Test for Chemical Reactivity

An understanding of how chemicals are used in your facility needs to occur before any detailed testing is performed. Quantitative reactivity testing need only be performed when data, such as heat of reaction and safe operating temperatures, are not available from other sources. For example, in a warehouse where no chemical or physical processing is being done, material suppliers may be able to pro- 

When you get into a situation where reactivity testing is necessary, it is essential to work with someone who understands what the tests are, when you should do what tests, what their limitations are, and how to interpret and use the results. CCPS (1995a) provides a thorough discussion of test methods. Other references such as CCPS (1995b) and Leggett (2002) present approaches for conducting reactivity screening tests. 

The selection and use of testing equipment and procedures, and particularly the interpretation of the results, requires competent people. Some major companies have their own testing facilities, but there are a number of testing houses and consultancies available that you could use. 

The results of reactivity screening tests will give a preliminary indication of  

More complicated explosibility tests need expert advice and specialized facilities. If your calculations or testing demonstrate potentially explo- 

---

Test for Chemical Reactivity Process Knowledge and Documentation Process Safety Information Identification of Major Hazards... 

While collecting reactivity data, identifying hazards, and testing for chemical reactivity, much important information will be generated. Your facility or company will need to document basic reactivity properties (e.g., heat of reaction), the hazard information, and test results. An organized approach will be needed for storing this information and making it accessible to users when needed. 

Table A.4, taken from the CCPS Guidelines for Chemical Reactivity Evaluation and Application to Process Design, shows the questions which need to be asked regarding the safety of the proposed reaction, the data required to answer those questions and some selected methods of investigation. The experimental analysis is extremely specialized, and companies should consider outsourcing the tests if they do not have specialists in this area.

Guidelines for Chemical Reactivity Evaluation and Application to Process Design (CCPS 1995a). Explains test methods for evaluating reactivity hazards and shows how this information is used in the design of chemical reaction processes. 

Five of nine respondents to the CSB survey frequently use both screening and more sophisticated approaches, including adiabatic calorimetry, to determine the thermal stability or compatibility of process materials. Seven of nine respondents use screening alone for chemical reactivity testing. The most often used testing objectives are ... 

These findings have possible implications for chemical reactivity for example, will the C=C near-double-bonds in C102BN undergo addition reactions We have carried out a preliminary HF/STO-3G test of this and found that HC1 did indeed add to C102BN, with AE(0 K) = —49 kcal/mole. For HC1 + ethylene, the HF/STO-3G AE(0 K) is —58 kcal/mole. While the computational level was very low, these results are at least encouraging. They further suggest that addition processes may also occur at the short C-C bonds that we have found in C2xBxNx systems. 

Predictive in vitro test methods are as well developed as nonanimal test alternatives, including specific cell-based assays.22 Such cellular assays include the culture of keratinocytes that represent very often the first cells in the skin to encounter potential reactive chemicals. Purified keratinocytes are cultured with a specific test chemical, and the production of proinflammatory cytokines or chemokines are then measured. Another cell population that can be used to test for chemicals inducing contact allergy are Langerhans cells (LCs). LCs are the... 

Shaker proteins in which various S4 residues were converted to cysteine were tested for their reactivity with a water-soluble cysteine-modifydng chemical agent that cannot cross the membrane. On the basis of whether the cysteines reacted with the agent added to one side or other of the membrane, the results indicated that in the resting state amino acids near the C-terminus of the S4 helix face the cytosol after the membrane is depolarized, some of these same amino acids become exposed to the exoplasmic surface of the channel. These experiments directly demonstrate movement of the S4 helix across the membrane, as schematically depicted in Figure 7-33 for voltage-gated Na" channels. 

One of the most sensitive tests of the dependence of chemical reactivity on the size of the reacting molecules is the comparison of the rates of reaction for compounds which are members of a homologous series with different chain lengths. Studies by Flory and others on the rates of esterification and saponification of esters were the first investigations conducted to clarify the dependence of reactivity on molecular size. The rate constants for these reactions are observed to converge quite rapidly to a constant value which is independent of molecular size, after an initial dependence on molecular size for small molecules. The effect is reminiscent of the discussion on the uniqueness of end groups in connection with Example 1.1. In the esterification of carboxylic acids, for example, the rate constants are different for acetic, propionic, and butyric acids, but constant for carboxyUc acids with 4-18 carbon atoms. This observation on nonpolymeric compounds has been generalized to apply to polymerization reactions as well. The latter are subject to several complications which are not involved in the study of simple model compounds, but when these complications are properly considered, the independence of reactivity on molecular size has been repeatedly verified. 

The other detonability length scale is the detonation cell width, X (also called cell size) which is the transverse dimension of diamond shaped cells generated by the transverse wave stmctnre at a detonation front. It has a fish scale pattern (see Figure 4-4). Detonation cell widths are nsnally measured by the traces (soot) deposited on smoke foils inserted in test vessels or piping surfaces. The more reactive the gas-air mixture, the smaller is the cell size. The same is tme for chemical indnction length as a qualitative measure of detonability. The cell width, X, is a parameter that is of practical importance. The transition from dehagration to detonation, propagation, and transmission of a detonation, can to some extent be eval-... 

The Patterns scheme has been tested for its capacity to predict nC NMR chemical shifts of the CH7- carbon of monomers (CH =CXY)159 and in evaluating the reactivities of small radicals towards monomers.160... 

---