I N D U S T R I A L A N D ENGINEERING CHEMISTRY
724
The weight increase was 17 g. or the equivalent of 1 mol of ammonia. The formula of the new compound probably is
]
(CHs)2N - C - S
[
!I
s
Zn.NH3
2
Lead dithiocarbamates do not give addition products with ammonia, nor does ammonia cause them to air-cure.
1 2 3 4
5
TABLEVI11 Same as Table I using CsHloNHa S . C S . NCrHlo-0.49 --PRESS CURE---OXIDE Min. O F . Cure AIR CURE h-one 15 286 Under None, 75 days ZnO 15 230 OK OK, 1 3 d a y s 15 286 PbO OK None, 13 days MgO 15 286 Under OK, 13 days 15 286 Under OK, 13days Ca(0H)z
Rubber-100;
sulfur-4.0; PRESS CURE 15 min., OXIDE 280° F.
.....
; zll0” 3 PbO
4 5
MgO Ca(0H)n
TABLEI X oxide-0.5; tetramethylthiuram disulfide-0.25 -OVEN CURE-50 min., 176’F. 7--AIR CURE---As is AfterNH3 As is After N H I
.,... . . . . .
None None None None
Over Under Under Fair
Over None Under Under
..
...
None None None Good, 8 days
Faii,’8 ‘days None hTone Good, 8 days
Vol. 15, No. 7
show a t ordinary temperatures. When used with zinc oxide or litharge they assume the properties of the zinc or lead salts. Ammonia causes zinc dithiocarbamates of secondary amines to air-cure in absence of metallic oxides so that they function as rapidly as by the aid of calcium hydroxide or magnesia. The ammonia, is believed to be held as an addition product to the zinc salts, and probably increases the basicity of the accelerator, thereby giving greater curing power. With thiuram disulfides the ammonia first forms the corresponding dithiocarbamate. The data check the previous assumptions and show the shifting from one metallic salt to another during vulcanization. This is believed to be due to the interfering action of hydrogen sulfide. Metallic oxides apparently do not fix hydrogen sulfide sufficiently t o prevent the interchange of metallic radicals. Litharge stops the zinc salt from aircuring and magnesia speeds its action. Lead and magnesium sulfhydrates evidently react with zinc dithiocarbamates to form lead or magnesium salts and precipitate the zinc as the sulfide. It will be recalled that litharge does not prevent the action of hydrogen sulfide on thiuram disulfides.
TABLE X Rubber--100;
Mg0-0.5;
PRESS CURE
SIILPUR 5 min.. 240 -_ 4 0 Under 6 0 Fair 8.0 OK
F.
tetramethylthiuram disulfide-0.5 ----AIR CURE------^ As is After N H I
OK, 5 0 d a y s O K 34 days Ovkr, 27 days
OK, 13 days OK, 13 days OK, 13 days
RELATIVEACTIONOF VARIOUSOXIDES The idea of continual decomposition and re-formation of metallic dithiocarbamates during vulcanization a t once suggests a possibility of the shifting from one metallic salt to that of another metal. Upon studying the action of various oxides on a certain metallic dithiocarbamate, their action was found to be so widely different that the results could be recorded qualitatively by the feel of the cured vulcanizate. Considering acceleration purely as a time factor, the relative action of the common oxides has been recorded through the time necessary to give an under, fair, OK, or over cure. This was partly necessary in order t o correlate air cures properly with press or oven cures, since, air cures do not lend themselves readily to machine tests. The treatment with ammonia gas consisted merely of exposing the stocks, in thicknesses not over 0.25 in., to the dry gas over night a t atmospheric pressure, or for shorter periods when using higher pressure. All stocks were then exposed to air for a t least one day before being cured in press or oven. The entire data are given in Tables I to X.
DISCUSSIOK OF DATA From the foregoing data it was found that lead dithiocarbamates do not air-cure except by the aid of calcium hydroxide or magnesia, and then but slowly. The lead salts are high-temperature accelerators and require the presence of litharge or zinc oxide. Litharge used as an aid to the dithiocarbamates of zinc, calcium, or magnesium gives practically the same results as if the lead salt had been used. Zinc dithiocarbamates air-cure most rapidly with calcium hydroxide and magnesia, more slowly with zinc oxide, and not a t all in the presence of litharge. For high-temperature cures calcium hydroxide and magnesia lose their value and become secondary to zinc oxide and litharge. I n each case the resultant cure corresponds closely to that of the metallic salt of the oxide used. Calcium and magnesium dithiocarbamates of secondary amines are rather unstable, decomposing with rising temperature and thereby losing the high curing power which they
FIG.2
I n conclusion, there is shown in Fig. 2 a graphical outline of the many reactions which take place with dithiocarbamates and thiuram disulfides derived from secondary amines. All these reactions take place a t room temperature. Nitrostarch a s a Constituent of Explosives The use of nitrostarch in the manufacture of safety explosives is increasing, and this substance is now important in the explosives industry, state C. A. Taylor and W. H. Rinkenbach, assistant explosives chemists of the Interior Department, who have conducted a series of studies of the materials, constitution, and analysis of numerous types of explosives a t the Pittsburgh Experiment Station of the Bureau of Mines. Nitrostarch is made by nitrating starches with a mixture of sulfuric acid and nitric acid, details of the method varying considerably among different manufacturers. Commercial nitrostarch is in reality a mixture of compounds of various degrees of nitration, being comparable in this respect with nitrocellulose. Like the nitrocellulose, nitrostarch is not a true nitro compound, being an orgstnic nitrate.
