V O L U M E 25, N O
1109
7, J U L Y 1 9 5 3
zones, the reagents are strongly adsorbed and remain a t the origin. I n the chromatographic systems studied the R f value of a compound appears to be related t o the size of the molecule and the number arid kind of functional groups which the molecule contains. h n i n c r e w in molecular weight tends to increase the I?, value, as does a decrease in the number of functional groups. Changing the nature of the functional group by means of some reaction. such as reducing a ketone to an alcohol, always results in a change of R, value, so that the separation by chromatography is easily effected. I n some cases where the product of a reaction is a highly oxygenated compound, such as the oxidation of ritral to geranic acid by chromic acid, the I?, value of the product is lonand is obscured by the acetic acid used in the reagent. Such reactions are listed in Table I11 as “no reaction.” The authors have found these reactions and their subsequent aiialysis on chromatostrips to be useful in a number of mays: t 1 j I n inany cases the compound may be positively identified h\- means of the reactions. (2) A wealth of information can be obtaine(l on a compound with the expenditure of a small amount of (*ompound. (3) Considerable time can be saved. Thus if a derivative is desired from a particular compound, its formation
may be readily checked on a chromatostrip without the necessity of extensive purification, recrystallization, etc. -4s an example, a-terpineol does not form a 3,5-dinitroberizoate, and this was quickly checked by means of the chromatostrip reaction. (4) Il-here it is desired t o perform macro reactions, the conditions of the reaction and its progress may sometimes be checked rapidly. The list of reactions presented in this paper is intended to illustrate what can be accomplished in the way of identifying constituents of essential oils by the use of chromatostrips. 0.A lation with hydrogen peroxide. nitric acid, and potassium permanganate has been tried with success, and many other reactions of a specific or general nature may be employed as the occasion arises. LITERATURE CITED
(1) Kirchner, J. G., and 3Iillei, .J. 11 , I d Eng. Chem., 44, 318 (1952). (2) Kirchner, J. C.. AIiller, J. AI., and Keller, C. J.. ANAL CHEX.,23,.
420 (1981).
( 3 ) Miller, J. XI., and Kirchner, J. G.. Ibid., 24, 1450 (1952). (4) Redemann, C. E., and Lucas, H. J., ISD. ENG.CHEY.,- ~ A L
E D ,9, 521 (1937). R E C E I V Efor D reriew January 26, 1453.
Accepted April 13, 1953.
Microanalysis of Organic Salts by the Use of Cation Exchange Resins CECIL T i . YAN ETTEY AVD . \ I i R Y B. WIELE, Sorthern Regional Research Luboratory, Peoria, I l l . The ability of unifunctioiial, high capacity synthetic resins to exchange hydrogen ions quantitatively for metallic or organic cations suggested their use for the determination of organic salts on a micro scale. Successful analyses of 46 salts of organic acids or bases are reported. The accuracj and precision of the method are indicated by an aterage recovery of 99.87q~,with a standard deviation of 0.21%, on 20 determinations of a sample of pure sodium oxalate. Results are expressed as “exchange equh alent.” The method offers the advantages of speed, simplicit?, and accuracy o+erconientional micromethods for determining organic salts.
T
HE most common micromethod for the determination of salts of organic acids is to weigh the ash from the compound as the sulfate, oxide. or free metal (4). The halogen or sulfate salt of a n organic base is commonly determined gravimetrically by precipitating the halide as the silver salt or the sulfate as barium sulfate. -in alternate method. n.hich is here described. consists of passing a solution of the organic salt through a cation exchange resin in the acid form and titrat’ing the effluent whirh contains acid equivalent to the salt content of the initial solution Wiesenherger (8) has applied this microanal>-tical techniqur to the determination of a number of inorganic salts. In a numl~er of papers. H:muelson has described similar techniques on a macro scale (5). I n addition to its simplicity and speed, the method has the follon-ing ndvant’ages: Some salts that cannot he determined bjthe ashing method without special treatment-such as salts of nickel (d)-can he determined by this method. The method is readily a1)plicable to the determination of the number of equivalents of cations in solutions without the need for evaporation. Ammonium salts of organic acids and salts of organic bases can be determined. If desired, the sodium salt of the acid can be recovered after titration of the effluent. The titration can be checked by rerunning the titrated effluent through the ion exchange column. I n most cases, the cations can be quantitatively displaced and specifically determined if desired. For example,
the ammonium ion could be eluted from the ion exchangc resin with an acid and determined by the Kjeldahl procedure. Although the method has not been compared directly with rwently reported methods for the determination of salts ( I , &7), i t apprars t’ohave advantages over them in certain applications. MATERIALS
Micro ion exchange column, as shown in Figure 1. This column was so constructed that the delivery tip was about 25 mm. below the top of the ion exchange bed. Consequent,lv, the length of the capillary side arm depends on the amount a6d mesh size of the resin used; 0 . i gram of 20- to 40-mesh ion exchange resin occupied a column length of 4 to 5 cm., whereas a like amount of 50- to 100-mesh resin required only 2.5 to 3 cni. Dones 50 ion exchange resin of the above mesh size, either 9 or 16% cross linked. Only a limited number of other ion exchange resins were tested and these were found to give low recovery (95 to 98%) of titratable acid in the efijuent. Standardized 0.01 1V sodium hydroxide. Mixed indicator, one part 0.0470 aqueous cresol red and three parts 0.04% aqueous thymol blue (color changes at pH 8.2 to 8.7) ( 2 ) . PROCEDURE
Preparation of Ion Exchange Resin. h stock supply of the ion exchange resin was prepared by allowing 8 to 10 grams of the resin t o stand for at least 30 minut,es in each of three 50-ml. portions of 3 N hydrochloric acid. It was then washed free of acid
1110
ANALYTICAL CHEMISTRY
and stored in distilkd water. Aiportion of this resin was placed in the column as described below arid tested with a standard salt, such as sodium oxalate, t o determine that the resin would give quantitative exchange. An occasional stock preparation gave only 96 to 99% recovery of acid. Such lots were either discarded or regenerated again with hydrochloric acid, and retested. Resin from used columns usually was combined and accumulated for regeneration. From those columns which had been used for metallic ions giving insoluble chlorides, or for large organic molecules which were eluted with difficulty, the resin was discarded.
i i f Tubing
2mm. Bore 4Copillary Tubing
I
Figirre 1.
Table IT.
lnalysis of Salts of Organic Bases Exchange Equig::iL No. of determinations
rlv. Mean deviation, Compound Benzyl-isothourea hydrochloride 3 202.5 1.0 A. ;I Brucine sulfate.7H’rO 3 509. ti 7 Choline 138 8 0.: - ~ ~rhloride .~~. ..~. . . ~ ~ ~ Diethylamine hydrobroniid? 3 153.4 0.i Glycine ethyl ester hydrochloride 3 138.0 0.6 Histidine hydrochloride.H?O 2 207.5 0.5 4 OR 4 0.R Hydroxylamine hydrochloride Lysine hydrochloride 4 184.0 1.0 o-Methoxvaniline hvdrochloride 3 180 5 1.5 p-Methogybenzene -diaroniuni 3 231.0 3.0 acid sulfate 6 375 5 4.3 3lorphine sulfate.5HzO Quinine hydrochloride.2H20 3 384.9G 1.7 o Results using 95% cross-linked Domes 80 only.
_
_
Theory 202 506 139.8 154.0 139.5 209.5 69.5 182.7 159.6 ?32.1 379.2 396.7
_ ~~~~
was corrected for a blank of 0.05 to 0.12 nil. determined by p:wing 25 ml. of distilled water through the column in the same n u n ner as the sample. Each deterniination required about 10 minutes of elapsed time. Potassium stearate and sodium oleate were disPolred in 80% ethyl alcohol for analysis. The resin column was pretreated with 80% ethyl alcohol before the samples were applied. Resin Capacity at Breakthrough. Successive 10-ml. samples cont,aining known amounts of the order of 0.078 meq. of catioii were passed through the column as deacribed above until the titration of the effluent showed that some of the cation was not being exchanged. -4t least 0.75 meq. could be put on the column before the loss amounted to 1%, a level considered permissible for ordinary microanalytical work. Determinations were made with solutions of barium, copper, lead, and sodium salts. The presence of different cations in successive samples had no detrimental effect on the results.
3licro Ion Exchange Column
CALCULATIONS
Method of Analysis. About 0 . i to 1 gram of the prepared resin 0.03 t o was slurried into the colunin. The sample-usually, 0.08 meq.-was weighed into a 20-ml. beaker and dissolved in 10 nil. of water. The wlution was allowed to flow through the column a t not more than 2 to 3 ml. per minute and was followed by three S m l . washes. The lesulting 25-ml. effluent was titrated to the first permanent color change, usually in a carbon diosidefree atmopphere, using 4 or 5 drops of indicator. This titration
In the same way that the titration of an organic acid permits the calculation of the neutral equivalent value, the titration of the effluentfrom the ion exchange resin in the present determination can be used to calculate an “exchange equivalent” value. This value is equal to the molecular weight of the aalt or to a submultiple of it. The calculations are as follows: Sample weight in milligrams- - exchange equivalent Milliliters of base X normality of ba-e
Table I. .4ualysis of Salts of Organic Acids Exchange Equivalent
xo. of AV. (It~tC1.illinations Mean deviation 1 88.6 0.4 rirnnionium adipate 91 7 0.0 3 Amnionium tartrate 0.5 3 i i i ,8 Ammoniuin xylonate 0.7 256.7 4 Barium acetate 422.1 2.4 4 Barium maltobionate 132.9 4 0.3 Cadmium acetate.2HzO 168.9 4 0.1 Calcium acetate 241.2 4 0.8 Calcium 2-ketogluconate.31~~0 365.3 4 1.8 Calcium lactohionateU 0.6 4 200.1 Copper acetate.Hz0 0.7 3 378.2 Lead acetate.3HzO 1.6 3 298.0 Lead gluconate 4 0. 8 120.7 Magnesium lactate.2H20 0.4 4 85.8 Manganese acetate 123.1 0.7 4 Nickelous acetate.4HzO 204.6 1.1 4 Potassium acid phthalate 4 251.1 2.5 Potassium dinitrobenzoate 231.0 2.7 3 Potassium 2-ketogluconate 1.9 4 325 0 Potassium stearate 1 6 6 . 4 0.9 4 Silver acetate 0.1 4 136.3 Sodium acetate.3H20 4 0.3 182.9 Sodium benzenesulfonate 3 1.4 148.9 Sodium benzoate 0 .1 4 9 8 . 6 Sodium citrate.2Hs0 0.4 4 107.5 Sodiiim a-cyanoacetatC 0.3 4 88.3 Sodi~imformate 3.2 6 291.9 Sodium oleates 0.8 140.8 Sodium potassium tartrate.4HzO 1.1 111.8 Sodium pyruvate 1.5 162.2 Sodium salieylate 1.2 3 81.9 Sodium succinate 4 218.6 1.1 Zinc acetate.ZH20 0.5 4 90.8 Zinc fumarate 138. $1 0.3 4 Zinc lactate.2HzO Compound
3 i
a
Ash &s sulfate gave a n equivalent weight of 369.
b Ash as sulfate gave anequivalent weight of 292.
~
~-
Theorg 90.0 92.0 183.1 255.4 425.7 133.2 158. 240. 377.0 199.6 379.3 298.6 119.2 86.5 124.4 204.2 230. 0 232.2 322.4 186.9 136 0 180.1 144.0 98.0 107.0 88 0 304 3 141.1 110.0 160.0 81.0 219.5 89.7 139.7
b-
For an acid salt, such as potassium acid phthalate, the samplcb can be titrated before passage through the column and this titration suhtlncted from the titration of the effluent. RESULTS
Values obtained on ?4 salts of organic acids with 13 different inorganic cations are reoorted in Tallle I, and 12 salts of organic bases in Table 11. All of the compounds were analytical standards, analytical reagents, Eastman White Label compounds, or compounds synthesized or isolated a t this laboratory. The compounds prepared at this laboratory were shown t o be a t least 98% pure by analysis for carbon and hydrogen or ash, except in the two cases noted in Table I. Each value reported is the average of the indicated number of determinations, which were made on a t least two different columns by two different operators. The accuracy and precision of the method were indicated bv calculating the average and standard deviation of results from twenty IO-ml. samples, each containing 0.075 meq. of Kational Bureau of Standards sodium oxalate. The average was 99.87% of the theoretical with a standard deviation of 0.21%. Erratic and low recovery of acid was obtained when the quinine and brucine salts reported in Table I1 were passed through columns containing the 16% cross-linked resin. A possible explanation for this observation is that the quinine and brucine cations are so large that they cannot reach the ewhange sites within a resin as highly cross linked as this. S o trouble waq encountered in analyzing salts of acids, such as
1111
V O L U M E 2 5 , NO. 7, J U L Y 1 9 5 3 gluconic and lactobionic, which can form lactones (see Table I). Attempts to measure carbonate salts were unsuccessful. I n addition t o the analysis of the organic salts reported, t h e method has been used for the determination of sodium chloride in dextran solutions. ACKNOWLEDGMENT
The authors are giateful to F. R. Stodola who supplied sample5 of many of the organic -alts reported.
1942. . 24, 300 (1952). ( 5 ) Pifer, C. IT., and Kollish, E. G., A N . ~ LCHEM., (6) Ibid., p. 519. ( 7 ) Ychrnall, JI., Pifer, C. IT., and Wollish, E. G., Ibid., 24, 144fi (1952).
(8)
Wiesenberger, E., Mikrochemie cer. Mibrochinz. d c t a , 30, 176-h (1942).
for rrvieiv February 11, 1953. Accepted .Ipril 2 7 , 1953. lien. tion of f i r m names or commercial products under zi proprietary nnnie or names of their manufacturer does not constitute an endorsement of sucli firms o i products by the U. 9 . Department of ;\griculture. RECEIVED
LITER-ITURE CITED
(1) Fritz, J . S., ASAL.(-’HEY.. 24,306 (1952). (2) Kleinzeller, A , . and Trim, A . R., -4rznZ!4.3t, 69,241 [I944
(3) Kunin, R., and Myers, R. J., “Ion Exchange Resins,” p. 127, Kew York, John Wiley 8- Sons, 1950. (4 1 Siederl, J. B., and Siederl, J’., “Organic Quantitative JIicroanalysis,” 2nd ed., pp. 62-5, Sew York, John Wiley & Soils,
1,
Reduction of Nitroguanidine and Its Derivatives by Titanous Chloride PAUL D. STERNGLANZ, RCTII C. THOMPSON’, ~ N DF . i L T E R L. S I V E L L Chemical Research Dicision, Laboratory of .-idr.anced Research, Remington Rand, Inc., South Sorwalk, Conn. 7m c m and Hiilbert’s titanous chloride reduction method
h ( 2 ) for determining the nitro group fails when applied to
nitroguaiiidine and its derivatives, which belong to a class of organic compounds called nitroammonocarbonic acids ( I O ) . For example, Kouha and coauthors ( 6 ) obtained erratic results when they tried t o reduce nitroguanidine by this method. They were able t o analyze the compound satisfactorily by prolonging the boiling period and carrying out the reduction in a more concentrated acid solution. I n their modification, however. four instead of the theoretical six equivalents of titanous ions react with the nitro group. Zimmerman and Lieber ( I O ) then applied Kouba’s modification ( 6 ) to several nitroammonocarbonic acids. They found that nitroguanidine could not lie analyzed with any precision. and that nitroaniinoguaiiidine reacted with only 3.4 equivalents of titanous ions instead of the esprcted 4. However, xhen they modified Kouba’s method ( 5 ) 1))- adding bivalent iron as a reducing aid. they succtwicd in reducing the nitroammonocar1)onic acids completely, with a consumption of six equivalents of trivalent titanium. Since the amount of bivalent iron needed for each type of compound had to be empirically determined. they conceded that the method is of limited value. The existing titanous chloride reduction methods for nitroammonocarbonic acids (5, 6, I O ) are unsatisfactory; either they cannot be duplicated easilj- by other investigators or they are definitely empirical in nature (6, I O ) . .I study was made. therefow, to find a modification which does not have such limitations. In the proposed method the reduction proceeds rapidly a t room temperature with the consumption of six equivalents of trivalent titanium. The essential conditions are a 20070 miriim u m escess of titanous chloride and a weakly arid. buffered mrtliuni. REAGENTS
An approximately 0.3 S titanous chloride solution was prepired and stored as described by Siggia (8). Its strength was checked against that of the ferric alum solution before each series of experiments was run. Periodically the titanous solution was standardized againEt pure p-nitroaniline by the described method. An approximately 0.1 S ferric alum solution was used for back titration. The Reinhardt-Zimmermann procedure and the method described by Siggia (8) mere used interchangeably for standardizing the ferric solution. Buffer: potassium citrate, 800 grams per liter of aqueous rolution. Indicator: anlmoniuni thiocj-anate, 250 grams per liter of aqueous solution. . Tank carbon dioxide was used for conducting the titrations in :in inert, atmosphere. Contaminating osygen was removed by 1
Present address Wesleyan University, Sliddletown Conn.
passing the carbon dioxide through a 250-ml. gas washing hottlc. filled with vanadous sulfate solution ( 7 ) and through two 125-ml. gas nashing bottles filled with titanous chloride solution. IPP4R4TUS
A 250-ml. flat-bottom flask with outer 24/40 ground-glass joint was used. The inner joint member was sealed a t the top except for a hole, and a ring seal for a gas introduction tube. The hole served as a gas vent and was made large enough so that a funnel or buret tip could be inserted. The gas introduction tube served as a carbon dioxide inlet and reached to within 1 inch of the bottom of the flask. A4magnetic stirrer was used PROCEDURE
Take a sample 1.2 to 2.4 meq. in size [ I meq. = gram niolecular weight/( 1000 X 6 X number of nitro groups)]. Introduce the sample into the flask and dissolve in 10 ml. of 10qo acetic acid, heating on a steam bath, if necessary. For espediency, dissolve the two alkyl nitroguanidines in glacial acetic acid before diluting with water. Displace the air in the flask bv means of powdered dry ice (about 10 ml.) and purified tank carbon dioxide. The purpose of adding dry ice is to ensure faster displacement of air. When the dry ice has disappeared, bring the solution to room temperature; add 10 ml. of the potassium citrate buffer, followed by a measured excess of titanous chloride (200T0 minimum). Stir the solution approximately 3 minutes; add 20 ml. of hydrochloric acid (1 to 1) and 5 ml. ot ammonium thiocyanate solution, in the order given. Back titrate the excess titanou. chloride with the standard ferric :iluni solution. DISCUSSION
.In attempt W R S made first to reduce nitroanimonocarlionic acids by Kouba’s method (5) in a boiling titanous chloride-hydrochloric acid solution. LOK and erratic results were obtained, in agreement with those reported by Zimmerman and Lieher ( I O ) . It was reasonalile to assume that the reduction might go to completion if the reduction potential of tiivalent titanium \vere increased. One may to increase the reducing power of titanium is l)), raising the p H ( 3 ) . This effect has been clearly demonstrated on certain nitro compounds which Kolthoff and Ro1)inson ( 4 ) and Butts and coworkers ( I ) were investigating. -4 rapid, sisequivalent reduction a t room temperature occurred \Then the compounds were dissolved in a Imffered, weakly acid medium: in a mineral acid medium, the compounds would have required a t least a IO-minute boiling treatment for complete reduction. The rapid method was accordingly applied in this laboratory t o the nitroammonocarbonic acids. hgain, low7 and erratic results were obtained. Attrmpts to make the reductions complete
