Simplified methods for the evaluation of the parameters of the time course of plasma concentration in the one-compartment body model with first-order invasion and first-order drug elimination including methods for ascertaining when such rate constants are equal

The uninhibited ethane decomposition was studied from 550 to 640°C with the object of determining the overall mechanism. The reaction was found to be accurately of the first order at the higher pressures and lower temperatures employed, and to have an activation energy of 73·1 kcal under these conditions. The rate was decreased slightly by an increase in surface area, and the order was then somewhat greater than unity. At 640°C there was a transition to an order of 3/2 at a pressure of about 60 mm. Evidence is adduced in support of the conclusion that the initiating reaction is a second-order split of C 2 H 6 into 2CH 3 , as proposed by Küchler & Theile, and that the terminating step is C 2 H 5 + C 2 H 5 at the higher pressures and H + C 2 H 5 at the lower ones. The mechanism is shown to give a satisfactory interpretation of the time-course of the reaction, of the effects of adding ethylene and hydrogen, and of the effect of increasing the surface area. Calculated rates, using the rate constants for the elementary steps, are in good agreement with experiment.

Download Full-text

Vulcanization of Elastomers. 12. Perbunan with Thiuram Monosulfide and Sulfur. I

Rubber Chemistry and Technology ◽

10.5254/1.3542369 ◽

1959 ◽

Vol 32 (1) ◽

pp. 128-138 ◽

Cited By ~ 1

Author(s):

Walter Scheele ◽

Horst-Eckart Toussaint

Keyword(s):

Activation Energy ◽

Natural Rubber ◽

Temperature Dependence ◽

Induction Period ◽

Rate Constants ◽

The Other ◽

Tetramethylthiuram Disulfide ◽

First Order ◽

The One ◽

Limiting Value

Abstract The vulcanization of Perbunan 2818 by tetramethylthiuram monsulfide plus sulfur (1 mole monosulfide per gram-atom S) was thoroughly studied. The following results were shown: The limiting value for dithiocarbamate formation is 66 mole per cent of the initial thiuram monosulfide, indicating a two-thirds transformation. The limiting value is practically independent of temperature. The formation of dithiocarbamate can be described as a reaction of the first order. The formation of dithiocarbamate is characterized by an induction period which grows longer with lowering of the temperature, and at 100° C it amounts to about 100 minutes. The rate constants for dithiocarbamate formation were calculated, and it was shown that they were practically the same as those for the vulcanization of Perbunan with tetramethylthiuram disulfide. The activation energies as derived from the temperature dependence of the rate constants for dithiocarbamate formation in the vulcanization of Perbunan by thiuram monosulfide plus sulfur on the one hand and with thiuram disulfide on the other, are only very slightly different and are practically the same as the activation energy for dithiocarbamate formation during the vulcanization of natural rubber with thiuram monosulfide plus sulfur. The results were thoroughly discussed in light of the present conceptions of the course of thiuram vulcanizations.

Download Full-text