Propene acid-catalyzed hydration

Arrange the following compounds in order of increasing rate of acid-catalyzed hydration ethylene, 2-cyclopropylpropene, 2-methylpropene, propene, 1-cyclopro-pyl-l-methoxyefliene. Explain the basis of your prediction. 

FIGURE 6.9 Mechanism of acid-catalyzed hydration of 2-methyl propene. 

The acid-catalyzed hydration of propene proceeds through formation of the secondary carbocation and then attack by water to form propanol. 

Neither the AdE3 nor the AdE2 mechanism is consistent with available data concerning the acid catalyzed hydration of propene to 2-propanol in supercritical water at 375 C and 34.5 MPa. More data are being accumulated to sustain a rigorous kinetic examination of the hydration/dehydration mechanism. 

Problem 12.50. The acid-catalyzed hydration of propene, i.e., addition of water to propene, yields a mixture of two different products. What are the two products Write the step-by-step mechanism for the reaction. (Hint The first step is addition of a proton from sulfuric acid to propene.) Which is the major product and why ... 

The mechanism for the acid-catalyzed hydration of alkenes is quite similar to what we have already proposed for the addition of HCl, HBr, and HI to alkenes and is illustrated by the hydration of propene to 2-propanol. This mechanism is consistent with the fact that acid is a catalyst. An is consumed in Step 1, but another is generated in Step 3. 

Propose a three-step mechanism similar to that for the acid-catalyzed hydration of propene. 

Propanol (isopropyl alcohol) is manufactured commercially by the acid-catalyzed hydration of propene (eq. 3.1 3). it is the main component of rubbing alcohol and is used in many household and personal care products. 

Propanol is prepared commercially from the acid-catalyzed hydration of propene (see A Word About... Industrial Alcohols on page 208). Write out all of the steps in this acid-catalyzed mechanism. 

Because no electrons are required to achieve an electrical balance in the half-reaction, conversion of propene to 2-propanol is neither oxidation nor reduction this reaction can be brought about by acid-catalyzed hydration of propene. 

Figures 2a and 2b display the acid catalyzed E2 and El mechanisms for the dehydration of 1-propanol and 2-propanol. Note that the El mechanism involves four more rate constants (kinetic parameters) than the related E2 dehydration mechanism. Chemists employ the terminology (1) Adg3 to describe the hydration mechanism which forms 2-propanol from propene in Figure 2a, and Ad 2 to refer to the mechanism which forms 2-propanol from propene in Figure 2b. In this paper we do not distinguish between bare carbocations, Il-complexes, encumbered carbocations and symmetrically solvated carbocations, since these intermediates all manifest themselves similarly in the El kinetic model.

The commercial production of f-butyl methyl ether has become important in recent years. In 2002, worldwide consumption of MTBE was about 7 billion gallons. With an octane value of 110, it is used as an octane number enhancer in unleaded gasolines. It is prepared by the acid-catalyzed addition of methanol to 2-methyl-propene. The reaction is related to the hydration of alkenes (Sec. 3.7.b). The only difference is that an alcohol, methanol, is used as the nucleophile instead of water. 

Besides the above reactions, any kind of acid-catalyzed reactions such as cracking of cumene, alkylation of benzene with propene, hydration of olefins, isomerization of cyclopropane, esterification of acetic acid with ethanol, etc. can be used for the estimation of the acidic property of solid acids. Skeletal isomerization of li-butane to -butane is used to check whether a solid acid has superacidity, since the isomerization is known not to be catalyzed even by 100% sulfuric acid. However, it should be noticed that the differentiation between acid strength and acid amount is not easy from the measurement of catalytic activity for an acid-catalyzed reaction. Characterization of acid catalysts by use of model reactions has been reviewed recently by Guisnet. ... 

Tokuyama A process for hydrating propene to propenediol, catalyzed by an aqueous solution of 12-tungstosilicic acid. Developed by Tokuyama (a Japanese company) and commercialized in Japan... 

Later, the CMRs were also used in an attempt to carry out homogeneous catalytic reactions for example, hydration of propene. Lapkin et al prepared a carbon membrane from a macroporous phenohc resin and constructed a CMR for the hydration reaction. In this gas phase continuous catalytic membrane reactor, the flat carbon membrane was used as a contactor for carrying out reactions at high temperature and pressure. In particular, the hydration of propene, catalyzed by an aqueous solution of phosphoric acid, was selected as a suitable model reaction. Olefin and water were fed separately in order to have the additional benefit of an increased alcohol concentration in the product stream because of the absence of steam in the propene feed. 

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