Development of Karl Fischer Reagents
Development of Karl Fischer Reagents
Development of Karl Fischer Reagents
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I-1. Questions & Answers about <strong>Karl</strong> <strong>Fischer</strong> <strong>Reagents</strong><br />
40<br />
2RCSSH+I2 � RCSSSSCR+2HI<br />
(d) Vinyl ether and 2,3-dihyd<strong>of</strong>urane, dihydroprane<br />
ROCH=CH2+I2+R'OH � ROCH(OR')CH2I+HI<br />
(e) Ascorbic acid (Vitamin C)<br />
(f) Amines and aminoalcohols (pKa9 or higher)<br />
These consume iodine gradually.<br />
1.2 Inorganic compounds<br />
(a) Ammonia<br />
This reacts with iodine to produce nitrogen iodide<br />
NH3+3I2 � NI3+3HI<br />
(b) Hydroxylamines<br />
2NH2OH+3I2+2SO2+2CH3OH � 6HI+2HSO4CH3+N2<br />
(c) Ferric chloride<br />
Iron(III) salt causes the following reaction, with the result<br />
that only 5.5 molecules <strong>of</strong> water are titrated.<br />
FeCl3 � 6H2O+5.5I2+6SO2+6CH3OH �<br />
FeI2+9HI+3HCl+6HSO4CH3<br />
(d) Metal oxides<br />
Manganese dioxide, ferric oxide and lead dioxide react with<br />
<strong>Karl</strong> <strong>Fischer</strong> reagent. However, the reaction is not<br />
quantitatively constant, since these substances do not<br />
dissolve readily in the reagent.<br />
MnO2+I2+2SO2+2CH3OH � MnI2+2HSO4CH3<br />
However, interference does not occur with hydrogen<br />
peroxide, sodium peroxide, barium peroxide, pottasium<br />
persulfate or ammonium persulfate, since these substances<br />
react selectively with sulfur dioxide.<br />
H2O2+SO2 � H2SO4<br />
Na2O2+SO2 � Na2SO4<br />
(e) Weak acids and oxides<br />
Boric acid, metaboric acid, boron oxide and arsenic trioxide<br />
all react with <strong>Karl</strong> <strong>Fischer</strong> reagent.<br />
H3BO3+3I2+3SO2+6CH3OH � 6HI+3HSO4CH3+B(OCH3)<br />
HBO2+2I2+2SO2+5CH3OH � 4HI+2HSO4CH3+B(OCH3)<br />
As2O3+3I2+3SO2+3CH3OH � 2AsI3+3HSO4CH3<br />
(f) Salts<br />
In general, the weakly acidic salts <strong>of</strong> alkaline metals react<br />
with <strong>Karl</strong> <strong>Fischer</strong> reagent in the same way as oxides.<br />
Carbonates, bicarbonates, sulfites and pyrosulfites react in<br />
approximately constant amounts.<br />
K2CO3+I2+SO2+CH3OH � 2KI+CO2+HSO4CH3<br />
KHCO3+I2+SO2+CH3OH � KI+HI+SO2+HSO4CH3<br />
Na2SO3+I2+CH3OH � 2NaI+HSO4CH3
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