Acetone, acid strength

Previous attempts to estimate Drago parameters for solid surfaces met with limited success. Fowkes and co-workers (198-201) calculated Q and Ex values for SiOj, TiOj, and Fe Oj using a combination of UV and IR spectroscopies and a flow calorimeter. They determined heats of adsorption of pyridine, triethylamine, ethyl acetate, acetone, and polymethylmethacrylate (PMMA) in neutral hydrocarbon solutions. However, their results did not provide consistent Q/Ea parameters for the surface acid sites. It should be noted that the heats determined were for high surface coverages, and these values provide a lower bound for the actual acid strength distribution. 

To compare acid strength between acetone and acetylacetone, one considers the stabilities of the carbanions formed. The carbanion of acetone is similar to the carbanion formed by ionization of a hydrogen from carbon 1 or 5 of acetylacetone. Since the predominant carbanion for acetylacetone is formed by carbon 3 ionization, it is more stable than the acetone carbanion, therefore, more readily formed. This implies that acetylacetone is more acidic than acetone. 

A detailed survey of this figure reveals that the nickel sulfate heated at temperatures above 450° has a number of acid sites having acid strength lower than pK = +1.5, but has no or little catalytic activity. The acidity of acid strength higher than pK = — 3.0 best correlates with the catalytic activity for the depolymerization reaction. This is further confirmed by the fact that nickel sulfate and cupric sulfate lost entirely their catalytic activity when the acid sites whose acid strength is equal to or lower than pK = — 3 were poisoned with dicinnamal-acetone, a basic indicator of pK = — 3 12). 

Similar to the results of CO and benzene adsorption, Bosacek and Kubelkovi [737] found that the strength of interaction between acetone and framework OH groups increased with the acid strength of the protonic sites (cf. also [729]). 

Figure 8.8 Comparison of acid strength of different zeolites with those of sulfuric acid and the Hammett indicator scale (see text), on the basis of the observation of (i) different protonated molecules at the acid sites and (ii) the NMR chemical shifts of mesityl oxide ( ) and acetone [ ]. [After the Scheme of Haw, reference 32 with permission. Copyright 1996 American Chemical Society.]...

Thermal stability of raw TATP (but well washed to neutral pH) depends markedly on the type (Fig. 10.12) and amount (Fig. 10.13) of acid used as the catalyst used in its preparation. The decomposition of TATP begins around 145 °C when hydrochloric or nitric acid is used. The amount of catalyst in this case does not have a measurable influence on the thermal stability of prepared T ATP (acid to acetone molar ratio c/ a from 2.5 X 10 " to 5 X 10 ). A significant influence was however found when using sulfuric or perchloric acid. A low concentration of these two acids ( c/ a < 1 X 10 ) yields product that decomposes above 145 °C just as in the case of pure TATP. Higher concentrations however yield TATP that decomposes during melting, or even before that, in the solid phase (Fig. 10.13, Table 10.3). It is presumed that the lower thermal stability is a result of a combination of two factors—overall residual acidity within the TATP crystals and acid strength [57]. 

The OH groups on the binary oxides of different compositions show different acidic strength. The acidic strength, measured by O — H frequency shift in IR absorption on adsorption of acetone, decreases with increasing MgO content. 

Cosolvents ana Surfactants Many nonvolatile polar substances cannot be dissolved at moderate temperatures in nonpolar fluids such as CO9. Cosolvents (also called entrainers, modifiers, moderators) such as alcohols and acetone have been added to fluids to raise the solvent strength. The addition of only 2 mol % of the complexing agent tri-/i-butyl phosphate (TBP) to CO9 increases the solubility ofnydro-quinone by a factor of 250 due to Lewis acid-base interactions. Veiy recently, surfac tants have been used to form reverse micelles, microemulsions, and polymeric latexes in SCFs including CO9. These organized molecular assemblies can dissolve hydrophilic solutes and ionic species such as amino acids and even proteins. Examples of surfactant tails which interact favorably with CO9 include fluoroethers, fluoroacrylates, fluoroalkanes, propylene oxides, and siloxanes. 

---