Acid generation from formation

Figure 5 Acid Generation from Formation of Rearrangement Products...

Several triflates and metal salt hydrates were tested as Lewis acid catalysts (each 10 mol%) and the best results were obtained using Yb(OTf or Ni(C104)2-6H20. The stereoselective formation of bicyclic y-lactones (7) could be obtained from bicyclic nitronate (9) via the hydrolytic process by the action of a strong acid generated from Lewis acid with a small amount of water in both nitroalkene (5) and the Lewis acid. This new methodology of one-pot reaction also involves a new type of intramolecular HAD reaction of nitroalkenes as heterodienes, which provides stereochemically defined bicyclic nitronates. 

Japanese chemists have reported that hypobromous acid generated from NBS and water reacts with the 4, 5 -didehydroadenosine derivative (3) to give (4) as the major product. The formation of (4) represents the first instance of N,4 -cyclization with concomitant ring cleavage of the base moiety in a purine nucleoside. 

As described earlier (Section 4.4.1.1), the intermediates of the Curtius reaction are acyl azides, which themially rearrange to isocyanates. One of the classical procedures for the preparation of acyl azides consists of the formation of hydrazides from esters and hydrazine, followed by treatment of the hydrazides with nitrous acid, generated from sodium nitrite and acetic, hydrochloric or sulfuric acid. Acyl azides are commonly used in the crude state or in solution since they are thermally unstable and potentially explosive. 

Figure 3.80. Two-photon induced dual-channel fluorescence image formation within a photosensitive polymer film containing 43e2 and triarylsulfonium hexafluoroantimonate as photoinduced acid generator. (From Ref. [118] with permission of the American Chemical Society.)...

Low concentrations of organic acids at temperatures less than 80 C occur for several reasons. One reason is the decreased organic acid generation from kerogen as a result of low thermal stress. The second reason is that dilution can occur where upward-moving acid-rich, formation waters mix with acid-poor waters of meteoric or other origins. This situation may exist in the Palo Duro Basin of west Texas (13) and the Pleistocene of offshore Louisiana (5). The third reason is that bacterial consumption of organic acids can occur at temperatures less than 80 C... 

Acetic acid (C2) is typically the most abundant of the monocarboxylic acids and comprises more than 50mol% of the total acids generated from source rocks during hydrous pyrolysis. Barth et al. (1989) conducted a series of hydrous pyrolysis experiments on aliquots of a powdered shale sample from the Kimmeridge Clay Formation. The aliquots were isothermally heated for 72 h at temperatures ranging from 200 to 350 °C. Acetic acid in the reacted waters increased with increasing temperature. The percent of acetic... 

The 1,4-isomer has been similarly generated from terephthalonitdle [623-26-7] (56) using a mixed Pd/Ru catalyst and ammonia plus solvent at 125 °C and 10 MPa (100 atm). It is also potentially derived (57) from terephthaUc acid [100-21-0] by amination of 1,4-cyclohexanedimethanol (30) [105-08-8], Endocyclization, however, competes favorably and results in formation of the secondary amine (31) 3-a2abicyclo[3.2.2]nonane [283-24-9] upon diol reaction with ammonia over dehydration and dehydrogenation catalysts (58) ... 

Mechanisms in Chlorine Dioxide Generation from Chlorite. The reactions between sodium chlorite and chloriue-based oxidizers and acids are complex and involve the formation of the proposed unsymmetrical intermediate, [CI2O2] (16,18,22,36,108,135—140). 

Coe et al. reported an efficient modification for the preparation of /-substituted indole analogs for biology screening in good yield. The intermediate P-nitrostyrene 44, prepared from the condensation of 43 with DMFDMA, underwent methanolysis and reduction to provide the aniline acetal intermediate 45. Alkylation of amine 45 was carried out employing standard conditions of reductive alkylation to provide A-alkyl analogs represented by 46. The indole 47 was generated by formation of the oxonium ion (from 46) under acidic conditions, followed by cyclization, accompanied by loss of methanol. 

A unique method to generate the pyridine ring employed a transition metal-mediated 6-endo-dig cyclization of A-propargylamine derivative 120. The reaction proceeds in 5-12 h with yields of 22-74%. Gold (HI) salts are required to catalyze the reaction, but copper salts are sufficient with reactive ketones. A proposed reaction mechanism involves activation of the alkyne by transition metal complexation. This lowers the activation energy for the enamine addition to the alkyne that generates 121. The transition metal also behaves as a Lewis acid and facilitates formation of 120 from 118 and 119. Subsequent aromatization of 121 affords pyridine 122. 

Optically active five- or six-membered cyclic A -acyliminium ions of this type are generated from the a-inethoxy derivatives, easily obtainable through anodic methoxylation of intermediates that are prepared via ex-chiral-pool syntheses from certain natural amino acids. Reaction of 5-substituted five-membered cyclic A -acyliminium ions with various nucleophiles leads to the predominant formation of cw-products with moderate selectivity. The trans-selective reaction with alkyl copper reagents appears to be an exception. 

Iminium ions bearing an electron-withdrawing group bonded to the sp carbon of the iminium function are very reactive dienophiles. Thus, iminium ions 26 generated from phenylglyoxal (Scheme 6.15, R = Ph) or pyruvic aldehyde (R = Me) with methylamine hydrochloride, react with cyclopenta-diene in water at room temperature with good diastereoselectivity [25] (Scheme 6.15). If glyoxylic acid is used, the formation of iminium salt requires the free amine rather than the amine hydrochloride. 

Very recently, a sandwich assay for prostatic acid phosphatase antigen was carried out using two cascaded enzyme reactions to provide amplification of the immunochemical event. In one format, an optical readout was used whereby a forma-zan dye was generated by reaction of a dye precursor and NADH generated from the second enzyme cycle. In the electrochemical format, the NADH generated in the second enzyme cycle was used to reduce Fe(CN) to FeCCN) " which was then detected amperometrically. While the use of Fe(CN) in ECIA has appeared in the... 

Overall, we demonstrated electrode potential- and time-dependent properties of the atop CO adsorbate generated from the formic acid decomposition process at three potentials, and addressed the issues of formic acid reactivity and poisoning [Samjeske and Osawa, 2005 Chen et al., 2003,2006]. There is also a consistency with the previous kinetic data obtained by electrochemical methods the maximum in formic acid decomposition rates was obtained at —0.025 V vs. Ag/AgCl or 0.25 V vs. RHE (cf. Fig. 12.7 in [Lu et al., 1999]). However, the exact path towards the CO formation is not clear, as the main reaction is the oxidation of the HCOOH molecule ... 

---