Tert-butyl alcohol, protonated

Step 1 Protonation of tert butyl alcohol to give an alkyloxonium ion... 

The molecularity of an elementary step is given by the number of species that undergo a chemical change m that step Transfer of a proton from hydrogen chloride to tert butyl alcohol is bimolecular because two molecules [HCl and (CH3)3COH] undergo chemical change... 

FIGURE 4 7 Potential energy diagram for proton transfer from hydrogen chio ride to tert butyl alcohol... 

The first step of this new mechanism is exactly the same as that seen earlier for the reaction of tert butyl alcohol with hydrogen chloride—formation of an alkyloxonmm ion by proton transfer from the hydrogen halide to the alcohol Like the earlier exam pie this IS a rapid reversible Brpnsted acid-base reaction... 

Step 3 in Figure 5 6 shows water as the base which ab stracts a proton from the car bocation Other Bronsted bases present in the reaction mixture that can function in the same way include tert butyl alcohol and hydrogen sulfate ion... 

We can extend the general principles of electrophilic addition to acid catalyzed hydration In the first step of the mechanism shown m Figure 6 9 proton transfer to 2 methylpropene forms tert butyl cation This is followed m step 2 by reaction of the car bocation with a molecule of water acting as a nucleophile The aUcyloxomum ion formed m this step is simply the conjugate acid of tert butyl alcohol Deprotonation of the alkyl oxonium ion m step 3 yields the alcohol and regenerates the acid catalyst... 

Step 3 This step is a fast acid base reaction that follows the nucleophilic substitution Water acts as a base to remove a proton from the alkyloxonium ion to give the observed product of the reaction tert butyl alcohol... 

The product is a te/t-butyloxonium ion (or protonated tert-butyl alcohol). 

The photodecomposition of isopropyl alcohol on silica gel produces a seven-line spectrum having a hyperfine separation of 20.7 G and an amplitude ratio of 1 6.7 20.2 31 21.1 7.4 1.5 (68). This spectrum was attributed to SiOCMe2 formed from the ether surface groups. In addition to this spectrum the spectrum of the methyl radical was also observed. Irradiation of adsorbed tert-butyl alcohol produced a three-line spectrum which was attributed to SiOMe2OCH2 (68). Apparently the splitting from the methyl protons was too small to be observed. 

At the outset of our studies of the reactivity of I and II, it was necessary to investigate claims that tertiary henzamides were inappropriate substrates for the Birch reduction. It had been reported that reduction of A,A-dimethylbenzamide with sodium in NH3 in the presence of tert-butyl alcohol gave benzaldehyde and a benzaldehyde-ammonia adduct. We formd that the competition between reduction of the amide group and the aromatic ring was strongly dependent on reaction variables, such as the alkali metal (type and quantity), the availability of a proton source more acidic than NH3, and reaction temperature. Reduction with potassium in NH3-THF solution at —78 °C in the presence of 1 equiv. of tert-butyl alcohol gave the cyclohexa-1,4-diene 2 in 92% isolated yield (Scheme 3). At the other extreme, reduction with lithium in NH3-THF at —33 °C in the absence of tert-butyl alcohol gave benzaldehyde and benzyl alcohol as major reaction products. ... 

Fig. 2. A plot of the chemical shifts of the proton signals (ppm) for the 1,10-phenanthroline complexes of the lanthanides in D2O. The shifts are below the methyl signals of tert-butyl alcohol...

This interpretation was proved correct by considering the oxidation of a sample of diphenylmethane that had an isotopic purity of 97.0% a,a-dideuterio and 2.7% a-deuterio by mass spectrometry. The oxidation rate observed after the initial 15-second period (see Figure 2), during which the undeuterated and monodeuterated material were destroyed, yielded a second-order rate constant, ki = 0.0148 mole"1 per second. There is thus an appreciable isotope effect ku/kD of about 6 in the ionization of diphenylmethane by potassium ferf-butoxide in DMSO(80%)-tert-butyl alcohol (20% ) at 25°C. This compares with a value of fcH/ D of 9.5 reported for the ionization of triphenylmethane (16). The observation of primary isotope effects of this magnitude requires that the protonation of the diphenylmethide ion by tert-butyl alcohol in DMSO solution does not proceed at the diffusion rate which would, by the principle of microscopic reversibility, require the absence of an isotope effect in the deprotonation step. 

Alcohols are basic enough to accept a proton from strong acids, e.g. HCl and H2SO4, and able to dissociate completely in acidic solution. Sterically hindered alcohols, e.g. tert-butyl alcohol, are strongly basic (higher pA a values), and react with strong acids to give oxonium ions (ROH+). 

Studies on the use of proton-exchanged zeolites have also been conducted.12-14 Since tert-butyl alcohol and tert-butyl methyl ether (MTBE) are important gasoline octane enhancers, their synthesis by the addition of water and methanol to isobutylene attracted special attention. Among other processes, clay-catalyzed additions have been studied.15... 

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 ... 

The order of acidity of various liquid alcohols generally is water > primary > secondary > tertiary ROH. By this we mean that the equilibrium position for the proton-transfer reaction (Equation 15-1) lies more on the side of ROH and OHe as R is changed from primary to secondary to tertiary therefore, tert-butyl alcohol is considered less acidic than ethanol ... 

The equilibrium constant for proton transfer from hydrogen chloride to tert-butyl alcohol is much greater than 1. 

The proton being transferred is partially bonded to the oxygen of tert-butyl alcohol and to chloride at the transition state. 

Samarium(II) iodide promotes comparable transformations of aldehydo sugar 31 to ring contracted product 34 (Scheme 10) [51]. The presences of HMPA and tert-butyl alcohol as a proton source are necessary to obtain good conversion to cyclopentane derivatives. The reac-... 

The reaction of a carbocation with a neutral nucleophile such as water gives a protonated alcohol. Tertiary butyl carbocation, for example, reacts with water (neutral nucleophile) to give protonated tert-butyl alcohol, which eliminates a proton to give tert-butyl alcohol (Scheme 2.5). 

Acid-Catalyzed Elimination Reactions. The simplest kind of elimination reaction is catalyzed by acids and proceeds through a transitory carbonium ion (p. 44). Consider tert-butyl alcohol. In the presence of acid, an oxonium ion is formed (I) which can dissociate into water and a carbonium ion (II). As with all carbonium ions, there are then four courses of reaction open. (1) It can react with another water molecule or anion. (2) It can rearrange. (3) It can abstract a hydrogen atom with a pair of electrons from another molecule. (4) It can attract an electron pair from the carbon-hydrogen bond of an adjacent carbon atom so as to liberate a proton and to form an olefin (III to IV). The fourth possibility is the process by which many acid-catalyzcd elimination reactions occur. 

PROBLEM 4.9 Write an equation for proton transfer from hydrogen chloride to tert-butyl alcohol. Use curved arrows to track electron movement, and identify the acid, base, conjugate acid, and conjugate base. 

Of special importance is a mixed lithium-magnesium complex, since the individual metal enolates show much lower enantiofacial discrimination. (2/l,3/ )-Dipivaloyltartaric acid is not a useful proton source, however, tert-butyl alcohol, 3,4-dimethyl-5-phenyl-2-imidazolidinone and 2-(Ar-isopropyl-Ar-methylamino)-l-phenylpropanoI (9-H) yield highly enantiomerically enriched (R)- or (S )-oc-damascone (11), especially in the presence of lithium (+)- or (-)-2-(Ar-iso-propyl-A -methylamino)-1 -phenylpropanolate (9-Li) as an auxiliary. 

Certain alcohols, notably tertiary alcohols, are not readily acylated or phos-phorylated in the condensed phase under conditions that normally succeed for primary alcohols. Likewise, tertiary alcohols or thiols are not acylated or phosphorylated in the gas phase. Alkylation is the more general reaction. For example, tert-butyl alcohol under ICR conditions condenses with protonated carbonyl and phosphoryl compounds to produce ions of the type X=0+But, where X = C or P. The process has been described previously as a displacement reaction of the type shown in equation 11 (10, 16). 

This reaction could also be responsible for the formation of tert-butyl radicals on photobleaching the trapped electrons. No such effect was observed by Bennett et al. (6) because Na+ is the parent ion in their experiment. In their system protonated alcohol ions are not formed, and Reaction 6 is not possible. Apparently in tert-butyl alcohol the electrons on photobleaching do not react with the parent alcohol contrary to the behavior observed with alcohols containing an a-hydrogen atom (6, 36). In y-irradiated tert-butyl alcohol both (CH3)2C(OH)CH2 and (CH3)3C are observed (9), and the electrons presumably disappear by Reaction 6 rather than becoming trapped. 

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