seen from the familiar solubility product relationship : KBp= [Ag+][X-] or [Ag+] = Ka, [X-I
(1)
Table II. Typical Titration Results of Mixed Halides in Li-K Nitrate Melt
Halides c1 Br
c1
I Br I
c1 Br I
Taken,
Found,
mg. 52.2 63.9 39.4 12.2 110.5 38.2 25.9 109.3 57.7
mg. 51.7 63.3 40.1 11.6 110.5 37.2 25.2 108.5 56.4
The modified Nernst equation, then, may be written as follows:
where E” is the sum of the appropriate constants. Plots of e.m.f. os. log[X-] give straight lines having slopes predicted by Equation 2. In a typical example, the experimental slope is 86.7 (for the chloride) as compared with the calculated slope 86.9. This is true, of course, only in cases where the melts have been saturated with silver halides. Hence, the present study has demonstrated that the silver electrode functions like a specific halide electrode in the melt under these conditions, and it may therefore be used for such purposes in certain fused salt solutions.
ACKNOWLEDGMENT
The author thanks Donald 0. Rudin, Department of Basic Research, Eastern Pennsylvania Psychiatric Institute, Philadelphia, for his kind permission to use some of the facilities of the institute. LITERATURE CITED
(1) Flengas, S.N., Rideal, E., Proc. Roy. SOC.(London)A233.443 11956). ( 2 ) Harrington, G. ‘W., Tien,’ H. T., J. Phiis. Chem. 66, 173 (1962). ( 3 ) Kolthoff, 1. M., Laitinen, H. A., “DH and Electro Titrations,” pp. 114L16, Wiley, New York (1941.). (4) Tien, H. T., Harnngton, G. W., Inorg. Chem. 2, 369 (1963).
Department of Chemistry Northeastern University Boston 15, Mass.
H. Ti Tien
Determination of Trimethylolpropane in Polyesters and Polyurethane Foams SIR: Very little is found in the literature on the identification and determination of polyols in synthetic polyesters. Similarly, there is a void in the literature on the identification and determination of components of polyurethane foams. In the analysis of polyesters, the conventional approach has been the saponification of the polyester followed by recovery, identification and estimation of the products of the saponification. In 1954, Kappelmaier, Mostert, and Boon (3) introduced a new approach to polyester analysis. The alkyd resin was reacted with excess amine to free the poly01 and convert the acid component to the corresponding amide. More recently, Esposito and Swann (2) qualitatively determined polyols by reacting esters prepared from phthalic anhydride with butylamine to free the poly01 which was then acetylated to convert the poly01 to the polyol acetate. The acetate was then identified by a procedure utilizing gas chromatography. A semiquantitative determination of polyols in polyesters
Table 1.
Trimethylolpropane Results on Polyesters
Sample A
B
C D
Trimethylolpropane, % 1.22,1.13 2.56,2.41 2.98,2.56 2.39,2.63 1.41,l.G
Lab prepareda Known trimethylolpropane content of
1.6270.
930
ANALYTICAL CHEMISTRY
by methanolysis is presented by Percival
(4).
The following work was initiated in an attempt to provide a quantitative procedure for the determination of polyols in polyesters particularly the small amounts of trimethylolpropane found in polyester formulations used in the production of flexible polyurethane foams and for the determination of trimethylolpropane in the polyurethane foams made from these polyesters. EXPERIMENTAL
Gas Chromatography Unit. The unit used to obtain the chromatograms was a ChromAlyzer 100 (Dynatronics Instrument Corp., Chicago, Ill.) equipped with a Sargent SR-30 recorder. The following parameters were used: Column size, 14-foot copper tubing .(3/16-inch 0.d.). Column packing, 20% ’Ucon 50HB2000 on 30- to 60-mesh Celite 545. Column, injection, and detector temperature 220’ C. isotherm. Helium gas flow, 130 ml. per minute for polyester analysis; 33 ml. per minute for polyurethane analysis. Detector cell current, 280 Fa. Attenuator setting, super sensitive. Reagents. All chemicals used were reagent grade. Procedure. An accurately weighed 5-gram sample of resin or foam was refluxed with 10 ml. of phenethylamine (b.p. 198’ to 200’ C.) for 3 hours. For the reaction of the foam it was first necessary to bring the amine t o reflux temperature before adding the foam which had been shredded. This brought about instant physical breakdown of the foam structure. If this is not done the foam absorbs the amine within its cell structure and, upon
physical breakdown of the foam, the amine is released onto the bare flask surface and is badly burned. After reflux, the reaction mass was cooled so that 25 ml. of acetic anhydride and 2 drops of water could be added. The mix was refluxed for another 90 minutes. The mix was cooled and 35 ml. of water were added. The mix was refluxed for another 5 minutes and, then, was cooled. The heterogeneous mix was then quantitatively transferred to a separatory funnel. It was estracted once with 20 ml. of chloroform and then twice with 10 ml. of chloroform. The collected chloroform layers were then washed 5 times with 50-ml. portions of water. The chloroform solution was then diluted to 50.00 ml. in a volumetric flask. A pinch of anhydrous sodium sulfate was added to dry the chloroform solution. A 30.0-pI. injection was made into the gas chromatography unit. The area under the elution curve for the trimethylolpropane triacetate was determined by means of a mechanical integrator in the work on polyesters. For the work on the foams, a greater degree of precision was desired because of the lower trimethylolpropane content. In this case, the area was determined by cutting out and weighing the paper forwed by the elution curve and the base line. Because of tailing of a previously eluted compound, the base line was not horizontal and the lower precision of the mechanical integrator can be understood. To further increase the precision of the foam analysis the helium gas flow rate was reduced to 33 ml. per minute. This greatly increased the detector sensitivity. Dimbat, Porter, and Stross ( I ) state that the area is inversely proportional to the gas flow for a given detector assembly. The retention time for the trimethylolpropane triacetate was 14.9
minutes a t the 33 ml. per minute slow flow rate whereas it had been 6.2 minutes a t the 130 ml. per minute rate. The amount of trimethylolpropane was then determined by relating the area for a sample to that obtained for a standard. A straight line relationship between the trimetliylolpropane content and the area was (demonstrated.
Since a urethane functional group is a “half-ester”, it was theorized that the aminolysis technique might be used on polyurethane foams as well as polyesters. The scheme was applied to urethane foam whose trimethylolpropane content was known to be 1.16%. Six determinations of trimethylolpropane in this urethane foam gave results ranging from 1.10 to 1.24%. The average mean deviation was -0.03%. In the above work it was noted that the diacetate of diethylene glycol was eluted in both the polyester and the polyurethane foam work. The diethylene glycol might have been determined in a manner similar to that described above for the trimethylol-
RESULTS AND I)ISCUSSION
Following the itbove analytical scheme, trimethylolp.ropane was determined on lab-prepared adipate polyester of known trimethylolpropane content as well as several commercially available polyesters known to be used in flexible polyurethane foam production. The results are summarized in Table I.
propane. I n fact, it is probable that any poly01 whose acetate can be characterized by gas chromatography might be determined similarly. LITERATURE CITED
( 1 ) Dimbat, M. Porter, P. E., Stross, F. H., ANAL.&EM. 28, 290 (1956). (2) Esposito, G. G., Swann, M. H., Ibid., 33, 1854 (1961). (3) Kappelmaier, C. P. A., Mostert, J., Boon, J. F., Verfroniek 27, 291 (1954). (4) Percival, D. F.,’ANAL.CHEM.35, 236 (1963).
ROBERT E. WITTENDORFER Plastics Division NOPCO Chemical Co. North Arlington, N. J.
Some Zone-Refining Calculations on Phena nthreiie-Anthracene System SIR: In recent yews, a number of investigators (3, 6, 6) have pointed out that controlled freezing methods may be used as an aid in elucidating uncertain regions of many phase diagrams. A project utilizing these techniques is currently in progress a t these laboratories and the work has involved the development of a computer program for the computation of zone refining concentration profiles. The calculations to follow are an example: They are based upon the zone refining experiment and phase diagram reported by Joncich and Bailey (2) for the phenanthrene-anthracene system, . and although performed primarily because this system with its discontinuity ap-
C*(x
peared to provide ideal test input data, the results are presented ?%cause of their possible general interest.. A mathematical model is provided by the following relationships for the solute concentration at a distance x along the nth pass: dC*(x
+ I ) - Cn(X)l/Z < x < ( L - 2)
+ 6)/dZ
= [C*(Z
+ 6) - C(Z)l
(3)
. C*(x)
(4)
where
C
=
C* =
[Cn-dx dC*(x
[C*(Z C(Z) = ko(C)
+ & ) / d x= for 0
+ 6 ) - C * ( x ) = [I - exp(f6/D)]
(1)
D L
+ 6) -
f 1 6
Cn(Z)I/(L - z) (2) for (t- 2) < x < L
= = =
= =
solute concentration in the solid solute concentration in the liquid diffusivity i n the liquid length of material involved growth rate zone length effective thickness of the diffusion layer
i
B
70
-
-
EXPERIMENTAL RESULTS OF
a a
a
407
\‘
40-
sp
30 20
-
10-
0
-i-L_L
0
05
IO
15
I
20
25
ZONE
Figure 1. passes
30 35 LENGTHS
40
45
50
55
Concentration profiles for 1, 2, 5, and 18
05
IO
1.5
20
25 3 0 3 5 40 ZONE LENGTHS
45
50
55
Figure 2. Concentration profiles for different growth rate parameters Experimental results of Joncich and Bailey superimposed on calculated profiles VOL. 36, NO. 4, APRIL 1964
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