Piperidine, formation constants with

The general interests in chelation of metals have continued to lead to new forms of polyaminopolycarboxylic acids. Examination of the acid dissociation constant of ethyl-ene-bis-N,N -(2,6-dicarboxy)piperidine (9) showed that they were nearly identical with those of EDTA. However, the formation constants for metal chelates of (9) are lower by 0.5 to 3.7 log 3 units. 

Rate and equilibrium constants have been reported for the reactions of butylamine, pyrrolidine, and piperidine with trinitrobenzene, ethyl 2,4,6-trinitrophenyl ether, and phenyl 2,4,6-trinitrophenyl ether in acetonitrile, hi these reactions, leading to cr-adduct formation and/or nucleophilic substitution, proton transfer may be rate limiting. Comparisons with data obtained in DMSO show that, while equilibrium constants for adduct formation are lower in acetonitrile, rate constants for proton transfer are higher. This probably reflects the stronger hydrogen bonding between DMSO and NH+ protons in ammonium ions and in zwitterions.113 Reaction of 1,3,5-trinitrobenzene with indole-3-carboxylate ions in methanol has been shown to yield the re-complex (26), which is the likely precursor of nitrogen- and carbon-bonded cr-adducts expected from the reaction.114 There is evidence for the intermediacy of adducts similar to (27) from the reaction of methyl 3,5-dinitrobenzoate with l,8-diazabicyclo[5.4.0]undec-8-ene (DBU) cyclization eventually yields 2-aminoindole derivatives.115... 

The investigations of Bunnett el al. (1957) on the rates of substitution of nine 1-substituted 2,4-dinitrobenzenes with piperidine is almost equivalent to an isotope effect study. Six of these reactions (X = Br, d, I, SO.C Hj, SO2.C6H5 and p-O.C3H4.NO2) showed the same rate within a factor of 4-7. This result is easily explained on the basis of the bimolecular mechanism (24). In these 6 reactions the second step is not rate-limiting the overall rate constant is therefore not influenced by the energetic requirements (energy and entropy of activation) for breaking the C—X bond. The variation in rate by the factor 4-7 is probably due to the individual effects of the X-substituents on the rate of formation of the C—bond. 

This effect explains the lower equilibrium constant in complexes with salicylidenebutylamine and piperidine. Moreover, this effect, in the case of secondary amines, is strong enough as to prevent the formation of hexacoordinated complex in reaction of any of the complexes with bidentate Schiff base. The system Co-BSB-secondary amine cannot be considered as dioxygen carrier. 

The V (1—1) frequency shifts upon complexation of diiodine with about 100 Lewis bases. The complex is formed in cyclohexane at 20 °C. Although the diiodine stretch cannot be observed by IR spectroscopy, since it does not produce a dipole moment variation, the polarization of the I—I bond by complex formation renders the vibration IR active. The frequency shifts are calculated from the free diiodine value of 210 cm measured by Raman spectroscopy. The highest frequency shift is found for piperidine (39.5 cm ). In the interpretation of these results, it must be noted that the normal coordinate describing v(I—I) is expected to mix with v(B- 1) because the two bands are generally close. Hence, the frequency shift v(I—I) is not simply related to the change in force constant of the I—I bond upon complexation. 

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