Pyridines iodination

A Fischer reagent had been made with pyridine, iodine, sulphur trioxide and formamide, instead of methanol. The bottle detonated after being stored for a couple of months. The authors put it down to the decomposition of formamide into ammonia and carbon oxide, which created the overpressure that caused the bottle to detonate. 

Lithium iodide is the electrolyte in a number of specialist batteries, especially in implanted cardiac pacemakers. In this battery the anode is made of lithium metal. A conducting polymer of iodine and poly-2-vinyl pyridine (P2VP) is employed as cathode because iodine itself is not a good enough electronic conductor (Fig. 2.3a). The cell is fabricated by placing the Li anode in contact with the polyvinyl pyridine-iodine polymer. The lithium, being a reactive metal, immediately combines with the iodine in the polymer to form a thin layer of lithium iodide, Lil, which acts as the electrolyte ... 

This preparation illustrates an efficient two-step process for the transformation of a cycloalkenone to the corresponding a-substituted derivative. The first step involves the installation of an a-iodo substituent by a process thought to involve nucleophilic addition of pyridine, iodine capture of the resulting enolate, and pyridine-promoted elimination of pyridine.5 The resulting vinyl iodides are superior to other vinyl halides as participants in a variety of transition-metal catalyzed coupling reactions, illustrated here by the Suzuki coupling with an arylboronic acid. Other coupling partners that... 

One mole of iodine will consume 2 x 96 485 coulombs of electricity. The Karl Fischer titration is widely used for the determination of water in pharmaceuticals. Quantitation in this case is not based on the total amount of current which flows through the solution but the reduction of iodine is simply used to indicate the endpoint of the titration. The reagent consists of mixture of anhydrous methanol, anhydrous pyridine, iodine and sulphur dioxide. The equation for the reaction of water with the reagent looks complicated (see below)... 

Ma and Wu [152] have carried out SERS studies on pyridine-iodine charge-transfer complex on pc-Ag electrode. 

Excess pyridine, iodine, and methanol are required for quantitative consumption of water. Sulfur dioxide reduces iodine quantitatively in the presence of excess water. The excess iodine present in the mixt makes a visual detn of the end point difficult. Therefore, the endpoint can be detnd electrometri-... 

At room temperature pyridines react reversibly with halogens and interhalogens, e.g. IC1, to give unstable adducts, which behave as mild halogenating agents. X-Ray diffraction studies of the pyridine-iodine complex have given its structure (73). 

The molar enthalpies of complexation of pyridine with iodine are - 36 kJ mol-1 (CC14) and - 34 kJ mol 1 (C6H12) by calorimetry, with corresponding values of - 33.1 and - 34.6, respectively, using the UV absorbance of the pyridine/iodine complex (84JCS(P2)731, 87JCS(P2)1713). For 2,6-dimethylpyr-idine the complex formation constant is reduced considerably from that for pyridine itself (from 106 to 46 in cyclohexane), but the enthalpy of formation remains sensibly constant, and thus independent of steric considerations. 

Examination of the Py-MS results may provide some understanding of the variation observed between the different maceral types. A distribution pattern of the type shown in Table III has been determined for a select number of macerals which also have been reacted in the pyridine-iodine mixture. In examining the three different possible cases for activation of coal maceral benzylic groups, [1] and possibly [3] would appear to be the most important. From the Py-MS results alkyl pyridines have been found to be much less abundant than alkyl phenols which is not surprising considering the percentage of oxygen compared to... 

Formamide. Bottles containing a modified Karl Fischer reagent (pyridine, iodine, and sulfur trioxide) with formamide replacing methanol developed gas pressure during several months and exploded.6... 

Bis(pyridine)iodine(I) tetrafluoroborate (IPy2BF4) is a mild source of electrophilic iodine. 1 -Bromo- 1-alkynes react stereoselectively with this reagent, in presence of a nucleophile, to give 65-80% of 2-functionalized 1-bromo-1-iodo-l-alkenes (equation 61)515. 

Many reagents convert primary amines into nitriles. Some of these have been mentioned above and represent serious limitations on methods for generating carbonyl compounds. Other ways of oxidizing amines to nitriles are the use of nickel peroxide,lead tetraacetate," copper(I) chloride plus oxygen and pyridine," iodine pentafluoride and benzeneseleninic anhydride. double bromination-dehy-drobromination can be effected for the preparation of nitriles with 2 equiv. of NBS and trimethyl-amine. Likewise, fluorination and elimination of HP gives nitriles." ... 

As for many other nucleophiles, the nitrite anion undergoes addition to the iodonium ion generated by the reaction of alkenes and 1,3-alkadienes with electrophilic iodine reagents. Two procedures have been described bis(pyridine)iodine(I) tetrafluoroborate136,137 [prepared from mcrcury(II) oxide and tctrafluoroboric acid supported on silica gel and pyridine on dichloromethane] and copper(II) tetrafluoroborate [prepared from copper(II) oxide and te-trafluoroboric acid] and iodine138 139. trans Addition would be expected for all products from mechanistic considerations, however, only the cyclohexene adduct 1 has been shown to have trans configuration ( H-NMR spectroscopy)139. 

In a mixture of 20 mL of dioxane and 10 mL of H20 are dissolved 1.38 g (20 mmol) of NaN02 and 0.54 g (5 mmol) of 1,3-cyclooctadiene, then 1.86 g (5 mmol) of bis(pyridine)iodine(I) tetrafluoroborate are added. After 15 min of stirring at r.L, the solution is extracted with CH2CI2, dried with anhyd Na2S04 and evaporated under reduced pressure to leave the crude product in 60% yield, containing 15% of 1 -nitro-1,3-cyclooctadiene by H-NMR analysis. 

Bis(pyridine)iodine(I) tctr lodinations. Good >1 from the parent enaminooe peptides with this reagent 1 Reaction with alkynes. simultaneously introducing sulfides undergo cyclizatkx... 

P(C3H3N)]C1 or mCsHsNiai Monopyridineiodine(I) chloride or chloro(pyridine)iodine-(I), 7 176... 

Several new methods for the preparation of 1-haloalkynes have been described. High yields of bromo compounds, e.g. 28, are obtained by treatment of alkynes with triphenylphosphine/carbon tetrabromide, or with a concentrated aqueous solution of potassium hypobromite and potassium hydroxide (equation 1). 1-Iodoalkynes are produced from terminal alkynes and bis(pyridine)iodine(I) tetrafluoroborate in methanol in the presence of sodium methoxide (equation 2) or from alkynes with a mixture of iodine, potassium carbonate, copper(I) iodide and tetrabutylammonium chloride under phase-transfer catalysis. Lithium acetylides 29 (R = Ph, t-Bu, HOCH2 etc.) react with zinc iodide and bis(trimethylsilyl) peroxide to yield 1-iodoalkynes. The method has been... 

A typical rechargeable battery based on this idea has been constructed. It uses the [Ni(TTL)]a, polymer as the anode, poly-2-vinyl-pyridine-iodine (P2VP (x/2)l2) (68) complex as the cathode, and aqueous KI solution as the electrolyte solution (Equation 13). In the discharging process, electrons flow from the anode [Ni(TTL)]a to the cathode P2VP (x/2)l2 through the load circuit the iodide (or polyiodide) ions formed at the cathode then enter the electrolyte while an equivalent amount of iodide ions from the electrolyte solution intercalate into the oxidized metal tetrathiolene polymer (anode). The electrolyte concentration is therefore conserved. Upon recharging with an opposite... 

The high regioselectivity of this reaction is the result of the formation of pyridine-iodine complexes 5, in which electrophilicity of the a-carbons in pyridine ring is signihcantly amplihed, which in its turn governs the formation of 2-fluoropyridines over the other isomers (Scheme 6.3). 

---