~~~
Table II.
Aliphatic Monocarbonyl Content of Various Organic Solvents ~l~~ Aliphatic 2,4-Dinitrophenylhydazones Found. 3rd ass Rate 1st pass Max.b 2nd ass Max.*
(Ml./Hr.) (pmole/l.) (mp) (pmore/l.) (mp) (pmope/l.) Solvent 50 8 362 0 ... Benzene 58 0 .. ... Carbon tetrachloride 47 7 362 0 ... Chloroform Cyclohexane Ethylene chloride n-Heptane n-Hexane (Fisher) 47 11 362 1 362 n-Hexane (Phillips) 37 333 362 14 362 0 Methyl cyclohexane Methylene chloride n-Pentane Petroleum ether Toluene a Calculations based on readings at maxima using a molar absorptivity of 22,500 for saturated aldehydes and ketones. b Maxima in CHCll on total derivatives. RESULTS A N D DISCUSSION
Results of the study are presented in Table 11. The efficiency of the reaction column in removing carbonyl contaminants from the various solvents studied is readily evident from the data in Table 11. Although it is to be expected that different lots of a given solvent will vary in their degree of contamination with carbonyls, relative contamination for the different solvents of a given grade should be fairly constant. The data in Table I1 could, therefore, ostensibly be used as an index for selection of a solvent. Although the work reported here was pertinent to the aliphatic monocarbonyl contaminants in the various solvents, limited experiments with aromatic carbonyls dissolved in hexane indicate that these react instantaneously on contact with the reaction column. This is manifested by the formation of a
red band a t the top of the column. This phenomenon takes place only when the aromatic carbonyl is put on the column in a solvent in which the resulting hydrazone is insoluble or feebly soluble. The data of Cheronis and Levey (2) suggest that aromatic carbonyls react more rapidly than aliphatics with DNPH. Vicinal dicarbonyls which form bis(hydrazones) also precipitate as a red zone when the parent carbonyl is put on the column in an aliphatic hydrocarbon solvent. As mentioned earlier, unwashed chloroform could not be purified on the reaction column. This is attributed to the formation of acetaldehyde via the dehydrogenation of DNPH of the ethyl alcohol used as a preservative (4). Theoretically, doubling the constituents making up the column while keeping the flow rate the same as reported in Table 11, should be as efficient as making two passes of the
solvent over a standard column. This was not attempted, since, as the data show, one pass over a standard column will purify most solvents to a satisfactory degree. The data in Table I1 were obtained on two reaction columns. In theory a reaction column can be used indefinitely, a t least for the purification of some solvents, since DKPH from the DNPHsaturated solvent displaces any DNPH lost from the column through reaction. In this laboratory a single column has been used over 6 months for the purification of benzene with no loss in efficiency. However, columns used for the purification of hexane become dark with time. This is attributed to the accumulation of decomposition products of DNPH, these being virtually insoluble in hexane. As a consequence, new columns are constructed periodically for purification of this solvent. Purification of solvents can be put on a continuous basis. At the flow rates given in Table 11, approximately 1 liter per 24 hours per column can be obtained. LITERATURE CITED
(1) Begemann, P. H., De Jong, trav. chim; 78,275 (1959). (2) Cheronis, K. D., Levey, Microchem. J. 1, 223 (1957). (3) Corbin, E. A,, Schwarts, Keenev. hl.. J . Chromatog.
(1960): '
K., Rec. V. M.,
D. P., 3, 322
(4) Caddis, -4. SI., Ellis, R., Currie,
G. T., unpublished data.
RECEIVED for review April 25 1961.
Accepted June 28, 1961. Work done at a laboratory of the Eastern Utilization Research and Development Division, Agricultural Research Service, U. S.D. A., Washington 25,,D. C. The use of trade names does not imply endorsement of the product or its manufacturer by the U. S. Department of hgriculture.
An Acid Method for the Volumetric Estimation of Water-Soluble Dithiocarbamates M. L. SHANKARANARAYANA and C. C. PATEL Department o f Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore- 1 2, India Dithiocarbamates have been estimated previously by reaction with a strong acid, the carbon disulfide evolved being converted into a xanthate and the latter estimated iodimetrically. In the present method, a water-soluble dithiocarbamate is reacted with a decinormal mineral acid and the excess acid is determined to compute the amount of dithiocarbamate present. This method is applicable
1398
ANALYTICAL CHEMISTRY
for the determination of a dithiocarbamate in a thiuram disulfide.
D
mixture containing
find a variety of applications as plant fungicides, anal! itical reagents, accelerators in the rubder industry, and collectors in the flotation of minerals. Hence, methods for their estimation are becoming more ITHIOCARBAMATES
important. I n the acid method for the determination of a dithiocarbamate, employed by Callan and Strafford (d), the dithiocarbamate is decomposed by gently boiling with 30% sulfuric acid, the carbon disulfide evolved is absorbed in alcoholic potassium hydroxide to form an alkali metal xanthate, which is estimated iodimetrically, and the amount of dithiocarbamate is computed from the titer value. In Roth
and Beck’s method (8), carbon disulfide is split off from the dithiocarbamate or thiuram disulfide by phosphoric acid (80%) in the presence of pyridine. The rest of the procedure is the same as that of Callan and Strafford (2). I n place of the mixture of pyridine and phosphoric acid, Roth has recently employed a mixture of pyridine and formic acid (7). However, these methods are rather time consuming and tedious and cannot be used for the determination of a dithiocarbamate in the presence of thiuram disulfide, since carbon disulfide is split off from both these compounds on boiling with the acids. The acid method described in this paper is simpler and compares favorably with the iodine method (9)*
When a dithiocarbamate is reacted with a known amount of a mineral acid, it gives rise to the corresponding dithiocarbamic acid (Equation 1). The latter being unstable (f), it dissociates into carbon disulfide and the respective amine (Equation 2). The amine formed reacts immediately with the acid to form amine hydrogen sulfate (Equation 3). The reactions involved are represented below, using potassium diethyl dithiocarbamate as an example:
S
C4H5
/I
\
+ H2S04
N-C-SK
2
/
CIHS
s
CZH5
\
2
/
CzH; Cas
2
\
+
/I
S-C-SH
(1)
+ K2SO4
s I!
N---C--SH*
/
C2H5
(A.R.), redistilled carbon disulfide, and diethylamine (Merck). The crystals Table 1. Results of Analysis of Dithiowere purified as described previously carbamates (9). Dithiocarbamate, SODIUM DIETHYLDITHIOCARBAMATE DithioGrams Error, (CzHs)*NCS2Na.3Hz0. The British carbamate Taken Found yo Drug Houses laboratory reagent was recrystallized from distilled water. Potassium di- 0,0802 0,0801 - 0 , 1 3 ethyl 0.0907 0.0906 -0 11 TETRAETHYL DITHIOCARBAMATE, (C, 0.44 0.0907 0.0911 H&NCSzN(C2H6)2. Prepared by the 0.18 0.1103 0.1105 addition of carbon disulfide to cooled 0.1484 0.1481 -0.20 and mechanically stirred diethylamine. 0,1484 0.1492 0.27 The resulting solid product was filtered, 0.1497 0.1495 -0.13 washed several times with petroleum 0.1707 0.1704 -0.18 ether, and dried in vacuo. 0.11 0.1774 0.1776 PIPERIDINIUM CYCLOPENTAMETHYL0.22 0.1774 0.1778 0.3548 0.3540 -0.22 ENE DITHIOCARBAMATE, C6&oNCS2H20.11 0,3548 0.3552 NC6HI0. Prepared as suggested by Elderfield (4) and purified further by Sodium diethyl 0.0605 0.0602 -0.49 washing repeatedly with petroleum 0.0736 0.0734 -0.26 ether. This compound is not too solu-.__-_ 0.1172 0.1168 -0.34 ble and takes a long time to dissolve in 0.1227 0.1223 -0.32 water. For quick work, the compound 0.2064 0.2053 -0.53 can be dissolved easily in dilute alcohol or acetone. Tetraethyl 0.0638 0.0636 -0.31 All these compounds were dried and 0.0648 0.0646 -0.30 preserved in vacuo. They were ana0.0879 0.0875 -0.45 lyzed iodimetrically (9) and found to be Piperidinium 0.0398 0.0396 -0.50 over 99.7% pure except sodium diethyl pentamethyl- 0,0796 0.0793 -0,37 dithiocarbamate, which was found to be ene 0.0876 0.0872 -0.45 99.5% pure. Solutions containing 0.5 0.0994 0.0991 -0.30 to 3% dithiocarbamate were prepared in distilled water. Piperidinium pentamethylene dithiocarbamate solution was prepared sometimes in 10% alcohol. and the mixture was kept aside for THIURAM DISULFIDE. Prepared by 20 minutes for the completion of the the oxidation of potassium diethyl reactions. The excess acid was then dithiocarbamate by iodine, as suggested back-titrated with 0.1N sodium hyby Grodzki ( 5 ) . The product was droxide. From the data, the amount of washed several times with distilled acid consumed was computed, and the water and recrystallized from petroleum weight of the dithiocarbamate calether. A solution containing 0.5 to culated. 2% of thiuram disulfide was prepared in acetone or alcohol. The compound in solution was inert to 0.1.V sulfuric acid. 1 M1.1N Ha01 = Procedure. Dithiocarbamate solumol. wt. of dithiocarbamate grams tion (10 ml.) n-as pipetted into a 2 x 1000 conical flask and neutralized, if necessary, with acetic acid (0.05.2’) using phenolphthalein indicator. Then 30 The results obtained with different dithiocarbamates are given in Table I. ml. of 0.lN sulfuric acid were added,
C2H5
\
2
NH
/
+ 2CS2
(2)
CZHS
Table II.
Results of Analysis of Dithiocarbamate in Presence of Thiuram Disulfide
CZHI
2
\
/
NH
+ HzSOi-
C?HS
DithiocarbamatP Potassium diethyl
Sodium diethyl The over-all reaction shows that 1 mole of the dithiocarbamate consumes 1 mole of sulfuric acid. Similar reactions are expected with other watersoluble dithiocarbamates.
Tetraethyl
EXPERIMENTAL
Reagents. POTASSIUMDIETHYL Piperidinium pentamethylene DITHIOCARBAMATE, (CZHS)ZNCS~K. Prepared as suggested by Delepine (3) employing potassium hydroxide
Mixture, Gram DithioThiuram rarbamate disulfide 0 0721 0 0956 0 0633 0 0499 0 0633 0 0988 0 1396 0 0456 0605 0005 0878 0926 0926 1456 3034 0.0638 0.0638 0.0879 0 0879 0 0876 0 0920 0 P 0 0 0 0 0
0650 1300 0439 0500 lo00 1642 1642 0,1098 0,2196 0,0923 0 1846 0 1210 0 1210 0 0 0 0 0 0 0
VOL. 33,
Dithiocarbamate
Error,
Found, G. 0 0719 0 0630 0 0630 0 1393
-0 -0 -0 -0
34 47 47 21
0602 0602 0873 0922 e922 1451
-0 -0 -0 -0 -0 -0
49
0 3019
-0
49
0.0636 0.0636 0.0875 0 0875 0 0872 0 0914
-0,31
0 0 0 0 0 0
NO. 10, SEPTEMBER 1961
“c
49
56 43
43 34
-0 31
-0.45
-0 45
-0 45 -0 65
1399
The results of analysis given in Table I show that water-soluble dithiocarbamates can be estimated with an error not greater than 0.5%.
DISCUSSION
ACKNOWLEDGMENT
Recently, Martin (6) reported that the mechanism of decomposition of dithiocarbamate is not clear in the ESTIMATION OF DITHIOCARBAMATE IN PRESENCE OF THIURAMDISULFIDE. presence of an acid. The quantitative Dithiocarbamates are oxidized to the results obtained by the present method corresponding thiuram disulfides on explain the validity of the proposed exposure to the atmosphere. It was, simple mechanism for the decompositherefore, thought desirable to estimate tion of the dithiocarbamate and the a dithiocarbamate in the presence of corresponding acid. as given by the thiuram disulfide to find out the appliEquations 1 and 2. The dithiocarbamic cability of the present method. For this acid is so unstable that after mixing purpose, dithiocarbamate in aqueous the solution of the dithiocarbamate and solution and thiuram disulfide in acetone or alcohol were mixed. If a turbidity the mineral acid, the over-all reaction, is developed in the mixture, a clear according to the Equations 1 to 3, solution is obtained by the addition of exceeds 95% in as short a time as 2 acetone or alcohol. The dithiocarminutes. bamate in the mixture was then estiSoni and Trivedi (10) infer from the mated as described above. The result,s pH and the conductometric measureof analysis are given in Table 11. The ments that sodium diethyl dithioresults of Table I1 show that a dithiocarbamate is a diacidic base and carbamate can be estimated with a diethyl dithiocarbamic acid is an amphonegative error of less than 0.6% in the lyte. The present investigation does not presence of thiuram disulfide by the acid support this view. method.
The authors thank M.R.A. Rao for
his interest in the work. LITERATURE CITED
(1) Bode, H., Neumann, F., 2.anal. Chem. 169,410 (1959). (2) Callan, T., Strafford, N., J. SOC. Chem. Ind. (London)43,1(1924). (3) DelBpine, M.,Bull. SOC. chim. France 3,643 (1908). (4) Elderfield, R. C., “Heterocyclic Com666,Wiley, New York, 1950. poundsJJJp. (5) . , Grodzlu. M.. Ber. deut. chem. Gea. 14,2754(1881j. (6) Martin, A. E.,ANAL.CHEM.25, 1260 (1953). (7) Roth, H.,Angew. C h m . 73, 167 (1961). (8)Roth, H.,Beck, W., Mihrochim. Acta 1957. 844. (9) Shankaranarayana, M. L., Patel, C. C., 2.anal. Chem. 179,263 (1961). (10) Soni, K.P.,Trivedi, A. M., J . Indian Chem. SOC.37,349 (1960).
RECEIVED for review December 13, 1960. Accepted June 9,1961.
Spectrophotometric Determination Of 2-Furaldehyde, 5-(Hydroxymethyl)-2-f ura Idehyde, Cinna maldehyde, and Citral with p-Aminodimethylaniline and m-Phenylenediamine PEKKA LINK0 Department of Flour and Feed Milling Industries, Kansas State University, Manhattan, Kan.
b Sensitive spectrophotometric methods were developed for the quantitative determination of 2-furaldehyde, 5-(hydroxymethyl)-2-furaldehyde, cinnamaldehyde, and citral. These compounds were determined individually by measuring the absorbance of the color developed at room temperature with 0.025M p-aminodimethylaniline (p-ADA) at 495, 495, 510, and 466 mp, respectively. 2-Furaldehyde gave a specific violet color with m-phenylenediamine (m-PhDA) in the presence of oxalic acid. Employing m-PhDA and p-ADA, respectively, 2-furaldehyde and 5-(hydroxymethyl)-2-furaldehyde could be determined quantitatively in the presence of each other.
I
N CONNECTION with a study of non-
enzymatic browning of wheat and wheat products, a sensitive method for the determination of 2-furaldehyde (F) and 5-(hydroxymethyl)-2-furaldehyde (HMF) was necessary. Relatively small quantities to be analyzed called 1400
ANALYTICAL CHEMISTRY
for a method that would not be affected by the characteristic yellow-to-brownish color of the extracts of the material. It was also desired to determine both F and H M F in the presence of each other without removing F by steam distillation, to avoid the possible formation of these compounds during distillation (16). Keeney and Basette (9) recently developed a sensitive colorimetric method for the quantitative determination of F and its derivatives, employing the thiobarbituric acid reaction introduced by Dox and Plaisance (5). Despite its convenience and rapidity, the method was difficult to adapt for wheat and wheat germ samples because of the marked interference by the color of the extracts. The values obtained by this method during preliminary trials also appeared high, probably from the reaction of thiobarbituric acid with other compounds (3). Similarly, methods based on the characteristic absorption in the ultraviolet region (10, 13) by F and H M F proved unsatisfactory.
m-Phenylenediamine (m-PhDA) hydrochloride in the presence of oxalic acid has long been the official method for the determination of citral (2). Wearn et al. (15) extended the use of this reagent to other a,p-unsaturated aldehydes, including F. The reaction is given, however, with a number of other reactive aldehydes and ketones. Wachsmith and Leaners (14) similarly used p-phenylenediamine in acetic acid to determine cinnamddehyde. Many organic compounds (1, 4, 6, 11, 12) have been employed with varying degrees of success for colorimetric detection and quantitative determination of F. HMF, and other reactive aldehydes. Recently, Hunig et al. (8) introduced paminodimethylaniliie (p-ADA) as a very sensitive colorimetric reagent for unsaturated carbonyl compounds. Furthermore, p-ADA stannous chloride double salt is stable and easy to prepare. This reaction has now been adapted for the quantitative determination of a number of unsaturated aldehydes.
