaction is that, under the catalytic influence of the ethoxide, the hydrazone is transformed into a diimine which then decomposes in the same way as does phenyldiimine (p. 286) ... 

In organic chemistry, replacement of oxygen by sulfur leads to Umpolung phenomena We have selected this O- and S-perturbation because there is a re-... 

Experimental thermodynamic data have been reported for dibenzo-l,4-thiazino[3,2-/ ][l,4]thiazine 166 <1997MI565> compared to the corresponding oxazinooxazine, replacement of oxygen by sulfur increases ring strain. Crystallographic data show that the nitrogen centres in 166 are /7-periplanar <1994JCM458>. 

A. Reactions Involving Replacement of Oxygen by Hydrogen. In reactions 9-37 to 9-41,... 

In English, azidine is the name suggested for the radical —C(=NH)N3 by analogy with amidines which are derived from the amides by replacement of oxygen in CONH2 by the... 

Termination for infixes to indicate replacement of oxygen atoms and/or hydroxyl groups thto-, nitrido-... 

As expected, the replacement of oxygen by nitrogen raises the barrier to ring inversion, and the measured barrier for the 2,4-dimethyl derivative (37) is 53 kJ mol-1. The barrier to inversion at N-2 is similar to that for ring inversion at 47 (ax- ts) and 54 (eq - ts) kJ mol-1. The most rapid process however is inversion at N-4 (79T1391). 

Donald F Halpern and Gerald G Vernice Replacement of Oxygen by Fluorine 199... 

As in the coronands, binding site identity plays an important role in the complexation preferences of cryptands. Replacement of oxygens by sulfur or nitrogen in the bridges (45b-d) results in decreased stability and selectivity for alkali metal and alkaline earth cations (as was also noted for the coronands).66,164 Selectivity is then shifted toward softer metal ions such as Ag+, Tl+, Cd2+ and Pb2+. 

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