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[en] We have introduced a new, effective and direct multihalogenations of 2,2',5',2"-terthiophene under mild and ambient conditions using 2-halo-4,5-dichloropyridazin-3(2H)-ones. The present system is a rapid and facile methods. 2-Halopyridazin-3(2H)-ones are easily prepared from 4,5-dichloropyridazin-3(2H)-one, which is commercially available, stable, and reusable. We envision more useful cascade multihalogenation of oligothiophenes or compounds involving terthiophene moiety, and efforts in this direction are under way. Recently, we demonstrated utility as synthetic auxiliaries of 2-substituted-pyridazin-3(2H)-ones due to pyridazin-3(2H)-ones are inexpensive, stable and easily prepared heterocycles. 2-Halopyridazin-3(2H)-ones were also developed as useful and eco-friendly electrophilic halogenating agents. Since pyridazin-3(2H)-ones have some advantages involving the formation of stable anions and the electron acceptable moiety, we explored the application of 2-halopyridazin-3(2H)-ones for the halogenation of electron rich compounds as electrophilic halogen sources
[en] Graphical abstract: The presence of one halogen opposite the N results in strong attraction between P and N. This force is little affected by identity of Y atoms, whether H or halogen. Highlights: → Strong attractive force directly between trivalent P and N atoms. → P...N force is unlike H-bonds or halogen bonds, but stronger than both. → Multiple halogenation beyond a single atom on P slightly weakens the interaction. - Abstract: The attractive noncovalent interaction of a P atom with N is derived primarily from two sources. Charge transfer from the N lone pair into the σ* antibonding orbital of a P-X bond that is turned away from the N atom combines with attractive Coulombic forces. As in the case of H-bonding, which is parallel in some ways to P...N attraction, placement of an electron-withdrawing substituent on the P atom enhances both of these components, and strengthens the overall interaction. However, in stark contrast with H-bonding, halogenation beyond monosubstitution does not lead to any further strengthening of the P...N noncovalent bond. Indeed, di and tri-substitution lead to small reductions in the interaction energy. In all cases, the geometry which contains a P...N bond is more stable than other candidate structures, some of which contain hydrogen or halogen bonds.
[en] Because of a moderate reaction rate, it is possible to determine the course of the sequential electrophilic halogenation of 1-SB9H9. The directive effect of the sulfur heteroatom does not correlate with the ground-state charge distribution of 1-SB9H9. It appears that initial attack is at the 6 position instead of the anticipated 10 position. In the care of monobromination and monoiodination there is a significant degree of rearrangement to also give the thermodynamically more stable 10 isomer in the reaction mixture (ΔH/sub isomerization/ = 6.8 kcal/mol). Only the 6 isomer results from monochlorination. Rearrangement is also a significant factor as halogenation becomes more extensive. The initial halogenation of SB11H11 is analogous to that of 1-SB9H9. The site of initial deuteration was not established clearly, but under forceful conditions deuteration was not complete and 6,7,8,9,10-D5-1-SB9H4 and 7,8,9,10,11,12-D6-1-SB11H5 were obtained
[en] This paper reports that conventional halogenation reactions involving f elements typically employ high-temperature conditions. Recent synthetic techniques use halogenation agents that are either inherently reactive or have been activated by physical methods such as photolysis. These techniques allow lower temperature syntheses. Consequently, they have significant advantages with respect to safety, material compatibility, and accountability, as well as providing routes to thermally unstable materials
[en] with respect to the great importance of radioiodine labelled compounds as diagnostics in nuclear medicine, practically carrier-free iodination methods have been examined for aliphatic and aromatic compounds. the nuclides used often are the cheaply available iodine-131 (T1/2 = 8.04 d) and the neutron deficient iodine -123 (T1/2=13.2 h) which is very interesting for in vivo applications. the nucleophilic substitution reaction has been used for isotopic and non-isotopic exchange of halogen in long chain fatty acids such as 17- iodo - heptadecanoic acid and 16-bromo - hexadecanoic acid. an exchange of 123 I-for-I in 17- iodo - heptadecanoic acid was achieved with 80% radiochemical yield within 30 min.in refluxing in acetone . in 16-bromo-hexadecanoic acid a yield of 75% was only attained after 8 hours by I-for - Br exchange in acetone as a solvent. by this non-isotopic exchange , however, a high specific activity of of about 300 Ci/m.mole is obtained