Dehydration of 2-butanol

The primary products obtained from 2-butanol are of mechanistic. significance and may be compared with other eliminations in the sec-butyl system 87). The direction of elimination does not follow the Hofmann rule 88) nor is it governed by statistical factors. The latter would predict 60% 1-butene and 40% 2-butene. The greater amount of 2-alkene and especially the unusual predominance of the cis-olefin over the trans isomer rules out a concerted cis elimination, in which steric factors invariably hinder the formation of cis-olefin. For example, the following ratios oicisjtrans 2-butene are obtained on pyrolysis of 2-butyl compounds acetate, 0.53 89, 90) xanthate, 0.45 (S7) and amine oxide, 0.57 86) whereas dehydration of 2-butanol over the alkali-free alumina (P) gave a cisjtrans ratio of 4.3 (Fig. 3). 

Dehydration of 2-Butanol and 2-Pentanol over Various Aluminas at HLSV = 0.5... 

Exercise 17-24 What features of the base-catalyzed dehydration of 3-hydroxybutanal make it a more favorable and faster reaction than would be expected for a base-catalyzed dehydration of 2-butanol Give your reasoning. 

The set of catalysts selected for the dehydration of 2-butanol was also tested for the Friedel-Crafts acylation of anisole [69, 70]. The catalytic test was performed in the liquid phase due to the high boiling points of the reactants and products of this reaction. Anisole was reacted with acetic anhydride at 120 °C in the absence of solvent. In principle, acylation can occur on both the ortho and para positions of anisole. The main product (>99%) over all catalysts in this study was para-methoxyacetophenone, indicating that the reaction predominantly takes place inside the zeolite micropores. The same trend in catalytic activity as in the 2-buta-nol dehydration reaction is observed the conversion of anisole into para-nicihoxy-acetophenone increases upon increasing Ge content of the catalyst (Fig. 9.17) [67]. The main cause of deactivation for this reaction is accumulation of the reaction products inside the micropores of the zeolite. The different behavior of Ge-ZSM-5, compared with ZSM-5, may therefore be due to improved diffusional properties of the former, as the presence of additional meso- and macropores allows for... 

A somewhat different situation evolves if both stereogenic centers of a dia-stereoisomer take part in the bond activation. Although the actual SE is small and the precise mechanistic course may be more complicated than usually anticipated [28], let us address the Mn+-mediated dehydration of 2-butanol (21) and some of... 

It has been concluded that, for most cases, catalysis over zeolites occurs within the intracrystalline voids. Strong supporting evidence for this was provided by Weisz (71), who compared the rates of dehydration of 2-butanol over Linde lOX and 5A zeolites at relatively high temperatures and low conversion. The rate constant per unit volume of 5A was 1/lOO-l/lOOOth that for lOX, a magnitude consistent with the ratio of available surface areas for the external area of 1-5/x-sized 5A crystals and for lOX, where the internal surface area was available to the alcohol. The strong driving force for occlusion within the intracrystalline zeolite voids is exemplified by the rapid adsorption kinetics and rectangular adsorption isotherms observed for molecules whose dimensions are not close to those of the entry pores. 

As side-products diminishing the reaction selectivity butenes were detected which were originated in the consecutive dehydration of 2-butanol. 

The dehydration of 2-butanol is somewhat more complicated than shown above since the 2-butene formed as the major product is a mixture of m-2-butene and trans-2-butene. Trans-2-butene is... 

Under conditions of kinetic control, the dehydration of 2-butanol follows the Saytzeff rule, but a greater yield of m-2-butene than trans-l-batenc is obtained. These observations have no parallel in acid- or base-catalysed or pyrolytic eliminations. However, the dehydration of 2,3-dimethyl-2-butanol gives 2,3-dimethyl-l-butene (88.4%) and 2,3-dimethyl-2-butene (9.9%) and is thus oriented towards the Hofmann rule despite being more probably a carbonium ion process. Under similar reaction conditions the quite distinctly different products arising from the secondary alcohol, 3,3-dimethyl-2-butanol [3,3-dimethyl-1-butene (70%), 2,3-dimethyl-l-butene (23.5%), 2,3-dimethyl-2-butene (3.9%), l,l-dimethyI-2-methylcyclopropane (2.1%)] are accommodated in terms of concerted rather than a carbonium-ion mechanism. 

Balandin A.A., Klabunovskii E.I. and Litvin E.F. (1961) On composition of mixture of butenes forming at catalytic dehydration of 2-butanol, Izv. Akad. NatikSSSR, Otdel. Khim. Nauk, 1863-1870 Chem. Abstr. 1962, 56, 7112c. 

Isagulyants G.V., Derbentsev Yu.I., Klabunovskii E.I. and Balandin A.A. (1964) On mechanism of catalytic dehydration of 2-butanol on the surface of alumina, Izv. Acad. Nauk SSSR, Ser. Khim. 985-990 Chem. Abstr. 1964, 61, 8158h. 

The hydroxyapatite-catalyzed dehydration of 2-butanol, examined by Bett and Hall in 1968 (34), was shown to be amenable to a special method of obtaining the site density. They determined the number of product molecules which desorbed from the surface at infinite flow rate using a microcatalytic reactor. 

EXAMPLE Acid-catalyzed dehydration of 2-butanol Step I Protonation of the hydroxyl group (fast equilibrium). 

One of the most active areas of research in dehydration reactions is the use of heterogeneous catalysts (such as metal oxides, alumina, and zeolites) to catalyze the elimination of water from alcohols. Not only do the catalysts lower the temperatures required for dehydration, but they can also alter product distributions. For example, dehydration of 2-butanol produced 45% of 1-butene when the dehydration was catalyzed by alumina but 90% of 1-butene when zirconia was the catalyst. A wide variety of mechanisms have been considered for these reactions. The effect of the catalyst is a function of the nature of the acidic and basic sites on the catalyst surface, the size of openings into which organic molecules may fit, molecular shape, and... 

C. D. Baertsch, K.T. Komala, Y.H. Chua and E. Iglesia, Genesis of Brpnsted acid sites during dehydration of 2-butanol on tungsten oxide catalysts, J. Catal, 205(1), 44-57, 2002. 

An example of a reaction leading to gaseous products that can use this collection technique is the add-catalyzed dehydration of 2-butanol described in Experiment [9], The products of this reaction are a mixture of aUcenes 1-butene, trans-2-hutene, and cis-2-butene, which boil at —6.3,0.9, and 3.7°C respectively and s c-butyl ether (2,2 -oxybisbutane) which boils at 123 °C. While all four compounds are formed in the reaction mixture, the setup is designed to collect the gases and thus the three alkenes. 

The E1 Elimination Reaction Dehydration of 2-Butanol to Yield 1 -Butene, trans-2-Butene, and cis-2-Butene... 

Purpose, This experiment illustrates the variety of pathways that are available to acid-catalyzed elimination reactions of secondary (2°) alcohols via car-bocation intermediates. The dehydration of 2-butanol forms a mixture of gaseous alkene products. The alkenes formed in this reaction are separated and identified by using one of the most powerful instrumental techniques available to the modem research chemist for the separation of complex mixtures gas chromatography (GC). 

As discussed earlier, many alcohols can dehydrate to yield more than one isomeric alkene. In the present reaction involving the dehydration of 2-butanol, at least three alkenes are usually formed—1-butene, trans-1-butene, and cis-2-butene ... 

Acid-Catalyzed Dehydration of 2-Butanol—An E1 Reaction (Section 10.6)... 

As an illustration of the principle of microscopic reversibility, notice that the mechanism presented in this section for the add-catalyzed dehydration of 2-butanol to give 2-butene is exactly the reverse of that presented in Section 6.3B for the acid-catalyzed hydration of 2-bufene fo g ive 2-butanol. 

Isomerization of 1-butene, Dehydration of 2-butanol, and Polymerization of propylene These reactions which are known to be catsdyzed by acids were studied over niobic acid to characterize the acidic nature of niobic acid. The catalytic activity and selectivity of niobic acid evacuated at various temperatures for isomerizations of 1-butene are shown in Fig. 3.29. The niobic acid evacuated at 373 K for 2 h exhibited the highest activity. The selectivity indicates that Bronsted acid is acting as the active sites. The activity decreases with increase of evacuation temperature and the selectivity becomes almost 2, suggesting that Lewis acid is also acting as active sites. On evacuation at 773 — 873 K, the activity almost disappeared. An interesting finding is that the activity of niobic acid evacuated at 573 K followed by exposure to water vapor and then evacuated at 373 K becomes almost the same as that evacuated at 373 K, whereas the niobic acid once evacuated at 773 K does not increase in activity even if exposed to water... 

Catalyst Surface area (m g ) Phase byXRD SO,2- content (wt%) Amounts of NH3 irrevenibly adsorbed at 303 K Isomerization of 1-butene at 373 K Dehydration of 2-butanol at 473 K... 

The relationship between acid strength and catalytic activity has been quantitatively investigated. The acid strength distribution (only Lewis sites were present on the aluminas) measured by thermal desorption of pyridine is shown in Table 3.16, and the rate of dehydration of 2-butanol was measured over the aluminas of which the acid... 

---