Amines DABCO

Azirines. Azirines (2) are formed from vinyl azides (1) when the azides are refluxed in toluene in the presence of a tertiary amine. DABCO is particularly effective N,N-diethylaniline is the least effective amine. Yields are higher than those obtained by thermolysis in aprotic solvents. 

Inasmuch as the use of epichlorohydrin concept, Agel et al. [13] developed a new and cheap type of anion exchange membranes (AEM) by preparing the polyepichlorohydrin (PECH) graft quaternary amines (DABCO, TEA) for use in alkaline cells. It s a quasi-gas impervious polymer membrane. The ionic conductivity was much improved to 10 S cm due to the low crystallinity and the anion exchange between Cf and OH ions on the polymer side chains. For the first time, the alkaline SPE employed in alkaline fuel cell, the test results exhibited good performance and could tolerate at high temperature up to 120°C. 

For the bicyclic amine DABCO stereoelectronic effects have been observed [59]. DABCO quenches DBO with lower rate constants than tertiary amines with similar electron donor strength, which can be explained by a hindered proton transfer in the initially formed exciplex. The resulting aminoalkyl radical is destabilized due to the unfavorable orientation of the amine lone pair and carbon radical center in a 60° angle. Noteworthy, the observed effects are much smaller than for alkoxyl radicals, which are known to react with amines exclusively via hydrogen atom transfer (see below). Similar observations have been reported for the quenching of triplet-excited benzophenone [29,195]. Also, stereoelectronic effects are deemed responsible for the three times lower quenching rate of DBO by diisopropylsulflde compared to dimethylsulflde. 

Strong bases, such as potassium acetate, potassium 2-ethylhexoate, or amine—epoxide combinations are the most useful trimerization catalysts. Also, some special tertiary amines, such as 2,4,6-tns(A7,A7-dimethylarninomethyl)phenol (DMT-30) (6), l,3,5-tris(3-dimethylaminopropyl)hexahydro-j -triazine (7), and ammonium salts (Dabco TMR) (8) are good trimerization catalysts. 

Hydroxy group containing tertiary amines are also used because they become incorporated into the polymer stmcture, which eliminates odor formation ia the foam (3). Delayed-action or heat-activated catalysts are of particular interest ia molded foam appHcations. These catalysts show low activity at room temperature but become active when the exotherm builds up. In addition to the phenol salt of DBU (4), benzoic acid salts of Dabco are also used (5). 

Amine catalysts for polyurethane appHcations are sold by Air Products (Dabco), Abbott (Polycat), Kao Corporation (Kaolizer), Tosoh Corporation (Toyocat), and Union Carbide (Niax). 

In recent years there has been some substitution of TDI by MDI derivatives. One-shot polyether processes became feasible with the advent of sufficiently powerful catalysts. For many years tertiary amines had been used with both polyesters and the newer polyethers. Examples included alkyl morpholines and triethylamine. Catalysts such as triethylenediamine ( Dabco ) and 4-dimethyla-minopyridine were rather more powerful but not satisfactory on their own. In the late 1950s organo-tin catalysts such as dibutyl tin dilaurate and stannous octoate were found to be powerful catalysts for the chain extension reactions. It was found that by use of varying combinations of a tin catayst with a tertiary amine... 

Together with a shift of the proton from the a-carbon to the alkoxide oxygen, the tertiary amine is eliminated from the addition product to yield the unsaturated product 3. Early examples of the Baylis-Hillman reaction posed the problem of low conversions and slow reaction kinetics, which could not be improved with the use of simple tertiary amines. The search for catalytically active substances led to more properly adjusted, often highly specific compounds, with shorter reaction times." Suitable catalysts are, for example, the nucleophilic, sterically less hindered bases diazabicyclo[2.2.2]octane (DABCO) 6, quinuclidin-3-one 7 and quinuclidin-3-ol (3-QDL) 8. The latter compound can stabilize the zwitterionic intermediate through hydrogen bonding. ... 

The nucleophilic displacement reactions with azide, primary amines, thiols and carboxylatc salts arc reported to be highly efficient giving high (>95%) yields of the displacement product (Table 9.25). The latter two reactions are carried out in the presence of a base (DBU, DABCO). Radical-induced reduction with tin hydrides is quantitative. The displacement reaction with phenolates,61j phosphines,6M and potassium phthalimide608 gives elimination of HBr as a side reaction. 

Place Arcol Polyol F-3022 (100 g, 0.1 eq., 56 OH, mixed PO/EO triol from Bayer) into a suitable container. To this add distilled water (3.3 g, 0.4125 eq.), Niax Silicone L-620 (0.5 g, a silicone surfactant from OSi Specialties), and Niax C-183 (0.12 g, an amine catalyst from OSi Specialties). Thoroughly blend this mixture without incorporating air bubbles. Then add Dabco T-9 (0.25 g, stannous octoate from Air Products) and mix again. The T-9 must be added last because it is quite water sensitive, so its exposure to the water-containing polyol blend should be kept to a minimum. To this polyol blend, quickly add Mondur TD-80 (42.6 g, 0.4868 eq., a mixture of 80% 2,4-TDI and 20% 2,6-TDI isomers from Bayer) and immediately stir at 3000 rpm for 5 s. Quickly pour the reaction mixture into a suitable container such as a 1-qt paper or plastic cup and allow the foam to free-rise. The stir blade may be wiped or brushed clean. 

Normally the reaction Is useful for the conversion of alkyl halides to primary amines without concomitant formation of secondary amines.29 Treatment of polymer 17 with hexamethylenetetramine in a mixture of ethanol/THF afforded an insoluble resin. Using diazabicyclooctane (DABCO), we demonstrated that the reaction could be limited to attack by a single nitrogen in a multifunctional amine, so we did not anticipate crosslinking via bis-quat salt formation. Hydrolysis of 2 with anhydrous HC1 in ethanol generated free amino groups as evidenced by a positive ninhydrin test, but quantitative hydrolysis could not be achieved and the product remained insoluble. One would have expected a simple bis-quat to hydrolyse and open the crosslinked structure. 

Enantioselective hydrogenation of 2,3-butanedione and 3,4-hexanedione has been studied over cinchonidine - Pt/Al203 catalyst system in the presence or absence of achiral tertiary amines (quinuclidine, DABCO) using solvents such as toluene and ethanol. Kinetic results confirmed that (i) added achiral tertiary amines increase both the reaction rate and the enantioselectivity, (ii) both substrates have a strong poisoning effect, (iii) an accurate purification of the substrates is needed to get adequate kinetic data. The observed poisoning effect is attributed to the oligomers formed from diketones. 

Pt/Al2C>3-cinchona alkaloid catalyst system is widely used for enantioselective hydrogenation of different prochiral substrates, such as a-ketoesters [1-2], a,p-diketones, etc. [3-5], It has been shown that in the enantioselective hydrogenation of ethyl pyruvate (Etpy) under certain reaction conditions (low cinchonidine concentration, using toluene as a solvent) achiral tertiary amines (ATAs triethylamine, quinuclidine (Q) and DABCO) as additives increase not only the reaction rate, but the enantioselectivity [6], This observation has been explained by a virtual increase of chiral modifier concentration as a result of the shift in cinchonidine monomer - dimer equilibrium by ATAs [7],... 

Silk can be readily dyed with conventional high-reactivity dyes of the dichlorotriazine, dichloroquinoxaline or difluoropyrimidine classes. Exhaust dyeing at 60-70 °C and pH 5-6 gives satisfactory results, especially if a mildly alkaline aftertreatment is given to enhance fixation. Dichlorotriazine dyes can also be applied by pad-batch dyeing with bicarbonate and a batching time of 4-6 hours. The relatively low reactivity of aminochlorotriazine dyes, however, results in moderate to poor build-up on silk. Tertiary amine catalysts such as DABCO (7.66) can be used to accelerate the dye-fibre reaction and increase the fixation substantially [116], but it is difficult to achieve satisfactory compatibility in mixture dyeings by this method (section 7.4.2). 

DABCO = l,4-diazabicyclo[2,2,2]octane (triethylene diamine) (22) is a moderately basic amine, removable by sublimation, that causes enantiomeriza-tion of amino acid residues that have been reacted to form Schiff s bases (RR C=NCHR2CO-). 

The long known132 electron donor-acceptor complexes between tertiary amines and carbon tetrahahdes are simple systems. Thus, l,4-diaza[2,2,2]bicyclooctane (DABCO) or quinuclidine afford solid complexes with carbon tetrabromide142. 

The approach to polyketide synthesis described in Scheme 5.2 requires the relatively nontrivial synthesis of acid-sensitive enol acetals 1. An alternative can be envisioned wherein hemiacetals derived from homoallylic alcohols and aldehydes undergo dia-stereoselective oxymercuration. Transmetallation to rhodium could then intercept the hydroformylation pathway and lead to formylation to produce aldehydes 2. This proposal has been reduced to practice as shown in Scheme 5.6. For example, Yb(OTf)3-cata-lyzed oxymercuration of the illustrated homoallyhc alcohol provided organomercurial 14 [6]. Rhodium(l)-catalyzed hydroformylation of 14 proved successful, giving aldehyde 15, but was highly dependent on the use of exactly 0.5 equiv of DABCO as an additive [7]. Several other amines and diamines were examined with variation of the stoichiometry and none proved nearly as effective in promoting the reaction. This remarkable effect has been ascribed to the facilitation of transmetallation by formation of a 2 1 R-HgCl DABCO complex and the unique properties of DABCO when both amines are complexed/protonated. 

The aldehyde can be replaced by an imine and the reaction is then called the aza-Baylis-Hillman reaction [87, 88]. (3-Amino-a-methylene structures obtained in this way could further be converted to a range of biologically important molecules, such as p-amino acids [89]. First reaction of this kind was published in 1984 [90]. Tosylimines and ethylacrylate reacted in the presence of DABCO as catalyst to give p-aminoesters. First three-component aza-Baylis-Hillman reaction was published in 1989 by Bertenshaw and Kahn [91], with imine formation in situ from an aldehyde and an amine. In the presence of triphenylphosphine as catalyst, the reaction with methylacrylate led to the formation of the p-amino-ot-methylene esters and ketones in good yields (Scheme 38). 

The reaction of diisopropyl sulfide with sulfur monochloride and DABCO afforded l,2-dithiolo-3-thiones 98 and 99 (1999JOC4376). Dithiole ring formation had been assumed to be similar to that produced from tertiary diisopropyl-amines. However, in the case of diisopropyl sulfide only one isopropyl group was... 

The reaction can be performed in diethyl ether in the presence of iron(III) acetylaceto-nate, as reported by Nagano and Hayashi in 2004, or in the presence of FeCl(salen) or iron(III) chloride/triethylamine, as described by Bedford and coworkers (Scheme 39). The latter compared several ligands (amines , phosphines ) and the best results were obtained with triethylamine, TMEDA or DABCO. In all cases, the reactions have to be performed in refluxing diethyl ether and the Grignard reagent has to be added at once Unfortunately, these reaction conditions are only useable on a very small scale (1 mmol) but they cannot be used for large-scale applications. 

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