hydrochloride in toluene on the Teflon was used as the stationary phase. It was found experimentally that 22.5 ml of 2M hydrochloric acid were required to elute 2-naphthol-3,6disulfonic acid disodium salt to its maximum concentration. This compared favorably with a maximum elution volume (a) of 18.7 ml calculated using the equation, 0 = Vm DV,
+
where 0 is the volume needed to elute to maximum solute concentration; V, = 2.6 ml, the volume of the stationary phase; V , = 5.4 ml, the volume of the mobile phase; D = 5.12, the distribution ratio. This and other examples showed that the actual column behavior can be reliably predicted from a knowledge of column parameters and the use of an expression which was originally designed to describe solvent extraction behavior.
Several quantitative column separations of sulfonic acids with similar functional groups present were obtained with a Teflon column with 5% (v/v) Alamine 336 hydrochloride in toluene as a stationary phase. The distribution ratios for 2-naphtho1-3,6-disulfonic acid disodium salt, 2-naphthol-6sulfonic acid sodium salt, and 2-naphthol-8-sulfonic acid sodium salt in 2M hydrochloric acid are 5.12, 12.3, and 39.6, respectively. Using this technique it was possible to separate two sulfonic acids whose separation factor was only 3.2 with no difficulty on a 1.3 X 7.6 cm Teflon column using a flow rate of 0.5 ml/min. The first component was eluted with 2M hydrochloric acid, and the second component was stripped off with 0.1M perchloric acid. The results of these separations are given in Table V. RECEIVED for review May 20, 1968. Accepted July 1, 1968.
An Ion Exchange Method for the Determination of Aliphatic Amides and Esters Mohsin Qureshi, Saidulzafar Qureshi, and Suresh Chandra Singhal Chemical Laboratories, Aligarh Muslim Uniaersity, Aligarh, (U.P.),India An ion exchange method for the determination of amides and esters has been developed. The amide or ester is passed through a 30 X 0.8 cm (i.d.) column of Amberlite IR-120 resin in the Hf form at a flow rate of 2 ml per minute. The column is maintained at a temperature of 80 O C . The effluent is recycled three times and is finally titrated with standard alkali. The method is simple, fast, reproducible, and suitable for water soluble aliphatic amides and esters.
DETECTION AND DETERMINATION of esters and amides have received considerable attention during recent years (1-16). Some novel methods for the detection of these substances are based on the use of ion exchange resins and enzymes (14-16). The classical method for the determination of esters and amides based on saponification is tedious and time-consuming. The limitations of the classical methods have been admirably (1) B. V. Ioffe and Z . I. Sergeeva, Zhur. Anal. Khim., 12, 540 (1957). (2) David C. Winner, ANAL.CHEM., 30, 77, 453 (1958). (3) H. Roth and Ph. Schuster, Mikro. Chim. Acta, 6, 837 (1957). (4) Vivian Goldenberg and Paul E. Spoerri, ANAL.CHEM.,30, 1327 (1958). (5) Willard T. Haskins, ANAL.CHEM., 33,445 (1961). (6) Leonard0 Colapinto, Chimica (Milan), 12, 334 (1956). (7) Charles A. Reynolds, Record Chem. Progr., 24 (3), 157 (1963). (8) William R. Post and Charles A. Reynolds, ANAL.CHEM., 36, 781 (1964). (9) Theodore M. Bednarski and D. N. Hume, Anal. Chim. Acta., 30, 1 (1964). (10) J. Berger and I. Uldall, Acta. Chem. Scand., 18, 1311 (1964). (1 1) Sidney Siggia, “Quantitative Organic Analysis via Functional Groups,” 2nd. Ed., John Wiley & Sons, New York, Chapman & Hall, Ltd., London, 1954, pp 46-7. (12) R. D. Tiwari, J. P. Sharma, and I. C. Shukla, Talanra, 13, 499 (1966). (13) Joe A. Vinson, James S. Fritz, and Charles A. Kingsbury, Talanta, 13, 1673 (1966). (14) P. W. West and Mohsin Qureshi, Anal. Chim. Acta, 26, 506 (1962). (15) P. W. West, Mohsin Qureshi, and S. Z. Qureshi, Anal. Chim. Acta., 36, 97 (1966). (16) Mohsin Qureshi and S. Z . Qureshi, Anal. Chim. Acta., 34, 108 (1966).
discussed by Bednarski and Hume (9). Moreover, the classical method is applicable only to macrogram quantities. After saponification, either back titration is used or an ion exchange procedure is used to get rid of excess alkali (9, 12). As far as we are aware no attempt has been made to use ion exchange resins both for hydrolysis and for the release of an equivalent amount of the acid. The present communication describes the catalytic hydrolysis of esters and amides quantitatively by ion exchange resin in H+ form. This method is based on our previous work on qualitative analysis (15,16). The ion exchange method offers many advantages over the earlier methods: The hydrolysis of esters and amides is done using ion exchange resins as catalysts. Ion exchangers are selective and more efficient catalysts, and this can be utilized in developing more selective procedures. The ammonium salt formed in cases of amides is automatically converted into the corresponding acid by the resin in the H+ form which also acts as an exchanger. The method therefore becomes simpler, faster, and more compact. EXPERIMENTAL
Apparatus. ION EXCHANGE COLUMN.A 60 cm long column (borosilicate glass) provided with outer and inner tubes (id. 3.3 cm and 0.8 cm, respectively) is used. The upper portion of the column is fitted with a small funnel and the lower portion with a glass stopcock. The resin in H+ form is filled in the inner tube up to a height 30 cm over a glass wool bed. There are two holes in the outer tube. The lower hole is connected with a steam bath through a rubber tube; the upper hole serves to pass out the steam. The temperature (80 “C) of the inner tube remains constant throughout the experiment. Reagents. All chemicals used were of reagent grade. Amberlite IR-120 resin was used in Hf form. Amides and esters solutions were prepared in demineralized water: formamide 0.50% (v/v); acetamide 0.20 % (wtiv); propionamide 0.20 (wtiv); N-N-dimethyl formamide 0.50% (v/v); ethyl formate 0.50% (v/v); ethyl acetate 0.40% (v/v); ethyl malonate 0.40 (v/v); ethyl cyanoacetate 0.40% (v/v); n-valeramide 0.40 % (wtiv); N-methyl formamide VOL. 40, NO. 12, OCTOBER 1968
1781
Amide Formamide
Acetamide
Propionamide
N-N-dimethyl formamide Valeramide
N-methyl formamide Chloroacetamide
Succinamide
Ester Ethyl formate"
Table I. Determination of Amides by Ion Exchange Method Amount taken, mg Amount found, mg No. of detn Recovery, % 2.26 3.39 4.52 5.65 1.00 1.60 2.00 2.80 1.96 2.35 2.74 3.54 2.37 2.85 3.79 4.74 4.00 5.60 7.20 8.00 2.02 3.03 4.04 5.05 3.00 4.00 5.00 6.00 2.40 2.88 3.84 4.80
2.25 3.39 4.50 5.61 0.99 1.59 2.00 2.80 1.94 2.36 2.72 3.55 2.36 2.86 3.78 4.72 3.98 5.65 7.22 8.03 1.99 3.02 3.99 5.07 2.98 3.99 5.01 6.00 2.39 2.84 3.82 4.75
4 5 5
*
4 4 4 5 5 4 4 4 5
4 4 4 4 4 4 4 4 4 3 4 4 5
4 4 4 4 4 5 5
99.6 100.0 99.6 99.3 99.0 99.4 100.0 100. 0 99.0 100.4 99.3 100.3 99.6 100.3 99.7 99.6 99.5 100.9 100.3 100.4 98.5 99.7 98.8 100.4 99.3 99.8 100.2 100.0 99.6 98.5 99.5 98.9
Table 11. Determination of Esters by Ion Exchange Method Amount taken, mg Amount found, mg No. of detn Recovery,
1.65 2.06 2.47 2.88 Ethyl acetate 2.16 2.88 3.96 4.75 Ethyl malonate 1.68 2.10 2.94 4.10 Ethyl cyano2.13 acetateb 3.40 3.85 4.25 Temperature maintained at 40 "C for the reaction.
1.63 2.05 2.47 2.88 2.16 2.85 3.92 4.76 1.67 2.08 2.90 4.04 2.12 3.38 3.85 4.25
4 4 5 4 4 4 4 4
98.8 99.5 100.0 100.0 100.0 99.0 99.0 100.2 99.5 99.1 98.7 98.5 99.5 99.4 100.0 100.0
Std dev, 0.65 0.00 0.00 0.00 0.00 0.00 0.49 0.88 0.00 0.00 0.00 0.90 0.00 0.00 0.90 0.00 0.70 0.00 0.68 0.90 0.81 0.00 0.25 1.00 0.00 1.00 0.50 0.00 0.42 0.50 0.73 0.80
Std dev, % 0.00 0.40 0.37 0.00 0.00 0.60 0.00 0.00 0.32 0.40 0.60 0.20 0.40 0.70 0.00 0.00
(1
b
Experiments show that under the conditions of this determination, the hydrolysis of ethyl cyanoacetate involves only the ester and not Cyanoacetic acid does not hydrolyze significantly under the conditions of the experiment.
the nitrile.
0.50 (v/v); chloroacetamide 0.50 (wt/v) and succinamide 0.08 (wtiv). All the solutions were standardized by the saponification method (11). A standard solution of 0.05Nsodium hydroxide and phenolphthalein indicator were used. Ion Exchange Procedure. An accurately measured (0.4-2 ml) sample solution is taken in a 100-ml beaker and mixed with approximately 10 ml of demineralized water. It is transferred to the inner tube which has been previously adjusted to a constant temperature by passing the steam in the 1782 *
ANALYTICAL CHEMISTRY
outer tube. The stopcock is opened and the effluent is collected in an Erlenmeyer flask at the rate of 2 ml/minute. The effluent is recycled for three or four times. Then the column is washed with 100 ml of hot water. The effluent is collected in the same flask and is titrated with sodium hydroxide solution using phenolphthalein as indicator. The time varies from 20 to 40 minutes with increase in C atoms in amide or ester for a single determination. A blank determination is carried out under identical conditions, and this value is subtracted from the original reading. The weight and the per-
centage of the substance can be calculated from the following formulas : Weight of amide or ester
=
Volume of NaOH soln. (ml) x eq wt of sample Normality of NaOH s o h X 1000 amide or ester =
Weight of sample found x 100 Weight of sample taken RESULTS
Table 111. Effect of Common Organic Compounds in Determination of Amides by Ion Exchange Method Amide Compound addeda Found, Formamide Acetone 98.5 n-Butanol 98.5 98.8 Formaldehyde Diet hanolamine 99.5 Iso-butyl methyl loo. 0 ketone Added in 50 fold weight excess over amide. times are 30 minutes. Q
Results for determinations of amides and esters are summarized in Tables I and 11. EFFECT OF ORGANIC COMPOUNDS ON DETERMINATION
A study of the effect of substances likely to interfere with the quantitative determination of amides showed no interferences. DISCUSSION
When aqueous solutions of the sample come into contact with heated cation exchange resin (H+ form), they hydrolyze the sample quantitatively into corresponding carboxylic acid. In the case of an amide, the ammonia gas formed reacts with the acid to give the ammonium salt. The ammonium ions of the salt exchange with hydrogen ions of the resin converting the resin in NH4+ form. The mechanism of the reaction is therefore : ESTERS R’COOR”
+ HOH
RH+ -t
R’COOH free acid
+ R”OH
(R’ = H or alkyl group)
(1)
hIDEs RH+
+ HOH +COOH + NHs NHa + 6COOH +COONH4 +COONHi + RH+ e +COOH + R +CONH2
-t
-t
”4’
free acid (@ = H or alkyl group)
(2)
The free acid liberated in the two cases is titrated with a standard solution of sodium hydroxide. The method gives very good results in the case of aliphatic amides and esters. The data on the kinetics of amides by ion exchange resins is needed. The work of Bolton and Henshall (17) shows that the rate constant decreases as we go from acetamide to butyr(17) P. D. Bolton and T. Henshall, J. Chern. Soc., 1962, 1226.
All reaction
Table IV. Rate Constants for Amides (17) Rate constant in 10-8 Amides Temperature mole-’ sa-’ Acetamide Propionamide Butyramide Iso-butyramide N-methyl acetamide N-N-dimethyl acetamide
63.05 62.70 63.20
62.70 63.10 63.10
0.205 0.280 0.157 0.174 0.009
0.010
amide, and it appears that the rate constant of valeramide may be either equal to or less than that of butyramide. Because valeramide was successfully determined, it should be possible to determine butyramide and iso-butyramide by this method, also. In the case of N-N-dimethylacetamide, the rate constant becomes too small and the method fails. For similar reasons, the method does not work with benzamide and other aromatic amides. This method is equally applicable to both amides and esters. The sulfoxide method (13), which gives good results with esters, is not applicable to amides. In the ion exchange method, no excess alkali or acid is added. The acid is added in the form of an easily separable solid ion exchanger which hydrolyzes the amides and esters and, after hydrolysis, which can be easily separated from the bulk of the solution. Therefore, the method increases in sensitivity and selectivity. The results in Table I11 show that the common organic impurities do not interfere in the ion exchange method. ACKNOWLEDGMENT
The authors thank A. R. Kidwai for research facilities. RECEIVED for review October 17, 1967. Accepted June 5 , 1968. Thanks are due to the C.S.I.R. India, for financial assistance given to one of us (S.C. Singhal).
VOL. 40, NO. 12, OCTOBER 1968
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