Alcohol sensing

Park S.S., Mackenzie J.D., Thickness and microstructure effects on alcohol sensing of tin oxide thin films, Thin Solid Films 1996 274 154-159. 

Other sensing applications include water sensing by direct absorption of the 3H4 —> 3F4 transition of Tm3+ at 1.47 /an [259] and alcohol sensing by evanescent wave in undoped fluoride glass fibers [260]. 

Alcohol sensing. An etched FBG was used [28] to discriminate between methanol (n - 1.326), ethanol (n - 1.359), and isopropyl alcohol (IPA) n =1.378) (Fig. 9). The FBG was written using a KrF excimer laser (248 nm) with a length of 2.5 mm. It was etched down to 15 pm diameter using a 52% solution of hydrofluoric (HF) acid and then to a diameter of 6 pm with a 13% HF solution. The plot of the center wavelengths of the thinned FBG vs ambient refractive index is shown in the next figure. 

Another unusual alcohol sensing method is based on using the BaCe03-based protonic conductor which is used as an electrolyte for humidity sensing (sect. 4), A cross-sectional view of the sensor is presented in fig. 64 (Hibino and Iwahara 1992b, Iwahara and Hibino 1993). The operating temperature is 723 K and the sensor response with various alcohol... 

The mechanism of alcohol sensing is proposed as follows. Ethanol is subject to dehydrogenation on BaCe03 and produces CH3CHO and H2. The sensor detects the hydrogen produced at the protonic conductor surface. 

A base material used for alcohol sensing is the perovskite oxide with rare-earth elements, which shows p-type semiconducting properties. The most commonly used rare earth is lanthanum. In this case, to retain a perovskite structure with semiconducting characteristics is important. Other rare earths are used instead of lanthanum. However, lanthanum is the most reasonable choice of the rare-earths series from the expense viewpoint. Methane sensing is also attempted by using the rare-earth-containing perovskite oxide. The perovskite oxide does not act as base material but as the auxiliary electrode to accelerate methane combustion. 

Friedel-Crafts (Lewis) acids have been shown to be much more effective in the initiation of cationic polymerization when in the presence of a cocatalyst such as water, alkyl haUdes, and protic acids. Virtually all feedstocks used in the synthesis of hydrocarbon resins contain at least traces of water, which serves as a cocatalyst. The accepted mechanism for the activation of boron trifluoride in the presence of water is shown in equation 1 (10). Other Lewis acids are activated by similar mechanisms. In a more general sense, water may be replaced by any appropriate electron-donating species (eg, ether, alcohol, alkyl haUde) to generate a cationic intermediate and a Lewis acid complex counterion. 

The first example is the plasma-borne retinol-binding protein, RBP, which is a single polypeptide chain of 182 amino acid residues. This protein is responsible for transporting the lipid alcohol vitamin A (retinol) from its storage site in the liver to the various vitamin-A-dependent tissues. It is a disposable package in the sense that each RBP molecule transports only a single retinol molecule and is then degraded. 

Addition and elimination processes are the reverse of one another in a formal sense. There is also a close mechanistic relationship between the two reactions, and in many systems reaction can occur in either direction. For example, hydration of alkenes and dehydration of alcohols are both familiar reactions that are related as an addition-elimination pair. 

In this sense it should be mentioned that (Ala)n is dissolved by hexafluorisopropanol (HFIP) without conformation change and that stretched fibers of (Leu) shrink in HFIP (20 °C) at about 60 % only by disorientation of (Leu)n molecules, because no conformation change occurs according to X-ray measurements 122,123). An interaction of the OH-group of the alcohol with the back-bone-CO-NH-groups is not very likely because, in this case, conformation changes should be observed. 

I Elimination reactions are, in a sense, the opposite of addition reactions. They occur when a single reactant splits into two products, often with formation of a small molecule such as wateT or HBr. An example is the acid-catalyzed reaction of an alcohol to yield water and an alkene. 

Base-induced rearrangement of bicyclo[2.2.2]octane oxide 67 gives predominantly bicyclo[2.2.2]octanone 68 (Scheme 5.15), which once again indicates that close proximity between the carbenoid center and the C-H bond into which it may insert is important if such an insertion is to occur [30]. In comparison, the sense of product distribution is reversed for the related substrate bicyclo[2.2.2]octadiene oxide 70 on treatment with LDA [15, 22], alcohol 72 being the favored product. 

Mioskowski et al. have demonstrated a route to spirocyclopropanes. As an example, treatment of epoxide 100 with n-BuLi in pentane stereoselectively gave tricyclic alcohol 101, albeit in only 47% yield (Scheme 5.21) [29]. With a related substrate, epoxide 102 stereoselectively gave dicydopropane 103 on treatment with PhLi uniquely, the product was isolable after column chromatography in 74% yield [35]. As was also seen with attempts to perform C-H insertion reactions in a non-transannular sense, one should note that steps were taken to minimize the formation of olefin products, either by the use of a base with low nudeophilicity (LTM P) and/or by slow addition of the base to a dilute solution (10-3 m in the case of 102) of the epoxide. 

In a more general sense, this reduction method provides a convenient pathway for converting an aromatic carboxyl group to a methyl group (see Table I).7 Previously, this transformation has been achieved by reduction of the acid to the alcohol with lithium aluminum hydride, conversion of the alcohol to the tosylate, and a second reduction either with lithium aluminum hydride [Aluminate(l —), tetrahydro, lithium,... 

Ethanol Electrodes The reliable sensing of ethanol is of great significance in various disciplines. The enzymatic reaction of ethanol with the cofactor nicotinamide-adenine dinucleotide (NAD+), in the presence of alcohol dehydrogenase (ADH)... 

Sulfonic peracids (66) have also been applied recently to the preparation of acid sensitive oxiranes and for the epoxidation of allylic and homoallylic alcohols, as well as relatively unreactive a, p - unsaturated ketones. These reagents, prepared in situ from the corresponding sulfonyl imidazolides 65, promote the same sense of diastereoselectivity as the conventional peracids, but often to a higher degree. In particular, the epoxidation of certain A -3-ketosteroids (e.g., 67) with sulfonic peracids 66 resulted in the formation of oxirane products (e.g., 68) in remarkably high diastereomeric excess. This increased selectivity is most likely the result of the considerable steric requirements about the sulfur atom, which enhances non-bonded interactions believed to be operative in the diastereoselection mechanism <96TET2957>. 

It may be noted that the additions of protonic molecules HA (alcohols, amines, thiols, etc. see Section III,C) to isocyanides may be related to these reactions, in the formalistic sense anyway, since they involve additions of A (in conjunction with H+) to the isocyanide. In a few instances the additions of HA can be accomplished by adding first A" and then H to the reactant species. However, no studies on HA additions have yet elucidated a mechanism for these reactions, so to draw a conclusion on the similarities of these reactions on mechanistic grounds is not appropriate. Because of this, and also for convenience, these subjects will be treated separately. 

Since amines react more readily than alcohols in noncatalyzed reactions with anhydrides, the reaction is more difficult and initially required stoichiometric catalyst loadings [107], but could be performed in a catalytic sense with an O-acylated azlactone as acylating agent, which does not react with a benzylic amine at —50°C, but is capable of acylating the catalyst [108, 109]. Depending on the buUdness of the substrate, selectivities ranged from S = 11 to 27 (s = [ enantiomer l]/[ enantiomer 2])-... 

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