Determinations acrylonitrile

Analytical Methods for Determining Acrylonitrile in Biological Materials... 

Methods for determining acrylonitrile in environmental samples are quite good. It may be assumed that the normal incentives for both research and the development of commercial methods of analysis will result in new analytical methods for acrylonitrile that have improved sensitivity and selectivity. Degradation products of acrylonitrile in environmental media are difficult to determine. This difficulty is not as much an analytical problem as it is a problem of knowing the fundamental environmental chemistry of these compounds in water, soil, air and biological systems. 

Like styrene content determination, acrylonitrile content in nitrile rubber can be determined with IR spectra following the quantitative analysis method. Butadiene units, adding up to an acrylonitrile unit in the polymer chain, show a strong tendency to add... 

The polarograph is adjusted to the acrylonitrile start potential (-1.7 V). To determine acrylonitrile, the operations described previously for styrene are repeated by using a solution of acrylonitrile in a DMF-water (95 + 5 v/v) mixture to make the standard solution of acrylonitrile. The voltage, V cn which the maximum polarographic reading occurs is noted. 

Residual amounts of styrene and acrylonitrile monomers usually remain in manufactured batches of styrene-acrylonitrile copolymers and acrylonitrile-butadiene-styrene terpolymers (ABS), As these copolymers have a potential use in the food packaging field, it is necessary to ensure that the content of both of these monomers in the finished copolymers is below a stipulated level. In a polarographic procedure [9, 10] for determining acrylonitrile (down to 2 ppm) and styrene (down to 20 ppm) monomers in styrene-acrylonitrile copolymer, the sample is dissolved in 0.2 M tetramethylammonium iodide in dimethyl formamide base electrolyte and polarographed at start potentials of -1.7 V and -2.0 V, respectively, for the two monomers. Excellent results are obtained by this procedure. Table 5.3 shows the results obtained for determinations of acrylonitrile monomer in some copolymers by the polarographic procedure. 

High performance liquid chromatography, using the reverse phase mode has been used to determine acrylonitrile monomer and related compounds, including meth-acrylonitrile in polyacrylamide (Method 51). 

Shanks has determined residual butadiene and styrene in polymers with an analytical sensitivity of 0.05 to 5 ppm by analysis of the equilibrated headspace over polymer solutions and determined acrylonitrile, alpha-methyl styrene and styrene monomers by headspace analysis over heated solid polymer samples. 

In a polarographic procedure for determining acrylonitrile (down to 2 ppm) and styrene (down to 20 ppm) monomers in styrene-acrylonitrile copolymer, the sample is dissolved in 0.2 M tetramethyl ammonium iodide in dimethyl formamide base electrolyte... 

The methanol azeotropic-distillation procedure was also applied to a synthetic solution of acrylonitrile in 6% hydrochloric acid extractant. Polarographic analysis of the methanol-acrylonitrile azeotrope was not possible, however, owing to the presence of an appreciable amount of free acid originating from the hydrochloric acid extractant, in the distillates, which interfered in the polarography of acrylonitrile. In a further experiment, a 6% hydrochloric acid solution of 47.3 ppm of acrylonitrile was neutralised by the addition of a small excess of solid calcium oxide. Methanol and sulfuric acid were added and the azeotropic distillation continued as before. It can be seen from Table 11.1 (sample B) that under these conditions more than 90% of the added amount of acrylonitrile was recovered in the first 8 ml of methanol distillate. A preliminary neutralisation with lime was incorporated, therefore, into the procedure for determining acrylonitrile in 6% hydrochloric acid extraction liquids. This procedure should also be applicable to the determination of acrylonitrile in the 3% aqueous acetic acid extractant recommended by the Food and Drug Administration (FDA) [3]. 

Detailed procedures for determining acrylonitrile monomer in the various extractants are described next. 

Provided that a suitable sample size is taken for analysis, the azeotropic distillation-polarographic procedure can be used for determining acrylonitrile in extractants in concentrations down to 1 ppm or a little lower. Thus, it is seen from Table 11.1 that approximately 90% of the added amounts of acrylonitrile is recovered when the procedure is applied to 500 ml of a 0.75 ppm solution of acrylonitrile in the distilled-water extractant. The method can be used for achieving a similar level of sensitivity in the determination of acrylonitrile in the other aqueous alcoholic or oily extractants for plastics recommended by the British Plastics Federation [4] and the FDA [3]. This level of sensitivity is quite adequate for the examination of extractants that have been brought into contact with styrene-acrylonitrile copolymers under the British Plastics Federation and FDA extractability-test conditions. 

Acrylonitrile reacts with the sodium salt of 4.5-dimethvl-A-4-thiazoline-2-thione (73J (R4 = R5 = Me) to yield 3-(2-cyanoethyl)-4.5-dimethyl-A-4-thiazoline-2-thione (74) (R4 = R, = Me) (Scheme 35 (160). Humphlett s studies of this reaction showed that the size of the R4 substituent is a determinant factor for the S versus N ratio (161. 162). If R4 == H, 100% of the N-substituted product (74) is obtained this drops to 50% when R4 = methyl, and only the S-substituted product (75) is obtained when R4 = phenyl. The same trend is observed with various CH2 = CH-X (X = C00CH3. COCH3) reagents (149). The S/N ratio also depends on the electrophilic center for CH2 = CH-X systems thus S-reaction occurs predominantly with acrylonitrile, whereas N-substitution predominates with methvlvinvlketone (149). 

Standard test methods for chemical analysis have been developed and pubUshed (74). Included is the determination of commonly found chemicals associated with acrylonitrile and physical properties of acrylonitrile that are critical to the quaUty of the product (75—77). These include determination of color and chemical analyses for HCN, quiaone inhibitor, and water. Specifications appear in Table 10. 

Analytical investigations may be undertaken to identify the presence of an ABS polymer, characterize the polymer, or identify nonpolymeric ingredients. Fourier transform infrared (ftir) spectroscopy is the method of choice to identify the presence of an ABS polymer and determine the acrylonitrile—butadiene—styrene ratio of the composite polymer (89,90). Confirmation of the presence of mbber domains is achieved by electron microscopy. Comparison with available physical property data serves to increase confidence in the identification or indicate the presence of unexpected stmctural features. Identification of ABS via pyrolysis gas chromatography (91) and dsc ((92) has also been reported. 

Copolymers of VF and a wide variety of other monomers have been prepared (6,41—48). The high energy of the propagating vinyl fluoride radical strongly influences the course of these polymerizations. VF incorporates well with other monomers that do not produce stable free radicals, such as ethylene and vinyl acetate, but is sparingly incorporated with more stable radicals such as acrylonitrile [107-13-1] and vinyl chloride. An Alfrey-Price value of 0.010 0.005 and an e value of 0.8 0.2 have been determined (49). The low value of is consistent with titde resonance stability and the e value is suggestive of an electron-rich monomer. 

The ratio of monomers can be varied from zero acrylonitrile up to approximately 60% to produce copolymers of zero to about 50% acrylonitrile. This is, of course, a cmcial factor in determining the properties of the final material. Rubbers with low acrylonitrile content have extremely low glass... 

There is supporting evidence in the literature for the validity of this method two cases in particular substantiate it. In one, tests were made on plastics heated in the pressure of air. Differential infrared spectroscopy was used to determine the chemical changes at three temperatures, in the functional groups of a TP acrylonitrile, and a variety of TS phenolic plastics. The technique uses a film of un-aged plastic in the reference beam and the aged sample in the sample beam. Thus, the difference between the reference and the aged sample is a measure of the chemical changes. 

Example 13.6 The following data were obtained using low-conversion batch experiments on the bulk (solvent-free), free-radical copol)mierization of styrene (X) and acrylonitrile (Y). Determine the copolymer reactivity ratios for this pol5Tnerization. 

Example 13.7 A 50/50 (molar) mixture of st5Tene and acrylonitrile is batch polymerized by free-radical kinetics until 80% molar conversion of the monomers is achieved. Determine the copolymer composition distribution. 

Determine the copolymer composition for a styrene-acrylonitrile copolymer made at the azeotrope (62 mol% styrene). Assume = 1000. One approach is to use the Gaussian approximation to the binomial distribution. Another is to synthesize 100,000 or so molecules using a random number generator and to sort them by composition. 

Thus the IR active modes will be determined by the matrix elements of the polarlsablllty matrix and not by a combination of the surface selection rule and the normal IR selection rules l.e. all of the Raman active modes could become accessible. This effect has been formalized and Its significance assessed In a discussion (12) which compares Its magnitude for a number of different molecules. In the case of acrylonitrile adsorption discussed In the previous section, the Intensity of the C=N stretch band appears to vary with the square of the electric field strength as expected for the Stark effect mechanism. 

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