Methanol effect phenols

Reduction of coumarins to the dihydro-derivatives has frequently been achieved, but a more efficient procedure has emerged from a new study of this conversion. The most effective method was catalytic reduction in ethanol at 150 °C and under a high pressure (1500 psi) of hydrogen of give mostly the 2-hydroxy-3-phenylbutanoate, which was readily cyclized with PPA to the dihydrocoumarin. Hydroboration of 3-arylcoumarins, followed by oxidation, gave isoflavanones the latter have been dehydrogenated (with DDQ) to isoflavones. A reaction of wide potential value is the selective hydrolysis by zinc and methanol of phenolic acetates in the presence of aUphatic acetate groups. 

The solventless reaction in the presence of diallq ltin(iv) complexes led to a conversion of 42% with 78% selectivity to diphenyl carbonate. Starting from phenyl acetate, total conversion was obtained at 220 "C with higher selectivity to diphenyl carbonate (95%). Transesterification with higher alcohols was also examined, giving better conversion due to higher nucleophilicity compared to phenol. However, a steric effect was evidenced as fert-butanol was unreactive. Transesterification of ethylene carbonate (l,3-dioxolan-2-one) with methanol to dimethyl carbonate was also reported early. " Today, both transesterifications with methanol and phenol are integrated into the value chain of bisphenol-A polycarbonate production and commercialised by Asahi Kasei Corporation (Scheme 21.12). ... 

However, a second mole of alcohol or hemiformal caimot be added at the ordinary pH of such solutions. The equiUbrium constant for hemiformal formation depends on the nature of the R group of the alcohol. Using nmr spectroscopy, a group of alcohols including phenol has been examined in solution with formaldehyde (15,16). The spectra indicated the degree of hemiformal formation in the order of >methanol > benzyl alcohol >phenol. Hemiformal formation provides the mechanism of stabilization methanol is much more effective than phenol in this regard. 

Swain and Eddy have queried the wide applicability of the S l and Sif2 mechanisms and favored a push-pull termolecular process for the reaction of pyridine with methyl bromide in benzene solution for example, they have suggested that the effects observed on the addition of methanol, phenol, p-nitrophenol, and mercuric bromide to the reaction mixture can be explained by an intermediate of type 168. ... 

The activation of persulfates by various reductant viz. metals, oxidizable metals, metal complexes, salts of various oxyacid of sulfur, hydroxylamine, hydrazine, thiol, polyhydric phenols, etc. has been reported [36-38]. Bertlett and Colman [39] investigated the effect of methanol on the decomposition of persulfates and proposed the following mechanism. 

Compounds with a smaller/C., and larger pKa are less acidic, whereas compounds with a larger/Ca and smaller plsimple alcohols like methanol and ethanol are about as acidic as water but substituent groups can have a significant effect, tert-Butyl alcohol is a weaker acid, for instance, and 2,2,2-trifluoroethanol is stronger. Phenols and thiols, the sulfur analogs of alcohols, are substantially more acidic than water. 

Combined effect of BTMA Br3 and ZnCl2 in acetic acid provides a new excellent bromination procedure for arenes. That is, while such reactive aromatic compounds as phenols, aromatic amines, aromatic ethers, and acetanilides have been easily brominated by BTMA Br3 in dichloromethane in the presence of methanol, the reaction of arenes, less reactive compounds, with BTMA Br3 in dichloromethane-methanol did not proceed at all, even under reflux for many hours. However, arenes could be smoothly brominated by use of this agent in acetic acid with the aid of the Lewis acid ZnCl2 (Fig. 13) (ref. 16). 

The use of ethanol as an achiral auxiliary gave the adduct 53 with 55% ee, while neopentyl alcohol and methanol gave 96 and 87% ee, respectively. These results suggested that the achiral alcohol might exert a steric effect on the stereoselectivity. However, the increase in enantioselectivity from 55% to about 96% when 2,2,2-trifluoroethanol (TFE) was used instead of ethanol indicates a possible significant inductive effect also. Good enantioselectivities were also obtained with carboxylic acids and phenols. 

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 ... 

The authors presume that the observed effect is due to acid catalysis by methanol, but no catalysis by phenol was observed. Pietra and Vitali111 have shown earlier that phenol catalyses the reaction of l-fluoro-2,4-dinitrobenzene with piperidine in benzene. 

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