A series of solutions containing stabilizer was compared nith a series of solutions containing no stabilizer. These were titrated periodically up to 20 days. K e found that with a nominal water equivalence of 1.70 mg. of w t e r per ml. of Karl Fischer Reagent, the solutions containing the pyridinium iodide stabilizer decomposed at a rate of 0.015 mg. of water per ml. of solution per day. The solutions without the stabilizer added decomposed at a rate of 0.040 mg. of water per ml. of solution per day. Teflon tubing has given the best service as the tubing connections between the solution reservoirs and the burets. Certain other plastic tubing samples were either not flexible (cracks developed after several days use) or reacted with the Karl Fischer Reagent to reduce the titer. Green silicone rubber sheeting served
well for the valve diaphragm. This material was not only inert to the reagents, but also sealed well around the O-ring. DISCUSSION
The Model KF-3 Aquameter appesrs to be applicable to the titration of organic solvents Tvith a wide range of dielectric constants. The reproducibility did not appear to be affected by dielectric constant but rather by the concentration of mater. The titration times of 2 to 3 minutes for liquid samples appear to be smaller than those reported by Burns and hIuraca for solid samples with the Model KF-2. Just as with the Model KF-2, the KF-3 shows a marked improvement in reproducibility for forward Karl Fischer titration as opposed to the back titration. This again is due to the sensing
of the approach to the endpoint when carrying out a forward titration. The addition of pyridinium iodide as a stabilizer cut the reduction rate of the Karl Fischer Reagent titer from 0.040 to 0.015 mg. of water per ml. of solution per day. S o comparison was made with commercially available Karl Fischer Reagent. LITERATURE CIlED
(1) Blomgren, Erik, Jenner, Hans, British Patent 772,983 (Feb. 2, 1955). ( 2 ) Burns, E. A., Muraca, R. F., ANAL. CHEM. 34,848 (1962). (3) Frediani, H. -4., Zbid., 24, 1126 (1952). (4) Phillips, J. P., “Automatic Titrators,” 98-101. 195-6, Academic Press, Iiew p.
York, 1959.
DENXISR. GERE CLIFTONE. MELOAN Department of Chemistry Kansas State University Manhattan, Kan.
Titrimetric Determination of Salts of Nitro Compounds SIR: Although many weak bases have been titrimetrically determined in glacial acetic acid with perchloric acid ( 5 ) , no report was found in the literature concerning the titration of salts of nitro compounds. EXPERIMENTAL
A Beckman Zeromatic pH Meter equipped with glass and calomel electrodes was used in all titrations. The reagents were prepared and standardized according to ( I ) and (Q), respectively. Because the absolute electrode potential was not important, the p H meter was not standardized, but was set t o indicate a value of about 12 on the pH scale. This setting provided a change of about 6 units a t the end point and by plotting the titration curve-Le., the milliliters us. meter reading-in usual manner, this change was quite sufficient to determine molecular weights with an accuracy of three figures. Small amounts of m t e r do not effect the accuracy or precision of the end point ( 2 ); therefore, the titrations were carried out without special precautions to esclude moisture-Le., operation in a dry bos, etc. Hon-ever, the equipment was dried prior to use. Because the technique may be adapted to nearly any .xmple size, the amount of material used will vary. A typical titration is given. Into a 100-ml. beaker were placed 0.4794 gram of potassium cyclohexylnitronate and about 15 ml. of glacial acetic acid. The solution was stirred magnetically, the electrodes of a p H 598
ANALYTICAL CHEMISTRY
meter were immersed in the solution, and the meter was set to indicate a value of about 12. -4 0.lOlOX solution of perchloric acid ( 1 ) was used as titrant and the graph was plotted in the usual manner, The end point occurred a t 29.3 ml. of titrant which corresponds to a molecular weight of 168 (calculated 167). Results are listed in Table I. All nitroparaffin salts were prepared and purified. A 10% escess of nitroparaffin was added to a solution of the appropriate base in methanol and the solution stirred until a constant p H was attained. The methanol was evaporated in vacuo to a thick slurry and dry
Table I. Nonaqueous Titration of Selected Weak Bases
Salt Lithium l-propanenitronate Sodium 2-propanenitronate Potassium 2-propanenitronate Potassium cyclohexylnitronate Potassium 2,5-dinitrocyclopentane (3) Dipotassium 2,5-dinitrocyclopentane (3)
RIolecular weight Calcd. Found 95 0 94.5 111
116
127
127
167
168
212
212
250
250
Silver phthalhydrazide 269 269” Commercial sodium 82.2 83.7 acetate a Titration performed to ascertain accuracy of the method.
ether !vas added. The salt was filtered, washed with ether, and dried in vacuo for 24 hours. DISCUSSION
Availability of a reliable and simple method for determining the purity of salts of nitroalkanes is important because investigators in the field frequently must find good purification methods for these salts. These compounds, which often arise directly from nitration procedures in alkaline media ( 3 ) are valuable starting materials for the synthesis of nitroalcohols, polynitroalkanes, etc. Moreover, a convenient method of establishing the puritl- oi nitroalkane salts should stimulate studies of the phyical properties of such compounds, especially in the field of spectrophotometry and nuclear magiietic reponance. LITERATURE CITED
(1) Fritz, J. S., “Acid-Base Titrations in
Iion-Aqueous Solvents,” G. Frederick bmith Chemical Co., Columbus, Ohio, 1952 ( 2 ) Fritz, J. S.,AYAL.CHEV. 22, 1028 (1950). (3) Feuer, H., Shepherd, J. W., Savides, C., J . Anz. Chem. Soc. 78, 4364 (1956); 79, 5768 (1957). 14) Seaman. W., Allen, E., . 4 ~ 4CHEM. ~ 23, 595 (1951). (5) Streuli, C. A,, Ibid., 34, No. 5, 302R (1962).
HENRYFEUER
BEWETF. VIXCEST,JR.
Department of Chemistry Purdue University Lafayette, Ind.
