Determination of Fluorine in Organic Compounds with Cerous Nitrate

Abstract

HE increasing importance of organic fluorine com-T pounds makes a simple, reliable method for the determination of fluorine in such compounds extremely desirable.Reliable methods for the determination of chlorine, bromine, and iodine in organic compounds have been available for many years. However, fluorine differs considerably in its chemical behavior and the usual halogen methods cannot be applied for its determination.Halogens are generally determined in organic compounds by decomposition of the compound and then determination of the halide ion. The fluorine-to-carbon bond is much more stable than the other halogen-to-carbon bonds and this makes the problem of decomposing organic fluorine compounds, to transform the fluorine to the fluoride ion, somewhat more difficult than in the case of the other halogen compounds.In the case of compounds of the less stable type, where the Buorine is on a side chain or in certain aliphatic compounds, the decomposition may be accomplished by refluxing with metallic sodium or potassium in absolute alcohol or any other suitable inert solvent. Drogin and Rosanoff (16) applied this method for chlorine, bromine, and iodine, but Whearty (69) was not very successful in applying it to the analysis of several Buorine compounds. Vaughn and Nieuwland (57) used sodium in liquid ammonia or if the compound was insoluble in liquid ammonia, added ether. In a few cases where the carbon bonded to the fluorine is also bonded to oxygen, as with carbonyl fluorides, fluorinated alcohols, or sulfonyl fluorides, decomposition may be accomplished by refluxing with aqueous or alcoholic tassium hydroxide. This was used by Morgan and Tunstall &I with boron beta-diketone fluorides.Piccard and Buffat (46) heated fluorobenzene in a glass tube with potassium at 400' C. and obtained a rapid removal of the fluorine. Similarly Simons and Block (53) and Elving and Ligett (17) decomposed fluorocarbons and other fluorine compomds by heating with sodium or potassium in an evacuated tube.Kimball and Tufts (39) recommended thermal decomposition. Although chlorine, bromine, and iodine can be transformed to free ions by this method a t moderately high temperatures, Meyer and Hub (40) found that fluorine bonded to aromatic rings required 2 hours' heating at 1000" C. in a nickel or platinum bomb tube for com lete transformation into the fluoride ion.B o c k e m d r (9) considered the general methods of decomposition and used a combustion method. The fluorine compound was burned in an atmosphere of oxygen at 900' C. in a platinum tube with the exit end of the tube packed with granular calcium oxide, Hubbard and Henne (80) used a similar method in a silica tube packed with granular quartz. Bigelow (8) modified the method slightly. The method appears to be very useful for gaseous compounds and very volatile liquids, but has not been used for stable solid substances.Another method which appears to have eneral application is sodium eroxide fusion using a Parr born% (36, 46). Hahn and Reid g d ) , Bigelow (8), and Locke, ...

Determination of Fluorine in Quantitative Organic Microanalysis

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Photoelectric Titrimeter

“…In a previous investigation (8) of the titration of fluorine with cerous nitrate using methyl red, sometimes the visual detection of the equivalence point was very difficult. In an attempt to improve this, the authors devised the present instrument for a photoelectric method.…”

Titrations with Photoelectric Titrimeter

“…TITRATION OF FLUORIDE WITH THORIUM NITRATE Originally this investigation was begun on the design (16) and application of an instrument to the titration of fluoride with cerous nitrate, using methyl red (18). However, because of the variation of the pH at the equivalence point and the difficulty of maintaining a constant 80 °C.…”