Reagents unstable

The energy requirement is an obstacle to the physical characterization of chemiluminescent compounds because the availability of a reaction of high exothermicity renders most such reagents unstable. They are usually generated in situ by mixing stable precursors with appropriate reagents. The observation of blue chemiluminescence from a solution of oxalyl chloride and hydrogen peroxide was first reported in 1963,510 now well... 

A further advancement in organic synthesis was the accomplishment of multi-step syntheses comprising 20 and more steps and the synthesis of rather unstable organic compounds. It was now feasible to do an experiment on a milligram scale and to separate and identify products from by-products in order to analyze them separately. The application of selective reagents or reaction conditions allowed the synthesis of enantiomerically or diastereomerically pure compounds. 

If the compound to be tested is insoluble in water, it should be brought into solution by the addition of a little dioxan. Alcohols and some methyl ketones frequently react slowly in such cases it is advisable to employ a large excess (4-5 fold) of the relatively unstable reagent (3NaOI -> NaI03 -f- 2NaI). Quinones and hydroquinones also give the iodoform reaction. 

Synthetic Equivalent A reagent carrying out the function of a synthon which caimot itself be used, often because it is too unstable. 

For continuing polymerization to occur, the ion pair must display reasonable stabiUty. Strongly nucleophilic anions, such as C/ , are not suitable, because the ion pair is unstable with respect to THE and the alkyl haUde. A counterion of relatively low nucleophilicity is required to achieve a controlled and continuing polymerization. Examples of anions of suitably low nucleophilicity are complex ions such as SbE , AsF , PF , SbCf, BE 4, or other anions that can reversibly coUapse to a covalent ester species CF SO, FSO, and CIO . In order to achieve reproducible and predictable results in the cationic polymerization of THE, it is necessary to use pure, dry reagents and dry conditions. High vacuum techniques are required for theoretical studies. Careful work in an inert atmosphere, such as dry nitrogen, is satisfactory for many purposes, including commercial synthesis. 

Sulfation is defined as any process of introducing an SO group into an organic compound to produce the characteristic C—OSO configuration. Typically, sulfation of alcohols utilizes chlorosulfuric acid or sulfur trioxide reagents. Unlike the sulfonates, which show remarkable stability even after prolonged heat, sulfated products are unstable toward acid hydrolysis. Hence, alcohol sulfuric esters are immediately neutralized after sulfation in order to preserve a high sulfation yield. 

Fig. 3. (a) Reaction of pytidoxal 5 -phosphate (PLP) witii an amino-temiinal amino group of hemoglobin (Hb). The reagent is in the form of a Schiff s base with tris(hydroxymethyl)aminomethane [77-86-1] (Tris) buffet, and the reaction is a transamination, (b) The resulting unstable Schiff s base is reduced with... 

The standard reduction potential of Cr " (Table 2) shows that this ion is a strong reducing agent, and Cr(II) compounds have been used as reagents in analytical chemistry procedures (26). The reduction potential also explains why Cr(II) compounds are unstable in aqueous solutions. In the presence of air, the oxidation to Cr(III) occurs by reaction with oxygen. However, Cr(II) also reacts with water in deoxygenated solutions, depending on acidity and the anion present, to produce H2 and Cr(III) (27,28). 

Ethers are weakly basic and are converted to unstable oxonium salts by strong acids such as sulfudc acid, perchlodc acid, and hydrobromic acid relatively stable complexes ate formed between ethers and Lewis acids such as boron trifluodde, aluminum chlodde, and Gtignatd reagents (qv) (9) ... 

The first method involves generation of an unstable vinyllithium denvative at low temperatures from the corresponding vinyl halide or 1-hydroalkene Addition of zinc chloride and warming to room temperature gives the stable vinyl zinc reagent [100, lOI, 102, 103] (equations 69-72)... 

The use of azide reagents is also important for the synthesis of cyclic sulfur(VI)-nitrogen systems. The reaction of SOCI2 with sodium azide in acetonitrile at -35°C provides a convenient preparation of the trimeric sulfanuric chloride [NS(0)C1]3 (Eq. 2.16). " Thionyl azide, SO(N3)2 is generated by the heterogeneous reaction of thionyl chloride vapour with silver azide (Eq. 2.17). This thermally unstable gas was characterized in situ by photoelectron spectroscopy. The phenyl derivative of the six-membered ring [NS(0)Ph]3 can be prepared from lithium azide and PhS(0)Cl. ... 

A different type of behaviour is observed with the chloro Lewis acid BCI3. With this reagent halogen exchange occurs to produce the acyclic cation [N(SC1)2] , as the [BCU] salt, rather than NSCf. " Thiazyl trichloride NSCI3 is predicted to be unstable with respect to NSCl -1-Cl2. ... 

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