SYNTHESIS OF 1-IODOHEPTANE

o-Phenylene phosphorochloridite:

• Place llOg (1.0 mol) of catechol (pyrocatechol) in a 500-ml three-necked flask supported on a water bath and moisten it with about 2 ml of water. 

• Equip the flask with an efficient mechanical stirrer, a large double surface reflux condenser and a 250-ml dropping funnel. 

• Connect the mouth of the condenser to an efficient gas absorption trap. 

• Add 206 g (131 ml, 1.5 mol) of phosphorus trichloride from the dropping funnel during 1 5 minutes with vigorous stirring. 

• There is a brisk evolution of hydrogen chloride and the contents of the flask soon solidify, stopping the stirrer. 

• Leave the reaction mixture standing at room temperature for 1 hour, and then heat the water bath to boiling. 

• The solid mass soon melts and stirring again becomes possible. 

• Continue to heat on the boiling water bath with stirring for 2 hours. 

• Arrange the flask for distillation under reduced pressure (water pump); insert a trap cooled in an acetone-Cardice mixture between the receiver and the pump. 

• Distil the product and collect the o-phenylene phosphorochloridite as a fraction of b.p. 98°C/25mmHg (91 °C/ 18mmHg). The yield is 165g (95%); the product crystallises in the refrigerator, m.p. 30 °C. About 50 g of unreacted phosphorus trichloride is collected in the trap.

Heptyl o-phenylene phosphite:

• Place 87.0 g (0.5 mol) of o-phenylene phosphorochloridite, 39.5 g (0.05 mol) of dry redistilled pyridine and 500 ml of dry ether, in a 2-litre conical flask and cool to 0°C. 

• Add 58.1 g (0.5 mol) of heptan-1-ol dissolved in 400 ml of dry ether during about 5 minutes with occasional shaking. 

• Stopper the flask and allow the reaction to proceed at room temperature overnight. 

• Filter off the precipitated pyridinium chloride under suction, wash well with dry ether and remove the ether from the combined filtrate and washings on a rotary evaporator to obtain 127.0 g (100%) of heptyl o-phenylene phosphite as a colourless oil of sufficient purity for use in the next stage.

1-Iodoheptane:

• In a conical flask, stir magnetically at room temperature a solution of 50.9 g (0.20 mol) of heptyl o-phenylene phosphite in 500 ml of dry dichloromethane and add 50.8 g (0.20 mol) of iodine. 

• After 1 hour (1) transfer the solution to a separatory funnel and wash the organic layer with 400 ml of 10 per cent aqueous sodium thiosulphate solution to remove any residual unreacted iodine. 

• Wash the organic layer twice with 400 ml portions of 5 per cent aqueous sodium hydroxide solution to remove the o-phenylene phosphoroiodate by-product, followed by two 400 ml portions of 5 per cent aqueous sodium metabisulphite, and finally with 400 ml of a saturated solution of sodium chloride. 

• Dry the organic layer with anhydrous calcium sulphate, filter and remove the solvent on a rotary evaporator. The yield of crude 1-iodoheptane is 41.8 g (92%). 

• Fractionally redistil the product under reduced pressure using a nitrogen capillary leak when 39 g (86%) of the pure material having b.p. 96-104 °C/46-48mmHg is obtained.

Notes to keep in mind:

1. The reaction may be monitored by g.l.c. by the direct loading of a sample (0.1 pi) on to an S.E. 30-column, 1.5 m, held at 170 °C (nitrogen flow 40 ml/minute). The retention time of 1 -iodoheptane is 52 seconds; that of heptyl o-phenylene phosphite under the same conditions is 4 minutes.