Hydration of Isobutylene

The acid-catalyzed hydration of isobutylene produces ter-butyl alcohol. The reaction occurs in the liquid phase in the presence of 50-65% H2SO4 at mild temperatures (10-30°C). The yield is approximately 95%  

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The other significant industrial route to /-butyl alcohol is the acid cataly2ed hydration of isobutylene (24), a process no longer practiced in the United States. Raffinate 1, C-4 refinery streams containing isobutylene [115-11-7], / -butenes and saturated C-4s or C-4 fluid catalytic cracker (ECC) feedstocks (23)... 

C4 cuts, after extraction of butadiene, are preferred as feed to isobutylene extraction units because the isobutylene concentration (about 30-40%) is higher than in C4 streams from catalytic cracking. The basic reaction in isobutylene extraction is the reversible hydration of isobutylene to tertiary butyl alcohol in the presence of sulfuric acid. 

Gupta and Douglas [AIChE J., 13 (883), 1967] have studied the catalytic hydration of isobutylene to f-butanol, using a cation exchange resin catalyst in a stirred tank reactor. 

The rate of hydration of an olefin increases with acidity. It has recently been demonstrated that the hydration of isobutylene follows the Ho acidity function, i.e. dlogkj — dHo) = 1, where Hq is the acidity function defined by equation (10). The behaviour of secondary and tertiary alcohols in 0-55 % H2SO4 is very similar (Beishlin, 1963). 

Pseudoliquid-phase catalysis (bulk type I catalysis) was reported in 1979, and bulk type II behavior in 1983. In the 1980s, several new large-scale industrial processes started in Japan based on applications of heteropoly catalysts that had been described before (5, 6, 72) namely, oxidation of methacro-lein (1982), hydration of isobutylene (1984), hydration of n-butene (1985), and polymerization of tetrahydrofuran (1987). In addition, there are a few small- to medium-scale processes (9, 10). Thus the level of research activity in heteropoly catalysis is very high and growing rapidly. 

Izumi et al. (162, 166) observed high activities of heteropolyacids for the hydration of isobutylene in dilute solution, as follows. The activation energy is 4 kcal mol 1 lower for H3PW12O40 than for HNO3. The reaction order with... 

A commercial process for the separation of isobutylene from a mixture of isobutylene and -butenes through direct hydration of isobutylene to give tert-butyl alcohol has been established by use of a concentrated solution of heteropolyacids (6, 163, 170). The reaction order in the heteropolyanion varies from 1 to 2 as the concentration of heteropolyanion increases from 0.05 to 10 mol dm-3. This increase corresponds to a change from the first to the second term in Eq. (11a). At concentration of the heteropolyanion greater than 0.5 mol dm-3, path B in Scheme 3 becomes dominant. 

The data of H2S04, HC1, HNO3, and HC104 also fit this equation. On this basis, they suggested that the hydration of isobutylene in the presence of heteropolyacids and inorganic acids proceeds via a common mechanism, in which the rate-limiting step is the conversion of the 7t-complex into a carbenium ion (Scheme 3). The complexation effect as described above is possibly included in the value of Ho according to this explanation. 

Hydration of olefins to alcohols is equilibrium limited and hence CD is potentially suitable for such applications. The catalysts used for the process are acidic catalysts such as cation-exchange resins or zeolites. The hydration of isobutylene to produce tert-h ity alcohol via CD results in a higher conversion and there is no need to recycle the water. The hydration process is catalyzed by acidic ion-exchanged resins at 85°C and about 1200 kPa. The CD process configuration involves feeding the isobutylene below the catalyst zone and the water is fed above the catalyst zone. Flooding of the reaction zone is introduced in the process to improve the contact between the catalyst and the liquid and to ensure that the water is in constant contact with the catalyst sites. Flooding of the catalyst zone apparently improves the catalyst lifetime and performance because catalyst deactivation is caused by mass transfer and liquid distribution problems. Some recent publications on the hydration of isobutylene include a patent and a study of the kinetics of the hydration process and discussions on the merits of the application of CD for hydration. 

The protonation of alkenes, the essential first step in acid-catalyzed alkene isomerization, alkylation, hydration, and so on, is considered to involve the initial overlap of the carbon p-orbital forming the tc bond with the vacant s-orbital of the proton, forming a three-center bonded or tc complex" "" (Scheme 6.40). Taft seems to be the first to have suggested the initial formation, in acid-catalyzed hydration of isobutylene, of a proton tc complex of the type described originally by Dewar, in which the proton is embedded in the TC orbitals which extend above (or below) the plane of the C-C double bond. ... 

For further comparison one can estimate a value for isobutylene, as follows Eberz and Lucas S give AT, = 7.5 X 10 for the hydration of isobutylene to f-bulyl alcohol Arnett and Hofelich interpolate pAt. —14.7 for r-butyl alcohol. Combination of these results yields pAT, s — 11 for protonation of isobutylene. 

O 21.59% (CHj)jCOH. Prepd from acetyl chloride and dime thy [zinc Butlerow, Ann. 144, 1 (1867). Manuf by catalytic hydration of isobutylene Kreps, Nachod. U.S. 

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