The unknown solution is placed in both cells and the spectrophotometer is balanced on zero absorbance with cell 1 in the light path. Cell 2 is then placed in the light path and the observed absorbance, A,, is the necessary cell correction. As the cell correction is a linear function of the observed absorbance of the solution being determined, it is convenient to construct a cell correction curve. This curve is a plot of the cell corrections for several samples, obtained in the same manner as A , , plotted against the corresponding observed absorbances of these samples. T h a t the absorbances of the cells remain constant is a n assumption which can be verified experimentally by the measurement of the cell correction for a given solution before and after a series of nie:tsurements.
rvhich were 90% uranium, but could be adapted for most binary alloys of thcse metals. It should also be useful for the dctermination of niobium in niobium metal, in niobium(V) oxide. and in other niobium alloys and salts. LITERATURE CITED
(1) Atkinson, R. H., Steigman, J., Hiskev, C. F., .%SAL. CHEV. 24, 477 (1952). ( 2 ) Bacon, -4.,Milner, G. K.C., Analysl 81, 456 (1956). (3) Bacon. A , . Milner. G. W. C.. “Auplicjtions of Differential SI;ectfills, W. IT,, “Preparation of Primary Standard UiOa,” U. S. .ltomic E n e r u Commission. Rept. HW-39767 ( 3 5 5 ) . ( 7 ) 131yo11,T . C., Goward, G. IT., I -
APPLICATIONS
The procedure described, a rapid and accurate method for the analysis of binary alloys of uranium and niobium. was used for the analysis of alloys
~
~
Hartmann, h l . D., “Determination of Xiobium in Uranium-Siobiuni ,411oys,,” U. S. Atomic Energy Commission, Rept. WAPD-CTA IGLAL146 f 1955).
(8) Freelanh, bl. Q . , Fritz, J. S.,AS.\L CHEM.27, 1737 (1955). ( 9 ) Geld, I . , Carroll, J., I b i d . , 21, 1098 (1949). (10) Hiskey, C. F., Ibid., 21, 1440 (1949). ( 1 1 ) Blinger, P., Koch, W.,Arch. E ~ S P F I hii’tenu;. 13, 127 (1939). (12) Palilla, F. C . , Adlei, S . , Hiskey, C. F., i l s . 4 ~ CHEM. . 25, 926 (1953). ( 1 3 ) Patterson, J. H., Evans, H. B.,
“Spectrophotometric Determination of Siobium in Uranium Ternary Alloys,” U.S. iltomic Energy Commission, ANL-5410, 59 (1955). (14) Susano, C. D., IIenis, O., Tall)ott, C. K., r\sar,. CIIEM. 28, 1072
(1956). (15) Telep, G . , Boltz, D. F., Ibzd., 24, 163 (1952). 116) Thanheiser. G.. M i t t Kuiser-Tl-iihelm I n k Eisenforsch. Dilsseldo,;i 22, 255 (1940). (17) I-oung, I. G., Hiskey, C. F., ~ S A L . CIIEM. 23, 506 (1951). .
I
RECEITEDfor review September 15, 1956. Accepted )\larch 29, 1957. Work performed in .4mes Laboratory of the [-,8. .ltornic Energy Commisyion.
Infrared Spectrophotometric Procedure for Analysis of Cellulose and Modified Cellulose ROBERT T. O’CONNOR, ELSIE F. DuPRE, and ELIZABETH R. McCALL Southern Regional Research laboratory, New Orleans, l a .
The potassium bromide disk technique can b e used for rapid, simple, and reproducible measurement of the infrared spectra of cotton fibers, yarns, and fabrics. Applications of the procedure show that chemical modification can be detected, the character of the modification identified, and the extent o f treatment quantitatively estimated. Preliminary experiments indicate that considerable information can be obtained of interest to studies of the oxidation of cotton, to determinations of position of modifying substituents within the cellulose molecule, and to investigations of crystallinity and cross linkage. YLI
4
limited number of evamplei
aiidysib in cotton or c-elluloqe research have been devribetl. These fen applications have been limited in scope, usually to Iijdrogen bonding studies by nieasurenieiit5 of the fundamental -0-H stretching vibrations a t about 3.0 microns (21-15) or of tlie overtones of these Tibratioris in tlie nenr-infrared 998
ANALYTICAL CHEMISTRY
( I C ) , and to investigations of oxidat~ion effects liy observation of the carbon>-1 C-0 st’retching in the 5.8- to 6.0micron region (81). Rnpicl acceptance of infrared ahsorption as a tool in cotton researrh h [ ~ q been prevented mainly by the lack of :i simple, satisfactory technique for measurement. Cotton cannot he dissolved in a solvent suitalde for absorption measurements without consitlernble modification. Cotton fibers or f:tl)ricAs are opaque to infrared radiation. Rowen. Hunt: and Plyler (81) studied the rlianges produced by various oxidizing agents in the absorption of cellulose acetate films cast on glass plates. Mann antl Narrinan (11-14) prepared ose films on glass plates in their invesbigat’ions of the reaction of cellulose with heavy n-ater and their development of an infrared method for the estimation of crj-stallinity. Such films are unsuibable for cotton, not only because tlie technique used to producae them may result in changes in structure, but also because the procedure 1%-oultlnot be applicable to sever:il de-
graded or cIieinical1~-modified cottons. Even when applicable, no precise q m n titative measurements can lie made. :IS the film thickness cannot be accwately measured. Forziati antl coworkers (6) descritierl :I method for preparing a fine cotton ponder from mhicli infrared spectr:i could be obtained as a 1L’ujol mull. This method also is not entirely sntisfactory because the grinding results in some change of structare, as evidencetl by loss of crystallinity, and Kujol mulls do not lend theniselves to accurate quantitatire measurements of bsntl intensities. Mtchell. Bockinan, and Lee (16) used pyrrole as a solvent in their measurements of the near-infrared spectra to deterniine acetyl content. Such solvents, however. are suitable only for investigations confined to a narrow spectral range. The pottissium bromide disk technique (5, 9 , 2.2, 2 5 ) offers a n ideal means for obtaining infrared spectra of cellulose or modified cellulose, particularly if satisfactory disks can be prepared \vitliuut>excessive grinding. This paper
tlescribes such a technique which permits measurement of infrared spectra of any modified or unmodified cotton finer, yarn, or fabric, simply and rapidly without modification of the sample. -1pplications of the procedure are illustrated by the measurement of the spectra of several esterified and etherified celluloses. Analysis of these spectra shows t h a t chemical modification t l m be detected, the type of modification identified, and the extent of inodification quantitatively estimated.
infrared spectrophotometer with sodium chloride optics. Perkin-Elmer potassium bromide die. Cenco-HyVac vacuum pump, capable of developing a vacuum of 0.1 mm. of mercury or better. Hand-operated hydraulic prebs of 30-ton capacity with a 4-inch rani. Dubrovin vacuum gage jvith a range of 0 t o 20 mm. with smallest scale divisions of 0.1 mm. Potassium bromide, infrared quality, powdered, Harshaw Cheniical Co. \Tiley mill, intermediate model.
APPARATUS A N D REAGENTS
PROCEDURE
I ' c r k i n - l h e r Model 21 double-beam
I
1 sample of 0.5 to 1 gram of cotton
I1
I
;.i 9
i
i i
I
6
IO 12
8
Figure 1 .
14
16 18 20 22 24 26 28 30 DIFFRACTOMETER ANGLE, 20
42
43
X-ray diffraction patterns of Deltapine cotton Peak a t right is for internal standard A. Ground in Wiley mill 6. Ground in vibratory-type ball mill
I
I
I
I
I
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I
I
I
I
I
I
I
I
I
12
1 3 1 4
100
'/ a 40-
0-w 320-
p
6 8.5
10-
8 9 6 943
a IOO-
2
60-
A
tl
CELL-OH
30 20 IO
I
2
\Tiley mill through a. 20-mesh screw. About 2 mg. of this sample (accurately weighed) is mixed with 350 mg. of potassium bromide (weighed on a pharmaceutical torsion balance). An intimate niixturr is obtained by grinding the sample and potassium broniidc thoroughly in a niullite mortar; 300 mg. of t,his mixture is used to make the disk The mixture of cotton and potasbiuni bromide is placed in the die, u-hich is t h m assembled and evacuated to about 3 mni. of nicrcury. Khile still being cxvacuat'ed the die is subjected to a 1)rcssure of 2600 pounds. Thc v x u u n i is further increased bo 1 mm. of mercury and the sample is pressed undcr thcsc conditions for 10 minutes. Infrared absorption measurcnirnts arc made using the following settings on tlic spectrophotoinet'cr: Resolution Suppi eesion Gain Response Slleed
927 3 6 1 4
The instrument is set a t 100% transiiiittancc a t 5 niicrons with a blank llotassium bromide disk in each beam. These standard disks are made with 300 nig. of potassium bromide according to the method used for pressing thc saniple disks. RESULTS A N D DISCUSSION
3t
I
fibcr, fal)ric, or yarn is cut in a sni:ill
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3
4
5
6
Figure 2. A. 6.
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7 8 9 IO II WAVE LENGTH (MICRONS)
Infrared spectra of Deltapine cotton Ground in Wiley mill Ground in vibratory-type ball mill
15
Crystallinity. Excessive grinding of n cotton fiber, fabric, or yarn causes :t considerable loss of crystallinity (17, 24) n-hic.h is readily detectable by x-ray diffraction patterns (Figure 1) ( 6 ) . l I a n n and llarrinan (ll-l.$) have described a n infrared spectrophotoniet~ric method for nieasurilig degree of crystallinity by means of partial deuteration of the cellulose molecule and measurement of the iiiteiisities of the -0-H and -0-D stret,ching vibrations a t 2.8 t'o 3.3 and :it 3.7 to 1.2 microns, respect,ively. Crystallinity can be detected in t,lie infrared spectra of cellulose wit'liout any pretreatment.. Spectra of Deltapine purified cotton are shown in Figure 2 . Curve -4 is the spectrum of a sample cut in n \]-;ley mill to pass through a 20-mesh wreen. Cur\.e B represents the s:inie rotton after grinding in a vibratory l i d 1 mill of the type descrihed l g Forzinti and coworkers ( 6 ) . 1,oss of car\-stnllinity during the grinding is clearly indicated in t,he broad absorption region hetween about' T.O and 9.5 microns. The more highly ci snmple exhibits n series of sharp bids, probahlj- arising from variouh deforiiintions, each of n-hich, in the \vc,!lformed cr!.stalline material, OCVUIT :it fixed resolvable freqiiencies. The 1.ibratory ball mill sample s h o w only a broad siiiooth absorption in this regioii. These spectra are similar to the coni; parison between infrared spectra u i VOL. 29, NO. 7 , JULY 1957
e
999
crystalline and solution samples of long-chain compounds (IO, 15). For such materials spectra of the crystals exhibit a series of discrete sharp bands arising from-CH, deformations about the long chain. I n the spectra of solutions of the crystals these bands are replaced by a broad smooth absorption region. The fact that cotton cannot be ground to a fine powder without modification means that a satisfactory Nujol mull type of spectra cannot be obtained. I n the normal preparation of potassium bromide disks, recommendations that the sample be ground to pass a 250mesh screen are included in order that the resulting spectra may be free of excessive scattering. Hence, although vibratory ball mills are available which can grind even stiff cotton fabric to a fine powder, sufficient grinding to meet this requirement would cause considerable modification of the cotton. A series of experiments was designed to ascertain just how little grinding could be employed and still permit measurement of satisfactory spectra. The particles that would not pass through the 20-mesh screen were used to prepare a disk; the resulting spectrum was identical to that shown in curve A , Figure 2. X-ray diffraction patterns show that, ivhile grinding in a vibratory ball mill to pass a 250-mesh screen will almost completely decrystallize the cotton, a sample cut in a Wiley mill to pass a 20-mesh screen retains most of its crystallinity (Figure 1) (6). Spectra of larger-sized particles of cotton showed no appreciable increase in degree of crystallinity. It was, therefore, concluded that cutting in a Wiley mill to pass a 20-mesh screen did not cause any appreciable modification of the cotton sample. This is in agreement with a conclusion of Schmenker and Whitwell (24) that “cotton yarn is not degraded significantly by a single pysage through a Wiley mill fitted with a 20-mesh screen.” This was adopted as a satisfactory and convenient procedure. The x-ray patterns shored no evidence of decrystallization and the infrared spectra showed satisfactory freedom from excessive scattering. Similarity in the indices of refraction of cellulose and potassium bromide is the principal reason why the sample does not have to be ground to pass a 250-mesh screen in order to obtain a satisfactory infrared spectrum. Cotton is birefringent and the average of its indices of refraction is 1.564, while potassium bromide is 1.559. Harvey, Stewart, and Achhammer ( 8 ) , in a recent investigation of index of refraction and particle size as factors in infrared spectrophotometry, found that the index of refraction relationship makes it possible to obtain satisfactory ANALYTICAL CHEMISTRY
spectra of nylon without grinding the sample to a fine powder. Cyanoethylation and Acetylation. Infrared absorption spectra of several chemically modified cottons, obtained by the procedure recommended above, have been examined t o determine whether the type of modification can be identified and t o ascertain whether quantitative estimations of the amount of modification can be obtained from intensity measurements. Cyanoethylation and acetylation are two chemical modifications which have received considerable attention. These
processes are actually partial cyanoethylation and partial acetylation, but to avoid repetition, the term partial is used here only with acetylation. This is in agreement with most common usage, both here and in subsequent discussions of esterifications and etherifications. I n Figure 3 the infrared spectra of cyanoethylated and partially acetylated cottons are compared n-ith the spectrum of unmodified cotton. The band at 4.45 microns in cyanoethylated cotton (Figure 3,B) arises from a stretching vibration of the C=S and
80604020 -
100-
0
8060 -
z
0
I I :
CELL-O-CHiCHf CzN
40201
-
100-
80:
2
6040-
V
k 20I
C
I1
p 100-
2 -80-
i
60-
40
-
20r IOOL
20 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 1 4 1 5 WAVE LENGTH (MICRONS)
Figure 3.
infrared spectra of chemically modified:cotton A.
B. C.
D. E.
Unmodified control Cyanoethylated Acetylated Torylated Merylated
‘0°/
T B
k-i
F
4 WAVE LENGTH MICRONS
* G
Figure 4. increase in intensity of 4.45-micron band with increase in degree of cyanoethylation
Figure 5. Quantitative relationships between band intensities and degree Qf modification A.
Cyanoethylated, 4.45-micron band Acetylated, 5.68-micron band Torylated, 12.35-micron band Tosylated, 6.25-micron bond
8. C. D.
WAVE LENGTH MICRONS
Figure 6. Increase in intensity of 5.68-micron band with degree of acetylation
j
C
40c
IO 2
3
4
5
6
7
8
WAVE
Figure
9
1
0
1
1
1
2
1
3
1
4
LENGTH (MICRONS1
7. Infrared spectra of Stoneville 28 cotton A. 8. C.
Unmodified control Acetylated Acetylated and tosylated
1
5
can be used for identification of this modified cotton. The increase in intensity of this band as the degree of cyanoethylation is increased is shown in Figure 4. I n Figure 5,A, the degree of cyanoethylation, as measured by the macro-Kjeldahl nitrogen content, is plotted against the intensity of the C=N absorption band. This figure shows that the degree of cyanoethylation can be accurately determined from the infrared spectra of the treated cotton fiber or fabric, Because the infrared method is specific, determining only nitrile nitrogen in cornfirison with total nitrogen determination by the Kjeldahl procedure, it has a particular advantage in the analysis of samples containing other nitrogen groups. Figure 3,C, is the spectrum of a partially acetylated cotton. An intense band, arising from a stretching vibration of the C 4 group of the ester, is observed a t 5.68 microns, and can be used to detect a partially acetylated cotton. Figure 5, B, shows the relationship between the intensity of the 5.68-micron band and the per cent acetyl groups as determined by the Eberstadt method according to the modification of Genung and Mallatt (‘7). Figure 6 shows the increase in intensity of this band as a function of the amount of acetylation. These data shorn that measurements of infrared intensities of the C=O stretching vibrations can be used for quantitative determinations of the degree of partial acetylation of cotton. Tosylation and Mesylation. Tosylation (esterification with p-toluenesulfonyl chloride) and mesylation (esterification with methylsulfonyl chloride) reactions of cellulose have been studied for some time. Addition of one or the other of these groups to the cellulose molecule has recently been suggested as a n intermediate step in the further modification of cotton. Comparison of the spectra of cotton modified with these two agents M ith that of unmodified cotton (Figure 3) reveals several bands by which the tosylated or inesylated cotton can be identified. Both modified cottons exhibit the prominent bands a t about 7.3 and 8.5 microns, arising from the covalent sulfonate group, -O-S02-R ( 2 , 3, 23). From Colthup’s assignments (3) for the sulfonate group a third band might be expected between 16 and 19 microns. This is beyond the limit of rock salt optics used in these investigations. Spectra of both tosylated and mesylated cotton in the region from 15 to 25 microns, obtained with potassium bromide optics, exhibit only broad bands a t 18.1 and 19.0 microns, respectively. Barnard, Fabian, and Koch ( 1 ) failed to find any bands in this region characteristic of the sulfone which Colthup has also asVOL. 29, NO. 7, JULY 1 9 5 7
* 1001
signed to this group between 16 and 19 microns. The spectra of both tosylated and niesylated cotton exhibit two bands in the 12- to 13-micron region which are not observed in the spectra of the unmodified cotton. These bands probably arise from some vibration of the sulfur group, because they are exhibited in the spectra of both tosylated and niesylated cotton. The bands with maxima a t 12.32 niicrons in the spectrum of tosylated cotton and a t 12.10 microns in the spectrum of mesylated cotton are n d observed in the spectra of the respective reagents. They must, therefore, arise from the C-0-S group formed during the modification reaction. The bands at 12.66 microns in tosylated cotton and a t 13.20 microns in mesylated cotton most probably arise from a C-S stretching. Although this vibration is usually found a t somewhat longer wave lengths, it does exhibit considerable variation ( 2 , S). I n the spectra of the tosylated cellulose, the band is probably unresolved from the C-H out-ofplane deformations about the aromatic ring with two adjacent free hydrogen atoms-Le., para substituted. The spectrum of the tosylated cotton exhibits the C=C skeletal in-plane vibrations of the aromatic ring a t about 6.25 and 6.7 microns. These bands distinguish tosplated from niesylated cellulose. The spectrum of unmodified cotton exhibits the expected C-H stretching band at 3.4 microns. This band is observed unchanged in the spectrum of tosylated cotton. The stretchings of the aromatic ring C-H groups ob1 iously are unresolved from the similar stretchings of the cellulose molecule. The spectrum of mesylated cotton, however, reveals a second band with maximum a t 3.25 microns, very piobably arising from a C-H stretching of the methyl group adjacent to the sulfonate. The intensity of this band increases with degree of mesylation and can be used both to identify and to measure quantitatively the degree of mesylation. It also differentiates between tosylation and mesylation. Tosylated or mesplated cotton can be detected and quantitatively deterniined by use of the sulfonate bands a t 7.3 and 8.5 microns. Both of these bands are of only moderate intensity and occur in a region nhere the unmodified cotton exhibits some absorption, arising principally from a C-H deformation band a t 7.2 microns and a C-0 and/or C-OH deformation with maximum at about 8.6 microns. For quantitative purposes the intensities of these bands can be best followed by the differential technique (LO). I n this procedure a disk of the unmodified cotton is placed in the reference beam of the 1002
ANALYTICAL CHEMISTRY
Figure 8.
Infrared spectra of acylated cottons A.
E. C. D.
E.
Cellulose acetate Cellulose cinnamate Cellulose stearate Unmodified control Cellulose benzoate
6 66 40
20 100-
CELL-OH
WAVE LENGTH IMICRONSI
Figure 9.
Infrared spectra of acylated cottons A.
B. C.
D. E.
Cellulase phenylacetate Phenylacetic acid Unmodified control Cellulose phenylundecanoate Phenylundecanoic acid
infrared spectrophotometer and a disk of the modified cotton in the sample beam. The resulting spectrum is the difference between the spectra of the two samples, with the interfering absorption arising from the cellulose molecule automatically subtracted. The sensitivity of these bands can, of course, be somewhat increased by preparing disks containing a greater portion of sample to potassium bromide. The bands b e h e e n 12 and 13 microns can also be used t o detect or t o quantitatively estimate the concentration of ted or mesylated cellulose. I n the case of the tosyl'ated compound probably both a sulfur group and an aromatic ring vibration are being measured, but as both of these are varying directly with the amount of tosylation, a satisfactory determination can he achieved n-ith correct calibration. These bands have the advantage of soinervhat higher sensitivity for the detection of these groups. Khether a particular cotton is tosylatetl or niesylated can be readily determined by the appearance of the :iromatic ring bands a t 6 2 5 and 6.7 microns. These bands could, again probably by the differential technique. be used to measure the concentration of tosyl modification in the presence of niesyl. Measurement of intensities at 7.3 or 8.5 microns or between 12 and 13 microns n-ould establish total niesyl plus tosyl modification. Measurement :it 6.25 microns (a-nich would be preferred over the weaker 6.7-micron band) n ould determine tosyl. Concentration of the niesyl substitution could then be had by difference. Curves relating the sulfur content to the measured intensities of the ahsorption bands a t 6.25 and 12.35 microns in a series of tosylated cottons are reproduced in Figure 5,C and D. These curves show that either band can be used for a satisfactory quantitative determination of the degree of tosylation. The sulfur contents were determined by a Parr peroxide fusion method (4, I S ) . I n Figure 7 the spectra of unmodified cotton and of partially acetylated rotton are compared with t h a t of a cotton modified both by partial acetylation and by tosylation. The detection or determination of the extent of acetyLition b!. the use of the band a t 5.68 inivrons is not affected by the tosylation, nor is the detection or determination of the tosylation by means of the bands a t 6.25, 7.3, 8.5, or 12.3 microns affected by the partial acetylation. I n cottons modified by two separate treatments, often it nil1 be possible to detect and measure quantitatively the extent of each treatment. Acylation. T h e infrared spectra of a number of acylated cottons are sh0n.n in Figures 8 a n d 9. The
agents used in obtaining t h e modified cottons can be grouped as follows: Major Division Saturated acids Aromatic acids
Example Acetic Stearic
Figure 8, A 8,c
Benzoic 8, E Phenylacetic 9, '4 Phenylundecanoic 9, D
Cnsaturated acidsa Cinnamic 8, B Aromatic acid Tvith nnsaturation in side chain. Cottons acylated with each of these three major classes of acylating agents can be readily identified bs inspection of their infrared absorption spectra. The cottons acylated with saturated acids exhibit the strong 5.7-micron band mentioned earlier in connection with partially acetylated cellulose. This band does not occur in the unmodified cotton and can be used both to identify and to determine the degree of the acylation. The aromatic acids may be divided into two subgroups. benzoic acid types and conipounds containing the phenylacyl group, C6H5(CH2).C=0. Aromatic acids can be differentiated from the ssturated acids by appearance of the C=C stretching vibration bands of the aromatic ring a t about 6.25 and 6.7 microns and by the characteristic aromatic ring band a t about 14.2 microns. These bands can be used to identify acylation of a cotton with a n y aromatic acid. For quantitative measurement of the degree of acylation, the C=O stretching vibration a t about 5.73 microns can be used, as in the measurement of partial acetylation. Benaylation can be distinguished from acylation with the acids containing the phenylacyl group by examination of the bands found in the spectra just above 6.0 microns and in the 13to 15-micron region. Conjugation of the C-0 group with the aromatic ring, as in benzoic acid, gives rise to the conjugated C=C stretching vibration a t 6.32 microns ( 2 ) . This conjugation in the benzylated cotton also causes :t decrense in the intensity of the band a t about 6.7 microns, so that the band a t 6.25 microns is the most intense in the spectra of cotton treated with benzoic acid. I n the region from 6.0 to 6.8 microns, the spectrum of the cellulose treated 11ith benzoic acid, therefore, reveals two bands: a moderately strong band with a maximum a t 6.25 microns and a neak band a t 6.35 microns. Not more than a very neak inflection is observed a t 6.7 microns. The spectra of cotton treated with phenylacetic acid or phenylundecanoic acid, however, reveal a strong band a t 6.7 microns, a
weak band at 6.25 microns, and nothing more than a weak inflection a t 6.35 microns. B y these differences the two types of acylation n ith aromatic compounds csn be distinguished. The spectrum of benzoylated cotton reveals the ring vibration band characteristic of aromatic compounds at 14.14 microns, not observed in the spectrum of the unmodified cotton. This band is also observed in the spectra of the cotton treated TI ith phenylacetic and phenylundecanoic acids, \\ ith mayima a t 14.4 and 14.3 microns, respectivelv. Cottons modified with these t n o reagents also exhibit a second band with maxima a t 13.0 to 13.1 microns. This band, not observed in the spectrum of the cotton treated with benzoic acid. is characteristic of the phenylacyl group (1 9). It can also be used to differentiate between a c j lation with a benzoic acid and a phenylacetic acidtype reagent. The infrared spectrum of the cinnaniic acid-treated cotton (Figure 8, B ) is differentiated from all others by the appearance of the strong band a t 6.15 microns, arising from a stretching vibration of the C=C group in the side chain. This band could be used both to identify this type of modification and to measure the degree of acylation with cinnamic-type reagent. although once identified, the amount of a c j lation could probably be more accurately etimated by use of the C=@ stretching vibration. I n the spectra of several of the acylated cottons (Figure 8,B; Figure 9. A and D),in addition to the strong C=O stretching band a t about 5.73 microns a second weaker band is obeervedat somewhat shorter TI ave lengths This band is not observed in the spectra of the pure acids. Cinnamic acid, for example, exhibits a strong acid C=O stretching band a t 5.90 microns ( S u ~ o l paste) (19), but no other band in this region. I n the spectrum of the cotton treated with cinnamic acid, strong bands are observed a t 5.83 microns, the expected position of the C=O ester, and a t 5.58 microns. The band mith maxinium a t about 5.6 microns is also observed in the spectra of the cottons treated nith phenylacetic acid and phenylundecanoic acid. although it is not obseri~edin the spectra of these t n o acids (Figure 9.B and E ) . The appearance of t n o C=O binds may present a method for determining the position of substituents on the cellulose molecule-Le., either on the 6 position (primary) -OH group as differentiated from one of the 2 or 3 position (secondary) -OH groups, or possibly, substitution in the easilj accessible amorphous region as coinpared with the less accessible crystalline region. Considerable additional research is required to evaluate the potential usefulness of these band. VOL. 2 9 , NO.
7,JULY 1957
1003
For such investigations, infrared absorption spectra a t considerably higher resolution than afforded with sodium chloride optics should be selected. Carboxyalkylation. Carboxyalkylation reactions of cotton can be distinguished from acylation by means of infrared spectra, because in t h e former no ester C=O stretching bands are observed. Carboxyalkylated cottons reveal no bands in t h e 5micron region (Figure 10). Unmodified cotton cellulose exhibits a band of moderate intensity a t 6.10 microns. I n the spectra of the carboxyalkylated celluloses, additional bands are observed in the region between 6.0 and 6.4 microns. Cotton carboxyalky-lated with chloroacetic acid (Figure 10, C) exhibits a broad band a t about G.2f microns. Cotton carboxyethylated with acrylic acid (Figure 10,D) reveals the 6.10-micron band and a broad band with maximum a t 6.40 microns. The breadth of the latter band indicates that it may consist of two bands unresolved by the sodium chloride prism. I n cotton treated with maleic acid (Figure 10,B), a very broad band appears over the region from 6.10 to 6.28 microns, probably arising from the 6.28micron band of the carboxylalkylated cotton unresolved from the 6.10-micron band of the unmodified cotton. I t is possible, too, that a third band with a maximum b e h e e n these tv-o is unresolved in these spectra. The hands in carbovyallcylated cottons between 6.0 and 6.4 microns arise from stretching vibrations of the COOion. These carboxyalkylation reactions are conducted in an alkali medium, resulting in the formation of the sodium salts rather than the free acids. This assignment is verified by a comparison of the spectra of the carboxyalkylated cotton before and after a hydrochloric acid wash (Figure 11). By this treatment the bands between 6.1 and 6.4 microns, arising from the COO- ion, are modified to the free acid, C=O, stretching mode a t the normal position about 5.8 microns. The assignment also explains why, in the spectra of the carboxyalkylated cottons, no bands are normally observed in the 5-micron region of C=O stretching. The bands produced by the carboxyalkylation reactions appear in these spectra as rather weak bands. It must be emphasized that the curves reproduced in Figures 10 and 11 represent spectra of cotton modified only to a slight extent. The degree of substitution of these carboxyalkylated cottons is, in all cases, less than 0.1 and for most of the samples, of the order of 0.04 to 0.05. It mould be of considerable interest to study the intensities of these bands with increasing degree of substitution. For such an investigation a spectrophotometer capable of
1004
ANALYTICAL CHEMISTRY
resolving the bands in the 6.0- to 6.4micron region should be used. Investigations of these bands a t a higher resolution might well result in an increased understanding of the mechanism of these types of reactions, particularly of the positions in which the etherification reactions are taking place on the cellulose molecule. SUMMARY
I n Table I are listed a number of
characteristic absorption bands observed in the spectra of cotton and modified cotton, together with the most probable correlation with vibrating groups which give rise to them and their specific uses in the examination of modified cotton by means of infrared absorption spectra. The procedure described has been used for the quantitative estimation of the degree of cyanoethylation, acetylation, tosylation, and the like. The bands listed in Table I can be used in
40 2o
CELL-OH
300
60-
5 40-
3.00 w 9
E 20-
-
6
7.0 759
20
o1
2
4'
3
Figure 10.
'
5
'
1
6 7 0 9 IO 1'1 I 2 WAVE LENGTH (MICRONS)
I3
I4
I5
I6
Infrared spectra of etherified cottons A.
E. C.
D.
-
CELL-O-CH~C::~
Unmodified coniral Modified with maleic acid Carboxymethylated Carboxyethylated
50
a 40 w
3 60I50 40-
I
5
I
6
L
7 5
6
7
L5
I 6
I
7
WAVE LENGTH (MICRONS)
Figure 1 1 . Infrared spectra, 5 to 7 microns, of etherified cottons, before and after acid wash A, C, E. 6,
D, F.
Maleic acid-modified, carboxyethylated, respectively, before acid wash Same after acid wash
carboxymethylated,
studies of the infrared spectra of various chemically treated cottons such as flameproofing with THPC [tetrakis (hydroxymethy1)phosphonium chloride-methylolmelamine copolymer] or other reagents. as PNECHBr3 (phosphonitrilic chloride allyl ester-bromoform adduct) or BAP (bromoformtriallyl phosphate polymer). Preliminary investigations indicate that infrared spectra obtained by means of the procedure described may be of considerable assistance in studies of oxidation or heat treatment of cotton or in investigations of the position of sub-
stituents within the cellulose molecule and possibly of the degree of crystallinity and of cross linkage. The procedure described provides, for the first time, a means whereby such investigations can be made by a simple, rapid, and reproducible infrared technique.
LITERATURE CITED ACKNOWLEDGMENT
The authors gratefully acknowledge the assistance given by several members of the Cotton Chemical Processing and the Cotton Fiber Sections of this laboratory in discussions of the various
~~~
Table
I.
Absorption Bands Useful in Investigation of Modified Cellulose
Approximate Position of Band RIaximum, Vibrating Group hlost Probably Giving Rise XBr Disk to Observed Spectra. Absorption Band hIicroris Free 0-H and 2 . 8 to 3 4 bonded 0-H, stretching C-H stretching of 3.25 CH, adjacent t o SO3 ( 7 ) C-H etretchings of 3.4 both unmodified and most modified cottons 4.45 C s - S stretching 5.58
C=O
5.68
C=O stretching (ester) C=O stretching (acid) C=C stretching aliphatic
5.8
6.15
(?I
stretching
6.25,6.70
C=C stretching (aromatic ring)
6.28
COO- ion stretching C=C stretching of conjugated aromatic ring C-H deformation
6.32 7.25 7.3, 8 . 5 8.6 12.1 to 12.3 12.7 to 13.2 13.1 14.2
-0-SO?-R fonate group) C-0 stretching and/or C-OH deformation C70-S stretching C-S stretching CsHsCH*C=O (phenylacetyl group) C-H deformation about aromatic ring
chemically modified cottons and for supplying several of the samples measured. They are indebted to Joseph J. Creely of the Cotton Fiber Section for the x-ray patterns of Figure 1.
Specific Use in Application to Cotton and Modified Cotton Investigations of extent and type of hydrogen bonding
Barnard, D., Fabian, J. RI., Koch, 1949,2442-54. H. P., J . Chem. SOC. Bellamy, L. J., “The Infra-Re:, Spectra of Complex RIolecules, Wiley, N e w York, 1954. Colthup, N. B , J . Opt. Soc. Anzer. 40, 397-400 (1950). Fisher, H. L., “Laboratory Manual of Organic Chemistry,” 4th ed., Wile\*. New York. 1938. (51 Ford. “hf. A , . Wiikinson, G. R., 338-41 (1954). 7 . K., Rowen, ’. D., J . Research X a t l . Bu;.‘ Standards 45, 109-113 (1950). (7) Genung, L. B., Mallatt, R. C., IND. ENG. CIIEM., A N A L . ED. 13, 369-74 (1941). (8) Harvey, 11. R., Stewart, J. E . , Achhammer, 13. G., J . Research N a t l . Bur. Standards 5 6 , 225-33 (1956). 01. Spectroscopy
Identification of mesylation, especially to differentiate from tosylation Characteristic of all cottons, modified and unmodified Identification and quantitative measurement of cyanoethylation Probable determination of position of substituent Identification and quantitative measurement of acylation Differentiation betxeen esterification and etherification with an acid (after HCl n-ash) Identification and quantitative measurement of modification with a nonaromatic, unsaturated compound, or aromatic compound containing unsaturated side chain Evidence for acylation Kith aromatic compound. Means for differentiation between tosylation and mesylation Evidence for etherification Rith an acid and resulting salt formation Evidence for acylation Yith benzoic-type reagent Characteristic of spectrum of unmodified cotton Evidence for tosylation or mesylation Characteristic of spectrum of unmodified cotton Identification and quantitative measurement of tosylation or mesylation Identification and quantitative measurement of tosylation or mesylation Identification and quantitative measurement, of acylation with phenylacetic acid-type reagent Identification and quantitative measurement of modification with aromatic compound
Rlann, J., Marrinan, H. J., Trans. Faradail Soc. 52.481-7 (1956). * , (12) Ibid., pp. 487-92. (13) I b i d . , pp. 492-7. (14) Marrinan, H. J , Xann, J., J . A p p l . Chem. ( L o n d o n ) 4, 204-11 (1954). (15) Meyer, R. J , Schuette, H. A., Abstracts of Paners. 128th Meet(16) (17) Nelson, M. L., Conrad, C. M., Textile Research J . 18, 155-64 (1948). (18) pa’; instrument CO., LIoline, 111 , Direction Booklet KO.116. (19) Randall, H. lI., Fowler, R. G , Fnson. Kelson, Danel. J. R . , ‘(Infrared Determinatcon of Organic Structures,” S‘an Nostrand, Ken, York, 1949. (20) Robinson, D. Z., A u ~ L CHEW . 23, 273-7 (1951). (21) Rowen, J. TI-., Hunt, C. M., Plyler, E. K., J . Research N a t l . Bur. Standards 39. 133-40 (1947). (22) Schiedt, IT.,Rdnwein, H., 2.’Katurjorsch. 7b, 270-7 (1952). (23) Schreiber, K . C., ASAL. CHEJI. 21, 1168-72 (1949). (24) Schwenker, R. F., TT’hitdl, J. C., Texfile Research J . 23, 804-8 ( 1953). (25) Stimson, M. M., O’Donnell, M. J., J . Am. Chem. SOC.74, 1805-8 (1952).
RECEIVEDfor review January 10, 1957. Accepted March 18, 1957. Southwide Chemical Conference, ACS, Memphis, Tenn., December 1956. Mention of names of firms or trade products does not imply that they are endorsed or recommended by the U. S. Department of Agriculture over other firms or similar products not mentioned. VOL. 29, NO. 7, JULY 1957
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