Butyl alcohols kinetics

Mikolajczyk and coworkers have summarized other methods which lead to the desired sulfmate esters These are asymmetric oxidation of sulfenamides, kinetic resolution of racemic sulfmates in transesterification with chiral alcohols, kinetic resolution of racemic sulfinates upon treatment with chiral Grignard reagents, optical resolution via cyclodextrin complexes, and esterification of sulfinyl chlorides with chiral alcohols in the presence of optically active amines. None of these methods is very satisfactory since the esters produced are of low enantiomeric purity. However, the reaction of dialkyl sulfites (33) with t-butylmagnesium chloride in the presence of quinine gave the corresponding methyl, ethyl, n-propyl, isopropyl and n-butyl 2,2-dimethylpropane-l-yl sulfinates (34) of 43 to 73% enantiomeric purity in 50 to 84% yield. This made available sulfinate esters for the synthesis of t-butyl sulfoxides (35). 

Kinetic data at 25 C for the conversion of tert-butyl bromide to tert-butyl alcohol in a solvent of 90% acetone and 10% water are tabulated. Time is in hours, concentration in gmol/liter. Find the rate equation. 

Fig. 1 Lewis and Funderburk found that the H/D primary kinetic isotope effects (25 °C in aqueous t-butyl alcohol) for proton abstraction from 2-nitropropane by pyridine derivatives all exceed the maximum isotope effect that could have been derived from the isotopic difference in reactant-state zero-point energies alone (a value around 7). The magnitude of the isotope effect increases with the degree of steric hindrance to reaction presented by the pyridine derivative, the identical results for 2,6-lutidine and 2,4,6-collidine ruling out any role for electronic effects of the substituents. The temperature dependence shown for 2,4,6-collidine is exceedingly anomalous the pre-exponential factor Ahis expected to be near unity but is instead about 1/7, while the value of AH — AH = 3030 cal/mol would have generated an isotope effect at 25 °C of 165 if the pre-exponential factor had indeed been unity.

SnI reactions are generally carried out in polar protlc solvents (like water, alcohol, acetic acid, etc.). The reaction between tert-butyl bromide and hydroxide Ion yields tert-butyl alcohol and follows the first order kinetics, i.e., the rate of reaetlon depends upon the concentration of only one reactant, which Is tert- butyl bromide. 

Libiszowki J, Kowalski A, Duda A, Penczek S (2002) Kinetics and mechanism of cyclic esters polymerization initiated with covalent metal carboxylates, 5. End-group studies in the model E-caprolactone and L,L-dilactideAin(II) and zinc octoate/butyl alcohol systems. Macromol Chem Phys 203 1694—1701... 

Of the seven hydroxyl-containing peroxides listed in Table 2, six are tert-butylperoxy derivatives. Although the fert-butyl group kinetically stabilizes the peroxide so that its combustion enthalpy can be measured, its presence makes finding suitable reference compounds such as hydrocarbons and ethers to compare in reactions 2-9 more difficult. Reaction 6 is the only reaction for which there are enthalpy of formation data for the requisite comparison compounds. Three hydroxy peroxides, all from the same source, have remarkably consistent enthalpies of reaction 6 in both the liquid and gas phases. The mean values derived from the viciwaZ-dioxygen substimted alcohols, 2-tert-butylperoxyethanol, 2-fert-pentylperoxyethanol and 3-fert-butylperoxy-1,2-propanediol, are —304.0 + 4.1 kJmol (Iq) and —257.1 + 6.0 kJmol (g). However, these values... 

Teton, S., A. Mellouki, G. Le Bras, and H. Sidebottom, Rate Constants for Reactions of OH Radicals with a Series of Asymmetrical Ethers and rert-Butyl Alcohol, hit. J. Chem. Kinet., 28, 291-297 (1996). 

Enzymatic kinetic resolution is a key step in the synthesis of the platelet aggregation inhibitor Lotrafiban (Figure 10.11). A disclosed process involves CaLB in tert-butyl alcohol/water (88 12) at 50 °C the substrate concentration was only r> g I 1 owing to its low solubility in this medium [122]. By exploiting the higher solubility in 88% [BMIm][PF6] and the better thermal stability of the biocatalyst in this medium, a higher rate was observed, the reaction was performed at 40 54 1. 1 at 75 °C, and the biocatalyst (Novozym 435) could be recycled 10 times. 

Highly regioselective dialkylation of naphthalene was performed with 2-propanol380 and tert-butyl alcohol381 over dealuminated H-mordenite, and with tert-butyl alcohol over HY and Beta zeolites.382 Selectivities are within 60-84%. Computational modeling showed that the kinetic diameter of the 2,6-disubstituted isomer is smaller than that of the 2,7 isomer, which may explain the selective formation of the former within the appropriate zeolitic framework.382... 

Use of scavengers. Can fert-butyl alcohol (TBA) be applied without constraints in reaction kinetic measurements No, TBA influences the kLa-value considerably (alpha factor). B 3.2.2... 

The same effect was also observed for tertiary butyl alcohol (TBA), a substance which is frequently used as a radical scavenger in kinetic experiments (see Section B 4.4). Depending on its concentration (c(TBA) = 0-0.6 mM) alpha values up to afO = 2.5 were measured (Gurol and Nekouinaini, 1985). Since TBA is hard to oxidize by molecular ozone in contrast to phenols (kD(TBA) 3 10 3 L moF1 s pH = 7, Hoigne and Bader, 1985), the effect of TBA on kLa can also be studied in mass transfer experiments with ozone. 

More complex rate expressions were observed when the reaction was carried out in the absence of solvents or when other solvents, such as H20 or ter/-butyl alcohol, were used. Complex rate expressions arise because a number of effects come into play, including preferential sorption in the hydrophobic zeolite, competition for adsorption at the titanium center, and competitive diffusion and reaction. It is therefore difficult to obtain unambiguous answers to mechanistic questions from kinetics. 

Although theoretical and computational advances now afford powerful insights into the mechanisms of heterogeneous catalysis, especially on acidic, zeolitic solids (6a-d), experimental studies (7, 8) still hold sway. This we hope to demonstrate here by reference to the wide range of techniques—spectroscopic, kinetic, and analytical—that we have brought to bear in our studies of the catalytic dehydration of butyl alcohols. 

Fig. 3. Kinetics of n-butyl alcohol consumption (a) and dehydration (b) in HZSM-5 (flow microreactor, sample I, 399 K) (A) Water ( ) di-n-butyl ether, n-butene (X) unreacted n-butyl alcohol.

The kinetics of adsorption and dehydration of the butyl alcohol were measured in situ via the time-dependences of the line intensities at 1460-1470 cm-1 (CH deformation vibrations) and 1640 cm 1 (deformation vibrations of adsorbed H20), respectively. 

The picture is different for the bulkier tert-butyl alcohol the kinetics of its adsorption at room temperature are markedly retarded with increasing crystallite sizes of HZSM-5 and they exhibit a t12 dependence (t is the time after adsorption) (see Fig. 3c of ref. 8d). This is symptomatic of a diffusion-influenced process. 

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... 

For isobutyl alcohol, no increase in the rate coefficient is observed at the initial stage of purging and afier return to the initial alcohol-helium flow, the rate coefficient reaches only a half of the previous level (Fig. 6b). The kinetic effects (8a-d,j, k) observed during purging for various butyl alcohols and catalysts, as well as the phenomenology of isotopic exchange mentioned later, are quantitatively describable in terms of the reaction mechanism discussed in the next section. 

All steady-state and transient kinetic data for the dehydration of all butyl alcohols over HZSM-5 and AAS catalysts may be rationalized in terms of the reaction mechanism presented in Scheme 1. 

Note that the rate coefficients k determined by our kinetic studies with the static FTIR reactor for all four butyl alcohols are the true rate coefficients for the forward step of stage II of Scheme 1, i. e., k = k+//. But under the steady-state conditions of the flow microreactor, the observed reation rate, Wbuoh, of butyl alcohol dehydration is less than or equal to the product (k+//N) of the rate... 

Thus, reaction intermediate r/// for dehydration of butyl alcohols can exist in two forms, i.e., butyl silyl ether (BSE) and adsorbed butyl carbenium ion (BC1). Our NMR and kinetic data imply the existence of reversible transformations between BSE, BCI, and adsorbed butene (BuadJ that ar shown in Scheme... 

It is interesting that, for reaction mixtures consisting of molecules with dimensions close to the cross-sections of the catalyst pores (as in the case of butyl alcohol dehydration in HZSM-5), the reacting mixture may be envisaged as a liquid with dimensions less than three. This, in turn, introduces additional factors with respect to the unanalyzed peculiarities of mass-transfer kinetics in the catalyst pores. 

Mertens R, von Sonntag C (1994) Determination of the kinetics of vinyl radical reactions by the characteristic visible absorption of vinyl peroxyl radicals. AngewChem Int Ed Engl 33 1262-1264 Mezyk SP, Madden KP (1999) Self-recombination rate constants for 2-propanol and ferf-butyl alcohol radicals in water. J Phys Chem A 103 235-242... 

Typical acid-catalyzed reactions like the dehydration of alcohols and double bond shifts in olefins have been mentioned occasionally as reactions catalyzed by organic heterogeneous catalysts. An extensive kinetic study of the dehydration of tertiary butyl alcohol over pyrolized polyacrylonitrile has been describ-... 

Hiatt et a/.34a-d studied the decomposition of solutions of tert-butyl hydroperoxide in chlorobenzene at 25°C in the presence of catalytic amounts of cobalt, iron, cerium, vanadium, and lead complexes. The time required for complete decomposition of the hydroperoxide varied from a few minutes for cobalt carboxylates to several days for lead naphthenate. The products consisted of approximately 86% tert-butyl alcohol, 12% di-fe/T-butyl peroxide, and 93% oxygen, and were independent of the catalysts. A radical-induced chain decomposition of the usual type,135 initiated by a redox decomposition of the hydroperoxide, was postulated to explain these results. When reactions were carried out in alkane solvents (RH), shorter kinetic chain lengths and lower yields of oxygen and di-te/T-butyl peroxide were observed due to competing hydrogen transfer of rm-butoxy radicals with the solvent. 

An investigation of the spectral and kinetic characteristics of radical cations of para-halogeno-A,A-dimethylanilines and / ara-halogenodiphenylamines in water/terr-butyl alcohol has been performed in view of the fact that such species are probable intermediates in photonucleophilic substitution of halogen638. Bathochromic shifts in the absorption maxima of the radical cations were observed in the order H=F < Cl < Br. The disappearance of the radical cations obeys second-order kinetics and the rate constants are close to the diffusion-controlled values. The radical cations arise from the singlet excited states of the halogenoarylamines and homolysis of the carbon-halogen bond competes with their formation. 

We have now established sufficient background to consider briefly the kinetics of reactions in water where apolar solutes are involved. For example, if the hydration characteristics of t-butyl alcohol in water are controlled to a marked extent by the hydration of the apolar t-butyl group, then it is likely that the same state of affairs exists for, say t-butyl chloride and other alkyl halides and related compounds in water. In other words, the hydration properties can be characterized by the general statement that, in the solvent co-sphere, water-water interactions > water-solute interactions, but that in the activation process water-solute interaction will increase. Since for apolar solutes, Cp3 > 0, and assuming that in the transition state, Cp3 0, then a tentative prediction is that ACp < 0 and — —Cp3. 

The amide group is readily hydrolyzed to acrylic acid, and diis reaction is kinetically faster in base than in acid solutions (5,32,33). However, hydrolysis of N-alkyl derivatives proceeds at slower rates. The presence of an electron-with-drawing group on nitrogen not only facilitates hydrolysis but also affects the polymerization behavior of diese derivatives (34,35). Widi concentrated sulfuric acid, acrylamide forms acrylamide sulfate salt, die intennediate of the former sulfuric acid process for producing acrylamide commercially. Further reaction of the salt widi alcohols produces acrylate esters (5). In strongly alkaline anhydrous solutions a potassium salt can be formed by reaction with potassium / Y-butoxide in tert-butyl alcohol at room temperature (36). 

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