WiNiom A. Foreman rand Donald R. Paulron California Stote College 10s Angeles, 90032
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Partial Analysis 01VinyI-AS~~S~OS floor Tile A t k experiment for beginning organic chemistry
O n e problem associated with the undergraduate organic laboratory has been that it rarely gives the student a feeling for the types of experiments routinely carried out in industrial chemical laboratories. Because of this deficiency we have developed an experiment for the beginning organic laboratory which introduces thin-layer chromatography to the student while at the same time presenting the student with a typical industrial analysis problem. Vinyl-asbestos floor tiles are widely used floor coverings which are to be found in both homes and commerical buildings. They are composed of binder and filler. The binder constitutes some 20-25% of t,he tile and is made of a vinyl polymer, plasticizer, and minor processing aid components. In the case of embossed tiles the printing ink can be considered a part of the binder. The filler contains asbestos, limestone, and pigments. In this experiment the binder is isolated, and its major components identified. The vinyl-polymer is poly(viny1 acetate)poly(vinyl chloride) which can be readily identified by the infrared spectrum of a thin film of the polymer (1). The plasticizers are usually diesters of phthalates, sebecates, and adipates as well as other less common types. The tlc of plasticizers was first performed by Peereboom (2) and later by Braun (5). These authors used bisbutyl sebecate (DBS) as their standard and reported RA variations of 10.06. We have found that better results are obtained if bis(Zethylhexy1) sebecate (DOS) is used as standard since most commercial samples of DBS which we have examined show the presence of two spots on the tlc plate. Listed in the table are the R, values which we have obtained for fourteen different plasticizers using methylene chloride as the developing solvent. The R., values which students obtain will depend upon the procedure used, especially the size of the developing tank. However, they should be related to our R, values by a simple multiplicative factor and should be within *0.08 of our values. Samples of most of these plasticizers can be obtained from the major chemical supply houses. We have -
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A ball-mill such as that used in geology classes to grind rock samples works very well. % T h eTHF must he purified not only because of the peroxide daneer hut because the stabilizer used in THF will interfere with the&~ticiner analvsis. Acetone mav he substituted far T H F
steam bath
572
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Journal of Chemical Education
RA Valuer (DOS = 1.00) Chromatographed on E. Merck Darmstadt Silica Gel F254 Plates Using Methylene Chloride a s Eluent
Phthalates DEP Bisethylphthalate DOP Bis(2-ethylhexyl)phthalate BBP Benzylbutylphthalate DMEP Bis(methoxyethyl)phthdate DIOP Bisisooctylphthalate DIDP Bisisodecylphthalate DUP Bisundecylphthalate Adipates DOA Bis(2-ethylhexyladipate) DIDA Bisisodecyladi~ate ~. Sebecates DBS Bishutylsebecate DOS Bis(2-ethvlhexvl)sehecate
found the most reproducible RA values are obtained by using precoated silica gel plates which are readily available from numerous sources. Several good books on plastics analysis are available (4-6). Experimental Binder isolation Break the tile into s m d pieces and grind these into a coarse powder.' Into a 250-ml round bottom flask equipped with stirring and a reflux condenser add 5 g of powdered tile and 150 ml of freshly distilled tetrahydrofuran.2 Reflux the mixture with stirring for 1 hr and cool it to room temperature. Filter the milky-grey mixture with saction through a Biichner funnel which has been filled with 1in. of filter aid. Then filter the solution 8. second time using grwity filtration and a X42 filter paper. Concentrate the solution down to 20-30 mlJ and add slowly with stirring 150 ml of methanol. The white solid which precipitates is the vinyl polymer. Filter off the polymer with suction and redissolve it in a minimum amount of tetrahydrafuran. Reprecipitate the polymer by slowly adding metbanol with stirring until no more polymer precipitates. Filter the polymer off again and air dry it. The original methsnol solution containing the plasticizer is now concentrated3 to about 30-40 ml and filtered to remove any precipitate which may have formed. Then evaparete the solution down8 to a few tenths of a milliliter of an involatile liquid; this is the plasticizer. Polymer Identification Prepare B 1% solution of the dry. polymer in dichloromethnne by gently warming and agitating. Into three aluminum cups pour respectively 10, 15, and 20 ml of the polymer solution and
allow the solvent to evaporate off by itself without disturbing the cup.' Once the solvent has completely evaporated, warm the cup on a steam bath for 5-10 min, after which cool and peel off the polymer film from the cup. Choose the best polymer film and take an infrared spectrum by placing the film across the spectrophotometer sample beam using a KBr pellet holder.5
TLC ldentificotion o f Plasticizer Take a 5 X 20-cm tlc plate and s t 1.5 em from the bottom edge gently trace a line across the plate using a soft pencil. On this line mark three points at 1.5, 2.5, and 3.5 cm from the side. At 10 cm up the plate from this line cut a groove across the plate through the'silice.gel layer all the way down to the glass plate. Make a 10% benzene solution' of your plasticizer concentrate. If necessary filter again. On the marked spots place 1 spots of: dibutyl sebacilte (DBS), plasticizer solution, and 5% di(2-ethylhexyl) sebacate (dioctyl sebacate, DOS), respectively. Develop the plate in dichloromethane, after which allow the solvent to evaporate off and visualize as follows: 'The best thickness far the polymer film will depend upon the spectrometer used. Alternatively, the polymer may be taped over a piece of cardboard with a hole cut in the center. 'The tlo plate will inevitably show the presence of non-plastioieer components such as processing aids. These are usually less soluble in benzene than in methanol.
(1) Examine the plate under a. uv lamp and outline any spots that may appear. (2) Place the plate in an iodine chamber, once the spots become visible outline any additional spots. (3) Allow the iodine to sublime off the plate, then in a. hood sorw the plate witha solutionof SbCL in CCI.- (1 , :5). , Place the platein an oven at l l O T for l d m i n to obtain a permanent record. Determine the RA values of your plasticizer components relative to both DBS and DOS by measuring the distance from the center of each spat to the origin line and dividing this value by the similar value obtained for DBS and DOS. From the references given, identify the plasticizer components. Confirm your identification by running a tlc of your plasticizer against a known sample of plssticizer and compare Rn values in several solvents. Literature Cited (1) HOMMEL. D.
0.."Infrared Spectra of Polymers." Interscience. New
York. 1966,
J. Chromatog., 4, 323 (1960). (3) B ~ m n D.. , "Plaatioiser Analyais Using Chromatographic Methods," in P ~ m a r n N. , J., (Editoi), "Plaatiaization and Plastioin~r Processes." Advances in Chemiatry Series No. 48. American Chemical Society, 1965, pp. 95-107. (4) H & a ~ * rJ.. . AND w ~ m ~H. s .A.. "Identifiostion and Analyeis of Plastics:' Iliffe Books. D. Van Noatrand. London. 1965. (5) K n o 8 ~ .A,. A N D A. LAASE, "Introdwtion to the Chemical Analysis of Plastics." Iliffe Booka. London. 1969. (6) W m n s ~ M.. . T E N ~ . E RH.. . OSTAOMOW. H., "Die Analyse von Weichmaohern" (Chernie. Physik and Teohnologie der Kunstatoffe in E i n z ~ Ldarstellungen 11). Springer-Vedag, Bsdin. 1967. (2) Pmnrsooht, J. W. C.,
Volume 49, Number 8, August 1972
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