Halides self-alkylation

A similar type of catalyst including a supported noble metal for regeneration was described extensively in a series of patents assigned to UOP (209-214). The catalysts were prepared by the sublimation of metal halides, especially aluminum chloride and boron trifluoride, onto an alumina carrier modified with alkali or rare earth-alkali metal ions. The noble metal was preferably deposited in an eggshell concentration profile. An earlier patent assigned to Texaco (215) describes the use of chlorinated alumina in the isobutane alkylation with higher alkenes, especially hexenes. TMPs were supposed to form via self-alkylation. Fluorinated alumina and silica samples were also tested in isobutane alkylation,... 

Sulfonates such as mesylates or tosylates are readily prepared from alcohols under mild conditions, and are therefore attractive alternatives to halides as electrophiles. Although sulfonates often undergo clean displacement by nucleophiles, alternative reaction pathways are accessible to these intermediates, which can lead to unexpected results. If the nucleophile used is strongly basic, metalation instead of displacement of the sulfonate can occur. Some potential reactions of such metalated sulfonates include fragmentation into sulfenes and alcoholates, or into sulfmates and carbonyl compounds, or self-alkylation (Scheme4.15). 

In practice this reaction is difficult to carry out with simple aldehydes and ketones because aldol condensation competes with alkylation Furthermore it is not always possi ble to limit the reaction to the introduction of a single alkyl group The most successful alkylation procedures use p diketones as starting materials Because they are relatively acidic p diketones can be converted quantitatively to their enolate ions by weak bases and do not self condense Ideally the alkyl halide should be a methyl or primary alkyl halide... 

Recall from Section 5.3 that radical substitution reactions require three kinds of steps initiation, propagation, and termination. Once an initiation step has started the process by producing radicals, the reaction continues in a self-sustaining cycle. The cycle requires two repeating propagation steps in which a radical, the halogen, and the alkane yield alkyl halide product plus more radical to carry on the chain. The chain is occasionally terminated by the combination of two radicals. 

C-Alkylation takes place in the reaction of methyl nitroacetate with alkyl halides the products are useful intermediates for preparing amino acids (Eq. 5.1).2 The requisite nitro acetate is prepared by self condensation of nitromethane.3... 

The self-ionisation of aluminium chloride and bromide in nitrobenzene has been studied in great detail [15], and the rates of the forward and back reactions have been determined so that all the relevant equilibrium constants are known. The whole body of evidence available shows that self-ionisation of the initiator, with or without other ionogenic reactions in the initiator solutions, can be regarded as well established for all aluminium halides and as highly probable for the alkyl aluminium halides. Moreover, the ionogenic reactions are relatively slow and - except under the dirtiest conditions - the concentration of ions in the initiator solution will be very much less than [A1X3]0. 

Since the extent of self-ionisation of aluminium chloride and bromide in the alkyl halide solvent is very small (Table 1) ([AlX+2]/[AlX3] approximately 10"4) the isobutene whose concentration is always kept very low, reacts preferentially with the much more abundant A1X3 to form the complex, and if any isobutene does react with AlX+2, the resulting... 

Proposition 1 The initiator solutions of aluminium halide, A1X3, in alkyl halide RX contain ions formed by the self-ionization of the aluminium halide ... 

Pyridinecarboxylic acids exist largely in the zwitterion form in water (57JA2050). They can be converted into esters with alcohols and mineral acid catalysis, and by use of diazoalkanes. Use of alkyl halides in alkali gives N-alkylbetaines. Esters can also be formed from acid chlorides but the latter are liable to self-quaternization. 

Recently, catalyst 50 (n > 4) was reported highly active and selective for olefin synthesis from alkyl halides with aqueous sodium or potassium hydroxide without the formation of by-product alcohols 172). The active catalyst structures were suggested to involve self-solvated polymeric alkoxides 173) 52 and/or complexed hydroxides 53. 

Alkyl- and Atylhydridohalonium Ions. The self-condensation of alkyl halides in strongly acidic media represents a convenient preparative route to symmetric dialkylhalonium ions 127 [Eq. (4.97)]. This reaction involves hydridohalonium ions 126 as intermediates that subsequently undergo nucleophilic attack by excess alkyl halide. 

Disconnection 37 again uses the natural polarity of the carbonyl group but at the next bond 37 since we hope to use some enolate derivative 38 in an alkylation reaction. But—and it is a big but—do not think for a moment that you can make 37 just by mixing the ketone 39 with an alkyl halide and some base. The problem is that the ketone is itself electrophilic and the self-condensation by the aldol reaction (chapter 19) is generally preferred to alkylation. 

The enamines prepared from acetaldehyde or monosubstituted acetaldehydes undergo self-condensation in the reaction mixture very readily so that alkylation is practically impossible. Enamines prepared from disubstituted aldehydes are exclusively iV-alkylated on treatment with aliphatic alkyl halides,218 whereas allyl halides cause... 

RCH2X/RCH2X- self-exchange (60-80 kcal mol-1) and an E° pertaining to (100), and not (101). Thus, calculated E° values of methyl halides (Hush, 1957) are around —0.75 V, far above experimental Ein around or below —1.8 V. This behavior would of course be expected for an electrochemically irreversible process, as alkyl halide reduction indeed is found to be experimentally (Mann and Barnes, 1970), and hence the above assumptions are self-consistent. In the following discussion, we shall use E° values for reaction (100) for alkyl and aralkyl halides, with suitable corrections for the formation of resonance-stabilized radicals like benzyl and 4-nitrobenzyl. 

Polymerizations which are second order in Lewis acid have also been observed, including self-initiated polymerizations with AlBrj [181], and isobutene polymerizations initiated by alkyl esters and halides activated by TiCU [175,182],... 

Synthesis of aldehydes and ketones. This substance can function as a protected cyanohydrin of formaldehyde in an extension of Stork and Maldonado s synthesis of ketones from aldehydes, RCHO —> RCOR, by way of cyanohydrins (4, 300-301). Thus the anion of 1, generated with LDA, does not undergo self-condensation, but can be alkylated the product on hydrolysis gives the homologous aldehyde of the alkyl halide. Thus the reagent serves as the latent anion of formaldehyde, HC=0. An example is shown in equation (I). 

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