Replacement of hydrogen by oxygen

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... 

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) ... 

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

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). 

Takken (2) identified thiazoles and 3-thiazolines from the reaction of 2,3-butanedione and 2,3-pentanedione with ammonia, acetaldehyde and hydrogen sulfide at 20 °C. Study of tetramethylpyrazine (5) also showed that it can be readily formed in 3-hydroxy-2-butanone and ammonia model reaction at 22 C. Recent study of the model reaction of 3-hydroxy-2-butanone and ammonium acetate at low temperature revealed an interesting intermediate compound, 2-(l-hydroxyethyl)-2,3,4-trimethyl-3-oxazoline, along with 2,4,5-trimethyloxazole, 2,4,5-trimethyl-3-oxazoline, and tetramethylpyrazine were isolated and identified 4,5). We hypothesized that with the introducing of H2S, replacement of oxygen by sulfur could happen and sulfur-containing heterocyclic compoimds such as thiazoles and thiazolines could be formed along with oxazoles, oxazolines and pyrazines. 

A method that is important preparatively and is based on replacement of oxygen by sulfur consists of treating oxiranes with sodium hydrogen sulfite 389 it leads to sodium / -hydroxy sulfonates 390... 

Sulfur or the thiol group may be substituted for functional groups as well as for hydrogen in the presence of nickel sulfide catalysts. Simultaneous replacement of oxygen by sulfur in carbonyl compounds and hydrogenation to thiols may be carried put over nickel sulfide catalysts. 

He also regarded ethylene and homologous hydrocarbons as formed from carbonic oxide by replacement of one equivalent of oxygen by hydrogen and... 

The replacement of oxygen by sulfur results in a red shift of the first absorption band of around 0.21 eV. However, the substitution of the terminal hydrogen for the methyl group does not modify the band position, fir the four derivatives there is a flux of charge from the phenolic part toward the rest of the molecule. This flux is larger in pCA and pCMe, 0.22 e, than in pCTA and pCTMe , 0.13 e. Consequently, the delocalization of the charge is larger in the excited state of the 0X0 derivatives that becomes more stable than the thio derivatives. 

Metal alkoxides are compounds in which a metal is attached to one or more alkyl groups by an oxygen atom. Alkoxides are derived from alcohols by the replacement of the hydroxyl hydrogen by metal. 

Once more, replacement of the hydroxyl hydrogen by a group or an atom more electronegative than hydrogen, replacement of the hydroxyl oxygen by its third period counterpart, or, a combination thereof, will enhance n—a interaction and should lead to a preference for the crowded W conformation over the Y con-. formation. This expectation is confirmed by ab initio calculations in which the preferred conformation for NH2OF is found to be the more crowded W con-former314. ... 

Replacement of a methyl hydrogen by fluorine leads to a situation where the dominant interaction is no— Ocf, since in this molecule the C—H bond acquires a donor ability comparable to the oxygen lone pair and the C—F bond is a better acceptor than an 0—H bond. The molecule CH2F—OH can exist in the syn, gauche and anti conformations shown below. 

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