Acidity and Basicity Measurements

Yokoyama, M. Chikuma, and H. Tanaka, Chem. and Pharm. Bull. (Japan), 1972,20,2000. V. I. Ryaboi, V. A. Shenderovich, and N. E. Shchukina, Zhur. priklad. Khim., 1973,46,1095. 

Acidity and Basicity Measurements. Nishiguchi and Iwakura have determined the Hammett and o- values of the 3-ethylthioureido, 3-ethylureido, thioacetamido, acetamido, methylaminothiocarbonyl, and methylaminocarbonyl groups by measuring the dissociation constants of the relevant meta and pam-substituted benzoic acids. The investigators, on the basis of a comparison of the subsequently derived ai and on values 

The dissociation constants of monothio-oxamides and 1-mercapto-thiocarbonylpyrrolidine have been determined by spectrophotometric and potentiometric methods, respectively. 

Ylides of Sulphur, Selenium, and Tellurium, and Related Structures 

This review attempts to cover the literature of the topic which has appeared since Volume 1 of this series, up to the end of 1971. Thus, complete coverage of this field is available through the use of three sources the book Ylid Chemistry , up to the end of 1965 Volume 1 of this series for 1966—1969 this review for 1970 and 1971. 

Once again it is necessary to report that no significant work has been published directed towards a theoretical description and understanding of the nature of the bonding in sulphonium ylides. Perhaps such work will be stimulated by the boom in X-ray crystallographic structure determinations of sulphur ylides and also by recent theoretical work on phosphonium ylides.  

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The acid-base properties of isoxazole and methylisoxazoles were studied in proton donor solvents, basic solvents or DMSO by IR procedures and the weakly basic properties examined (78CR(Q(268)613). The basicity and conjugation properties of arylisoxazoles were also studied by UV and basicity measurements, and it was found that 3-substituted isoxazoles were always less basic than the 5-derivatives. Protonation increased the conjugation in these systems (78KGS327). 

The study of acid-base interaction is an important branch of interfacial science. These interactions are widely exploited in several practical applications such as adhesion and adsorption processes. Most of the current studies in this area are based on calorimetric studies or wetting measurements or peel test measurements. While these studies have been instrumental in the understanding of these interfacial interactions, to a certain extent the interpretation of the results of these studies has been largely empirical. The recent advances in the theory and experiments of contact mechanics could be potentially employed to better understand and measure the molecular level acid-base interactions. One of the following two experimental procedures could be utilized (1) Polymers with different levels of acidic and basic chemical constitution can be coated on to elastomeric caps, as described in Section 4.2.1, and the adhesion between these layers can be measured using the JKR technique and Eqs. 11 or 30 as appropriate. For example, poly(p-amino styrene) and poly(p-hydroxy carbonyl styrene) can be coated on to PDMS-ox, and be used as acidic and basic surfaces, respectively, to study the acid-base interactions. (2) Another approach is to graft acidic or basic macromers onto a weakly crosslinked polyisoprene or polybutadiene elastomeric networks, and use these elastomeric networks in the JKR studies as described in Section 4.2.1. 

Interpretation of Measurements in Experimental Catalysis P. B. Weisz and C. D. Prater Commercial Isomerization B. L. Evering Acidic and Basic Catalysis Martin Kilpatrick Industrial Catalytic Cracking Rodney V. Shankland... 

We saw in Section J that a salt is produced by the neutralization of an acid by a base. However, if we measure the pH of a solution of a salt, we do not in general find the neutral value (pH = 7). For instance, if we neutralize 0.3 M CHjCOOH(aq) with 0.3 M NaOH(aq), the resulting solution of sodium acetate has pH = 9.0. How can this be The Bronsted-Lowry theory provides the explanation. According to this theory, an ion may be an acid or a base. The acetate ion, for instance, is a base, and the ammonium ion is an acid. The pH of a solution of a salt depends on the relative acidity and basicity of its ions. 

The first systematic measurements of the reactions of ions with molecules in the gas phase were initiated largely by workers associated with analytical mass spectrometry.4-6 It was the rapidly expanding area of ion-molecule reactions which led to the origin of Gas-Phase Ion Chemistry as a distinct field.7 The discovery that ion-molecule equilibria in the gas phase can be determined by mass spectrometric techniques8 led to an explosion of thermochemical measurements based on determination of equilibria by a variety of techniques.9 Significantly, for the first time, information could be obtained on the thermochemistry of reactions which had solution counterparts of paramount importance such as acidities and basicities. These were obtained from proton transfer equilibria such as,... 

Similarly, all pH indicators mentioned can be used for measurement of acidic and basic gases. Figure 14 shows the example of deprotonated bromophenol blue when dissolved in silicone and upon exposure to ammonia when the color of bromophenol blue changed from yellow to blue40 41. 

Similarly, all pH indicators mentioned in sections 4.1-4.3 can be used for measurement of acidic and basic gases. 

The coordination of transition metal ions in acidic chloroaluminate melts has not been firmly established. However, in the case of AICb-EtMelmCI. the E0 values of simple redox systems that are electrochemically accessible in both acidic and basic melt, e.g., Hg(II)/Hg [51], Sb(III)/Sb [52], and Sn(II)/Sn [53] exhibit a large positive potential shift on going from basic melt, where metal ions are known to exist as discrete anionic chloride complexes, to acidic melt. Similar results were observed for Cu(I) in AlCh-NaCl [48]. This dramatic decrease in electrochemical stability isprima facie evidence that metal ions in acidic melt are probably only weakly solvated by anionic species such as AICI4 and AECI-. Additional evidence for this is derived from the results of EXAFS measurements of simple metal ions such Co(II), Mn(II), and Ni(II) in acidic AlCh-EtMelmCl, which indicate that each of these ions is coordinated by three bidentate AICI4 ions to give octahedrally-coordinated species such as [ M (AIC14) 2 ] [54]. Most transition metal chloride compounds are virtually... 

That this reaction does not take place to a measurable extent does not prevent us from knowing that the ions produced would be the acidic and basic species. Therefore, we can predict that Na2S03 would be a base in liquid S02 because it contains S032 and SOCl2 would be an acid because it could formally produce S02+ if it were to dissociate. Thus, we predict that Na2S03 and SOCl2 would react according to the equation... 

Phenolic substances can be measured directly, without colour development, by the difference in their ultraviolet absorption in acidic and basic... 

Austin et al. [132] measured the ionic strength dependence of the liposome-water distribution of several acidic and basic drugs and modelled the data with a combination of electrostatic and ion pair models. They concluded that the increased apparent Dmw values at higher ionic strength were due primarily to the reduction in surface potential and not to ion pairing. Ion pairing was also excluded because the apparent Dmw varied at fixed ionic strength with the... 

Standardization of pH meters is essential and must be done on a regular basis. The starting point in standardization is to adjust the meter and electrodes using a standard buffer solution of pH 7.00 and adjusting the meter to this pH. The second step is to set a second point, which is in the range of pH levels expected to occur in the measurements. Thus, if the pH values are all expected to be acidic, the second point will commonly be set using a buffer of 4.01 if they are expected to be basic, then a pH 10.00 buffer will be used. If both acidic and basic pH values are likely, the meter can be standardized using all three buffers. 

Hydrogen bond donor solvents are simply those containing a hydrogen atom bound to an electronegative atom. These are often referred to as protic solvents, and the class includes water, carboxylic acids, alcohols and amines. For chemical reactions that involve the use of easily hydrolysed or solvolysed compounds, such as AICI3, it is important to avoid protic solvents. Hydrogen bond acceptors are solvents that have a lone pair available for donation, and include acetonitrile, pyridine and acetone. Kamlet-Taft a and ft parameters are solvatochromic measurements of the HBD and HBA properties of solvents, i.e. acidity and basicity, respectively [24], These measurements use the solvatochromic probe molecules V, V-die lliy I -4-n i in tan iline, which acts as a HBA, and 4-nitroaniline, which is a HBA and a HBD (Figure 1.17). 

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