Reactive substances/materials

Suong oxidizers have more potential incompatibilities than perhaps any other chemical group (with the exception of water reactive substances). It is safe to assume that they should not be stored or mixed with any other material except under carefully controlled conditions. Common oxidizing agents listed in decreasing order of oxidizing strength include ... 

The corrosive effects to be considered (mainly simple corrosion of metals) are, as would be expected from the edible nature of foodstuffs which are not excessively either acidic or basic but which may contain sulphur, less severe than those often encountered with inedible materials containing reactive substances. The importance of corrosive efiects where foodstuffs are concerned lies not so much in the action of the foodstuffs on the metal involved as in the resultant metal contamination of the foodstuff itself, which may give rise to off-flavours, in the acceleration of other undesirable changes (by the Maillard reaction for example), and in the possible formation of toxic metallic salts. Metal ions generally have threshold values of content for incipient taste effect in different liquid foodstuffs. Except in the case of the manufacture of fruit juices and pickles, process plant failure through corrosion must be rare. Nevertheless all foodstuffs, particularly liquid ones, should be regarded as potentially corrosive and capable of metal pick-up which may be undesirable. 

Water-Reactive Substances Water-reactive substances will chemically react with water, particularly at normal ambient conditions. For fire protection purposes, a material is considered water-reactive if a gas or at least 30 cal/g (126 kj/kg) of heat is generated when it is mixed with water (NFPA 704, 2001), using a two-drop mixing calorimeter. 

The first four questions address substances that are reactive with air, water, or ordinary combustibles—materials that are almost certain to be in close proximity to the reactive substances. The next question addresses self-reactive materials. This is followed by a final question combined with a series of steps for addressing chemical incompatibility. 

If you are certain that NO self-reactive substances are present, then proceed to the next question (Question 12). If you are uncertain as to whether a material is self-reactive, a chemist or other expert should be consulted. Annex E to NFPA 704 (2001) gives a method for calculating an "instantaneous power density," defined as the product of the enthalpy... 

The chemical structure of the epoxy matrix constituent as well as processing are reported to strongly influence 11 -I3> the thermoset network and hence the properties and durability of the crosslinked polymer 11 ,4-16). The cure of a reactive prepolymer involves the transformation of low-molecular-weight reactive substances from liquid to rubber and solid states as a result of the formation of a polymeric network by chemical reaction of some groups in the system. Gelation and vitrification are the two macroscopic phenomena encountered during this process which strongly alter the viscoelastic behavior of the material. 

Compatibility of Explosives with other Substances The term compatibility refers almost exclusively to chemical reactivity between materials, that is, the ability of a given expl to exist unchanged under certain conditions of temp moisture, when in the presence of some other material. If this condition exists, the two materials are said to be compatible. Incompatibility of an expl and another material in which it may be in contact may result in loss of effectiveness of the expl, or it may result in extreme hazard... 

Reports a standardized method for direct determination of TBA value in oils, fats, and lipid extracts. Unlike distillation and extraction methods, this technique determines total reactive substances without previous isolation of the volatile fraction. Furthermore, the solvent of choice is organic (l-butanol) rather than aqueous. This protocol is reported as the official (AOCS) method to determine TBA value (direct method) of animal and vegetable fats and oils, fatty acids and their esters, partial glycol esters, and similar materials. 

Phosphorus reacts with chlorine to yield PC13 and PC15. These are reactive substances that serve as the starting materials for making many other materials that contain phosphorus. Moreover, P4 burns in air to yield P4Oio, which reacts with water to produce phosphoric acid, another important chemical of commerce, as shown in the following equations ... 

A reactive chemical is a substance which may cause fire or explosion by reacting with itself or with other substances. Reactive chemicals are divided into two categories self-reactive substances and reactive substances with other materials. 

Two conditions can give rise to the spontaneous combustion of a fuel. One condition involves contact of the material with air. The other is the spontaneous ignition of an unstable self-reactive substance when it is kept at a sufficiently high temperature. Silane (SiH 4 ) and phosphine (PH 3 ) are the examples of the former case, and a mixed atmosphere of air and nickel carbonyl(Ni(CO) 4 ) or carbon disulfide (CS 2 ) are examples of the latter. 

In this chapter, reactive substances will be classified into several types for each type, major informative past accidents will be described. Accidents involving hazardous materials in earthquakes will also be discussed here. 

Ammonium nitrate, both an oxidizer and a self—reactive substance, is still used in fertilizers and as a raw material for explosives. The following two are typical accidents involving ammonium nitrate. 

When the unusual bromine cleavage of oxytocin and vasopressin, reported by du Vigneaud and his associates, was repeated with a simplified tripeptide model, N-carbobenzyloxy-(S-benzyl-L-cysteinyl-L-tyrosyl-L-iso-leucine (CXV) (Ressler and du Vigneaud, 1957), bromine or NBS liberated a ninhydrin-reactive material in 40% yield. Paper chromatography proved isoleucine to be the sole ninhydrin-reactive substance present. The ultraviolet spectrum of the reaction mixture showed the characteristic 260 mM absorption for a dienone (CXVI). 

The occurrence of a chemical reaction in a process brings several complications into the material balance procedures described in the previous sections. TTie stoichiometric equation of the reaction imposes constraints on the relative amounts of reactants and products in the input and output streams (if A B, for example, you cannot start with 1 mol of pure A and end with 2 mol of B). In addition, a material balance on a reactive substance does not have the simple form input = output, but must include a generation and/or consumption term. 

Self-reactive substances need to be subjected to temperature control if their self-accelerating decomposition temperature (SADT) is less than or equal to 55 °C. Test methods for determining the SADT as well as the derivation of control and emergency temperatures are given in the UN Recommendations for the Transport of Dangerous Goods, Manual of Tests and Criteria, Part II, section 28. The test selected shall be conducted in a manner which is representative, both in size and material, of the package. 

Shelf Storage Test The test material is stored under similar conditions as in retail and is evaluated for the effectiveness of antioxidants in prolonging the premium quality of the product. Periodic evaluation of the hpid oxidation products (primary or secondary) by chemical tests (e.g., peroxide value, conjugated diene value, 2-thiobarbituric acid reactive substances, hexanal content) or sensory evaluation will be used to find out the onset of oxidation. The main drawback of this kind of evaluation is the time taken therefore, rapid evaluation or accelerated methods are often preferred (19, 51). 

Ferrocene, Fe(Ti5-C5H5)2, and related cyclopentadienyl complexes of transition metals in fact are far more thermally stable, less reactive substances than ionic cyclopentadienides, and have an extensive derivative chemistry that is typically aromatic in that their C-H bonds can undergo such electrophilic substitution reactions as Friedel-Crafts alkylation or acylation, nitration, and so on. Moreover, as a substituent, the ferrocenyl group (ri -f sl l5)Fc(ri -( 5l I4) (=R) is even more effective than a phenyl substituent in stabilizing carbenium ions [RCH2]+. The redox and photochemical properties of many metaUocenyl residues make them versatile substituents with many chemical and materials applications. ... 

The formation of dark-colored polymeric material, such as has been observed also on the electrochemical reduction of 1,2-dihydrophthalazine13 and on treating 2-tosylisoindoline with potassium t-butoxide,6 might reasonably have been taken as a signal that isoindole had been formed and was a very reactive substance. The trapping of isoindole produced by the base-promoted elimination of benzyl alcohol from 2-benzyloxyisoindo-line (12) was more definitive (Eq. I)14 it showed that isoindole was formed, although spectroscopic characterization of the intermediate was still not possible. 

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