Acknowledgment
The author expresses his appreciation to Edward Dickinson, Australian Road Research Board, and Keith Martin, Division of Building Research, Commonwealth Scientific and Industrial Research Organization, for their active interest and helpful advice, to Reginald Parker for infrared analysis, and William Grunden for assisting with the experimental work, and to the directors of ICIANZ for permission to publish this paper. literature Cited
Beitchman, B. D., J . Res. Nut. Bur. Stand., 64C, 13 (1960). Blokker, P. C., Van Hoorn, H., Fifth World Petroleum Congress, Section VI, paper 27, 1959. Garten, V. A., Weiss, D. E., Rev. Pure Appl. Chem., 7, 69 (1957). Hveem, F. N., Zube, E., Skog, J., Proc. Assoc. Asphalt Paving Technol., 32, 271 (1963).
Labout, J. W. A., Van Oort, W. P., Anal. Chem., 28, 1147 (1956). Lubbock, F. J., Kershaw, R . W. (to Balm Paints Pty., Ltd.), Australian Patent Application 21435 (May 8, 1967). Martin, K. G., J . Appl. Chem., 14,423 (1964). Martin, K. G., J . Appl. Chem., 16,197 (1966a). Martin, K. G., Proc. 3rd Conf. A.R.R.B., 3, 1433 (1966b). Martin, K. G., Proc. 4th Conf. A.R.R.B., 4 , 1477 (1968). Traxler, R. N., “Asphalt, Its Composition, Properties and Uses,” p 108, Reinhold, New York, 1961. Traxler, R . N., National Asphalt Paving Association, Q.I.P. Publ., 75 (1964). Volkova, V. L., Avtom. Dorogi, 12, 25 (1958). Wright, J. R.: Campbell, P. G., J . Appl. Chem., 12, 256 (1962). RECEIVED for review March 26, 1970 ACCEPTED August 21, 1970
COMMUNICATIONS
Organotin Compounds in Stabilization of Polyvinyl Chloride ( PVC) The syntheses and the evaluation of the following new organotin compounds are described: Dibutyltin di-3-pentadecylphenolate, dibutyltin dialeuritate, dibutyltin di(2-pentadecyl-4methoxyphenyl)mercaptide, and dibutyltin disalicylaldehyde.
C o m p o u n d s having structure R,SnX4 n , where R is an organic radical bonded t o the tin atom through a carbon atom and X is an organic radical bonded to the tin atom through an oxygen or sulfur atom or an acid group, are used as stabilizers for polyvinyl chloride (PVC). The efficiency of organotin compounds is attributed to their polyfunctionality. The C-Sn bond, which can be broken a t processing temperatures to give free radicals which then combine with free radicals in degrading PVC, prevents further dehydrochlorination of PVC (Kenyon, 1953). In addition, X groups can replace labile chlorine atoms in PVC by an ester exchange reaction which removes the probable sites of initiation of degradation of the polymer (Frye et al., 1964a). The stabilizing action of organotin compounds a t high temperatures may be attributed t o the additional effect of sulfur compounds in destroying peroxide groups which catalyze the dehydrochlorination of PVC (Frye et al., 196413). I n the process of removing cashew kernels, a dark oily phenolic product, cashew nut shell liquid (CNSL), is obtained. Distillation of this oily liquid under reduced pressure gives us an alkenyl phenol, namely 3-pentadecenyl phenol in 60% yield. This phenol on hydrogenation gives pure 3-pentadecyl phenol m p 5O-l0C. CNSL is used to produce such items as cation-exchange resins, chemicalresistant tiles, pesticides, surface active agents, foundry core oil, paint and varnishes, and rubber chemicals. Shellac has been used in applications such as surface coatings, printing ink, insulation materials, food, phar~
214
Ind. Eng. Chem. Prod. Res. Develop., Vol. 10, No. 2, 1971
maceuticals, cosmetics, and in handicrafts. During the hydrolysis of shellac, an acid known as aleuritic acid is obtained in 33% yield, m p 100°C. This acid contains three free hydroxyl groups. Recently soaps of this acid have been found t o be good heat stabilizers for PVC. The present investigation was undertaken to explore the possibilities of obtaining some useful new tin stabilizers for PVC from CNSL and shellac. Experirnental
Methods for the synthesis of these compounds are shown below:
BuI
+
%
-
B‘\
BuP = O
7-
where
9R=
bc.,,,.
R=
0c1 I OCH,
0
R
-0-
0-
R=
Preparation of 2-Pentadecyl-4-methoxyphenylmercaptan
II
C-CH,-(CHJ,-CH-CH-(CH,)j-CH,OH
I
OH
(yHO
I
OH
Preparation of Dibutyltin Di-3-pentadecylphenolate
First Method. In a 100-ml round bottomed flask fitted with a reflux condenser with a guard tube were placed 4 grams of sodium salt of 3-pentadecylphenol, 1.8 grams of dibutyltin diiodide, and 25 ml of xylene. The mixture was refluxed for 48 hr. At this stage, the xylene soluble part did not show a positive test for iodine. The xylene was removed under reduced pressure and the residual compound was dissolved in 60-6°C petroleum ether. The solution was filtered. The petroleum ether was distilled off under reduced pressure from the filtrate. The residual compound weighed 4.2 grams. Second Method. I n a 100-ml round bottomed flask were placed 3.04 grams of 3-pentadecylphenol and 1.6 grams of dibutyltin oxide, and the mixture was stirred well. The mixture was kept under reduced pressure a t 60°C until most of the dibutyltin oxide went into solution. Then the temperature was raised to 90" C and the mixture was kept under reduced pressure for another 2 hr. The mixture was then cooled, dissolved in 30 ml of dry 60-@ C petroleum ether, and filtered. The petroleum ether was distilled off when 3.2 grams of semisolid was obtained. Anal. Found: C, 69.21; H, 10.22; Sn02, 18.18. Calcd. for CsoHssOsSn:C, 71.53; H , 10.49; SnOz, 17.94. Preparation of Dibutyltin Di( 2-pentadecyl-4met hoxyphenyl)mercaptide
Preparation of 3-Pentadecylphenylmethyl ether. 3-Pentadecylphenol was methylated by dimethyl sulfate, bp 181P C / 2 mm (lit. bp 180-l°C/2 mm). Preparation of Di( 2-pentadecyl-4-methoxyphenyl)disulfide
I n a 250-ml round bottomed flask fitted with a reflux condenser were placed 15.0 grams of 3-pentadecylphenylmethyl ether, 100 ml of 60-6" C petroleum ether, 0.2 gram of anhydrous aluminum chloride, and 3.3 grams of sulfur monochloride. The mixture was refluxed for 48 hr. No more HC1 was evolved a t the end of this period. The solution was cooled, washed with water, and dried over anhydrous sodium aulfate. I t was filtered and the petroleum ether was distilled off. The residual liquid weighed 14.0 grams. On distillation under reduced pressure, the fraction collected a t 220-5" Ci0.25 mm analyzed as di(2pen tadecyl-4-methoxypheny1)disulfide. Anal. Found: C, 75.93; H , 10.05; S, 9.03. Calcd. for C44H7402S2: C , 75.7; H, 10.59; S, 9.16.
I n a 250-ml 3-necked flask, fitted with stirrer and refluxing condenser were placed 12.0 grams of di(2pentadecyl-4-methoxyphenyl)trisulfide, 20 ml of hydrochloric acid, 25 ml of water, and 70 ml of 60-6" C petroleum ether. The mixture was heated on a water bath and 2.5 grams of zinc dust was added slowly in '5 hour with stirring. The mixture was refluxed for 4 hr more and then filtered. The filtrate was washed with water, dried over anhydrous sodium sulfate, and filtered. Petroleum ether was distilled off from filtrate. The residue was dissolved in methanol and cooled. A solid having mp 33-4" C was separated. Yield 9.5 grams (sometimes the mercaptan remains in liquid form). Anal. Found: C, 75.25; H , 10.42; S, 9.1. Calcd. for CZZHJaOS: C, 75.43; H , 10.85; S, 8.64. Its 2,4-dinitro derivative is bright yellow colored crystals (from methanol), mp 58OC. Anal. Found: C, 65.24; H, 7.0; N , 5.0. Calcd. for: C2RHloN205S: C, 65.12; H, 7.75; N , 5.42. Preparation of Dibutyltin Di( 2-pentadecyl-4-methoxyphenyl) mercaptide
In a 50-ml round bottomed flask was placed 3.5 grams of 2-pentadecyl-4-methoxyphenylmercaptan heated to 60" C. To this was added, in 14 hr, 1.5 grams of dibutyltin oxide, keeping the mixture under reduced pressure. After complete addition of dibutyltin oxide, the mixture was kept under reduced pressure at 90" C for 1 hr. The mixture was then dissolved in 60-6" C petroleum ether and filtered. Petroleum ether was removed to give a pale yellow liquid. Yield 3.6 grams. Anal. Found: C, 68.17; H, 10.06; SnO?, 16.17. Calcd. for Cj2HS202S2Sn: C, 67.05; H , 9.88; Sn02, 16.19. Preparation of Dibutyltin Dialeuritate
I n a 50-ml round bottomed flask were placed 4.0 grams of aleuritic acid and 2.0 grams of dibutyltin oxide. The mixture was mixed well and kept for 2 hr under reduced pressure a t 70-80°C and M hr at 100°C. At this stage, most of the dibutyltin oxide went into solution. The mixture was then dissolved in dry acetone and filtered. Acetone was distilled off. The residual compound had mp 62OC. Anal. Found: C, 56.85; H , 9.77; Sn02, 17.10. Calcd. for C40H7,010Sn:C, 57.22; H, 9.53; SnOz, 17.96. Preparation of Dibutyltin Disalicylaldehyde
I n a 100-ml round bottomed flask were placed 4.86 grams of dibutyltin diiodide, 3.62 grams of the sodium salt of salicylaldehyde, and 50 ml of benzene. The mixture was refluxed for 3 to 4 hr. The mixture was then filtered, and benzene was distilled off under reduced pressure. The residual compound was dissolved in alcohol and reprecipitated by petroleum ether, mp 143°C. Yield 2.4 grams.
Preparation of Di( 2-pentadecyl-4-methoxyphenyl)trisulfide
Testing of PVC Stabilizers
In a 250-ml round bottomed flask, fitted with a reflux condenser, were placed 28.0 grams of 3-pentadecylphenylmethyl ether, 60 ml of dry, 60-6' C petroleum ether, and 12.0 grams of sulfur monochloride. The solution was refluxed for 30 hr. The solution was washed with water, dried over anhydrous sodium sulfate, and filtered. The filtrate on cooling gave a white solid which was recrystallized from 60-6°C petroleum ether m p 59OC. Yield 18.0 grams. Anal. Found: C, 72.31; H , 10.33; S, 13.70. Calcd. for C44H74S203: C , 72.33; H , 10.14; S, 13.15.
The test method for the evaluation of PVC stabilizer system is basically dependent on the particular type of processing equipment and techniques being used for the manufacture of the finished products. Based on this, a number of test procedures (Cohen) have evolved through the years and some of them are given here: Oven heat stability, press stability, mill heat stability, and Brabender plastograph or rheomet, r. The first two methods are static types of tests and are adaptable to molding and coating techniques. The Ind. Eng. Chem. Prod.
Res. Develop., Vol. 10, No. 2, 1971
215
32
24
0-
1
1
10
20
I
30
1
1
1
1
50 60 70 T I M E IN M I N U T E S .
40
1
1
80
90
1
100
1
110
120
Figure 1. Graph showing leucometer readings of aged PVC samples against time 0 Dibutyltin di-3-pentadecylphenolate V Dibutyltin disalicylaldehyde
0
Dibutyltin dialeuritate 0 Dibutyltin di(Z-pentadecyl-4methoxyphenyl) mercaptide
A
Mark 292
0 Dibutyltin diiaurate
0
others are dynamic tests. These two tests together with the oven test are used for calendering and extrusion techniques. I n the present investigation, the oven heat stability test was used. The stabilizers described earlier are evaluated in plasticized PVC using the following compounding recipe: Resin DOP
X Stearic acid
100 parts 50 parts 2 parts 0.5 part
where X = tin compounds. Stearic acid and stabilizer were dissolved in plasticizer and then mixed with PVC resin (SR-10, a suspension polymer of K value 66) in a side edge runner till a uniform mix was obtained. The sheets of thickness 0.01 to 0.02 in. were taken on a two-roll mixing mill after milling for 10 min with equal cutting on each side. The roller temperature was maintained a t 150°C. The sheets were further evaluated for heat stability. Samples of size 1 x 2 in. were cut from the sheets and kept on glass plates. These samples were then aged in an oven a t 180°C. The samples were removed after every 10 min, and the color developed was measured on a Lange photoelectric leucometer. The percent reflectance values of the aged PVC samples were plotted against time of aging in Figure 1. Discussion
The comparative stabilizing action of the four new organotin compounds synthesized from indigenous raw materials along with the control compounds, namely dibutyltin dilaurate and Mark 292, is shown in Figure 1. Two groupings are recognized: (1) containing R&-0linkages and (2) containing R&n-Slinkages. In the first group Sn is bonded to the substituted aromaticialiphatic compounds through oxygen, while in 216
the second group Sn is bonded to a substituted aromatic ring through sulfur. Figure 1 shows that dibutyltin disalicylaldehyde is slightly superior to dibutyltin di-3-pentadecylphenolate. Both the compounds have substitution in the aromatic ring. Dibutyltin di-3-pentadecylphenolate has a long alkyl chain in the meta position whereas disbutyltin disalicylaldehyde has an aldehyde group in the ortho position with respect to Sn-0 link. Superior stabilizing action of dibutyltin disalicylaldehyde may be due to the presence of an oxidizable aldehyde group, which may be supressing the oxidative degrading action of oxygen in PVC a t the processing temperature. I t is reported (Chevassus and Broutelles, 1963) that the soaps of hydroxy acids such as ricinoleic acid are superior heat stabilizers. I t was therefore predictable that dibutyltin dialeuritate should act as a good stabilizer, since it contains free hydroxy groups. Figure 1 shows that dibutyltin dialeuritate gives very good original clarity and good stabilizing action up to 50 min. However, it develops color after 50 min. The commercial product dibutyltin dilaurate has superior stabilizing action up to 60 min. However, after 60 rnin i t also develops color rapidly. Among the types of organotin compounds where Sn is bonded to the substituted aromatic /aliphatic compounds through oxygen, it is observed that the organotin compounds in which R2Sn is linked through
Ind. Eng. Chern. Prod. Res. Develop., Vol. 10, No. 2, 1971
II
0-C-R (acid) group are superior t o those compounds in which RrSn is linked through -0-Ph (phenolic) group. Comparison of dibutyltin di(2-pentadecyl-4-methoxypheny1)mercaptide with Mark 292, a commercial organotin mercaptide, shows that both give good heat stability u p to 90 min. However, after 90 min, dibutyltin di(2pentadecyl-4-methoxypheny1)mercaptidedeveloped color, whereas Mark 292 did not. Since the chemical structure of Mark 292 is not known to us, it can only be said that the activity of dibutyltin di(2-pentadecyl-4-methoxypheny1)mercaptide can be upgraded in a suitable synergistic mixture. The comparison between the development of color of PVC compounds containing dibutyltin di-3-pentadecylphenolate and dibutyltin di(2-pentadecyl-4-methoxyphenyl)mercaptide, on aging shows the latter to be superior. Literature Cited
Chevassus F., Broutelles, R., “The Stabilization of Polyvinyl Chloride,” Chap. 4, Edward Arnold Publishers, 1963, p 112. Cohen, S.,“Evaluation and Comparison of Heat Stability Tests Using an Oven, Mill, Press and Brabender Plastograph,” Bibliography No. 258, Argus Chemical Corp., Brooklyn, N. Y. Frye, A. H., Horst, R. W., Paliobagis, M. A., J . Polyrn. Sci., A-2, 1765 (1964a). Frye, A. H., Horst, R . W., Paliobagis, M. A., ibid., p 1801 (196413). Kenyon, A. S., NBS Circ., 525, 81 (1953). National Chemical Labomtory, NANASAHEB D. GHATGE’ Poona 8, India SUBHASH P. VERNEKAR RECEIVED for review June 1, 1970 ACCEPTED January 7, 1971 I
T o whom correspondence should be addressed.
