Phosphorus pentachloride, replacement

Treatment of dehydroepiandrosterone (13-3) with phosphorus pentachloride replaces the hydroxyl at position 3 with retention of configuration (13-4). It had been established prior to this work that catalytic reduction of unsaturation in steroids proceeds almost invariably from the bottom side to afford reaction products as their 5a epimers, as for example... 

Phosphorus pentachloride Replacement of alcohol groups by chlorine... 

Phosphorus oxide chloride phosphorus pentachloride Replacement of hydroxyl by chlorine s. 7, 585 9, 634 pyridine derivatives s. H. M. Wuest et al Chlorides from N-oxides... 

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 ... 

Assemble in a fume-cupboard the apparatus shown in Fig. 67(A). Place 15 g. of 3,5-dinitrobenzoic acid and 17 g. of phosphorus pentachloride in the flask C, and heat the mixture in an oil-bath for hours. Then reverse the condenser as shown in Fig. 67(B), but replace the calcium chloride tube by a tube leading to a water-pump, the neck of the reaction-flask C being closed with a rubber stopper. Now distil off the phosphorus oxychloride under reduced pressure by heating the flask C in an oil-bath initially at 25-30, increasing this temperature ultimately to 110°. Then cool the flask, when the crude 3,5-dinitro-benzoyl chloride will solidify to a brown crystalline mass. Yield, 16 g., i.e,y almost theoretical. Recrystallise from caibon tetrachloride. The chloride is obtained as colourless crystals, m.p. 66-68°, Yield, 13 g Further recrystallisation of small quantities can be performed using petrol (b.p. 40-60°). The chloride is stable almost indefinitely if kept in a calcium chloride desiccator. 

Pyrazolesulfonic acids, like (493), have high melting points (Table 24) and probably exist as the zwitterions (497). They are very stable to hydrolysis and only afford pyrazolones at high temperatures. The replacement of the SO3H group by bromine has also been reported (B-76MI40402). Pyrazole-3-, -4- and -5-sulfonic acids react with phosphorus pentachloride to form sulfonyl chlorides. 

Hydroxy and mercapto substituents at the 3- and 5-positions can also exist in tautomeric forms (see Section 4.01.5.2) and can be alkylated at either the substituent or the ring nitrogen atom. 3-Methoxy groups are not replaced by nucleophiles, but both 3- and 5-alkylthio groups react readily, as does 3-methoxy-l,2-benzisothiazole. Alkylthio compounds can be oxidized to sulfoxides and sulfones, and the latter readily undergo nucleophilic replacement. All the hydroxy compounds react with phosphorus pentachloride to give the chloro derivatives. 

In a 2-1 three-necked flask equipped with a stirrer, a reflux condenser, and a dropping funnel (Note 1) 832 g (4 0 moles) of phosphorus pentachloride is stirred with 250 ml. of phosphorus oxychloride (Note 2) To this is added with stirring 264 g (272 ml, 4 4 moles) of methyl formate (Note 3). During the addition the reaction vessel is cooled in an ice bath to maintain a reaction temperature of 10-20° The addition requires about 1.75 hours When the addition is complete, the solution is stirred at a temperature under 30° until all the phosphorus pentachloride has dissolved (about 1 hour) Then the stirrer is removed, the reflux condenser is replaced by a distilling head, and the reaction... 

Reductive removal of halogen substituents has been of value in the synthesis of pyrimidines and purines since the time of Fisher (1899). Natural purines were de-oxygenated in a sequence of reactions involving the replacement of hydroxyl by chlorine through the reaction with phosphorus pentachloride and the reduction using zinc dust and water [152], 2-Chloropurines 45 are not reduced under these conditions. The 2-iodopurines are however reduced by zinc and water [152]. The elec-... 

In a 5-L, three-necked, round-bottomed flask equipped with a rubber- or mercury-sealed mechanical stirrer and a reflux condenser carrying a drying tube are placed 340 g. (4 moles) of cyanoacetic acid (Note 1) and 2 1. of anhydrous ether. To the stirred solution, 834 g. (4 moles) of phosphorus pentachloride is added in portions through the third neck of the flask, which is sealed between additions. The mixture is cooled occasionally with an ice bath to prevent excessive refluxing, and, after the addition is complete, stirring is continued for 0.5 hour or until the phosphorus pentachloride dissolves completely. The reflux condenser is removed and replaced with apparatus for downward distillation (Note 2), and the ether is distilled from a water bath at 50-60° (Note 3), after which most of the phosphorus oxychloride is removed at reduced pressure (20-25 mm. with a bath temperature of 55-65°) (Note 4), the receiver being cooled in an ice-salt bath. The red, oily residue is dissolved in 200 ml. of benzene and the benzene and residual phosphorus oxychloride distilled under reduced pressure. This operation is repeated with 200 ml. of fresh benzene to ensure complete removal of phosphorus oxychloride (Note 5). The residue is then cooled to room temperature (Note 6) and is transferred to a 500-ml. pressure-... 

There have been several further examples of the replacement of hydroxyl or oxo substituents with halogens in 1,7-phenanthrolines using phosphorus halides or oxyhalides.96,169-171,215 In 4,10-dioxo-l,4,7,10-tetrahydro-1,7-phenanthroline (100) there are marked differences in the ease with which the two oxo groups are replaced by halogen.171 With 1 mole of phosphorus pentachloride, the product is 4-chloro-10-hydroxy -... 

Replacement of the carbonyl function by two chlorines occurs with phosphorus pentachloride in ether ... 

Carboxylic acids react with phosphorus trichloride, phosphorus pentachloride, or thionyl chloride with replacement of OH by Cl to form acyl chlorides, RCOC1 ... 

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