Ethanol protonation

Towner RA, Reinke LA, Janzen EG, et al. 1991. Enhancement of carbon tetrachloride-induced liver injury by a single dose of ethanol proton magnetic resonance imaging (MRI) studies In vivo. Acta Biochem Biophys 1096 222- 230. 

Main reaction paths of the thermal desorption of ethanol are proposed in Scheme 5. The species observed directly by NMR spectrscopy are surrounded by broken lines. At temperatures less than 323 K, the dehydration did not proceed, and only reversible desorption took place. The protonated ethanol dimer is transformed into protonated ether at temperatures exceeding 323 K. Diethyl ether is formed only in the gas phase by replacement with ethanol. Protonated ethanol monomer probably gives ethylene via the ethoxide at temperatures exceeding 333 K (169). 

Tertiary alcohols (butyl and amyl) react very slowly with the metal, but methanol or ethanol protonate the intermediate radical anions more rapidly and can suppress side reactions propan-2-ol may provide an effective compromise. Water and ammonium salts have also been used for protonation, but have an undesirable effect on many reactions, and should be avoided for quenching purposes while any metal remains. Any excess of metal is best consumed by the addition of a simple diene (isoprene or penta-1,3-diene), since the metal will often react more rapidly with the (protonated) product than with the quenching agent, leading to overreduction. Inverse quenching has been advocated for especially sensitive products. ... 

Ishikawa et detected the free-induction signals of xenon atoms polarized by spin-exchange optical pumping. The temperature dependence of dissolution and spin-polarization transfer of xenon atoms in ethanol is measured by simultaneous detection of both xenon and ethanol protons. 

Song S, Tsiakaras P (2006) Recent progress in direct ethanol proton exchange membrane fuel cells (DE-PEMFCs). Appl Catal B Environm 63 187-193... 

Y n-Butanol Ethanol Proton donor and proton acceptor capabilities (alcohols, nitriles)... 

Ionisations 2, 3 and 5 are complete ionisations so that in water HCI and HNO3 are completely ionised and H2SO4 is completely ionised as a monobasic acid. Since this is so, all these acids in water really exist as the solvated proton known as the hydrogen ion, and as far as their acid properties are concerned they are the same conjugate acid species (with different conjugate bases). Such acids are termed strong acids or more correctly strong acids in water. (In ethanol as solvent, equilibria such as 1 would be the result for all the acids quoted above.) Ionisations 4 and 6 do not proceed to completion... 

However, many substances, notably alcohols, have a greater proton affinity than the hydrogen fluoride molecule, and so behave as bases, for example ethanol ... 

The mechanism of the formation of these three compounds is based on the initial reaction between ethanol and a strong acid such as sulphuric acid, which involves protonation of the ethanolic oxygen to form the ion (1). 

This derivative condenses either on itself (64) or on the anhydrobase, giving the trimethine dye. Indeed, the nucleophilic a-carbon of the dye—the proton is labile and can be replaced (70, 71)—is liable to add onto the electrophilic /3-carbon of the alcene derivative. The neocyanine results from elimination of a molecule of ethanol. 

Electronegative substituents m a molecule can affect acidity even when they are not directly bonded to the lomzable proton Compare ethanol (CH3CH2OH) with a related compound m which a CE3 group replaces the CH3 group... 

FIGURE 1 8 Electrostatic potential maps of ethanol and 2 2 2 tnfluoroethanol As indi cated by the more blue less green color in the region near the OH proton in 2 2 2 trifluoro ethanol this proton bears a greater degree of positive charge and is more acidic than the OH proton in ethanol... 

Step (2) Ethanol acts as a base to remove a proton from the carbocation to give the alkene products (Deprotonation step)... 

When applied to the synthesis of ethers the reaction is effective only with primary alcohols Elimination to form alkenes predominates with secondary and tertiary alcohols Diethyl ether is prepared on an industrial scale by heating ethanol with sulfuric acid at 140°C At higher temperatures elimination predominates and ethylene is the major product A mechanism for the formation of diethyl ether is outlined m Figure 15 3 The individual steps of this mechanism are analogous to those seen earlier Nucleophilic attack on a protonated alcohol was encountered m the reaction of primary alcohols with hydrogen halides (Section 4 12) and the nucleophilic properties of alcohols were dis cussed m the context of solvolysis reactions (Section 8 7) Both the first and the last steps are proton transfer reactions between oxygens... 

Step 7 Proton transfer from the conjugate acid of the product to ethanol... 

Step 4 Proton transfer steps to yield ethanol and benzoate ion... 

Cationic rings are readily reduced by complex hydrides under relatively mild conditions. Thus isoxazolium salts with sodium borohydride give the 2,5-dihydro derivatives (217) in ethanol, but yield the 2,3-dihydro compound (218) in MeCN/H20 (74CPB70). Pyrazolyl anions are reduced by borohydride to pyrazolines and pyrazolidines. Thiazolyl ions are reduced to 1,2-dihydrothiazoles by lithium aluminum hydride and to tetrahydrothiazoles by sodium borohydride. The tetrahydro compound is probably formed via (219), which results from proton addition to the dihydro derivative (220) containing an enamine function. 1,3-Dithiolylium salts easily add hydride ion from sodium borohydride (Scheme 20) (80AHC(27)151). 

SG sols were synthesized by hydrolysis of tetraethyloxysilane in the presence of polyelectrolyte and surfactant. Poly (vinylsulfonic acid) (PVSA) or poly (styrenesulfonic acid) (PSSA) were used as cation exchangers, Tween-20 or Triton X-100 were used as non- ionic surfactants. Obtained sol was dropped onto the surface of glass slide and dried over night. Template extraction from the composite film was performed in water- ethanol medium. The ion-exchange properties of the films were studied spectrophotometrically using adsorption of cationic dye Rhodamine 6G or Fe(Phen) and potentiometrically by sorption of protons. 

Thiochrome (2,7-dimethyl-5//-thiachromine-8-ethanol 3,8-dimethyl-2-hydroxyethyl-5//-thiazolo[2,3 l, 2 ]pyrimido[4, 5 -d]pyrimidine [92-35-3] M 262.3, m 227-228 , pK st 5.8 (thiazol-N protonation). Crystd from chloroform. 

Figure 18.16 One-dlmenslonal NMR spectra, (a) H-NMR spectrum of ethanol. The NMR signals (chemical shifts) for all the hydrogen atoms In this small molecule are clearly separated from each other. In this spectrum the signal from the CH3 protons Is split Into three peaks and that from the CH2 protons Into four peaks close to each other, due to the experimental conditions, (b) H-NMR spectrum of a small protein, the C-terminal domain of a cellulase, comprising 36 amino acid residues. The NMR signals from many individual hydrogen atoms overlap and peaks are obtained that comprise signals from many hydrogen atoms. (Courtesy of Per Kraulis, Uppsala, from data published in Kraulis et al.. Biochemistry 28 7241-7257, 1989.)...

Figures 1.9a and b demonstrate the effeet of proton broadband deeoupling in the C NMR speetrum of a mixture of ethanol and hexadeuterioethanol. The C//j and CH2 signals of ethanol appear as intense singlets upon proton broadband deeoupling while the CD3 and CD2 resonanees of the deuteriated eompound still display their septet and quintet fine strueture deuterium nuelei are not affected by H decoupling because their Larmor frequeneies are far removed from those of protons further, the nuelear spin quantum number of deuterium is 7/3=/ in keeping with the general multiplieity rule (2nx Ix+ 1, Seetion 1.4), triplets, quintets and septets are observed for CD, CD2 and CD3 groups, respeetively. The relative intensities in these multiplets do not follow Paseal s triangle (1 1 1 triplet for CD 1 3 4 3 1 quintet for CD2 1 3 6 7 6 3 1 septet for CD3).

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