Sulfonic acid group titration

The procedure described below was developed by Pobiner (1983) and consists of the nonaqueous potentiometric titration of lignin with tetra-n-butylammonium hydroxide in the presence of an internal standard, p-hydroxybenzoic acid. As is true also for conductometric titrations of lignin (see Chap. 7.7), phenolic hydroxyl and sulfonic acid groups may be coincidentally determined by this procedure. 

In the conductometric titration of sulfonic acid groups in pulp (Katz et al. 1984), it is first necessary to convert all the acid groups to their protonated form. The pulp is then dispersed in water containing 0.001 M sodium chloride and the conductivity monitored during titration with 0.1 M sodium hydroxide. The... 

The initial high conductivity is attributable to the protons from the highly dissociated sulfonic acid groups. As alkali is added, the conductivity drops linearly as H+ is replaced by the less conducting Na+ ion. The horizontal portion of the curve corresponds to the titration of weaker carboxylic acid... 

Fig. 7.7.3. Conductometric titration curve of a refiner mechanical pulp made from sulfonated spruce chips (3.47g). End point A corresponds to titration of the sulfonic acid groups and end point B coresponds to titration of the sulfonic and carboxylic acid groups. (Katz et al. 1984)...

The second direct method depends on the ability of aqueous potassium chloride, adjusted to pH 4 with carbon dioxide, to selectively elute hydrogen ions from sulfonic acid groups in pulps that first have been converted to their hydrogen form with 0.1 M hydrochloric acid (Cappelen and Schoon 1966). Carbon dioxide is removed from the eluent by sparging with nitrogen and the remaining acid is titrated with 0.1 M sodium hydroxide. Again, a correction factor for interference from carboxylic acids is required. This factor, as before, is based on the protons eluted from bleached pulps by the eluent. As the results depend on the concentration of potassium chloride used, the letter is adjusted so that the sulfonate content corresponds to the sulfur content of pulps assumed to contain only acidic sulfur. 

Figure 3.29. Potentlometric (a) and conductometric (b) titration of a latex with sulfonic acid groups. Redrawn from K. Furusawa, W. Norde and J. Lyklema, Kolloid Z. Z. Polymere 280 (1972) 908.

Carboxylic and sulfonic acid groups import acidity to organic compounds. Most carboxylic acids and sulfuric acids are readily dissolved in water, and their titration with a base is straightforward. If solubility in water is not sufficient, the acid can be dissolved in ethanol and titrated with aqueous base. Aliphatic amines and many saturated cyclic amines can be titrated directly with a solution of a strong acid. Esters are determined by saponification with a measured quantity of standard base. The excess base is titrated with standard acid. 

Carboxylic and sulfonic acid groups are the two most common structures that impart acidity to organic compounds. Most carboxylic acids have dissociation constants that range between 10 " and 10 , and thus these compounds are readily titrated. An indicator that changes color in a basic range, such as phenolphthalein, is required. 

I. M. Kolthoff and T. Kameda have preferred to examine the purity by titrating the indicator solution conductometrically. The sulfonic acid group in sulfonephthaleins behaves as a strong acid and in a titration with alkali, the conductivity diminishes just as in the case of a strong acid. A break occurs in the titration curve when the sulfonic acid group is neutralized, and thereafter the conductivity increases until the phenol group is neutralized. A second break occurs at this point and from there on the conductivity increase is due to the free alkali added. Thus two breaks are obtained and for pure preparations the quantity of alkali required to reach the first point should equal the quantity used up between the first and second. Relatively few of the samples investigated by the author fulfilled this requirement. 

The vapor-phase nitration of benzene with NO2 was investigated by Suzuki et al. using polyorganosiloxanes bearing sulfonic acid groups and silica-supported benzenesulfonic acid catalysts [31]. Phenylsulfonic polysiloxane was the most active among the polysiloxanes tested, its activity was not related to the concentration of acid sites as determined by a titration method, however. From the partial pressure dependence of the reaction rate it was concluded that the formation of NO as the active species was the rate-limiting step [32]. 

All resins were used in their forms. The sulfonic acid group concentrations were measured by Purolite, using a standard procedure of ion-exchange with Na followed by aqueous titration with standard NaOH solution. Water contents of the fully swollen resins were also determined by Purolite. 

Alterations to the fibers that affect the apparent frequency of acidic or basic groups, such as hydrolysis, susceptibility to hydrolysis, or the introduction of sulfonic acid groups [24, 66], can affect the acid- and/or basecombining capacity of hair. Therefore, permanent-waving and especially bleaching can affect these titration parameters [8]. The effects of cosmetic treatments and environment on these parameters are described in detail in Chapter 5. 

The water uptake and ion exchange capacities for poly(ether sulfone) membranes are given in Table 3.10. The ion exchange capacities, determined by H NMR spectroscopy, are in good agreement with the values calculated from the initial monomer composition. However, using the titration method, the values are somewhat lower, which is rationalized by the fact that only a part of the sulfonic acid groups is... 

PPO and PPOBr were sulfonated by reacting with chlorosulfonic acid in chloroform [49]. The degree of sulfonation was determined by acid-base titration method. Under the reaction conditions only mono-aryl substitution of PPO and PPOBr occurred. The polymers were converted to the salt form by replacing the proton of the sulfonic acid group with Na-cation. Sulfonated PPO (SPPO) and sulfonated brominated PPO (SPPOBr), both in the Na-cation form (SPPONa and NaSPPOBr), were used for water removal studies. 

Sodium hydroxyalkanesulfonates may be determined in the presence of an unsaturated hydrocarbon, including sodium alkenesulfonate. The sulfonates are converted to the free sulfonic acids using a slight excess of 2,4-dinitrobenzene-sulfonic acid. The hydroxyl group of the sulfonic acid liberated is acetylated in ethyl acetate solution by a known excess of acetic anhydride. The unconsumed anhydride is hydrolyzed by a pyridine-water mixture and the acids titrated potentiometrically with standard sodium hydroxide solution. The hydroxy-alkanesulfonate content is calculated after correction for any traces of acidity or alkalinity in the original sample. 

The amount of the ester sulfonates, besides the mono- and disalt of the a-sulfo fatty acid, can be calculated by two titrations, one in the acid and one in the basic range. In the basic range both sulfonates and carbocylate functionalities are negatively charged and titrated with the cationic surfactant hyamine. In acid medium the RCOOH group is protonated and no longer available for the titration. Since hyamine-methylene blue (acid conditions) titrates only sulfonate and hyamine-phenol red (basic conditions) determines both sulfonates and carbo-cylates, substraction of the titration value with phenol red from the double value of the titration with methylene blue yields only the a-sulfo fatty acid ester. This is the only species of the three which has merely the sulfonate function [106]. 

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