With reagent regeneration

While reversible sensors are the ideal sensors, those irreversible sensors containing an immobilized reagent that can be regenerated approach the ideal 

Mediated electrochemical sensors aside, there are few sensors involving a reaction at the sensing microzone by which the analyte is not retained to some extent during the time the analytical response is generated. Such is the case with sensors based on luminescence quenching and a few others. Although many of the reactions on which the analytical measurement rests in sensors based on acid—base reactions involve retention of protons, the sensors in question are dealt with in this Section. 

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The general mechanism of coupling reactions of aryl-alkenyl halides with organometallic reagents and nucleophiles is shown in Fig. 9.4. It contains (a) oxidative addition of aryl-alkenyl halides to zero-valent transition metal catalysts such as Pd(0), (b) transmetallation of organometallic reagents to transition metal complexes, and (c) reductive elimination of coupled product with the regeneration of the zero-valent transition metal catalyst. 

The regeneration of carbonyl compounds from dithioacetals and dithiolanes is often done with reagents that oxidize or otherwise activate the sulfur as a leaving... 

Despite the enormous importance of dienes as monomers in the polymer field, the use of radical addition reactions to dienes for synthetic purposes has been rather limited. This is in contrast to the significant advances radical based synthetic methodology has witnessed in recent years. The major problems with the synthetic use of radical addition reactions to polyenes are a consequence of the nature of radical processes in general. Most synthetically useful radical reactions are chain reactions. In its most simple form, the radical chain consists of only two chain-carrying steps as shown in Scheme 1 for the addition of reagent R—X to a substituted polyene. In the first of these steps, addition of radical R. (1) to the polyene results in the formation of adduct polyenyl radical 2, in which the unpaired spin density is delocalized over several centers. In the second step, reaction of 2 with reagent R—X leads to the regeneration of radical 1 and the formation of addition products 3a and 3b. Radical 2 can also react with a second molecule of diene which leads to the formation of polyene telomers. 

Other drying agents are activated alumina and bauxite, silica gel, sulfuric acid, and concentrated solutions of calcium chloride or sodium thiocyanate. Plants of this type usually require a packed tower for countercurrent treatment of the gas with the reagent, together with a regenerator for the dehydrating agent. 

Oxo aldehydes57 Hydrogen peroxide and Co(II) Reducing iron carbonyls-Co(III) is the purifying reagent regenerated with hydrogen peroxide... 

Doyle J.B., Prish E.A. and Downs W. (Babcock and Wilcox Co.), Integrated injection and bag filter house system for SOx-NOx-particulate control with reagent/catalyst regeneration, U.S. Patent 4,793,981 (1988). 

Some reactions of the perstannapropellane 18-8 have been established with reagents that are small enough to avoid the steric shielding by the aryl groups (Scheme 18-7). Reaction with methyl iodide and then with methyllithium, or reaction in the reverse sequence, gives the l,3-dimethylbicyclo[l.l.l]pentastannane propellane 18-13, and this can be photolysed to regenerate the propellane 18-8.90... 

Onium salts can also be used to support reagents that would transform a substrate. After reaction the IL phase can be recovered and the reagent regenerated for being reused in another cycle. For example, carboxylic acids have been supported on onium halides. Simply synthesized by quatemarisation of methylimidazole followed by acid hydrolysis, this compound can react with epoxides to afford halo-hydrines in 76-95% yields [58], Additionally, an OS supported version of TEMPO has been used in oxidation of alcohol into ketone [59] (Fig. 21). 

Thiol protection. As a Michael reaction donor, this reagent forms adducts with thiols. Regeneration of the thiols is by treatment with pyrrolidine in MeCN. 

Protection of enones. This silyllithium reagent (2 equiv.) in the presence of Cul (1 equiv.) adds to the /3-position of ,)8-unsaturated ketones at —23° in 65-99% yield.The original a, -unsaturated keto group can be regenerated by bromination followed by desilylation with base (70-80%, yield). In the case of cyclic ketones, CuBra regenerates enones directly. With open-chain ketones, 8-bromo ketones are obtained, but treatment with NaHCOa regenerates the... 

The regeneration of carbonyl compounds from dithioacetals and ketals is done best with reagents that oxidize or otherwise activate the sulfur as a leaving group and facilitate hydrolysis. Among the reagents that have been found effective are nitrous acid, -butyl hypochlorite, PhI(02CCF3)2, DDQ, SbCls, and cupric salts,... 

Using stoichiometric amounts of an alkylzinc reagent and catalytic amounts of Ni(0)/DBU, Mori was able to prepare a number of p-aUcylated or arylated a,-P-unsaturated carboxylic acids from alkynes and CO2 (Scheme 5.12) [56, 57]. Through a frans-metalation reaction with the oxanickelacyclopentenone intermediate, the alkyl zinc reagent effected the reductive elimination of the product from the nickel center with concomitant regeneration of the active zerovalent catalyst. 

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