Chemicals DABCO

The effect of the type of catalyst is illustrated in Figure 4. The carbon dioxide emission curves using DABCO as a catalyst show an "autocatalytlc" effect. So far this phenomenon has remained unexplained it may be due to physical (diffusion hindrance) or chemical effects. 

The second example concerns a photo-induced e.t. with this same chemical system, to which an amine (e.g. DABCO) is added as an electron donor. The fast decay to the relaxed triplet excited state of benzophenone remains unchanged, but this is now followed by two further reactions the forward e.t. step which forms the radical ions, and the back e.t. of these ions to restore the initial system. 

Diazabicyciooctane (DABCO) was used as purchased from Aldrich Chemical Company, Inc. 

DABCO is previously dried at 20-27°C (room temperature) under reduced pressure (2 mm) Dichloromethane was used as purchased from Aldrich Chemical Company, Inc., (99.9%). 

The second in situ technique is NMR. An autoclave fitting with the NMR cavity was designed by Gerardin et al. [59] and allows to follow the evolution of many parameters of the synthesis via the NMR characteristics of the different nuclei versus temperature and reaction time. The first measurement that can be reached now is the absolute value of the pH in hydrothermal conditions and the quantitative evolution of the concentration of protons in the bomb with the parameters of the synthesis [60], They proved that 14N NMR chemical shifts of well chosen amine compounds (imidazole and DABCO which possess complementary pKas) are precise pH indicators in aqueous solutions from room temperature to 475 K. Use of both amines permit to cover a wide range of about 9 pH units, with a precision of 0.1 pH unit. 

The proton transfer reaction along a hydrogen bond between aliphatic dicarbox-ylic acids and DABCO, investigated by solid state NMR (Fig. 3.2.24), has shown that intramolecular O-H O and intermolecular N H-O hydrogen bonds are strong interactions, with proton chemical shifts of around 16 1.5 ppm, and N-0 and 0-0 bond lengths of around 2.55-2.60 A, while intermolecular N+-H- - O interactions are weaker and are characterised by a S1H of about 12.3 ppm and by an N-0 bond length of about 2.7 A [71, 72],... 

DABCO catalyst (triethylenediamine, Air Products and Chemicals, Inc.) was purified by sublimation and stored in a desiccator. 

Dimethylindole shows chemical reactivity comparable to the physical quenching by DABCO (Table 2). 

NiCl2dppe, DMF (anhydrous grade) and DABCO were obtained from Aldrich Chemical Company, Inc., and used without further purification. NiC dppe can also be obtained from Strem Chemicals Inc. Diphenylphoshine (DPP) was obtained in an... 

AI3-26794 Araldite accelerator 062 BDMA Benz-enemethanamine, N,N-dimethyl- Benzyl-N,N-dimethyl-amine Benzylamine, N,N-dimethyl- Benzyldimethyl-amine N-Benzyldimethylamine N-Benzyl-N,N-dimethyl-amine CCRIS 6693 Dabco B-16 Dimethyl-benzylamine N,N-Dimethylbenzylamine N,N-Dimethyl-N-benzylamine N,N-Dimethylbenzenemethanamine EINECS 203-149-1 NSC 5342 Pentamin BDMA N-(Phenylmethyl)dimethylamine Sumine 2016 UN2619. Amine-based catalyst for flexible slabstock PU foam. Used as a polyurethane catalyst and an epoxy curing agent. Liquid mp = -75° bp = 181° d° = 0.915 7.m = 252, 268, 265 nm (cyclohexane) slightly soluble in H2O, freely soluble in EtOH, Et20 LD50 (rat orl) = 265 mg/kg. Air Products Chemicals Inc. Pentagon Chems. Ltd. -... 

Second, the most repeatedly determined value of kq Is that of l,4-dlazablcyclo(2.2.2)octane (, DABCO). In 1968, Ouannes and Wilson (145) discovered that 2, is a powerful Inhibitor of I02 reactions In solution and then demonstrated that It also quenches IO2 In the gas phase. In contrast to jS, does not react chemically with i02, either In gas phase or In solution [kq > 100 X kf (82)]. Structural reasons for this behavior will be explained later. The published values of kq (DABCO) are scattered and show no evident solvent effect. Formerly, very small solvent effects were reported, though with limited amount of data (68, 72, 146). 

If weakly nucleophilic 2,2,2-trifluoroethanol (TFE) is used as solvent (and hence in high concentration), photoisomerizations from 53 to 54 (and back) are indeed observed, but with no adduct formation whatsoever ). If, however, l,4-diazabicyclo[2.2.2]octane (DABCO) is added to the irradiated solution, the 1,2-adduct 60b is obtained in 92% chemical yield [79]. The addition of DABCO was done with the intention [72e] of increasing the relatively slight reactivity of the ketene group B by converting it to the highly reactive acylammonium group O [80] Scheme 24). 

The catalytic effect of DABCO on the addition of protic nucleophiles to dieneketenes is not limited to the case at hand. The ortho-qwao acetates rac-62 and rac-63 are additional examples the corresponding 1,2-adducts rac-64 and 65) can be obtained in this manner in high chemical yield (Scheme 25) [72e]. 

Fig. 19 Self-assembly processes involved in the dimerization of a calix-tetraporphyrin 23 with DABCO reprinted with permission from [49], Copyright (2003) American Chemical...

DABCO 8154 Cyclic tertiary amine catalyst Air Products and Chemicals, Inc. 

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