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Pyrochemical reactions

Although pyrochemical reactions are very important in the chemical industry (coking, cracking, etc.), reactions of this type are seldom used nowadays in preparative organic chemistry in the laboratory.106a [Pg.894]

One of the oldest pyrochemical reactions is the formation of biphenyl from benzene. The older prescriptions require that benzene vapor be passed through a red-hot iron tube, whereby biphenyl is accompanied by hydrogen, carbon, and terphenyls as pyrolysis products. Zanetti and Egloff255 give 750° as the optimum temperature for production of biphenyl, larger proportions of by- [Pg.894]

Wibaut and his colleagues260 studied the pyrochemical formation of biphenyl from benzene under pressure and in presence of catalysts (nickel or iodine), which permit the use of lower temperatures. However, the proportion of side reactions then increases, e.g., formation of methane when nickel is used as catalyst. [Pg.895]

Noble metals also catalyse the formation of carbon-carbon bonds in the aromatic series. For example, if 0-terphenyl is dissolved in decalin and passed with hydrogen over charcoal coated with palladium and platinumat 490°, there is 77% conversion into a product containing 82.5% of triphenylene 261 [Pg.895]

Mattox and Grosse262 report the formation of biphenyl, anthracene, and naphthalene from benzene, toluene, or butylbenzene in presence of a chromium-aluminum dehydrogenation catalyst and if 1 -phenyl-frws-l,cis-3, f/my-5-heptatriene is heated for 15 min with palladized charcoal in an evacuated tube at 180°, a very good yield of 2-methylbiphenyl is obtained 263 [Pg.895]


Some limestones, more often the coarse crystalline types, can never be calcined successfully. Such stone tends to decrepitate during preheating or calcination into fine particles that interfere with this pyrochemical reaction. The adaptabiflty of a stone for calcination can only be ascertained with surety by empirical methods. Possibly the greatest influence on lime quaflty is the size gradation of limestone. Narrow gradations, such as... [Pg.171]

Intermolecular union of two aromatic nuclei can be effected by means of aluminum chloride in the same way as in the pyrochemical reactions discussed above except that presence of a catalyst permits reaction at lower temperatures. [Pg.899]

The major types of pyrotechnically useful pyrochemical reactions and devices are the following ... [Pg.6]

Data of heats of formation of compounds for the purpose of deter-mining the enthalpies (heat outputs) of pyrochemical reactions, together with other pertinent data (on phase changes, melting points, etc.), are found in Circular 500 NBS and Metallurgical Thermochemistry by Kubaschewski and Evans, Lange s Handbook contains reprinted data from the former. ... [Pg.14]

Theoretical approaches to solid reactions are represented by two books Chemistry of the Solid State" by W. E. Garner contains two chapters that touch on the subject of pyrotechnics. Chapter 9, The Kinetics of Exothermic Solid Reactions, presents data on substances that decompose exothermically. Chapter 12, Solid—Solid Reactions, by A. J. E. Welch, treats interaction of solids but without reference to pyrochemical reactions,... [Pg.14]

Todates and periodates, largely unknown quantities in pyrochemical reactions with few highly specialized exceptions, seem to have attracted much more interest outside of the United States as one can see by perusing the list of references in Supplement 1 to Mellor, Volume IL Explosive salts containing these anions have been described in Russia by Lobanov. ... [Pg.63]

Creation of flame or glow from pyrochemical reactions proceeding from ambient temperatures was the subject of Part II, Primary Flame and Glow. In all subsequently described applications, heat was the s( irce of useful secondary phenomena, viz. radiation (light), aero-solization (smoke), kinetic energy (PAD, noise), but the heat was not utilized as such, e.g. for heat transfer plain and simple, excq t in an accessory capacity. [Pg.187]

Undoubtedly, one can produce other gases by pyrochemical reaction or by combining a heat source with a pyrogenic decomposition reaction. These include the halogens and pseudo halogens, such as cyanogen. The latter is formed from heavy-metal cyanides ... [Pg.241]

Titanium and zirconium powders, other than the very hne powders described above, are on the market for powder metallurgical purposes and will undoubtedly play a part in future pyrochemical reactions other than for primers or first fires. Zirconium foil is also available and is replacing aluminum foil in oxygen-filled flash bulbs. ... [Pg.334]

The word pyrotechnics, according to its modern meaning, is somewhat of a misnomer, since it is fixed in people s mind as dealing with fireworks and firecrackers. No better and perhaps more dignified word has been found, though the author has attempted to speak of pyrochemistry and pyrochemical reactions wherever it seemed proper. [Pg.391]

The term "Pyrochemical Processing" is commonly applied to a family of chemical processes that utilize oxidation-reduction reactions to effect chemical separations at elevated temperatures. [Pg.377]

The anode residues must be chemically processed to recover the plutonium remaining in the residues. This may amount to about 10% of the feed mass if delta alloy is the feed metal. Either aqueous or pyrochemical processes may be used for anode recovery. One pyrochemical process used for recovery utilizes oxidation of the plutonium with zinc chloride to form plutonium chloride salt, followed by calcium reduction of the PUCI3 contained in the salt phase to produce pure plutonium metal (the impurities follow the zinc metal obtained from the oxidation reaction and are discarded to waste). Impurities more stable than calcium chloride remain in the salt phase and are also... [Pg.400]

The w,causes electrochemical exchange between the Mg and the Ag ion. The heat of reaction of this exchange provokes the pyrochemical effect. I a peroxide oxidizes Mg powd with incandescence (Ref 5). The mixt explodes when Heated to redness. When the mixt is exposed to moist air spontaneous combustion occurs., When carbon dioxide gas is passed over a mixt of powd Mg and Na peroxide, the mixt explodes (Ref 6). Stannic oxide, heated with Mg, explodes (Ref 13)., A mixt of sulfates and Mg may cause an expln (Ref 17.) It has been detd experimentally that a mixt of Mg powd with trichloroethylene or carbon tetrachloride will flash or spark under, Heavy impact (Ref 2l). Mg alloy powders contg more than 50% Mg readily ignite in air (Ref 20)... [Pg.24]

The lignite type ashes have comparatively low fouling propensity when the sodium content is below 4 per cent because of the limited amount of clay minerals available for sintering reaction. That is, in some lignite and sub-bituminous coals there is an excess of sodium and calcium available for the high temperature reactions, and the rate of deposit formation depends on the silicate content of ash (2,29). The bituminous coal type ash has an excess of silicates, i.e. the ash is pyrochemically acidic and the rate of sintering depends on the availability of sodium, calcium and iron species in the flame heated deposit material. [Pg.151]

The pyrochemical conversion of diphenylmethane into fluorene and of bibenzyl into phenanthrene, first effected by Graebe,264 is fully analogous to that of biphenyl from benzene. These reactions, as well as the preparation of carbazole from diphenylamine, were carried out by Zelinsky and his co-wor-... [Pg.895]

Even if we disregard the element lithium whose behavior at the top of the vertical column in the periodic system tends to resemble that of the elements of the second column (Ca, Sr, Ba), there is no Coordination between spontaneous flaming and heat output from the reaction with water, though there may be a connection with the melting point of the metals when we keep in mind the influence of renewal of the surface on reactivity. Table 3 shows these relations. In calculating enthalpies in pyrochemically unusual cases of this kind, one must clearly state if the water is included as a reactant and also if the considerable heat of solution plays a part. In the cited study, the heats of formation of the hydroxides dissolved in an infinite amount of water were given, rather than the true heats of reaction, which may have been intentional. [Pg.44]

The theory of fire transfer from a pyrochemical ignition mixture to a powder grain, such as the surface of a double-base propellant, has been the subject of much speculation and falls outside the scope of this book. Total heat output, pressurization by gaseous reaction products, glowing solid particles, and condensing vapors will contribute in varying degree to the creation of a stable flame-front on the propellant surface. [Pg.195]

In discussing the field of delay timing by pyrochemical means, the first question to arise might be the caiculation of the burning time (rate) from the reactions of the components and their chemical and physical properties. Japanese scientists have attempted to arrive at complex formulas, but it is doubtful whether such formulas are of practical help, partly because of insufficient data on the factors involved and partly because of the numerous external factors other than those residing in the chemical components themselves. [Pg.200]

Brock mentions the use of burnt lime and water as a heat source for food cans. This reaction furnishes 0.26 kcal/g of calcium oxide (CaO), and w4iile not exactly classifiable as pyrochemical is said to be abk to produce a temperature as high as 450°C—enough to set fire to guncotton, sulfur, wood, and sometimes straw. ... [Pg.225]

It is more difficult to make hydrogen by pyrochemical means. This was done in France prior to World War I for filling balloons. The so-called Silicot process, described in Mellor, by Remy, and also in a French patent, combines silicon in the form of ferrosilicon and soda lime into a mixture called Hydrogenite. The reaction proceeds exothermically, perhaps according to the equation... [Pg.240]

In Chapter 19, it was indicated that the dispersion of alkali metals at high altitudes is a new tool in space exploration. Instead of merely evaporating the metals by pyrochemical heat sources, one might think of producing them by chemical reaction and dispersing the resulting metal vapors in the rarefied atmosphere. [Pg.249]

A noteworthy statement is that the inception of a reaction coincides almost always with the temperature at which one or the other of the reactants undergoes recrystallization. This may occur by partial fusion on the surface (sintering) that can take place (as proved by Hedvall) below actual fusion temperature accompanied by diffiisicm processes, sintering, and recrystallization with consequent shrinkage. These observations appear to derive from ceramic mixtures but may be applicable to pyrochemical combinations. [Pg.290]


See other pages where Pyrochemical reactions is mentioned: [Pg.40]    [Pg.894]    [Pg.87]    [Pg.274]    [Pg.291]    [Pg.40]    [Pg.894]    [Pg.87]    [Pg.274]    [Pg.291]    [Pg.23]    [Pg.378]    [Pg.451]    [Pg.382]    [Pg.458]    [Pg.184]    [Pg.211]    [Pg.46]    [Pg.202]    [Pg.230]    [Pg.235]    [Pg.236]    [Pg.275]    [Pg.275]    [Pg.276]    [Pg.278]    [Pg.288]   


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