Acid-base-coupled temperature effect

The increase in temperature enhances the dissociation of water and leads to a decrease in its acidity scale (defined by — log Ke). The strength of acids and bases is therefore appreciably modified compared with normal conditions. Concurrent with the decrease in the dielectric constant of the medium, the effect of hydrothermal conditions on the behavior of acid-base couples of the type HA/A and may therefore be very different. This is the case for solvents such as water or alcohol, for example [43). This explains why (he basicity of the chlorine ion is much higher under hydrothermal conditions. In water at 500°C and 2kbar, the equilibrium constant of... 

Hydroxyethyl)-pyridine was dehydrated to 2-vinyl-pyridine in liquid phase over solid acid catalysts, with very high selectivity and fairly good reaction rate at relatively low reaction temperature (160°C). The catalytic activity is well correlated with the presence on the catalyst surface of medium to weak Bronsted acid sites. The analysis of coke left behind onto the catalyst and the effect of partial poisoning of catalytic activity by CO2 indicate that the reaction takes place through two mechanisms, involving either a Bronsted acid site or a couple of acid-base sites. 

In this text. Shields and Seybold carefully review the thermochemical principles involved in the measurement and prediction of acid dissociation constants. They further provide an extraordinarily useful comparison of several theoretical models that have been proposed, whether for more specific or more general applications, examining their relative utilities and ranges of applicability. Importantly, the authors tightly couple their analysis to the rich physical organic chemistry associated with all of the various functional groups that may serve as conjugate acids or bases, and they do so not only for the case of aqueous solution, but also for non-aqueous solvents. They wrap up with some welcome discussion of temperature effects, isotope effects, and other phenomena that can extend the utility of acid dissociation constants as reporters of electronic structure and reactivity. 

The Suzuki coupling of 2-iodo-2-cyclohexen-1-one and 4-methoxy-phenylboronic acid is achieved using silver(l) oxide as a suspension in aqueous THF as the base. Unlike earlier reports,15-17 in which up to 6 equiv of Ag2mild conditions, rapid conversion can be achieved at room temperature for a large variety of sensitively functionalized partners in near quantitative yields (see Table).18... 

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