Bases amines and

The synthesis of 1-ethoxy-1-butjme has been reported previously, but the preparations have required multistep sequences. Two of the procedures use 1,2-dibromo-l-ethoxy butane which is dehydrohalogenated in two successive steps, first by an amine base and then by either powdered potassium hydroxide or sodium amide no yields are given. The... 

The furans 63 are a convenient source of functionalised cyclopentenones 65 through sequential ring expansion to the 2,6-dihydropyran-3-ones 64 and base-catalysed isomerisation the choice of amine base and solvent is important (Scheme 41) . 

Allenyltrichlorosilanes can also be prepared by Sn2 displacement of propargylic chlorides with a Cu or Ni complex of HSiCl3 [56]. The reaction requires an amine base and a donor solvent such as THF or propionitrile (Table 9.32). Conditions can be adjusted to favor the propargylic or allenic silane, which is not isolated, but treated directly with various aldehydes to afford allenylcarbinols (A) or homopropargylic alcohols (B). These reactions presumably proceed by an SE2 pathway, such that the allenyl products arise from the propargylic silane and vice versa. 

The synthesis of pure metalacycle la from [Ir(COD)Cl]2 and LI requires only amine base and heat, followed by precipitation and removal of amine hydrochloride. However, this complex was typically generated in situ during early studies by the treatment of a combination of [lr(COD)Cl]2 and LI with an amine base, such as uPrNH2, l,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), or l,8-diazabicyclo[5.4.0] undec-7-ene (DBU). If a 1 1 ratio of iridium to ligand is used, a mixture of la and [Ir(COD)Cl]2 is produced. Helmchen et al. have reported that catalyst activation in the presence of tetrahydrothiophene (THT) prevents coordination of the k -phosphoramidite [71]. 

Nucleophilic addition of phenolic nucleophiles to l,l-dicyano-2-arylethenes in the gas phase and in water has been studied theoretically" using the semiempirical AMI method and the Cramer-Truhlar solvation model SM2.1. The difference between the Brpnsted coefficients (a" = 0.81 and P" =0.65) determined for the gas-phase reaction is indicative of a small positive transition state imbalance of / = 0.16. For reaction in water the estimates (a" = 0.61 and P" = 0.36, giving I = 0.25) are close to the experimental values (a" = 0.55 and P" = 0.35) obtained with amine bases, and the small imbalance is as expected for a reaction involving no hybridization change at the incipient carbanion site. 

The authors proposed that the Brpnsted base interaction on the catalyst is imperative for reactivity. Catalysts lacking a basic amine moiety, specifically mono- and bis-ureas, did not promote the asymmetric catalytic addition well, if at all. In screening a variety of amine bases and bis-ureas, it became apparent that presence of a Brpnsted base was necessary for catalytic activity (Scheme 61) [113]. The reactivity was extremely low in absence of Brpnsted base (Table 2, entry 2), but slightly improved with presence of NEtj (Table 2, entry 1). Combined, a chiral Brpnsted acid and Brpnsted base increase conversion and showed some enantiose-lectivity (Fig. 8). 

Many amine bases and carboxylic acids in proteins titrate with anomalously high or low pA s (Table 5.4). The reasons are quite straightforward, and depend on the microenvironment. If a carboxyl group is in a region of relatively low polarity, its pKa will be raised, since the anionic form is destabilized. Alternatively, if the carboxylate ion forms a salt bridge with an ammonium ion, it will be stabi-... 

A novel peroxocopper complex with -coordination is formed when copper(II) perchlorate is reacted with the tridentate ligand 4-methyl-2,6-bis(pyrrol-idinomethyl)phenol (HL) in methanol solution, in the presence of air, triethyl-amine base, and 3,5-di-teri-butylcatechol [142], The four copper(II) ions in [Cu4L2(02)(0Me)2(C104)] (32) form a near-planar rectangle, with alternate methoxo (Cu... Cu = 3.03 A) and phenolato (Cu... Cu = 2.99 A) bridging ligands. 

Bernasconi, C. F. Moreira, J. A. Huang, L. L. Kittredge, K. W. Intrinsic rate constants for proton transfer from a monoketone to amine bases and electrostatic effects on the intrinsic rate constants for the deprotonation of cationic ketones by OH". /. Am. Chem. Soc. 1999, 121, 1674-1680. 

A study of the role of base and ligand in the isomerization of manganese-coordinated conjugated alkynyl carbonyls to the corresponding allenyl carbonyls shows that manganese requires a ligand prior to isomerization with amine bases and the efficacy of these bases correlates with p Ka (Scheme 97). Potassium /-buloxide led to rapid isomerization in the absence of added ligand.140... 

But what about this cyclisation In stronger protic bases like KOH in water, all the cyclisations are reversible and the more stable ketone 27 is formed by thermodynamic control. In buffered conditions (weak amine base and weak acid) only the more reactive aldehyde enolises and 30 is formed by kinetic control. 

Several combinations of monomers used to prepare polyanhydrides are classified as aliphatic, aromatic, aliphatic-aromatic, amine-based, and fatty acid-based polyanhydrides. The structures of these monomers determine... 

Wilkinson s catalyst in the presence of an amine base and triethylborane enables a reaction between aldehydes and epoxides that is equivalent to nucleophilic opening of an epoxide by an oxyanion (Equation 15). Interestingly, the catalyst interacts with the epoxide prior to the carbonyl function <2005AGE129>. 

The conversion of (1) to the iminium ion (2) occurs by an ionic 2-type elimination mechanism. In support of this mechanism, the Polonovski reaction is accelerated by the addition of acetate ion or amine bases, and markedly decelerated when carried out in acidic media. These observations point to the involvement of the counterion in the removal of the proton from the a-carbon. Further support... 

Vinyl sulfides are prepared from sulfoxides under a variety of conditions. These include reaction with acetic anhydride at reflux, with trifluoroacetic anhydride in the presence of an amine base and with acetic anhydride in the presence of an acid catalyst. In fact, precautions must be taken in certain Pum-merer reactions discussed in the preceding sections to avoid competing vinyl sulfide formation. 

In recent pioneering studies, Crimmins has reported the use of acyloxazolidine-thione auxiliaries (18) and TiCl4 for the preparation of either syn aldol adducts as a function of the stoichiometry of the amine base and metal (Eq. (8.6)) [11]. The use of 1 2 TiCl4 and TMEDA or sparteine yielded the normal 1,2-syn Evans aldol adduct 21 however, the use of 2 1 TiCU Pr2NEt leads to dramatic reversal to give the non-Evans , 2-syn diastereomer 20 in remarkable diastereoselectiv-ity (>99 1). 

Moving on in the search for an improved second version of the reductive dialkylation, it was decided to retain the conditions as initially established for the first two steps (formation of the free amine base and the synthesis of the mono-cyclobutyl intermediate). Focusing instead on the final part—the addition of the second cyclobutyl equivalent—the pH was rigorously controlled to stay within a narrow window between 5.7 and 6.0 by continuously adding HOAc via a pump connected... 

The displacement of halogen from phosphonic dihalides with thiols in the presence of an appropriate base leads to 5,S-diesters rather than (9,5-isomers (equation 30 Z = 0)2-7374,375 gych a reaction has been employed in the determination of the enantiomer composition of chiral thiols. The NMR spectra for a series of phosphonodithioates 163 (Z = O, R = Me, Ph, PhCH2) and also for analogous trithiophosphonates 163 (Z = S, R = Me or Ph) in which the group R is derived from a chiral thiol, showed that the best separation of P NMR signals for the diastereoisomeric forms was achieved when R = Me. Displacement reactions which involve the loss of chlorine from R2P(Z)C1 (Z = or Se ). RP(0)(SR )CP and RP(S)(NHR )C1 by thiols in the presence of a tertiary amine base, and many more, are widely exemplified. 

The product from the addition of an enolate of a 1,3-dicarbonyl-type compound with an aldehyde (or ketone) dehydrates readily to give the a,(3-unsaturated dicarbonyl product. This is known as the Knoevenagel condensation reaction, typically carried out under mild conditions with an amine base, and is a useful method for the formation of alkenes bearing electron-withdrawing substituents (see Section 1.1.3). 

The greater part of this chapter is concerned with the Diels-Alder and hetero-Diels-Alder reaction. The asymmetric version of both of these reactions can be catalysed with metal-based Lewis acids and also organocatalysts. The catalytic asymmetric 1,3-dipolar cycloaddition of nitrones and azomethine ylides is also discussed. Again, most success in this area has been achieved using metal-based Lewis acids and the use of organocatalysts is begiiming to be explored. This chapter concludes with a brief account of recent research into the asymmetric [2+2]-cycloaddition, catalysed by enantiomerically pure Lewis acids and amine bases, and also the Pauson-Khand [2- -2- -l] cycloaddition mediated by titanium, rhodium and iridium complexes. 

Other methods include use of intelligent pigging as well as corrosion prediction models developed by C. De Waard and some other modifications that have been published and commercialized by several other investigators. However, after prediction and/or detection of corrosion incidents inside the pipelines, the most cost-effective method of control is the use of corrosion inhibitors. These are usually amine based and are thus water dispersible. They are usually blended with vapour phase inhibitors and probably some flow enhancers. 

Oil-soluble scavengers These scavengers are used in high-temperature applications (from ambient up to 350°F [177°C]) or when water tolerance of the hydrocarbon is an issue. These products are typically amine-based and perform as effectively as water-soluble additives. These products react with H2S irreversibly to form a thermally stable, oil-soluble alkyl sulfide, and they are often the product of choice for viscous heavy oils and resids. They are also preferred by many users over water-soluble additives in finished fuels to avoid any possibility of haze formation. 

Deleterious Effect of Quaternary Amines. Anion exchange membranes are all amine based and amines, even quaternary, may not be compatible with silver halide electrodes because they accelerate silver deposition on the cathode. 

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