to. such biologically important cornpounds as the sterols as well as to the essential oils is evident. Because the essential oils usually contain aldehydes, interference is minimized in the determination of the hydroxyl content of these compounds. Linalobl, citronellol, borneol, and geraniol analyzed only 75 to 80% pure by this method; however, determinations are quantitative for essential oils that can easily be obtained in the pure hydroxyl form. Ethers do not react with the reagent
under the described conditions of the procedure. LITERATURE CITED
(1) Berezin, I. V., Doklady Akad. Nauk S.S.S.R. 99,663 (1954).
(6) Elving, P. J., Warshoweky, B., IND. ENQ.CKEM., ANAL,ED. 19,1006 (1947). (7) Fritz, J. S., Bchenk, Q. H., ANAL CHEM. 31 1808 (1959).
(8) M:;lenbacher, V. C., "Organic AnalVol. I, p. 1-65, Interscience, York 1958 (9) Porter, 6.' C., ANAL. CHEM.27, 805
&??;
((3)2christenen, ~ ~ 2 ~B. ~E.,~Clarke, Rsvf/ $ 4***R. e 163, 'A.,; ~ (1g6 ) 955)* ~Robinaon, ~ W. T., Jr., Cundiff, R. H., IND. ENQ. CHF,M., ANAL. ED. 17, 265
(1945). (4) CunditT, R. H., Markunaa, P. C., ANAL.CHEX 30,1450 (1958). (5) Cundiff, R H., Markunaa, P. C., Anal. Chim. Acta 20, 600 (1959).
SenSabaUgh, A. J V Markunas, p. c-, Tala& 3,307 (1960). RECEIVEDfor review January 11, 1961. Accepted March 20, 1961. Division of Analytical Chemist 139th Meeting, ACS, St. Louis, Mo.,%arch 1961.
Water Determination by Reaction with 2,2-Dimethoxypropane F. E. CRITCHFIELD and E. T. BISHOP Development Department Technical Center, Union Carbide Chemicals Co., South Charleston, W. Vu.
b Water reacts quantitatively with 2,2-dimethoxypropane, using methanesulfonic acid catalyst, to form acetone and 2 moles of methanol. The infrared absorption at approximately 5.87 microns of the acetone formed can be used to determink water in materials that cannot be analyzed by Karl Fischer reagent because of interferences. The method can be used to determine as low as 0.05% water in various organic solvents. It has been applied to the determination of water in dodecanethiol and several Inorganic hydrates.
T
HE KARL FISCHER METHOD for determining water ia by far the most versatile of the numerous methods developed to date. However, there are cases where this method cannot be applied readily because of interferences, and alternate procedures are required. Interferences in the Karl Fischer method are generally restricted to compounds that readily undergo oxidation-reduction reactions with the reagents, or organic compounds that readily add iodine. Organic reducing agents, such as mercaptans, hydrazine, and ascorbic acid, and inorganic salts, such as stannous chloride, ferric chloride, and cupric chloride, interfere in the method. This paper describes an alternate method for determining water that is based upon its rapid and quantitative acid-catalyzed reaction with 2,2dimethoxypropane (I): OCH,
HsO
+ CHI-&-C&
H+
-+
bCH8
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ANALYTICAL CHEMISTRY
8
CHj CHa
+ 2CHaOH
Acetone formed in the reaction is determined from its infrared absorbance a t 5.87 microns (carbonyl band). Although the infrared method can be used for the direct determination of water in certain cases, special calcium fluoride optics must be used and matrix effects are sometimes serious. Also, other hydroxylic compounds may interfere. EXPERIMENTAL
Apparatus. Beckman IR-5 infrared spectrophotometer or equivalent, equipped with a 0.1-mm. cell. Reagents. Dry Carbonyl-Free Methanol. Distill 3 gallons of methanol from a mixture containing 50 grams of 2,4-dinitrophenylhydrazine and 15 ml. of reagent grade hydrochloric acid. Reflux for 4 hours and collect the distillate until the head temperature reaches 84.8" C. Dry the methanol by allowing it to stand over '/Isinch pellets of Linde Molecular Sieves Type 4A for at least 24 hours. Occasionally mix during this period. Pass the methanol through a column acked with Linde Molecular Sieves %ype 4A ( owder) The water content of the rnetEanol should be below 0.05% as determined by Karl Fischer reagent. Methanesulfonic Acid. 0.1N in dry carbonyl-free methanol. Prepare from Eastman Organic Chemicals grade methanesulfonic acid. Carbon Tetrachloride. Merck reagent grade (for spectrophotometric use). 2.2-Dimethomrouane. The Dow -- Chemical Co. Procedure. PiDet 5.0 mi. of the 0.1N methaneeultonic acid and 2.0 ml. of the 2,2-dimethoxypropane into
each of two 25-ml. volumetric flasks. Reserve one of the flasks as a blank. Provide a third volumetric flask for a carbonyl blank on the sample (sample blank). Accurately weigh or pipet an amount of sample containing no more than 0.1 gram of water into the sample and sample-blank flasks only, adding the same amount, within *2%, to each. Dilute each of the three flasks to volume with carbon tetrachloride. Determine the absorbance of each solution a t approximately 5.87 microns in a 0.1-mm. cell using a base line technique. Correct the sample for carbonyl content, and, from a reviously prepared calibration curve, letermine the grams of water corresponding to the net absorbance of the sample. Calibration Curve. Follow the procedure outlined above and prepare standards containing 0.02, 0.05, 0.08, and 0.10 gram of water. Omit the sample blank. DISCUSSION
Under the conditions of the method, the reaction of 2,2dimethoxypropane with water is practically instantaneous to form the theoretical amount of acetone. This was checked by preparing calibration curves . from acetone and water. In the absence of a strong mineral acid, however, the reaction is not quantitative in a reasonable length of time. Methanesulfonic acid waa selected for this particular application because it is a strong mineral acid that is soluble in organic solvents and is commercially available as the anhydrous material. Because carbonyl compounds present in the sample interfere, it is necessary to provide, in addition to the customary
Table 1. Determination of Water in Various Solvents by Reaction with 2,2Dimethoxypropane
p
Water, by Weig t Karl Solvent Fischer Infrared Ethyl alcohol 0.05 0.05 Isopropyl alcohol 0.15 0.13 Acetonitrile 0.04 0.05 Methyl Cellosolvea 0.81 0.86 Methanol 0.13 0.16 Methanol 1.29 1.30 0 Trademark of Union Carbide Chemicals Co. Table II. Determination of Water in Dodecanethiol by Reaction with 2,2Dimethoxypropane
0.51 0.98 1.57 1.71
0.52 0.96 1.49 1.61
102 98 95 94
reagent blank, a sample blank to obtain a measure of the interference. Scope. This method has been applied to the determination of water in several organic solvents and compared with the water content as determined by titration with Karl Fischer reagent. The agreement between the two methods is good as shown by the data in Table I. These data also show that good results can be obtained by this method with water concentrations as low as 0.05%. With
a 15-ml. sample, a net absorbance of approximately 0.05 was obtained a t this concentration of water; therefore, this is close to the lower limit of sensitivity of the method. In order to illustrate the applicability of the method to samples that cannot be analyzed by the Karl Fischer method, data were obtained for the determination of known concentrations of water in dodecanethiol. These data (Table 11) show an average recovery of 97 f 3% in the range of 0.5 to 1.6% water. The method can be used to determine water in inorganic hydrates that cannot be analyzed by Karl Fischer reagent because of interference due to oxidation-reduction side reactions. Examples of this application are shown in Table 111. Although aluminum chloride hexahydrate can be analyzed satisfactorily by the Karl Fischer method, this salt is included in order to provide a comparison between the methods. The hydrates used in this study were all commercial grade material and were analyzed as received. With the exception of aluminum chloride hexahydrate, all of these salts contain water in excess of the theoretical. However, the difference between the water found in cobaltous chloride hexahydrate and the theoretical is within the experimental error of the method. Interferences. Since this method is based upon the determination of the infrared absorption of the carbonyl group of acetone, most carbonyl cornpounds will interfere. I n some cases, this interference can be corrected for by an independent carbonyl deter-
Table 111, Determination of Water in Inorganic Hydrates by Reaction with 2,2 -Dlmethoxypropane
Water, %by Weight Hydrate Theoretical Found Aluminum chloride hexahydrate 44.7 43.Oa Cobaltous chloride hexahydrate 45.4 46.3 Cupric chloride dihydrate 21.1 25.2 Cupric sulfate pentah drate 36.0 39.8 Ferric c d r i d e hexahydrate 40.0 44.9 Btannous chloride dihydrate 16.0 19.9 a 43.5% by Karl Fischer reagent.
mination of the sample. Of course, if the carbonyl absorption is sufficiently resolved from that of acetone, no interference will occur. Basic substances, such as amines and salta of weak acids and strong b w s , will interfere by reacting with the methanesulfonic acid catalyst essential for quantitative reaction of water. Alkali metal hydroxides will not only destroy the catalyst, but will react to form water. LITERATURE CtTED
(1) Erley, D. S., ANAL. CHEM.29, 1564 (1957). RECEIVED for review December 27, 1980. Accepted March 20, 1961. Division of
Analytical Chemistry, 139th Meeting, ACS, St. Louis, Mo., March 1961.
Dete r mina tio n of DieIs-AIde r Active Dienes with Tetracyanoethylene MARA OZOLiNS and GEORGE H. SCHENK Chemistry Deparfmenf, Wayne Stafe University, Detroit 2, Mich.
b Tetracyanoethylene (TCNE) has been used to determine aliphatic, alicyclic, and aromatic 1,3-dienes via a rapid and quantitative Diels-Alder reaction at room temperature. The analytical scheme for the visual and photometric titrations consists of adding the diene to a weighed excess of TCNE in methylene chloride, allowing the reaction to proceed quantitatively, and back-titrating the excess TCNE with 0.05M cyclopentadiene in alcohol. A warning indicator of phenanthrene in benzene and pentamethylbenzene indicator in methylene chloride are successively added. The breakup of the red pentamethylbenzene-TCNE x complex is taken as the end point.
F
general titrimetric methods have been developed for determining dienes by the Diels-Alder reaction, although a number of methods have utilized maleic anhydride for the determination of anthracene. Ubaldini, Crespi, and Guerrieri (17) determined anthracene by adding an excess of maleic anhydride, refluxing in chlorobenzene, and extracting the excess away from the water-insoluble adduct with hot water. Funakubo, Matsumoto, and Hiroike (3) modified this method by performing a two-phase titration of the excess maleic anhydride as maleic acid, using water at 55' as the second phase. Polgar and Jungnickel (10) reviewed EW
diene determinations by the addition of maleic anhydride and recommend an iodine-catalyzed method, especially for isomeric mixtures. One general diene method is that of Putnam, Moss, and Hall ( 1 0 , which utilizes fi-elimination of chloride ion from the adduct of the diene and chloromaleic anhydride. However, chloromaleicanhydride is,unfortunately, less reactive than maleic anhydride. p-Nitrobenzenediaeonium salts have also been used for the general determination of 1,3denes by colorimetric (1) and titrimetric methods (16). Tetracyanoethylene (TCNE) has been reported by Middleton, Heckert, Little, and Krespan (9) to react quantitatively VOL. 33, NO. 8, JULY 1961
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