138
ANALYTICAL CHEMISTRY
which was subsequently digested with acid. Before analysis, the silver ion had to be removed t o prevent reaction with the Nessler’s reagent. If interfering cations were present a Rochelle salt solution was used to complex them. This procedure, however, could be applied to only a limited number of cations present in low concentration. I n some instances, a modified Kjeldahl method was employed to separate the ammonia. The present method is well suited to the analysis of mixtures. The preliminary pass through the column removes interfering cations, which are subsequently eluted and discarded. The comparatively gentle treatment of the elutriate containing the anions, including cyanate, exchanged sodium ions, and neutral molecules with O . 1 N acid a t room temperature for 10 minutes should convert only the most easily hydrolyzable substances to ammonium ion. The second pass of the solution through the column retains only sodium ion and anions or molecules that are converted by mild acid treatment to cations. Of these cations only those that on elution interfere with the Nessler’s reaction will prove troublesome. It seems unlikely that many substances other than the cyanate ion will exhibit this sequence of chemical behavior. Ammonium ion and cyanate ion can be readily determined in solutions containing both, without resorting to a method of differences. The procedure is easy to perform and fairly rapid. In the
current atudy, 24 analyses per day are made routinely by a single analyst. ACKNOWLEDGMENT
The authors gratefully acknowledge the generous grant from the Research Corp. of New York which made this study possible. LITERATURE CITED
ilmerican Public Health Association, New York, “Standard Methods for the Examination of Water and Sewage,” 1933. Dodge, B. F., and Zabban, W., Plating, 39, 381 (1952). Duval, C., Anal. Chim. Acta., 5 , 506 (1951). Hertig, O., J . SOC.Chem. Ind. (London),20, 838 (1901). Hertig, O., Z . angew. Chem., 14, 585 (1901). Kistiakowsky, G. B., Manglesdorf, P. C., Rosenberg, A. J., and Shaw, W. H. R., J . Am. Chem. SOC.,74, 5015 (1952). Kistiakowsky, G. B., and Shaw, W. H. R., Ibid., 75,866 (1953). Ibid., p. 2751. Martin. E. L.. and McClelland. ANAL.CHEY..23.’ 1519 (1951). Ripan-Tilici, R., Z . anal. Chem.,’ 99, 415 (1934). Ibid., 102, 32 (1935). Rosenberg, A. J., thesis, Harvard University, 1952. Shaw, W. H. R., and Bordeaux, J. J., work in progress. R‘illiarns, H. E., “Cyanogen Compounds,” pp. 400-2, London, Edward Arnold and Co., 1948. 1
,
R E C E I V for ~ D review J u n e 14,1864. Accepted October 1, 1954.
Determination of High Molecular Weight Ketones L. D. METCALFE and A. A. SCHMITZ Research Division, Armour & Co., Chicago,
111.
A simple rapid method for the determination of high molecular weight ketones uses hydroxylamine hydrochloride and a high molecular weight amine in nonaqueous solvents. The method has been used to determine varying amounts of carbonyl compounds in mixtures, and has been used successfully as a control procedure.
H
YDROXYLAMISE hydrochloride has been used as a reagent for the determination of aldehydes and ketones in analytical procedures for a number of years. The reactions involved are
+ NHzOH*HCl-+ RCH=KOH + HzO + HCl RCOR‘ + NHZOH*HCl-+ RR’C=NOH + H20 + HCl RCHO
(1) (2)
The use of the reagent was reported by Brochet and Cambier (2)as early as 1895 for the quantitative determination of formaldehyde. Bennett and Donavan (1) and Marasco ( 5 ) later used it to determine acetone. The procedures employing hydroxylamine reagent to determine carbonyl compounds are of four general types: titration of the hydrochloric acid produced as shown in the above equations ( 3 , 9); neutralization of the hydroxylamine hydrochloride liberating free hydroxylamine to react with the carbonyl groups, followed by titration of unreacted hydroxylamine (10, 11); determination of the water produced in the reaction using Karl Fischer reagent ( 7 ) ; and measurement of the change in pH caused by the liberation of hydrochloric acid as indicated in Equations 1 and 2 ( 4 , 8). An excellent summary of hydroxylamine procedures has been prepared by Mitchell (6). -4procedure has been developed t o fill the need for a rapid and simple determination of high molecular weight aliphatic ketones
in the presence of varying amounts of free fatty acid. S o previously mentioned method could be applied to the determination of such ketones as stearone and palmitone, because of their limited solubility in all but a few suitable solvents. Using as the reagent 0 . 5 5 hydroxylamine hydrochloride in a mixed solvent of 65% isopropyl alcohol and 35y0 methanol, the analytical procedure has been used effectively to determine these ketones. X measured excess of an organic base (octadecenylamine) in isopropyl alcohol is added to facilitate complete reaction between the ketone and hydroxylamine hydrochloride by combining with the hydrochloric acid liberated. At the end of the reaction period, unreacted amine is titrated m-ith standard hydrochloric acid solution in isopropyl alcohol to a bromophenol blue end point. A titration is run on a blank containing the exact quantities of hydroxylamine hydrochloride and octadecenylamine used with the sample. The difference between blank and sample titrations gives a direct measure of the carbonyl groups present in the sample. Since hydrochloric acid formed in the reaction is never liberated and is constant, it does not, affect the titration of either the sample or the blank. Under these conditions, any free fatty acid present mill not affect the tit,ration. If amine salts of the fatty acid are formed, they will titrate as free amine. -4 procedure using free hydroxylamine in a proper solvent mixture, omitting the organic base, may be used. However, since the stability of a solution of free hydroxylamine is poor, this procedure is impractical where a great number of control analyses must be made constantly. -1lthough the results of this paper deal entirely with ketones, the procedure has been applied successfully to some high molecular weight aldehydes. REAGENTS
Hydroxylamine Hydrochloride Reagent. Dissolve 35 grama of hydroxylamine hydrochloride (reagent grade) in 350 ml. of
V O L U M E 2 7 , NO. 1, J A N U A R Y 1 9 5 5
139
are very easily compared with the blank determination using methanol, heating if necessary. Dilute to 1 liter with isopropyl alcohol. the 500-ml. Erlenmeyer flasks. Amine Reagent. Dissolve 140 grams of octadecenylamine (ilrmeen SD, Armour and Co., Chicago, Ill.) in isopropyl CALCULATIONS yo ketone = alcohol to make 1 liter of solution. Theoretically, any amine that gives a sharp bromophenol blue end point when titrated with standard hydrochloric acid in isopropyl (ml. blank - nil. titration) X N HC1 X mol. mt. of ketone alcohol and which forms an isopropyl alcohol-soluble hywt. of sample (grams) X 10 X number of carbonyl groups in molecule drochloride may be used as a substitute for amine. drmeen S D satisfies these requirements. Apparent niolecular weight of ketone = Standard Hydrochloric Acid in Isopropyl Alcohol. Prepare a wt. of sample (grams) X 1000 X no. of carbonyl groups 0.5N solution by dissolving 43.5 ml. of concentrated hydro_____ chloric acid in 300 ml. of isopropyl alcohol. Dilute this solution (ml. blank - ml. titration) X N HC1 to 1 liter with additional isopropyl alcohol. Standardize according to one of the usual procedures. This solution should be .4n equation for estimating the sample weight of an unknown standardized weekly, although it will keep without changing having one carbonyl group and consisting mostly of ketone is aa strength for several weeks if stored in a well-stoppered bottle. follows: weight of sample in grams = 0.007 X molecular !?eight Bromophenol Blue Indicator. Prepare a 0.1% solution in Formula 3A alcohol. of ketone. A N A L Y T I C I L PROCEDURE
DISCUSSION AND RESULTS
Melt the sample, and if turbid, filter in an oven a t 100" C. to obtain a sparkling clear sample. Weigh into a 250-ml. glassstoppered volumetric flask. Choose the sample weight so that about half the reagent will remain unreacted after the reaction is complete (see Calculations for equation by which size of sample may be estimated). Pipet 25 ml. of the amine reagent into the flask, and then pipet 25 ml. of the hydroxylamine hydrochloride reagent into the flask. I t is important to add the reagents in this sequence if this method is applied to aldehydes, to prevent the formation of acetals 5 ith the isopropyl alcohol. For difficultly soluble samples, heat the flask moderately on a hot plate, swirling the contents until the sample is dissolved. Place the flask in a water bath a t 70" C., loosen the stopper momentarily to expel air, then stopper firmly. -4fter heating for 30 minutes, remove the flask from the water bath. Add 0.5 ml. of bromophenol blue indicator and titrate with the standard alcoholic hydrochloric acid to a green color; then continue adding the acid in increments of 0.1 ml., shaking after each addition until a yellow end point is reached. Make a blank determination, following the same procedure without the sample. Care should be taken to titrate the blank and the sample a t about the same temperature. Titration of some samples will not give a sharp end point; hence, it is helpful to run the blank first and then titrate the sample to the same color. When an electrically heated water bath is not available, the procedure is modified as follows. The samples are weighed into 500-ml. glass-stoppered Erlenmeyer flasks, the reagents are then added as before, and the flasks are stoppered. -4sheet of heavy asbestos paper is placed on top of an ordinary steam bath, and the flasks are placed on the asbestos paper. The asbestos keeps the alcohol from boiling. The procedure is followed exactly as before. With a light background the end points of the samples
Strong acids or bases in the sample will interfere with the titration. They may be removed effectively by washing the samples with boiling water. Weak organic bases will interfere also; they may be removed by washing the sample with hot dilute aqueous mineral acid, after which the acid must be removed by washing the sample x-ith boiling water. Some metals and their salts may oxidize the hydroxylamine. Such contaminants can be removed by filtering the sample in an oven a t 100" C. Some results obtained on high molecular weight ketones using the described method are summarized in Tables I, 11, 111, and IV. The ketones were prepared and purified in the Research Division Laboratories of Armour and Co. Tables I11 and IV show the results of analyses of samples subjected to various reaction periods a t 70" C. The period commenced from the time solution of the sample was attained by heating the flask gently on a hot plate.
Table 111. Per Cent Ketone Determined in Crude Laurone at \-arious Reaction Periods Reaction Time (at 70' C.), Min. 0 2
15 30 120
Ketone Found, 7% 88.5 90.5 91.6 90.8 91.6
Table IV. Per Cent Ketone Determined in Purified Stearone at Various Reaction Periods Table I.
Determination of Carbonyl in Purified Ketones Con~pound~
Laurone Nyristone Palmitone Stearone Dilieptyl ketone Oleone S o n y l heptadecyl ketone Dionyl ketone
No. of Detns.
of Theoretical& Carbonyl Found 99.5 i1.0 9 9 . 2 =t1 . 0 99.2 f 1 . 0 99.0fl.0 9 9 . 0 =t1 . 0 99.1f1.0 99.0 f 1 . 0 9 8 . 2 =k 1 . 0
5
5 5
5 4 5 3 2
.ill compounds were of 95% purity or higher. for 30 minutes a t 70' C
b All samples were run
Table 11. Determination of Carbonyl in Ketone-Fatty Acid Mixtures of Detns. 3 3 3 3 3 3 3 3 3
K O .
Mixture" Laurone 80%-lauric acid 20% Laurone: 5O%-lauric acid: 50% Laurone 20%-lauric acid, 80% Palmito& 80%-palmitic acid, 20% Palmitone' 5O%-palniitic acid, 50% Palmitone: 20%-pa!miti,c acid. 80% Stearone, 80%-stearic acid, 20% Stearone, 5O%-stearic acid, 50% Stearone. 20%-stearic acid, 80% a
Ketone Found, % 78.5 49.0 20.7 78.2 51.4 20.4 78.9 52.5 21.0
Prepared gravimetrically using materials of known purity.
Reaction Time (at 70' C J , hlin. 0 15 30
c,o
Ketone Found, % 91.5 96.2 98.8 98.8
LITERATURE CITED ( 1 ) Bennett, A. H., and Donavan, F. R., A d y s t , 47, 14fj-52 (1922). (2) Brochet, A., and Cambier, R., Compt. rend., 120, 449-54 (1895). (3) Bryant, W. M. D., and Smith, D. SI., J. Am. Chem. Soc., 57, 57-61 (1935). (1) Byrne, R. E., Jr., ANAL.CHEM.,20, 1245 (1948) (5) Marasco. ll., Ind. En@. Chem., 18, 701-2 (1926). (6) Xtchell, J., Jr., "Organic Analysis," Vol. I, p. 243, Kew York, Interscience Publishers, 1953. ( 7 ) Mitchell, J., J r , and Bryant, W. 11.D., J . Am. Chem Soc., 63, 573-4 (1941) (8) Roe, H. R., and Mitchell, J., Jr., ANAL.CHEY..23, 1758-60 (1951). (9) Smith, D. ll., and Jlitchell, J., Jr., Ibid., 22, 750-5 (1950). (10) Stillman, R. C., and Reed, R. 11..Perfumeru Essent. Oil Record, 23,228 (1932). (11) Troszolo, A. AI., and Lieber, E., ANAL. CHEM.,22, 764-8 (1950). R E C E I V E for D reyiew Juls 20, 1954.
Accepted September 17, 1054.
