ANALYTICAL CHEMISTRY
652
to the characteristics sought. It is orily n a t u r a l t h a t increased sorting proficiency results from d E M I T 1-ER increased familiarity with the system. For example, pure s K gamma emitters may ebe found rapidly by IT first selecting those isotopes which decay by isomeric transition, then rejecting thoseTvhich emit elec4N + I SERIES trons (to eliminate RADIOACTIVE internal converqion cases); the lessexperiDAUGHTERS: enced 11ould possibly m e the more tedious method of selccting the gamma emittere, Figure 1. Drawing of Punched Card for Phosphorus-32 then rejecting the Illustrating coding arrangement and punches necessary to describe the isotope alpha emitters, positron emitter., etc. I t is felt that the codification of radioisotopes by punched cards These claqsifications plus the coding arrangement qhon.n on is a valuable addition to the scientific library. The modest Figure 1 may be placed on a blank Keysort card. This may be number of cards needed for the ?>-,tern resulted in a minimum of attached to the container holding the cards, where it will serve eypense in time and material., while the time required to identify as a ready indev to the system while sorting. a certain isotope from a given pet of properties has been greatly The atomic number designation is accomplished by using two reriuceJ in the authoi s' laboratory by this card ??.stem. adjacent groups of four holes. The group on the left de-cribes the class of ten, while the group on the right describes the unitq. LITER-IlURE CITED For evample, 4 + 2 ( 6 ) punched in the left-hand group and i + 1 ( 8 ) punched in the right-hand group designate atomic number 68 (1) Bonine, J. J., and Laing, II,,S i t c l e o i i z c s , 11, ( 2 ) , 65 (1953) ( E r ) . Finding an isotope card for revision purposes is aided by ( 2 ) Lenihan, J. 11.A , , Brit. J . ,4ppl. P h y s . , 3, 29 (1952). this feature, and 1s the only reason for the inclusion of this feature (3) Murphy, G. AI., J . Chein. Educ., 24, 556 (1947). (4) Katl. Bur. Standards, Ciic 499 and supplements in the system. The cards are manually sorted n-ith a McBce Keysorter needle RECEIVED for revleu .luguot 2 1 , 1953. lccepted J a n u a r y 2 2 , 195%. probe by the standard method of selection and rejection according
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Identification of Polyhydric Alcohols in Polymeric Esters J. F. SHAY', SUSAN SKILLING2,and R. W. STAFFORD American Cyanamid Co., Stamford, Conn.
By a modified saponification procedure, the poll-hydric alcohol fraction of a polyester resin can be separated. The component alcohols can be identified by infrared spectral analysis, using the spectra of commercial alcohols as comparative standards. The method provides an effective means of identification for individual polyhydric alcohols and for binary mixtures.
T
HE original polyester (alkyd) resins contained glycerol ex-
clusively as the polyhydric alcohol component and hence presented no analytical problem in this respect. The gradual replacement of glycerol, in whole or in part, by other polyhydric alcohols, however, soon necessitated a series of analytical investigations which culminated qualitatively in the procedure proposed by Orchin ( 8 ) ,which in the past has been applied successfully to polyhydric alcohol fractions isolated according to methods developed in this laboratory ( I S ) . The Orchin procedure, vhich 1
Present address, Fortier Plant, American Cyanamid Co , Avondale,
La 2
Present address, H a r r a r d Mediral School, Cambridge, Mass.
is based on the oxidative scission of vtc-diols with periodic acid, was applicable a s follows to the polyhydric alcohols commercially available at that time: Glycerol, if present, is converted to formic acid b y oxidation with a solution of periodic acid which has been carefully neutralized Kith standard alkali; the formation of formic acid is detected with methyl red indicator. Ethylene glycol is converted to formaldehyde, which can be detected by a color test involving alkaline phloroglucinol ( 1 2 ) . Propylene glycol yields acetaldehyde, which also gives a red coloration n ith alkaline phloroglucinol. hcetaldehyde may be distinguished from formaldehyde by the iodoform reaction. Diethylene glycol, which is not a vzc-diol, is not cleaved by periodic acid oxidation. I n the absence of the above polyalcohols, the presence of diethylene glycol can be substantiated by the preparation of the 3,5-dinitrobenxoate. Periodic acid oxidation has been applied by a number of eubsequent investigators, most of whom were concerned with quantitative estimations, Kewburger and Bruening ( 7 ) determined glycerol in the presence of ethylene and propylene glycols by titration of the formic acid liberated upon oxidation with potassium periodate. Pohle and Mehlenbacher ( I O ) analyzed mix-
V O L U M E 2 6 , NO. 4, A P R I L 1 9 5 4
-
I
\-
100
-
'v\ - SO
-
2
-0
-
I 3 d
D
Figure 1.
FREQUENCY IN CM? Infrared Spectra of Some Commercial Polyalcohols A. B.
C.
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Figure 2.
Infrared Spectra of Some Comniercial Polyalcohols A. B.
Ethylene glycol 1,Z-Propylene glycol 1,3-Butylene glycol
tures of glycerol, propylene glycol, and trimethylene glycol by first determining glycerol as formic acid. Propylene glycol was then measured by titration of the iodine which is liberated when pot:issiuni iodide is added to t,he oxidized solution; trimethylene glj-col is determined by acet.yl value. Francis (3) start,ed with the periodic oxidation procedure in determining the diglyc.ols in mistures of ethylene and propylene glycols. After the dietillntion of the result,ing aldehydes, the diglycols are osidized with potassium dirhromate and are measured polarographically brfore and after oxidat,ion. Cannon and Jackson ( 2 ) have modified the method of JVarshowsky and Elving to determine
T
1,5-Pentanediol 2,5-Hexanediol
C. 1,lO-Decanediol-Nujo1
small anounte of 1,2-prop) lene glycol in ethylene glyrol. rlfter oxidation with periodic acid, the aldehydes are removed by distillation and determined polarographically. Among other approacheswhich have been suggested for the analysis of polyhydric alcohols may be included the f o l l o ~ i n g :Palfray, Sabetay, and Libmann (9) have described an entrainment procedure for the isolation (and estimation as such) of polyhydric alcohol fractions. Refluxing with cyclohexane, using a DeanStark trap, entrains ethvlene glycol, trimethylene glycol, and prop1 lene glycol Turpentine entrains these, and in addition, diethylene glycol and glycerol. Hough ( 6 ) has applied paper
I
- 100 - 50
-0
I
ID0
FREQUENCY IN CM:'
Figure 3.
Infrared Spectra ,of Some Commercial Polyalcohols A.
Diethylene glycol I?. Dipropylene glycol C. Triethylcne glycol
Figure 4.
Infrared Spectra of Some Commercial Polyalcohols
A . Z-Methyl-1,3-pcntanediol B . 2-Methoxymethyl-2,4-dimethyl-l,5-pentanediol C . Z-Ethoxymethyl-2,4-dimethyl-1,5-pentanedioI
A N A L Y T I C A L CHEMISTRY
654
100
50
ml. of an approximately 0.5A' solution of potassium hydroxide in absolute alcohol. The insoluble dipotassium salts are removed by filtration and the filtrate is made slightly acid F i t h concentrated hydrochloric acid. The precipitated potassium chloride is removed by filtration and the filtrate is concentrated to approximately 5 ml. The concentrated solution is transferred to a separatory funnel, using 10 to 15 ml. of water, and then extracted with an equal volume of ether. The water layer is made slightly alkaline and then dried by evaporation, using anhydrous alcohol to assist the dehydration. The evaporation residue is extracted with alcohol, filtered, and the filtrate evaporated under a stream of dry air until the added alcohol is removed. The residue from this trentment represents the polyhydric alcohol fraction.
0
1
I
I
900 FREQUENCY IN CM:' I100
Figure 5.
n
Infrared Spectra of Some Commercial Polyalcohols
A.
2-R.Iethyl-2,4-pentanediol 2-Ethyl-1,3-hexanediol (octylene glycol) C . 2,2'-(Isoprop> lidene-bis-p-pheny1enory)dipropanol
B.
partition chromatography t'o the separation of polyhydric alcohols. Wurzschmitt ( 1 4 ) used t\To methods to analyze mist,ures of ethylene glycol, diethylene glycol, and diethylene glycol monoethj.1 ether: Of these three, ethylene glycol alone reacts with alkaline copper sulfate t o give a blue complex; the intensity of the color wzts used to estimat'e the quantity of the glycol and the others were determined indirectly from the density; diethylene glycol monoethyl ether is insoluble in 72.5% potassium hydroxide solution. Jaffe and Pinchas (6) have estimated dipentaerythritol in the presence of pentaerythritol by the infrared spectroscopy of the corresponding acetat,es in carbon tetrachloride solut'ion. The development of unsat,urated polyesters during t'he past few years has demonstrated the great potential flesibility of thew polymers, which are apparently rest,ricted only by the available variet'y of acidic and alcoholic components. Perhaps as a result, the number of commercially available polyhydric alcohols hay recently- increased greatly. The analyt'ical problems introduced by so many polyalcohols exhibit,ing such close structural relationship are virtually unsolvable by either chemical methods alone or by the limited approaches already cited. I t was the opinion of the wesent investigators that infrared spectroscopy might be advantageously applied to this problem. The application of infrared analysis to the identification of organic chemicals (1, 11) and specifically t o monohydric alcohols in plasticizers ( 4 ) , a problem similar to the one presented here, had been discussed earlier. No attempt is made in this paper to include t,he theory or fundamental methods involved in infrared analysis. The subsequent discussion is confined to the extent to which the method is successful as applied to the identificat.ion of polyhydric alcohols, and the limitations and difficulties encount,ered.
FREQUENCY IN CM?
Figure 6.
Infrared Spectra of Some Commercial Polyalcohols A.
Glyoerol
B. Trimethylol ethane-Nujol C. Trimethylol propane-Xujol
EXPERIMENTAL
Isolation of Alcohol Fraction. The unsaturated polyester as received is usually dissolved in an inert solvent or potential crosslinking agent. As a preliminary step, it is usually isolated from the solution by precipitation with a nonsolvent such as petroleum ether. A 10-gram portion of the precipitated polyester is dissolved in a small volume of benzene or acetone and saponified with 250
FREQUENCY IN CM!
Figure 7.
Infrared Spectra of Some Commercial Polyalcohols A . 1 2 6-Hexanetriol B . $e&aerythritol-Nujol C. Mpentaerythritol-Nujol
655
V O L U M E 26, NO. 4, A P R I L 1 9 5 4
the intense and the less intense bands. The usual thickness is less than 10 microns. Vertical comparison of curves A and B indicates that a mixture of ethylene and propylene glycols would present a less difficult problem than does the mixture of propylene and dipropylene glycols. The same is true of mixtures involving diethylene and dipropylene glycols. DISCUSSION OF EXPERI-MENTAL RESULTS
The identification of a single, unknown polyhydric alcohol :after extraction from the resin, involves only a careful comparison of its infrared spectrum with the set of spectra of known standards. Providing the unknown is one whose spectrum is among the standards, identification is very simple and can usually be accomplished using only the region shown in the curves presented here. The C--0 vibrations give the strongest absorption in this region, but since these often overlap from one compound to the next, the lower, weaker bands (below 1000 cm.-1) of other single bond vibrations are extreme117 useful i n complete identification.
FREQUENCY IN CM:'
Figure 8.
Infrared Spectra of Some Commercial Polyalcohols A. B.
Tetramethylol cyclohcxanol-Nujol Inositol-Nujol
C. Sorbitol-Nujol
Infrared Analysis of Polyhydric Alcohols. Comparison of the infrared spectrum of the separated fraction with the spectra of a selection of commercially available polyhydric alcohols usually permits the identification of the glycol or glycols present in the polyester. The spectra shown in Figures 1 through 8 illustrate 24 comniercia1 polyalcohols and hence represent a set of comparative standards. These data were obtained on a Perkin-Elmer spectrometer, Model 21, equipped with a sodium chloride prism. The liquid glycols were prepared by spreading a thin film between two rock salt plates and the solids were examined as Xujol mulls on rock salt plates. (Per cent transmission is shown, since spectra are not compensated for cell-window losses nor for Sujol 15 hen used.) Before examination, the samples were dried over a desiccant to prevent interference by more than 1 to 2% water. The curves are presented approximately in order of increasing complexity of structure, with the dihydroxy compounds followed by the tri-, tetra-, penta-, and hexahydroxy alcohols. T o conserve space, only the region from 650 to 1550 cm.-1 is shown. A few other differences occur in the rest of the spectrum, but this region is the most characteristic for each glycol and the one used for identification purposes. The absorption contributed by Nujol is designated by Atr. Resolution of Mixtures. The spectra shown in Figure 9 have been included to illustrate the problem presented by mixtures of the common glycols and the manner in which such an occurrence can usually be resolved. The bands are marked with symbols designating the glycol to which the absorption is totally or partially assigned. Ethylene glycol is represented by E, diethylene by DE, propylene by P , and dipropylene by DP. Curve A represents a mixture of ethylene and diethylene glycols. Inspertion and comparison with the curves of the individual compounds (Figures 1.4 and 3A, respectively) show that all bands found in h t h glycols are present In this composite, and account for all absorption bands observed. A 1 t o 1 mixture would approximate the observed intensities. Curve B, representing roughly a 1 to 1 mixture of prop?-lene and dipropylene glycols (Figures 1B and 3B, respectively), shows a spectrum which is less easily resolved into its component absorptions. Since both compounds absorb a t nearly the same frequencies in many cases, it is important that a sample thickness be used which shows both
IS00
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Figure 9.
700
I100
IN
CM'I
Infrared Spectra of Some Glycol Mixtures E. Ethylene glycol DE. Diethylene glyool P. DP.
Propylene glycol Dipropylene glycol
The infrared spectrum of a mixture of tu-o or more polyhydric alcohols, which do not interact, shows all the absorption bands of each component. This makes possible the identification of certain mixtures, although there are definite limitations to the suecess of this method. Fourteen mixtures of the more common polyhydric alcohols, in different ratios and different combinations, were examined in the course of this investigation. Identification of a mixture of two liquid glycols, in ratios of 1 to 1, 2 t o 1, and 3 to 1, was found possible and almost alwajs successful. Even combinations of polyhydric alcohols which are closely related structurally could be identified. Propylene and ethylene, dipropylene and diethylene glycols, ethylene glycol, and glycerol were among the mixtures which were identified. The only difficulty encountered was that of regulating the thickness of the sample. It must be thick enough for detection of a small amount of a glycol in the presence of another and not so thick as to cause blanking out or destruction of ,the well-defined contour of strong absorption bands. Often the shape of a band or the relative intensity of one band t o another was the means of detecting and identifying a mixture. Once a mixture has been identified, the proportions of the com-
ANALYTICAL CHEMISTRY
656 ponents may be roughly estimated by comparison with similar mixtures of known composition. I n some cases, where each component has some unique absorption without interference from the other, a rough quantitative analysis may be made on the basis of the spectra of pure samples of the components involved. Mixtures of a solid and a liquid glycol were more difficult t o detect. Often the solid did not appear to have dissolved, and so little of it was suspended in the liquid that it probably only scattered light and gave no characteristic absorption of its own. Only the liquid n*as identified in these cases. I n other mixtures, such as that of ethylene glycol and sorbitol, it was sometimes possible to detect a shoulder on the side of a band, indicating the presence of a t least one other component mixed with the liquid glycol. Hoxever, this was insufficient evidence for complete identification. Probably solvent fractionation means will have t o be used t o separate solid and liquid glycols, with infrared analysis then being applied to the separate fractions. Several mixtures of three glycols (in 1 t o 1 ratio) were examined. I n one case all three were identified (ethylene, diethylene, and triethylene glycols), but as a general rule the evidence is usually inadequate for distinguishing three glycols in a mixture. Unless one of them is particularly unique-e.g., aromatic-and absorbs characteristically without interference from the other two, infrared analysis is not successful in complete identification of most mixtures of more than tivo polyhydric alcohols. coYcLusIoYs
Polyhydric alcohols can be readily isolated from unsaturated polyester resins. The components of the separated alcohol fraction can usually be identified by infrared spectral analysis, using the spectra of dried commercial polyalcohols for comparison. The infrared method is effective for individual glycols and for mixtures of two liquid glycols, with the components present over
a reasonably wide range. Mixtures of a liquid and a solid glycol require further fractionation prior to identification. The infrared identification of the components of ternary mixtures is only possible in special cases. ACKNOWLEDGM EIVT
The contribution of Martha &I.Taylor in preparing the illustrative spectra for publication is gratefully acknowledged. LITERATURE CITED
(1) Barnes, R. B., Gore, R. C., Liddel, Urner. and Williams, 1.. Z.,
“Infrared Spectroscopy, Industrial Applications and Bibliography,” New York, Reinhold Publishing Corp.. 1944. (2) Cannon, W. A., and Jackson, L. C . , ASAL. CHE~!.,24, 1053-5 (1952). (3) Francis, C.T., Ibid., 21, 1238-9 (1949). (4) Haslam, J., Soppet, W.,and Willis, H. A , , J . Appl. C‘hem. (London),1951,112-24. (5) Hough, Leslie, S a t u r e , 165,400 (1950). (6) Jaffe. J. H., and Pinchas, Shraga. . ~ S . A I . . C H E Y . , 23, 1164 (1951). ( i ) Sewburger, S. H., and Bruening, C . F., J . Assoc. Ofic. A g r . C‘hemisls, 30, 651-5 (1947). (8) Orchin, Milton, Ibid., 26, 99 (1943). (9) Palfray, Leon, Sabetay, Sebastien, and Lihmann. Gahrielle, Compt. rend., 223,247-9 (1946). (10) Pohle, W. D., and hlehlenbacher. V. C., J . A m . Oil Chemists’ SOC.,24, 155-8 (1947). (11) Randall, H. 11..Fowler, R. G.. Fuson, S . , and Dangl., J. R..
“Infrared Determination of Organic Structures.” New Tork, D. Van Nostrand Co., 1949. (12) Stafford, R . W., and Williams, E. F., “Protectil-e and Decorative Coatings.” Vol. 5, Chap. 1. p. 106, New Tork. John Wiley & Sons, 1946. (13) Ibid., pp. 133-4. (14) Wureschmitt, Bernhard, 2.anal. Chem., 133, 12-17 (1951).
RECEIVED for review May 6 , 1953. Accepted Sorember 21, 1953.
Identification of Dicarboxylic Acids in Polymeric Esters Preparation and Properties of Diethyl Esters and Potassium Salts R. W. STAFFORD, J. F. SHAY’, and R. J. FRANCEL American Cyanamid Co., Stamford, Conn.
The diethyl esters of eight selected dicarboxylic acids were prepared and purified. Various physical properties were determined on the purified products; the potential applicability of these properties to the analysis of mixtures of esters was evaluated. The resolution of mixtures was found possible by the application of distillation and/or ultraviolet and infrared spectroscopy. The dipotassium salts were prepared from the diethyl esters, and the Kappelmeier procedure was evaluated in the process. As characteristic derivatives, the salts were found to he less applicable to the identification of the acids than were the esters.
T
HE increasing variety of acidic components used in the formulation of polymeric esters has introduced analytical complications which seriously qualify the previously reliable procedures used in the investigation of these commercially important resins. I n recognition of the need for modified and/or I
La.
Present address, Fortier Plant, American Cyanamid Co., Avondale,
new analytical procedures for this purpose, a scrips of investigations was carried out in this laboratory. Attention was concentrated on the dicarboxylic acids, as represented by eight commercially important compounds. As the initial result of this work, a method employing the infrared spectra of the ’V-benzylamides was proposed (26) for the identification of these acids as they occurred in commercial polyesters; the method was based on data obtained during one phase of the broader investigation. I n the present paper, data derived from alternative lines of study, performed concurrently on the same eight acids, are reported and discussed. Originating in 1935, the first reported methods (3, 5, 8, 9, 11) for the analysis of alkyd resins were naturally aimed a t the determination of phthalic arid. Perhaps the simplest and most reliable of these earlier procedures is t h a t devised by Kappelmeier who subsequpntly discussed his technique, perfected for the resins commercially available at the time, in some detail (IO). The method is based on the quantitative precipitation, under controlled conditions, of dipotassium phthalate monoalcoholate during saponification of the polyester with potassium hydroxide dissolved in absolute alcohol. Although primarilr
