Tertiary amine hydrogen bonding

One method we have developed for avoiding polymerization with the adsorbed water layer is to use a base catalyzed reaction in supercritical CO2 (SCF CO2). We have shown that SCF CO2 has the unique property of removing all adsorbed water from the silica surface. Once removed the amine base catalyses the reaction of the silane with the surface. As shown in Figure 1, the preadsorbed amine hydrogen bonds to the surface silanol and renders the Si-0 group of the silanol more nucleophilic for reaction with the silicon atom of the incoming chloro or alkoxysilane. Triethylamine is the preferred amine as it binds to all isolated silanols from SCF CO2 and is not removed with subsequent exposure to flowing SCF CO2 solvent. Furthermore a tertiary amine should be used as primary and secondary amines such as ammonia are known to react with CO2 to produce carbamates. " ... 

Primary and secondary amines can participate m mtermolecular hydrogen bonding but tertiary amines lack N—H bonds and so cannot... 

Amines that have fewer than six or seven carbon atoms are soluble m water All amines even tertiary amines can act as proton acceptors m hydrogen bonding to water molecules... 

Amines, like ammonia NH3, are polar compounds and, except for tertiary amines, form intermolecular hydrogen bonds leading to higher boiling points than non-polar compounds of the same molecular weight, but lower boiling points than alcohols or acids. The smaller molecules, containing up to about six carbon atoms, dissolve in water. Aliphatic amines are similar in basicity to ammonia and form water-soluble salts with acids ... 

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 intrinsic moisture sensitivity of the epoxy resins is traceable directly to the molecular structure. The presence of polar and hydrogen bonding groups, such as hydroxyls, amines, sulfones and tertiary nitrogen provides the chemical basis for moisture sensitivity, while the available free volume and nodular network structure represent its physical aspect. 

Because the tertiary amines cannot be brominated by NBS, they do not influence the o/tAo-bromination of phenols. Though the hydrogen bonding between the phenolic OH and NBS will be formed, the bonding is inferred to be weaker than that between the OH and the (V-bromoamines. The nucleophilicity (or basicity) of the nitrogen atom of A -bromoamines is stronger than that of NBS. This is why traces of A -bromoamines can react with phenols continuously. 

Tertiary amines can be converted to amine oxides by oxidation. Hydrogen peroxide is often used, but peroxyacids are also important reagents for this purpose. Pyridine and its derivatives are oxidized only by peroxyacids. In the attack by hydrogen peroxide there is first formed a trialkylammonium peroxide, a hydrogen-bonded complex represented as R3N-H202, which can be isolated. The decomposition of this complex probably involves an attack by the OH moiety of the H2O2. Oxidation with Caro s acid has been shown to proceed in this manner ... 

Murahashi S-I, Nakae T, Terai H, Komiya N (2008) Ruthenium-catalyzed oxidative cyana-tion of tertiary amines with molecular oxygen or hydrogen peroxide and sodium cyanide sp3 C-H bond activation and carbon-carbon bond formation. J Am Chem Soc 130 11005-11012... 

All amines are relatively weak bases, which react with C02, H2S, and COS forming bonds that can easily be broken at elevated temperatures. Primary amines are chemically stronger than secondary, which in turn are stronger than tertiary. Weaker amines have greater selectivity for H2S, which is especially high for tertiary amines where the nitrogen atom does not have a free hydrogen association to form the carbamate ion by direct reaction... 

The very unusual selective hydrogenation of ,/3-unsaturated aldehydes to the unsaturated alcohols, Eq. (30), has been accomplished using [RhCl(CO)2]2 in the presence of tertiary amines under oxo conditions (162). RhCl(PPh3)3 systems under similar conditions reduce the olefinic bond (162), as do Co2(CO)8 systems in the presence of amines or phosphites (163). Further details on the versatile Rh(BH4)(amide)py2Cl2 systems (/, p. 280) have appeared (164, 165) ketones are also slowly hydrogenated (166), and 1,5,9-cyclododecatriene has been selectively reduced to cyclododecene (167). 

The first experimental data for a reaction involving proton transfer from a hydrogen-bonded acid to a series of bases which were chosen to give ApK-values each side of ApK=0 are given in Fig. 15 (Hibbert and Awwal, 1976, 1978 Hibbert, 1981). The results were obtained for proton transfer from 4-(3-nitrophenylazo)salicylate ion to a series of tertiary aliphatic amines in aqueous solution, as in (64) with R = 3-nitrophenylazo. Kinetic measurements were made using the temperature-jump technique with spectrophoto-metric detection to follow reactions with half-lives down to 5 x 10"6s. The reciprocal relaxation time (t ), which is the time constant of the exponential... 

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