impedance method as well) is the assumption that the coulombs needed t o charge the double layer will be identical in the pure supporting electrolyte and in the solution containing the reactant (adsorbed or not). However, it is most likely that the doublelayer capacity will be the greatest in pure supporting electrolyte (reactant adsorption generally tends to lower the capacity) so that the estimate of the amount of reactant adsorbed from the &-intercept may be slightly too low. Accordingly, a &-intercept significantly above the double-layer value is good evidence for the adsorption of electroactive reactants. It is also worth noting that correction for double-layer charging contributions is much more straightforward for the
potentiostatic current integration procedure than for chronopotentiometry. Indeed, most of the published data in which standard chronopotentiometry has been used to measure quantities of adsorbed reactant contain, at best, errors due to the lack of adequate correction for double-layer charging. ACKNOWLEDGMENT
Helpful preliminary experiments were performed by Robert J. Barro and Harry E. Kellcr 111. Discussion with R. A. Osteryoung and George Lauer also assisted with the progress of this work. LITERATURE CITED
(1) Anson, F. C., AXAL.CHEM.,36, 520 (1964). (2) Christie, J., Lauer, G., Osteryoung,
R. A,, Anson, F. C., Ibid.,
35, 1979 (1963.) (3) Christie, J., Lauer, G., Osteryoung, R. A,., J . Electroanal. Chem., in press. (4) Conway, B. E., "Electrochemical Data," p. 231-3, Elsevier, New York, 1952. (5) Delahay, P., "New Instrumental Methods in Electrochemistry," p. 207, Interscience, New York, 1954. (6) Gierst, L., Thesis, Univ. of Brussels, 1952. (7) Laitinen, H. A , , Chambers, L. M., ANAL.CHEM.36, 5 (1964). (8) Laitinen, H. A., Randles, J. E. B., Trans. Faraday SOC.51, 54 (1955).
FREDC. ANSON Division of Chemistry and Chemical Engineering California Institute of Technology Pasadena, Calif.
Work supported in part by the U. S. Army Research Office (Durham).
Determination of Aldehydes in the Presence of Acids, Acetals, and Ketones, Using a Silver Oxide-tert-Butylamine Complex SIR: Silver oxide has been used for determining aldehydes via t,he following reaction: RCHO
+ Ag20
-t
RCOOH
+ 2Ag
Several investigators (1-4) used solid silver oxide for the oxidation, the reaction being a two-phased one with the attendant difficulties of reaction time with particle size of the silver oxide. To circumvent the solid silver
Table 1.
oxide, Siggia and Segal (6) employed a homogeneous oxidation, using a n ammoniacal silver oxide solution (Tollen's reagent). This was successful, but had the disadvantages of precautions with reagent and the fact that generally only water-soluble systems could be handled. Proceeding along the same l i e of a soluble silver ion oxidant for aldehydes, tert-butylamine offered a more stable silver complex than ammonia; also, this
36y0 Solution
n-Propionaldehyde
0.1N
Filtered immed.
...
Benzaldehyde
30 10 30 60 30 45 135 20
Crotonaldehyde
135 180 65
n-But yraldehyde n-Valeraldehyde
-
0.2N
...
10
30 Filtered immed.
60
p-C hlorobenzaldehyde
Filtered immed.
...
...
20 45 90 90 30 60 120 30 60 120
0.1N Reagent Sample in aliquot Aldehyde taken, gram found, % 0.1228
36.1
0.1228 0.1228 0.0960
36.1 36.1 97.9'
934
ANALYTICAL CHEMISTRY
Silver oxide, Fisher Sci-
0.2N Reagent
Sample in aliquot taken, gram
0.1186 .. ~ _ 0.1071 0.1071 0.1071 0.1389 0.1389 0.1406 0,1476 0.1476 0.1476 0.1476 0.0907
...
...
... ... ...
_ .
98.4 98.0 98.0 98.1 96.0 96.2 96.4 89.4 95.6 95.6 97.1 88.0
... ... ... ...
...
Aldehyde found, yo
Found, other methods, % 36.3"
...
... ...
0.0960
Hydroxylamine hydrochloride (7), using the reagent in ethyl alcohol as solvent. b Bisulfite method of Siggia and Maxey (6). c Water used as solvent. a
EXPERIMENTAL
Reagents. entific Go.
Determination of Aldehydes by Silver-tert-Butylamine Reagent
Time, minutes Reagent Aldehydes Formaldehyde
system was quite adaptable t o analysis of water-insoluble systems for aldehydes. This reagent maintains the advantages of the older silver oxide systems in that it permits determination of aldehydes in the presence of ketones, carboxylic acids, and acetals.
... ... .
.
I
...
I
... ...
.
.
... 0.1476 0.1476 0.1476 0.1314 0.0907 0.0907 0.0907 0.1561 0.1561 0.1561
97.4"
98.3~
... ...
... ...
36.2*
...
... ... ...
97.9 98.7 99.2 99.0 93.2 97.9 98.2 97.5 97.2 97.3
98. 45 97.8" 97.4" 99.3"
98.6" 97.30
tert - Butylamine, (CH&CNH2, Eastman White Label grade. Silver Oxide Reagent. One liter of approximately 0.2N reagent is prepared by adding exactly 24.5 *O.l gram of silver oxide to a 1-liter reagent bottle. A magnetic stirring bar and 500 ml. of deionized water ai'e added. Exactly 72.0 & 0.1 ml. of tert-butylamine are added, the bottle is stoppered, and the contents are stirred vigorously with a magnetic stirrer until nearly all of the silver oxide has dissolved (approximately 3 hours). The reagent prepared in this manner has an excess of silver oxide, which can be removed by filtering. An excess of tert-butylamine should be avoided in the preparation of the reagent. After filtration, the reagent is diluted with water to 1 liter for 0.2N or to 2 litem for 0.1N reagent. Freshly prepared 0.2N reagent is recommended for aromatic aldehydes, whereas the 0.1N reagent is adequate for aliphatic aldehydes and has been effective after having stood for two weeks. Procedure. A sample of aldehyde (0.015 to 0.020 mole) is weighed into a 100-ml. volumetric flask and diluted t o the mark with 2B ethyl alcohol. A 10-ml. aliquot is then transferred t o a 250-ml. glass-stoppered flask t h a t contains a 50-ml. aliquot of the reagent. T h e reaction mixture is agitated for a few minutes; the formation of 9 brown turbidity or a silver mirror indicates a positive reaction. The solution is allowed to stand a t room temperature and is shaken periodically for the appropriate period of time (Table I). At the end of the reaction time, the solution is filtered through a medium-porosity fritted-glass crucible, and the filtrate is acidified with 10 ml. of concentrated nitric s,cid. Ferric alum indicator is added, and the excess silver ion is titrated with standard potassium thiocyanate solution. A 50.0ml. blank of the reagent is also titrated. The silver mirrors formed on the flask by the reaction can be removed by dissolving with concentrated nitric acid. Calculation. M Mt' ( A - B ) X NK~C XN ?!Lu= -grams of samalt: % Aldehyde where
A B C
= ml. KSCN for the blank. = ml. KSCN for the sample. =
number of aldehyde carbonyls per molecule. RESULTS AND CISCUSSION
I n the investigation of silver amine complexes, the saturzhed aliphatic primary amines from C1 t o Cd formed a soluble complex with silver oxide in aqueous solution. It, was also estab-
lished that the availability of the silver oxide as a n oxidant depended upon the amine that formed the complex. The primary amines which were the most effective were iso-propylamine and tertbutylamine. The iso-propylamine complex does not appear t o be as strong an oxidant as the tert-butylamine complex and, therefore, might find application in systems where the stronger oxidant might not be workable. As indicated above, two concentrations of reagent are used. The 0.1N reagent is applicable to the aliphatic aldehydes; however, 0.2N must be used in analyzing the aromatic aldehydes, since the oxidation proceeds rather slowly with the 0.1N reagent (Table I). The procedure was applied to a mixture of n-butyraldehyde in glacial acetic acid (Table 11) and in methyl ethyl ketone (Table 111). I n samples where large quantities of the acid were present, it was advisable to either first neutralize the acid present in the sample or t o add 10 ml. of 6N sodium hydroxide per liter of 0.2N amine silver oxide reagent. The former approach is recommended. When analyzing for n-butyraldehyde in the presence of methyl ethyl ketone, it was necessary to use the 0.1N reagent and a sample size such that 50y0 of the reagent was consumed. The data indicated a more concentrated reagent slowly oxidized the ketone. When a 10-ml. aliquot of an acetal free of aldehyde was added t o a 50.0-ml. aliquot of 0.2N reagent, no measurable interference was found. Alcohols do not interfere; in fact, ethyl alcohol is used as solvent in the analysis. Some halogenated organic materials would interfere. A sample of n-caproic aldehyde analyzed 92.0% by the amine silver oxide reagent, however, the result obtained by the hydroxylamine hydrochloride method was 98.0%. It may be t h a t a material was present (ketone or acid) which gave high oximation values. This was not investigated further. Aromatic aldehydes can be determined, as shown in Table I. However, some difficulty was experienced with anisaldehyde and cinnamaldehydei.e., the results obtained were low. It is interesting to note that by this amine, silver oxide reagent crotonaldehyde can be determined, but acrolein and cinnamaldehyde cannot. This identical behavior was noted with the ammonia silver oxide reagent used by Siggia and Segal (6). I n the case of acrolein, it may be t h a t the quality of
Table II. Determination of n-Butyraldehyde in Glacial HAC-0.2N tertButylamine-Silver Oxide in 0.06N NaOH
3 n-butyraldehyde in glacial HAC Reaction Retime, covery, minutes Added Found % ' 30 5.26 5.23O 99.4 45 23.7 23.0b 97.0 45 46.3 46.0b 99.6 45 69.0 68.Sb 99.7 45 91.4 91.8* 100.4 Not diluted with 2B ethyl alcohol Diluted with 2 B ethyl alcohol. Wt.
Table 111. Determination of n-Butyraldehyde in Methyl Ethyl Ketone-0.1 N fert-Butylamine-Silver Oxide Reagent
Reaction time, minutes 30 128 30 60 30 110 30 95 30 87
Wt. % n-butyraldehyde in MEK Recovery, yo Added Found 5.70 5.67 99.5 5.89 103.3 27.5 27.3 98.9 27.4 99.3 48.7 48.6 99.9 49.1 100.8 68.8 69.0 100.3 69.1 100.4 91.8 91.6 99.8 92.3 100.5
the sample played a role in the poor recoveries; a pure sample of acrolein is difficult t o prepare and maintain. ACKNOWLEDGMENT
The authors are grateful to the following for their aid in carrying out the experimental program: C. A. Laflamme and C. R. McClure. LITERATURE CITED
(1) Bailey, H. C., Knox, J. H., J . Chem. SOC.1951,2741. (2) Mitchell, J.,Jr., Smith, D. M., ANAL.
CHEM.22, 746 (1950). (3) Ponndorf, W., Ber. 64, 1913 (1931). (4)Seiael. H.. Heiss. F. T.. ANAL.CHEM. . 26. 977-19 (1954).' (5) Siggia, S:, Maxey, W., Ibid., 19, 1023-5 (1947). (6) Siggia, S., Segal, E., Ibid., 25, 640 (1953). (7) Smith, D.M., Mitchell, J., Jr., Ibid., 22, 750-5 (1950).
JOHN A. MAYES J. KUCHAR EDWARD SIDNEY SIGGIA Olin Mathieson Chemical Corp. New Haven, Conn.
VOL. 36, NO. 4, APRIL 1964
935
