quired for different amounts of nickel, copper, and chromium in the presence and absence of cobalt (to a maximum of 100 p g . ) are shown in Table I. These results were obtained by following the extraction technique detailed in Procedure, the exceptions being that the iron interference was tested with and without fluoride present and the others were tested with a standard addition of 5 ml. of fluoride. The resistance of the iron complex to complete decomposition (following two acid washes as in Procedure) and the removal of iron interference with ammonium fluoride is also indicated. The introduction of a second alkali wash removes the free naphthol which is liberated when the last traces of inter-
fering complexes are decomposed by the final acid treatment. This reduces the blank value, particularly at 362 mp. The results given in Table I, size of reagent blank, and the sensitivity of the reagent to cobalt, taken together, enabled the construction of the table given in the Procedure which relates cell size, sample aliquot, and amyl acetate volume to the expected cobalt content. The method can be applied to alloys of nickel and copper by suitable selection of aliquot and reagent volumes (see Tables I and 11). LITERATURE CITED
(I) American Society for Testing Naterials, "ASTM Methods of Chemical
Analysis of Metals," pp. 54-5, Philadelphia, Pa., 1964. (2) Boyland, E., Analyst 71, 230 (1946). ( 3 ) British Standard 1121, Part 42, 1961. (4) Claassen, A,, Daamen, A., Anal. Chim. Acta 12, 547 (1955). (5) . , Cozan. E.. AXAL. CHEM. 32. 973 (1960). ' ' (6) Rooney, R. C., rMeta2lurgia 58, 205 il9)nS). (7j-zm:, 6 2 , 175 (1960).
XAWJEL NEEDLEMAN
Department of Supply Defence Standards Laboratories Australian Defence Scientific Service hlaribyrnong, Victoria, Australia The author thanks the Chief Scientist, Autralian Defence Scientific Service, Department of Supply, Melbourne, Victoria, Australia, for permission to publish this paper.
Spectrophotometric Deterrnina tio n of Cyclohex a none Oxime in Sulfuric Acid Solution of Epsilon-Caprolactam SIR: RIost of the current industrial processes for the production of t-caprolactam involve the 13eckmann rcarrangement of cyclohexanone oxime in concentrated sulfuric acid. This reaction proceeds nearly quantitatively and a very small amount of the oxime remains unchanged in the Ueckrnann rearrangement solution. .A number of methods for the quantitative determination of the olime have been reported-e.g., the gravimetric determination of the oxime by 2,4-dinitrophenylhydrazine (4, the spectrophotometric determination of 1chloro-1-nitrosocyclohexane(9) or formhydroxaniate (3) derived from oxime, and polarography ( I O ) , However, these methods have many limitations, e-pecially for the determination of trace amounts of the o\;ime. The present paper report- a novel method for the determination of trace amounts of the oxime in wlfuric acid wlution of t-caprolactam. It is ha-ed on the analysis of an azo dye compo-cd of sulfanilamide 1-naphthyl)-ethylenediamine, a and -Y-( proccdure firqt uied hy Shinn (8) in the determination of nitrous acid. Also included 1- a quantitative modification of Feigl's spot test ( 2 ) ,in which an azo dye composed of sulfanilic acid and 1-naphthylamine, the Griess-Ilosvay reagent (5, 6 ) , is ana1yzc.d. .A comparison betneen Shinn'q reagent and the Griess-Ilosvay reagent is described. EXPERIMENTAL
hbsorbance measurements were made with a Hitachi EPU-2 spectrophotometer in a 1.000cm. quartz cell. p H determinations were made with a Hitachi-Horiba AI-3 type p H meter with a glass electrode. Apparatus.
Reagents. *A 0.2% sulfonamide solution was prepared by dissolving 0.2 gram of sulfanilamide in about 70 nil. of distilled water on a water b a t h a t 50" C., followed b y dilution t o 100 ml. with distilled water. A 0.1% N-(1-naphthyl)-ethylenediamine dihydrochloride solution was stored in a red bottle. Iodine-acetic acid solution was prepared by adding 1 . 3 grams of iodine to 100 ml. of glacial acetic acid; t h e supernatant liquid was used after undissolved iodine settled. Procedure. Ten grams of the Beckm a n n rearrangement solution [cyclohexanone oxime is usually rearranged with more t h a n 1.5 molar ratio of sulfuric acid at 110' t o 120' C. (4)] of cyclohexanone osime is weighed accurately and then brought t o a total volume of 250 nil. with distilled water. T h e diluted Beckmann rearrangement solution (26 ml.) is pipetted into a conical flask equipped with a condenser, and 1 N sulfuric acid is added t o make t h e solution contain approximately 1.72 grams total weight of sulfuric acid in order to obtain a suitable p H range in t h e color reac-
Then, 5.0 ml. of the iodine-acetic acid solution is added a t a temperature below 10' C., followed by the addition of 10 ml. of a 50% aqueous solution of sodium acetate. The solution is kept a t a temperature between 14' and 18' C., and excess iodine is decomposed by addition of O.1N sodium thiosulfate solution. Ten miililiters of the 0.1% S-(1-naphthyl)ethylenediamine dihydrochloride solution is added and diluted accurately to 250 nil. with distilled water. T h e absorbance is read a t 540 inp after 2 minutes. Equivalent amounts of the reagents are added t o distilled water in t h e reference cell. RESULTS AND DISCUSSION
Color Reaction. The color reaction involved may be indicated by the fo!!owing successive reactions : Cyclohexanone oxime is readily hydrolyzed in acidic media to cyclohexanone and hydroxylamine, which is oxidized quickly and quantitatively into nitrous acid by iodine in acetic acid solution.
NOH
0
+
+
-
+
",OH 212 HZO HNO, 4HI (2) tion. T h e solution is refluxed for 1 When Reaction 2 is carried out in the hour. After cooling, 5.0 ml. of t h e presence of sulfonamide, the nitrous acid 0.2% sulfonamide solution is added. produced serves as a diazotization agent. 8
0
N m I
VOL. 38, NO. 7, JUNE 1966
917
4.0 ? 70
x
Y
3.5
E
2 2
a
3.0
2 LL
2I
P.5 P.0 2.5 3.0 PH IN COLOR DEVEL. REACTION
3.5
Figure 1. Dependence of molar absorptivity of cyclohexanone oxime on pH in color development reaction
Therefore, Reaction 4 between nitrous acid and hydriodic acid can be suppressed. 2x02'
+ 21' + 4H' 1 2 + 2Hz0 + 2x0
(4)
After removal of excess iodine, p-sulfanioylbenzenediazoniuni salt formed is coupled with A'-(1-naphthyl)-ethylenediamine to produce an azo dye, p-{ 4- [ (2aminoethyl) - aminolazo )benzenesulfonamide. I n order to obtain good precision, accuracy, and high sensitivity, a stable azo dye having high absorbance must be formed.
I n addition, Reaction 4 must be suppressed as completely as possible, for which purpose an easily diazotized aromatic amine must be selected. Satisfying these requests, our method using Shinn's reagent proved to be superior as follows: (1) The time re-
Table I. Dependence of Molar Absorptivity of Cyclohexanone Oxime on the Composition of Sulfuric Acid Solution of e-Caprolactam
quired for color development is decreased to 2 minutes or less. When the Griess-Ilosvay reagent is used, for 10 minutes to half an hour is required to obtain complete coloration. (2) As the color developed is stable, the absorbance remains unchanged for more than 3 hours and good precision is obtained. (3) Both sensitivity and solubility are higher, when compared with the GriessIlosvay reagent. Effect of p H . By changing the quantity of sulfuric acid added, the relationship between molar absorptivity and p H a t color development was investigated (Figure 1). Maximum molar absorptivity, the value of which is 3.93 X lo4,is observed a t pH = 3.05. p H effect can be explained as follows: Although the rate of Reaction 4 is decreased with the decrease of p H ( I ) , Reaction 3 is accelerated a t a lower p H range because the rate of diazotization is determined by the amounts of both the ammonium form of aromatic amine and the nondissociated form of nitrous acid (12). In addition, Reaction 5 does not take place in the ammonium form of the amine (If). Therefore, a lower or higher p H range is unsuitable. The results show that maximum molar absorptivity is observed at p H 3.05. Effect of Acetic Acid Added. Oxidation of hydroxylamine t o nitrous acid takes place smoothly only when carried out in acetic acid solution. However, the excessive addition of acetic acid lowers p H a t the color develop-
c
4.0
-
3.8
'
$ Y
zK 3.6 .
; 2
P.4 .
(L
; I
3.P
Composition of soln. (70 by wt.) E-
Caprolactam
Sulfuric acid
Molar absorptivity
0 80 90 100
100 20 10 0
3.7-3.5 x 104 3.6 3.3 3.0
918
ANALYTICAL CHEMISTRY
a
X
3.0
'
'
0 1 .o P.0 ACETIC ACID (ml./P50 ml. COLOR DEVEL. SOLN.)
3.0
Figure 2. Dependence of molar absorptivity of cyclohexanone oxime on added quantity of acetic acid to color development solution at p t l 3.05
i
! 0
5
10
15
PO
TEMP. "C.
Figure 3. Dependence of molar absorptivity of cyclohexanone oxime on temperature in diazotization and coupling reactions 0
A
Diazotization Coupling reaction
ment reaction. I n the experimental procedure described above, the effect of the quantity of acetic acid added upon the molar absorptivity was investigated. *is shown in Figure 2 it is suitable to add 0.5 to 1.0 ml. of acetic acid. Effect of Temperature. T h e effect of temperature is shown in Figure 3. There is a rapid decrease of molar absorptivity above 10' C. This indicates thermal unstability of the diazonium salt. However, the coupling reaction is too slow a t a lower temperature and it must be carried out above 14' C. Effect of Presence of e-Caprolactam and e-Aminocaproic Acid. To a series of sulfuric acid solutions of e-caprolactam, a known amount of cyclohexanone oxime was added and the niolar absorptivities of the solutions were compared. Table I shows that prefence of e-caprolactam affects only slightly the molar absorptivity of cyclohexanone oxime. However, no effect i3 observed by the presence of e-aminocaproic acid. Therefore, the complete hydrolysis of €-caprolactam is recommended. Effect of Ferrous and Ferric Ions. In the determination of nitrous acid using the Griefs-Ilosvay reagent, Rider ( 7 ) showed 10 p.p.m. of iron formed precipitates with 1-naphthylamine and a 4% deviation was observed in the presence of 40 p.p.m. of ferrous ion. On the other hand, in the determination of the oxime using Shinn's reagent, neither ferric nor ferrous ions affect the molar absorptivity, when present in amounts less than 5,000 p.p.ni., respectively. Measurable Range. Ten to 700 p.p.m. of the oxime can be measured. Contents higher than 700 p.p.m. of cyclohexanone oxime cause precipitation of the azo dye. This defect can be partly improved by the addition of alcohol.
Table II. Precision of the Recommended Procedure Results, yo Range, % 0.0063 0 0138 0 Ol5S 0.0056 0.0257 0.0564
0.0066 0.0146 0.0155 0.0055 0.0258 O,O538
0.0066 0.0130 0.0161 0.0055 0.0257 0.0535
0.0003 0.0022 0.0006 0,0001 0.0001 0.0029
Quantitativity of Successive Reactions. If Reaction 4 can be suppressed completely, the molar absorptivity of cyclohexanone oxime muqt be equal t o t h a t of nitrous acid. 13s adjusting to pH 3.05 a t the color reaction and controlling the temperature at the diazotization and the coupling, the same molar absorptivity is obtained when diazotization is carrried out starting from nitrous acid, hydroxyl-
amine, and cyclohexanone oxime. This means that successive Reactions 1, 2, 3, and 5 proceed quantitatively. Accuracy and Precision of Recommended Procedure. Known amounts (200-500 p.p.m.) of cyclohexanone oxime added t o the mixture composed of 36.5% by weight purified 6-caprolactam and 63.5% concentrated sulfuric acid were determined. The maximum error was 8 p.p.m. Good precision was obtained by the procedure and examples are shown in Table 11. I n the neckmann rearrangement of both cyclohexanone oxime and its dihydrochloride using 100% concentrated sulfuric acid (the molar ratio was 2.5) a t 115’ C., the unchanged oxime was 311380 and 243-278 p.p.m., respectively. LITERATURE CITED
(1) Chakravarti, K., Sengupta, K. K.,
J.Indian Chem. SOC.41,861 (1961).
(2) Feigl, F., “Spot Tests in Organic Applications,” p. 161, Elsevier, Amsterdam, 1954. (3) Filippov, M. P., Ruch’eva, X. I., Kodner, M. S., Zavodsk. Lab. 29, 549 ( 1963). (4) Fukumoto, O., Kogyo Kagaku Zasshi 64, 1285 (1961). (5) Griess, P., Ber. 12, 427 (1897). (6) Ilosvay, L., Ilosvay, N., Bull. SOC. Chim. 2. 247 (1889). (7) Ride
