Dehydration of isobutyl alcohol

We have characterized (8e-i) this intermediate using solid-state 13C CP/MAS NMR, 2H NMR, and two dimensional (2D). /-resolved 3C NMR spectroscopy in the course of dehydration of isobutyl alcohol and /er/-butyl alcohol in HZSM-... 

Thus, for the dehydration of isobutyl alcohol, the species has the structure of the isobutyl silyl ether, this ether being the true reaction intermediate, since 100% of the isobutyl alcohol reactant is dehydrated (8e) into it via reaction + II of Scheme 1. In the absence of the additional flow of isobutyl alcohol molecules, it is stable up to 398 K, but decomposes spontaneously upon... 

Isobutylidenediurea is used as a slow-release fertilizer. If there is a surplus of isobutyraldehyde, recent work has shown that it can be decarbonylated to propylene over a palladium on silica catalyst.220 There is also the possibility of dehydrogenation to methacrolein for conversion to methaciylic acid, then to methyl methacrylate. Dehydration of isobutyl alcohol would produce isobutylene for conversion to methyl-ferf-butyl ether, although this would probably be uneconomical. 

The retardation of the rate by alcohols was observed also in the dehydration of isobutyl alcohol and isopopyl alcohol.This was also attributed to the solvation of the network of acid groups by hydrogen-bonded alcohol. 

The dehydration of isobutyl alcohol over Si02—AI2O3 yields a mixture of butenes in which the fraction of n-butene is 33%. Since the rate of skeletal isomerization of isobutene to n-butenes is significandy lower than the rate of formation of a-butenes in dehydration, n-butenes must be primary products. This indicates that the reaction proceeds via the 1 mechanism. Formation of n-butenes is associated with the formation of the least stable isopropyl carbenium ions, which are readily rearranged by hydride or methyl transfer to form more stable tertiary or secondary carbenium ions. 

The aldol condensation of acetone to diacetone alcohol is the first step in a three-step process in the traditional method for the production of methyl isobutyl ketone (MIBK). This reaction is catalysed by aqueous NaOH in the liquid phase. (3) The second step involves the acid catalysed dehydration of diacetone alcohol (DAA) to mesityl oxide (MO) by H2S04 at 373 K. Finally the MO is hydrogenated to MIBK using Cu or Ni catalysts at 288 - 473 K and 3- 10 bar (3). 

Major markets as solvents and intermediates have made the ketones important commercial products lor many years. Acetone and mcthylethyl ketone have had the most impact on the chemical industry Acetone Is used s an intermediate In methyl isobutyl ketone, methyl methacrylate, diucelonc alcohol. ketone. hisphenol-A. phiwnc. and mesityl oxide Acetone is largely produced by dehydration of isopropyl alcohol In the production of phenol from cumene, acetone is produced as a by-product This mute to acetone has tended to control its price. 

Fig. 6. Rate constants for dehydration of butyl alcohols into butene over HZSM-5 under steady-state conditions and subsequent desorption of butene when the helium-alcohol flow is switched to pure helium flow, (a) rec-Butyl alcohol at 369 K ( ) sample I (A) sample 2 (O) sample 4. (b) Isobutyl alcohol at 397 K ( ) sample 2. The horizontal lines on the extreme right denote the reaction rate constants after returning to the previous helium-butyl alcohol flow.

A solution of 8.2 g. (0.040 mole) of purified aluminum isopropoxide and 2.75 g. (0.011 mole) of 4-keto-l,2,3,4-tetrahydrochrysene in 25 cc. of dry toluene is refluxed for four hours, in an oil bath. After the solution has cooled slightly, 25 cc. of dry isopropyl alcohol is added to facilitate removal of acetone, the water is removed from the reflux condenser, and a water condenser set for downward distillation is attached to the top by means of a short bent tube (a Hahn partial condenser with a 1-cm. layer of isobutyl alcohol in the inner condensing tube may be used). The mixture is heated at such a rate that slow distillation occurs (2 to 5 drops per minute, the volume of solution should be maintained by further addition of solvent as needed). When the test for acetone is completely negative, f the toluene solution is cooled and the aluminum salt is decomposed with cold 10% sulfuric acid (from 5 cc. of concentrated sulfuric acid and 80 cc. of water). The product is separated with the toluene, and the solution is washed with dilute aqueous ammonia and water, and then evaporated at room temperature under a stream of air (solutions of secondary alcohols which are susceptible to dehydration should be evaporated at room temperature a stream of air should not be used with carbinols boiling below 200°). There is obtained 2.10 g. (76%) of colorless 4-hydroxy-l, 2,3,4-tetrahydrochrysene melting at 156-158°. Two recrystallizations from a mixture of benzene and petroleum ether bring the melting point to 160-162°. 

Firstly, we have the acetone aldol self-condensation reaction over basic sites to give diacetone alcohol (DAA). Dehydration of this alcohol yeilds mesityl oxide (MSO) winch, in turn, can be selectively hydrogenated over reduced metal sites to finally give methyl isobutyl ketone (MIBK). In addition to the aldol condensation route, the acetone carbonyl functional group can also be directly hydrogenated over reduced metal sites yielding 2-propanol. Other reaction by-products such as methane, propane, diisopropyl ether and diisobutyl ketone have been detected in some experiments, but in very low amounts, lower than 2% of the total reaction products. 

Stepanov AG, Romannikov VN, Zamaraev KI. C CP/MAS NMR study of isobutyl alcohol dehydration on H-ZSM-5 zeolite. Evidence for the formation of stable isobutyl silyl ether intermediate. Catal Lett 1992 13 395 05. 

Isobutyl alcohol [78-83-1] forms a substantial fraction of the butanols produced by higher alcohol synthesis over modified copper—zinc oxide-based catalysts. Conceivably, separation of this alcohol and dehydration affords an alternative route to isobutjiene [115-11 -7] for methyl /-butyl ether [1624-04-4] (MTBE) production. MTBE is a rapidly growing constituent of reformulated gasoline, but its growth is likely to be limited by available suppHes of isobutylene. Thus higher alcohol synthesis provides a process capable of supplying all of the raw materials required for manufacture of this key fuel oxygenate (24) (see Ethers). 

Melhyl-l-propanol Isobutyl Alcohol) and 2-Phenyl-1-propanol Herling and Pines (SO) studied the dehydration of 2-methyl-l-propanol and 2-phenyl-1-propanol. The two alcohols were passed over alumina under nonacidic conditions at temperatures of 350° and 270°, respectively (Tables III and IV). The 2-methyl-l-propanol underwent, in part, skeletal isomerization forming butenes, whereby the ratio of cisjtrans 2-butene produced was four to six times greater than the equilibrium ratio. The extent of skeletal isomerization depended to some extent on the method of preparation of the alumina. 

Fig. 2. Relation (8b) between the activity of ZSM-5 and AAS in isobutyl alcohol dehydration to butene at 3971C and the number of (a) Brensted acid sites [B] (b) strong Lewis acid sites, [LL , and (c) weak Lewis acid sites, [L]weak. (A) NaHZSM-5 sample 2 (9) HZSM-5, sample I (O) HZSM-S, sample 3 ( ) HZSM-5, sample 4 ( ) amorphous aluminosilicate, AAS.

The first spectrum could be recorded 25 s after admission of alcohol to the catalyst. For all the zeolite samples of various crystallite sizes (Table I) at 296 K, the adsorption was complete within 25 s for sec- and isobutyl alcohols. The dehydration process of these alcohols in the zeolitic pores was, however, slower. For a given alcohol (/ -, sec-, or iso-) the kinetics of water elimination were identical for catalysts of different crystallite sizes. This firmly establishes the absence of any diffusion limitation for dehydration for these three alcohols. 

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. 

For all four alcohols in the zeolitic catalysts with small enough crystallite sizes—when diffusion limitations also disappear—dehydration kinetics are well approximated by the exponental function, a fact that is explicable in terms of the unimolecular decay of molecules of butyl alcohol adsorbed on identical active sites. With isobutyl alcohol, for example, the rate coefficient k may be written... 

Transient kinetic phenomena of another type were observed in the so-called purging experiments, whereby we switched from feeding the flow reactor with a helium-butyl alcohol mixture to one with pure helium and then back to the previous helium-butyl alcohol. A typical response of a catalyst to such purging is given in Fig. 6, referring to the dehydration of sec- and isobutyl alcohols over HZSM-5. For sec-butyl alcohol, the rate of butene formation initially increases by a factor of about 10 upon purging and then drops to zero. Return (8k) to the... 

The temperature effect on the dehydration of alcohols in the presence of alumina as has been shown by the work of Sabatier and Mailhe,41 Brown and Reid,°°b and Pease and Yung08 was not checked by Adkins,° b who used what were presumably better conditions experimentally. The rate of dehydration increases in the order of butyl, propyl, isobutyl, ethyl, isopropyl, and secondary butyl alcohols. Although ethanol and ethyl ether give the same rate of dehydration, butyl alcohol gives a faster dehydration late than does butyl ether. Hence, the hypothesis advanced at one time that olefin formation from alcohols was through intermediate ether formation cannot hold. 

In Table 3.33 the activities of CaX and CaA for dehydration of butyl and isobutyl alcohol are compared.Over CaX, both alcohols are dehydrated rapidly in the temperature range of 503 — 533 K, with the isobutyl alcohol showing somewhat greater activity. This behavior is compatible with the fact that both are primary alcohols and should resemble each other. Both CaX and CaA show litde difference in activity with butyl alcohol which can penetrate both crystals. However, the isobutyl alcohol, which... 

Knozinger and Schengllia studied the kinetic isotope effect of the dehydration of t-butanol, rsr-butanol and isobutyl alcohol over alumina and found that the deuteration of the hydroxyl group does not give rise to an isotope effect, whereas substitution of 8-proton by deuterium produces an appreciable effect. From the dependence of the isotope effects on substrate structure and temperature, it was concluded that at temperatures below 573 K alcohols are dehydrated via 2-like reaction intermediates over alumina. With increasing temperature, the contribution of the ionic structure increased so that at elevated temperatures — depending on the reactant structure — the reaction may proceed via an l-mechanism. 

Anhydrous stannous chloride, a water-soluble white soHd, is the most economical source of stannous tin and is especially important in redox and plating reactions. Preparation of the anhydrous salt may be by direct reaction of chlorine and molten tin, heating tin in hydrogen chloride gas, or reducing stannic chloride solution with tin metal, followed by dehydration. It is soluble in a number of organic solvents (g/100 g solvent at 23°C) acetone 42.7, ethyl alcohol 54.4, methyl isobutyl carbinol 10.45, isopropyl alcohol 9.61, methyl ethyl ketone 9.43 isoamyl acetate 3.76, diethyl ether 0.49, and mineral spirits 0.03 it is insoluble in petroleum naphtha and xylene (2). 

The conversion of acetone to methyl isobutyl ketone (MIBK) also uses a combination of base catalysis with a hydrogenation catalyst [35], The base component converts the acetone to diacetone alcohol (DAA) via an aldol reaction, which is then dehydrated by the silica to give mesityl oxide (MO). The final step is the hydrogenation of the MO to MIBK over the metal component. The action of the base catalyst in the absence of the hydrogenating metal has been studied [36]. As well as the aldol condensation reactions shown below, the cesium oxide also hydrogenated MO to MIBK, albeit at a low level (Scheme 21.3). 

---