Dialkyl ethers alkylation

The cleavage of dialkyl ethers by hydrogen halides was discussed in Section 16 8 where It was noted that the same pair of alkyl halides results irrespective of the order in which the carbon-oxygen bonds of the ether are broken... 

Attack by the halide nucleophile at the sp hybridized carbon of the alkyl group is anal ogous to what takes place in the cleavage of dialkyl ethers Attack at the sp hybridized carbon of the aromatic nng is much slower Indeed nucleophilic aromatic substitution does not occur at all under these conditions... 

An important feature of sulfation chemistry is the thermal instability of the acid sulfate, which breaks down to a mixture of products including the parent alcohol, the dialkyl sulfate (R0S020R), the dialkyl ether (ROR), isomeric alcohols, olefins (R CH=CH2), and esters (R0S03R). Because of the thermal instability of the acid sulfate it is necessary to avoid high sulfation temperatures and to neutralize the acid sulfation product soon after its formation. An aging time of about 1 min at 30-50°C is adequate for the second reaction whereby the desired alkyl hydrogen sulfate is formed. In practice the minimum sulfation feasible temperature is determined by the need for the feedstock and reaction mixture to be mobile liquids (Table 3). 

Dialkyl and alkyl aryl ethers can be cleaved with iodotrimethylsilane ROR -bMe3SiI — Rl-bMe3SiOR. A more convenient and less exjjensive alternative, which gives the same products, is a mixture of chlorotrimethylsilane and Nal. Alkyl aryl ethers can also be cleaved with Lil to give alkyl iodides and salts of phenols in a reaction similar to 10-73. Triphenyldibromophosphorane (Ph3PBr2) cleaves dialkyl ethers to give 2mol of alkyl bromide. ... 

The initiation reaction in the polymerization of vinyl ethers by BF3R20 (R20 = various dialkyl ethers and tetrahydrofuran) was shown by Eley to involve an alkyl ion from the dialkyl ether, which therefore acts as a (necessary) co-catalyst [35, 67]. This initiation by an alkyl ion from a BF3-ether complex means that the alkyl vinyl ethers are so much more basic than the mono-olefins, that they can abstract alkylium ions from the boron fluoride etherate. This difference in basicity is also illustrated by the observations that triethoxonium fluoroborate, Et30+BF4", will not polymerise isobutene [68] but polymerises w-butyl vinyl ether instantaneously [69]. It was also shown [67] that in an extremely dry system boron fluoride will not catalyse the polymerization of alkyl vinyl ethers in hydrocarbons thus, an earlier suggestion that an alkyl vinyl ether might act as its own co-catalyst [30] was shown to be invalid, at least under these conditions. 

Thus the reaction site, the double bond, participates in the charge and polymerization can take place. That the vinyl group conjugated with the oxygen atom is more basic than an ordinary ether oxygen is shown by the fact that alkyl vinyl ethers can be polymerised readily in dialkyl ethers as solvents. 

Method C Aqueous NaOH (50%, 40 ml), the alcohol (0.1 mol), TBA-HS04 (5 mmol) and an excess of the alkyl halide (ca. 2.0 mol used as the organic solvent) are stirred together (see Table 3.1 for reaction time and temperature). On completion of the reaction the organic phase is separated, washed well with H20 and evaporated. The residue is extracted with Et20 (3x15 ml) and the extracts are fractionally distilled to yield the dialkyl ether. 

Ethers are the least reactive of the functional groups. The cleavage of C-O bond in ethers takes place under drastic conditions with excess of hydrogen halides. The reaction of dialkyl ether gives two alkyl halide molecules. 

Taft and coworkers ° have reported lithium ion affinities, AGu+, for various types of compounds. Values of AGu+ for alkyl thiols, dialkyl sulfides, alcohols and dialkyl ethers (sets CP3, CP4, CPS and CP6, Table 10) were correlated with equation 27. The regression equation for the alkyl thiols is equation 58 ... 

Enhanced acidity also characterizes the sp -carbon bonded hydrogen compared to the sp one. As a consequence, alkyl vinyl ethers are more acidic than dialkyl ether and thus can be deprotonated more easily. 1-Ethoxy-1-lithioethene 54252-254 gener-... 

Suzuki T, Oriyama T (1999) Novel reactions of ethylene acetals with silyl-substituted nucleophiles. A mild and efficient procedure for the synthesis of homoallyl alkyl ethers and unsymmetrical dialkyl ethers. Synth Commun 29 1263-1269... 

R" may be alkyl or aryl. For dialkyl ethers, the reaction does not end as indicated above, since R OH is rapidly converted to R OR by the sulfonic acid (reaction 0-16), which in turn is further cleaved to R 0S02R" so that the product is a mixture of the two sulfonates. For aryl alkyl ethers, cleavage always takes place to give the phenol, which is not converted to the aryl ether under these conditions. Ethers can also be cleaved in a similar manner by mixed anhydrides of sulfonic and carboxylic acids733 (prepared as in 0-33). p-Hydroxy alkyl perchlorates734 and sulfonates can be obtained from epoxides.735 Epoxides and oxetanes give dinitrates when treated with N2Os,736 e.g.,... 

Alternatively, alkyl aryl ethers can be prepared from support-bound aliphatic alcohols by Mitsunobu etherification with phenols (Table 7.13). In this variant of the Mit-sunobu reaction, the presence of residual methanol or ethanol is less critical than in the etherification of support-bound phenols, because no dialkyl ethers can be generated by the Mitsunobu reaction. For this reason, good results will also be obtained if the reaction mixture is allowed to warm upon mixing DEAD and the phosphine. Both triphenyl- and tributylphosphine can be used as the phosphine component. Tributyl-phosphine is a liquid and generally does not give rise to insoluble precipitates. This reagent must, however, be handled with care because it readily ignites in air when absorbed on paper. 

SAMPLE SOLUTION (a) In the reaction of dialkyl ethers with excess hydrogen bromide, each alkyl group of the ether function is cleaved and forms an alkyl bromide. Because bromocydopentane and 1-bromobutane are the products, the starting ether must be butyl cyclopentyl ether. 

Dialkyl ether Hydrogen halide Two alkyl Water... 

With acyclic ethers. In a study of THF polymerization using PFjT gegenions Dreyfuss (25) show that in the presence of dialkyl ethers chain transfer occurs and continues to occur after equilibrium is reached. The ultimate conversion to polymer is not affected but the intrinsic viscosity of the polymer decreases with time (Fig. 6). The reaction involved is essentially the reverse of the initiation reaction with trialkyl oxonium salts (equation 5). In the case of transfer the dialkyl ether reacts with the propagating oxonium ion to give a trialkyl oxonium ion which has one long chain alkyl and two short alkyls derived from the ether. 

If a n-propyl group in a dialkyl ether is replaced by an isopropyl VM group, then Vm increases about 2cm3 mol-1, regardless of the nature of the other alkyl groups. (R-3.2.1)... 

Obama et al. [9] reported two factors significant in modeling structure- Vm relationships in isomeric dialkyl ethers (1) the existence of side chains and (2) the difference between the numbers of C atoms in the two alkyl groups. The first factor causes Vm to increase (i.e., a branched dialkyl ether has a greater Vm value than that of its linear isomer) ... 

Vm (branched di-n-alkyl ether) > Vm (unbranched dialkyl ether) (R-3.2.2)... 

Similarly, they derived relationships for alkenes, alkylbenzenes, alkanols, dialkyl ethers, mono-, di-, and trialkyl amines, and alkyl halides. For example, the equation for dialkyl ethers (C4-C8) is... 

This model is based on Sw data spanning 5 log units. Nirmalakhandan and Speece [36,37] discuss the model s validity and robustness in detail. They performed a test using experimental Sw data for esters, ethers, and aldehydes that were not included in the training set. They noted reasonably good agreement between experimental and estimated data for the test set and indicated that eq. 11.5.4 is applicable to dialkyl ethers, alkanals, and alkyl alkanoates, but not for ketones, amines, PAHs, and PCBs. Nirmalakhandan and Speece [37] expanded the model above for the PAHs, PCBs, and PCDDs. However, their model has been criticized by Yalkowsky and Mishra for incorrect and omitted data [38]. The revised model is [38]... 

Cleavage of dialkyl ethers.1 Methyl, allyl, and benzyl alkyl ethers are cleaved by this combination to the alcohols and methyl, allyl, and benzyl iodide (75-90% yield). The reagent also cleaves epoxides to frans-2-iodoalkanols (—70% yield). 

At lower temperatures the oxonium salt or the alkyl hydrogen sulfate may react by an SN displacement mechanism with excess alcohol in the reaction mixture, thereby forming a dialkyl ether. Although each step in the reaction is reversible, ether formation can be enhanced by distilling away the ether as fast as it forms. Diethyl ether is made commercially by this process ... 

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