Phosphorus pentachloride bonding

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. 

B. Reactions.—This year has seen the publication of a number of papers on the reactions of olefins and acetylenes with phosphorus pentachloride, to produce new phosphorus-carbon bonds. An investigation into the structural requirements of trisubstituted olefins (40) undergoing the above reaction has shown that both steric and electronic factors are important, e.g. an adduct forms with (40 X = CH3) but no reaction occurs for (40 X = Ph). Further examples of the reactions of unsaturated ethers include the formation and decomposition of adducts from a-methoxystyrene... 

With one mole of phosphorus pentachloride, MeNHa.BFa gives a series of mixed halides (13) of which only one (/i = 1) was isolated. In each halide the fluorine atoms were shown to be bonded to boron by the appearance of iiB-isp and absence of spin-spin coupling. An analogous A-phenyl... 

There have apparently been no recent developments in reagents for desulphurizing sulphoxides that use pentavalent phosphorus compounds. Reagents that were reviewed in 1984 include phosphorus pentasulphide, thiophosphoryl bromide, Lawesson s reagent (1), and phosphorus pentachloride in the presence of a trap for CD ions. The traps used included an enamine or an N, JV-dialkylaniline. Presumably, the net effect of this reaction is to generate phosphorus trichloride in situ. The three thiophosphorus reagents obviously function because the P=S bond is some 150 kJ moD weaker than the P=0 bond . 

Kinetic studies of alkene-phosphorus pentachloride reactions in benzene show the effects of substituents when the double bond is terminal.88 When the alkene is conjugated, the standard work-up conditions (using sulphur dioxide) produce alk-1-enylphosphonyl dichlorides (103), instead of 2-chloroalkylphosphonyl dichlorides (104).87... 

The behavior of phosphorus pentachloride toward carbon-carbon multiple bonds has received considerable attention, and the procedure described represents but one example of a wide variety of derivatives of unsaturated phosphonic acids which are accessible. Indene was the first olefinic compound to be reacted... 

Exercise 16-31 Work out reasonable mechanisms for the reactions of phosphorus pentachloride and sulfur tetrafluoride with carbonyl groups. Both phosphorus and sulfur can accommodate five or more) bonded atoms, and the structure of phosphorus pentachloride in the solid state is [PCI4 ] [PCl60]. 

All these halides are gases, volatile liquids, or low-melting solids. For example, phosphorus trichloride is a colorless liquid that boils at 76°C, and phosphorus pentachloride is an off-white solid that melts at 167°C. Both fume on contact with moist air because of a reaction with water that breaks the P-Cl bonds, converting PCI3 to phosphorous acid (H3P03), and PCI5 to phosphoric acid (H3P04) ... 

A simple method for introducing a triple bond into an organic compound is to treat an appropriate dihalide with a strong base. Since vicinal dihalides (usually the bromide) are readily formed by reaction of bromine with an alkene, and geminal dihalides from aldehydes or ketones with phosphorus pentachloride, the method is a useful general procedure for the preparation of terminal and non-terminal alkynes from readily available starting materials. 

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