Aliphatic alcohols, carbonium ions from

That the observed spectrum was the result of a chemical reaction between the hydrocarbon and the catalytically active centers of the silica-alumina surface (chemisorption), and not due to a general sur-fatochromic spectral shift, was demonstrated from the spectrum of this compound adsorbed on a nonacidic or very weakly acidic silica gel (29). The spectrum (Fig. 30, Curve B) of silica gel exposed to triphenylmethane vapor for 1000 hours at 100°C was identical to the spectrum (Curve A) of an alcoholic solution of this hydrocarbon. The close agreement between these spectra suggested that on silica gel the triphenylmethane was physisorbed. This was further evidenced by the marked loss of spectral intensity (Curve C) attendant to a four hour evacuation at 100°C. In contrast, on silica-alumina where the hydrocarbon was chemisorbed as the carbonium ion, no decrease in absorbance was noted even after 48 hr evacuation at 275°C. These data constituted the first direct demonstration of the formation of carbonium ions as a consequence of chemisorption of a tertiary hydrocarbon on the surface of a cracking catalyst by a reaction involving the rupture of an aliphatic C-H bond. The generality of this process of carbonium ion... 

Ion cyclotron resonance studies of 3-methoxyalkanethiols and homologous sulphides MeO(CH2) SMe (n = 1—3/ have provided information on the reactivity profile of the methoxymethyl cation towards alcohols, thiols, and amines, and on the preferential abstraction of hydride ion from the carbon atoms that are alpha to sulphur (confirming that, in gas-phase reactions, S is more able than O to stabilize a neighbouring carbonium ion). Gas-phase acidities of dimethyl sulphoxide and representative aliphatic sulphones reveal a lower degree of stabilization of the cr-sulphonyl carbonium ions. ... 

Erythromycin is a macrolide antibiotic isolated from Streptomyces erythraeus. It has a similar spectmm of activity to that of the early penicillins and was therefore often used as a substimte in patients who displayed life-threatening penicillin allergies. Erythromycin is a base, where the aliphatic tertiary amino group has a pKa of 8.8. Despite this, oral preparations are difficult to formulate because the tertiary alcohols at the 6 and 12 positions cause instability in stomach add. As with many tertiary alcohols in strong add, the C-OH bond can break to form highly reactive carbonium ions, in this case at dther the 6 or 12 positions. An intramolecular cydisation via the carbonyl oxygen at C-10 with the electrophilic carbonium ions results in formation of the inactive eiythralosamine (Fig. 8.15). 

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