Tert-Butyl alcohol dehydration

In summary, for n-, sec-, and isobutyl alcohols there is no diffusion limitation for the dehydration, whereas for the bulkier tert-butyl alcohol, dehydration in channels of HZSM-5 under certain conditions is influenced by diffusion. 

The poisoning is particularly fast for tert-butyl alcohol dehydration over... 

Stepanov AG, Zamaraev KI, Thomas JM. CP/MAS and H NMR study of tert-butyl alcohol dehydration on H-ZSM-5 zeolite. Evidence for the formation of tert-butyl cation and tert-bntyl silyl ether intermediates. Catal Lett 1992 13 407-22. 

Stepanov AG, Sidelnikov VN, Zamaraev KI. In situ C-solid-state NMR and ex situ GC-MS analysis of the products of tert-butyl alcohol dehydration on H-ZSM-5 zeolite catalyst. Chem Eur J 1996 2 157-67. 

Z. W. Qi and K. Sundmacher, Multiple product solutions of tert-butyl alcohol dehydration in reactive distillation, Ind. Eng. Chem. Res. 45, 1613—1621 (2006). 

These common features suggest that carbocations are key intermediates m alcohol dehydra tions just as they are m the reaction of alcohols with hydrogen halides Figure 5 6 portrays a three step mechanism for the acid catalyzed dehydration of tert butyl alcohol Steps 1 and 2 describe the generation of tert butyl cation by a process similar to that which led to its for matron as an intermediate m the reaction of tert butyl alcohol with hydrogen chloride... 

Like the reaction of tert butyl alcohol with hydrogen chloride step 2 m which tert butyloxonium ion dissociates to (CH3)3C and water is rate determining Because the rate determining step is ummolecular the overall dehydration process is referred to as a ummolecular elimination and given the symbol El... 

FIGURE 5 6 The El mecha nism for the acid catalyzed dehydration of tert butyl alcohol... 

IS reversible with respect to reactants and products so each tiny increment of progress along the reaction coordinate is reversible Once we know the mechanism for the for ward phase of a particular reaction we also know what the intermediates and transition states must be for the reverse In particular the three step mechanism for the acid catalyzed hydration of 2 methylpropene m Figure 6 9 is the reverse of that for the acid catalyzed dehydration of tert butyl alcohol m Figure 5 6... 

We now have a new problem Where does the necessary alkene come from Alkenes are prepared from alcohols by acid catalyzed dehydration (Section 5 9) or from alkyl halides by dehydrohalogenation (Section 5 14) Because our designated starting material is tert butyl alcohol we can combine its dehydration with bromohydrm formation to give the correct sequence of steps... 

Many novel features emerged. The acid was the strongest organic acid then known, and the / -oxo ester was unusually stable, and contained a high proportion of the enol form. The tertiary alcohol was very resistant towards dehydration, in sharp contrast to tert-butyl alcohol. In 1931, Swarts reported the Kolbe-type electrolysis of trifluoroacetic acid and its salts, isolating hexafluoroethane for the first time, and demonstrating that it was very stable. 

Oxirane Process. In Arco s Oxiiane process, tert-buty alcohol is a by-product in the production of propylene oxide from a propylene—isobutane mixture. Polymer-grade isobutylene can be obtained by dehydration of the alcohol, tert-Butyl alcohol [75-65-0] competes directly with methyl-/ -butyl ether as a gasoline additive, but its potential is limited by its partial miscibility with gasoline. Current surplus dehydration capacity can be utilized to produce isobutylene as more methyl-/ -butyl ether is diverted as high octane blending component. 

There are currendy three important processes for the production of isobutylene (/) the extraction process using an acid to separate isobutylene (2) the dehydration of tert-butyl alcohol, formed in the Arco s Oxiiane process and (i) the cracking of MTBE. The expected demand for MTBE will preclude the third route for isobutylene production. Since MTBE is likely to replace tert-buty alcohol as a gasoline additive, the second route could become an important source for isobutylene. Nevertheless, its availability will be limited by the demand for propylene oxide, since it is only a coproduct. An alternative process is emerging that consists of catalytically hydroisomerizing 1-butene to 2-butenes (82). In this process, trace quantities of butadienes are also hydrogenated to yield feedstocks rich in isobutylene which can then be easily separated from 2-butenes by simple distillation. 

The desired extraction process is the exothermic proton-catalyzed hydrolysis of isobutylene to tert-butyl alcohol. This alcohol is further dehydrated to yield pure isobutylene. At low concentrations the hydrolysis reaction is favored ... 

It competes direcdy with MTBE as an octane enhancer in the gasoline pool. Since MTBE is more desirable than tert-butyl alcohol because of its total miscibility with gasoline, tert-butyl alcohol will be an important source of isobutylene used in the manufacture of MTBE. High purity isobutylene, C4Hg, can be obtained by dehydration of tert-butyl alcohol, C4H1qO. 

Methyl f-Butyl Ether. MTBE is produced by reaction of isobutene and methanol on acid ion-exchange resins. The supply of isobutene, obtained from hydrocarbon cracking units or by dehydration of tert-butyl alcohol, is limited relative to that of methanol. The cost to produce MTBE from by-product isobutene has been estimated to be between 0.13 to 0.16/L ( 0.50—0.60/gal) (90). Direct production of isobutene by dehydrogenation of isobutane or isomerization of mixed butenes are expensive processes that have seen less commercial use in the United States. 

A dilute solution of ethanol is obtained, which can be concentrated by distillation to a constant-boiling point mixture that contains 95.6% ethanol by weight. Dehydration of the remaining few percent of water to give absolute alcohol is achieved either by chemical means or by distillation with benzene, which results in preferential separation of the water. Ethanol also is made in large quantities by fermentation, but this route is not competitive for industrial uses with the hydration of ethene. Isopropyl alcohol and tert-butyl alcohol also are manufactured by hydration of the corresponding alkenes. 

However, we found that TBSE is a rather stable species, decomposing only upon heating above 373 K. Thus, at 296 K it behaves as a side intermediate species, through which only a small fraction of tert-butyl alcohol molecules dehydrate. The main reaction stream bypasses the TBSE structure, proceeding presumably through the terf-butyl cation ion as the key intermediate (Scheme 4). 

The peroxide processes convert propylene to its epoxide while reducing the hydroperoxide to the corresponding alcohol (e.g., tert-butyl alcohol or phenyl methyl carbinol). Because the processes produce the alcohols in larger amounts than PO, their success depends upon finding uses for the alcohols. tert-Butyl alcohol can be dehydrated to isobutylene and hydrogenated to isobutane for recycle to the PO process. It can also be converted to MTBE. Phenyl methyl carbinol can be dehydrated to styrene, making this process a more involved... 

Other methods that have been less regularly used are the dehydration of alcohols with dimethyl sulfoxide to form symmetrical ethers,62 the photochemical transformation of benzylic chlorides with tert-butyl alcohol,63 or radical reactions of hexafluoroacetone with alkanes.64 Mercury acetate promoted couplings of alcohols with vinyl acetate or vinyl ethyl ether to form vinyl... 

Ion-exchange resins can also be used for dehydration [8]. The superacidic Na-fion-H catalyzes selective alkene formation from 1-propanol, 2-propanol, and tert-butyl alcohol at 433 K [45]. Ion-exchange resins have found industrial application in the production of isobutylene from ieri-butyl alcohol [46]. 

Dehydration to produce alkenes is practiced in industry in the manufacture of ethylene from ethanol over alumina, in the production of isomeric C4 alkenes from tert-butyl alcohol catalyzed by ion exchange resins, and in the transformation... 

ALCOHOL terc-BUTILICO (Spanish) (75-65-0) see tert-butyl alcohol. ALCOHOL C-8 (111-87-5) see octanol. ALCOHOL C-9 (143-08-8) see 1-nonanol. ALCOHOL 0-10(112-30-1) see n-decanol. ALCOHOL, DEHYDRATED or ALCOHOL, DENATURED (containing an additive used to make it unfrt for use as a beverage) or ALCOHOL ETILICO (Spanish) (64-17-5) see ethanol. 

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