Primary amines protonation

Other systems are ambiguous and require a careful consideration of the magnitudes of the derived rate constants before a conclusion can be drawn. An extreme case can be found in the pH dependence of the solvolysis of m-[Co(en)2(H20)Cl]2+.330 The rate is independent of pH in the range 7—9, where the complex is almost entirely in the form of ris-[Co(en)2(OH)Cl]+ and it is usually, and probably correctly, assumed that the pH independent rate constant is that for the uncatalyzed aquation of this species.180 However, consideration ought to be given to the possibility that the observed process is the base catalyzed hydrolysis of the aquo complex in which a primary amine proton is removed. Problems of this sort are discussed in ref. 301, p.84. 

Correction must be made for the pATa of the deuterated solvent. Bases are stronger in deuterium-containing acidic media than in the analogous protium-containing one. For primary amine protonation in the pH range, A pKa is —0.55 units, and for weaker bases, —0.35 units (60JA15). A standard value of 0.4 was therefore used in all cases. 

No smooth association of type C2 is possible between the A-[Co(sen)]3+ and [Sb2(cZ-tart)2] ions (Fig. 40, B) when the hydroxyl and the carboxyl oxygen atoms of the chiral anion are hydrogen bonded to the secondary and primary amine protons, respectively. These protons are directed along the pseudo-C2 axis of the complex, since the apical methyl substituent lies in the vicinity of the distal carboxyl group and imposes steric hindrances [311]. When the second [Sb2(Z-tart)2] anion is coordinated to the A-[Co(sen)] + cation, the BCD spectral changes were positive for the A2 component and negative for the Ea component, which demonstrated association along both the C2 and C3 axes. The reorientation of the first anionic species is likely to occur [310]. 

Section 22 19 The N—H stretching frequency of primary and secondary amines appears m the infrared m the 3000-3500 cm region In the NMR spectra of amines protons and carbons of the type H—C—N are more shielded than H—C—O... 

Fig. 9. An inclusion complex formed between a protonated primary amine and a chiral crown ether.

The protonated form of poly(vinyl amine) (PVAm—HCl) has two advantages over many cationic polymers high cationic charge densities are possible and the pendent primary amines have high reactivity. It has been appHed in water treatment, paper making, and textiles (qv). The protonated forms modified with low molecular weight aldehydes are usehil as fines and filler retention agents and are in use with recycled fibers. As with all new products, unexpected appHcations, such as in clear antiperspirants, have been found. It is usehil in many metal complexation appHcations (49). 

The 1 2 metal complex dyes are dyed either at neutral pH or with ammonium acetate, and the exhaustion achieved by the effect of van der Waals forces. The pH is then aUowed to go slightly acidic to form salt linkages between the dye anion and the protonated primary amine groups in the wool (NH3 ). AU the dyes have similar dyeing properties and the conditions of appHcation do not damage the wool. 

The present authors have found that the preparation of 7V-acetyl aziridine derivates provides the most secure method of differentiating aziridines from primary amines which are alternate reaction products in a number of cases. The infrared spectra of the former derivatives show only a peak at 1690 cm" for a tertiary amide peaks at ca. 3440 and 1530 cm" indicative of a secondary amide are absent. Acetylation also shifts the aziridine ring protons to a lower field in the NMR by ca. 1 ppm relative to the parent aziridine. The A"-acetyl aziridines are hydrolyzed with 3% methanolic potassium hydroxide. " Published NMR spectra of several 16j5,17j -aziridines reveal resonance patterns resembling those of the respective epoxides. " ... 

Formation of C—Nu The second mode of nucleophilic addition, which often occurs with amine nucleophiles, involves elimination of oxygen and formation of a C=Nu bond. For example, aldehydes and ketones react with primary amines, RNH2, to form imines, R2C=NR. These reactions proceed through exactly the same kind of tetrahedral intermediate as that formed during hydride reduction and Grignard reaction, but the initially formed alkoxide ion is not isolated. Instead, it is protonated and then loses water to form an imine, as shown in Figure 3. 

Reaction of an aldehyde or ketone with a secondary amine, R2NH, rather than a primary amine yields an enamine. The process is identical to imine formation up to the iminium ion stage, but at this point there is no proton on nitrogen that can be lost to form a neutral imine product. Instead, a proton is lost from the neighboring carbon (the a carbon), yielding an enamine (Figure 19.10). 

Reduction Conversion of Nitriles into Amines Reduction of a nitrile with LiAIH4 gives a primary amine, RNH . The reaction occurs by nucleophilic addition of hydride ion to the polar C=N bond, yielding an imine anion, which still contains a C=N bond and therefore undergoes a second nucleophilic addition of hydride to give a dianion. Both monoanion and dianion intermediates are undoubtedly stabilized by Lewis acid-base complexafion to an aluminum species, facilitating the second addition that would otherwise be difficult Protonation of the dianion by addition of water in a subsequent step gives the amine. 

As discussed in the three preceding sections, the key intermediate in diazotizations is the A-nitroso derivative of the primary amine, the formation of which is usually the rate-determining step of diazotization. The subsequent steps are faster and therefore not easily accessible to study. The sequence of protonation, deprotonation, protonation, and dehydration in Scheme 3-36 seems to be the most reasonable mechanism. 

Mechanishc studies indicated the possibihty of alkynylmercury chlorides as intermediates. They would react with amines to give 2-aminovinyhnercury chlorides which could be protonated to give enamines (or imines in the case of primary amines) (Scheme 4-13) [260]. 

The first structurally characterized example of a platinum(II) derivative containing a saturated tetraamine macrocycle, 6,13-dimethyl-l,4,8,ll-tetraazacyclotetradecane-6,13-diamine has been reported (80).251 The species crystallizes as the colorless tetra-cationic complex from dilute HC104 solution by slow evaporation, where the two pendant primary amines are protonated. Other macrocyclic tetraamine complexes including [Pt([14]aneN4)]Cl2 have also been described.252... 

Many times an analyte must be derivatized to improve detection. When this derivatization takes place is incredibly important, especially in regards to chiral separations. Papers cited in this chapter employ both precolumn and postcolumn derivatization. Since postcolumn derivatization takes place after the enantiomeric separation it does not change the way the analyte separates on the chiral stationary phase. This prevents the need for development of a new chiral separation method for the derivatized analyte. A chiral analyte that has been derivatized before the enantiomeric separation may not interact with the chiral stationary phase in the same manner as the underivatized analyte. This change in interactions can cause a decrease or increase in the enantioselectivity. A decrease in enantioselectivity can result when precolumn derivatization modifies the same functional groups that contribute to enantioselectivity. For example, chiral crown ethers can no longer separate amino acids that have a derivatized amine group because the protonated primary amine is... 

Derivatization of the optically active aldehydes to imines has been used for determination of their enantiomeric excess. Chi et al.3 have examined a series of chiral primary amines as a derivatizing agent in determination of the enantiomeric purity of the a-substituted 8-keto-aldehydes obtained from catalysed Michael additions. The imine proton signals were well resolved even if the reaction was not completed. The best results were obtained when chiral amines with —OMe or —COOMe groups were used [2], The differences in chemical shifts of diastereo-meric imine proton were ca. 0.02-0.08 ppm depending on amine. This method has been also used for identification of isomers of self-aldol condensation of hydrocinnamaldehyde. 

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