Olefin hydration

Many catalysts for the hydration of olefins in general, and of ethylene in particular, are described in the patent Hterature. Practically all of them are acidic. There has been a patent Hterature review through 1937 of the types of catalysts used (47,48) and a general review of olefin hydration (88). 

There have been a number of isolated studies of metal-ion catalyzed nucleophilic reactions of other groupings. Particularly interesting is the induced nucleophilic attack on olefins. Hydration is normally very sluggish. Enzymes can speed up such reactions. Aconitase, an iron-containing enzyme, catalyzes the isomerization of citric acid to isocitric acid, through the intermediacy of cis-aconitic acid. A possible mechanism has been suggested based on the following Co(III) model chemistry. Rapid cyclization of the maleate ester produces Ai and AS chelated malate half ester ... 

The hydration of acetylene produces acetaldehyde which then can be converted to acetic acid and other derivatives. The process is similar to olefin hydration employing a sulfuric acid solution containing also a mercurous sulfate catalyst. 

A major limitation on the production of alcohols by olefin hydration is the fact that the products consist almost solely of secondary or tertiary alcohols (excepting, of course, ethyl alcohol). The normal or primary alcohols are made by other means (but also from petroleum hydrocarbons). It appears more difficult to prepare C5 and higher alcohols by the hydration of olefins since they are produced commercially by other means. One of the problems encountered (81) is excessive polymerization of the higher olefins when contacted with aqueous sulfuric acid. 

Direct Oxidation. Direct oxidation of petroleum hydrocarbons has been practiced on a small scale since 1926 methanol, formaldehyde, and acetaldehyde are produced. A much larger project (29) began operating in 1945. The main product of the latter operation is acetic acid, used for the manufacture of cellulose acetate rayon. The oxidation process consists of mixing air with a butane-propane mixture and passing the compressed mixture over a catalyst in a tubular reaction furnace. The product mixture includes acetaldehyde, formaldehyde, acetone, propyl and butyl alcohols, methyl ethyl ketone, and propylene oxide and glycols. The acetaldehyde is oxidized to acetic acid in a separate plant. Thus the products of this operation are the same as those (or their derivatives) produced by olefin hydration and other aliphatic syntheses. 

The catalytic hydration of olefins can also be performed in a three-phase system solid catalyst, liquid water (with the alcohol formed dissolved in it) and gaseous olefin [258,279,280]. The olefin conversion is raised, in comparison with the vapour phase processes, by the increase in solubility of the product alcohol in the excess of water [258]. For these systems with liquid and vapour phases simultaneously present, the equilibrium composition of both phases can be estimated together with vapour-liquid equilibrium data [281]. For the three-phase systems, ion exchangers, especially, have proved to be very efficient catalysts [260,280]. With higher olefins (2-methylpropene), the reaction was also performed in a two-phase liquid system with an ion exchanger as catalyst [282]. It is evident that the kinetic characteristics differ according to the arrangement (phase conditions), i.e. whether the vapour system, liquid vapour system or two-phase liquid system is used. However, most kinetic and mechanistic studies of olefin hydration were carried out in vapour phase systems. 

The best catalysts for olefin hydration are not necessarily those which have proved most satisfactory for the reverse reaction. Some of the successful hydration catalysts are not typical dehydration catalysts. The more obvious reasons are (i) different adsorption characteristics of the catalyst is desirable, e.g. stronger adsorption of olefin relative to alcohol, (ii) under the conditions used for the hydration, ether formation cannot be suppressed as readily as in the dehydration, (iii) at high pressures, the olefins tend to polymerise much more than at the low pressures used for the dehydration. 

It may be concluded from all these results that the presence of acid centres is unavoidable for a catalyst to be active in olefin hydration. The possible role of basic centres is less clear they might participate in a fast step which follows the rate-determining step. 

For the same reaction under similar conditions and on supported H3P04, another equation was applied [287]. It is based on Taft s mechanism for homogeneously catalysed olefin hydration [291,292] [see scheme (B), p. 327] according to which water enters into the reaction scheme in a fast step which follows the rate-determining step and therefore appears in the rate expression in a negative term, viz. 

With ion exchangers as catalysts for olefin hydration, special attention was paid to transport problems within the resin particles and to their effects on the reaction kinetics. In all cases, the rate was found to be of the first order with respect to the olefin. The role of water is more complicated but it is supposed that it is absorbed by the resin maintaining it in a swollen state the olefin must diffuse through the water or gel phase to a catalytic site where it may react. The quantitative interpretation depends on whether the reaction is carried out in a vapour system, liquid-vapour system or two-phase liquid system. In the vapour system [284, 285], the amount of water sorbed by the resin depends on the H20 partial pressure it was found at 125—170°C and 1.1—5.1 bar that 2-methyl-propene hydration rate is directly proportional to the amount of sorbed water... 

The observed structure effects are similar, as in the reaction catalysed by sulphuric acid. On this basis and with the notion of the strong acidity of the heterogeneous catalysts used, it is possible to assume a mechanism similar to olefin hydration (Sect. 3.1) or alkylation (Sect. 3.3). Olefin protonation by the catalyst seems to be the first step, which is followed by the interaction with the nucleophile, in this case the alcohol. 

Lower alcohols (amyl and below) are prepared by (a) hydrogeneration of carbon monoxide (yields methanol), (b) olefin hydration (yields ethanol, isopropanol, secondary and tertiary butanol), (c) hydrolysis of alkyl chlorides, (d) direct oxidation, and (e) the 0X0 process,... 

A graphical representation of the dependence of the activity per acidic site of the zeolites on their Si/Al ratio is given in Fig. 2. It is known that zeolite acidity is enhanced by incrasing the Si/Al ratio (ref. 17,18). Therefore, the obtained linear correlation strongly suggests that the activity of zeolites in hydration of alkynes is a direct and single function of the acid strength and is not dependent of the zeolite framework. Such a result is consistent with the correlation obtained in olefin hydration (ref. 19). 

Robinson begins 30 year hydrate research effort with study of paraffin/olefin hydrates 1963 McKoy and Sinanoglu apply Kihara potential to vdWP theory... 

The volume of activation, A V, which is — RT 8 lnk)Jdp, has been suggested as a criterion of mechanism (Whalley, 1964). Known volumes of activation for A-SB2 reactions, measured near 25°, seem to be limited to olefin hydration (—12 cm3 mole-1 for isobutene at 35°, Baliga and Whalley, 1965) and allylmercuric iodide cleavage ( — 11 cm3 mole-1 at 25°, Halpem and Tinker, 1965). It is impossible to generalize from so few examples, but, in principle, it seems possible that AV is less dependent on structural ramification than AS, and therefore easier to interpret. Against this must be weighed the experimental difficulties in... 

Asymmetric olefins, which carry more alkyl substituents at the Ce center than at the Ca center, are also hydroborated by the unhindered BH3 with considerable regioselectivity (Table 3.1). After oxidative workup, one isolates the alcohol in the a position almost exclusively. According to what has already been stated, as the more bulky reagent, 9-BBN reacts with more sensitivity to steric effects than BH3 and its secondary products. It therefore makes possible olefin hydrations with almost perfect regiocontrol. 

Solvomercuration of Olefins Hydration of C=C Double Bonds through Subsequent Reduction... 

HPAs, however, is their solubility in polar solvents or reactants, such as water or ethanol, which severely limits their application as recyclable solid acid catalysts in the liquid phase. Nonetheless, they exhibit high thermal stability and have been applied in a variety of vapor phase processes for the production of petrochemicals, e.g. olefin hydration and reaction of acetic acid with ethylene [100, 101]. In order to overcome the problem of solubility in polar media, HPAs have been immobilized by occlusion in a silica matrix using the sol-gel technique [101]. For example, silica-occluded H3PW1204o was used as an insoluble solid acid catalyst in several liquid phase reactions such as ester hydrolysis, esterification, hydration and Friedel-Crafts alkylations [101]. HPAs have also been widely applied as catalysts in organic synthesis [102]. 

Lyondell Chemical Co. Direct olefin hydration Olefins (ethylene or propylene, butene) Direct hydration of olefins to corresponding alcohol in vapor phase ether is prime side reaction NA NA... 

Catalytic hydration of olefins Hydration of light olefins such as ethylene, 128 propylene, and butenes (at high pressure and high water-to-olefin ratio) in the presence of catalyst... 

Many catalytic reactions form a range of products rather than only a single one. In most such cases, the pathway to a co-product branches off from that to the main product after the first or a few early steps. The network then consists of cycles that have a step or pathway segment in common. Typical examples are the formation of isomeric products in paraffin oxidation and olefin hydration, hydrohalogenation, hydroformylation, and hydrocyanation, as well as paraffin by-product formation in hydroformylation. 

Thus, if the olefin is strongly bonded to Pd (II) before the transition state, Pd(II) attack cannot be a simple electrophilic attack on the olefin, such as is the proton attack in olefin hydration. It is rather a rearrangement of a TT-bonded to a o-bonded adduct. There is no reason to expect that the transition state for this rearrangement would have much polar character. The small effect of olefin substitution on rate indicates that this transition state is, in fact, nonpolar. 

Thallic ion, on the other hand, does not form stable 7r-complexes and has a high positive charge. Thus, its attack on olefins would be expected to be electrophilic, and the transition state would have considerable polarity, analogous to a proton in the hydration of an olefin, and the eflFect of structure on rate for the Tl(III) oxidation of olefin parallels that of olefin hydration. Alkyl substitution on vinyl C—2, which stabilizes the positive charge, greatly accelerates the rate, and dialkyl substitution on C—2 (isobutene) increases the rate still further. 

Excellent surveys of olefin hydration, alkylation, isomerization, poljmieri-zation, disproportionation, hyorocar-bon separation, coordination compounds etc. 

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