Butene chlorohydrin/oxide

The chlorohydrin process uses slaked lime (or caustic soda) to saponify, or dehy-drochlorinate propylene and butene chlorohydrins to produce the corresponding oxides. The oxides may then be converted to the glycols by acidic hydrolysis [31.24]. 

Due to the presence of a terminal double bond in 1-butene, oxidation of this isomer via a chlorohydrination route is similar to that used for propylene. 

Alkenes are converted to halohydrins by the treatment of halides and water. When halohydrins are treated with a strong base (NaOH), an intramolecular cyclization occurs and epoxides are formed. For example, 1-butene can be converted to butylene oxide via butylene chlorohydrin. 

For instance, the reaction of cis- and tra/w-2-butene oxide with aluminium chloride yields mainly erythro- and threo-chlorohydrin (after hydrolysis) respectively [66]. 

Smaller uses of 1-butene are in 1,2-butylene oxide, butyl mercaptan, and butyl phenols. Butylene oxide, produced by the chlorohydrin process, is used as a corrosion inhibitor in chlorinated solvents. Butyl mercaptan is a precursor for organophosphate herbicides, pharmaceutical intermediates, and is used as a gas odorant. 

A further oxidation is then performed to establish the carboxylic acid moiety at C-1, which will form the macrolactone later in the synthesis. Sodium chlorite is commonly used as an oxidizing agent and is often applied for saturated and aromatic aldehydes. Hypochloric acid (HOCl) and sodium hypochlorite (NaOCl) are formed as byproducts and have to be destroyed before they can attack the substrate or the product, because they are stronger oxidizing agents. In this case, 2-methyl-2-butene (43) is added to the reaction mixture forming a chlorohydrin 44. 

Alkene epoxidation is a very useful reaction in industry and organic s)mthesis. The resultant epoxides are essential precursors in the s)mthesis of various important substances like plasticizers, perfumes, and epoxy resins [1]. For example, over 5,000,000 and 70,000 metric tonnes of propylene and butene oxides, respectively, are produced per year [2]. Current commercial production of propylene oxide (PO) usually employs the chlorohydrin process or the Halcon process, which gives rise to disposal problem for the resultant salts or large amounts of coproducts. As a result of increasing stringent enviromnent legislation, there is currently much interest in the research and development of environmentally friendly methods for preparation of PO without any coproduct. 

Nevertheless, the factors that affect the electrophilicity of alkyl halides operate here, and lead to synthetically useful levels of selectivity. At one extreme, in the presence of Lewis or protic acid, the epoxide opens towards the side that gives the more stabilised cation, which is usually the more substituted side, leading to regioselectivity appropriate to an S l reaction. At the other extreme, in the absence of Lewis or protic acid, the reaction is S 2 in character, and takes place on the side best able to support an SN2 transition structure, which is usually the less substituted side. A simple example is the opening of 1-butene oxide 4.176 with chloride ion, which gives each of the chlorohydrins as the major product, 4.177 in acidic and 4.178 in neutral conditions.402... 

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