Catalysis amine

Resoles are usually those phenolics made under alkaline conditions with an excess of aldehyde. The name denotes a phenol alcohol, which is the dominant species in most resoles. The most common catalyst is sodium hydroxide, though lithium, potassium, magnesium, calcium, strontium, and barium hydroxides or oxides are also frequently used. Amine catalysis is also common. Occasionally, a Lewis acid salt, such as zinc acetate or tin chloride will be used to achieve some special property. Due to inclusion of excess aldehyde, resoles are capable of curing without addition of methylene donors. Although cure accelerators are available, it is common to cure resoles by application of heat alone. 

Intermolecular cross aldolization of metallo-aldehyde enolates typically suffers from polyaldolization, product dehydration and competitive Tishchenko-type processes [32]. While such cross-aldolizations have been achieved through amine catalysis and the use of aldehyde-derived enol silanes [33], the use of aldehyde enolates in this capacity is otherwise undeveloped. Under hydrogenation conditions, acrolein and crotonaldehyde serve as metallo-aldehyde enolate precursors, participating in selective cross-aldolization with a-ketoaldehydes [24c]. The resulting/ -hydroxy-y-ketoaldehydes are highly unstable, but may be trapped in situ through the addition of methanolic hydrazine to afford 3,5-disubstituted pyridazines (Table 22.4). 

VIII. Formation of the Phosphorus-Carbon Bond Using Chiral Amine Catalysis.122... 

VIII. FORMATION OF THE PHOSPHORUS-CARBON BOND USING CHIRAL AMINE CATALYSIS... 

The formation of oxygen-containing heterocyclic compounds is also a consequence of the Maillard reaction. Amines and amino acids have a catalytic effect upon the formation of 2-furaldehyde (5), 5-(hydroxy-methyl)-2-furaldehyde (11),2-(2-hydroxyacetyl)furan (44),2 and 4-hy-droxy-5-methyl-3(2//)-furanone (111) (see Ref. 214). This catalytic effect can be observed with several other non-nitrogenous products, including maltol. The amino acid or amine catalysis has been attributed to the transient formation of enamines or immonium ions, or the 1,2-2,3 eno-lization of carbohydrates. Of interest is the detection of A -(2-furoyl-... 

In enzymic decarboxylations the mechanistic pathway seems to involve Schiff base formation between an —NH2 from a lysine residue and a C=0 of the keto acid.52 Likewise, with small-molecule primary amines, catalysis of decarboxylation of /3-ketoacids53-58 has been ascribed to a Schiff base intermediate. The overall reaction for oxalacetate is... 

The widely accepted mechanism of amine catalysis of the Baylis-Hillman reaction... 

Figure 8.7 Amine catalysis of silylaytion reaction, mechanism HI.

Figure 8.8 Amine catalysis of silylation reaction, mechanism 2.

Scheme 6.6. Ligand effects on intermolecular C-H amination catalysis.

For reactions which usually involve enol or enolate intermediates, enamine formation has been postulated for primary and secondary amine catalysis in order to explain abnormally high catalytic effects and abnormal rate laws. Shilov, Yashinov and coworkers (for the last paper of the series, see Volkova... 

In contrast to primary amine catalysis, the enamine mechanism has been ruled out for D—H exchange in isobutyraldehyde catalysed by secondary amines. Catalytic rate constants were explained by considering only the... 

Primary amine catalysis (usually involving a lysine residue) has been recognised to play an important role in various enzyme-catalysed reactions. Examples are the conversion of acetoacetate to acetone catalysed by acetoacetate decarboxylase, the condensation of two molecules of S-aminolevulinic acid catalysed by -aminolevulinic deshydratase during the biosynthesis of porphyrins, and the reversible aldol condensation of dihydroxy-acetone phosphate with glyceraldehyde which in the presence of aldolase yields fructose-1-phosphate (64) (For reviews see, for example, Snell and Di Mari,... 

Important parameters for understanding the efficiency of primary amine catalysis are the ketone + amine to enamine equilibrium constants. Unfortunately, data are very scarce. Equilibrium constants for the interconversion (65) of [2H6]acetone and protonated enamine in water ( H =... 

The analogy between primary amine catalysis and some enzyme-catalysed biochemical processes has been stressed. There is not doubt that further studies of amine catalysis would help in understanding enzyme catalysis via organic... 

Amidines, N-(l,2,4-thiadiazol-5-yl)-, rearrangement, 56, 103 Amidoximes, 1,2,4-oxadiazol-3-yl-, rearrangements, 56, 55 Amidyl radicals, see Radicals, nitrogen Amination, asymmetric, of carboxylic acids by chiral nitroso compds, 57, 41 Amines, catalysis of 3-acyl-1,2,4-oxadiazole arylhydrazone rearrangement by, 56, 87 Amines, thionitroso-, formation, 55, 20 Aminium cation radicals, see Radicals, nitrogen... 

Difficulty finding conditions that would allow both efficient sequencing and suppression of the O-to-N shift led us to investigate tertiary amine catalysis of thiocarbamylation. Complete reaction of ONCS showed little effect of solvent on coupling. Adding 1.5 to 2.5 equivalents of acetic acid, however, decreased the fraction of the desired product (Table HI). 

Table III. Tertiary-amine catalysis of thiocarbamylation with ONCS...

That coupling could be catalyzed without tertiary amines led to examination of non-tertiary amine catalysis of thiocarbamylation. Tests with sodium salts revealed a moderate catalysis by acetate, and weaker effect of formate (data... 

The reaction of benzofuroxan with malononitrile and amine catalysis proceeds to give 3-amino-quinoxaline-2-carbonitrile 1,4-dioxide (6). In this case, the primary adduct is stabilized by an intramolecular proton shift rather than by an elimination rcaction. " - Benzimidazoles can also be formed through this reaction (see also Houbcn-Weyl, Vol. E8a, p 303). 

In the case of tertiary amine catalysis of the reactions of acid chlorides, phosgene and chloroformates, an initial complex formation has been widely thought to be likely, viz. 

The tertiary-amine catalysis will favour the intramolecular cyclization reactions which will lower the crosslink density of the network in comparison with the situation if only intermolecular reactions took place. 

Two main routes have been described for the preparation of hydantoins cyclization of urea-derivatized amino acids and of carbamate-bound amino acid carboxamides (Figure 15.10) [95, 96]. In the first route, a bound amino acid is treated with an isocyanate to obtain the urea that is subsequently cyclized and released by acid (HC1) or base (tertiary amines) catalysis upon warming (60-100 °C) [95, 97]. The second route employs a carbamate linkage to attach the amino acid through the amino... 

Due to the complications generated by the catalysis with tertiary amines, at this moment the most widely used catalyst to obtain rigid polyether polyols is KOH, but some polyethers, especially of very high functionality, are obtained by tertiary amine catalysis. 

The removal of the catalytic effect of the remnant tertiary amines in the rigid polyether polyols synthesised in amine catalysis [36]. 

The remnant tertiary amines in the polyether polyols obtained in amine catalysis have a negligible effect in the reaction of -NCO groups with hydroxyl groups, in polyurethane fabrication. Generally, the formulations made with these polyols are corrected, by the decrease of the concentration of the amines used as catalysts in the foaming processes, in order to obtain similar reactivities as neutral polyols. 

It is well known that EO, a very reactive monomer in anionic polymerisation, can be added to the hydroxyl groups in the tertiary amine catalysis until 8-9 EO units/hydroxyl groups are added. One must remember that in the same type of catalyst reaction, PO can only be added until a maximum of 1-2 PO units/hydroxyl groups is reached [31]. 

The contrasting behavior in the DNBF-C6H5NH2 system, where tertiary amine catalysis is not required, reflects the greater stability of a complexes formed by this highly electron deficient substrate. These results and Scheme IV indicate that the more reactive DNBF electrophile can differenti-... 

The position is similar in basic catalysis. The hydroxyl ion has no strong claims to uniqueness, being merely the anion of a weak acid. According to the Bronsted-Lowry acid-base definition, a base is any species which has a tendency to accept a proton. This obviously includes anions like OH-, CH3COO, HPCL , as well as uncharged basic molecules like ammonia and the amines. Catalysis by all these species was first found in the decomposition of nitramide (Bronsted and Pedersen, 15), and subsequently in many other reactions. 

---