Alcohols ether formation from

Protection of alcohols. Ether formation from ROH and 4-XCf,H4CH2Br mediated by NaH in DMF is easily achieved. Such ethers are cleaved by Pd-catalyzed processes. 

Ether formation from alcohol and alkanoyl chloride Wacker-Chemie Bachhuber (1993)... 

The rate constants kTS and kST define an equilibrium constant (ATeq) connecting the singlet and triplet carbenes. An estimate of Ktq, and hence AGSX, for BA can be obtained from the experiments described above. The time resolved spectroscopic measurements indicate that BA reacts with isopropyl alcohol with a rate constant some five times slower than the diffusion limit (Table 7). This, in conjunction with the picosecond timescale measurements, gives a value for ksr. The absence of ether formation from the sensitized irradiation, when combined with the measured rate constant for reaction of 3BA with isopropyl alcohol, gives an upper limit for k-. These values give Keq and thus AGST 2 5.2 kcal mol-1 (Table 8). 

Group II The activity drops more than the Ni surface concentration (Fig. 13), i.e., at least about 20 times. However, for several reactions this drop is two or more orders of magnitude. The reactions included in this group are methanation and Fischer-Tropsch synthesis, isomerization, de-hydrocyclization or hydrogenolysis of alkanes, ether formation from alcohols, metathesis of alkylamines, and possibly other reactions. 

This is again a direct analogy with ether formation from alcohols (see Sect. 2.2.4). The acidic sites might be the Al3+ ions because rehydration of the alumina surface does not enhance the rate, in contrast to deamination [149],... 

However, the investigations of the mechanism of olefin and ether formation from alcohol (Sect. 2.2) revealed the importance of basic sites. It is feasible that, for esterification also, pairs of acidic and basic sites might be necessary. 

Other silane byproducts than triethylsilanol or ether formation from two molecules of crotyl alcohol are not observed. Side reaction which decreases the yield of 8 may be the reduction of aldehyde 7 to the corresponding alcohol 27, if water instead of the crotyl alcohol attacks the activated aldehyde 23. 

But the rates of cyclisations to form 3-, 5-, 6- and 7-membered rings are greater than the rates of corresponding bimolecular reactions. This is kinetics but the smaller loss of entropy (fewer degrees of freedom lost in the cyclisation) is also a factor. We should not expect a good yield in an acid-catalysed ether formation from two alcohols. If the reaction worked at all, we should get dimers of each alcohol as well as the mixed ether 51. 

It has been shown that only those alcohols that form detectable surface alco-holate species on alumina undergo bimolecular dehydration with ether and water as reaction products (340). Thus, ether formation is the dominant reaction direction of methanol and ethanol at low temperatures, and the tendency toward ether formation is reduced as the chain length increases and chain branching occurs (28, 340). The same trends are observed for the stability and surface concentrations of the surface alcoholate species (27, 28, 47, 340). Alcoholate formation is due to a dissociative chemisorption step of the alcohol that occurs on A1—O pair sites (47, 340, 354-358). One is, thus, led to the conclusion that incompletely coordinated Al3+ ions and O2- ions are both important sites in the ether formation from alcohols and that their participation should be detectable by specific poisoning. 

Parera and his co-workers (359-362) have studied the poisoning effect of amines, pyridine, phenol, and acetic acid. A reduced rate of ether formation from methanol at the standard temperature of 230°C was observed when the poisons were present in the feed. In most cases the original activity was recovered, although rather slowly. Most probably the poisons were either displaced by alcohol and/or water or removed from the surface by chemical transformations. 

Figueras Roca and co-workers (346) have used preadsorbed TCNE to poison the basic sites specifically. The rate of ether formation from methanol and ethanol responded very sensitively to the poisoning with TCNE, so that the participation of basic sites in the bimolecular alcohol dehydration seems to be proved. 

DBSA is also applicable to other reactions in water. Ether formation from two alcohols is such an example [40]. We tried formation of symmetric ethers from benzylic alcohols in water using 10 mol% of DBSA as a catalyst. The reactions were found to proceed smoothly in water to afford the corresponding symmetric ethers in high yields (Table 13.8, entries 1 and 2). It should be noted that the etherification of the substrate shown in entry 1 in the presence of TsOH instead of DBSA gave only a trace amount... 

The reactions of butan-l-ol (Scheme 3) were explored over silica-supported Pt-Au catalysts (and also Ni-Cu powders). It was confirmed that metals are active in ether formation from higher alcohols, although sensitive to the presence of sodium ions. Alloying decreased the activity of pure Pt for ether formation, ascribed to the diminished number of active ensembles (perhaps containing 4 atoms), although it was not eliminated (unlike Ni-Cu alloys).The percentage formation of C4 hydrocarbons (butane, butene),butanal. 

Maybe one of the most important questions to be answered relates to the degree of dissociation of Brpnsted acids and bases in ionic liquids. Acids are ubiquitously used as catalysts to initiate reactions such as the Fischer-type esterification or ether formation from alcohols. 

The time-resolved method was applied to another photodissociation reaction [124], Upon the photoexcitation of diazo compounds (Fig. 16), nitrogen is dissociated to yield the singlet carbenes. In alcoholic solvents such as methanol, the O—H bond is inserted into the carbene part quickly (within 40 ps for diphenylcarbene), and an ether is formed. The AH and AV values for the ether formation from DPDM in methanol were measured by the time-resolved method. A similar TG signal to the DPCP case was observed after the excitation of DPDM in methanol. The signal rises within 50 ns after the excitation and decays monotonously. The time profile of the signal was found to be expressed well with a tri-exponential function... 

Regioselective monoalkyl ether formation from naphthalene-1, 4-diols using alcohols (prim, or sec.) containing HCI. 

Acidic clays are widely applied in the dehydration of alcohols [38]. Although similar to zeolites in their capacity to induce the formation of both alkenes and ethers, selective alkene synthesis is possible. Various layered materials (clays, ion-exchanged montmorillonite, pillared layered clays) are very active and, in general, selective in transforming primary, secondary, and tertiary aliphatic alcohols to 1-alkenes [39-43]. Al -exchanged montmorillonite, however, induces ether formation from primary alcohols and 2-propanol [41]. Substituted 1-phenyl-1-ethanols yield the corresponding styrene derivatives at high temperature (653-673 K) [44]. 

The LiBCCfjFjla-LiOTf/MgO combination catalyzes benzyl ether formation from alcohols (10 examples, 72-100%). The method is valuable for dealing with substrates containing base sensitive funetionalities. ... 

Finally, a word of caution when using [BF4] and [PF ]" ionic liquids - they are not stable and give off HF, particularly when heated in the presence of a proton source or a metal salt [21]. There are many examples of this in this chapter. An example of a HF-catalyzed reaction is ether formation from alcohols is a classic acid-catalyzed reaction. An ether formation reaction was found to occur in a range of [BF4] ionic liquids, with an example being the addition of methanol to ten-butanol to form methyl-tert-butyl ether (MTBE) [306]. The author is of the opinion that [Bp4] ionic liquids (even hydrophobic ones) can dehydrate alcohols to ether and refers to these ionic liquids as dehydrators. All that is happening here is a simple HF-catalyzed reaction. With many authors not aware of this phenomenon, they resort to all kinds of inappropriate explanations for what is occurring. 

Habenicht, C., Kam, L.C., Wilschut, M.J. and Antal, M.J., Jr., Homogeneous catalysis of ethyl terf-butyl ether formation from tert butyl alcohol in hot, compressed liquid ethanol, Ind. Eng. Chem. Res., 1995, 34(11), 3784-3792. 

The bimolecular ether formation from alcohols proceeds at much lower temperatures than the olefin formation.Over alumina, it occurs even at 400 — 410 The... 

Benzylatnine. Warm an alcoholic suspension of 118-5 g. of finely-powdered benzyl phthalimide with 25 g. of 100 per cent, hydrazine hydrate (CAUTION corrosive liquid) a white, gelatinous precipitate is produced rapidly. Decompose the latter (when its formation appears complete) by heating with excess of hydrochloric acid on a steam bath. Collect the phthalyl hydrazide which separates by suction filtration, and wash it with a little water. Concentrate the filtrate by distillation to remove alcohol, cool, filter from the small amount of precipitated phthalyl hydrazide, render alkaline with excess of sodium hydroxide solution, and extract the liberated benzylamine with ether. Dry the ethereal solution with potassium hydroxide pellets, remove the solvent (compare Fig. //, 13, 4) on a water bath and finally distil the residue. Collect the benzylamine at 185-187° the 3ueld is 50 g. 

Diethyl ether is the principal by-product of the reaction of ethyl alcohol with diethyl sulfate. Various methods have been proposed to diminish its formation (70—72), including separation of diethyl sulfate from the reaction product. Diethyl sulfate not only causes an increase in ether formation but is also more difficult to hydroly2e to alcohol than is ethyl hydrogen sulfate. The equiUbrium constant for the hydrolysis of ethyl hydrogen sulfate is independent of temperature, and the reaction rate is proportional to the hydrogen ion concentration (73—75). 

Dianion formation from 2-methyl-2-propen-l-ol seems to be highly dependent on reaction conditions. Silylation of the dianion generated using a previously reported method was unsuccessful in our hands. The procedure described here for the metalation of the allylic alcohol is a modification of the one reported for formation of the dianion of 3-methyl-3-buten-l-ol The critical variant appears to be the polarity of the reaction medium. In solvents such as ether and hexane, substantial amounts (15-50%) of the vinyl-silane 3 are observed. Very poor yields of the desired product were obtained in dirnethoxyethane and hexamethylphosphoric triamide, presumably because of the decomposition of these solvents under these conditions. Empirically, the optimal solvent seems to be a mixture of ether and tetrahydrofuran in a ratio (v/v) varying from 1.4 to 2.2 in this case 3 becomes a very minor component. 

This ether formation arises from conversion of the phenol to a cyclohexanone, and ketal formation catalyzed by Pd-Hj and hydrogenolysis. With Ru-on-C, the alcohol is formed solely (84). 

A solution of 200 g of 1 -p-chlorophenvl-2-phenyl-4-(N-pvrrolidino)-butanol-2 in 750 ml of concentrated hydrochloric acid is refluxed for 9 hours thereby causing a dehydration of the butanol compound, and the formation of the hydrochloric acid addition salt of a 1 -p-chloro-phenyl-2-phenyl-4-(N-pyrrolidino)-butene. The hydrochloride salt formed crystallizes in the oily lower layer of the two phase reaction mixture and is removed therefrom by filtration. The filtrate is again refluxed for 9 hours, cooled to0°C,and a second crop of the hydrochloric acid addition salt of the dehydration product is obtained and filtered off. The filtrate containing residual amounts of 1 -p-chlorophenyl-2-phenyl-4-(N-pyrrolidino)-butanol-2 is again refluxed for 9 hours to yield an additional crop of the salt of the dehydration product. The several fractions of the butene compound are combined and triturated with several small portions of hot acetone and recrystallized from alcohol-ether mixture. The hydrochl or ic acid addition salt of the dehydration product, 1 -p-chlorophenyl-2-phenyl-4-(N-pyrrolidino)-butene hydrochloride, melts at about 227°C to 228°C. 

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