Methanol acidity

The spectra of niclosamide in methanol (Fig. 3a) and methanolic base (Fig. 3c), show four bands with the same 2max values but max values increase in base. In methanolic acid (Fig. 3b) only two bands appeared [19]. This could be explained in terms of resonance effects as well as the dissociation of the phenolic-OH group to phenolate in base [20,21]. The possible resonance structures of niclosamide are shown below ... 

In Carter s studies toward the total synthesis of azaspiracid, the construction of "fragment B" requires the conversion of the y-lactone 91 into a furan acetal. In this connection, it has been uncovered that the desired furan acetal can indeed be formed in 64% yield under methanolic acidic conditions . 

Surprisingly, Lewis acids are seldom applied to the deprotection of TBS ethers even though in certain circumstances they have advantages. A case in point is the transformation depicted in Scheme 4,39.5S The hydrolytic lability of the ox-alimide function in 39.1 precluded desilylation with TBAF or methanolic acid but trifluoroborane etherate in acetonitrile59 at 0 °C rapidly and cleanly accomplished the desired desilylation to give the diol 39,2 in 93% yield. 

Ultraviolet Spectrum. Methanolic acid—282 nm (A = 130a) aqueous alkali—291nm. 

Ultraviolet Spectrum. Methanolic acid—238 nm (A = 370 b). No alkaline shift. 

Ultraviolet Spectrum. Methanolic acid—211 nm (Aj=300b) methanolic alkali—315 nm (A = 547 a). 

Solvolyses of structures containing relatively polar C—C(CN)2 bonds have been found by other workers, when the bond cleaved is in a four-membered ring and in larger ring structures adduct (143) gives (144) in methanol. Acid catalysis may play a role it may too in other cases involving cleavage of other kinds of bonds. ... 

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