Alkylation oxygen

Cleavage of alkyl aryl ethers by hydrogen halides always proceeds so that the alkyl-oxygen bond is broken and yields an alkyl halide and a phenol as the final prod nets Either hydrogen bromide or hydrogen iodide is normally used... 

Oxiranones (a-lactones) (Section 5.05.3.2.1), e.g. (6), in accord with their putative facile opening to zwitterions (Scheme 18), usually react readily with nucleophiles by alkyl-oxygen cleavage (Scheme 41) (71JA557), rather than the acyl-oxygen cleavage common for esters. 

The designation Ac signifies acyl-oxygen fission, whereas A1 is alkyl-oxygen fission. When n-amyl alcohol was hydrolyzed in 0-enriched water, the 0 appeared in the product acid rather than the alcohol, showing that alkyl-oxygen fission could not have occurred. Carpenter gives many examples of isotopic studies. 

Al, as shown in structure 3), the molecularity (1 or 2), and the ionic form of the substrate [A for conjugate acid RC(OH)OR and B for conjugate base RCOOR]. Note that alkyl-oxygen fission constitutes nucleophilic substitution and is therefore equivalent to the classification ... 

One example of normal-phase liquid chromatography coupled to gas chromatography is the determination of alkylated, oxygenated and nitrated polycyclic aromatic compounds (PACs) in urban air particulate extracts (97). Since such extracts are very complex, LC-GC is the best possible separation technique. A quartz microfibre filter retains the particulate material and supercritical fluid extraction (SPE) with CO2 and a toluene modifier extracts the organic components from the dust particles. The final extract is then dissolved in -hexane and analysed by NPLC. The transfer at 100 p.1 min of different fractions to the GC system by an on-column interface enabled many PACs to be detected by an ion-trap detector. A flame ionization detector (PID) and a 350 p.1 loop interface was used to quantify the identified compounds. The experimental conditions employed are shown in Table 13.2. 

Alkylated, oxygenated and nitrated polycyclic aromatic compounds... 

Figure 13.16 LC separation of urban air particulate exrtact (a), along with the GC/FID cliro-matogram (b) of an oxy-PAC fraction (transfeired via a loop-type interface). Reprinted from Environmental Science and Technology, 29, A. C. Lewis et al., On-line coupled LC-GC-ITD/MS for the identification of alkylated, oxygenated and nirtated polycyclic aromatic compounds in urban air particulate exti acts , pp. 1977-1981, copyright 1995, with permission from the American Chemical Society.

A. C. Eewis, R. E. Robinson, K. D. Bartle and M. J. Pilling, On-line coupled EC-GC-ITD/MS for the identification of alkylated, oxygenated and nitr-ated polycyclic aromatic compounds in urban ah particulate extr acts . Environ. Sci. Technol. 29 1977-1981 (1995). 

Therefore, transesterification reactions frequently fail when R is tertiary, since this type of substrate most often reacts by alkyl-oxygen cleavage. In such cases, the reaction is of the Williamson type with OCOR as the leaving group (see 10-14). With enol esters, the free alcohol is the enol of a ketone, so such esters easily... 

In the special case of 3-lactones, where small-angle strain is an important factor, alkyl-oxygen cleavage is observed (Bal2 mechanism, as in the similar case of hydrolysis of P-lactones, 10-10), and the product is not an amide but a P-amino acid ... 

In the hydration of compounds 2f and 2g, besides the expected ester, three other products (acetic acid, an alkene, and alcohol) were observed. These products were postulated to arise via a fragmentation of the intermediate vinyl cation, 6, as shown in Scheme II. The importance of the fragmentation path is presumably determined by the stability of the alkyl cation formed by the alkyl oxygen fission. 

Saponification of Ionized Esters by Intramolecular Hydrogen Transfer Cleavage of the Alkyl/Oxygen Bond... 

Isotopes can also be used to solve mechanistic problems that are non-kinetic. Thus the aqueous hydrolysis of esters to yield an acid and an alcohol could, in theory, proceed by cleavage at (a) alkyl/ oxygen fission, or (b) acyl/oxygen fission ... 

Alkaline hydrolysis of the acetate (22 — 23) can be shown not to involve fission of the alkyl-oxygen C—O linkage, so the alcohol... 

Esters, RC02R, where the alkyl group R can form a relatively stable carbocation, e.g. (177) from (178), have been shown—by lsO labelling experiments—to undergo alkyl-oxygen cleavage ... 

NMR studies on the alkoxide initiators confirm that all the lactones polymerize via an acyl— oxygen scission, including /3-PL (which, by contrast, opens at the alkyl—oxygen bond with (251)). Monomer coordination and subsequent ring opening may be observed by 111 NMR spectroscopy. Coordination is also observed with 7-BL and 7-VL, although these adducts are stable to insertion and polymerization does not proceed. 

The effectiveness of micellar control on the rate and stereochemical course of hydrolysis at a saturated carbon atom was found to be fairly striking. Chiral 1-methylheptyl trifluoromethanesulfonate [45] undergoes hydrolysis via alkyl-oxygen bond fission, and the hydrolysis rate was only 1/300 (for CTAB) or 1/350 (for SDS) as fast as the rate in pure water (Okamoto et al., 1975). Interestingly, the 2-octanol formed shows net inversion (70%) in a nonmicellar... 

The acid-catalysed hydrolysis of phosphinic esters (158) is relatively insensitive to the substituent (R = Me, Et, Pr1, or Bu1) attached to phosphorus this contrasts with the base-catalysed process.126 The acid hydrolysis of the phosphinic esters (159) (see Organophosphorus Chemistry , Vol. 7, p. 129 for the base hydrolysis) takes place with alkyl-oxygen fission in an SnI process.127... 

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