to a 2nd equivalent of alkyl iodide, as in the conversion of primary alcohols into alkyl iodides. HI is subject to the same Markovnikov and anti-Markovnikov guidelines as HCl and HBr. Although harsh by modern standards, HI was commonly employed as a reducing agent early on in the history of organic chemistry. Chemists in the 19th century attempted to prepare cyclohexane by HI reduction of benzene at high temperatures, but instead isolated the rearranged product, methylcyclopentane (see the article on cyclohexane). As first reported by Kiliani, hydroiodic acid reduction of sugars and other polyols results in the reductive cleavage of several or even all hydroxy groups, although often with poor yield and/or reproducibility. In the case of benzyl alcohols and alcohols with α-carbonyl groups, reduction by HI can provide synthetically useful yields of the corresponding hydrocarbon product (ROH + 2HI → RH + + I2). This process can be made catalytic in HI using red phosphorus to reduce the formed I2. See also Hydroiodic acid References External links International Chemical Safety Card 1326 Hydrogen compounds Iodides Mineral acids Nonmetal halides Diatomic molecules Iodine compounds Reducing agents