THE TEMPERATURE COEFFICIENT OF PHOTOCHEMICAL REACTION RATE

1923 ◽  
Vol 45 (10) ◽  
pp. 2285-2296 ◽  
Author(s):  
Richard C. Tolman
Keyword(s):  
Temperature Coefficient ◽  
Photochemical Reaction ◽  
Reaction Rate

Mechanism of Rubber Vulcanization with Sulfur

1938 ◽  
Vol 11 (1) ◽  
pp. 107-130
Author(s):  
W. K. Lewis ◽  
Lombard Squires ◽  
Robert D. Nutting
Keyword(s):  
Natural Rubber ◽  
Temperature Coefficient ◽  
Chemical Reactions ◽  
Chemical Reaction ◽  
Reaction Rate ◽  
Complex Behavior ◽  
Double Bonds ◽  
Irreversible Reaction ◽  
Sulfur Addition

Abstract THAT vulcanization of rubber with sulfur always involves a chemical reaction consisting in the addition of sulfur to the double bonds of the rubber molecule has been conclusively established (18, 28). The facts indicate that this addition of sulfur to rubber is an irreversible reaction (31). The temperature coefficient of the reaction is high, increasing about 2.65 fold per 10° C. at ordinary curing temperatures (31). Furthermore, the reaction is apparently exothermic (4, 24). It is noteworthy that catalysts are apparently necessary, since synthetic rubbers prepared from pure materials add sulfur slowly, if at all. The proteins and perhaps the resins in natural rubber undoubtedly serve as accelerators. The curves for combined sulfur vs. time of cure for typical mixes are shown in Figures 1 and 2. Figure 1 is taken from the data of Kratz and Flower (16); the composition and temperature of cure for this mix are shown in Cranor's Table I (9). Figure 2, curve 1, is from Table I of Eaton and Day (10), and curve 2 from data obtained in this laboratory (27, Table I). Superficial inspection of these curves shows extraordinary divergence of type. Figure 1 is a typical fadeaway curve, characteristic of most chemical reactions, where the reaction rate decreases with decreasing concentration of the reacting materials. Curve 1, Figure 2, is an entirely different type, where the rate of sulfur addition is constant until nearly 70 per cent of the initial sulfur has reacted. Curve 2, Figure 2, shows even more complex behavior. Again the rate is constant in the initial portions of the cure. However, following this period, the rate increases markedly but later falls off, approaching zero, to give an S-shaped eurve.

Structural reasons for the formation of multicomponent products and the influence of high pressure

2021 ◽  
Vol 77 (3) ◽  
Author(s):  
Krzysztof A. Konieczny ◽  
Julia Bąkowicz ◽  
Damian Paliwoda ◽  
Mark R. Warren ◽  
Arkadiusz Ciesielski ◽  
...  
Keyword(s):  
High Pressure ◽  
Photochemical Reaction ◽  
Unit Cell Volume ◽  
Reaction Rate ◽  
Crystalline Form ◽  
Reaction Centre ◽  
High Elasticity ◽  
Reaction Proceeds ◽  
Kinetics Of

(S)-(−)-1-Phenylethanaminium 4-(2,4,6-triisopropylbenzoyl)benzoate (S-PEATPBB) undergoes a photochemical reaction in its crystalline form upon UV irradiation and forms three different products: the first product is the result of a Yang cyclization with the participation of the δ-H atom of o-isopropyl (product D) and the second and third products are obtained via a Norrish–Yang reaction with the involvement of the γ-H atom of 2-isopropyl (product P) and 6-isopropyl (product Z). These products are formed in different proportions (D > P >> Z). The path and kinetics of the reaction were monitored step-by-step using crystallographic methods, both under ambient and high-pressure conditions. The reactivity of S-PEATPBB depends strongly on the geometry of the reaction centre and the volume of the reaction cavity. Due to the geometrical preferences making the cyclization reaction easier to proceed, product D dominates over the other products, while the formation of product Z becomes difficult or almost impossible at high pressure. The reaction proceeds with an increase of the unit-cell volume, which, suppressed by high pressure, results in a significant decrease of the reaction rate. The crystal lattice of S-PEATPBB shows high elasticity. The quality of the partially reacted crystal remains the same after decompression from 0.75 GPa to 0.1 MPa.

Photochemical reaction of superoxide radicals with 1-naphthol

2021 ◽  
Author(s):  
Ying Liu ◽  
Mengyu Zhu ◽  
Yadong Hu ◽  
Yijun Zhao ◽  
Chengzhu Zhu
Keyword(s):  
Photochemical Reaction ◽  
Reaction Rate ◽  
Surface Reaction ◽  
Atmospheric Model ◽  
Bulk Water ◽  
Reaction Rate Constant ◽  
Photochemical Reactions ◽  
Order Reaction ◽  
Reaction Pathways ◽  
Second Order Reaction

he photochemical reactions between 1-naphthol (1-NP) and superoxide anion radical (O2•−) were investigated in detail by using 365 nm UV irradiation. The results showed that the conversion rate of 1-naphthol decreased with the increase of the initial concentration of 1-naphthol, while the raising pH and riboflavin concentration accelerated the photochemical reaction. The second-order reaction rate constant was estimated to be (3.64 ± 0.17) × 108 L mol−1 s−1. The major photolysis products identified by using gas chromatography-mass spectrum (GC-MS) were 1, 4-naphquinone and 2, 3-epoxyresin-2, 3-dihydro-1, 4-naphquinone, and their reaction pathways were also discussed. An atmospheric model showed that both bulk water reaction and heterogeneous surface reaction deserved attentions in atmospheric aqueous chemistry.

Degradation of 4-chlorophenol mediated by Fe(III)-NTA in homogeneous and heterogeneous systems

2004 ◽  
Vol 49 (4) ◽  
pp. 123-128 ◽  
Author(s):  
O. Abida ◽  
C. Emilio ◽  
N. Quici ◽  
R. Gettar ◽  
M. Litter ◽  
...  
Keyword(s):  
Photochemical Reaction ◽  
Heterogeneous System ◽  
Reaction Rate ◽  
Heterogeneous Systems ◽  
Homogeneous System ◽  
Initial Reaction Rate ◽  
Initial Reaction ◽  
Iron Salt ◽  
Positive Role ◽  
Total Disappearance

In this work, the comparison of 4-chlorophenol (4-CP) degradation by two different AOT processes has been performed: a) a homogeneous system with Fe(III)-NTA (1:1 complex), b) a TiO2/Fe(III)-NTA heterogeneous system. In both cases, NTA appears to play a positive role in the photochemical reaction. In the homogeneous system, the iron salt is the only absorbing species and is proved to be able to photoinduce 4-CP degradation ([4-CP] = 0.1-0.2 mM, [FeNTA] = 0.3-0.9 mM, pH 4, λ = 365 nm). The progress of the reaction was positively affected by the FeNTA concentration, and the reaction kept going even after the total disappearance of FeNTA. However, 4-CP complete degradation requires the presence of oxygen, otherwise the reaction stops. In the heterogeneous system ([4-CP] = 2.0 mM, [FeNTA] = 1.0-2.0 mM, [TiO2] = 0.1 and 1.0 g L-1, pH 3, λ = 300-400 nm), an important effect of the complex on the degradation extent and on the initial reaction rate can be seen, which overcomes the effect of non-complexed Fe(III). This behaviour is more important at the highest TiO2 concentration.

Experimental investigation and kinetic modeling of the negative temperature coefficient of the reaction rate in rich propane—oxygen mixtures

1997 ◽  
Vol 46 (12) ◽  
pp. 2006-2010 ◽  
Author(s):  
V. I. Vedeneev ◽  
L. B. Romanovich ◽  
V. Ya. Basevich ◽  
V. S. Arutyunov ◽  
O. V. Sokolov ◽  
...  
Keyword(s):  
Experimental Investigation ◽  
Temperature Coefficient ◽  
Kinetic Modeling ◽  
Reaction Rate ◽  
Negative Temperature Coefficient ◽  
Negative Temperature
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