Methods halogens

During all membrane exposures, concentrations of halogens and chlorine dioxide were periodically monitored by "wet chemical methods". Halogens were determined by the DPD colorimetric method described in references [13] and [14]. Chlorine dioxide at reasonably high concentrations (>10 ppm) can be determined by direct colorimetry [] ]. The intrinsic green color appears to obey Beer s law. At lower concentration levels, this chemical is determined by the DPD method. 

Halogen in organosilicon compounds may be either directly linked to silicon or may be part of a substituent group. Total halogen is usually determined by alkali fusion methods. Halogen attached directly to silicon is easily hydrolysable by aqueous alcohols and the halogen acid so produced can be estimated by direct alkali titration or by indirect procedures. 

Nucleophilic Reactions.—Attack on Saturated Carbon. The Arbusov reaction has been used extensively as a preparative method. Halogen has been the group most commonly displaced by phosphorus, although amino, alkoxy, and acetate leaving groups have also been used. 

The rotational motion of the ammonium ions in ammonium trifluorozincate has been studied over the temperature range 298-1K by H NMR methods. Halogen NQR studies of [MX4] and [MXs]" salts (M = Cd or Zn X = Cl, Br or I) have been reported. ... 

Alternate methods that do not involve a metal-based oxidation have also been described. These methods halogenate an oxazoline with subsequent dehydrohalo-genation to effect overall net oxidation. Williams and co-workers used BrCCl3 and DBU to oxidize oxazolines (Scheme 1.15). Reaction of 50 with BrCCls in the presence of two equivalents of DBU generates 51 in 87% yield. Similarly, 52... 

Substituted L-tryptophans produced by this method (halogen introduced enzymatically indicated with an asterisk) ... 

Hygrometry the powder mnst contain as httle water as possible. Effectively humidity causes the grains to aggregate, which is risky for pneumatictransfer. But the polymer powder must not be completely diy either, so as to avoid the formation of fish eyes during dissolntion process. Method halogen desiccators. 

The interactions present in halogen-bonded systems are in general weak, thus the need to use quantum mechanical methods that include electron correlation for an accurate description. In particular, these interactions are sensitive, not only to the basis set used but also to the level of electron correlation used, the counterpoise correction and the inclusion of spin-orbit effects for bromine and iodine. In contrast with the widely accepted idea that hydrogen bonded systems are reasonably well described with MoUer-Plesset perturbation (MP2) methods, halogen bond interactions are overestimated at this level. Therefore, for an accurate description of these systems a coupled cluster method is advised, preferably with single and double excitations (CCSD) or with perturbative triple excitations (CCSD(T)). This problem pertains also to density functional theory methods (DFT) where some methods lead to better results than others and the choice of the best functional is not straightforward. DFT methods have the advantage over wave function methods that time... 

Beilstein s test A method for detecting the presence of halogen in an organic compound. A piece of copper gauze is heated in an oxidiz-... 

The most widely used reactions are those of electrophilic substitution, and under controlled conditions a maximum of three substituting groups, e.g. -NO2 (in the 1,3,5 positions) can be introduced by a nitric acid/sul-phuric acid mixture. Hot cone, sulphuric acid gives sulphonalion whilst halogens and a Lewis acid catalyst allow, e.g., chlorination or brom-ination. Other methods are required for introducing fluorine and iodine atoms. Benzene undergoes the Friedel-Crafts reaction. ... 

Carius method The quantitative determination of S and halogens in covalent (organic) compounds by complete oxidation of the compound with cone, nitric acid and subsequent estimation of precipitated AgX or BaS04. 

Methods of producing B —C bonds include hydroboration, nucleophilic displacement at a boron atom in BX., (X = halogens or B(0R>3) by e.g. a Grignard reagent, and a psewiio-Friedel-Crafts reaction with an aromatic hydrocarbon, BX3, and AICI3. 

NakatsujI H, Kuwano R, Merita H and Nakal H 1993 Dipped adcluster model and SAC-CI method applied to harpooning, chemical luminescence and electron emission in halogen chemisorption on alkali metal surface J. Mol. Catal. 82 211-28... 

A complete set of trihalides for arsenic, antimony and bismuth can be prepared by the direct combination of the elements although other methods of preparation can sometimes be used. The vigour of the direct combination reaction for a given metal decreases from fluorine to iodine (except in the case of bismuth which does not react readily with fluorine) and for a given halogen, from arsenic to bismuth. 

None of the halogens reacts directly with oxygen but all form oxides by indirect methods. 

An enhancement of the simple substructure approach is the Fragment Reduced to an Environment that is Limited (FREL) method introduced by Dubois et al. [7] With the FREL method several centers of the molecule are described, including their chemical environment. By taking the elements H, C, N, O, and halogens into account and combining all bond types (single, double, triple, aromatic), the authors found descriptors for 43 different FREL centers that can be used to characterize a molecule. 

The following data ( fable 1) for niolcctilcs, including hydrocarbon s, strained ring system s. molecn les with heieroatom s, radicals, and ions conies from a review by Stewart. For most organic molecules,, YM 1 reports heals of formation accurate to within a few kilocalories per rn ol. bor soni e molecules (particularly inorgari ic compoun ds wdth several halogens, such as perch loryl fluoride, even the best sem i-em pineal method fails completely. 

The Sodium Carbonate-Zinc Method for Detecting Nitrogen, Halogens and Sulphur in Organic Compounds. 

The method is general for all organic halogen compounds and is the standard method for almost all such compounds, except of course... 

Estimation of Halogens, Carlus s Method. Semi-micro Scale. 

Liquid sulphur compounds should be weighed and introduced into the Carius tube by precisely the same methods as those described for liquid halogen compounds (p. 442). 

Two simple methods for the semi-micro estimation of halogens are available, (a) the Carius method, and (b) the Parr bomb method. It should be emphasised that there are other methods available for these estimations on the true micro scale, but they do not lend themselves, by virtue of the balances, apparatus and manipulation required, to semi-micro work, or to the intermittent usage which class-work necessarily entails. 

N-Benzylamides are recommended when the corresponding acid is liquid and/or water-soluble so that it cannot itself serve as a derivative. Phe benzylamides derived from the simple fatty acids or their esters are not altogether satisfactory (see Table below) those derived from most hydroxy-acids and from poly basic acids or their esters are formed in good yield and are easily purified. The esters of aromatic acids yield satisfactory derivatives but the method must compete with the equally simple process of hydrolysis and precipitation of the free acid, an obvious derivative when the acid is a solid. The procedure fails with esters of keto, sul phonic, inorganic and some halogenated aliphatic esters. 

This method cannot be applied to polynitro amines, since these are so weakly basic that they can be diazotised only under special conditions in strongly acidic solutions. In such cases use may, however, be made of the mobility oonfared upon halogen atoms by the presence of nitro groups in the orlko and para positions. Thus the valuable reagent 2 4-dinitrophenylhydrazine is readily prepared by the condensation of 2 4-dinitrochlorobenzene with hydrazine ... 

THE SODIUM CARBONATE - ZINC METHOD FOR THE DETECTION OF NITROGEN, SULPHUR AND HALOGENS IN ORGANIC COMPOUNDS... 

When an organic compound is heated with a mixture of zinc powder and sodium carbonate, the nitrogen and halogens are converted into sodium cyanide and sodium hahdes respectively, and the sulphur into zinc sulphide (insoluble in water). The sodium cyanide and sodium hahdes are extracted with water and detected as in Lassaigne s method, whilst the zinc sulphide in the residue is decomposed with dilute acid and the hydrogen sulphide is identified with sodium plumbite or lead acetate paper. The test for nitrogen is thus not affected by the presence of sulphur this constitutes an advantage of the method. 

Ruthenium is a hard, white metal and has four crystal modifications. It does not tarnish at room temperatures, but oxidizes explosively. It is attacked by halogens, hydroxides, etc. Ruthenium can be plated by electrodeposition or by thermal decomposition methods. The metal is one of the most effective hardeners for platinum and palladium, and is alloyed with these metals to make electrical contacts for severe wear resistance. A ruthenium-molybdenum alloy is said to be... 

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