Aralkyl halides

Certain of the monoalkylated ethyl phenylacetates have been further alkylated with alkyl and aralkyl halides to produce the corresponding disuhstituted phenylacetic esters.4 Ethyl 2-phenyl-propanoate has been alkylated by methyl iodide to give pure ethyl 2-methyl-2-pheny]propanoate in 81% yield. Similarly, the alkylations of ethyl 2-phenylhexanoate with methyl iodide, M-butyl bromide, and benzyl chloride gave the corresponding pure dialkylated products in 73%, 92%, and 72% yields, respectively. 

The reaction of 2 -aminofluorans with aralkyl halides is solely used to prepare 2 -diaralkylaminofluorans developing red or green colors. 

The scope and limitations of the Lewis acid-catalyzed additions of alkyl chlorides to carbon-carbon double bonds were studied.51 Since Lewis acid systems are well-known initiators in carbocationic polymerizations of alkenes, the question arises as to what factors govern the two transformations. The prediction was that alkylation products are expected if the starting halides dissociate more rapidly than the addition products.55 In other words, addition is expected if the initial carbocation is better stabilized than the one formed from the dissociation of the addition product. This has been verified for the alkylation of a range of alkyl-and aryl-substituted alkenes and dienes with alkyl and aralkyl halides. Steric effects, however, must also be taken into account in certain cases, such as in the reactions of trityl chloride.51... 

Choride ion is considerably less reactive than the azide ion. Thus, although values of kc 1/ kn2o have been quite widely available from mass law effects of chloride ion on the solvolysis of aralkyl halides, normally the reaction of the chloride ion cannot be assumed to be diffusion controlled and the value of kn2o cannot be inferred, except for relatively unstable carbocations (p. 72). Mayr and coworkers251 have measured rate constants for reaction of chloride ion with benzhydryl cations in 80% aqueous acetonitrile and their values of logk are plotted together with a value for the trityl cation19 in Fig. 7. There is some scatter in the points, possibly because of some steric hindrance to reaction of the trityl cations. However, it can be seen that chloride ion is more... 

The outline procedure involves the initial reaction of the 2,4,6-triphenyl-pyrylium halide with the primary amine to yield the corresponding 2,4,6-triphenylpyridinium halide (see Section 8.4.1, and also Section 5.15.3, p. 768) this reaction proceeds either at room temperature in a suitable solvent, or more efficiently under reflux in benzene with azeotropic removal of water. Pyrolysis of the pyridinium halide under controlled conditions then yields the alkyl (or aralkyl) halide in good yield. The mechanism of the reaction in this case is probably of the Sn2 type. 

The ready replacement of the halogen in an alkyl or an aralkyl halide illustrated in Expt 5.157 by reaction with sodium or potassium cyanide is inapplicable in the case of aryl halides wherein the halogen is relatively inert. However, aryl bromides can be converted into nitriles in good yield by heating them for several hours at about 200 °C with copper(i) cyanide in the presence of pyridine (e.g. 1-naphthonitrile, Expt 6.168). This displacement may be achieved more readily by using dimethylformamide as the solvent, when reaction is usually completed in a few hours at reflux temperature.63... 

It has been suggested562-564 that the fast decomposition of aralkyldimethylphenylammo-nium halides 385 to aralkyl halides and dimethylaniline in chloroform (equation 252) invloves the formation of the positively charged triple ion 386 (equation 253), consisting... 

Electrochemical reduction of aryl halides in the presence of olefins (94), (equation 54) leads to the formation of arylated products (95). Electroreduction of several aralkyl halides at potentials ranging from -1.24 V to -1.54 V (see) gives products which involve dimerization, cyclization, and reduction to the arylalkanes. Carbanions and/or free radicals were again postulated as intermediates79. Aryl radicals generated from the electrochemical reduction of aryl halides have been added to carbon-carbon double bonds80,81. Electrochemical reduction of aryl halides in the presence of olefins leads to the formation of arylated products78. Preparative scale electrolyses were carried out in solvents such as acetonitrile, DMF and DMSO at constant potential or in liquid ammonia at constant current. The reaction is proposed to involve an S l mechanism. 

In order to improve cell and blood-brain-barrier permeability of the polar tetrahydropterins model studies were performed by applying the concepts of the Bodor system. 6-Mono- and 6,7-disubstituted 5,6,7,8-tetrahydropterins (172) have been acylated with nicotinoyl chloride at N-5 (173) followed by quaternization of the pyridine moiety by various alkyl and aralkyl halides (174), respectively (Scheme 27). Reduction of the pyridinium residue to its 1,4-dihydro stage afforded new types of potentially active conjugates (175) (Scheme 27) <90MI 718-07,91MI718-03). 

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. 

This section deals with the difficult problem of establishing the most plausible initiation mechanism for polymerisation systems in which cocatalysis is ascribed to alkyl or aralkyl halides. This type of cocatalysis is by no means a general phenomenon. We have already mentioned in preceding sections dealing with other types of cocatalysis that, for example, r-butyl chloride is not a cocatalyst in the polymerisation of isobutene induced by titanium tetrachloride and that 1-phenylethyl chloride is not a cocatalyst in conjunction vdth stannic chloride - Indeed, the reaction... 

Recent developments in Kennedy s laboratory on the use of boron chloride in conjunction with alkyl and aralkyl halides for the synthesis of polymers with predetermined structure were discussed by that author at two recent meetings Kennedy also kindly provided us with manuscripts of forthcoming papers which are discussed below. 

There are numerous examples of quaternizing alkylations of imidazoles using such diverse reagents as alkyl, alkenyl or aralkyl halides, ethyl chloroacetate, phenacyl bromide or dimethyl sulfate. Since water is frequently held very tenaciously by imidazole quaternary salts the compounds are often best prepared in anhydrous conditions (e.g. dry benzene solvent in a dry nitrogen atmosphere) even though the reaction is commonly slower in non-polar solvents. 

Halogen atom abstraction. The metal radicals react with alkyl and aralkyl halides (RX, X = Cl, Br, I) to yield CpM(CO)3X and R. The metal halide product is a species known independently, and its formation in these reactions was verified by IR. The organic free radicals were not detected directly, but were inferred from the final organic products determined by GC these products were consistent with those known to be formed when R undergoes dimerization and disproportionation reactions. 

In the preparation of hydrocarbons an alkyl, aryl, or aralkyl halide is mixed with an excess of an aromatic hydrocarbon, and anhydrous aluminum chloride is added in small portions. The reagents must be free from moisture. If the reactants are not liquid or the reaction is very vigorous, a solvent is used. Benzene, nitrobenzene, carbon disulfide, or o-dichlorobenzene may be employed as solvents. When polyhalides are used, more than one molecule of the hydrocarbon may react. For example, benzene with chloroform yields triphenylmethane, and benzene with carbon tetrachloride gives triphenylmethyl chloride ... 

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