Alcohols to olefin

For further dehydration, for example, of aldoximes and amides to nitriles, of alcohols to olefines, as well as the synthesis of heterocycles like oxiranes and aziridines see Section 18.5. 

The second mode of addition of alcohols to olefins, to produce ethers, has been found to occur only with cyclic olefins. Thus in 1966 Kropp reported that cyclohexenes (39)-(42) produce tertiary ethers upon photolysis in methanol in the presence of high-energy sensitizers such as benzene, toluene, or xylene<79) ... 

Alcohols, their corresponding olefins and alkyl cations are in equilibrium, with the alcohol generally predominating over the olefin (Purlee et al., 1955 Taft and Riesz, 1955 Boyd et al., 1960). The alkyl cation concentration is extremely low and this species never exists as more than a transient intermediate whose relation to the solvent is little known. In 5% H2SO4 the ratio of alcohol to olefin is about 1200 to 1 at 50° for the isobutylene-tertiary butyl alcohol system (Taft and Riesz, 1955). As the temperature increases the ratio of alcohol to olefin at equilibrium decreases (Boyd et al., 1960). This can be illustrated by examining the position of equilibrium in equation (8). Values of Kp, [alcohol (1)]/ [olefin (g)], were shown to vary from 5 54 at 50° to 1-34 at 70°. The equilibrium constant [alcohol (l)]/[olefin (1)] can be calculated from... 

Amberlyst 15 resin was found to catalyze the addition of primary alcohols to olefins. The activity displayed was higher than for soluble anhydrous p-toluenesul-fonic acid. The addition of methanol or -butanol to isobutene is weU-estabhshed as an industrial process [7]. 

Boron phosphate is used as an acid catalyst for dehydration of alcohols to olefins isomemization of olefins nitration of aromatic hydrocarbons polymerization of aldehydes and other synthetic reactions. It also is used as a flux in silica-based porcelain and ceramics special glasses and acid cleaners. 

Several insulator oxides, such as AI2O3 and Si02, can hydrate reversibly to give hydroxides of the type A1(0H)3, AIO(OH), or Si(OH)4, and, not surprisingly, can catalyze dehydration reactions such as the conversion of alcohols to olefins at elevated temperatures ... 

Moreover, intramolecular addition of alcohol to olefin was shown to give comparable yields to the platinum-based system [55]. 

A tandem reaction was also tried by Floreancig et al., who reported an example of intramolecular addition of alcohol to olefin [57]. In this case, reaction started with the... 

Rate equations for the catalytic dehydration of alcohols to olefins... 

For the oxidation of allylic alcohols to olefinic aldehydes see also Section 48 (Aldehydes from Alcohols). 

Fig. 1.11. Net reaction (a) for the hydration of olefins (R = CH3, R = H) or (b) for the addition of alcohol to olefins (R = CF3, R = alkyl) via the reaction sequence (1) solvomercuration of the olefin (for mechanism, see Figure 3.37 regioselectivity Figure 3.38) (2) reduction of the alkylmercury compound obtained (for mechanism, see Figure 1.12).

Dit fereni observations led Ziesecke to the proposal that the homologation reaction proceeds via dehydration of the alcohols to olefins which are (hen carbonylatcd by a hydroformylalion-type process (56J. This theory is supported by the fact that r-butanol is homologated to give 3-methylbutanol and not neopemyl alcohol, as would be expected (cf. Equation (16))-... 

The addition of alcohols to olefinic compounds provides an easy method for making ethers which may otherwise be difficult to obtain, particularly those which contain a second functional group. 

These represent hydrolysis of diethyl ether, synthesis of iV-mono-ethylaniline from alcohol and aniline, and dehydration of alcohols to olefins. Promoting the catalyst differently effects these reactions, in accord with the multiplet theory. Thus, the addition of the oxides of Fe, Ni, and Zn accelerates the first reaction and slows down the second and the third one 351). Incidentally, as has been found by the author and Sokolova 352), Nb20s and TaEOs are good catalysts in obtaining monoethylamine as well as in esterification of alcohols with acids, and they carry out the condensation of acetaldeyde into crotonaldehyde 353). 

Y. Addition of carboxylic acids and alcohols to olefins and acetylenes... 

Acid-catalysed addition of alcohols to olefins leads to ethers. It is catalysed by concentrated sulfuric acid,151 hydrochloric acid, acid salts, or aluminum chloride and hydrogen tetrafluoroborate and perchloric acid have also proved valuable,152,153 as has boron trifluoride.154 Addition of trisubstituted ethylenes such as isobutene and isopentene to alcohols is particularly easy it yields te/T-alkyl ethers.151 Disubstituted ethylenes react less easily, requiring higher temperatures and giving poorer yields. Cycloalkenes react only if there is a substituent attached to one of the doubly bonded atoms.155 Primary alcohols add more easily than do secondary ones, and tertiary alcohols rarely add at all. 

As indicated from the very high yields obtained, there is substantially no dehydration of the alcohol to olefin and no appreciable nitrile formation. 

I.IO per deuterium atom for the methyl carbon calculated from experiments I and 2 and 1 and 3, respectively. The ratio kjk2 differs from kjk by a small, but definite amount. From the ratio of alcohol to olefin product in the various experiments, one concludes that there is no D—CHg isotope effect in the substitution or elimination reaction. Then, if we make the plausible assumption that there is no D—CHg isotope effect in the substitution reaction, one calculates from the experimental data a value of 1.80 for the ratio of proton to deuteron loss in the elimination reaction. This value is calculated by neglecting a possible secondary isotope effect in the elimination reaction. 

An unusual addition reaction of alcohols to olefins involving the net formation of a C-C bond between two sp -hybridized carbon atoms through the action of Wilkinson s catalyst and BF3-Et20 has been reported (eq 44). The reaction appears to be reasonably general and is interpreted in terms of a radical-based process. ... 

Both unimolecular dehydration of alcohols to olefins and dehydrogenation to CO and aldehydes have been reported in the literature (Tolstopyatova et al., 1961 Tosun and Rase, 1972 Ganichenko, 1967 Minachev, 1973), but permanent dehydration activity was observed only at reaction temperatures higher than 300°C due to the contamination of the oxide surfaces with product water molecules. 

Aluminas are active and very selective catalysts for the dehydration of alcohols to olefins and to ethers (346,347). In particular, alumina-based catalysts are reportedly used in industrial processes for the production of DME from methanol, as shown in Equation (3.2). 

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