Pyridine, pentachloro

Treatment of sucrose with sulfuryl chloride in pyridine at 50° afforded443 a complex mixture of products from which were isolated, in low yields, one tetrachloro and two pentachloro derivatives. 

Potassium Pentachloro-pyridino-iridite, [Ir pyCl5]K2, is prepared by heating a mixture of potassium hexachloro-iridite, [IrCl6]K3, and pyridine at 100° C. It is a reddish-brown salt which forms an orange-coloured solution in water, and on heating with chlorine yields pentachloro-pyridino-iridic acid, [Ir pyCljjH. 

The analogous pyridine compound, [Pt pyCl5]K, potassium pentachloro-pyridino-platinate, has been prepared.2 It crystallises in silky yellow needles. Bromine acts upon the salt, with formation of the corresponding pentabromo-derivatives. 

From these observations it was concluded that the major products of the reduction of niobium(V) chloride with anhydrous pyridine were tetrachlorodi-(pyridine)niobium(IV) and l-(4-pyridyl)pyridinium dichloride. Oxidation-reduction titrations indicated that this reduction accounted for approximately 70% of the reaction products. In view of the rapid reaction of tantalum(V) halides with pyridine to form 1 to 1 adducts, it was assumed that the remaining 30% of niobium (V) which was not reduced was present in the reaction mixture as pentachloro(pyridine)niobium(V). On this basis the following over-all reaction is proposed ... 

The only alkyl group reported as reductively removed is the di-phenylmethyl substituent from N3 in compound 165.153 Deoxygenation of N-oxides can be done thermally (heating in toluene with oxygen transfer to solvent) for compounds of type 166,44 or more commonly by use of phosphorus derivatives, as described for compounds 32, 33,45 166,44 and 167.61 Halogens can be reductively removed from [l,2,3]triazolo-[4,5-6]pyridines 160,146 168,220 and 169,142 and from pentachloro derivative 164, giving dichloro compound 170.208 Removal of thiol groups by reduction... 

Pentafluoropyridine (292) is reduced440 in dry DMF at a mercury cathode to perfluoro-4,4 -bipyridyl (293) in the presence of hydroquinone as proton donor, 2,3,5,6-tetrafluoropyridine (294) is obtained [Eq. (150)]. Pentachloro-pyridine gives on reduction in dry DMF very little bipyridyl derivative, but tetrachloropyridine and bis(tetrachloropyridyl) mercury. 

TABLE 21. Extent of the PT of pentachloro-phenol pyridine complexes in... 

Determined by H NMR of crude products refers to the relationship between the pyridine ring and the larger number of alkyl groups or the highest priority group. Product contains traces of pentachloro-l-(2-pyridyl)cyclopropane. 

When chlorinated with an excess of phosphorus pentachloridc, 5,8-dichloropyrido[2,3-rf]pyridazine affords, dependent on the reaction temperature and time, the corresponding 3,5,8-trichloro, 2,3,5,8-tetrachloro or2,3,4,5,8-pentachloro derivatives 3, 4, and 5, respectively. The facility of introduction of a chloro substituent into the pyridine part decreases thus in the order position 3 > 2 > 4.8 7... 

The Michaelis-Arbuzov-like coupling of aryl bromides and tris(trimethylsilyl) phosphite occurs quite quickly in the presence of NiCl2 at 150 for pentachloro- and pentafluoro-pyridines, the coupling takes place at the 4-position, but the presence of a CN... 

Heteroaromatic Polyhalogeno-compounds.—Rate constants for the reactions of various polyfluoro- and chloropolyfluoro-pyridines with ammonia in dioxan-water have enabled the separate effects of fluorine and chlorine atoms that are ortho, meta, and para to the reaction centre to be determined. In each case the order is ortho > meta > para for fluorine, 31 23 0.26 and for chlorine, 86 24 6.9, both sequences being relative to a hydrogen atom at the same position. Both pentafluoro- and pentachloro-pyridine undergo Arbusov reactions at C-4 with (EtO)3P, the chloro-compound also giving the 2,4-bis(diethoxyphosphinyl) derivative. 3-Chloro-2,4,5,6-tetrafluoro- and 3,5-dichloro-2,4,6-trifluoro-pyridines are readily converted into the corresponding 4-iodo-compounds with Nal and DMF. ... 

Heterocyclic Thiols.—Representative synthetic methods described in the recent literature cover the synthesis of tetrachloropyridine-2-thiol from pentachloro-pyridine A -oxide and thiourea, the synthesis of 2-phenylthiazole-5-thiols from the S -acetyl compounds, and syntheses of 4-phenyl-l,2-dithiolan-3-... 

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