ELOlSA B. MANO and
L.
C. 0.CUNHA LIMA
lnstitufo Nacional de Tecnologia, Loboraf6rio de Borracha e Pldsticos, Avenida Venezuela, 82, Rio de laneiro, Brazil CELLULOSIC GROUP b A new method for the rapid identification of cellulose derivatives in Two reactions appeared to exhibit molding mixtures or commercial goods best results for the detection of the i s described. Cellulose acetate, cellucellulosic group. Both must be used lose acetate-butyrate, cellulose nitrate, as they give different additional informamethylcellulose, ethylcellulose, hydroxytion and the procedures are described ethylcellulose, c a r ~ o x y m e ~ ~ y l c ~ ~ ~ u l obelow. se, and cellulose were investigated. All The first is the development of a pink except methyl- and hydroxyethylcolor on filter paper impregnated with cellulose, which react similarly in all aniline acetate through the hydroxytests, can be distinguished easily. methyliurfural resulting from cellulose. No special reagents or eqwiprnent are cellulose derivatives must be decomrequired and the meihod can be posed by warming with phosphoric acid; ~ as received ~ ethis is not ~ necessary ~ applied to the ~ for ~cellulose l itself without the need for prior purification. (5). The method is rapi The application of this reaction to chromatography required for the cellulose nitrate gives a yellow spot inidentification of the acetate grsu stead of a pink one. The reaction is independentiy of any other graup can carried oilt as foiiows: be done in about 2 hours. r o A, T ~ o a small~ fragment ~ of the ssmplc in a test tube add 1 N APPLYING several methods to detect various cellulose derivatives in molding mixtures or commercial goods, a new scheme was developed for their rapid identification. The proposed method was tried on 35 artificial samples specially prepared to test the efficiency of the scheme (8). The sample as received, unless in the form of a powder or film,was reduced to small fragments by filing or cutting and submitted to a cellulosic group detection. If positive, i t is observed if the sample is totally soluble either in acetone or in mater, by warming it with the solvent in a test tube. Being totally soluble in one of these solvents, the solution is discarded and the scheme can be followed using the integral sample. If some material remains insoluble, it. is necessary to obtain some acetone extract and some water extract to repeat the cellulosic group detection in each one. This is easily done in a test tube, because total extraction is not necessary. Complete insolubility in acetone and water may indicate cellulose and the cellulosic group detection must be repeated again in the insoluble residue. Brocedures are described to identify the following cellulosics: cellulose acetate, cellulose acetate-butyrate, cellulose nitrate, methylcellulose, ethylcellulose, hydroxyethylcellulose, carboxymethglcellulose, and cellulose.
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a
ANALYTICAL CHEMISTRY
Procedure B. T o a small fragment of the sample in a test tube add about 0.5 mI. of benzene and 1 ml. of 93% HzS04; Mrarrn carefully in a water bath until a n intense yellow develops which rapidly turns reddish; immediately cool t h e tube and layer with 0.5 ml. of ethyl alcohol without stirring. A blue or green ring between the two liquid phases is a positive test for cellulosics, except for ethylcellulose, which shows a violet one (7). The procedure to obtain the acetonesoluble and/or water-soluble extracts and/or insoluble residue, whenever the ~ sample is not totally soluble either in acetone or in water, is as follows: Use about 0.3 gram of sample, warming it with about 8 ml. of acetone; decant the solution directly over a small funnel fitted with a fluted filter paper and receive the filtrate in a watch g!ass; ~ ~ the solvent ~ evaporate m-ith warm air, obtaining the extract as a film. llpply drop of 86% K,3P644;cover t h e openProcedures A and B to this film. Wash ing of the tube vith filter paper, the residue from the acetone extraction fixing i t with the rlanip which holds in the test tube, warming it with acetone t h e tube. Yet the filter paper and discarding the liquid; dry it wjth cover Il-ith I drop of aniline acetate warm air. Extract this residue w t h about 8 ml. of warm water; filter the solution t o intercept the vapors comsolution as above. One milliliter of the ing from the 'tube, and heat strongly filtrate must be separated for Procedure t o carbonization of the sample. B F; evaporate the remaining in a watch pink spot on the paper is a positive test glass, and again apply Procedures A for cellulosics (31, except for cellulose and B. If some residue remains unnitrate which exhibits a yellow spot. dissolved, that may indicate cellulose; Prepare the anikne acetate solution in this case i t is necessary to repeat the immediately before use by adding 50% washings with water and acetone to be acetic acid to freshly distilled. aniline sure the residue is truly insoluble, and until turbidity disappears. to apply Procedures -4and B to it. The second reaction for the detection of the cellulosic group was developed in CELLULOSE ESTERS this laboratory (7') and shows an intense yellow color which turns re6dish when a Cellulose nitrate is immediately decellulosic material is warmel with bentected by the yellow color with aniline zene and 93yo H2S04; on the addition acetate reaction (Procedure il), which is of ethyl alcohol it turns deep blue or confirmed through the well known reacgreen. Only ethylcellulose among tion with diphenylamine and sulfuric numerous samples of cellulosics preacid. sented a different behavior: It shows the Procedure C. To B amall fragment same yellow color changing to reddish, of t h e integral sample in a porcelain as expected, but after the addition of crucible add 1 drop of a 670 diphenylethyl alcohol it becomes ~ i o l e t . (Four amine solution in concentrated HtS04 samples of ethylcellulose were exam(sp. g?. 1.84). If a deep blue deined with the same results. Two of velops immediately, the test for nitrate them were obtained from Schillingis positive (4). Hillier SA.,one from Hercules Powder Cellulose acetate and acetate-butyrate eo., and one from nfuehlstein & Go. must be saponified. Methods for detecThey were examined as received and tion of acetic and butyric acids were after purification through methanol exreviewed and several techniques were traction followed by acetone solution and applied to numerous samples of comfilm preparation.) mercial goods from different origins, to The procedure is as follows:
evaluate their suitability without the necessity for previoua purification of the resins (8). Paper chromatography was used to detect acetic and butyric acids after saponification of cellulose esters. Several solvent systems and color reagents were tried : Ethyl alcohol-ammonium hydroxide and bromocresol green appeared to be the most convenient. The chromatogram can be developed in about 2 hours. The procedure is as f0:lows : Procedure D. To about 0.5 gram of the integral sample in a beaker add about 10 ml. of 15% N a O H aqueous solution; warm about 15 minutes, acidify with H2S04 solution, and keep the volume of the solution containing the acids as small as possible. Filter through cotton and distill about 1 ml. For t h e microdistillation use a test tube fitted with a cork with a glass tube bent ina Vshape. Receive the distillate containing the volatile acids in another test tube immersed in a beaker filled with cool water. To the acid distillate add l drop of NH40H solution (sp. gr. 0.90) and develop the ammoniumsalts by paper chroinatography in the conventional way (1). Use the ascending technique on Whatman No. 1 filter paper about 25 cm. long with 95% ethyl alcohol-aqueous K H 4 0 H (sp. gr. 0.90) 99:l v./v. as solvent ( 5 ) . Two hours at a temperature of 25’ to 30” C are sufficient to identify the acetic and/or butyric acids. Dry the chromatogram with warm air and immediately develop it with a 0.0470 bromocresol green ethanolic solution with a p H adjusted to 5.5 with citric acid or KaOH ( 1 ) . Under these conditions, with a solvent front of 17 cm., acetic and butyric acids are detected in a mixture of volatile acids by blue spots with R, values, respectively, of 0.49 and 0.71 at 25’ C. The acids are always identified by comparison with the R f values of standard 1% solutions of pure acids as their ammonium salts chromatographed under exactly the same conditions. Dry distillation of the calcium salts of the volatile acids was also used to detect acetic acid in the integral sample. If acetone is formed it can be identified through reaction with onitrobenzaldehyde (5). The procedure 4s as follows: Procedure E. Saponify exactly as under Procedure D ; distill about one third of the initial volume, and t o this distillate in a test tube a d d calcium oxide until no more solution is observed; heat carefully t o dryness and cover t h e test tube with filter paper fixing i t with the clamp which holds the test tube. Wet the filter paper cover with 1 drop of a saturated solution of a-nitrobenzaldehyde in a 8% solution of NaOH to intercept the vapors coming from the tube. Dry distillation of the calcium salt shows a blue or greenish blue spot if acetone is formed which indicates acetate group in the sample. The color is best observed by
wetting the spot on the filter paper with a 10% aqueous solution of HC1 (3). If the sample is cellulose acetate-butyrate this test is not very sensitive. CELLULOSE ETHERS
Carboxymethylcellulose is easily identified through its cupric (2) or lead salt (8); for the remaining ethers, no other satisfactory simple test was found for their identification. However, ethylcellulose can be distinguished immediately by its particular behavior when the cellulosic group is characterized, confirmation being through its physical properties : Methyl- and hydroxyethylcellulose remain without differentiation. The procedure for carboxymethylcellulose identification is as follows: Procedure F. T o the aqueous extract of the sample add a few milliliters of a 170 aqueous solution of cupric sulfate (8) or lead acetate (8). A flocculent precipitate indicates carboxymethvlcellulose. SCHEME
FOR ANALYSIS
test tube, decomposes immediately with evolution of nitrous vapors. Solubility, mixture 1:1 ethyl etherethyl alcohol. Insolubility, benzene. Procedure C, deep blue. Ethylcellulose. Heating in a test tube, melts; decomposes with smell of burning paper. Solubility, ethyl ether. Insolubility, ethylene glycol. Carboxymethylcellulose. Heating in a test tube, chars without melting; smell of burning paper. Solubility, ethylene glycol. Insolubility, ethyl ether. Procedure F, flocculent precipitate. Methylcellulose or Hydroxyethylcellulose. Heating in a test tube, chars without melting; smell of burning paper. Solubility, ethylene glycol. Insolubility, ethyl ether. Procedure F, no precipitate. Cellulose. Heating in a test tube, chars without melting; smell of burning paper. Solubility, Schweitzer reagent (6). Insolubility, all common solvents.
OF CELLULOSICS
The preceding remarks are summarified in a new scheme for analyeis of cellulosics applied directly on the integral sample :
Procedure A, pink or yellow
Procedure B, blue, green, or violet
LITERATURE CITED
(1) Block, R. J., Le Strange, R., Zweig, G.,
“Paper Chromatography -A Labor&tory Manual,” Academic Press, New York, 1953.
Acetone Extract Procedure A, pink Procedure B, blue or green Procedure A, yellow Procedure B, blue or green Procedure A, pink Procedure B, violet Water Extract Procedure A, pink Procedure B, blue or green Residue Procedure A, pink Procedure B, blue or green
Each cellulose derivative has the folloming characteristic behavior: Cellulose Acetate. Heating in a test tube, melts; decomposes with smell of burning paper and acetic acid. Solubility, chloroform. Insolubility, ethyl ether. Saponification, Procedure D, acetic acid; Procedure E, blue or greenish blue. Cellulose Acetate-Butyrate. Heating in a test tube, melts; decomposes with smell of burning paper, butyric a n d acetic acids. Solubility, chloroform. Insolubility, ethyl ether. Saponification, Procedure D, acetic and butyric acids; Procedure E, blue or greenish blue. Cellulose Nitrate. Heating in a
Cellulose acetate Cellulose acetate-butyrate Cellulose nitrate Ethylcellulose Methylcellulose Hydroxyethylcellulose Carboxymethylcellulose Cellulose
(2) Earart, M. H., Chapman, R. A., ANAL.CHEW24,1460 (1952). (3) Feigl, F., “Spot Tests,” Vol. 11, VD. -. 248, 355, Elsevier, Netherlands, 1954. (4) Houv$k, R., “Elastomers and Plastomers. Vol. 111, TI. 75, Elsevier, Netherlands, 1948. (5) . . Kennedy, E. P., Barker, H. A., ANAL.CHEM. 23 1033 (1951). (6) Luniak B., “The Identfication of Textile F’ibers,” TI. 94, Sir Isaac Pitman I% Sons, Ltd., ‘Lohdon, 1951. (7) Mano. E. B., Cunha Lima, L. C. O., 301.Instituto Nacional de .Tecnologia (Rio de Janeiro) 5, No. 12, 15 (1954). (8) Mano, E. B., Cunha Lima, L. C. O., Zbid., 5 , No. 13, 3 (1954). RECEIVEDfor review January 4, 1960. Accepted July 19, 1960. Taken in part from a study on qualitative analysis of lastics which has been done in the ubber and Plastics Laboratory of the Instituto Nacional de Tecnologia, Rio de Janeiro (Brazil).
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“Ob. 32, NO. 13, DECEMBER 1960
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