Sodium flame reactions

These concepts represent the theoretical framework for the interpretation of the majority of the published data for sodium flame reactions. Subsequent to the publication of Warhurst s review it was suggested by Smith and co-workers [63, 64] that there should be a correlation of the activation energy of sodium—alkyl chloride reactions with the net electronic charge on the halogen atom, the higher the charge... 

A general correlation [65] of sodium flame reaction rates with electron absorption coefficients has been made. This correlation covers a range of rate coefficients varying by a factor of three powers of ten. It is illustrative rather than conclusive and deserves further consideration. A formal similarity could also exist between the mechanisms for dissociative electron attachment of organic halides [66, 67] and the sodium flame reactions. These mechanisms can be either a direct dissociative mechanism... 

General correlation between sodium flame reaction rates and activation energies for the dissociative electron attachment reaction is evident but further data are necessary to extend this to more specific cases. 

The reactions of a number of such compounds have been studied and a wide variety of rates of reaction are evident. It is of interest to note that molecular hydrogen reacts with sodium vapour in the gas phase under conditions where it is used as a carrier gas in sodium flame studies. A slow steady decrease in total pressure occurs as a run proceeds which can be attributed to sodium hydride formation. This can have an effect on the saturation of the carrier gas with sodium vapour when very long runs are employed. Thomas [108] has shown that after about six hours there is a considerable reduction in the amount of sodium vapour emerging from the nozzle, an effect that is absent for nitrogen as a carrier gas. The literature on sodium flame reactions makes no mention of this effect with the exception of the paper by Hodgins et al. [109]. 

In the early 1930s sodium-flame reactions were studied [1] in which sodium vapour was brought into contact with organo halides in a carrier-gas leading to the formation of radicals ... 

Carbon monoxide is a highly flammable and poisonous gas. Its flammable limits in air are 12.5 to 74.2% by volume, and the autoignition temperature 700°C. It explodes when exposed to flame. Reactions with interhalogen compounds, such as, bromine pentafluoride or halogen oxides can cause explosion. It forms explosive products with sodium or potassium that are sensitive to heat and shock. 

The reaction mixture is heated to about 880° and maintained at that temperature until the sodium flame diminishes. (Above about 750°, sodium vapor swept out by the argon stream burns on exposure to air and shows up as a pointed flame issuing from the reaction vessel.) The white smoke is sodium oxide. Mild agitation with the stainless-... 

The introduction of competitive alkali metal flame reactions has allowed the experimental determination of activation energy differences for alkali metal flame reactions. The method involves the reaction of sodium or potassium with a pair of organic halides, one of which contains chlorine-36. Analysis of the solid halides produced provides a method of obtaining relative yields of the halides and thus relative rate coefficients. The use of a large temperature range (90—120°C) allows accurate measurements of activation energy differences and ratios of Arrhenius A factors. The values in Table 1 were so obtained. 

Detailed quantitative results for studies of the disproportionation/ dimerization ratio of ethyl and isopropyl radicals are given in Table 9. These sodium flame results suggest that the disproportionation reactions... 

Chapter 1 deals with the kinetics of the dissociation of diatomic molecules and the recombination of atoms, and Chapters 2 and 3 with the reactions of atoms and radicals with molecules, abstraction (metathetical) processes and addition to double and triple bonds. Data for the reactions of metal atoms with a variety of inorganic, organic and metal organic compounds, derived from sodium flame and molecular beam techniques, are discussed in Chapter 4 and rapid substitution at labile metal ions in solution in Chapter 5. The theory of, and the experimental results for, ion-molecule reactions, i.e. chemical processes resulting from binary collisions of positive or negative ions with neutral molecules, are discussed in Chapter 6 and the reactions of solvated electrons in Chapter 7. 

The diffusion cloud (flame) technique developed by Hartel and Polanyi in the 1930s is one of the early methods of studying rapid bimolecular chemical reactions imder pseudo-first-order, steady-state conditions. This method is the source of most measured rates for reactions of alkali metals with halogenated compounds and still serves as a basis for experimental and theoretical studies. In most applications of the technique, sodium metal is heated in an oven, mixed with an inert carrier gas, and allowed to diffuse into a backgroimd of a reactant gas. In very exothermic reactions the sodium flame is chemiluminescent otherwise the cloud is illuminated with a sodium resonance lamp. The reaction rate can be measured either by determining the distance the sodium diffuses until it all reacts or by spectroscopically measuring the total amount of sodium in the cloud. ... 

HAZARD RISK Dangerous fire hazard when exposed to heat or flame contact with strong oxidizers may cause fire vapors may flow to distant ignition sources and flash back forms explosive mixtures with powdered sodium or phosphorus trichloride and sodium violent reaction with silver perchlorate and dimethyl sulfoxide closed containers exposed to heat may explode decomposition emits toxic gases of hydrogen chloride, phosgene, carbon monoxide, carbon dioxide NFPA Code H 2 F 3 R 0. 

EXPLOSION and FIRE CONCERNS combustible when exposed to heat or flame reaction with sodium forms an ignitable product NFPA rating Health 3, Flammability 1, Reactivity 0 reacts violently with concentrated sulfuric acid (above 160°C) forms highly explosive mixtures with tetranitromethane may explode on standing involved in many plant scale explosions residue from vacuum distillation may explode spontaneously combustion by-products include oxides of nitrogen and carbon monoxide use dry chemical, carbon dioxide, or water spray for firefighting purposes. 

Water is the oxidizer in flaming reactions with potassium, rubidium, or cesium metal, which explosively burst into flame on contact. A plumsized piece of potassium thrown into water as a joke was said to have killed a German university student in the early part of the century. Sodium will not burst into flame when thrown onto cold water as long as the piece of metal can skim freely over the surface of the water. The moment it attaches itself to the wall of the vessel or is purposely held... 

That the flaming reactions of the alkali metals and water need no air may be shown by the fact that sodium (and after some delay, lithium) ignites in an atmosphere of steam and argon, and a lithium dispersion will ignite in liquid water under argon. ... 

In a somewhat different manner, the hydrolytic and heat-forming influence of water prevails in some fuel-oxidizer systems that are reactive in the common manner of pyrotechnical combinations, but will also be brought to an intensely-hot flaming reaction by the addition of small amounts of water. Most of these combinations contain sodium peroxide as the oxidizer. Aluminum and magnesium, mixed with sodium peroxide, have been recommended as igniters for the thermite mixtures described later. The magnesium/sodlum peroxide can even be initiated by carbon dioxide. The high reactivity of these combi-... 

Following a multiple-tube failure in a PFR superheater in 1987, two models were proposed to place deterministic limits upper limits on tiie number of tube failures following an initial leak. These were a reaction flame heat transfer model, to show that a large number of tubes could not be brought to the point of failure at the same time, and a piston expulsion model, where most of the sodium would be expelled from the SGU, blanketing the tubes with steam eind stopping the sodium water reaction when a certain number of tubes had failed. 

A further experiment investigated the heat flux through tubes in different regions of a sodium water reaction flame from an intermediate size leak in a PFR evaporator. It was... 

With the flame photometric method, sodium concentrations are directly detected as an intensity of the D line (589 nm), which is generated as a flame reaction of sodium during spraying of the sample into a flame. When measured by this method, the interference of coexistent elements is not too large (Table 2). The presence of glucose (above 1000 mg/dL), urea (300 mg/dL), or protein also interferes with the measurement of the serum or plasma sodium concentration [4]. 

Leak escalation. The jet issuing from a small leak forms a turbulent under-sodium "flame" [6.13] (Figure 6.9). The centre of the flame is a core of un-reacted steam at a temperature of 300-500X. This is surrounded by a reaction zone in which the sodium concentration is low on the inside, high on the outside. In the centre of this reaction zone, where the molar concentrations of sodium are equal, tempoatures of 1200-1400°C (depending... 

In the 1930s, Michael Polanyi studied the sodium-chlorine reaction in highly dilute flames ... 

---