Iodides, alkyl from alcohols

Halogenation of an alkane is required here. Iodination of alkanes, however, is not a feasible reaction. We can make alkyl iodides from alcohols or from alkenes by treatment with HI. A reasonable synthesis using reactions that have been presented to this point proceeds as shown ... 

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... 

A special apparatus (Fig. Ill, 40,1) renders the preparation of iodides from alcohols a very simple operation. The special features of the apparatus are —(i) a wide bored (3-4 mm.) stopcock A which considerably reduces the danger of crystallisation in the bore of the tap of the iodine from the hot alcoholic solution (ii) a reservoir B for the solid iodine and possessing a capacity sufficiently large to hold all the alkyl iodide produced (iii) a wide tube C which permits the alcohol vapour fix)m the flask D to pass rapidly into the reservoir B, thus ensuring that the iodine is dissolved by alcohol which is almost at the boiling point. An improved apparatus is shown in Fig. Ill, 40, 2, a and b here a... 

Indole, sodium salt, preparation of, 54, 60 Indole, 1-benzyl, 54, 50, 58 Indoles, iV-alkyl-, 54, 58, 60 Iodides, from alcohols, methyl iodide, and triphenyl phosphite, 51, 47 ... 

Tojo and co-workers reported a one-pot synthesis of alkyl nitrates from alcohols via the alkyl iodide the alcohol is treated with a mixture of iodine, triphenylphosphine and imidazole in diethyl ether-acetonitrile, and the resulting alkyl iodide is reacted in situ with silver nitrate (Equation 3.8). Reported yields for primary alcohols are good to excellent but yields are lower for secondary alcohols. 

During the endgame of the total synthesis of the stemona alkaloid (-)-stenine, Y. Morimoto and co-workers utilized the Finkelstein reaction to prepare a primary alkyl iodide from a primary alkyl mesylate. The mesylate was prepared from the corresponding primary alcohol with MsCI/EtsN. The resulting primary alkyl iodide was used in the subsequent intramolecular N-alkylation to construct the final perhydroazepine C-ring of the natural product. 

Alkyl chlorides, from alcohols, benzyl diloride, and triphenyl phosphite, 51,47 ALKYL IODIDES NEOPENTYL IODIDE, lODOCYCLOHEX-ANE,51,44... 

Direct substitution of F for OH by means of HF has no preparative importance. All the methods of preparing alkyl fluorides from alcohols proceed in principle by way of esters the alcohol is converted into the alkyl chloride, bromide, iodide, or / -toluenesulfonate, and then the halogen atom (see page 204) or the tosyloxy group (see page 229) is replaced by fluorine. 

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 ... 

New reagents for the primary and secondary alcohol to alkyl iodide conversion, with inversion at secondary centres, are diphosphorus tetraiodide (P2I4), a well characterized and stable solid, and mixtures of triphenylphosphine with iodine and imidazole or with 2,4,5-tri-iodoimidazole. The P2I4 system also iodinates tertiary alcohols. Trimethylsilyl iodide is known to convert alcohols into iodides (2,128), and some more systems that are believed to generate trimethylsilyl iodide in situ have been found to effect the alcohol to iodide conversion (c/. 3,151). Trimethylsilyl chloride-sodium iodide in acetonitrile produces iodides from alcohols direct or from their trimethylsilyl ethers. Hexamethyldisilane-... 

The determination of alkyl chain distribution of alcohol ether sulfates can be most easily performed by gas chromatography after cleavage of the sulfated ethoxy moiety with hydri-odic acid. This procedure is similar to that described under the analysis of ethoxylated nonionic surfactants. The alkyl iodides from cleavage may also be determined by HPLC (72). An alternative approach requires the decomposition of the sulfate and ethoxy groups with the mixed anhydrides of paratoluenesulfonic and acetic acid, followed by GC determination of the alcohol acetates (73). 

Place a mixture of 0-5 g. of finely powdered thiourea, 0-5 g. of the alkyl halide and 5 ml. of alcohol in a test-tube or small flask equipped with a reflux condenser. Reflux the mixture for a j)eriod depending upon the nature of the halide primary alkyl bromides and iodides, 10-20 minutes (according to the molecular weight) secondary alkyl bromides or iodides, 2-3 hours alkyl chlorides, 3-5 hours polymethy lene dibromides or di-iodides, 20-50 minutes. Then add 0 5 g. of picric acid, boil until a clear solution is obtained, and cool. If no precipitate is obtained, add a few drops of water. RecrystaUise the resulting S-alkyl-iso-thiuronium picrate from alcohol. 

Alkyl esters of trifluoromethanesulfonic acid, commonly called triflates, have been prepared from the silver salt and an alkyl iodide, or by reaction of the anhydride with an alcohol (18,20,21). Triflates of the 1,1-dihydroperfluoroalkanols, CF2S020CH2R can be prepared by the reaction of perfluoromethanesulfonyl fluoride with the dihydroalcohol in the presence of triethylamine (22,23). Triflates are important intermediates in synthetic chemistry. They are among the best leaving groups known, so they are commonly employed in anionic displacement reactions. 

The required xanthates 1 can be prepared from alcohols 5 by reaction with carbon disulfide in the presence of sodium hydroxide and subsequent alkylation of the intermediate sodium xanthate 6. Often methyl iodide is used as the alkylating agent ... 

The elimination of HX from an alkyl halide is a very general reaction and can be accomplished with chlorides, fluorides, bromides, and iodides.Hot alcoholic... 

Alkyl esters are efficiently dealkylated to trimethylsilyl esters with high concentrations of iodotrimethylsilane either in chloroform or sulfolane solutions at 25-80° or without solvent at 100-110°.Hydrolysis of the trimethylsilyl esters serves to release the carboxylic acid. Amines may be recovered from O-methyl, O-ethyl, and O-benzyl carbamates after reaction with iodotrimethylsilane in chloroform or sulfolane at 50—60° and subsequent methanolysis. The conversion of dimethyl, diethyl, and ethylene acetals and ketals to the parent aldehydes and ketones under aprotic conditions has been accomplished with this reagent. The reactions of alcohols (or the corresponding trimethylsilyl ethers) and aldehydes with iodotrimethylsilane give alkyl iodides and a-iodosilyl ethers,respectively. lodomethyl methyl ether is obtained from cleavage of dimethoxymethane with iodotrimethylsilane. 

There are also useful procedures for preparation of azides directly from alcohols. Reaction of alcohols with 2-fluoro-l-methylpyridinium iodide followed by reaction with lithium azide gives good yields of alkyl azides.75... 

Alkylzinc iodides These reagents are prepared by reaction of alkyl iodides with Zn/Cu in toluene-N,N-dimethylacetamide (DMA). In the presence of 1 equiv. of chlorotrimethylsilane they can add to aldehydes to form alcohols. DMA may be replaced as the cosolvent by N-methylpyrrolidone (NMP), but HMPT retards this reaction. This reaction can be used to obtain y-, 8-, and e-hydroxy esters from P-, y-, and 8-zinc esters (equation I). 

The conversion of 8 to 9 uses PPI13 and I2. The former is a nucleophile, the latter is an electrophile, so they react to give PI13P-L The P is attacked by the alcohol to give an O-P bond, and the I- then displaces PI13PC) from C to give the alkyl iodide. 

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