Dialkyl ether

When comparing alcohols with corresponding ethers, the a carbon atom of the ether is deshielded by about 10-12 ppm while the carbon in the / position experiences a shielding of about 3 ppm (Table 4.26)  

Using the increment formalism, this is rationalized as a p effect of the O-alkyl carbon to the a E nd a y effect to the /Tcarbon transmitted through the ether oxygen [210, 275-277]. Corresponding changes are observed for methoxy relative to hydroxy shift increments for a and fi carbons of cyclohexane [263-265]. 

Successive enhancement of 7 shieldings in the series ethyl, iso-propyl and f-butyl methyl ether (Table 4.26) is attributed to an increased number of gauche interacting methyl groups  

Conversion of diethyl ether into triethyloxonium tetrafluoroborate deshields the a while shielding the y carbon atom. The reason is not only the positive charge at oxygen but also an additional /I and y effect introduced by the third ethoxy group. 

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Fig. X-9. Zisman plots of the contact angles of various homologous series on Teflon O, RX , alkylbenzenes (f), n-alkanes , dialkyl ethers , siloxanes A, miscellaneous polar liquids. (Data from Ref. 78.)...

Step 3 The product of step 2 is the conjugate acid of the dialkyl ether It is deprotonated m the final step of the process to give the ether... 

Conversion to dialkyl ethers (Sec tion 15 7) On being heated in the presence of an acid catalyst two molecules of a primary alcohol combine to form an ether and wa ter Diols can undergo an intramo lecular condensation if a five membered or six membered cyclic ether results... 

Because they are widely used as solvents many simple dialkyl ethers are commercially available Diethyl ether and dibutyl ether for example are prepared by acid catalyzed condensation of the corresponding alcohols as described earlier m Section 15 7... 

The reaction follows a free radical mechanism and gives a hydroperoxide a compound of the type ROOH Hydroperoxides tend to be unstable and shock sensitive On stand mg they form related peroxidic derivatives which are also prone to violent decomposi tion Air oxidation leads to peroxides within a few days if ethers are even briefly exposed to atmospheric oxygen For this reason one should never use old bottles of dialkyl ethers and extreme care must be exercised m their disposal... 

A series of dialkyl ethers was allowed to react with excess hydro... 

Infrared The infrared spectra of ethers are characterized by a strong rather broad band due to antisymmetric C—O—C stretching between 1070 and 1150 cm Dialkyl ethers exhibit this band consistently at 1120 cm as shown m the IR spectrum of dipropyl ether... 

Epoxides are unusual m that the protons on the ring are more shielded than expected The protons m ethylene oxide for example appear at 8 2 5 instead of the 8 3 2-4 0 range just cited for dialkyl ethers... 

The ring carbons of an epoxide are somewhat more shielded than the carbons of a C—O—C unit of larger rings or dialkyl ethers... 

Section 16 7 Dialkyl ethers are useful solvents for organic reactions but must be used cautiously due to their tendency to form explosive hydroperoxides by air oxidation in opened bottles... 

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... 

LiAlH is soluble in ethers, 35-40 g/100 g diethyl ether at 25°C. Solubihty in THF, the other common solvent for LiAlH, is 13 g/100 g at 25°C. Polyethylene glycol diaLkyl ethers are also good solvents. 

Chain Transfer. A number of materials act as tme transfer agents in THF polymerization notable examples are dialkyl ethers and orthoformates. In low concentrations, water behaves as a transfer agent, and hydroxyl end groups are produced. The oxygen of dialkyl ethers are rather poor nucleophiles compared to THF and are therefore not very effective as transfer agents. On the other hand, orthoformates are effective transfer agents and can be used to produce alkoxy-ended PTHFs of any desired molecular weight (169). 

Carbon disulfide reacts with alkanols or diaLkyl ethers at 250—500°C over activated alumina catalyst to give diaLkyl sulfides. For example, methanol yields dimethyl sulfide [75-18-3]. 

Except for the special case of the epoxides, THE represents the largest use of a heterocycHc ether. Its consumption is also much larger than that of ethyl ether. Unlike the dialkyl ethers, THE is totally miscible in water at ambient conditions. Its cycHc stmeture also allows it to be more reactive than the dialkyl ethers. More than half of the THE produced is used as an intermediate in making other chemicals or elastomers. 

Lil, collidine, reflux, 10 h, quant.Aryl ethyl ethers are cleaved more slowly dialkyl ethers are stable to these conditions. 

Bromo-9-borabicyclo[3.3.0]nonane (9-Br-BBN), CH2CI2, reflux, 87-100% yield.9-Br-BBN also cleaves dialkyl ethers, allyl aryl ethers, and methylenedioxy groups. 

These unusual properties of fluorocarbons reflect theu nonpolar character, low polarizability, and overall relatively weak intermolecular attractions Saturated perfluoro-terr-ammes and -dialkyl ethers also closely resemble fluorocarbons rather than typical amines or ethers in their physical properties [4,... 

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