Phosphorus pentachloride chlorination

When unsubstituted, C-5 reacts with electrophilic reagents. Thus phosphorus pentachloride chlorinates the ring (36, 235). A hydroxy group in the 2-position activates the ring towards this reaction. 4-Methylthiazole does not react with bromine in chloroform (201, 236), whereas under the same conditions the 2-hydroxy analog reacts (55. 237-239. 557). Activation of C-5 works also for sulfonation (201. 236), nitration (201. 236. 237), Friede 1-Crafts reactions (201, 236, 237, 240-242), and acylation (243). However, iodination fails (201. 236). and the Gatterman or Reimer-Tieman reactions yield only small amounts of 4-methyl-5-carboxy-A-4-thiazoline-2-one. Recent kinetic investigations show that 2-thiazolones are nitrated via a free base mechanism. A 2-oxo substituent increases the rate of nitration at the 5-position by a factor of 9 log... 

Phosphorus pentachloride See Phosphorus pentachloride. Chlorine dioxide... 

Phosphorus and chlorine combine directly to form either the trichloride or the pentachloride depending on the relative amounts of phosphorus and chlorine used. 

Phosphorus trichloride reacts with chlorine in excess to give phosphorus pentachloride, an equilibrium being set up ... 

However, phosphorus pentachloride in the solid state has an ionic lattice built up of (PC ) and (PClg)" ions and these ions are believed to exist in certain solvents. Thus under these conditions the maximum covalency is reached with chlorine. In phosphorus pentabromide, PBrj, the solid has the structure [PBr4] [Br] . 

Phosphorus pentachloride is prepared by the action of chlorine on phosphorus trichloride. To push the equilibrium over to the right, the temperature must be kept low and excess chlorine must be present. Hence the liquid phosphorus trichloride is run dropwise into a flask cooled in ice through which a steady stream of dry chlorine is passed the solid pentachloride deposits at the bottom of the flask. 

The replacement of the —OH group by a chlorine atom (reaction 9.4) is a very general reaction of phosphorus pentachloride. For example, if concentrated sulphuric acid is written as (H0)2S02 then its reaction with phosphorus pentachloride may be written ... 

Treatment of a-thiocyanatoketones at low temperature with dry hydrogen chloride in ether solution gives satisfactory yields of 2-chloro-thiazole derivatives (188). The use of phosphorus pentachloride leads to the same results, but in this case chlorination can also occur at the 5-position (Scheme 97) (18, 68). 

Chlorine dioxide Ammonia, carbon monoxide, hydrogen, hydrogen sulflde, methane, mercury, nonmetals, phosphine, phosphorus pentachloride... 

Phosphorus pentachloride Aluminum, chlorine, chlorine dioxide, chlorine trioxide, fluorine, magnesium oxide, nitrobenzene, diphosphorus trioxide, potassium, sodium, urea, water... 

Direct chlorination of 3,6-dichloropyridazine with phosphorus pentachloride affords 3,4,5,6-tetrachloropyridazine. The halogen is usually introduced next to the activating oxo group. Thus, 1,3-disubstituted pyridazin-6(l//)-ones give the corresponding 5-chloro derivatives, frequently accompanied by 4,5-dichloro compounds as by-products on treatment with chlorine, phosphorus pentachloride or phosphoryl chloride-phosphorus pentachloride. 

Analogous chlorinations with phosphorus pentachloride proceed in higher yield and at lower temperature [61] (equation 46). 

Chloroquinazoline can be isolated, at best in 40% yield, by boiling 2-hydroxyquinazoline with phosphorus pentachloride in phosphorus oxychloride for 45 min, and attempts to improve this yield have proved fruitless. The yields are much higher when an aryl group is in position 4 w hich suggests an attack of the 3,4-double bond in 2-hydroxy- and 2-chloro-quinazolines by the chlorinating agent. 

Dihydro-l-oxo-3,4-benz-j8-carboline (166) reacted with phosphorus oxychloride and one mole of phosphorus pentachloride at 110° to give l-chloro-3,4-benz-j8-carboline (264). When, however, more than one mole of phosphorus pentachloride was used 265 was obtained, presumably by chlorination of 264. This chlorinating action of phosphorus pentachloride is analogous to that observed when an... 

The formation of the dichlorides is aided by increased temperature (60-80°C) and by an excess of PCI5 (2-2.3 moles/mole of 4-acetylpyrazole). With a larger excess of PCI5, further chlorination of the compounds occurs. With 3 moles of phosphorus pentachloride at 80°C in benzene, ketones 12a-d gave pyrazolyl-trichloroethylenes 16a-d in 75% yield. Then dichlorides 17a-d were converted quantitatively into pyrazolyltrichloroethylenes 16a-d in 1 h under the same conditions. 

In addition, it was clear that the presented scheme does not exhaust all the possible paths of anomalous chlorination. Thus, 4-acetyl-l,3,5-trimethylpyrazole with 4-5 moles of phosphorus pentachloride gave mainly 4-Q ,/3-dichlorovinyl-5-chloromethyl-l,3-dimethylpyrazole, and its precursor (according to GLC data) was the dichloride. It could be possible that in the case of 4-chlorovinyl derivatives of pyrazole the chlorination at the p position is facilitated by the electron-donating characteristics of the 4-pyrazolyl radical (86TH1). 

Thus, depending on the conditions, the reaction of methylpyrazolylketones with phosphorus pentachloride leads to products from substitution of the carbonyl oxygen by chlorine, o, /3-dichlorovinylpyrazoles, that can be dehydrohalo-genated with sodium amide to ethynylpyrazoles or to Q ,/3-dichloroethylenes. The... 

Dichloromethyl methyl ether has been prepared by the chlorination of chlorodimethyl ether in the liquid5-4 or gas phase,5 by the reaction of chlorodimethyl ether with sulfuryl chloride and benzoyl peroxide,6 7 and by the treatment of methyl formate with phosphorus pentachloride.8-10... 

Treatment of phthalocyaninesulfonic or -carboxylic acids with chlorinating agents such as phosphorus pentachloride or thionyl chloride leads to the corresponding acid chlorides, e.g. 7. 

Oxidative chlorination of 1,10-penanthroline using excess phosphorus pentachloride and phosphoryl chloride gave rise to high yields of products chlorinated meta and para to the annular nitrogens (92BCJ2007). 

In the Meisenheimer reaction of quinoline 1-oxides chlorine atoms usually enter the 2-and 4-positions, but not exclusively. 2,4-Dibromoquinoline 1-oxide was 6-chlorinated (57MI1), and the 5- and 6-nitroquinoline 1-oxides were 3-chlorinated to some extent (44JOC302). This reaction with phosphoryl chloride-phosphorus pentachloride has also been used in the preparation of chlorinated phenanthrolines (88YZ1148). 

Sometimes lateral chlorination can occur on a methyl or alkylthio substituent, especially when phosphorus pentachloride or its mixtures with phosphoryl chloride are used (91JHC1549). Reactions of 2-methyl-4(I//)-quinoline (67) exemplify this behavior (81CPB1069) (Scheme 31) 2-chloro-3- and -4-methyquinolines are also subject to methyl chlorinations by similar reagents (91JHC1549). Sulfuryl chloride and NCS are also likely to induce a proportion of lateral chlorination (83KFZ1055 86S835). 

Chlorination. When 75 was treated with chlorine in the presence of aluminium chloride, initial chlorination took place at the 5-position, but the reaction was rather unselective 5,8-di-, 5,7,8-tri-, and 5,6,7,8-tetra-chloroisoquinolines were also formed (64JOC329). Perchlorination has been achieved by initial reaction of the isoquinoline-aluminium chloride complex with chlorine, as above, followed by treatment with phosphorus pentachloride at 270°C in an autoclave [66JCS(C)2328]. Treatment of 1,8-dimethylisoquinoline with NCS gave the 5-chloro derivative (91NKK-1193). Meisenheimer reaction of isoquinoline 2-oxides with phosphoryl chloride gave 1-chloroisoquinoline (84MI2). 

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