Oxygen group reactions

A number of 1,2,3-oxathiazole 5-oxides are prepared from the reaction of thionyl chloride with various ethane derivatives having vicinal oxygen- and nitrogen-containing groups. Reaction of the 2-aminoethanol derivative (146) with SOCI2 gave (147) (see Chapter 4.34). 

The oxygen atom at 21 is similarly an expendable group. Reaction of 241 (obtained from 185 by the usual procedure for introduction of the 9a-fluoro group) with methanesulfonyl chloride affords the 21 mesylate (242a). Replacement of the leaving group at 21 with iodine by means of potassium iodide in acetone followed by reduction of the halogen with zinc in acetic acid leads to fluorometholone (243). ... 

The addition of a nucleophile to a polar C=0 bond is the key step in thre< of the four major carbonyl-group reactions. We saw in Chapter 19 that when. nucleophile adds to an aldehyde or ketone, the initially formed tetrahedra intermediate either can be protonated to yield an alcohol or can eliminate th< carbonyl oxygen, leading to a new C=Nu bond. When a nucleophile adds to carboxylic acid derivative, however, a different reaction course is followed. Tin initially formed tetrahedral intermediate eliminates one of the two substituent originally bonded to the carbonyl carbon, leading to a net nucleophilic acy substitution reaction (Figure 21.1. ... 

The thalleiochin reaction for the specific detection of quinine alkaloids carrying an oxygen group at C-6 of the quinoline nucleus (e. g. quinine and quinidine) [17], or the... 

Figure 8.12 Relationships between the catalytic properties and electronic structure of Pt3M alloys correlation between the specific activity for the oxygen reduction reaction measured experimentally by a rotating disk electrode on Pt3M surfaces in 0.1 M HCIO4 at 333 K and 1600 lev/min versus the li-band center position for (a) Pt-skin and (b) Pt-skeleton surfaces. (Reprinted with permission from Stamenkovic et al. [2007b]. Copyright 2007. Nature Pubhshing Group.)...

The electrochemical mechanism can be well explained with the mineral pyrite. The collector ion is xanthate ion (CT), a member in the anodic sulfydryl collectors group. Two electrochemical reactions occur on the surface of the pyrite. There is the formation of dixanthogen (C2) by anodic oxidation of xanthate ion (CT) on the surface of pyrite coupled with cathodic reduction of adsorbed oxygen. These reactions are shown below ... 

The oxygen-consuming reaction between a quinone derived from a simple catechin and a quinone derived from a gallocatechin results in the formation of a theafiavin. These compounds possess the benztropolone group that is based on a seven-membered ring. Figure 4 illustrates the formation of theaflavins. 

Other anomeric-oxygen exchange reactions have been recently investigated quite extensively. Closely related to the Koenigs-Knorr method is the introduction offluorine as the leaving group (Scheme 1, path B) (6,9-13). Because of the difference in halophilicity of this element as compared with bromine and chlorine, additional promoter systems besides silver salts were found useful as activators for glycosylation reactions (14-16). However,... 

The 2-chloroethyl group, which is often an effective toxo-phore, was then attached to phosphorus through oxygen. No reaction appeared to take place between ethylene chlorohydrin and diethyl phosphorochloridate in the absence of a tertiary base. In the presence of pyridine, however, which removed the hydrogen chloride formed, a smooth reaction took place at 0° with the formation of diethyl 2-chloroethyl phosphate,... 

A part of the oxygen not accounted for is bound in basic surface oxides which are present on any carbon. The structure of these groups has not been satisfactorily explained so far. Their chemistry seems important in oxygen transfer reactions. 

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