With Heat or Light

The thermal decomposition of a diorgano tellurium in which one of the Te-carbon bonds is weaker than the other occurs with loss of the weaker-bound organic group and formation of a diorgano ditellurium. For instance, a,tu-bis[4-ethoxyphenyltelluro] alkanes decompose above their melting points with formation of bis [4-ethoxyphenyl] ditellurium.  

Weakly bound organic groups, such as 2-alkoxyethyl, benzyl, acylmethyP, and trifluoro-methyl , are cleaved from the tellurium atom upon exposure to light. Dimethyl tellurium is 

Irgolic Organo Tellurium Compounds with 2 Te—C Bonds or 1 Te = C Bond 

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Carbenes have divalent carbon with a lone pair and hence only six electrons in the outer shell of the carbon atom. They are normally electrophilic and can form two bonds at once with a re-system.7 One way to make carbenes is by loss of nitrogen from diazocompounds such as diazoketones 33. The formation of very stable nitrogen is initiated by heat or light and compensates for the formation of the unstable carbene 30. Diazoketones are easily made by acylation of diazomethane with an acid chloride 31. Loss of a very acidic proton from the diazonium salt 32 gives 33. Normally the diazoketone and the alkene are combined and treated with heat or light.8... 

A free-radical initiator such as chlorine, bromine, or a peroxide (with heat or light) suggests that a free-radical chain reaction is most likely. Free-radical reactions were discussed in detail in Chapter 4. 

The mechanism of the Wohl-Ziegler bromination involves bromine radicals (and not imidoyl radicals). The radical initiator is homolytically cleaved upon irradiation with heat or light, and it reacts with Bra (which is always present in small quantities in NBS) to generate the Br- radical, which abstracts a hydrogen atom from the allylic (or benzylic) position. The key to the success of the reaction is to maintain a low concentration of Bra so that the addition across the C=C double bond is avoided. The Bra is regenerated by the ionic reaction of NBS with the HBr by-product. 

The product polymerized readily with heat or light to a polymer containing 65% silica. An octameric silsesquisiloxane has also been appended to polystyrene (5.28).94... 

When treated with heat or light nitrogen, can be eliminated from tetrazoles and 1,2,3-triazoles. Nitrile imides can be formed by photolysis or thermolysis of 2,5-disubstituted tetrazoles. The nitrile imides can then react... 

Polymer dispersed nematic films are made by one of two distinct processes. In one, the nematic is emulsified in either an aqueous solution of a film-forming polymer (for example, poly vinyl alcohol) or an aqueous colloidal dispersion (for example, a latex). This emulsion is coated onto a conductive substrate and allowed to dry, dming which time the polymer coalesces around the nematic droplets. Laminating a second conductive substrate to the dried film completes the device. Alternatively, the nematic is mixed with a precursor to the polymer to form an isotropic solution. When polymerization is initiated, typically with heat or light, nematic droplets nucleate in situ as the polymer chains grow. 

It is also prepared by a decomposition reaction with heat or light. For example, the silylenes are obtained by light irradiation of the cyclic compounds [9,12]. In contrast, silylenes form cyclic compounds as described below,... 

Diazobenzene is also a compound in which cyclometalation easily proceeds, as shown in eq. (15.29) and cyclometalated compounds are prepared by heating or light irradiation [87]. The five-membered ring compounds reacts with diphenyla-cetylene with heating or light irradiation to afford 2,3-diphenylindol as shown in eq. (15.29) [88]. 

PVC is an important and widely used polymer but it has poor thermal stability. With heat or light, it can undergo dehydrochlorination reactions, forming alkenes. 

Notice that the halogenation of hydrocarbons requires initiation with heat or light, which causes the chlorine-chlorine bond to break. 

The most common reaction of methylene chloride is its reaction with chlorine to give chloroform and carbon tetrachloride. This occurs by a free-radical process initiated by heat or light in the gas or Hquid phase. Catalytic chlorination to these same products is also known (see Chlorocarbons and Cm OROHYDROCARBONS, Cm OROFORM). 

Since the first plastic cellulosic was produced in 1868, there has been an evergrowing demand for specially compounded plastics. Using a post-reactor technique, plastics can be compounded by alloying or blending polymers in addition to using additives such as colorants, flame retardants, heat or light stabilizers, lubricants, fillers, and/or reinforcements (Fig. 6-6). With reinforcements the resulting reinforced compounds are usually referred to as reinforced plastics (RPs). 

Can polymerize exothermically with strong alkalis, heat or light Can form peroxides Colourless, wrater soluble liquid... 

Acrolein Allyl aldehyde, propenal) CH2 CHCHO -26 278 2.8-31.0 0.8 1.9 53 Colourless/yellow liquid Pungent unpleasant odour Water soluble Irritant Can polymerize exothermically with strong alkalis, heat or light Can form peroxides... 

When impure, the material is unstable towards heat or light and decomposes to give an explosive residue. The pine material is more stable to light, but detonates on heating or in contact with solid alkalies [1], Preparation by action of oxygen on diallylzinc gives improved yields, but there is a risk of explosion. The peroxide is also impact-sensitive if sand is admixed [2],... 

A solution, prepared by mixing saturated solutions of cadmium sulfate and sodium azide in a 10 ml glass tube, exploded violently several horns after preparation [1], The dry solid is extremely hazardous, exploding on heating or light friction. A violent explosion occurred with cadmium rods in contact with aqueous hydrogen azide [2], A DTA study showed a lesser thermal stability than lead azide [3], It is strongly endothermic (AH°f (s) +451 kJ/mol, 2.32 kJ/g). 

Combustion - A rapid chemical process that involves reaction of an oxidizer (usually oxygen in air) with an oxidizable material, sufficient to produce radiation effects, i.e., heat or light. 

Polymerization A process in which a hazardous materials is reacted in the presence of a catalyst of heat or light or with itself or another material to form a polymeric system, which often times is violent. 

Relationships existing between structure, stability and thermal, photochemical and explosive decomposition (sometimes spontaneous) of the inorganic azides has been extensively investigated and reviewed [1,2]. The ignition characterisitcs of explosive inorganic azides, with or without added impurities under initiation by heat or light have been discussed [3],... 

These techniques involve reactions in which the reduction of the precursor is carried out with liquid agents which can be aided with heat, plasma, light, ultrasound, microwave, or supercritical C02 [45,145-149]. Common reducing agents include NaBfb, [42], ethylene glycol [84], thiourea [48], sodium citrate [150], and formic acid [107]. 

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