November 1949
INDUSTRIAL AND ENGINEERING CHEMISTRY
inorganic compounds, and a number of resins including alkyds, cellulose derivatives, and the Vinylites. The solvent is stable toward many common reagents. The 3-methyl derivative has similar properties. ACKNOWLEDGMENT
The authors are appreciative of the aid of J. J. Benischeck, L. Burros, and E. Shoemaker in analyzing for sulfur and chlorine, and of H. Robinette in discussing polymer solubility tests. ui
LITERATURE CITED (1) Backer, H. J.. and Bolt, C. C., Rec. trav. chim., 54, 533 (1935); 55, 898 (1936). (2) Braun and Trampler, Ber., 43, 549 (1910) : “Beilstein’s Handbuch der oraanischen Chemie,” Vol. XVII, 1st suppl., p. 5 , 1934.
m
2637
(3) Evans, T. W., and Morris, R. C., U. S. Patent 2,360,859 (1944). (4) Farlow, M. W., Ibid., 2,233,999 (1941). ( 5 ) Grummitt, O., and Ardis, A., J . Chem. Education, 23, 73 (1946) (6) Hoffman, W. A., and iMortenson, C. W., U. S. Patent 2,394,776 (1946). (7) I. G. Farbenindustrie, French Patent 847,254 (1939). (8) Jordan, T. E., and Kipnis, Frank, J . Am. Chem. Soc., 71, 1875 (1949). (9) Merner, R. R., U. S. Patent 2,404,723 (1946). (lo) Morris, R. C., and Evans, T. W., Ibid., 2,357,344 (1944). (11) Morris. R. C.. and Shokal. E. C.. Ibid.. 2.360.860 (1944). (12) Ibid., 2,360,862 (1944). (13) Ibid., 2,391,330 (1945). (14) Morris, R. C., Shokal, R. C., and Snider, A. V., Ibid., 2,394,251 (1946). (15) Morris, R. C . , and Snider, A . V., Ibid., 2,368,597 (1945). (16) Morris, R. C., and Winkle, L. J. van, Ibid., 2,371,161 (1945) (17) Pierrotti, G. J., and Dunn, C. L., Ibid., 2,360,861 (1944). (l8) Zuydewijn, E. de R. van, Rec. trav. chim., 57,445 (1938). RECBIVED February 12, 1949.
Vulcanization Characteristics of Thiazoles COMPARISON OF 2-THIAZOLETHIOL AND ITS DISULFIDE WITH OTHER THIAZOLE ACCELERATORS A. J. BEBER AND R. A. MATHES The B. F. Goodrich Research Center, Brecksville, Ohio
,
Mercaptothiazoles have been the most widely used accelerators in the rubber industry for many years. The recent synthesis of the parent compound of this class, 2thiazolethiol, and its disulfide, 2,2’-dithiodithiazole,permits for the first time a comparisonof the effect on accelerating activity of various substituents on the mercaptothiazole nucleus. Conventional physical tests on tread type stocks show that 2-thiazolethiol a,”dits disulfidehave similar vulcanization characteristics compared to an arylsubstituted compound, 2-mercaptobenzothiazole, to an alkyl-substituted derivative, 4,5-dimethyl-2-mercaptothiazole, and to their corresponding disulfides.
A
LTHOUGH the mercaptothiazole class of accelerators has been known for more than twenty-five years and considerable interest (2, 6, 6) has been displayed as to the relative accelerating characteristics of 2-thiazolethiol, the parent compound has only recently been prepared. It was first described in the patent literature (S), and subsequently reported by the authors (4)together with the synthesis of its disulfide. Backer and Buisman ( I ) also described the preparation of 2-thiazolethiol. The isolation of this compound permits, for the first time, the direct comparison of the influence on the accelerating activity of the condensed arylene ring or alkyl substituents in the 4,5 positions of the mercaptothiazole nucleus. Sebrell and Boord (6) reported that 2mercaptobenzothiazole is much more reactive than 2-thiazolinethiol and thus demonstrates the enhanced accelerating effect of the benzene nucleus. This comparison was unsuitable, however, since the latter compound is saturated in the 4,5 positions and belongs to a different class of accelerators. That this viewpoint is now untenable is proved by the authors’ results which show that the accelerating activity of the unsubstituted compound is greater than that. of the benzene substituted derivative, 2-mercaptobenzothiazole. This compounding study compares 2-thiazolethiol and its di-
sulfide with 2-mercaptobenzothiazole (MBT); 2,2’-dithiobis(benzothiazole) (MBTS) ; a mixture of about 85% 4,5-dimethyl2-mercaptothiazole and 15% 4-ethyl-2-mercaptothiazole (MDT); and the corresponding mixed alkylthiazyl disulfides (MDTS) These accelerators are compared in tread type stocks containing an equal concentration by weight of accelerator, 1 part per 100 in natural rubber and 2 parts per 100 in GR-8. Although all the accelerators in this series respond to activation, the study was limited to the determination of the relative inherent accelerating properties rather than to the effect of activated combinations. The structural relationships of the different accelerators are shown by the conventional formulas. A study of the ultraviolet absorption spectra of the three mercaptothiazoles indicates that they exist chieflv in the form with the hydrogen on the nitrogen rather than on the sulfur:
.
S
A
HC C-SH
ll
HC-N
/I
2-Thiazolethiol (TT)
S
S /\
S /\
i:
I/
HC
C-S-S--C
CH
/I
H -N I‘ N--CH 2,2’-Dithiodithiazole (TTS) S S
2-Mercaptobenzothiazole (MBT)
2,2’-Dithiobis-(benzothiazole) (MBTS)
4,5-Dimeth 1 2 mercaptothiazorL(MDT)
2,2’-Dithiobis-(4,5dimethylthiazole) (MDTS)
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t-
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 41, No. 11
TENSILE @---M.D.T.
TENSILE
300
A-
T.T. M.B .T 0 ----M.D.T. 292" F.
.
---
MMtE%ESAT Figure 1.
Cure Curves for 2-Thiazolethiols in Natural Rubber
Figure 2.
Cure Curves for 2-Thiazolethiols in GR-S
M.B .T.
0 --- M.D .T.
A--T.T.
a ---
M.B 0 ---8.4.B.T.
L
0 -lo 21 Figure 3.
MINUTES AT 280' F. 131 %r,
is
.x.
4
i
MINUTES AT 300' F-
li i 5
Mooney Cure for 2-Thiazolethiols in Natural Rubber
Figure 4. Mooney Cure for 2-Thiazolethiols in GR-S
MOOKEY.The rates of scorching and curing vl-err determined by a Xooney plastometer according to the procedure of Shearer, Juve, and hIusch ( 7 ) . The following tests were performed according t o the A.S.'I'.TvI. method designated: tensile strength, modulus, and elongation, Method D 412-41; aging of natural rubhrr, D 572-12; aging of GR-R, D 865-47T; hardness, D 676-47T. FORAIGLA~. The following formula3 were uscd: Pale crepe rubber EPC black Zinc oxide Stearic acid Sulfur Pheny1-5-naphthylarriine Accrlerator
A -T
I 3---M.B
100 50
5 3 3
1
GR-S-10 EPC black Zinc oxide Stearic acid Sulfur Accelerator
100 42.5 5 3 2 2
1
.T .S.
.T.S.
.
0 -- -M.D .T .S
MINUTES AT 292' F. Figure 5 , Cure Curves for 2,2'-Dithioditbiazoles in Natural Rubber TEST METHODS
HI ~TERE:SIS. The temperature ris,. mcasuremt>ntswere detcrmined with a Goodrich flesometer a t 212" F.,with a %-pound load and a stroke of 17.5y0 (Method A, X.S.T.M. D 62311T). AT rrpresents the rise in temperature above 212 F. after 25 minutes of cyclic compression in the machine. Permanent set is expressed as the prrcentage loss in length of thc test cylinder after the testing cycle in the Goodrich flesomrtrr.
2-THIAZOLETHIOL
As Figures 1 and 2 shorn, tensile strength, modulus, and elongation valbes are in the same general range, in both natural rubber and GR-S, as the control accelerators (MDT and MBT). The Mooney cure tests (Figures 3 and 4)indicate a more rapid rate of cure, with greater scorch tendency. The hysteresis and permanent set (Table I) are the highest for any of the accelerators, which signifies a greater heat build-up in stocks cured with 2-thiazolethiol. Aging results (Table 11)compare closely in natural rubber; the apparent improved aging of MBT in GR-S is probably not significant since the difference in tensile strength between MBT and TT is slight. Hardness and rebound figures (Table 111)are in close agreemrnt, an indication that a similar state of cure was reached in all cases.
November 1949
INDUSTRIAL AND ENGINEERING CHEMISTRY
1
I
7ooC
2639
1
\
ELONGATION
60
! t 1 50
3000t
M.D .T .S.
TENSILE
-- ----*
,---7---
/-
/ -
a
+ T.T.S. M.B .T .S 0 --- M.D .T.S.
.
20 MINUTES AT 307' F. 40 80 Figure 6. Cure Curves for 2,2'-Dithiodithiazoles in GR-S
MINUTES AT 28QQ l? Figure 7.
Mooney Cure for 2,2'-Dithiodithiazoles in Natural Rubber
AND PERMANENT SET TABLE I. HYSTERESIS
40-min. cure at 292O F. (natural rubber) and a t 307;O F. (GR-9); permanent set after 25 min. in the machine. ---Natural Rubber-? -GR-SAccelerator A T , O F. P.S., % A T , O F. P.S., % TT 36 13 90 33 MBT 30 9 50 30 MDT 30 8 46 11 TTS 35 11 . 46 9 MBTS 30 8 40 18 MDTS 31 9 41 7 ~
TABLE 11. AGINGRESULTS -Tensile Strength-ElongationOriginal, Aged % Original, Aged, % Accelerator lb./sq. in. Ib./sq. in. retained % % retained Natural Rubber, 4 8 Hours in Bierer Bomb a t 155O F. (300 Lb./Sq. Inch); 40Min. Cure a t 292' F. TT 4250 2650 62 520 440 55 MBT 3900 2700 69 475 450 95 MDT 505 405 4250 2700 64 80 TTS 520 4200 3050 73 490 94 MBTS 470 3950 2650 415 67 88 MDTS 69 510 4400 3050 470 91 GR-S, 4 8 TT MBT MDT TTS MBTS MDTS
Hours a t 250° F., Test Tube Method; 40-Min. 2300 2200 2500 2875 2600 3175
1950 2050 1700 1650 2050 2050
85 93 70 58 79 65
535 525 495 460 560 475 ~
Cure a t 307O F. 300 56 320 61 210 42 220 48 290 52 250 53 ~~
~~
-
TABLE 111. HARDNESS AND REBOUND Natural rubber, 40-min. oure at 292' F.: GR-S, 40-min. cure a t 307O F. Shore Durometer Hardness Sohopper Rebound Accelerator Natural rubber GR-S Natural rubber GR-S TT 59 62 45 34 MBT 60 53 46 36 MDT 61 52 46 38 TTS 59 52 46 35 MBTS 59 52 46 36 MDTS 60 55 48 37
301 I 20 -
M F T E S A T , 30O0F, ,
,
,
,
!
the substituted compounds. The data presented fail to show any conclusive trend in behavior resulting from major differences in chemical constitution. Mooney test data for TT and TTS support the conclusion that activity is the only property which indicates any appreciable difference. Substituting alkyl groups or a benzene ring in the 4,5 position in the thiaaole nucleus fails to produce any major change in accelerating characteristics. ACKNOWLEDGMENT
The authors wish to thank A. E. Juve and R. *k, Crawford for suggestions and criticisms in the preparation of this paper. LITERATURE CITED
2,2'-DITHIODITHIAZOLE
The time-tensile, modulus, and elongation characteristics (Figures 5 and 6) are similar, in general, to the controls (MBTS and MDTS). The Mooney cure tests (Figures 7 and 8) indicate that TTS is more rapid curing and displays less delayed action effect, and show that the activity of MDTS lies midway between T T S and MBTS. The hysteresis values are somewhat higher in both natural rubber and GR-S, but the permanent set in GR-S is lower than MBTS (Table I). Aging results (Table 11) compare closely in natural rubber; in GR-S the apparent improved aging, as pointed out for MBT, is probably not significant. It had been presumed that the unsubstituted 2-thiazolethiol and its disulfide might exhibit improved accelerator qualities over
(1) Backer, H. J., and Buiuman, J. A. K., Rec. trav. chim., 64, 102
(1945). (2) Bruni, G., and Romani, E., Atti. acead. Lincei, [5 1 31,I, 86 (1922). (3) Jones, P. C (to B. F. Goodrich Co.), U.S. Patent 2,426,397 (Aug. 26, 1947). (4) Mathes, R. A., and Reber, A. J., J . Am. Chem. Soc., 70, 1451 (1948). ( 5 ) Sebrell, L. B. (to Goodyear Tire & Rubber Co.), U. S. P:tcent 1,591,441 (July 6, 1926). (6) Sebrell, L. B., and Boord, C. E., IND.ENG.CHEM., 15, 1009 (1923). (7) Sh&rer,'R., Juve, A. E., and Musch, J. H., I n d i n Rubbcr W o i I d , 117, 216 (19.27). RECEIVED November 17, 1948. Presented before a meeting of the Division of Rubber Chemistry, AWERICAN CHEMICAL SOCIETY, in Detroit, Mich., November 1948.
