Sensing acetate

The Ru(II)bipyridylcalix[4]diquinone receptor 43 selectively binds and senses acetate anions (from H NMR titrations in DMSO-d6 solution K= 9,990 M1) [37]. This receptor exhibited only weak luminescence because calix[4]diquinone is an electron acceptor, quenching the [Ru(bpy)3]2+ emission... 

For instance 59, the Re(I) bipyridyl analogue of receptor 43, also selectively senses acetate anions [37]. The lack of an electrostatic interaction accounts for a significantly lower stability constant for acetate (from H NMR titrations K= 1,790 M 1 in deuterated DMSO solution) and hence a smaller luminescence response than its [Ru(bpy)3]2+ counterpart. 

The Ru°bipyridylcalix[4]diquinone receptor 83 selectively binds and senses acetate anions (from NMR titrations in DMSO-de solution K = 9990 M ) [54]. This receptor is only weakly luminescent because the Ru (bpy)3 MLCT emission is partially quenched by oxidative electron transfer to the electron-poor calix[4]diquinone. Addition of acetate to acetonitrile solutions of 83 resulted in a five-fold increase in liuninescence intensity (60% for chloride) concomitant with a slight blue shift of the emission maximum. Anion binding causes this increase in emission intensity by interrupting the electron transfer pathway from the Ru°(bpy)3 to the calix[4]diquinone, thus reducing its quenching effect. 

Complexes of rheniiun(l)tricarbonylchloride with pyridyl ligands are lu-minophores and hence in anion sensing have principally been used as reporter groups. For instance calix[4]diquinone receptor 90 selectively binds and senses acetate in DMSO solution [54] (from H NMR titrations K = 1790 in DMSO-de solution). The receptor exhibits relatively weak lumi-... 

Owing to the instability of a-halogenoaldehydes it is occasionally preferable to use more stable derivatives, such as enol acetate prepared according to Bedoukian s method (204) and a-bromoacetals (4, 8, 10, 16, 22, 67, 101, 426). An advantage is said to be in the yield however, this appears to be slight. The derivatives react in the same sense as the aldehydes themselves, that is, the acetal group as the more polarized reacts first and enters the C-4 position. It is likely that the condensation and cyclization occur by direct displacement of alkoxide ions. Ethyl-a,/3-dihalogeno ethers (159, 164, 177, 248) have also been used in place of the free aldehydes in condensation with thioamides. 

Note that this inquiry into copolymer propagation rates also increases our understanding of the differences in free-radical homopolymerization rates. It will be recalled that in Sec. 6.1 a discussion of this aspect of homopolymerization was deferred until copolymerization was introduced. The trends under consideration enable us to make some sense out of the rate constants for propagation in free-radical homopolymerization as well. For example, in Table 6.4 we see that kp values at 60°C for vinyl acetate and styrene are 2300 and 165 liter mol sec respectively. The relative magnitude of these constants can be understod in terms of the sequence above. 

Liquid Fabric Softeners. The principal functions of fabric softeners are to minimize the problem of static electricity and to keep fabrics soft (see Antistatic agents). In these laundry additives, the fragrance must reinforce the sense of softness that is the desired result of their use. Most fabric softeners have a pH of about 3.5, which limits the materials that can be used in the fragrances. For example, acetals cannot be used because they break down and cause malodor problems in addition, there is the likelihood of discoloration from Schiff bases, oakmoss extracts, and some specialty chemicals. Testing of fragrance materials in product bases should take place under accelerated aging conditions (eg, 40°C in plastic bottles) to check for odor stabiUty and discoloration. 

A review discusses the condensation of aldehydes and ketones with glycerol to give 1,3-dioxanes and 1,3-dioxolanes. The chemistry of 0 0 and 0 S acetals has been reviewed, and a recent monograph discusses this area of protective groups in a didactic sense. ... 

A molecule with a lower energy LUMO will generally react more rapidly. The LUMO energies of acetic anhydride and ethyl acetate are 0.143 and 0.193 au, respectively. Which reagent is a better aeylating agent in the kinetic sense ... 

Viprostol (81) also incorporates a hydroxy group moved to C-16 and protects this from facile metabolic oxidation by vinylation. It is a potent hypotensive and vasodilatory agent both orally and transdermally. The methyl ester moiety is rapidly hydrolyzed in skin and in the liver so it is essentially a prodrug. It is synthesized from protected E-iodo olefin 78 (compare with 75) by conversion to the mixed organocuprate and this added in a 1,4-sense to olefin 79 to produce protected intermediate 80. The synthesis of viprostol concludes by deblocking with acetic acid and then reesterification with diazomethane to give 81 [19]. 

Practically, the result of reactions (48) and (49) is reaction (50). In reaction (50), we see that acetic acid acts as an acid in the same sense that it does in (48). In either case, it releases hydrogen ions. In (48) acetic acid releases hydrogen ions and forms H+(aq) and in (50) it releases hydrogen ions to NHs and forms NH/. In the same way, ammonia acts as a base in (50) by reacting with the hydrogen ion released by acetic acid. So reaction (50) is an acid-base reaction, though the net reaction does not show H+(aq) explicitly. 

Now by taking one more step we can view acid-base reaction in a broader sense. Suppose we mix aqueous solutions of ammonium chloride, NH4CI, and sodium acetate, CH3COONa. A sniff indicates ammonia has been formed. Reaction occurs,... 

Finally, in a study of Lewis-acid-catalysed intramolecular attack of acetals on vinylsilanes, to produce allylically unsaturated oxacyclics, it has been found (75) that the alkene stereochemistry can control the mode of cyclization in an exo- or endocyclic sense, as shown here ... 

Do not rely on the sense of smell to detect hydrogen sulphide leaks. Strips of v/et lead acetate paper turn black on exposure to hydrogen sulphide and offer a simple indicator, as do colour indicator tubes. For plant-scale operations, instrumental multi-point detectors and alarms are likely to be more appropriate. 

Rasmussen L.E.L., Lee T.D., Zhang A., Roelofs W.L., et al. (1997). Purification, identification, concentration and bioactivity of (Z)-7-dodecen-l-yl acetate sex pheromone of the female Asian Elephant, Elephas maximus. Chem Senses 22, 417-438. 

Another approach for ion-sensing (here copper and zinc) is based on the water-soluble ligand zincon and the ion pair with quaternary ammonium halides shown in Figure 17 which can be homogeneously dissolved in polymers such as plasticized poly(vinyl acetate), ethyl cellulose, and polyurethane. 

A tri-enzymatic sensing layer based on kinase-oxidase activities for the detection of acetate was also described. A reaction sequence using acetate kinase, pyruvate kinase and pyruvate oxidase enabled the production of H2O2 in response to acetate injection in the range 10 pM - 100 mM59. 

A rapid synthesis of carbon-14 labeled [l-14C]levulinic acid from simple building blocks has been demonstrated by Johansen and coworkers (Scheme 6.172) [324], In all three of the synthetic steps, starting from bromo[l-14C]acetic acid, microwave heating was used to accelerate the reactions, allowing a total preparation time of less than 1 h. The labeled levulinic acid was subsequently transformed into (5Z)-4-bromo-5-(bromomethylene)-2(5H)-furanone in a bromination/oxidation sequence (not shown), a potent quorum sensing inhibitor. 

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