Factors amine structure

Studies have shown that the HDN of 1,2,3,4-tetrahydroquinoline and 1,2,3,4-tetrahydroisoquinoline catalyzed by sulfided NiMo/Al203 occur via a nucleophilic substitution mechanism [121]. On the other hand, HDN of aliphatic amines with the same catalyst—N1M0/AI2O3—occurs by -elimination [117]. The nature of the base and the amine structure dictate whether the elimination will proceed via a monomolecular (El) or a bimolecular (E2) mechanism. Similarly, for HDN reactions that occur via nucleophilic substitution, these same factors determine if the reaction will follow a monomolecular (Sn 1) or a bimolecular (Sn2) mechanism. 

As described in the previous section polyol-isocyanate prepolymers are commonly chain extended by glycols or amines. These enable sequences of urethane and/or urea groups in close proximity to be produced in a chain. Such a sequence forms a stiff or hard chain segment with softening properties that may reasonably be predicted from Fig. 16.1 and other factors relating structure and properties discussed in Chapter 4. 

The factors that influence uranium extraction have been studied most extensively for amine-sulfate systemsThe effect of amine structure on the extraction of uranium and other metal ions is illustrated in Table XXX.Uranium (IV) is efficiently extracted by primary amines. The efficiency decreases with secondary and tertiary amines. With uranium (Vl) there does not seem to be much correlation between and amine class. With primary, secondary, and tertiary laurylamlnes, conditions given in... 

The polarity of the C—-OH bond, i.e., the basicity of the carbinol-amine, depends on its structure, particularly on the stability of the ring system (degree of aromatic character), and the electron affinity of the substituents on nitrogen and carbon. Of course, external factors also play an important role in the equilibrium temperature, polarity of the solvent, and presence or absence of catalysts (the solvent can also act as a catalyst). 

Heterocyclic structures analogous to the intermediate complex result from azinium derivatives and amines, hydroxide or alkoxides, or Grignard reagents from quinazoline and orgahometallics, cyanide, bisulfite, etc. from various heterocycles with amide ion, metal hydrides,or lithium alkyls from A-acylazinium compounds and cyanide ion (Reissert compounds) many other examples are known. Factors favorable to nucleophilic addition rather than substitution reactions have been discussed by Albert, who has studied examples of easy covalent hydration of heterocycles. 

Nucleophilic attack of amines on fully esterified derivatives of phosphoric acid and its thio-analogues may in general occur at phosphorus or carbon. In an attempt to correlate the rates with structural factors, a study has been reported on a series of compounds of the type (49), ... 

An alternative approach to increase the oxidation rate is the use of alkaline solutions, because bases enhance the reactivity of L-sorbose and weaken the adsorption strength of 2-KLG. Unfortunately, the rate enhancement at higher pH is accompanied by a drop in selectivity due to the poor stability of 2-KLG in alkaline solutions. To circumvent this problem, we have modified the platinum catalysts by adsorbed tertiary amines and carried out the oxidation in neutral aqueous solution [57], This allowed to enhance the rate without increasing the pH of the bulk liquid, which leads to detrimental product decomposition. Small quantities of amines (molar ratio of amine sorbose = 1 1700, and amine Pts = 0.1) are sufficient for modification. Using amines of pKa a 10 for modification, resulted in a considerable rate enhancement (up to a factor of 4.6) with only a moderate loss of selectivity to 2-KLG. The rate enhancement caused by the adsorbed amines is mainly determined by their basicity (pKa). In contrast, the selectivity of the oxidation was found to depend strongly on the structure of the amine. 

Twenty-two years later the isolation of the anti-pernicious anemia factor" was announced independently by Smith (5) and Riches (6). Seven years of chemical studies identified 5,6-dimethylbenzimidazole (7), D-ribose (5) and amino-propanol (9) as components of the anti-pemicious anemia factor", but the tetrapyrroline ring structure containing Co(III) awaited the X-ray crystallographic data on the cyano-derivative by Hodgkin and White (10—15). Once the structure of the antipemicious anemia factor was determined it was called Vitamin B12 (cyanocobal-amin). The recommendations of a number of commissions forms the basis of the present system of nomenclature for this molecule and these are presented in Fig. 1. 

It is well-established that the molecular and electronic structures of metal complexes of azamacrocycles are greatly affected upon N-alkylation (197). This is mainly due to two factors (a) the decrease of the ligand field strength and (b) the increase in the steric requirements upon going from a secondary to a tertiary amine donor function (251). To examine whether the properties of the dinuclear amine-thiophenolate complexes are affected by the N-alkyl substituents, analogous complexes of the... 

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