Materials Required : Ethosuximide : 0. The following determinations as stated in Table 5. The alkalimetry in non-aqueous titrations may also be carried out efficiently by using tetrabutylammonium hydroxide along with an appropriate indicatior. Materials Required : Tetrabutylammonium iodide : 40 g ; absolute methanol : 90 ml ; silver oxide : 25 g ; dry toluene : ml.
Procedure : Carefully dissolve 40 g of tetrabutylammonium iodide Bu 4 NI in 90 ml of absolute methanol, add to it 20 g of finely powdered purified silver oxide and finally shake the mixture thoroughly for 1 hour. Centrifuge about ml of the resultant mixture and test for iodide in the supernatant liquid. In case, it gives a positive test, add about 2 g more of silver oxide and shake for an additional period of 30 minutes. The said method may be repeated until the supernatant liquid obtained is completely free from iodide.
The mixture thus obtained is filtered through a fine sintered glass filter and finally rinse the container with 3 portions, each of 50 ml of dry toluene. These washings may be added to the filtrate and the final volume is made upto 1 litre with dry toluene. The clear solution may be flushed with CO 2 -free nitrogen for at least five minutes and duly protected from both CO 2 and moisture during storage. Materials Required : Benzoic acid : 60 mg ; dimethylbromide : 10 ml ; thymol blue solution 0.
Procedure : Accurately weigh about 60 mg of benzoic acid into 10 ml of previously neutralized dimethyl formamide to the blue colour of thymol blue 3 drops by titration against 0. Allow the benzoic acid to dissolve gradually and completely and titrate with 0. Materials Required : Chlorthalidone : 0. Titrate with 0.
The following pharmaceutical substances may be assayed by employing tetrabutylammonium hydroxide either by using a suitable indicator titrimetrically or potentiometrically as given in Table 5. The assay of the aforesaid pharmaceutical substances with tetrabutylammonium hydroxide is on a mole-for-mole basis. As these are monobasic acids in character, therefore, they react quantitatively in a non-aqueous media with the base titrant, employing typical acid-base indicators to detect the end-points.
Developed by Therithal info, Chennai. Toggle navigation BrainKart. Author : Ashutosh Kar Posted On : For the sake of convenience these typical titrations can be catego-rized into two broad groups, namely : a Acidimetry in Non-aqueous Titrations— It can be further sub-divided into two heads, namely : i Titration of primary, secondary and tertiary amines, and ii Titration of halogen acid salts of bases.
Titration of primary, secondary and tertiary amines 1. Methlyldopa In general, the reaction taking place between a primary amine and perchloric acid may be expressed as follows : The specific reaction between methyldopa and perchloric acid is expressed by the following equation : Materials Required : Methyldopa 0. Calculations : The percentage of methyldopa present in the sample is given by : 1.
Methacholine Clloride Materials Required : Methacholine chloride : 0. Equation : Mercuric acetate : It is essentially added to prevent the interference of the hydrochloric acid dis-placed through the formation of the relatively un-ionized HgCl 2 , thereby making a predominant shift in the equilibrium so that the titrimetric reaction is quantitative.
Calculations : The percentage of methacholine chloride in the sample may be calculated by the following expression : 1. Cognate Assays Table 5. Potentiometric Titrations These non-aqueous titrations may also be carried out with the help of potentiometric titrations which technique shall be discussed at length elsewhere in this book. Titration of Halogen Acid Salts of Bases In general, the halide ions, namely : chloride, bromide and iodide are very weakly basic in character so much so that they cannot react quantitatively with acetous perchloric acid.
Perform a blank determination and make any necessary correction. Each ml of 0. HCl amitriptyline hydrochloride. In order of decreasing strength, strong bases of value for non-aqueous titrations are potassium methoxide, sodium methoxide, lithium methoxide and tetrabutylammonium hydroxide. When ethanol is used as the medium for halide salts of weak bases the titrant is a volumetric solution of sodium hydroxide. In the titration of an acidic compound a volumetric solution of lithium methoxide in a methanol-toluene solvent is often used.
For many applications it is convenient to use a solution of tetrabutylammonium hydroxide in toluene. Elimination of poor solubility of substances: Organic acids and bases that are insoluble in water are soluble in nonaqueous solvent.
Enhancement of reactivity of substances: Non-aqueous solvents are useful for the titration of very weak acids or bases that cannot be titrated in water. Many water-insoluble compounds acquire enhanced acidic or basic properties when dissolved in organic solvents.
Thus the choice of the appropriate medium and titrant permits the determination of a variety of such materials by non- aqueous titration. Maintenance of speed, precision, accuracy and simplicity. Weak bases which have Kb values less than 10—6 can be titrated satisfactorily by non-aqueous titrations. The Karl Fischer titration for water content is another nonaqueous titration, usually done in methanol or sometimes in ethanol. Since water is the analyte in this method, it cannot also be used as the solvent.
The types of compounds, in a non-aqueous medium, that may be titrated as acids, usually by lithium methoxide or tetrabutyl ammonium hydroxide, include acid halides, acid anhydrides, carboxylic acids, amino acids, enols such as barbiturates and xanthines, imides, phenols, pyrroles and sulfonamides. The types of compounds, in a non-aqueous medium, that may be titrated as bases by perchloric acid, include amines, nitrogen-containing heterocyclic compounds, quarternary ammonium compounds, alkali salts of organic acids, alkali salts of inorganic acids and some salts of amines.
Many halide salts of weak bases and some quaternary ammonium compounds may be directly titrated in acetic anhydride using, preferably, potentiometric end-point detection or an indicator such as malachite green or crystal violet. Pharmaceutical Drug Analysis 2nd edition by Ashutosh Kar.
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Report this Document. Flag for inappropriate content. Non-Aqueous Titrations. Related titles. Amphiprotic Solvents. Aprotic Solvents— These are chemically inert substances such as benzene, chloroform, etc. Examples — benzene, toluene, carbon tetrachloride, etc. Protophilic Solvents— These are basic in nature and react with acids to form solvated protons. A strong protophilic solvent changes the weak acids to strong acids. Examples— liquid ammonia, amines, ether, etc. Protogenic Solvents— These are acidic substances and readily donate the proton.
These are used to increase the basicity of weak acid. They show a leveling effect on bases. Examples- sulfuric acid, formic acid, etc. Amphiprotic Solvents— These solvents have properties of both protophilic and protogenic solvents. Examples — alcohol, acetic acid, etc.
Non- aqueous titration has the following advantages -. It is useful for the titrations of very weak acids or bases.
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