iodine gives mostly diethyllead iodides. Mixing this fiolution with an aqueous 2N iodine solution hastens the decomposition to lead iodide. Removing lead from the alcoholic scrubber with water is not satisfactory. Iodine will precipitate from solution. Rinsing with potassium iodide is necessary. OTHER APPLICATIONS
Metallic mercury and organomanganese compounds were removed from air by crystalline iodine. Because of its strong oxidizing action, crystalline iodine should be useful for removing a host of organometallic conipounds from air.
Table IV. Collection of Tetraethyl and Tetramethyllead in Air Using Methanolic Iodine Scrubber Solution
Lead Added. ue. Sampling Tetra- Tetra- Scrubber methyl- ethyl- Efficiency, Rate lead C.F./M. lead 70 60 0 100.0 0.25 60 0 99.0 0.75 0.75 0 42 98.5 99.8 0.75 0 42 I
.
-
Because the crystalline iodine absorbent tube eliminates spills, the new tube may serve well as a dosimeter-
type test, attached to a workman, and powered by a Freon-aspirated air sampling device such as the Uni-Jet. An 8-hour sample may be collected from one can of Freon a t a slow sampling rate. LITERATURE CITED
(1) Dowling, T.,Davis, R. B., Charsha, R. C., Linch, A. L., Am. Ind. Hyg. Assoc. Quart. 19,330 (1958). (2) Snyder, L. J., Barnes, W. R., Tokos, J. V.,ANAL.CHEM.20,772(1948). (3) Henderson, S.R.,Snyder, L. J., Ibid., 33, 1172 (1961). RECEIVED for review June 6. 1960. Resubmitted March 24, 1961. Accepted June 12,1961.
Spectrophotometric Determination of Crotonaldehyde with 4-Hexylresorcinol A.
P.
ALTSHULLER and 1. R. COHEN
Robert A. Taft Sanitary Engineering Center, Cincinnati 26, Ohio
b A
spectrophotometric method has been developed for the determination of crotonaldehyde based on its reaction with 4-hexylresorcinol. The product formed has two analytically useful absorption maxima at 385 and 345 mp. The crotonaldehyde product obeys Beer's law in the 1 - to 20-pg.per-ml. range, Saturated aldehydes and ketones, alcohols, esters, acids, most hydrocarbons, and phenols do not interfere significantly. Unsaturated aldehydes, unsaturated ketones, and diolefins in excess interfere appreciably, as does nitrogen dioxide. Results of the analyses of a number of liquid mixtures are given.
C
can be separated and determined in the presence of other aldehydes by chromatographing the 2,4dinitrophenylhydrazonederivatives and then applying ultraviolet analysis to the separated hydrazones (7, 9). Polarographic analysis of the zone containing crotonaldehyde, acrolein, and propionaldehyde also permits the specific determination of crotonaldehyde (6, 6). Gas chromatography can be used to separate and analyze for crotonaldehyde in complex gas mixtures (3,4). However, all of these methods are complex and time consuming. Most of the other methods available are not specific for crotonaldehyde or even for a,P-unsaturated aldehydes. Benzidine hydrochloride (1) and rn - phenylenediamine dihydrochloride (10) have been used as colorimetric reagents. However, they react not
only with crotonaldehyde, but with other saturated and unsaturated aldehydes including formaldehyde (8). Recently, 4hexylresorcinol has been used as the reagent in a spectrophotometric method for acrolein ( 2 ) . Crotonaldehyde also reacts with Chexylresorcinol to form a product possessing a characteristic spectrum in the visible and ultraviolet regions ( 2 ) . Two of the bands in the ultraviolet can be used for quantitative analysis. Optimum reaction conditions have been evaluated. In the present work, crotonaldehyde has been determined in many liquid mixtures containing large quantities of other aldehydes, ketones, alcohols, esters, and phenols.
ROTONALDEHYDE
1 180
ANALYTICAL CHEMISTRY
EXPERIMENTAL
The materials used have been described previously (2). Procedure. To 2.5 ml. of ethyl alcohol containing the sample, 0.05 ml. (about 2 drops) of the alcoholic 4-hexylresorcinol solution is added, then 0.2 ml. of the 3% alcoholic mercuric chloride solution and 2.5 ml. of the saturated aqueous trichloroacetic acid solution. A blank is prepared similarly. The resulting solution is heated for 20 minutes a t 60" C., removed from the constant temperature bath, and cooled to room temperature. The absorbance of the solution is read immediately a t 385 mp. Occasionally, it is advantageous to use the peak a t 345 mp. These absorption bands are relatively constant (f1%) for 11/*hours of further reaction time. Instead of heating, an equally ac-
ceptable procedure is to react the solution a t room temperature for 1 hour and then read the absorbance. The intensity of the 385-mp peak is about 10% greater here than with heating, and the absorbance of the 385-mp peak is relatively constant between 1 and 2 hours of reaction time. RESULTS
Proportions of Reactants. The relative volumes of the reactant solutions were varied over nearly the same ranges as those used previously (9). The conditions for achieving maximum intensity for the crotonaldehyde product peak a t 385 mp are almost the same as the optimum conditions for acrolein. The only difference is a slight increase, about 575, in intensity of the product peaks a t both 385 and 345 mp when 0.2 ml. rather than 0.1 ml of 3% mercuric chloride solution is added. This change, along with addition of 0.10 ml. of 4-hexylresorcinol solution instead of 0.05 ml., increases the intensity of the 345mp peak about 10%. Trichloroacetic Acid Solution. The quantity of trichloroacetic acid solution was varied between 1.5 and 3.5 ml. The trichloroacetic acid was added to a mixture containing 55 pg. of crotonaldehyde in ethyl alcohol, 0.05 ml. of alcoholic 4-hexylresorcinol solution, and 0.2 ml of 3% alcoholic HgClz solution. The absorbances obtained using 1.5, 2.5, and 3.5 ml. of trichloroacetic acid solution a t 385 mp were 0.12, 0.39, and 0.39. Consequently, 2.5 ml. of trichloroacetic
acid appears to be about the minimum volume corresponding to optimum intensity. This is the same volume as used in the previous acrolein method. However, the procedure is insensitive to volume of acid in the 2.5- to 3.5ml. range. Spectra of Reaction Product. The product formed by the reaction of t h e crotonaldehyde with 4-hexylresorcinol has a band system consisting of two weak bands with maxima a t 540 and 495 mp, and of two bands of moderate intensity with masima a t 385 and 345 mp. These product absorption bands change on1.y slightly in intenPity over several hours. Over a 24-hour reaction period the band system changes appreciably (Figure 1). The band farthest in the ultraviolet remains about the same intensity, but its malimum shifts to 325 mp. The peak of the other ultraviolet band remains a t 385 mp, but it decreases t o about half of its maximum intensity. The band at 495 mp continues to peak near the same wave length. More significant is its fourfold increase in intensity. The band originally at 540 mp becomes a shoulder on the other more intense band in the visible. The absorbance of the maxima a t 385 and 345 mp are linear with concentration in at least the 10- t o 200pg. range of crotonaldehyde in the reaction misture. The absorptivities of the two maxima are very close. Both peaks of the crotonaldehyde product have absorptivities of 0.038 f 0.002 fig.-' ml. cm.-l based on the crotonaldehyde concentration in micrograms per milliliter of the reaction mixture. Products from Various Alkylresorcinols. The absorption spectra of
the products formed by reacting crotonaldehyde with 2-methylresorcinol, 4-ethylresorcinol, and 4-cyclohexylresorcinol were investigated. Crotonaldehyde reacts with 2-methylresorcinol to produce a very weak absorption spectrum characterized only by a very weak band a t 405 mp. 4-Ethylresorcinol reacts with crotonaldehyde to form a reaction product with a n absorption spectrum having bands with masima at about 535, 390, and 335 mp. The intensity of these bands is about half the intensity of the bands associated with the product formed by crotonaldehyde with 4-cyclohexylresorcinol. The product formed by crotonaldehyde with 4-cyclohexylresorcinol has a band system with maxima a t 540, 500, 385, and 340 mp. These bands have intensities only slightly higher than those of the product formed by crotonaldehyde with 4-hexylresorcinol. Since no really significant advantage appeared t o exist in using other 4-alkylresorcinols, 4-hexylresorcinol is the reagent of choice on the basis of availability and cost.
0.75
0.50 2
a
m
a
0
ln
I
I
-;'\
I
I
I
,-
\-.
I
0.25
,
b \ \
\
0.oc
300
400 500 600 WAVE LENGTH, m p
70C
Figure 1 . Absorption spectra of product formed after reaction between 54 pg. of crotonaldehyde and 4-hexylresorcinol reagent
-1 hour of reaction time _ _ _ _ - 22_ hours of reaction time Table 1.
Effect of Heating and Reaction Timeon Intensity of Absorption at 385 Mp
Reaction Time, Min. 45 60 90 Absorbance0 0 ... 0.55 0.72 0.79 0.81 5 0.33 0.62 0.73 0.78 0.79 10 0.62 0.68 0.74 0.74 0.74 15 0.70 0.72 0.74 0.75 0.75 20 0.73 0.74 0.74 0.74 0.74 30 0.74 0.74 0.74 0.74 0.72 For 100 pg. of crotonaldehyde in reaction mixture.
Heating Per. Absorbance a t at 60" C., End of Min. Heating Per.o
0
aldehydes form products with 4-hexylresorcinol t h a t have appreciable absorption in the 340- to 390-mp region (Table 11). The acrolein product has a weak maximum a t 410 mp. Fortunately, the residual absorption in the 340- to 390-mp region, although appreciable, is small compared to the strong absorption in the 500- to 650mw region. a-hlethylacrolein forms a product with a shoulder a t about 410 mp and a maximum around 325 mp. The 385-mp absorption maximum of the crotonaldehyde product occurs near a n absorption minimum for the amethylacrolein product ; 2-methyl-2butenal forms a weak product spectrum with a maximum at 390 mp about one fifth as intense as the maximum a t 385 mp possessed by the crotonaldehyde product.
30
Reaction with 4-Hexylresorcinol in Trifluoroacetic Acid. Trifluoroacetic
acid was substituted for trichloroacetic acid with all of the other reaction conditions held constant. The intensities of the peaks at 385 and 345 mp decreased between 5 and 10%. Consequently, it appears that there is no advantage in the use of trifluoroacetic acid as a part of the reaction medium. A similar result was obtained with acrolein (2).
120 0.73 0.75 0.72 0.71 0.71 0.71
Table II. Absorptivities for Products of Various Oxygenates and Hydrocarbons with 4-Hexylresorcinol Reagent (Absorptivities for 100- to 1000-pg. quantities of substances listed, after heating for 20 minutes at 60" C. and about 1 hour of
reaction time with reagents) a, Absorptivities, pg. -1 M1. Cm.-] Substances 385mp 345 mp 0.038 Crotonaldehyde 0.038 0.01 0.01 Acrolein Reaction Time and Temperature. 0.014 0,007 a-Meth ylacrolein 0.007 2-Methyl-2-butanal 0,007 T h e absorbances of reaction mixtures 0.0003 0.0001 Formaldehyde containing 100 pg. of crotonaldehyde 0,0003 0.0001 Acetaldehyde were measured over several hours after 0.0002 0.0002 Propanal 0, 5, 10, 15, 20, and 30 minutes of heat0.0002 Butanal 0.0003 0.0008 2-Methylpropanal 0.0004 ing a t 60" C. (Table I). Heating for 0.003 Furfural 0.003 20 or 30 minutes results in essentially 0.008 Cinnamaldehyde 0.005 maximum absorbance at the end of the 0.001 0.002 Benzaldehyde heating period. The absorbance re
