Preparation of Alkyl Iodides

Introduction. When phosphorus trichloride reacts with an alcohol, a chloride is formed. In the same manner when iodine is added to a mixture of red phosphorus and an alcohol, phosphorus triodide is first formed which reacts with the alcohol to give the halide  

The reaction between alcohol and phosphorus halide may proceed in another direction  

The compmmd formed may be called methyl phosphite by analogy to sodium phosphite, or better, phosphorus methoxide. In order to keep the rate of side reactions as slow as possible, it is necessary to add the iodine in small portions and to keep the temperature in the beginning below 20°. 

Add a minute drop of mercury to keep the product colorless. 

---

The small capacity apparatus is especially recommended for the use of students the consumption of iodine by a large class of students is not unreasonably high. Larger apparatus, e.g., 60 ml. and 100 ml. capacity holding 100 g. and 200 g. respectively of iodine, are generally preferred for routine preparations of alkyl iodides the bolt-head flask should then be of 250 or 500 ml. capacity. Thus for n-butyl iodide a typical preparation would employ 120 g. (148-5 ml.) of n.butyl alcohol, 21 75 g. of red phosphorus, and 200 g. of iodine. 

The preparation of alkyl iodides by the phosphorus and iodine method is described in an earlier volume of Organic Syntheses,5... 

The most widely used example of halogen exchange is provided by the preparation of alkyl iodides from chlorides or bromides using sodium iodide in a... 

Alkyl iodides (10, 212). The original procedure for preparation of alkyl iodides from triallyboranes (equation I) is limited to a yield of 66% based on the alkene. The... 

The exchange of chlorine or bromine atoms for iodine is an important method for the preparation of alkyl iodides. In general, the reactivity of... 

Because during the reaction the authors observed the transient back formation of the corresponding free alcohol R l-OH, they demonstrated that the reaction can be performed one-pot from 1-chloroethyl chloroformate, alcohol and Nal, thus discovering a new preparation of alkyl iodides as shown in scheme 75. 

Olah, G. A., Narang, S. C., Field, L. D. Synthetic methods and reactions. 103. Preparation of alkyl iodides from alkyl fluorides and chlorides with iodotrimethylsilane or its in situ analogs. J. Org. Chem. 1981,46, 3727-3728. 

Clark, J. H., Jones, C. W. The preparation of alkyl iodides from alkyl chlorides and bromides using potassium iodide supported on alumina. J. Chem. Res., Synop. 1990, 39. 

The nucleophile can also act as a leaving group, or vice versa. This problem is especially severe with reactions involving I, which is both an excellent nucleophile and an excellent leaving group. The preparation of alkyl iodides such as 2-iodobutane in enantiopure form is difficult for this very reason. 

Stone and Shechter have developed high-yield procedures for the preparation of alkyl iodides from alcohols, ethers, and olefins by reaction with a reagent described as 95% orthophosphoric acid in combination with potassium iodide. For the conversion of 1,6-hexanediol into 1,6-diiodohexane, a mixture of 65 g. of P2O5 and 231 g. (135 ml.) of 85% phosphoric acid is stirred mechanically and let cool to room temperature, potassium iodide and 1,6-hexanediol are added, and the mixture is stirred and heated as indicated. The initially homogeneous solution separates into... 

The constant-boiling aqueous solution of hydriodic acid can be conveniently used for the preparation of alkyl iodides. The solution contains about 57 per cent of hydriodic acid, boils at 127°, and has the specific gravity of 1.68 to 1.70. The exact composition varies with the pressure at which the acid is distilled. The... 

General procedure for preparation of alkyl iodides from (C6H50)3PCH3I 957 The appropriate alcohol (1 mole) is added cautiously to the crude iodide (1 mole) cooling is necessary for reactive alcohols. The method of working up is suited to the properties of the alkyl iodide ... 

Alkyl iodides (3, 160). The preparation of alkyl iodides by reaction of trialkylboranes with iodine and a base is improved by use of sodium methoxide in place of sodium hydroxide. Two groups on boron react rapidly in the case of trialkylboranes derived from terminal olefins, the third group also reacts, but more slowly (24 hr.). ... 

---