General classes of chemicals

Much use has been, and continues to be, made of simplified model schemes representative of general classes of chemical or themial feedback. The oregonator and Lengyel-Epstein models for the BZ and CDIMA systems have been given earlier. Pre-eminent among the more abstracted caricature models is the bnisselator introduced by Prigogine and Lefever [47] which has the following fomi ... 

The reader should note that there are a number of important terms that should be noted when dealing with hazardous materials. These terms include important properties of general classes of chemicals and of a few commonly used industrial chemicals. This section will attempt to familiarize the reader with the main points. This section is not intended for practicing industrial chemists, nor is it intended as anything other than a refresher for those with strong backgrounds in chemistry. It is intended to provide a brief introduction to chemistry for the safety manager who must, as a part of his responsibilities, deal with hazardous materials issues. 

One general class of chemical reactions is the reaction of metals or non-metals with oxygen to give oxides of the general formula M O. For example, iron can react with oxygen to give iron (111) oxide (Figure 4.2),... 

It all works much better if we consider some simpler cases that are less obvious in ordinary life but still have greater importance for medicine than skin or eye color. Take, for example, the disease phenylketonuria, which 1 mentioned briefly in Chapter 8. If left untreated it produces severe mental retardation and, in many cases, death before the age of 25. It is caused by an incapacity to convert the aminoacid phenylalanine into another aminoacid, tyrosine. It is not, however, a deficiency disease, because its harmful effects are not caused by a shortage of tyrosine, and cannot be avoided by adding tyrosine to the diet. Instead they are caused by the toxic effects on the brain of a substance called phenylpyruvate, which the body produces in its efforts to remove the excess of phenylalanine. The name of the disease reflects the fact that phenylpyravate, which belongs to a general class of chemical substances known as phenylketones, is excreted in the urine of affected people. This provides a simple method of diagnosis, and the disease is treated by carefully controlling the diet so that it provides no more phenylalanine than is needed for normal health. There is then no surplus to be converted into phenylpyruvate. 

Table V. General Classes of Chemicals that Inhibit Chemical Carcinogenesis...

Antifoam products are selected usually from a general class of chemicals including silicone oils, hydrophobic silicas, or glycols. The selection of the best product must be made after careful consideration of the process, the processing conditions, and the potential effect of the antifoam on product specifications or downstream processes. 

Table 3.5 lists important general classes of chemicals for which some members (but not necessarily all) have been identified as being carcinogenic substances. Listed for each general class are representative compounds that are "reasonably anticipated to be carcinogens" based on animal tests, selected from lists of substances identified as... 

Pisdtelle, L.J. (1990). Determination of initial rates for a general class of chemical reactions A methodology. International Journal of Chemical Kinetics, 22, 683-688. 

Generalized first-order kinetics have been extensively reviewed in relation to teclmical chemical applications [59] and have been discussed in the context of copolymerization [53]. From a theoretical point of view, the general class of coupled kinetic equation (A3.4.138) and equation (A3.4.139) is important, because it allows for a general closed-fomi solution (in matrix fomi) [49]. Important applications include the Pauli master equation for statistical mechanical systems (in particular gas-phase statistical mechanical kinetics) [48] and the investigation of certain simple reaction systems [49, ]. It is the basis of the many-level treatment of... 

Synthetic fluids are safe, noncorrosive, essentially nontoxic, and thermally stable when operated under conditions recommended by the manufacturers. Generally, these fluids are more expensive than petroleum oils, but the synthetics can usually be reprocessed to remove degradation products. There are several classes of chemicals offered permitting a wide temperature range of appHcation. Any heat-transfer fluid in use should be examined periodically to monitor degradation or contamination. 

Waxes are one of the two general classes of commercial antiozonants. Waxes are derived from petroleum and are of two common types, paraffin and microcrystalline (20—23). Typical carbon numbers are n = 20 50 for paraffin waxes and n = 30 70 for microcrystalline materials. If a wax is present ia a vulcanizate at a concentration exceeding its solubiUty, some of it will migrate to the mbber surface where it can form a physical barrier to prevent the penetration of ozone. Waxes, of course, are essentially unreactive towards ozone so that there is no appreciable chemical protection. Commercial waxes are... 

Chemical antiozonants comprise the second general class of commercial antiozonants. Of the many compounds reported to be chemical antiozonants, nearly all contain nitrogen. Compound classes include derivatives of l,2-dihydro-2,2,4-trimethylquinoline, A/-substituted ureas or thioureas, substituted pyrroles, and nickel or zinc dithiocarbamate salts (see also Antioxidants). The most effective antiozonants, however, are derivatives of -phenylenediamine... 

Most chemical reactions of industrial significance fall within the general class of reversible reactions given by... 

In accord with general Eyring TS theory, we may consider every elementary chemical reaction to be associated with a unique A- B supramolecular complex that dictates the reaction rate. In the present section we examine representative TS complexes from two well-known classes of chemical reactions Sn2 nucleophilic displacement reactions... 

Since general anesthetics are related to a variety of classes of chemical compounds, there is no general pattern that exists between their chemical structure and their activity. Particular patterns only exist for different groups of compounds (barbiturates, benzodiazepines, etc.). 

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