Benzoic acid titration method

The basicity of each solid was measured by the benzoic acid titration method using Hammett indicators [4]. 

Benzoic Acid Titration Method In this method (4) powered alumina samples were first activated in stream of N2 gas at 200°C. About 0.5g of the sample is weighed and taken into sample vial closed with a septum. Acid indicator (1 wt.% dissolved in benzene dried over molecular sieve 4A) is added to this sample and kept for 24 hrs. by constantly shaking the vial... 

Tert-butyl catechol is a weakly acidic molecule with a pKj value of 11.4(6) and hence basic alumina should favour its adsorption by assuming simple acid-base interactions. Hence, we measured the basicity of alumina. The change in surface chemistry due modification of alumina surface with alkali and acid can be measured by two methods, namely (1) Adsorption /Desorption of Gaseous acid molecule (CO2) (2) Benzoic acid titration method... 

The basic strength of a solid surface is defined as the ability of the surface to convert an adsorbed electrically neutral acid to its conjugate base, i.e. the ability of the surface to donate an electron pair to an adsorbed acid. The amount of base (basic sites) on a solid is usually expressed as the number (or mmol) of basic sites per unit weight or per unit surface area of the solid. It is also sometimes more loosely called basicity. There are two main methods for the measurement of strength and amount of basic sites benzoic acid titration method using indicators and geseous acid adsorption method. 

Benzoic Acid Titration Method Using Indicators... 

Potentiometric titration provides the principal method for determining pKa values and it is best applied to substances with pATa values <11. For example the pATa of benzoic acid can be determined as follows A 0.01 M solution of benzoic acid (50 ml) is titrated with 0.1 M KOH. The KOH is added in 0.5 ml increments it would be expected that 5 ml of 0.1 M KOH would be required to neutralise the... 

The British P 1993 [15] describes a procedure to determine benzoic acid in benzoic acid ointment that also contains salicylic acid. In this method, 2 g of the ointment is added to 150 mL water, and warmed until melted. The solution is titrated with 0.1 M NaOH, using phenolphthalein solution as the indicator. Salicylic acid is assayed by a spectrophotometric procedure, and its content subtracted from the total acid value to obtain the benzoic acid content. 

The detailed synthesis procedure and textural properties (surface area, Sggy in m2 g-1 pore volume, V in ml g"1 and main pore diameter, d in nm), determined by nitrogen adsorption from 8.E.T. method have been published elsewhere (refs. 13-18) and are summarized in Table 1, where the surface acidity and basicity of supports are also collected. These values were determined by a spectro-photometric method described elsewhere (ref. 19), that allows titration of the amount (in tunol g 1) of irreversibly adsorbed benzoic acid (BA, pKa> 4.19), pyridine (PY, pka= 5.25) or 2,6-diterbutyl-4-methylpyridine (DTMPY, pKa 7.5) employed as titrant agents of basic and acid sites, respectively. Furthermore, the apparent rate constant values of different supports in the gas-phase skeletal isomerization of cyclohexene (CHSI), in Mmol atm"1 g"1 s-1, at 673 K, are also collected in Table 1, because these values are another way of measuring the stronger acid sites of supports (ref. 19). 

Extraction using diethyl ether has also been used in another traditional method to determine the level of preservatives in a sample. In this case, benzoic acid can be extracted from a product at low pH using diethyl ether. By adjusting the pH of the product, and hence the ionisation of the acids themselves, it is possible to quantify benzoic acid in a soft drink in the presence of saccharin. After extraction the benzoic acid can be assayed spectrophotometrically or by titration (Egan et al., 1990c). 

Diazomethane is prepared from nitrosomethylurea8 by the method of Bachmann and Struve. The yield of diazomethane is determined by treatment of a 10-ml. aliquot of its ethereal solution with a solution of an excess of benzoic acid in ether, followed by titration of the excess acid with a standard alcoholic solution of potassium hydroxide. Then the diazomethane solutions are dried over pellets of potassium hydroxide at —50°. 

The solution is ca. 2 M. Yields were determined by nitrogen evolution on adding acetic acid, or spectrometrically from the visible absorption band at 500 m fi, which has e 2 as calculated from the nitrogen evolution. Yields estimated by addition of a standard solution of benzoic acid and titration with alkali were consistently much lower. Both methods underestimate the yield, since decomposition with acid gives tetramethyl-ethylene and some acetone azine in addition to the isopropyl ester.3 The nitrogen evolution method (and therefore the spectrometric method) probably underestimates the yield by ca. 10-20%, the titration method by more than 50%. 

Under the auspices of the International Union of Pure and Applied Chemistry, an Analytical Methods Committee carried out a critical examination of some primary standards suggested for use in acid-base titrations, with a view to making recommendations concerning practical applications. Some of the findings of this committee were as follows (1) Benzoic acid as a primary standard is not recommended because... 

In this method salicylic acid is determined in its compound preparations. A sample of 1 g of ointment or 1 ml of liquid preparation, containing 6% of salicylic acid and 12% of benzoic acid is dissolved in boiling water. The cooled solution is diluted to 500 ml with H20 and filtered, and a 100 ml portion of the titrate is diluted to 100 ml with H20. Salicylic acid is determined in the resulting solution by differential spectrophotometry at 297 nm (22). 

Specific surface areas of the catalysts used were determined by nitrogen adsorption (77.4 K) employing the BET method with Sorptomatic 1900 (Carlo-Erba). X-ray diffraction (XRD) patterns of powdered catalysts were carried out on a Siemens D5(K) (0/26) diffractometer with Cu Ko monochromatic radiation. The total amount of surface basic sites was determined via surface titration by benzoic acid from dry hexane solution as reported elsewhere [14]. Before the titration catalyst samples were dried at 300°C for 2 hours. 

Analysis of Reagent Purity diazomethane is titrated by adding a known quantity of benzoic acid to an aliquot of the solution such that the solution is colorless and excess benzoic acid remains. Water is then added, and the amount of benzoic acid remaining is back-titrated with NaOH solution. The difference between the amount of acid added and the amount remaining reveals the amount of active diazomethane present in the aliquot. Preparative Methods diazomethane is usually prepared by the decomposition of various derivatives of A-methyl-iV-nitroso-amines. Numerous methods of preparation have been described,. but the most common and most frequently employed are those which utilize N-Methyl-N-nitroso-p-toluenesulfonamide (Diazald 1), l-Methyl-3-nitro-l-nitrosoguanidine (MNNG, 2)f oriV-methyl-Mnitrosourea (3) ... 

Gross calorific value and ash content of waste materials can be determined by a calorimetric method. After a calorimetric analysis, the bomb washing can be used to determine of mineral content by elemental analysis. The sample is burned under controlled conditions in oxygen. The calorimeter is standardized by burning known amount of benzoic acid. The formation of acids can additionally be determined by titration. 

Benzoic acid and its salts may be determined by titration with sodium hydroxide after extraction of the benzoic acid from an aqueous food suspension into chloroform, and evaporation of the chloroform and any acetic acid present (AOAC method 963.19). Vanillin interferes with this determination and a more selective method involves the determination of benzoic acid in an ether extract by UV absorption at 272 nm, as described in AOAC method 960.38. An alternative method of isolating benzoic acid from food involves the use of steam distillation and TLC separation. These sample preparation techniques are used in AOAC method 967.15 prior to the determination of benzoic acid by UV absorption. 

One such method is the combination of titration with spectrophotometric determination, which is well established (Poppi and Pasquini, 1993). These authors used multivariate calibration, optimizing the FIA titration system for the selective determination of a mixture of acetic acid, benzoic acid, and hydrochloric acid, using NaOH as the titrant. The mixture containing the indicator-sample-alkaline gradient was analyzed using a spectrophotometer at 340-680 nm. This methodology allows the analysis of mixtures of acids in synthetic solutions within 1-5 min, although it is important to have data on the differences between the pKa values of the acids concerned. 

The B,P, method of estimation is by direct titration in ethanol phenol-phthalein or phenol red may be used as indicator, the colour change being quite sharp in the presence of ethanol, phenolphthalein being less sensitive. 1 ml 0 5N NaOH = 0 06106 g. Benzoic acid may also be titrated in a non-aqueous medium such as dimethylformamide, an alkaline methoxide or tetrabutylammonium hydroxide being used as titrant (see p. 793). 

Blake has described a non-aqueous titration method whereby the benzoic and salicyclic acids may be determined separately by differential titration with sodium methoxide in a medium of dimethylformamide. In... 

Make 20 ml of tincture distinctly alkaline with sodium hydroxide and evaporate to a low bulk to remove the alcohol. Then extract the alkaline solution with ether, wash the ether with water and add it to the other aqueous portion. Acidify the alkaline liquid and extract the benzoic acid with portions of ether. Wash the mixed ethers with water until free from mineral acid and either dry the ether and evaporate, or titrate the ether layer by the method given under Benzoic Acid. 

Basic properties of alkaline earth oxides have been measured by different methods such as titration with benzoic acid, adsorption of CO2, and others. Basicity distributions measured by the titration of outgassed samples of MgO, CaO and SrO are shown in Fig. 3.5. Magnesium oxide and CaO possess base sites stronger than H =26. 

Hydrolysis would then give alkali arising both from Bu°Li and EtOU, so the titration with acid would overestimate the amoimt of Bu Li present. Several methods have been devised for dealing with this problem. In one of these a weighed amount of benzoic acid in a mixture of dimethyl-sulphoxide, 1,2-dimethoxyethane and ether or hydrocarbon is titrated with the organolithimn solution. The indicator is triphenylmethane, which develops a red colour when all the benzoic acid is used up ... 

Reference to Tables 2.2 and 2.3 on p. lb and n will confirm that there is no difference in the lesults obtained (in 0 01 molai solutions) for benzoic acid when titrated with sodium hydroxide or for sodium benzoate when titrated with hydrochloric acid. The latter method, which is essentially the titiation of an anion, is advantageous for spaiingl) stduble acids which ma> decompose when heated to effect dissolution these should be dissolved in exacth 1 mole equivalent of cold sodium hydroxide so that the... 

---