Precision Semimicro Hydrogenation Apparatus - Analytical Chemistry

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a47

V O L U M E 2 4 , NO. 5, M A Y 1 9 5 2 Table I.

Precision of Results

All melting points were determined by means of t h e instrument. A fresh sample of t h e material was used for each determination; in t h e case of sulfanilamide, repeated determinations were also made automatically on a single sample Anthracene Benzoic Acid Aaobenzene ______ _____ Temp., DeviTemu., DoriTemp., DeviC. ation C. ation C. ation 216.0 -0.2 122.6 -0.1 -0.1 67.1 216.2 0 122.G -0.1 -0.1 67,l 216.2 0 122.8 +0.1 +0.3 67.5 216.2 0 +0.1 +0.2 122.6 67.0 216.2 0 +0.3 -0.1 123.0 67.1 Av. 67.2 122.7 216.2 Sulfanilamide (Single Sample)

Sulfanilamide

Ai‘.

164.6 164.6 164.6 164.6 165.0 164.7

-0.1 -0.1 -0.1 -0.1 f0.3

164.6 164.6 164.6 164.8 164.8 164.7

-0.1 -0.1 -0.1 +0.1 +0.1

Succinic Acid 187.0 187.2 187.2 187.0 187.0 187.1

-0.1

Table 11. Comparison of Results with Literature

I

I1 67.1

4 (14)

B (4)

...

...

67.2

Benzoicacid

122.7

Sulfanilamide

164 7

164.6

Succinic acid

187.1

186.8 182.3 182.7 182.8

Anthracene

216.2 216.5 216.18 217

1 2 2 . 8 122.30.5 1 2 1 . 4 122.375 122.43

...

... 183

216.4216.7

C (7)

...

ACKNOWLEDGMENT

-0.1 +O.l +O.l -0.1

Column I gives melting points obtained with instrument. Column I1 gives meltin points obtained with modified Hershberg apparatus. Columns A &rough E give melting points obtained from literature Azobenzene

measuring component, at heating rates less than 0.5” C. per minute in the Hershberg apparatus. The melting points so obtained agree very well with those obtained by use of the instrument described here. I n the case of azobenzene, which is deeply colored and darkens before melting, the precision and accuracy of the results are no less than in the case of the other materials studied. This fact would seem t o indicate, and visual observation bears out, that the extreme thinness of the liquid layer on the hot stage suffers no diminished transparency so far rn the sensing element is concerned. There is therefore no reduction in light intensity at the phototube when a sample darkens or chars prior to melting.

D (8) 68

122.45 121.7

E (6) 68 122.5

.., ...

165-66

166

189-90

188

216.5

217-18

215

of the thermometer, nor does the maximum deviation exceed twice this value. Table I1 gives a comparison with the literature values for the compounds employed. Agreement among the literature values themselves is not satisfactory. Accordingly, the melting points of the compounds employed in this investigation were determined by an independent method, using a modified Hershberg apparatus ( 2 , IS). A calibrated thermocouple was used in measuring the temperature of the bath in the Hershberg apparatus, and its output was read on the ~ e r v omillivolt potentiometer of the instrument. All compounds employed melted sharply within the limiting precision of the temperature

The authors wish to thank the Texas Co. for its support of a large part of this work, which was done under the Texas Co. Fellowship in Microchemical Analysis, and Harry Levin of the Beacon Laboratories of the Texas Co. LITERATURE CITED (1) Batcher, R. R., and Moulic, W., “The Electronic Control Handbook,” p. 298, New York, Caldwell-Clements, 1946. (2) Hershberg, E. B., IND. ENG. CHEM.,ANAL.ED.,8 , 3 1 2 (1936). (3) Houben, J., “Die Methoden der organischem Chemie,” 3rd ed., Vol. I, Leipaig, Georg Thieme, 1935. (4) Huntress, E. H., and Mulliken, S. P., “Identification of Pure Organic Compounds,” pp. 115, 146, 517, New York, John Wiley & Sons, 1949. (5) Kardos, F., ANAL.CHEM.,22,1569-70 (1950). (6) Kofler. L., and Kofler, A., “hlikromethoden zur Kennaeichnung organischer Stoffe und Stoffgemische,” pp. 224, 249, 270, 283, 295, Innsbruck, Universitlitsverlag Wagner G.m.b.H., 1948. (7) Landolt-Bornstein, “Physikalisch-chemische Tabellen,” Erg. I11 a, c, Supp. Vol., Berlin, Julius Springer, 1927. (8) Lange, N. A., editor, “Handbook of Chemistry,” 7th ed., pp. 377, 379, 383, 389, 643, Sandusky, Ohio, Handbook Publishers, 1949. (9) Lowe, J., 2.anal. C h a . , 1 1 , 211 (1872). (10) Matthews, F. W., ANAL.CHEM.,20, 1112 (1948). (11) Puckle, 0. S., “Time Bases,’’ p. 57, New York, John Wiley & Sons, 1944. (12) Schmitt, 0. N.. J . Sci. Instruments, 1 5 , 2 4 (1938). (13) Skau. E. L.. and Wakeham. H.. in “Techniaue of Organic

Chemistry,” 2nd ed., Vol. I, Part I, Chap. fII, New York, Interscience Publishers, 1949. (14) Timmermans, J., “Physico-Chemical Constants of Pure Organic Compounds,” pp. 181, 403, 480, New York, Elsevier Publishing Co., 1950. RECEIVEDfor review November 16, 1951.

Accepted February 21, 1952

Precision Semimicro Hydrogenation Apparatus F. A. VANDENHEUVEL Fisheries Research Board of Canada, Atlantic Fisheries Experimental Station, Halifax, N. S., Canada I T H few exceptions ( 4 , 5 ) ,all the laboratory hydrogenation apparatus described in the literature derive from the simple classical device shown in Figure 1. This is composed of a vessel, C , or hydrogenation cell, a graduated buret, B , and a leveling arrangement including a leveling bulb, L. I n the cell is shaken a mixture of unsaturated compound, catalyst, and a solvent when required; the hydrogen contained in the apparatus is absorbed as the reaction progresses. This system allows a measurement of the absorbed hydrogen t o be made and therefore can be used for determination of unsaturation values (absorption a t the completion of the reaction) and of hydrogenation rates. With this type of apparatus, hydrogenation values (a)are obtained with a precision of *3%, provided the proper technique is

used. If accuracy is not the main objective, this is the ideal equipment, being simple t o construct and easy t o handle. Many modifications have been proposed; some lead to somewhat better results but in no case is a precision better than 1% t o be expected. The sources of error are many and no apparatus proposed so far eliminates them all satisfactorily. When, instead of hydrogenation values, hydrogenation rates are required, the difficulties involved are greatly magnified. This type of study not only calls for a much higher precision but also numerous timed readings. The equipment shown on Figure 1 is unsuited for this type of work. The essential drawback is the practical impossibility of making frequent and precise readings when the pressure has t o be

ANALYTICAL CHEMISTRY

848 continuously adjusted by manual control. Even assuming this to be feasible, undesirable interferences due to other sources of errors inherent to the system come into play. Most of these stem from the fact that the system is not well defined thermodynamically. Small variations of temperature and pressure are impossible to avoid. They exert a distorting effect which precludes the accurate measurement of the volumes absorbed (8). Another less obvious but very important source of errors is due to agitation. It is not immediately realized that the system under observation is limited to the liquid phase; the hydrogen reaching the catalyst does not come directly from the gas phase but is supplied by the hydrogen dissolved in the liquid medium. Thus its concentration in this liquid is the thermodynamic factor affecting the reaction rate. Should this concentration vary in an uncontrollable manner, the system would no longer be defined Unless a large gas-liquid interface allows the hydrogen from the gas phase to diffuse and replace quantitatively the dissolved hydrogen used up by the reaction, fluctuations in hydrogen concentration will occur with subsequent distortion of the rate curve. Agitation efficiency and control are thus very desirable features The apparatus described fills these important requirements, along with several others of lesser importance. Essentially, it is derived from the simple device shown in Figure 1. Structural simplicity has been sacrificed t o a certain extent, but the handling of the apparatus is still very simple. There is a considerable gain in sturdiness, reliability, and precision. Hydrogenation values can be obtained with an accuracy better than 3~0.3%for a single determination, using amounts of material that will absorb as little as 1 cc. or as much as 50 cc. of hydrogen. (With the 50-cc. buret the volume absorbed should be a t least 10 cc.) True hydrogenation curves are obtained and precise readings can be made as frequently as one every 15 seconds.

No apparatus described in the literature allowed the determination of hydrogenation values with a precision better than 1%, and the precise study of catalytic hydrogenation rates under fully isobaric and thermostatic conditions, with semimicro and micro quantities. The new apparatus allows such studies to be made. Its features overcome the drawbacks of hydrogenation apparatus in general, and allow good control of the conditions used and easy manipulation. The precision is about 0.37, for one determination of the unsaturation value involving a few milligrams of unsaturated compound and the rate curves observed are reliable. This apparatus can be used for obvious analytical purposes as well as for the study of catalyst activity, catalyst selectivity, and behavior of unsaturated compounds under hydrogenation, and preparativework on a semimicro scale.

Saturation of the leveling fluid by hydrogen and exclusion of foreign gases. Efficient and controlled agitation. All-glass, leakproof, rigid construction. DESCRIPTION OF APPARATUS

The main parts of the apparatus ale: the hydrogenation cell, C (Figure 2), the buret, B, the leveling tube, L, the leveling liquid reservoir, R, the manostat, M, the needle valve, N , and stopcocks P, Q, and X. Appropriate manipulation of these stopcocks (straight-bore, three-way) allows the following connections to be made, excluding all others: (1) vacuum line V to cell, (2) hydrogen supply line to cell, (3) cell to buret, (4)buret to hydrogen supply line H , and ( 5 ) hydrogen supply line to bubbler tube Z' (in reservoir E ) . Buret B is connected to the leveling tube, L, by stopcock E (Figure 3). The latter also allows liquid t o be drawn either from the buret or from the leveling tube. Reservoir R contains a supply of leveling fluid maintained saturated in hydrogen (bubbler tube Z ' ) and free of other gases. The reservoir is connected to the base of the buret by tub€ 2. Opening of needle valve N will allow leveling fluid to flow in the buret, leveling tube, or both, depending on the position of stopcock E.

0 Av

E

N

2 Figure 1. Classical Hydrogenation Apparatus

This result was obtained by simultaneously incorporating the following features: Maintenance of preset pressure within 0.03 mm. of mercury. Maintenance of working temperature within 0.01 O C. Automatic leveling. Use of organic liquid of low density instead of mercury as leveling fluid.

7

Figure 2.

Diagram of Improved Apparatus

849

V O L U M E 2 4 , NO. 5, M A Y 1 9 5 2

I1

numerous small bubbles is created and maintained throughout the liquid. The construction of the plunger is shown in Figure 3 , B. The bodv is made of Carnenter stainless steel Yo. 5. The base, B,is made of soft sicel subsequently chromiuni platpd. The thickness of the fins, F , is 0.2 mm.; the top fin, T , is 0.5 mm. thick, the thickness of base B I S 1.2 mm. All the fins and the base are perforated by six holes of 2-mm. diameter. Between T and the next fin, a 2-mm. hole, H , is bored through the shaft on both sides. The weight of the stirrer is 16 grams. The agitation intensity can be varied by adjusting the rate of pulsation of the current, the amplitude of the movement, or both. Pulsations varying from 300 to 500 per minute are obtained by a system of cam and contacts operated by a synchromotor. The current is 12 volts direct current supplied by a rectifier (5 amperes). Car batteries can be used. This system allows a very steady state of agitation t o be maintained. PRESSURE MAINTEN4NCE AND AUTOMATIC LEVELING (FIGURE 2)

GH

. Figure 3.

Apparatus

The manostat, M ,can be connected to the cell-buret system by opening stopcock Y . A stand, S , supports the apparatus. CONSTANT-TEMPERATURE SYSTEiM

A water bath (28 liters) kept a t a temperature constant within 0.01' supplies thermostated water to the system (small centrifugal pump). The w-ater flows first into the jacket, Jb, surrounding the buret and leveling tube, then to tank K ; from K it flows back to the bath. Tank K is glass-sided; it can be moved up and down, sliding on a vertical track screwed on stand S. In its lower position, tank K rests on knob D. The cell is then fully accessible and can be easily disconnected from or adapted to the rest of the apparatus. A standard joint, St, is the connecting part. The cell is the only part of the apparatus ever removed. Khen tank K is made to slide up the track T , it occupies the upper position (dotted line). The cell is then surrounded by constant-temperature water. By means of a branch tube, the water is also circulated through the jacket, J m , housing electromagnet G. AGITATION

Agitation is effected by plunger-stirrer I actuated by magnet G. This magnet is screwed in the base of tank K in such a position that, when the tank occupies its upper position, the flat base of the cell rests squarely and centrally on G. The movement of the stirrer is not the conventional rotation; it is animated by rapid vertical oscillations. (A conventional rotary magnetic stirrer could be used if hydrogenation values were the only requirement. Kinetic studies, however, require a more efficient stirrer.) The effect is obtained by interrupting the exciting rurrent several times a second. When the current is passing through the coil, the stirrer, resting on a small spring, is pulled down; when the current is interrupted, the spring restores its initial position. The spring is made of six turns of gage 0.016-inch Wallace Barnes, Hamilton, Ontario, stainless steel spring wire. Length is 6 mm. relaxed. As a consequence of the particular shape of the stirrer, a very large gas-liquid interface due to

Thermostat N is a differential manometer half-filled with mercury. I t is branched on the connection between the cell and the buret. A slight lowering of pressure (such as caused by hydrogen absorption) causes the level in one branch to lower. This breaks a contact, W ; breaking this contact operates magnet Av (through the action of a sensitive electronic relay) which lifts the glass needle valve, AT. This causes leveling fluid to flow from reservoir IV R into the buret until the preset pressure is re-established. The position of contact W is adjustable by the rotation of knob Am. The operating pressure, which is the atmospheric pressure of the moment, is maintained by this sturdy arrangement within 0.03 mm. of mercury. Rlanipulation of knob 0 allows the adjustment of t h e needle valve opening gap and thereby the control of the compensating impulses in amplitude. This automatic setting of the level leaves the operator's attention entirely free, a condition prerequisite to precise observations. As leveling fluid, it is desirable to use the same solvent as in the cell. THE CELL

The hydrogenation cell (Figure 3, I ) is made of a KO. 34/45 standard joint. The lower section, made of the inner part of the joint, has a flat base. A certain length of glass rod, R, is fused by one end in the center of the base, perpendicularly to its plane. This rod acts as guide for the plunger, P (Figure 3, I1 and IV). The small stainless steel spring, 8, is located in the plunger shaft and sits on top of the glass rod, R; xhen magnet G is not energized, P occupies the position shown in Figure 3, IV. The top section of the cell (Figure 3, I ) is made of the outer part of the S o . 34/45 standard joint. I t comprises a central tube, A , ending in a hemispherical shield, M ,opening downward. The external diameter of the largest section of the shield is only 0.5 mm. smaller than the internal diameter of the bottom part of the cell. The purpose of the shield is to catch all the droplets projected from the liquid during the operation and to return them to the solution. The other end of tube A is scaled to a tube C bearing the inner part of a KO.12/30 standard joint, Stz. The outer part of this joint is a t the end of tube D. The latter bears, sealed inside, a small length of capillary tubing, E. A stainless steel wire, TY (1 mm. thick), is sealed by one end in this capillary tube (de Khotinsky cement). The other end is bent a t right angles. Asmallglass capsule (Figure 3 , I I I ) , K (containing the sample t o hydrogenate), can be inserted in tube A and supported by the bent end of the n ire (Figure 3, IV). A 90" rotation of D will cause the release of the capsule nhen this is desired. The side tube, V , is fitted with the outer part of a No. 12/30 standard joint, Stl, xhich a l l o ~ i sthe cell to be connected to the buret assembly. MICRO AIVD SEMIMICRO EQUIPMEYT

A precision borosilicate glass (1-, 2-, or 5-cc.) microburet body together with a leveling tube 12 mm. in diameter constitutes the micro combination. The semimicro combination comprises a 50- or 25-cc. precision, borosilicate glass buret body and a leveling tube 6 mm. in diameter.

a50

ANALYTICAL CHEMISTRY

Both can be incorporated in the same apparatus, as shown on Figure 4. However, by using special stopcocks (Figure 4, C), the system can be reduced to the two burets only, one micro and one 50 cc. or 25 cc. Either is used as the leveling tube when the other is used as buret (Figure 4,B ) . HYDROGEY SUPPLY

Electrolytic hydrogen (cylinder) is passed through a purifying train consisting of: reducing valve, mercury safety valve, porous plate gas-washing bottle containing an alkaline solution of sodium plumbite ( 7 ) ,p.latinized asbestos oven (300" to 350"), and porous plate gas-washing bottle containing the same solvent as used in apparatus (leveling liquid and solvent in the cell). The train is maintained under a slight pressure when not in use. The apparatus is ready to operate as soon as the oven has reached 300".

gen supply line. This is repeated several times; after each filling, the stirrer is operated for a few seconds in order to liberate foreign gases from the liquid. After the final filling, stopcocks Q and X are adjusted to connect the cell to the buret. By maneuvering stopcock E, the levels are equalized. The manostat is then connected to the system, and the automatic leveling mechanism and the stirrer are switched on. The apparatus is left operating until no more hydrogen is absorbed; the medium (catalyst and solvent) is then fully reduced and saturated with hydrogen. After a final careful adjustment, the level in the buret is read; subsequent release of the sample causes hydrogen absorption to be resumed. When the hydrogen value is the only requirement, the level is read when absorption ceases. Should a rate curve be required, readings are made a t timed intervals. A convenient technique to ensure on-time readings is to use a minute-sweep electric clock arranged so as to give an audible signal before (warning) and a t the preset time for the reading.

HYDROGENATION TECHNIQUE

A certain amount, of catalyst is placed in the bottom of the cell. For the determination of hydrogenatmionvalues, this amount need not be known. The spring is inserted inside the stirrer shaft and the stirrer is slipped on the guide rod. A standard amount of solvent is added, such that, when the stirrer is pulled down, about 1 mm. of liquid covers the top. The capsule containing the weighed sample is inserted in the central tube of the top part of the cell and secured in position .by rotating the bent end of the wire inward. MANOSTAT

Table I. Hydrogenation Values for Sample of Fumaric Acid with Platinum Black (Reduced PtOp) as Catalyst 1.736 1.734 1.737 1.735 1.738 1.735 1.738 1.739 1 739 1 737

1.r35 1.736 1.736 1.737 1.739 1.740 1.742 1.734 1.736 1.735 Av. 1.7368 Theoretical 1 7374 Largest deriation f r o m average

-

1.740 1.740 1.737 1.736 1.735 1.740 1.736 1.734 1.735 1.733

+0.005 -0.004

EXAMPLES

B

Hydrogenation Values. Table I gives a series of values determined by using variable amounts of fumaric acid (British Drug House-C.C.) in the presence of Adams cat,alyst (PtOt) (1). Ethyl alcohol (95%) was used as a solvent. The volumes absorbed were from 1.05 to 4.5 cc. (microburet) and from 12.1 to 50 cc.

Table 11.

Hydrogenation Rate of Methyl Oleate with Raney Nickel (Me oleate .W5 - 1. Run 9-266. Co 16.80) T, c, k -

Time 4 5 6 7 .8 9 10 11 12 13 14 18 22 24

Figure 4.

Microapparatus

Bottom and top parts of the cell are brought together (vaseline) and the cell is connected to the apparatus. Tank K is lifted and locked in its upper position; the constant-temperature water flow is directed through the apparatus. The buret is filled with hydrogen by opening stopcock E after the buret has been connected to the hydrogen supply; hydrogen thus replaces the liquid drained from the buret. Filling the cell with hydrogen is accomplished by connecting the cell first to the vacuum line (water pump), then to the hydro-

-

Concn. I. 0 . 6 6 9.49 8.45 7.49 6.65 5.93 5.25 4.66 4.15 3.71 3.34 2.15 1.34 1.04

In C d C 0.455 0.571 0.687 0.808 0.926 1.041 1.163 1.282 1.398 1.510 1.610 2.056 2.528 2,782

1/T In Co/C 0.1137 0.1142 0.1145 0.1154 0.1158 0.1157 0.1163 0.1166 0.1165 0.1162 0.1150 0.1142 0.1148 0.1159

The expression giving the theoretical hydrogenation value is

H.V. =

n 201.6

7

where n is the number of double bonds and M is the molecular weight. In this particular case, the theoretical value is 1.7374. In the series of experimental values, recorded in Table I, the average is 1.7368. The largest absolute deviation from the average is 0.005, thus less than 0.3%.

851

V O L U M E 2 4 , NO. 5, M A Y 1 9 5 2 The expression used in calculating experimental hydrogenation values is:

H.V.

=

V p - p, 100 X ___ _ _ 10-3117 T

273.1 X 0.0898 X 760

-

where

V = volume absorbed, cc. IT’ = weight of sample, mg. 1‘ = absolute temperature p = pressure p , = partial presssure of solvent a t T o 0.0898 X 10-3 = specific gravity of hydrogen NTP Hydrogenation Rate Curves. Pure methyl oleate (6) was hydrogenated with W5 Raney nickel as catalyst ( 3 ) and 95% ethyl alcohol as solvent. Table I1 shows, in column one, the time of the readings (7’ minutes) and in column two, the concentration, C, of methyl oleate present a t the tixqe of the reading. This concentration is expressed by the volume of hydrogen still t o be absorbed. I n column three are indicated the values of the ratio In C,/C where

C, is the initial concentration-Le., the volume absorbed a t the completion of the reaction. The value of K = 1/T In CJC, shown in column four is comprised within very narrow limits, indicating that the reaction is of the first order in respect to the concentration of methyl oleate. The rate curve is this case is a straight line (rate us. C) passing through the origin (slope = K ) . The remarkable consistency of the K value is indicative of the precision attainable. LITERATURE CITED

( 1 ) Adams, R., Voorhees, V., and Shriner, R. L., “Organic Syntheses,” Collective Vol. I, p. 463, New York, John Wiley & Sons, 1948. (2) Gruen and Halden, 2. deut. OZ. u. Felt Ind., 44, 2 (1924). (3) Hadkins, H., and Billika, H. R., J . Am. Chem. Soc., 70, 695 (1948). (4) Kuhn, K., and Moller, E. F., 2. angew. Chem., 47, 145 (1934). (5) Manegold, Erich von, and Peters, F., KoZZoid Z., 85, 310 (1938). (6) Mattil, K. F., and Longenecker, H. E., Oil & Soap, 21,16 (1934).

( 7 ) Pregl, Fritz, “Quantitative Organic Microanalysis,” 3rd English ed.. p. 216, editor, H. Roth, London, J. & A. Churchill, Ltd.. 1937.

(8) Smith, H.A.,Fuzek, J. F., and hferiweather, H. T., J. Am. Chem. Soc., 71, 3765 (1949).

RECEIVED for review August 27, 1951. Accepted February 5 , 1952.

Microdetermination of Aldrin and Dieldrin by Infrared M. D. GARHART, F. J. WITMER, AND Y. A. TAJIMA Physical and Physico-chemical Laboratories, Julius Hyman & Co., Denver, Colo. Toxicological and field residue studies that were prerequisites to the marketing of the new insecticides, aldrin and dieldrin, necessitated the development of analytical micromethods applicable for such studies. Infrared spectrophotometry was chosen as the analytical tool most likely to have the necessary selectivity and sensitivity. Procedures were thus developed with sensitivities of 0.0005 and 0.0007% for aldrin and dieldrin, respectively, with a probable error of &O.OOl%. Accuracy was attained by refinements of usual infrared spectrophotometric techniques. Absorption microcells were used to attain sensitivity. By the use of these methods of analysis, and techniques for preparations of samples described elsewhere in the literature, it has been possible to carry out a large scale program of toxicological and field residue studies on aldrin and dieldrin.

T

HE new alkali-stable polychloro organic insecticides, aldrin (Compound 118) and dieldrin (Compound 497) were reported in 1949 by Lidov et al. ( 5 ) . Dieldrin is the epoxy derivative of aldrin (Figure 1). Aldrin is used here in reference to the active ingredient 1J2J3J4J10J10-hexachloro-1,4,4a,5,8,8a-hexahydro-lJ4,5,8-dimethanonaphthalene.Dieldrin is used in reference to the active ingredient 1,2,3,4,10,10-hexachloro-6,7-epoxy1,4,4a,5,6,7,8,8a-octahydro-1,4,5,8-dimethanonaphtha~ene. The widespread use of these insect toxicants in toxicological studies and field residue studies with sprays and dusts necessitated the development of sensitive and specificanalytical methods. A colorimetric method for the determination of aldrin, described by Danish and Lidov (3), involves the reaction of aldrin with phenyl azide to form aldrinphenyldihydrotriazole. The triazole is then coupled with diazotized 2,4-dinitroaniline, producing a highly colored product. The intensity of the color is determined a t 515 mp. An analytical method was required for dieldrin and a complementary method for the determination of aldrin was also desired. The infrared spectrophotometric methods described here were devised to fulfill these needs, and have been found sensitive t o 1 t o 2 micrograms of dieldrin or aldrin. The spectra of aldrin and dieldrin are shown in Figures 2 and

ALDRIN

DIELDRIN

Figure 1. Planar Representation of Aldrin and Dieldrin

3. The 8.48-micron absorption peak of aldrin and the 10.98 micron absorption peak of dieldrin were chosen for the determinations. It is possible that aldrin and dieldrin would interfere with each other if present in the same solution. Aldrin and dieldrin were not used together in the entomological and toxicological tests. The quantity of insecticide in a sample is related to the height (intensity) of the absorption peak. The essence of this project was the determination of this relationship with the