Amines, titration acid method

Nonaqueous methods include the use of amine titration and adsorption of indicators for visual measurement of acid strength. This procedure allows both the determination of the total amount of acid sites and also the acid strength distribution. A disadvantage is that bulky molecules (amines and indicators) arc used and these may be excluded from entering small pores. With zeolites, the slow rate of diffusion and equilibration has to be taken into account. Spectroscopic measurement of acid strength may also be performed using amine titration and indicator adsorption. Ultraviolet or fluorescent indicators may be used. 

Butyl amine titration and ammonia thermodesorption methods were used to determine surface acidity of the catalysts. 

Similarly, the basicity can be defined when an acid is converted by its conjugated base. This allows to define acidity and basicity in the same scale. A similar expression can be proposed for interaction of bases with Lewis sites. The amine titration method, described by Tanabe et al. [33], consists of titrating a solid acid suspended in benzene with -butylamine using an indicator. Although this technique is widely applied in the fields of colloids and soil sciences [31], it has many limitations to deduce gas-solid phenomena, the surface Hammett acidity function also having doubtful physical meaning [6]. 

For the determination of strength and amount of a solid acid, there are two main methods an amine titration method using indicators and a gaseous base adsorption method. 

The amount of acid sites on a solid surface can be measured by amine titration immediately after determination of acid strength by the above method. The method consists of titrating a solid acid suspended in benzene with a-butylamine, using an indicator. The use of various indicators with different p o values (see Table 2.1) enables us a determination of the amount of acid at various acid strengths by amine titration. The experimental details such as the effects of titration time, volume of added indicator, pore size, and moisture on measured acid amount are given in Reference 2. 

The amine titration method gives the sum of the amounts of both Brensted and Lewis acid, since both proton donors and electron pair acceptors on the surface will react with either the electron pair (—N -) of the indicator or that of amine ( = N ) to form a coordination bond. This method is rarely applied to colored or dark samples where the usual color change is difficult to observe. However, the difficulty can be minimized by mixing a white substance of known acidity with the sample or by employing the spectrophotometric method.Calorimetric titration of a solid acid with amine is also available for the estimation of the acid amount of a colored or dark sample. Recently, Hashimoto et at. developed a method to measure the acid strength... 

Titrations with dibutylamine [111-92-2] can also be used to determine the NCO content of isocyanates and prepolymers. Generally, an excess of amine in a suitable solvent such as chlorobenzene [108-90-7] is added to the sample. The resulting solution is allowed to react and the unreacted amine is back- titrated with dilute hydrochloric acid. For low NCO content levels, a colorimetric method is often used. The isocyanate-containing species is titrated with amine and the unreacted amine is deterrnined using malachite green [569-64-2]. 

The free maleic acid content in maleic anhydride is determined by direct potentiometric titration (166). The procedure involves the use of a tertiary amine, A/-ethylpipetidine [766-09-6J, as a titrant. A tertiary amine is chosen as a titrant since it is nonreactive with anhydrides (166,167). The titration is conducted in an anhydrous solvent system. Only one of the carboxyhc acid groups is titrated by this procedure. The second hydrogen s dissociation constant is too weak to titrate (166). This test method is not only used to determine the latent acid content in refined maleic acid, but also as a measure of the sample exposure to moisture during shipping. 

Contaminant by-products depend upon process routes to the product, so maximum impurity specifications may vary, eg, for CHA produced by aniline hydrogenation versus that made by cyclohexanol amination. Capillary column chromatography has improved resolution and quantitation of contaminants beyond the more fliUy described packed column methods (61) used historically to define specification standards. Wet chemical titrimetry for water by Kad Eisher or amine number by acid titration have changed Httle except for thein automation. Colorimetric methods remain based on APHA standards. 

An assay method for benzaldehyde involves condensing benzaldehyde with hydroxyl amine hydrochloride to form an oxime. The released hydrochloric acid is then titrated. 

Procedure. To obtain experience in the method, the purity of analytical-grade potassium chlorate may be determined. Prepare a 0.02M potassium chlorate solution. Into a 250 mL conical flask, place 25.0 mL of the potassium chlorate solution, 25.0mL of 0.2M ammonium iron(II) sulphate solution in 2M sulphuric acid and add cautiously 12 mL concentrated sulphuric acid. Heat the mixture to boiling (in order to ensure completion of the reduction), and cool to room temperature by placing the flask in running tap water. Add 20 mL 1 1 water/phosphoric(V) acid, followed by 0.5 mL sodium diphenyl-amine-sulphonate indicator. Titrate the excess Fe2+ ion with standard 0.02M potassium dichromate to a first tinge of purple coloration which remains on stirring. 

In contrast to the acid, sodium nitrite should not in general be added in excess. Firstly, as far as the ratio of amine to nitrite is concerned, diazotization is practically a quantitative reaction. In consequence, it provides the most important method for determining aromatic amines by titration. Secondly, an excess of nitrous acid exerts a very unfavorable influence on the stability of diazo solutions, as was shown by Gies and Pfeil (1952). Mechanistically the reactions between aromatic diazonium and nitrite ions were investigated more recently by Opgenorth and Rtichardt (1974). They showed that the primary and major reaction is the formation of aryl radicals from the intermediate arenediazonitrite (Ar —N2 —NO2). Details will be discussed in the context of homolytic dediazoniations (Secs. 8.6 and 10.6). 

In the context of the stability of the nitrosoamine intermediate in the diazotization of heteroaromatic amines relative to that in the case of aromatic amines, the reversibility of diazotization has to be considered. To the best of our knowledge the reverse reaction of a diazotization of an aromatic amine has never been observed in acidic solutions. This fact is the basis of the well-known method for the quantitative analysis of aromatic amines by titration with a calibrated solution of sodium nitrite (see Sec. 3.3). With heteroaromatic amines, however, it has been reported several times that, when using amine and sodium nitrite in the stoichiometric ratio 1 1, after completion of the reaction nitrous acid can still be detected with Kl-starch paper,... 

Here we shall confine ourselves to the solvents benzene and 1,2-dichloroethane (class 8). Considering benzene, many investigators have demonstrated since the 1930s the feasibility of titrations in this solvent using both potentiometric and spectrophotometric methods, paying much attention to acid-base indicator reactions under the influence of primary, secondary and tertiary amines. Association of carboxylic acids in benzene was studied at a later stage, mainly on the basis of colligative properties, IR spectroscopy and solvent extraction. ... 

In an early work by Mertz and Pettitt, an open system was devised, in which an extended variable, representing the extent of protonation, was used to couple the system to a chemical potential reservoir [67], This method was demonstrated in the simulation of the acid-base reaction of acetic acid with water [67], Recently, PHMD methods based on continuous protonation states have been developed, in which a set of continuous titration coordinates, A, bound between 0 and 1, is propagated simultaneously with the conformational degrees of freedom in explicit or continuum solvent MD simulations. In the acidostat method developed by Borjesson and Hiinenberger for explicit solvent simulations [13], A. is relaxed towards the equilibrium value via a first-order coupling scheme in analogy to Berendsen s thermostat [10]. However, the theoretical basis for the equilibrium condition used in the derivation seems unclear [3], A test using the pKa calculation for several small amines did not yield HH titration behavior [13],... 

Analyses of Water Content. The water content of the PIQ starting materials was analyzed. The water content of amines was measured using a DuPont 321A moisture meter and those of the solvents were measured by Karl Fischer s reagent method. The water content of acid dianhydrides was measured by titrating the free acid. 

Gascon and co-workers developed an analytical method suitable for the determination of 1,2-epoxy-2,4,4-trimethylpentane.<2D The epoxide was heated at 100° in a sealed tube with di-n-butylamine, and the resulting product aoetylated with acetic anhydride. Titration with perchloric arid in aoetie acid containing a suitable indicator gave the amount of tertiary amine formed. 

IV) Amines 0.20% calcd as methylamine when detd using the proced IV for secondary amines described under Centr 1 but calcg % methyl-aniline from the formula [l0.7(Vt-V2)N] /W Ax 1.78, where V ml of NaOH soln required to titrate blank Vz=ml of NaOH soln required to titrate sample N=normality of NaOH soln W=wt of sample and A=% acidity as AcOH Note This method is not specific for amines but will detect other groups such as OH... 

Non-Aqueous Tltrimetry. A procedure for determining total amination is reported by MacDougall and Boyles (Ref 31 b). The procedure includes a digestion of the TATB in 0.1N perchloric acid-acetic acid soln, followed by titrimetric analysis. An excess of basic K acid phthalate is added and then back-titrated with the perchloric—acetic acid soln to a crystal violet end pt. The method requires a sample oontg 86mgs of TATB ( v l meq), and the digestion of the TATB requires 48 hrs. The authors estimate that 18 samples can be titrated in an 8-hr day. They conclude that the method is stoichiometric and that the relative std deviation is 0.1% for 1 meq amounts of TATB. Also, an IR scan is reported and presented as Fig 5... 

If the objective is to fingerprint surface acidity (so that one acidic solid can be distinguished more clearly from another), the nonaqueous titration method (26) would be appropriate. The original method could be made more selective for titration of Br0nsted acids by choosing recently recommended indicators (21) and using a sterically hindered amine (54) as the basic reagent. However, even an improved indicator method may have its drawbacks a sterically hindered amine is not perfectly selective,... 

This NMR titration method was subsequently applied to equilibrium IEs on acidity.30 33 Like the previous methods, it too benefits from the high sensitivity of 13C and 19F chemical shifts, and even 111 chemical shifts, to both isotopic substitution and state of protonation. Figure 1 shows the NMR titration of a mixture of tri(methyl-d)amine and tri(methyl-t/2)amine in D20, plotted according to Equation (19). The slope is 1.1618 0.0004. The intercept is -0.0061 0.0046, properly zero. The correlation coefficient is an impressive 0.999999, which is an indication of the accuracy achievable. Another remarkable result was the measurement of the relative basicity of the two exceedingly similar isotopomers of 1 -benzyl-4-methylpiperidine-2,2,6-t/3 (6). These are truly isotopomers (here stereoisomers), which bear the same number of isotopic substitutions and differ only in the position of the isotope, which is either axial or equatorial. 

Materials. Trimethylamine N-oxide dihydrate (98%) from Aldrich and N-dimethyldodecylamine N-oxide (97%) from Fluka Chemie were used as received. N-dimethylhexylamine N-oxide and N-dimethyloctylamine N-oxide were prepared by reaction of the corresponding tertiary amine with hydrogen peroxide (12). Both samples were isolated as crystalline solids and were >99% pure, based on acid/base titrations and spectrometric methods. Both samples were very hygroscopic. Reagent grade NaBr, 0.1 N and 2.0 N HC1 were from J.T. Baker Chemical Co. and the all solutions were prepared using distilled and deionized water. The pH was monitored using an Orion Ross combination pH electrode and an Orion EA 940 meter. 

Table 1 tabulates literature values for acidity constants of seven amine-Ptn complexes with notations on the temperature, ionic strength, total Ptn concentration, method employed, conditions and other remarks, and the reference number. At least six factors enter into comparing determinations of a single complex. First is the purity of the complex under investigation. Because they rely on chemical shifts of an individual species, NMR methods are less dependent on purity than potentiometric titrations, which are interpreted on the basis of equivalents of added base. Rarely is the raw titration data published, but in one case it is evident from a plot of the data that the titration curve reveals up to about 10% impurity [7], Without knowing whether the impurities are acidic, basic, inert, or even forming during... 

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