By Other Method

Halogeno-l,6-naphthyridines have also been made by the Meissenheimer reaction from 1,6-naphthyridine N-oxides and by a (copperless) Sandmeyer-type reaction from 1,6-naphthyridinamines. However, neither route has been developed into a practical preparative procedure, as indicated in the following examples. 

6-Naphthyridine 1-oxide (20) and and phosphoryl chloride gave a separable mixture of 2-, 3-, and 4-chloro-1,6-naphthyridine (21) and unsubstituted 1, 6-naphthyridine (reactants, 0°C— reflux, 10 min 50%, 9%, 15%, and 2%, respectively).232 

6-Naphthyridine 1,6-dioxide (22) likewise gave a mixture of chlorinated products from which the main constituents, 2,5- and 3,5-dichloro-l, 6-naphthyridine (23), appear to have been isolated.1069 

Diazotization of 3-phenyl-l,6-naphthyridine-2,7-diamine (24) in an excess of hydrochloric acid gave mainly 7-chloro-3-phenyl-l,6-naphthyridin-2-amine (25) along with three separable byproducts (10M HC1, — 10°C, HC1 gasj, substrate), — 10°C, 5h 20°C, 8h 4°C, 2 days 61%) analog likewise.564 

The reaction of N,N -bis-alkylideneureas 22 with phosphorous pentachloride affords bis(a-chloro)carbodiimides 23P 

Treatment of bis-alkylideneurea24 with triphenylphosphine dibromide gives bis(Q(-bromo)-carbodiimide 25.  

PhCF3C=NCON=CPhCF3 - - Ph3PBr2--------- PhCF3C(Br)N=C=NC(Br)PhCF3 

Heating of the perfluorinated azide 26 at 270-300 °C affords bis(trifluoromethyl)carbo-diimide 27.  

Thermolysis of perfluoroalkyl(N-pentafluorosulfanyl)azidoazomethines 28 afford N-perfluoroalkyl-N -pentafluorosulfanylcarbodiimides 29 (R = CF3, C2F5, NFaCFs).  

Lithium aluminum hydride (in excess) with tetrachloropyrazine in ether-tetrahydrofuran gave a low yield of trichloropyrazine (and a considerable quantity of unchanged tetrachloropyrazine) (888). 

Attempts to convert 2chloro-5-hydroxy-3,6-dimethylpyrazine into 3-hydroxy- 

5- dimethylpyrazine by reduction in alkaline solution with Raney nickel alloy were unsuccessful (312), but this transformation was effected by heating with powdered potassium hydroxide at 180-200° (312). Heating of 5,6-dichloro-2,3-dioxo-l,4-diphenyl-l,2,3,4-tetrahydropyrazine with phenol and 35% hydrogen bromide in acetic acid at 70° gave 2,3-dioxo-l, 4-diphenyl-l, 2,3,4-tetrahydropyrazine (853). 

Tetrafluoropyrazine with hydrazine gives 2,3,5-trifluoro-6-hydrazinopyrazine which on warming with aqueous copper sulfate gave trifluoropyrazine and 2,3-difluoro-5-hydrazino-6-methoxypyrazine similarly treated gave 2,3-difluoro-5-methoxypyrazine (885), but 2,3,5-trichloropyrazine could not be prepared from 

5- trichloro-6-hydrazinopyrazine (888). 2,3,5-Trichloropyrazine with hydrazine gave 2,5-dichloro-3-hydrazinopyrazine, which with cupric sulfate in acetic acid gave 

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When there is significant random error in all the variables, as in this example, the maximum-likelihood method can lead to better parameter estimates than those obtained by other methods. When Barker s method was used to estimate the van Laar parameters for the acetone-methanol system from these data, it was estimated that = 0.960 and A j = 0.633, compared with A 2 0.857 and A2- = 0.681 using the method of maximum likelihood. Barker s method uses only the P-T-x data and assumes that the T and x measurements are error free. 

One of the most attractive features of the CIDNP multiplet effect is that it allows detennination of the sign of the J coupling, which is often difficult to do by other methods. 

The analytical treatment of high frequency terms in the Hamiltonian proposed here allows to use SISM significantly longer integration time step than can be used by other methods of the same order and complexity. 

The chirality code of a molecule is based on atomic properties and on the 3D structure. Examples of atomic properties arc partial atomic charges and polarizabilities, which are easily accessible by fast empirical methods contained in the PETRA package. Other atomic properties, calculated by other methods, can in principle be used. It is convenient, however, if the chosen atomic property discriminates as much as possible between non-equivalent atoms. 3D molecular structures are easily generated by the GORINA software package (see Section 2.13), but other sources of 3D structures can be used as well. 

The thiazole ring can be obtained directly by other methods, but they have limited application. An example is the synthesis of Cook and Heilbron using a-aminonitriles or a-aminoamides and carbon disulfide (or thioacid derivatives) as reactants of type II. 

A statistical analysis allows us to determine whether our results are significantly different from known values, or from values obtained by other analysts, by other methods of analysis, or for other samples. A f-test is used to compare mean values, and an F-test to compare precisions. Comparisons between two sets of data require an initial evaluation of whether the data... 

Precipitation titrimetry is rarely listed as a standard method of analysis, but may still be useful as a secondary analytical method for verifying results obtained by other methods. Most precipitation titrations involve Ag+ as either an analyte or... 

The 0 temperature is that value of T for which B = 0 therefore 0 can be determined from the results above by graphical interpolation. Although there is some scatter in such a graph, the best value for the temperature at which B = 0 appears to be 308.4 K, which agrees well with values determined for this system by other methods. 

Total 1991 world production of sulfur in all forms was 55.6 x 10 t. The largest proportion of this production (41.7%) was obtained by removal of sulfur compounds from petroleum and natural gas (see Sulfurremoval and recovery). Deep mining of elemental sulfur deposits by the Frasch hot water process accounted for 16.9% of world production mining of elemental deposits by other methods accounted for 5.0%. Sulfur was also produced by roasting iron pyrites (17.6%) and as a by-product of the smelting of nonferrous ores (14.0%). The remaining 4.8% was produced from unspecified sources. 

An important newer use of fluorine is in the preparation of a polymer surface for adhesives (qv) or coatings (qv). In this apphcation the surfaces of a variety of polymers, eg, EPDM mbber, polyethylene—vinyl acetate foams, and mbber tine scrap, that are difficult or impossible to prepare by other methods are easily and quickly treated. Fluorine surface preparation, unlike wet-chemical surface treatment, does not generate large amounts of hazardous wastes and has been demonstrated to be much more effective than plasma or corona surface treatments. Figure 5 details the commercially available equipment for surface treating plastic components. Equipment to continuously treat fabrics, films, sheet foams, and other web materials is also available. 

A number of salts of the monofluoro- and hexafluorophosphoric acids are known and some are commercially important. The salts of difluorophosphoric acid are typically less stable toward hydrolysis and are less well characterized. Sodium monofluorophosphate [7631-97-2] the most widely used dentifrice additive for the reduction of tooth decay, is best known (see Dentifrices). Several hexafluorophosphates can be prepared by neutralization of the appropriate base using hexafluorophosphoric acid. The monofluorophosphates are usually prepared by other methods (57) because neutralization of the acid usually results in extensive hydrolysis. 

X-Ray Crystallography. Structural data exists on more than one thousand steroids. Comparisons of the conformations obtained by x-ray crystallography have been made to the conformations obtained by other methods (161). Several studies use x-ray crystal stmctures in the study of progestins. 

Mono- and diaLkylboranes obtained by controlled hydroboration of hindered olefins and by other methods can serve as valuable hydroborating agents for more reactive olefins. Heterosubstituted boranes are also available and used for this purpose. These borane derivatives show differences in reactivity and selectivity. 

Selective biomination at the mote substituted position makes possible connection of two different alkyl groups. The use of dialkylthexylboranes and dialkyUialoboranes allows fuU utilization of alkyl groups (370,371). Bicyclic and more complex boracycles can be transformed into carbon stmetures not readily available by other methods (372). 

Leaching. Extracting a soluble metallic compound from an ore by selectively dissolving it in a suitable solvent. The solvent is usually recovered by precipitation of the metal or by other methods. 

Starting compounds include hexa- and pentarylethanes the latter require higher temperatures (ca 100°C) than the former to break the carbon—carbon bond. In the presence of oxygen, stable radicals that are generated by other methods, eg, reduction of arylmethyl ethers and haUdes, also have been converted to diaralkyl peroxides (66). 

Although this reduction is more expensive than the Bnchamp reduction, it is used to manufacture aromatic amines which are too sensitive to be made by other methods. Such processes are used extensively where selectivity is required such as in the preparation of nitro amines from dinitro compounds, the reduction of nitrophenol and nitroanthraquinones, and the preparation of aminoazo compounds from the corresponding nitro derivatives. Amines are also formed under the conditions of the Zinin reduction from aromatic nitroso and azo compounds. 

Urea reacts with himing sulfuric acid in an exothermic reaction that needs agitation and cooling. After completion of the reaction, excess sulfur trioxide is removed by dilution or by other methods (45,46). A flow diagram of the process is shown in Figure 1. 

Carbon Reduction. The production of ferrovanadium by reduction of vanadium concentrates with carbon has been supplanted by other methods. An important development has been the use of vanadium carbide as a replacement for ferrovanadium as the vanadium additive in steelmaking. A... 

Ozone can be used to completely oxidize low concentrations of organics in aqueous streams or partially degrade compounds that are refractory or difficult to treat by other methods. Compounds that can be treated with ozone include alkanes, alcohols, ketones, aldehydes, phenols, benzene and its derivatives, and cyanide. Ozone readHy oxidizes cyanide to cyanate, however, further oxidation of the cyanate by ozone proceeds rather slowly and may require other oxidation treatment like alkaline chlorination to complete the degradation process. 

In the atomizing process, a stream of molten zinc is broken into tiny droplets by the force of a pressurized fluid impinging on the stream. The fluid can be any convenient material, although air is normally used. The atomized drops cool and soHdify rapidly in a coUection chamber. The powder is screened to specified sizes. Particulate zinc is also produced by other methods such as electrolytic deposition and spinning-cup techniques, but these are not of commercial importance. 

Methods of Purification. Although carbon dioxide produced and recovered by the methods outlined above has a high purity, it may contain traces of hydrogen sulfide and sulfur dioxide, which cause a slight odor or taste. The fermentation gas recovery processes include a purification stage, but carbon dioxide recovered by other methods must be further purified before it is acceptable for beverage, dry ice, or other uses. The most commonly used purification methods are treatments with potassium permanganate, potassium dichromate, or active carbon. 

Since diazaquinones are among the most powerful dienophiles, they undergo [4+2] cycloaddition (Diels-Alder) reactions with a great variety of dienes to give various heterocyclic systems accessible with difficulty by other methods. Diazaquinone reacts with butadiene and substituted butadienes, carbocyclic and heterocyclic dienes, 1-vinylcycloalkenes, polyaromatic compounds and vinylaromatic compounds to afford bicyclic and polycyclic bridgehead diaza systems, including diazasteroids (Scheme 56). 

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