FEBRUARY, 1937
INDUSTRIAL AND ENGINEERING CHEMISTRY
Acknowledgment The writers are indebted to L. A. Pinck for assistance i n identifying and analyzing some of the products.
205
(4)Gocket, H., Angew. Chem., 47, 555 (1934). ( 5 ) Jones, R. M., and Aldred, J. W. H., IND ENG.CHEM.,28, 272 (1936). (6) Williams, H.E.,"Chemistry of Cyanogen Compounds," p. 20 (1915).
(7) Ibid.,
Literature Cited (1) Buchanan, IND. ENG.CHEM.,15, 637 (1923). (2) Davis, R. 0. E . , Scholl, w., and Miller, R. R.,I b i d . , 27, 69 (1935), (3) Garby, C. D., Ibid., 17,266 (1925).
p.
24.
(8) Ibid., p. 25. RECEIVED September 12, 1936. Presented before the Division of F e r t i l i ~ e r Chemistry a t the QZnd Meeting of the American Chemical Society, Pittsburgh, Pa., September 7 t o 11, 1936.
Vulcanization Characteristics of Mercaptobenzothiazole Derivatives M. W. HARMAN Monsanto C h e m i c a l C o m p a n y , Nitro, W. Va.
The results of standardized vulcanization tests on forty-five condensation derivatives of mercaptobenzothiazole are reported. The materials alone and with added diphenylguanidine were compounded in a g u m stock and examined for curing value and scorching tendency. Twenty-seven of t h e compounds show upon activation a curing value equal t o or greater than mercaptobenzothiazole alone. Of these, eight show little or no scorch. The presence in t h e substituent
of the groups CO-, -NH-, -NOz, -OH, -S-, or -C1 seems to favor subsequent activation. On t h e other hand, certain combinations such as -CH2CO-NH-, -CH2*CO*O-, CaHb*CH2-, CloH,.CH2-, and aliphatic hydrocarbon chains tend to give compounds which are nonaccelerators. The effect of a given group varies not only according t o its position b u t also to t h e other groups present: nevertheless certain group tendencies are manifested.
ITHIX the past few years much progress has been of these materials exhibit the desired curing action when used made in the development of rubber vulcanization alone; some are activated more or less by diphenylguanidine; others remain unaffected. Primarily, the compounds of accelerators of the semi-ultra type which exhibit interest are those which alone or activated are stronger no prevulcanization or scorch during the preliminary processing. Most of the commercially important members of this but less scorchy accelerators than mercaptobenzothiazole. class are derivatives of mercaptobenzothiazole in which the However, certain ones which are strongly activated by diphenylguanidine and thereby show a moderate scorching hydrogen atom of the mercapto group is replaced by an tendency should not be overlooked since in many cases it is organic substituent. The increasing use of these products can be attributed to their possible to eliminate prevulfavorable curing characteristics Eanization by substituting a reBase Stoch Material Added tarding activator such as diand to the valuable physical A =&ctlerotor'h'- 0.15 phenylguanidine phthalate. It properties which they impart to Rubber /o 0 the cured stock. Naunton and Zinc Oxide 5 B s II II 'BS"-0.75 is also recognized that a comSulfur s his eo-workers (4), Twiss and " "cro.75 plete compounding study is D: ' I "0"- 0.75 stearic Acid a5 Jones (8), and Shepard (6)disnecessary for the proper evaluacussed .a' number o'f these. comtion of any accelerator. Plastometer Readinas 700% Modulus pounds in recent papers. Nuof Cures at 134%. in at mm. at 93 'c.Experimental Procedure merous references to their preparation and use also appear in the I n order to obtain a furst appatent literature (1,9, 3,5,?',10). proximation of the vulcanizaThe purpose of this paper is to tion characteristics and possi500 determine the effect of various bilities of these materials, they substituents upon the curing were compared alone and acvalue and scorching tendency of tivated by diphenylguanidine, 140 240 360 mercaptobenzothiazole conusing mercaptobenzothiazole *densation derivatives. Few FIUUREI as a control. The general test
W
14
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206
VOL. 29, NO. 2
m m
6
E-
u 750
0
1950 600
/ooo
ComparJSon of scorch
X=
Qhrs. 3 QSOC.
Conitul it
-on
1 -Oc& 13
-0
NO CURE
NO CURE
A represents mercaptobenzothiazole; B,C, and D represent various mercaptobenzothiazole derivatives activated by diphenylguanidine. Curve B displays the definite lag or induction period both in cure and scorch characteristic of true delayed action acceleration. Accelerator C is similar to A in cure but much less scorchy. D is an example of a strong scorchy accelerator. From a comparison of these modulus and plastometer curves, it is evident that the curing value and the amount of scorch are independent of one another. The mercaptobenzothiazole derivatives which follow have been classified according to certain similarities in structure. As far as possible, each class contains compounds with a, common substituent grouping attached to the thiol sulfur. Their curing and scorching properties are represented graphically by means of rectangular strips; the solid portion indicates the results obtained when 0.78 part of the derivative are added to the base stock; the entire strip, including the solid and blank portions, indicates the results obtained when 0.60 part of the derivative plus 0.15 part of diphenylguanidine are used.
Discussion
19 2o
c6"
-03 OH
uu
0
100
200
300 0
250 600 750 1000
FIGURIE 4 recipe is shown in Figure 1, along with several typical modulus and plastometer curves obtained from representative accelerators of this class. The 700 per cent modulus figures (in kg. per sq. cm.) of the 60-minute cures a t 134" C. were chosen t o express the acceleration value, and the Williams plastometer readings (Q), obtained after heating pellets of the uncured stock for 4 hours at 93" C., were selected to represent the degree of scorch. A plastometer reading of 250 is equivalent to no scorch, inasmuch as a gum stock compounded without an accelerator will give this figure; the scorching tendency is indicated by the magnitude of the higher readings. Curve
CLASSI. Compounds 1, 3, and 4 (Figure 2) exhibit the most desirable properties. Compound 1 is rather exceptional in that alone it is quite a rapid, high-modulus, nonscorchy accelerator. In this case activation is not necessary nor is it desirable. Compounds 3 and 4 alone have little or no curing action but, upon activation, surpass unactivated mercaptobenzothiazole and show substantially no scorch. Compound 2 alone is more scorchy than the control, and compound 5 shows no cure. The latter is the first example of a nonaccelerator which has negative groups present in the substituent. CLASS11. The members of this class (Figure 3) show little acceleration alone but are strongly activated; compounds 6 and 9 are most interesting since they are not scorchy but yet give high-modulus cures. Compounds 7 and 8 when activated have a scorching tendency about equal to unactivated mercaptobenzothiazole; that of compound 10 is somewhat greater. CLASS111. Compound 11 (Figure 4) is similar to the control in its properties, both alone and activated. Compounds 12, 14, 15, 18, 19, and 20 upon activation give a cure equal to or better than unactivated mercaptobenzothiazole, but. have a much greater scorching tendency. Compounds 13, 16, 17,and 21 show little or no acceleration value, either alone or with diphenylguanidine. Compounds 13, 16, and 17 are derivatives containing nonpolar constituents and display the
INDUSTRIAL AND ENGINEERING CHEMISTRY
FEBRUARY, 1937
control
a6 -ci
I
!
I
100
I
200
I t
so0
0
I
ado
I
I
500 750
4hm. at Q3'C.
-
I u
bl
'C&
28
-0
m
NO CUR€
29 -OH
-
Comparison of Sconh
Cornpariaon of Cure 7ooAModuius 60!&4'C.
XI
I
--
R5CHaCOX
CLASS
Z 6 -OH
207
ik
FIGURE5
m
inertness characteristic of this type. Compound 21 is the second example of a nonaccelerator containing negative groups, the carboxyl group evidently nullifying the effect of the hydroxyl group which was manifested in the three preceding compounds. CLASSESIV AND V. With the exception of compound 23 {Figure 5) which shows the inactivity typical of straightohain hydrocarbon substitution, the members of these classes when activated have a greater acceleration value than unactivated mercaptobenzothiazole and about the same scorch. CLASSVI. Compounds 27 and 28 (Figure 6) upon activation show greater acceleration value and less scorch than unactivated mercaptobenzothiazole. The other members of this class are of no particular value; 29 and 30 are further examples of inactive compounds which contain negative groups; 32 to 37, inclusive, which were prepared by reacting mercaptobenzothiozole with various substituted acetamides, might be considered along with 29 and 30; however, the net negative effects of their substituents are so extremely weak that they seem to exert little or no effect. CLASSVII. I n agreement with four previous examples, compounds 38, 39, and 40 (Figure 7) show the inertness characteristic of nonpolar substituents. The other members of this class are strongly activated. Compounds 41, 42, 44, and 45 show a scorching tendency equal to or greater than unactivated mercaptobenzothiazole; compound 43 shows the highest acceleration value and the least scorch.
m
,o
37 -N\
0
m
I
0
I
/oo I
200
'
m
800 0u
250
o
FIGURE6
CLASS
XZ
Ri5A-S.R
X. Control
38 %Ha39 -CHa.C&40 -Cy2CH&CH&Ha41 -CH~NHCS.NH-CHA43 -CHgNHCO.NHtHa-
43 -NU-
-Comparison of CUM 7oo%Mcdulus 601/.94'C.
Comparison of Scorch 4hrs. at 93'C.
n
Y
n
m
n
m
1
-
m
d6siijcC6H,, 44
-q"COOH
Acknowledgment The author wishes to thank E. W. Booth for his assistance in assembling the vulcanization data given, and the research staff of this laboratory for helpful suggestions.
Literature Cited (1) Evans, U.9. Patent 2,020,051(1935). (2) Harman, Ibid., 1,951,052(1934); 2,010,000(1935). (3) Horst, W.P.ter, U. S. Patent 1,941,142(1933). (4) Naunton, W. J. S., Baird, W., and Bunbury, H. M., J . Boc. Cham. Ind.,53, 127 (1934); Rubber Chem. Tech., 7 , 417 (1934). (6) Bcott, U. 8. Patents 1,732,486(1929); 1,784,498(1930); 1,965,160 (1934).
(6) Shepard, N. A., IND.ENQ.CHBM., 28,281 (1936).
(7) Sibley, U. S.Patent 1,936,099(1933). (8) Twiss, D.F.,and Jones, F.A., J. SOC.Chem. I d . ,54,13 (1935); Rubber Chern. Tech., 8,230 (1935). (9) Williams, I., IND. ENQ.CHBM.,16,362 (1924). (10) Zimmermann, U. S. Patent 1,960,197(1934). R ~ C B I VSeptember ~D 18, 1936. Presented before the Division of Rubber Chemistry at the 92nd Meeting of the American Chemical Society, Pittsburgh, Pa., September 7 to 11, 1936.
