Pyridinium complex

A. Heptoic anhydride enanthic anhydride). In a 250-ml. round-bottomed three-necked flask, equipped with a stirrer, dropping funnel, and thermometer, are placed 15.8 g. (16.1 ml., 0.2 mole) of dry pyridine (Note 1) and 25 ml. of dry benzene (Note 2). I hen 14.8 g. (15.5 ml., 0.1 mole) of heptoyl chloride (Note 3) is added rapidly to the stirred solution. The temperature rises only slightly, and a pyridinium complex separates. While stirring is continued, 13.0 g. (14.1 ml., 0.1 mole) of heptoic acid (Note 3) is added from the dropping funnel over a period of 5 minutes. The temperature rises rapidly to 50-65° (Note 4), and pyridine hydrochloride is formed. After stirring for 10 minutes, the solid is collected on a chilled Buchner funnel and washed twice with 25-ml. portions of dry benzene (Note 5). 

The pyridine used in the submitters procedures apparently reacts with the sulfuryl chloride to form an intermediate quaternary pyridinium complex which undergoes aminolysis to yield the sulfamide. 1 However, in many instances the pyridine may be replaced by an equivalent, quantity of the primary... 

Stacey and Turton61 objected to Isbell s mechanism on two counts first, that he did not specify that a proton acceptor must be used to promote the reaction and second, that the orthoacetate intermediate would not be applicable in the conversion which they demonstrated (by absorption spectra data) to take place on treatment with dilute, aqueous sodium hydroxide. (The presence of the proton acceptor seems implicit in Isbell s general description of the process of enolization.) The mechanism of Stacey and Turton is shown in Formulas XXIV to XXVIII it calls for the donation of electrons by pyridine to the incipient, ionic proton at C2 and elimination of acetic acid between C2 and C3 with the formation of the partially acetylated enediol-pyridinium complex. The pyridinium ion is removed by acetic acid. Electronic readjustment results in the elimination of acetic acid from positions 4 and 5. The final step, conversion of XXVII to XXVIII, was not explained. Stacey and Turton considered that with sodium hydroxide the reaction proceeds after deacetylation by a similar mechanism except that hydroxyl groups take the place of acetyl groups. Neither mechanism requires a free hydroxyl group at Cl, a condition considered by Maurer to be essential to kojic acid formation. 

Synthetically useful phosphorane-derived phenyliodonium triflates have been synthesized from the highly electrophilic pyridinium complex 20 <2002TL2359>. Similarly, benziodoxole 21 reacts with trimethylsilyl trifluoro-methanesulfonate (TMSOTf) and pyridine to form a precipitate of complex 22 (Equation 6) <2002TL5735>. The first example of a pentavalent iodine complex with a chelating polydentate nitrogen ligand 24 was obtained from diacetate 23 under similar conditions (Equation 7) <2002TL5735>. 

The reaction of (/ )-2,2 -di(bromoethyloxy)-l,r-binaphthyl with 4,4 -bipyridine gave bis-pyridinium complex, which with l,3-di(dibromomethyl)benzene afforded (9.4%) of the bis(dipyridinium) complex 32 <07OL5393>. 

A reversible solid-state HCl elimination reaction from a Cu(ii) pyridinium coordination complex has been reported. The reaction proceeds with a colour change from yellow (pyridinium complex) to blue (pyridine complex). This reaction suggests that other protic ligands may successfully be coordinated to metals using a solvent free approach in the future. 

The rates of photoinduced electron transfer (ET) reactions in a series of iridium (spacer)pyridinium complexes, [Ir(/r-dmpz)(CO)(Ph2PO-CH2-CH2-py+)]2 and [Ir( -dmpz)(CO)(Ph2PO-C6H4(CH2) -py+)]2 ( = 0 - 3), have been studied in acetonitrile solution at room temperature (99). The nuclear reorganization energies and electronic couplings in these systems have been evaluated. 

Glycosaminoglycans. — A thermodynamic study of the partition of chondroitin sulphate-hexadecyl pyridinium complexes in butanol-aqueous salt biphasic solutions has been reported. ... 

The luminescence and excited state electron transfer reactions of (dppe)Pt S2C2(2-pyridine(ium))(H) and (dppe)Pt S2C2(4-pyridine(ium))(H) are dependent on the protonation state of the pyridine [30-35]. The switching on of the luminescence in these compounds results from a change in the ordering of the electronic transitions in the pyridine and pyridinium substituted complexes. Unlike the quinoxaline-substituted complexes, the neutral pyridine complexes have a lowest lying d-to-d transition, which leads to rapid nonradiative decay of the ILCT excited states. However, upon protonation the ILCT becomes the low-lying transition. The pyridinium complexes are room temperature lumiphores with emission from ILCT and ILCT excited states (see Table Ic). 

The electrophilic character of the dienyl iron tricarbonyl complex 65 as such [109] or masked in the form of the labile pyridinium complex 64 [110] was exploited to label several enzymes in aqueous medium. Nucleophilic addition of the imidazole of histidine residues and/or the primary amine of lysine residues (depending on their accessibility) was shown to occur by spectroscopic methods (Scheme 6.17). 

A related procedure involves the diacylation of water by the pyridinium salts of acyl halides to afford anhydrides (Eq. 4). The reaction was earlier described by Minunni to involve an acyl pyridinium complex. 

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