Iodine-Pyridine-Sulfur dioxide

Limitations and interferences. The Karl Fischer reagent is composed of pyridine, sulfur dioxide, and iodine dissolved in either methyl alcohol or ethylene glycol monomethyl ether. Substances which react with any of these components will interfere. For example, Karl Fischer reagent will react with aldehydes or ketones in the presence of Methyl alcohol. 

The iodine and sulfur dioxide are present as addition compounds with pyridine. The reaction path has been shown to involve two distinct steps. The first step involves the reaction between iodine and sulfur dioxide in the presence of pyridine and water to form a salt of pyridine-A-sulfonic acid. Pyridine acts as a base to form pyridinium iodide ... 

Deoxygenation of sulfoxides. Sulfoxides are converted into sulfides in high yield when treated with 1 eq. of iodine and excess pyridine—sulfur dioxide complex in acetonitrile (80 ). If bromine is used, pyridine is omitted in order to... 

Iodine, 72, 293-295, 333, 452,579 Iodine-Dimethyl sulfoxide, 295 Iodine-Potassium iodate, 296 Iodine-Pyridine N-oxide, 296 lodine-Pyridine-Sulfur dioxide, 296 Iodine azide, 297 Iodine bromide, 297 lodoacetonitrile, 494 a-lodo acyl chlorides, 116 o-Iodoanisole, 130 lodobenzene, 130, 443 7r-(Iodobenzene)chromium tricarbonyl, 104 lodobenzene diacetate-Trimethylsilyl azide, 297... 

In order to achieve complete reaction, pyridine is added to bind the protons produced in the reaction. Pyridine also increases the solubility of iodine and sulfur dioxide by complex formation. The reagents are dissolved, and the reaction is carried out, in methanol or ethylene glycol monomethyl ether as... 

Karl Fischer method This is primarily used for low-moisture products and is suitable for determining moisture in dried vegetables and legumes. This sensitive titration method is based on the nonstoichio-metric reaction of water with iodine and sulfur dioxide in pyridine/methanol solution. 

A well-known use of pyridine as a cosolvent is in the Karl Fischer titration of water in organic solvents, described in Bassett et al. (1978). A solution of iodine and sulfur dioxide in pyridine/methanol or pyridine/cellosolve is fairly stable in the absence of water, but when it is added to a sample of a solvent containing water, reaction 7.7 occurs quantitatively. 

Another important example of a redox titration for inorganic analytes, which is important in industrial labs, is the determination of water in nonaqueous solvents. The titrant for this analysis is known as the Karl Fischer reagent and consists of a mixture of iodine, sulfur dioxide, pyridine, and methanol. The concentration of pyridine is sufficiently large so that b and SO2 are complexed with the pyridine (py) as py b and py SO2. When added to a sample containing water, b is reduced to U, and SO2 is oxidized to SO3. 

In this system a reagent originally prepared by reacting sulfur dioxide and iodine dissolved in pyridine and methanol is used. The reaction can be represented as follows ... 

Indium Iodine Acetonitrile, nitrogen dioxide, mercury(II) bromide, sulfur Acetaldehyde, acetylene, aluminum, ammonia (aqueous or anhydrous), antimony, bromine pentafluoride, carbides, cesium oxide, chlorine, ethanol, fluorine, formamide, lithium, magnesium, phosphorus, pyridine, silver azide, sulfur trioxide... 

Karl Fischer reagent analy chem A solution of 8 moles pyridine to 2 moles sulfur dioxide, with the addition of about 15 moles methanol and then 1 mole iodine used to determine trace quantities of water by titration. karl fish-or re a-jont Karl Fischer technique analy chem A method of determining trace quantities of water by titration the Karl Fischer reagent is added in small increments to a glass flask containing the sample until the color changes from yellow to brown or a change in potential is observed at the end point. karl fish-or tek nek kauri-butanol value analychem The measure of milliliters of paint or varnish petroleum thinner needed to cause cloudiness in a solution of kauri gum in butyl alcohol. kail-re byut-3n,ol, val-yu ... 

Water can be identified from its physical properties. Also, trace amounts of water may be determined by Karl-Fischer analysis. The Karl-Fisher reagent is a solution of iodine, sulfur dioxide and pyridine in methanol or methyl cel-losolve. Water of crystallization in hydrates can be measured by TGA and DTA methods. The presence of trace moisture in gases can be determined by mass spectrometry. The characteristic mass ion is 18. 

An alternative route is the reaction of iodine or bromine in pyridine with liquid sulfur dioxide at 20°C, which gives good to high yields of sulfites (106). 

It can also be used for rapid detn of small amts of water in miscellaneous materials. The KF reagent consists of sulfur dioxide-iodine in pyridine-methanol solution. It is available in commerce in strength equivalent to 5—6 mg water per 1 ml of reagent. It can also be prepd... 

Excess pyridine, iodine, and methanol are required for quantitative consumption of water. Sulfur dioxide reduces iodine quantitatively in the presence of excess water. The excess iodine present in the mixt makes a visual detn of the end point difficult. Therefore, the endpoint can be detnd electrometri-... 

In early work, iodine was electrochemically generated from an iodide salt in anhydrous methanol containing sulfur dioxide and pyridine. The titration reaction is... 

If cyclopentadienyliron dicarbonyl halides are allowed to react with themselves in the presence of Lewis acids, cations are formed in which the new substituent is the cyclopentadienyliron dicarbonyl halide itself, for example, [CjH6Fe(CO)i-X-(CO)2-FeC8H8]+ (X = Cl, Br, I). All three cations can be prepared best by treatment of the corresponding halides with boron trifluoride diethyl etherate all are isolated as tetrafluoro-borates.18 The bromine complex can also be obtained by a more complicated procedure by the reaction between C8H8Fe-(CO)2Br and AlBr3 in liquid sulfur dioxide 16 the iodine cation can be isolated from a melt of cyclopentadienyliron dicarbonyl iodide and aluminum chloride.17 In the latter two cases the hexafluorophosphate salts can be obtained. These binuclear cations are of special interest, because they are cleaved by electron donors,16-17 e.g., aniline, pyridine, benzonitrile, acetonitrile, acrylonitrile, with the formation of the corresponding [C8H8Fe(CO)2L]+ cations and the parent halide. Equations for preparation of the tetrafluoroborate are ... 

The classical method for the determination of low water contents in organic solvents is the nonaqueous iodometric titration introduced by Karl Fischer in 1935, using a solution of sulfur dioxide, iodine, and pyridine in a benzene/methanol mixture [139, 140], By replacing some of the toxic ingredients (pyridine, benzene, methanol), this titration method has more recently been developed into a simple and environmentally safe standard procedure [141]. 

Stoichiometry The Karl Fischer method usually consists of the titration of a sample in anhydrous methanol with a reagent composed of iodine, sulfur dioxide, and pyridine in methanol. In the titration the end point corresponds to the appearance of the first excess of iodine detected visually or by electrical means. 

CsH5NH+r -I-CsHsN SOj (19-38) This first step involves the reduction of iodine and the oxidation of sulfur dioxide, the water serving as a source of oxide ion. In the absence of methanol, the pyridine salt, pyridine sulfur trioxide, can be isolated as a stable product. The second step of the reaction involves methanol, with the formation of pyridinium methyl sulfate ... 

Preparation of reagent Even in the absence of water a reagent consisting of iodine, sulfur dioxide, pyridine, and methanol undergoes rapid initial loss in strength, followed by slower change. The reactions involve the formation of quaternary pyridinium salts and pyridinium iodide, for example,... 

The two-reagent method involves introduction of the sample into a reagent composed of pyridine, methanol, and sulfur dioxide. The titration reagent is iodine in methanol, which is relatively stable. This method is as precise as the usual one-reagent method, as long as no procedure is employed that involves the addition of excess iodine and back titration with water. 

For over 60 years, the specific titration of water has used a reagent developed by Karl Fisher, which consists of iodine, sulfur dioxide, and pyridine in methanol. The Karl Fisher titration of water is addressed in most analytical chemistry texts and is not presented here. A brief review with a pharmaceutical perspective has recently been published. However, the advantages and disadvantages of this method for the characterization of water associated with solids are discussed later. 

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