Amines titration

Fatty acid, MRNi hydrogenation, 32 243-245 Faujasites, 34 160-183 acidic sites, 27 151-154 alkaline and rare earth forms, 27 160-165 amine titration, 27 163 infrared smdies, 27 160-163 surface acidity and catalytic activity, 27 163-165... 

In summary, the preceding considerations make it evident that amine titrations generally give acidity values higher than the number of strong Br0nsted acid sites that constitute the primary seat of catalytic activity. 

Silica-alumina Amine titration with Hammett indicators extension of the acid strength scale 69... 

Alumina, silica-alumina Amine titration before and after chemisorption of water, alcohols, and amines. 75... 

The level can be confirmed by a standard dibutyl amine titration. A typical method is given in Appendix 6. Depending on the type of isocyanate used, the exact solvent for dissolution of the sample may have to be determined. 

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. 

Then, in a tricol, heated at 303 K under nitrogen, 5g (0.004 mole) of P-CDOTs were dissolved in 125 mL of DMAe (kept previously on molecular sieves) until the solution cleared. 7 mL (0.04 mole) of (3-aminopropyl)trimethoxysilane (APS) were added drop wise. The solution was vigorously stirred for 1 hour and then precipitated in 1.4 L of acetone (distilled twice, on molecular sieves). The white precipitate was kept under stirring for 2 hours and filtered. The product obtained (P-CDAPS) was dried 2 days at 353 K under vacuum and crushed to form homogeneous yellow powder. The reaction scheme expected is presented on Fig. 1. Si, N, C, N, H contents were determined by TGA, amine titration and elemental analysis. 

The soft experimental conditions in the synthesis of P-CDAPS were optimized using experimental design. The hybrid precursor P-CDAPS has been characterized in order to determine its structure. ETIR spectra show the presence of amino groups (1564cm ) on one hand and siloxane structure (1100-1000cm ) on the other hand, conhrmed by TGA measurements. This TGA gave a Si ratio of 5.80 0.04%., conhrmed by elemental analysis. N content was determined by elemental analysis at 2.98 0.02%, which corresponds to 2.13 0.04mmol/g of amine functions, also deduced from amine titration. 

Table 1 Proportions of total amino groups and p-CD (determined by elemental analysis), accessible amines (titration by conductimetry), specific surface areas, pore radii and adsorption capacities of lead cation and p-nitrophenol for the different samples...

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

Mixtures of groups 1 and 2, De-quaternisation of the benzalkonium salt by treatment with iodide, extraction of benzyl iodide and tertiary amine, titration with iodate [1]. The tertiary amine can be titrated with acid if useful. 

Zi et al. [91] studied Y zeolites dealuminated with H4EDTA and (NH4)2SiF6. The surface acidity of the zeolites was determined by n-butyl-amine titration, and the amount of strong (Ho < -3.0) acid sites was correlated with the cumene conversion. Both values showed a volcano-type curve if plotted against the amount of Al in the framework. The maximum in these plots was found to be around 30 alumimuns per unit cell, which agrees with the results pubhshed by DeCanio et al. [82]. 

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... 

The acid amount of solid catalysts, which was measured by amine titration with an indicator with pllfa = 3.3, was linearly correlated with the catalytic activity.In the case of decationized and metal-ion exchanged zeolites the catalytic activity is related to the surface acidity, as shown in Fig. 4.18. It was suggested that there were two mechanisms one was accelerated by acid and another was minor and independent of the surface acidity. Usually too strong acidity causes unfavorable side reactions such as olefin formation, as in the case of Z1O2 SC and Naflon. 

D. Atkinson, G. Curthoys et al.. The acidity of solid surfaces and its determination by amine titration and adsorption of coloured indicators. Chem. Soc. Rev. 8,475-479 (1979)... 

For titration of the amine, the sample is dissolved in 50 50 isopropanol/water to which excess NaOH and a small, precisely measured, amount of tri- -butylamine are added. Again, CO2 must be excluded. Titration with aqueous HCl gives two breaks, the first corresponding to excess NaOH and the second to the free amine (see Fig. 2). The amine titration is corrected for the spiked amount spiking allows a readily visible end point even when the sample has a low free amine content. The amine determination was subjected to a collaborative study which showed that at the 0.2-0.5% level repeatability by the same laboratory was in the range of 10%, and was 20% between laboratories (17). 

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